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  • 1. Abu El-Enen, M.M.
    et al.
    Abu-Alam, T.S.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Ali, K.A.
    Okrusch, M.
    P–T path and timing of crustal thickening during amalgamation of East and West Gondwana: A case study from the Hafafit Metamorphic Complex, Eastern Desert of Egypt.2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 263, p. 213-238Article in journal (Refereed)
    Abstract [en]

    The southeastern sector of the Hafafit Metamorphic Complex, southern Eastern Desert of Egypt comprises infrastructural orthogneisses of tonalite and syenogranite parentage, amphibolites, and a volcano-sedimentary association. These are overthrust by an obducted suprastructural ophiolite nappes via the Nugrus thrust. The protolith of the biotite–hornblende-gneisses was formed during island-arc accretion, while that of the garnet–biotite gneisses were formed in a within-plate regime, consistent with a transition to a post-collisional setting. The volcano-sedimentary association comprises interbedded and intercalated highly foliated metapelitic schists, metabasites, and leucocratic gneisses, deposited in a back-arc basin. The metapelites and the leucocratic gneisses originated from immature Fe-shales and arkoses derived from intermediate-mafic and acidic igneous rocks, respectively, via weak chemical weathering in a tectonically active island arc terrane. The intercalated amphibolites were derived from tholeiitic basalts generated in a back-arc setting.

    The volcano-sedimentary association was metamorphosed under upper-amphibolite facies conditions with pressures of 9–13 kbar and temperatures of 570–675 °C, as derived from conventional geothermobarometry and pseudosection calculation. A steep, tight clockwise P–T path is constrained and a geothermal gradient around 20 °C/km is estimated for the peak metamorphism. We assume that deformation and metamorphism are due to crustal thickening during the collision of East and West Gondwana, where peak metamorphism took place in the middle to lower crust at 33 km average crustal depth. This was followed by a subsequent quasi-isothermal decompression due to rapid exhumation during wrench tectonics. Sinistral transcurrent shearing with extensional denudation resulted in vertical ductile thinning that was accompanied by heat input from magmatism, as indicated by a higher geothermal gradient during retrograde metamorphism and exhumation of the complex.

    U–Pb data from magmatic zircons yields protolith ages of 731 ± 3 Ma for the biotite–hornblende gneisses and 646 ± 12 Ma for the garnet–biotite gneisses. Conforming to field evidence, our geochronology data point to a depositional age of the volcano-sedimentary cover at around 650 Ma. The age of metamorphism is constrained by a low Th/U ratio of a zircon grain crystallized at an age of 597 ± 6 Ma.

  • 2. Adam, B.
    et al.
    Klawonn, I.
    Svedén, J.
    Bergkvist, J.
    Nahar, N.
    Walve, J.
    Littmann, S.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Lavik, G.
    Kuypers, M.M.M.
    Ploug, H.
    N2-fixation, ammonium release, and N-transfer to the microbial and classical food web within a plankton community.2016In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 19, p. 450-459Article in journal (Refereed)
    Abstract [en]

    We investigated the role of N2-fixation by the colony-forming cyanobacterium, Aphanizomenon spp., for the plankton community and N-budget of the N-limited Baltic Sea during summer by using stable isotope tracers combined with novel secondary ion mass spectrometry, conventional mass spectrometry and nutrient analysis. When incubated with 15N2, Aphanizomenon spp. showed a strong 15N-enrichment implying substantial 15N2-fixation. Intriguingly, Aphanizomenon did not assimilate tracers of 15NH4+ from the surrounding water. These findings are in line with model calculations that confirmed a negligible N-source by diffusion-limited NH4+ fluxes to Aphanizomenon colonies at low bulk concentrations (<250 nm) as compared with N2-fixation within colonies. No N2-fixation was detected in autotrophic microorganisms <5 μm, which relied on NH4+ uptake from the surrounding water. Aphanizomenon released about 50% of its newly fixed N2 as NH4+. However, NH4+ did not accumulate in the water but was transferred to heterotrophic and autotrophic microorganisms as well as to diatoms (Chaetoceros sp.) and copepods with a turnover time of ~5 h. We provide direct quantitative evidence that colony-forming Aphanizomenon releases about half of its recently fixed N2 as NH4+, which is transferred to the prokaryotic and eukaryotic plankton forming the basis of the food web in the plankton community. Transfer of newly fixed nitrogen to diatoms and copepods furthermore implies a fast export to shallow sediments via fast-sinking fecal pellets and aggregates. Hence, N2-fixing colony-forming cyanobacteria can have profound impact on ecosystem productivity and biogeochemical processes at shorter time scales (hours to days) than previously thought.

  • 3. Ali, K.A.
    et al.
    Surour, A.A:
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Andresen, A.
    Single zircon Hf-O isotope constraints on the origin of A-type granites from the Jabal Al-Hassir ring complex, Saudi Arabia.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 256, p. 131-147Article in journal (Refereed)
    Abstract [en]

    The Jabal Al-Hassir ring complex in the southern Arabian Shield is an alkaline granite complex comprising an inner core of biotite granite that outwardly becomes a porphyritic sodic-calcic amphibole (ferrobarroisite–katophorite) granite. A combined study of mineral chemistry and single zircon Hf–O zircon isotope analyses was carried out to infer the magma sources of the Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. The granitic rocks show high positive initial ɛHf(t) values of +7.0 to +10.3 and δ18O values of +5.8‰ to +7.4‰ that are consistent with melting of a juvenile crustal protolith that was formed during the Neoproterozoic assembly of the Arabian-Nubian Shield (ANS). Crustal-model ages (Hf-tNC) of 0.71–0.94 Ga indicate minor contribution from an older continental crust in the formation of the Jabal Al-Hassir granitic rocks (crystallization age = 620 ±3 Ma), but any such component is likely to be Neoproterozoic in age. Temperature and oxygen fugacity (ƒO2) estimates suggested that the Jabal Al-Hassir A-type granite magma was generated at high temperature (820–1050 °C) and low ƒO2. Geochemical characteristics (e.g., low ƒO2), geochronological data, and Hf and O isotope compositions, indicate that the magmas of the Neoproterozoic A-type granites of the Jabal Al-Hassir ring complex were likely generated by crustal partial melting of a juvenile Neoproterozoic lower crustal tholeiitic rocks, following collision between East and West Gondwana in the final stages of the evolution of the Arabian Shield.

  • 4. Bellucci, Jeremy
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Humayan, M
    Hewins, R
    Zanda, B
    Pb-isotopic evidence for an early, enriched crust on Mars2015In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 410, p. 34-41Article in journal (Refereed)
    Abstract [en]

    Martian meteorite NWA 7533 is a regolith breccia that compositionally resembles the Martian surface measured by orbiters and landers. NWA 7533 contains monzonitic clasts that have zircon with U–Pb ages of 4.428 Ga. The Pb isotopic compositions of plagioclase and alkali feldspars, as well as U–Pb isotopic compositions of chlorapatitein the monzonitic clasts of NWA 7533 have been measured by Secondary Ion Mass Spectrometry (SIMS). The U–Pb isotopic compositions measured from the chlorapatitein NWA 7533 yield an age of 1.357 ±81Ga(2σ). The least radiogenic Pb isotopic compositions measured in plagioclase and K-feldspar lie within error of the 4.428 Ga Geochron. These data indicate that the monzonitic clasts in NWA 7533 are a product of a differentiation history that includes residence in areservoir that formed prior to 4.428 Ga with a μ-value (238U/204Pb) of at least 13.4 ±1.7 (2σ)and aκ-value (232Th/238U) of ∼4.3. This μ-value is more than three times higher than any other documented Martian reservoir. These results indicate either the Martian mantle is significantly more heterogeneous than previously thought (μ-value of 1–14 vs. 1–5) and/or the monzonitic clasts formed by the melting of Martian crust with a μ-value of at least 13.4. Therefore, NWA 7533 may contain the first isotopic evidence for an enriched, differentiated crust on Mars.

  • 5.
    Bellucci, Jeremy
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    Pidgeon, Robert
    Grange, Marion
    Reddy, Steven
    Timms, Nick
    A scanning ion imaging investigation into the micron-scale U-Pb systematics in a complex lunar zircon2016In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 438, p. 112-122Article in journal (Refereed)
    Abstract [en]

    The full U-Pb isotopic systematics in a complex lunar zircon ‘Pomegranate’ from lunar impact breccia 73235 have been investigated by the development of a novel Secondary Ion Mass Spectrometry (SIMS) scanning ion imaging (SII) technique. This technique offers at least a four-fold increase in analytical spatial resolution over traditional SIMS analyses in zircon. Results from this study confirm the hypothesis that the Pomegranate zircon crystallized at 4.302 ± 0.013 Ga and experienced an impact that formed, U-enriched zircon around primary zircon cores at 4.184 ± 0.007 Ga (2σ, all uncertainties). The increase in spatial resolution offered by this technique has facilitated targeting of primary zircon that was previously inaccessible to conventional spot analyses. This approach has yielded results indicating that individual grains with a diffusive distance of less than ~4 μm have been reset to the young impact age, while individual grains with a diffusive distance larger than ~6 μm have retained the old crystallization age. Assuming a broad range in cooling rate of 0.5–50 °C/year, which has been observed in a suite of similar lunar breccias, a maximum localized temperature generated by the impact that reset small prima- ry zircon and created new, high-U zircon is estimated to be between 1100 and 1280 °C.

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  • 6.
    Bellucci, Jeremy
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    A Pb isotopic resolution to the Martian meteorite age paradox2016In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 433, p. 241-248Article in journal (Refereed)
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  • 7.
    Bellucci, Jeremy
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Snape, Joshua
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, Alexander
    The Pb isotopic evolution of the Martian mantle constrained by initial Pb in Martian meteorites2015In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 120, p. 2224-2240Article in journal (Refereed)
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  • 8.
    Bengtson, Stefan
    et al.
    Swedish Museum of Natural History, Department of Paleobiology.
    Sallstedt, Therese
    Swedish Museum of Natural History, Department of Paleobiology.
    Belivanova, Veneta
    Swedish Museum of Natural History, Department of Paleobiology.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae2017In: PLoS biology, ISSN 1544-9173, E-ISSN 1545-7885, Vol. 15, no 3, p. 1-38, article id e2000735Article in journal (Refereed)
    Abstract [en]

    The ~1.6 Ga Tirohan Dolomite of the Lower Vindhyan in central India contains phosphatized stromatolitic microbialites. We report from there uniquely well-preserved fossils interpreted as probable crown-group rhodophytes (red algae). The filamentous form Rafatazmia chitrakootensis n. gen, n. sp. has uniserial rows of large cells and grows through diffusely distributed septation. Each cell has a centrally suspended, conspicuous rhomboidal disk interpreted as a pyrenoid. The septa between the cells have central structures that may represent pit connections and pit plugs. Another filamentous form, Denaricion mendax n. gen., n. sp., has coin-like cells reminiscent of those in large sulfur-oxidizing bacteria but much more recalcitrant than the liquid-vacuole-filled cells of the latter. There are also resemblances with oscillatoriacean cyanobacteria, although cell volumes in the latter are much smaller. The wider affinities of Denaricion are uncertain. Ramathallus lobatus n. gen., n. sp. is a lobate sessile alga with pseudoparenchymatous thallus, “cell fountains,” and apical growth, suggesting florideophycean affinity. If these inferences are correct, Rafatazmia and Ramathallus represent crown-group multicellular rhodophytes, antedating the oldest previously accepted red alga in the fossil record by about 400 million years.

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  • 9. Bezenjani, R. Nasiri
    et al.
    Pease, V.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Shalaby, M. H.
    Kadi, K. A.
    Kozdroj, W.
    Detrital zircon geochronology and provenance of the Neoproterozoic Hammamat Group (Igla Basin), Egypt and the Thalbah Group, NW Saudi Arabia: Implications for regional collision tectonics2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 245, p. 225-243Article in journal (Refereed)
  • 10. Bingen, B.
    et al.
    Corfu, F.
    Stein, H.J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    U-Pb geochronology of the syn-orogenic Knaben molybdenum deposits, Sveconorwegian orogen, Norway2015In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 152, p. 537-556Article in journal (Refereed)
    Abstract [en]

    Paired isotope dilution – thermal ionization mass spectrometry (ID-TIMS) and secondary ion mass spectrometry (SIMS) zircon U–Pb data elucidate geochronological relations in the historically important Knaben molybdenum mining district, Sveconorwegian Orogen, south Norway. This polyphase district provided c. 8.5 Mt of ore with a grade of 0.2%. It consists of mineralized quartz veins, silica-rich gneiss, pegmatites and aplites associated with a heterogeneous, locally sulphide-bearing, amphibolites facies gneiss called Knaben Gneiss, and hosted in a regional-scale monotonous, commonly weakly foliated, granitic gneiss. An augen gneiss at the Knaben I deposit yields a 1257±6 Ma magmatic zircon age, dating the pre-Sveconorwegian protolith of the Knaben Gneiss. Mineralized and non-mineralized granitic gneiss samples at the Knaben II and Kvina deposits contain some 1488–1164 Ma inherited zircon and yield consistent intrusion ages of 1032±4, 1034±6 and 1036±6 Ma. This age links magmatism in the district to the regional 1050–1020 Ma Sirdal I-type granite suite, corresponding to voluminous crustal melting during the Sveconorwegian orogeny. A high-U, low-Th/U zircon rim is present in all samples. It defines several age clusters between 1039±6 and 1009±7 Ma, peaking at c. 1016 Ma and overlapping with a monazite age of 1013±5 Ma. The rim records protracted hydrothermal activity, which started during the main magmatic event and outlasted it. This process was coeval with regional high-grade Sveconorwegian metamorphism. Molybdenum deposition probably started during this event when silica-rich mineralizing fluids or hydrous magmas were released from granite magma batches. An analogy between the Knaben district and shallow, short-lived porphyry Mo deposits is inappropriate.

  • 11. Bingen, B.
    et al.
    Solli, A.
    Viola, G.
    Torgersen, E.
    Sandstad, J.S.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Røhr, T.
    Ganerød, M.
    Nasuti, A.
    Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context.2015In: Norwegian Journal of Geology, Vol. 95, p. 365-396Article in journal (Refereed)
    Abstract [en]

    Zircon U–Pb geochronological data in 18 samples from Finnmarksvidda and one sample from the Repparfjord Tectonic Window, northern Norway, constrain the evolution of the Palaeoproterozoic Kautokeino Greenstone Belt and neighbouring units in a Fennoscandia context. The Jergul Complex is an Archaean cratonic block of Karelian affinity, made of variably gneissic, tonalite–trondhjemite–granodiorite–granite plutonic rocks formed between 2975 ± 10 and 2776 ± 6 Ma. It is associated with the Archaean Goldenvárri greenstone–schist formation. At the base of the Kautokeino Greenstone Belt, the Masi Formation is a typical Jatulian quartzite, hosting a Haaskalehto-type, albite–magnetite-rich, mafic sill dated at 2220 ± 7 Ma. The Likčá and Čáskejas formations represent the main event of basaltic magmatism. A synvolcanic metagabbro dates this magmatism at 2137 ± 5 Ma. The geochemical and Nd isotopic signature of the Čáskejas Formation (eNd = +2.2 ± 1.7) is remarkably similar to coeval dykes intruding the Archaean Karelian Craton in Finland and Russia (eNd = +2.5 ± 1.0). The Čáskejas Formation can be correlated with the Kvenvik Formation in the Alta–Kvænangen Tectonic Window. Two large granite plutons yield ages of 1888 ± 7 and 1865 ± 8 Ma, and provide a maximum age for shearing along two prominent NNW–SSE-oriented shear zones recording Svecokarelian transpression. The Bidjovagge Au–Cu deposit formed around 1886 to 1837 Ma and is also related to this NNW–SSE-oriented shear system. The Ráiseatnu Complex is mainly composed of granitic gneisses formed between 1868 ± 13 and 1828 ± 5 Ma, and containing metasediment rafts and zircon xenocrysts ranging from c. 3100 to 2437 Ma. The Kautokeino Greenstone Belt and Ráiseatnu Complex are interpreted as Palaeoproterozoic, pericontinental, lithospheric domains formed during rifting between Archaean cratonic domains. They accommodated oblique convergence between the Karelian and the Norrbotten Archaean cratons during the Svecokarelian orogeny.

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  • 12. Brengman, L.
    et al.
    Fedo, C.M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Micro-scale silicon isotope heterogeneity observed in hydrothermal quartz precipitates from the >3.7 Ga Isua Greenstone Belt, SW Greenland.2016In: Terra Nova, ISSN 0954-4879, E-ISSN 1365-3121, Vol. 28, p. 70-75Article in journal (Refereed)
    Abstract [en]

    Pillow basalt and chert form integral lithologies comprising many Archean greenstone belt packages. To investigate details of these lithologies in the >3.7 Ga Isua Greenstone Belt, SW Greenland, we measured silicon isotope compositions of quartz crystals, by secondary ion mass spectrometry, from a quartz-cemented, quartz-amygdaloidal basaltic pillow breccia, recrystallized chert and chert clasts thought to represent silica precipitation under hydrothermal conditions. The recrystallized chert, chert clasts and quartz cement have overlapping δ30Si values, while the δ30Si values of the quartz amygdules span nearly the entire range of previously published values for quartz precipitates of any age, despite amphibolite facies metamorphism. We suggest that the heterogeneity is derived from kinetic isotope fractionation during quartz precipitation under disequilibrium conditions in a hydrothermal setting, consistent with the pillow breccia origin. On the basis of the present data, we conclude that the geological context of each sample must be carefully evaluated when interpreting δ30Si values of quartz.

  • 13. Cabral, R.A.
    et al.
    Jackson, M.G.
    Koga, K.T.
    Rose-Koga, E.F.
    Hauri, E.H.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Price, A.A:
    Day, J.M.D.
    Shimizu, N.
    Kelley, K.A.
    Volatile cycling of H2O, CO2, F, and Cl in the HIMU mantle: A new window provided by melt inclusions from oceanic hotspot lavas at Mangaia, Cook Islands.2014In: Geochemistry, Geophysics, Geosystems, ISSN 1525-2027, Vol. 15, p. 4445-4467Article in journal (Refereed)
    Abstract [en]

    Mangaia hosts the most radiogenic Pb-isotopic compositions observed in ocean island basalts and represents the HIMU (high µ = 238U/204Pb) mantle end-member, thought to result from recycled oceanic crust. Complete geochemical characterization of the HIMU mantle end-member has been inhibited due to a lack of deep submarine glass samples from HIMU localities. We homogenized olivine-hosted melt inclusions separated from Mangaia lavas and the resulting glassy inclusions made possible the first volatile abundances to be obtained from the HIMU mantle end-member. We also report major and trace element abundances and Pb-isotopic ratios on the inclusions, which have HIMU isotopic fingerprints. We evaluate the samples for processes that could modify the volatile and trace element abundances postmantle melting, including diffusive Fe and H2O loss, degassing, and assimilation. H2O/Ce ratios vary from 119 to 245 in the most pristine Mangaia inclusions; excluding an inclusion that shows evidence for assimilation, the primary magmatic H2O/Ce ratios vary up to ∼200, and are consistent with significant dehydration of oceanic crust during subduction and long-term storage in the mantle. CO2 concentrations range up to 2346 ppm CO2 in the inclusions. Relatively high CO2 in the inclusions, combined with previous observations of carbonate blebs in other Mangaia melt inclusions, highlight the importance of CO2 for the generation of the HIMU mantle. F/Nd ratios in the inclusions (30 ± 9; 2σ standard deviation) are higher than the canonical ratio observed in oceanic lavas, and Cl/K ratios (0.079 ± 0.028) fall in the range of pristine mantle (0.02–0.08).

  • 14.
    Claesson, Stefan
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Bibikova, Elena V.
    Vernadsky Institute of Geochemistry and Analytical Chemistry, R.A.S., Moscow, Russia.
    Shumlyanskyy, Leonid
    M.P Semenenko Institute of Geochemistry, Mineralogy and Ore Formation, Palladina Ave. 34, 03680 Kyiv, Ukraine.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Can oxygen isotopes in magmatic zircon be modified by metamorphism? A case study from the Eoarchean Dniester-Bug Series, Ukrainian Shield2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 273, p. 1-11Article in journal (Refereed)
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    Claesson O Odesa PRECAM text and figures accepted 151108
  • 15. Crémière, A.
    et al.
    Lepland, A.
    Chand, S.
    Sahy, D.
    Kirsimäe, K.
    Bau, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Noble, S.R.
    Martma, T.
    Thorsnes, T.
    Brunstad, H.
    Fluid source and methane-related diagenetic processes recorded in cold seep carbonates from the Alvheim channel, central North Sea2016In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 432, p. 16-33Article in journal (Refereed)
    Abstract [en]

    Integrated petrography, mineralogy, geochronology and geochemistry of cold seep carbonate crusts and free gas from the Alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central North Sea. Free gas isotope characteristics coupled with carbonate δ13C values as low as − 66‰ VPDB, indicate a predominantly microbial methane source with minor thermogenic contribution. We estimate that ~ 70% of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane. The early stage of crust growth is represented by microcrystalline aragonite and Mg-calcite (10 to 40% mol MgCO3) cementing seafloor sediments consisting of clays, quartz, feldspar, and minor detrital low Mg-calcite and dolomite. Typical association of aragonite cement with coarse-grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor. Middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction. The later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts. In contrast to early generation cements, late generation cavity infills have rare earth elements and Y patterns with small negative Ce anomalies similar to seawater, consistent with carbonate precipitation in a more open, seawater dominated system. Aragonite U–Th ages indicate carbonate precipitation between 6.09 and 3.46 kyr BP in the northern part of the channel, whereas in the southern part precipitation occurred between 1.94 and 0.81 kyr BP reflecting regional changes in fluid conduit position.

  • 16. Deegan, F.M.
    et al.
    Troll, V.R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Jolis, E.M.
    Freda, C.
    Boron isotope fractionation in magma via crustal carbonate dissolution.2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 30774Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

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  • 17. Deegan, F.M.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Troll, V.R.
    Budd, D.A.
    Harris, C.
    Geiger, H.
    Hålenius, U.
    Swedish Museum of Natural History, Department of Geology.
    Pyroxene standards for SIMS oxygen isotope analysis and their application to Merapi volcano, Sunda arc, Indonesia2016In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 447, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Measurement of oxygen isotope ratios in common silicate minerals such as olivine, pyroxene, feldspar, garnet, and quartz is increasingly performed by Secondary Ion Mass Spectrometry (SIMS). However, certain mineral groups exhibit solid solution series, and the large compositional spectrum of these mineral phases will result in matrix effects during SIMS analysis. These matrix effects must be corrected through repeated analysis of compositionally similar standards to ensure accurate results. In order to widen the current applicability of SIMS to solid solution mineral groups in common igneous rocks, we performed SIMS homogeneity tests on new augite (NRM-AG-1) and enstatite (NRM-EN-2) reference materials sourced from Stromboli, Italy and Webster, North Carolina, respectively. Aliquots of the standard minerals were analysed by laser fluorination (LF) to establish their δ18O values. Repeated SIMS measurements were then performed on randomly oriented fragments of the same pyroxene crystals, which yielded a range in δ18O less than ± 0.42 and ± 0.58‰ (2σ) for NRM-AG-1 and NRM-EN-2, respectively. Homogeneity tests verified that NRM-AG-1 and NRM-EN-2 do not show any crystallographic orientation bias and that they are sufficiently homogeneous on the 20 μm scale to be used as routine mineral standards for SIMS δ18O analysis. We subsequently tested our new standard materials on recently erupted pyroxene crystals from Merapi volcano, Indonesia. The δ18O values for Merapi pyroxene obtained by SIMS (n = 204) agree within error with the LF-derived δ18O values for Merapi pyroxene but differ from bulk mineral and whole-rock data obtained by conventional fluorination. The bulk samples are offset to higher δ18O values as a result of incorporation of mineral and glass inclusions that in part reflects crustal contamination processes. The Merapi pyroxene SIMS data, in turn, display a frequency peak at 5.8‰, which allows us to estimate the δ18O value of the primary mafic magma at Merapi to ~ 6.1‰ when assuming closed system differentiation.

  • 18. Drake, H.
    et al.
    Tullborg, E.L.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Sandberg, B.
    Blomfeldt, T.
    Åström, M.E.
    Extreme fractionation and micro-scale variation of sulphur isotopes during bacterial sulphate reduction in deep groundwater systems.2015In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 161, p. 1-18Article in journal (Refereed)
    Abstract [en]

    This study conducted at the Äspö Hard Rock Laboratory, SE Sweden, determines the extent and mechanisms of sulphur-isotope fractionation in permanently reducing groundwater in fractured crystalline rock. Two boreholes >400 m below the ground surface were investigated. In the 17-year-old boreholes, the Al instrumentation pipes had corroded locally (i.e., Al-[oxy]hydroxides had formed) and minerals (i.e., pyrite, iron monosulphide, and calcite) had precipitated on various parts on the equipment. By chemically and isotopically comparing the precipitates on the withdrawn instrumentation and the borehole waters, we gained new insight into the dynamics of sulphate reduction, sulphide precipitation, and sulphur-isotope fractionation in deep-seated crystalline-rock settings. An astonishing feature of the pyrite is its huge variability in δ34S, which can exceed 100‰ in total (i.e., −47.2 to +53.3‰) and 60‰ over 50 μm of growth in a single crystal. The values at the low end of the range are up to 71‰ lower than measured in the dissolved sulphate in the water (20–30‰), which is larger than the maximum difference reported between sulphate and sulphide in pure-culture experiments (66‰) but within the range reported from natural sedimentary settings. Although single-step reduction seems likely, further studies are needed to rule out the effects of possible S disproportionation. The values at the high end of the range (i.e., high δ34Spy) are much higher than could be produced from the measured sulphate under any biogeochemical conditions. This strongly suggests the development of closed-system conditions near the growing pyrite, i.e., the rate of sulphate reduction exceeds the rate of sulphate diffusion in the local fluid near the pyrite, causing the local aqueous phase (and thus the forming pyrite) to become successively enriched in heavy S (34S). Consequently, the δ34S values of the forming pyrite become exceptionally high and strongly decoupled from the δ34S values of the sulphate in the bulk fluid. The Al-(oxy)hydroxide and calcite precipitates are explained by a combination of deposit and galvanic corrosion initiated by Al corrosion by H2S produced by sulphate-reducing microorganisms.

  • 19. El Albani, Abderrazak
    et al.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Canfield, Donald E.
    Riboulleau, Armelle
    Rollion Bard, Claire
    Macchiarelli, Roberto
    Ngombi Pemba, Lauriss
    Hammarlund, Emma
    Meunier, Alain
    Moubiya Mouele, Idalina
    Benzerara, Karim
    Bernard, Sylvain
    Boulvais, Philippe
    Chaussidon, Marc
    Cesari, Christian
    Fontaine, Claude
    Chi-Fru, Ernest
    Garcia Ruiz, Juan Manuel
    Gauthier-Lafaye, François
    Mazurier, Arnaud
    Pierson-Wickmann, Anne Catherine
    Rouxel, Olivier
    Trentesaux, Alain
    Vecoli, Marco
    Versteegh, Gerard J. M.
    White, Lee
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bekker, Andrey
    The 2.1 Ga old Francevillian biota: biogenicity, taphonomy and biodiversity.2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 6:e99438, p. 1-18Article in journal (Refereed)
    Abstract [en]

    The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth’s surface environments following the first appreciable rise of free atmospheric oxygen concentrations ~2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rodshaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

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  • 20. Eyal, Moshe
    et al.
    Be'eri-Shlevin, Yaron
    Eyal, Yehuda
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Litvinovsky, Boris
    Three successive Proterozoic island arcs in the Northern Arabian–Nubian Shield: Evidence from SIMS U–Pb dating of zircon2014In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 25, p. 338-357Article in journal (Refereed)
  • 21. Fleming, E.J.
    et al.
    Flowerdew, Michael
    Smyth, H.R.
    Scott, R.A.
    Morton, A.C.
    Omma, J.E.
    Frei, D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea.2016In: Marine and Petroleum Geology, ISSN 0264-8172, E-ISSN 1873-4073, Vol. 78, p. 516-535Article in journal (Refereed)
    Abstract [en]

    Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.

  • 22. Gardiner, N.J.
    et al.
    Roberts, N.M.W.
    Morley, C.K.
    Searle, M.P.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Did Oligocene crustal thickening precede basin development in northern Thailand? A geochronological reassessment of Doi Inthanon and Doi Suthep2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 240-243, p. 69-83Article in journal (Refereed)
    Abstract [en]

    The Doi Inthanon and Doi Suthep metamorphic core complexes in northern Thailand are comprised of amphibolite-grade migmatitic gneisses mantled by lower-grade mylonites and metasedimentary sequences, thought to represent Cordilleran-style core complexes exhumed through the mobilization of a low-angle detachment fault. Previous studies have interpreted two metamorphic events (Late Triassic and Late Cretaceous), followed by ductile extension between the late Eocene and late Oligocene, a model which infers movement on the detachment at ca. 40 Ma, and which culminates in a rapid unroofing of the complexes in the early Miocene. The Chiang Mai Basin, the largest such Cenozoic Basin in the region, lies immediately to the east. Its development is related to the extension observed at Doi Inthanon and Doi Suthep, however it is not definitively dated, and models for its development have difficulty reconciling Miocene cooling ages with Eocene detachment movement. Here we present new in-situ LA-ICP-MS and SIMS U–Pb age data of zircon and monazite grains from gneiss and leucogranite samples taken from Doi Inthanon and Doi Suthep. Our new zircon data exhibit an older age range of 221–210 Ma, with younger ages of ca. 72 Ma, and 32–26 Ma. Our monazite data imply an older age cluster at 83–67 Ma, and a younger age cluster of 34–24 Ma. While our data support the view of Indosinian basement being reworked in the Cretaceous, they also indicate a late Eocene–Oligocene tectonothermal event, resulting in prograde metamorphism and anatexis. We suggest that this later event is related to localized transpressional thickening associated with sinistral movement on the Mae Ping Fault, coupled with thickening at the restraining bend of the Mae Yuan Fault to the immediate west of Doi Inthanon. Further, this upper Oligocene age limit from our zircon and monazite data would imply a younger Miocene constraint on movement of the detachment, which, when combined with the previously recorded Miocene cooling ages, has implications for a model for the onset of extension and subsequent development of the Chiang Mai Basin in the early mid-Miocene.

  • 23. Gardiner, N.J.
    et al.
    Searle, M.P.
    Morley, C.K.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Spencer, C.J.
    Robb, L.J.
    The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: New insights from zircon U–Pb and Hf isotope data.2016In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 39, p. 401-422Article in journal (Refereed)
    Abstract [en]

    Two of the major granite belts of Southeast Asia are the Main Range and Eastern Province. Together, these are interpreted to represent the magmatic expression of the closure of Palaeo-Tethys during Late Palaeozoic to Early Mesozoic times. Recent geochronological and geochemical work has better delineated these belts within Peninsular Malaysia, thereby providing important constraints on the timing of Palaeo-Tethys suturing. However, the northern extension of this Palaeo-Tethyan suture is less well understood. Here we present new ion microprobe U–Pb zircon age data from northern Thailand and eastern Myanmar. Measured ages of 219 and 220 Ma from the Kyaing Tong granite imply northern extension of the Main Range Province into eastern Myanmar. The Tachileik granite in far eastern Myanmar yields an age of 266 Ma, consistent with published Eastern Province ages, and this therefore constrains the northern extension of the Palaeo-Tethys suture in eastern Myanmar. We further discuss how this suture may extend northwards into Yunnan. A Late Cretaceous age (70 Ma) measured in Thailand represents later magmatic activity, and is similar to published magmatic ages from central Myanmar. This younger magmatism is interpreted to be related to the subduction of Neo-Tethys prior to India–Asia collision. Further, we present new laser ablation zircon Hf isotope data from eastern Myanmar which suggest that Palaeoproterozoic crust underlies both the Main Range and Eastern Province granites. Our εHf model age of ca. 1750 Ma from Sibumasu, the basement underlying eastern Myanmar, lies within the range of other model ages reported thus far for the Baoshan Block north in Yunnan, interpreted by some to be the northern extension of Sibumasu.

  • 24. Gasser, D.
    et al.
    Jeřábek, P.
    Faber, P.
    Stünitz, H.
    Menegon, L.
    Corfu, F.
    Erambert, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Behaviour of geochronometers and timing of metamorphic reactions during deformation at lower crustal conditions: phase equilibrium modelling and U–Pb dating of zircon, monazite, rutile and titanite from the Kalak Nappe Complex, northern Norway.2015In: Journal of Metamorphic Geology, ISSN 0263-4929, E-ISSN 1525-1314, Vol. 33, p. 513-534Article in journal (Refereed)
    Abstract [en]

    This study investigates the behaviour of the geochronometers zircon, monazite, rutile and titanite in polyphase lower crustal rocks of the Kalak Nappe Complex, northern Norway. A pressure–temperature–time–deformation path is constructed by combining microstructural observations with P–T conditions derived from phase equilibrium modelling and U–Pb dating. The following tectonometamorphic evolution is deduced: A subvertical S1 fabric formed at ~730–775 °C and ~6.3–9.8 kbar, above the wet solidus in the sillimanite and kyanite stability fields. The event is dated at 702 ± 5 Ma by high-U zircon in a leucosome. Monazite grains that grew in the S1 fabric show surprisingly little variation in chemical composition compared to a large spread in (concordant) U–Pb dates from c. 800 to 600 Ma. This age spread could either represent protracted growth of monazite during high-grade metamorphism, or represent partially reset ages due to high-T diffusion. Both cases imply that elevated temperatures of >600 °C persisted for over c. 200 Ma, indicating relatively static conditions at lower crustal levels for most of the Neoproterozoic. The S1 fabric was overprinted by a subhorizontal S2 fabric, which formed at ~600–660 °C and ~10–12 kbar. Rutile that originally grew during the S1-forming event lost its Zr-in-rutile and U–Pb signatures during the S2-forming event. It records Zr-in-rutile temperatures of 550–660 °C and Caledonian ages of 440–420 Ma. Titanite grew at the expense of rutile at slightly lower temperatures of ~550 °C during ongoing S2 deformation; U–Pb ages of c. 440–430 Ma date its crystallization, giving a minimum estimate for the age of Caledonian metamorphism and the duration of Caledonian shearing. This study shows that (i) monazite can have a large spread in U–Pb dates despite a homogeneous composition; (ii) rutile may lose its Zr-in-rutile and U–Pb signature during an amphibolite facies overprint; and (iii) titanite may record crystallization ages during retrograde shearing. Therefore, in order to correctly interpret U–Pb ages from different geochronometers in a polyphase deformation and reaction history, they are ideally combined with microstructural observations and phase equilibrium modelling to derive a complete P–T–t–d path.

  • 25. Heinonen, A.
    et al.
    Andersen, T.
    Rämö, O.T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    The source of Proterozoic anorthosite and rapakivi granite magmatism: evidence from combined in situ Hf–O isotopes of zircon in the Ahvenisto complex, southeastern Finland.2015In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 172, p. 103-112Article in journal (Refereed)
    Abstract [en]

    The isotope compositions of massif-type anorthosites in Proterozoic anorthosite–mangerite–charnockite–granite (AMCG) complexes are commonly dominated by crustal values. Olivine-bearing anorthositic rocks in several AMCG suites have, however, been shown to display juvenile character, suggesting that variably depleted mantle reservoirs were involved in their genesis. A coupled in situ zircon Hf–O isotope dataset from the 1.64 Ga Ahvenisto AMCG complex in the 1.54–1.65 Ga Fennoscandian rapakivi granite–massif-type anorthosite province reveals correlated juvenile isotope signals (δ18Ozrn = 5.4–6.6‰; initial ϵHf = −1.1 to +3.4) in the most primitive gabbroic rock type of the suite suggesting a depleted mantle origin for the anorthositic rocks. This signal is not as prominent in the more evolved co-magmatic anorthositic rocks (δ18Ozrn = 6.3–7.8‰; initial ϵHf = −0.8 to +2.0), most probably owing to contamination of the mantle-derived primary magma by crustal material. A rapakivi granite associated with the anorthositic rocks has different isotope composition (δ18Ozrn = 7.4–8.6‰; initial ϵHf = −2.1 to +0.5) that points to a crustal source.

  • 26.
    Hode Vuorinen, Jaana
    et al.
    Stockholms universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Mansfeld, Joakim
    Stockholms universitet.
    Skelton, Alasdair D. L.
    Stockholms universitet.
    Compositional variations (major and trace elements) of clinopyroxene and Ti-andradite from pyroxenite, ijolite and nepheline syenite, Alnö Island, Sweden2005In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 81, p. 55-77Article in journal (Refereed)
  • 27. Jeon, H.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    A Critical Evaluation of U–Pb Calibration Schemes Used in SIMS Zircon Geochronology.2015In: Geostandards and Geoanalytical Research, ISSN 1639-4488, E-ISSN 1751-908X, Vol. 39, p. 443-452Article in journal (Refereed)
    Abstract [en]

    Precision and accuracy in SIMS zircon geochronology strongly depend on the method of determination of the interelement ion ratios (e.g., 206Pb/238U) from the measured secondary ion ratios (206Pb+/238U+). Six possible U–Pb calibrations (Pb/U–UO2/U, Pb/U–UO/U, Pb/U–UO2/UO, Pb/UO–UO2/U, Pb/UO–UO/U, Pb/UO–UO2/UO) based on simple power law relationships, and Pb/UO2-related one- and two- (a power law) dimensional ones were compared using data acquired on the 91500 zircon reference material from one hundred measurement sessions, to determine the most statistically reliable scheme. Taking advantage of U oxide species (UO and UO2) over atomic U, due to their similar energy distribution to Pb and higher intensities, the data calibrated with Pb/UO–UO2/UO showed the smallest mean uncertainties and dispersions, and provided the best-fit calibration curve consistently. Although it was demonstrated with Temora 2 that the unknown zircon age was not changed significantly by different calibrations, its precision could be improved using the Pb/UO–UO2/UO calibration in zircon geochronology.

  • 28. Jordan, T.A.
    et al.
    Neale, R.F.
    Leat, P.T.
    Vaughan, A.P.M.
    Flowerdew, M.J,
    Riley, T.R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Ferraccioli, F.
    Structure and evolution of Cenozoic arc magmatism on the Antarctic Peninsula; a high resolution aeromagnetic perspective2014In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 198, p. 1758-1774Article in journal (Refereed)
  • 29.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Balz, B.S
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon.2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, p. 431-434Article in journal (Refereed)
    Abstract [en]

    Constraining the origin and history of very ancient detrital zircons has unique potential for furthering our knowledge of Earth’s very early crust and Hadean geodynamics. Previous applications of the Ti-in-zircon thermometer to >4 Ga zircons have identified a population with relatively low crystallization temperatures () of ~685 °C. This could possibly indicate wet minimum-melting conditions producing granitic melts, implying very different Hadean terrestrial geology from other rocky planets. Here we report the first comprehensive ion microprobe study of zircons from a transect through the differentiated Sudbury impact melt sheet. The new zircon Ti contents and corresponding  fully overlap with those of the Hadean zircon population. Previous studies, which measured Ti in impact melt sheet zircons did not find this wide range because they analyzed samples only from a restricted portion of the melt sheet and because they used laser ablation analyses that can overestimate true Ti content. It is important to note that internal differentiation of the impact melt is likely a prerequisite for the observed low  in zircons from the most evolved rocks. On Earth, melt sheet

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  • 30.
    Kenny, G.G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kamber, B.S.
    Differentiated impact melt sheets may be a potential source of Hadean detrital zircon: Reply2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, article id e399Article in journal (Refereed)
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  • 31. Klawonn, I.
    et al.
    Nahar, N.
    Walve, J.
    Andersson, B.
    Olofsson, M.
    Svedén, J.B.
    Littmann, S.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kuypers, M.M.M.
    Ploug, H.
    Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea).2016In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229Article in journal (Refereed)
    Abstract [en]

    We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was eightfold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e. N2 was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.

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  • 32. Kleinhanns, I.C.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Nolte, N.
    Baero, W.
    Wilsky, F.
    Hansen, B.T.
    Schoenberg, R.
    Mode and timing of granitoid magmatism in the Västervik area (SE Sweden, Baltic Shield): Sr-Nd isotope and SIMS U-Pb age constraints.2015In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 212-215, p. 321-337Article in journal (Refereed)
    Abstract [en]

    Observed geochemical and geophysical signatures in the southern Svecofennian domain (SD) and the Transscandinavian Igneous Belt (TIB) are explained through a model of tectonic cycling and episodic south-westward migration of a subduction zone system. The Västervik area is located between these two major tectonic domains and as such has received much attention. Granitoids of the Västervik area were recently re-grouped and classified within the context of this larger regional tectonic model, but a discrepancy between previous relative age estimations and the few available granitoid age determinations was noted. To address this issue, we have dated 13 granitoid samples using a high spatial resolution secondary ion mass spectrometry (SIMS) U–Pb technique. Our new results constrain the intrusion of the majority of granitoids to 1819–1795 Ma, thus placing them into the TIB-1 period. This age range also encompasses our new ages from the central granodiorite belt and the Örö-Hamnö pluton, demonstrating a previous overestimation of older granitoid generations in the Västervik area. Nonetheless, it is shown that Askersund/TIB-0 magmatism, represented by an augen gneiss sample dated to 1846 Ma, is unambiguously present as far south as the Västervik region. The anatectically generated leucogranites reveal TIB-1 ages and, as expected, older inherited zircon derived from the parental metasedimentary Västervik formation. By simple Sr–Nd isotope modeling it is further possible to deduce that most TIB-1 granitoids follow a simple (assimilation-) fractional crystallization petrogenetic trend. The youngest granitoid generation was produced through low-pressure fluid-absent crustal melting. In conclusion, granitoids of the Västervik area fit well into the proposed model for south-westward migration of a subduction zone system active in the Svecofennian domain and represent a new tectonic cycle. It is therefore possible to link the Svecofennian domain and the Transscandinavian Igneous Belt within a single evolutionary scenario explaining the observed granitoid petrology, geochemistry and geochronology. The study area is located at the edge of a particularly long-lived active continental margin that started to operate during the supercontinent Columbia at ca. 1.8 Ga and the presented model explains how this margin initiated at its eastern end.

  • 33. Kotková, J.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Schaltegger, U.
    D'Azbac, F.-X.
    The fate of zircon during UHT–UHP metamorphism: isotopic (U/Pb, δ18O, Hf) and trace element constraints.2016In: Journal of Metamorphic Geology, ISSN 0263-4929, E-ISSN 1525-1314, Vol. 34, p. 719-739Article in journal (Refereed)
    Abstract [en]

    Garnet–clinopyroxene ultra-high-pressure (UHP) rocks from the northern Bohemian Massif contain zircon with micro-diamond inclusions. Trace element concentrations, oxygen and hafnium isotopic composition and U–Pb age of distinct textural domains in zircon characterize their growth conditions and temporal evolution. Diamond-bearing zircon mantle domains with relicts of oscillatory zoning have uniform Th/U ratios (~0.1–0.2), high-Ti contents (110–190 ppm, corresponding to temperatures of at least 1100 °C), and some (two of 17 mantle analyses) preserve steep heavy rare earth element (HREE) patterns with YbN/GdN = 10–11, with a weak negative Eu anomaly. These signatures are consistent with crystallization from a melt under UHP/ultra-high-temperature (UHT) conditions. Some of the bright-cathodoluminscence (CL) rims preserve Th/U and Ti values characteristic of the zircon mantles, but others show elevated Th/U ratios of ~0.3–0.4 and lower Ti contents (20–40 ppm; only 13 ppm in a rare low-CL outer rim). As they feature flat HREE patterns and negative Eu anomalies and commonly make embayments and truncate the mantle zoning, we suggest that they have formed through recrystallization in the solid state during exhumation of the rock, when both garnet and plagioclase were stable. The three zircon domains, that is, cores, mantles and rims, yield U–Pb concordia ages of 340.9 ± 1.5, 340.3 ± 1.5 and 341.2 ± 3.4 Ma respectively. When linked to the previously reconstructed P–T path of the rock, the error limits of the zircon mantle and rim ages constrain the exhumation of the rocks from depth of ~140 km (UHP) to ~80 km (HP) to a minimum rate of 1.5 cm yr−1. The zircon cores are heterogeneous in terms of Th/U ratio (below 0.1 but also above 0.2) and REE characteristics, and their εHf values scatter between −15.7 and +4.8 with similar values for individual domains within a single zircon grain suggesting a very localized control on hafnium isotope composition on a grain scale. The non-equilibrated εHf values as well as a large range of the Hf-depleted mantle model ages possibly reflect the presence of a heterogeneous population of old zircon. Consequently, the uniform and young 238U/206Pb ages may represent (near-)complete resetting of the U–Pb geochronometer during the UHP–UHT event at c. 340 Ma through dissolution–reprecipitation process. In contrast to Hf, the oxygen isotope composition of zircon is homogeneous, ranging between 7.8‰ and 9.6‰ VSMOW, reflecting a source containing upper crustal material and homogenization at UHP–UHT conditions. Our study documents that continental crust was subducted to mantle depths at c. 340 Ma during the Variscan orogeny and was subsequently very rapidly exhumed, implying that the sequence of events was faster than can be resolved by the secondary ion mass spectrometry technique.

  • 34. Kusebauch, C.
    et al.
    John, T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engvik, A.
    Apatite as probe for the halogen composition of metamorphic fluids (Bamble Sector, SE Norway)2015In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 170, p. 1-20, article id 34Article in journal (Refereed)
    Abstract [en]

    Halogen composition of replaced apatite formed during a regional metasomatic event (Bamble Sector, SE Norway) reveals information about the composition and evolution of the hydrothermal fluid. Infiltration and pervasive fluid flow of highly saline fluids into gabbroic bodies lead to scapolitization and amphibolitization, where magmatic Cl-rich apatite reacts with the hydrothermal fluid to form OH- and/or F-rich apatite. Apatite from highly altered samples adjacent to the shear zone has highest F (up to 15,000 µg/g) and lowest Br (4–25 µg/g) concentrations, whereas apatite from least altered samples has very low F (30–200 µg/g) and high Br (30–85 µg/g). In addition, individual replaced apatite grains show a zonation in F with high concentrations along rims and cracks and low F in core regions. Iodine concentrations remain rather constant as low values of 0.18–0.70 µg/g. We interpret all observed compositional features of replaced apatite to be the result of a continuous evolution of the fluid during fluid–rock interaction. Due to its high compatibility, F from the infiltrating fluid is incorporated early into recrystallized apatite (close to shear zone and rims of individual apatite grains). In contrast, Br as an incompatible halogen becomes enriched in the fluid and is highest in the most evolved fluid. Using experimental partition data between replaced apatite and fluid, we calculated F concentrations of the evolving fluid to decrease from 60 to <1 µg/g and Br to increase from ~1200 to ~5000 µg/g; I concentrations of the fluid are constant in the order of 370 µg/g. Although Cl is expected to show a similar behavior as Br, replaced apatite has constant Cl concentrations throughout the alteration sequence (~1 wt.%), which is likely the result of a rather constant Cl activity in the fluid. Chlorine stable isotope values of individual apatite grains are heterogeneous and range from −1.2 to +3.7 ‰. High δ 37Cl values are generally correlated with OH-rich zones of replaced apatite, whereas low δ 37Cl values are measured in F-rich zones of replaced apatite and in Cl-apatite of probably magmatic origin. Though apatite δ 37Cl values follow the general bulk trend, the individual δ 37Cl signature seems to reflect the highly localized composition of interfacial fluid at the reaction front. Our observations suggest that apatite can be used as a fluid probe for F, Br, and I to detect a compositional evolution of the fluid, which can be quantified by using experimentally derived partition coefficients. Partitioning of Cl and Cl stable isotopes between highly saline fluids and apatite is complex and likely controlled by more unknown factors than just the Cl concentration.

  • 35. Kusebauch, C.
    et al.
    John, T.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Klemme, S.
    Putnis, A.
    Distribution of halogens between fluid and apatite during fluid-mediated replacement processes.2015In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 170, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Apatite (Ca5(PO4)3(OH, F, Cl)) is one of the main host of halogens in magmatic and metamorphic rocks and plays a unique role during fluid–rock interaction as it incorporates halogens (i.e. F, Cl, Br, I) and OH from hydrothermal fluids to form a ternary solid solution of the endmembers F-apatite, Cl-apatite and OH-apatite. Here, we present an experimental study to investigate the processes during interaction of Cl-apatite with different aqueous solutions (KOH, NaCl, NaF of different concentration also doped with NaBr, NaI) at crustal conditions (400–700 °C and 0.2 GPa) leading to the formation of new apatite. We use the experimental results to calculate partition coefficients of halogens between apatite and fluid. Due to a coupled dissolution–reprecipitation mechanism new apatite is always formed as a pseudomorphic replacement of Cl-apatite. Additionally, some experiments produce new apatite also as an epitaxial overgrowth. The composition of new apatite is mainly governed by complex characteristics of the fluid phase from which it is precipitating and depends on composition of the fluid, temperature and fluid to mineral ratio. Furthermore, replaced apatite shows a compositional zonation, which is attributed to a compositional evolution of the coexisting fluid in local equilibrium with the newly formed apatite. Apatite/fluid partition coefficients for F depend on the concentration of F in the fluid and increase from 75 at high concentrations (460 μg/g F) to 300 at low concentrations (46 μg/g F) indicating a high compatibility of F in apatite. A correlation of Cl-concentration in apatite with Cl concentration of fluid is not observed for experiments with highly saline solutions, composition of new apatite is rather governed by OH concentration of the hydrothermal fluid. Low partition coefficients were measured for the larger halogens Br and I and vary between 0.7 * 10−3–152 * 10−3 for Br and 0.3 * 10−3–17 * 10−3 for I, respectively. Br seems to have D values of about one order of magnitude higher than I. These data allow an estimation of the D values for the other halogens based on a lattice strain model which displays a sequence with DF of ∼120, DOH of ∼100, DCl of ∼2.3 DBr ∼0.045, and DI ∼0.0025. Results from this experimental study help to better understand fluid–rock interaction of an evolving fluid, as it enables the composition of hydrothermally derived apatite to be used as a fluid probe for halogens at crustal conditions. It further shows the importance of mineral replacement as one of the key reactions to generate apatite of different composition.

  • 36. Kusiak, M.A.
    et al.
    Dunkley, D.J.
    Wirth, R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wilde, S.A.
    Marquardt, K.
    Metallic lead nanospheres discovered in ancient zircons.2015In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, p. 4958-4963Article in journal (Refereed)
    Abstract [en]

    Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U–Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages, in some cases yielding apparent Hadean (>4 Ga) ages from younger zircons. Documenting the composition and mineralogy of these Pb-enriched domains is essential for understanding the processes of Pb redistribution in zircon and its effects on geochronology. Using high-resolution scanning transmission electron microscopy, we show that Pb-rich domains previously identified in zircons from East Antarctic granulites are 5–30 nm nanospheres of metallic Pb. They are randomly distributed with respect to zircon crystallinity, and their association with a Ti- and Al-rich silica melt suggests that they represent melt inclusions generated during ultra-high temperature metamorphism. Metallic Pb is exceedingly rare in nature and previously has not been reported in association with high-grade metamorphism. Formation of these metallic nanospheres within annealed zircon effectively halts the loss of radiogenic Pb from zircon. Both the redistribution and phase separation of radiogenic Pb in this manner can compromise the precision and accuracy of U–Pb ages obtained by high spatial resolution methods.                           

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  • 37. Lahtinen, R.
    et al.
    Huhma, H.
    Lahaye, Y.
    Lode, S.
    Heinonen, S.
    Sayab, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Paleoproterozoic magmatism across the Archean-Proterozoic boundary in central Fennoscandia: Geochronology, geochemistry and isotopic data (Sm–Nd, Lu–Hf, O).2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 262, p. 507-525Article in journal (Refereed)
    Abstract [en]

    The central Fennoscandia is characterized by the Archean-Proterozoic (AP) boundary and the Central Finland Granitoid Complex (CFGC), a roundish area of approximately 40,000 km2 surrounded by supracrustal belts. Deep seismic reflection profile FIRE 3A runs across these units, and we have re-interpreted the profile and crustal evolution along the profile using 1.92–1.85 Ga plutonic rocks as lithospheric probes. The surface part of the profile has been divided into five subareas: Archean continent (AC) in the east, AP, CFGC, boundary zone (BZ) and the Bothnian Belt (BB) in the west. There are 12 key samples from which zircons were studied for inclusions and analyzed (core-rim) by ion probe for U–Pb dating and oxygen isotopes, followed by analyzes for Lu–Hf by LA–MC–ICP–MS.

    The AC plutonic rocks (1.87–1.85 Ga) form a bimodal suite, where the proposed mantle source for the mafic rocks is 2.1–2.0 Ga metasomatized lower part of the Archean subcontinental lithospheric mantle (SCLM) and the source for the felsic melts is related plume-derived underplated mafic material in the lower crust. Variable degrees of contamination of the Archean lower crust have produced “subduction-like” Nb–Ta anomalies in spidergrams and negative εNd (T) values in the mafic-intermediate rocks. The felsic AC granitoids originate from a low degree melting of eclogitic or garnet-bearing amphibolites with titanite ± rutile partly prevailing in the residue (Nb–Ta fractionation) followed by variable degree of assimilation/melting of the Archean lower crust. The AP plutonic rocks (ca. 1.88 Ga) can be divided into I-type and A-type granitoids (AP/A), where the latter follow the sediment assimilation trend in ASI diagram, have high δ18O values (up to 8‰) in zircons and exhibit negative Ba anomalies (Rb–Ba–Th in spidergram), as found in sedimentary rocks. A mixing/assimilation of enriched mantle-derived melts with melts from already migmatized sedimentary rocks ± amphibolites is proposed. The CFGC is characterized by both I-type and A-type (CFGC/A) intermediate and felsic granitoids. The I-type granitoids are divided into two groups at ≥ 1885 Ma and ≤ 1882 Ma, where the latter overlap in age with the CFGC/A granitoids. Both I-type CFGC and CFGC/A granitoids are interpreted to have formed from mixing of Paleoproterozoic SCLM-derived melts with crustal melts from hydrous and dry intermediate-felsic igneous sources, respectively. The geochemistry, dominantly δ18O values below 6.5‰ in zircons and TDM (2.11–2.42 Ga) of the CFGC granitoids favor the occurrence of older crust (ca. 2.1–2.0 Ga) in their genesis. The BZ granitoids are similar in age but more juvenile with TDM ages between 1.94 Ga and 2.16 Ga. The 1.92 Ga granodiorite in the BB is correlated with juvenile gneissic tonalites and granodiorites found from the AP boundary.

    We suggest that the present high-velocity lower crust under the CFGC is composed of melt-extracted granulites (crustal source age ≥ 2.0 Ga) and mafic cumulates which both formed during 1.90–1.88 Ga arc magmatism. The ≤ 1.88 Ga stage represents the end of compression/transpression and is followed by 1.87–1.86 Ga buckling, forming the Bothnian Oroclines.

  • 38. McAteer, Claire A.
    et al.
    Daly, J. Stephen
    Flowerdew, Michael J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Monaghan, Niamh M.
    Sedimentary provenance, age and possible correlation of the Iona Group, SW Scotland2014In: Scottish Journal of Geology, ISSN 0036-9276, E-ISSN 2041-4951, Vol. 50, no 2, p. 143-158Article in journal (Refereed)
  • 39. McKay, C.L.
    et al.
    Groenevold, J.
    Filipsson, H.L.
    Gallego-Torres, D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Toyofuku, T.
    Romero, O.E.
    A comparison of benthic foraminiferal Mn/Ca and sedimentary Mn/Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system.2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, p. 5415-5428Article in journal (Refereed)
    Abstract [en]

    Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related to Marine Isotope Stage 3 (35–28 ka), the Last Glacial Maximum (28–19 ka), Heinrich Event 1 (18–15.5 ka), Bølling Allerød (15.5–13.5 ka) and the Younger Dryas (13.5–11.5 ka). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal assemblage data.

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  • 40. Molnár, F.
    et al.
    Mänttäri, I.
    O'Brien, H.
    Lahaye, Y.
    Pakkanen, L.
    Johanson, B.
    Käpyaho, A.
    Sorjonen-Ward, P.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Sakellaris, G.
    Boron, sulphur and copper isotope systematics in the orogenic gold deposits of the Archaean Hattu schist belt, eastern Finland2016In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 77, p. 133-162Article in journal (Refereed)
    Abstract [en]

    The Hattu schist belt is located in the western part of the Archaean Karelian domain of the Fennoscandian Shield. The orogenic gold deposits with Au–Bi–Te geochemical signatures are hosted by NE–SW, N–S and NW–SE oriented shear zones that deform 2.76–2.73 Ga volcanic and sedimentary sequences, as well as 2.75–2.72 Ga tonalite–granodiorite intrusions and diverse felsic porphyry dykes. Mo–W mineralization is also present in some tonalite intrusions, both separate from, and associated with Au mineralization. Somewhat younger, unmineralized leucogranite intrusions (2.70 Ga) also intrude the belt. Lower amphibolite facies peak metamorphism at 3–5 kbar pressures and at 500–600 °C temperatures affected the belt at around 2.70 Ga and post-date hydrothermal alteration and ore formation. In this study, we investigated the potential influence of magmatic-hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope (B, S, Cu) studies of tourmaline and sulphide minerals by application of in situ SIMS and LA ICP MS analytical techniques.

    Crystal chemistry of tourmaline from a Mo–W mineralization hosted by a tonalite intrusion in the Hattu schist belt is characterized by Fe3 +–Al3 +-substitution indicating relatively oxidizing conditions of hydrothermal processes. The range of δ11B data for this kind of tourmaline is from − 17.2‰ to − 12.2‰. The hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry (e.g. dravite–povondraite compositional trend with Fe3 +–Al3 + substitution) and δ11B values between − 19.0‰ and − 9.6‰. The uvite–foitite compositional trend and δ11B ‰ values between − 24.1% and − 13.6% characterize metasomatic–hydrothermal tourmaline from the metasediment-hosted gold deposits. Composition of hydrothermal vein-filling and disseminated tourmaline from the gold-bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment-hosted tourmaline. Rock-forming (magmatic) tourmaline from leucogranite has δ11B values between − 14.5‰ and − 10.8‰ and the major element composition is similar to that of the metasediment-hosted tourmaline.

    The range of δ34SVCDT values measured in pyrite, chalcopyrite and pyrrhotite is from − 9.1 to + 8.5‰, which falls within the typical range of sulphur isotope data for Archaean orogenic gold deposits. In the Hattu schist belt, positive δ34SVCDT values characterize metasediment-hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite. The δ34SVCDT values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite. Purely negative values were only recorded from the pyrite-dominated gold mineralization within metavolcanic units. Therefore the shift of δ34SVCDT values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids. The range of measured δ65CuNBS978 values from chalcopyrite is from − 1.11 to 1.19‰. Positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks. Positive and negative δ65CuNBS978 values occur in the ores hosted by metavolcanic rocks. There is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains.

    Evaluation of sulphur and boron isotope data together and comparisons with other Archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the Hattu schist belt. Variations in major element and boron isotope compositions in tourmaline, as well as in the δ34SVCDT values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes. The results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original, distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes.

  • 41.
    Nemchin, A.A.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Humayun, M.
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Hewins, R.H.
    Lorand, J.-P.
    Kennedy, A.
    Grange, M.
    Zanda, B.
    Fieni, C.
    Deldicque, D.
    Record of the ancient martian hydrosphere and atmosphere preserved in zircon from a martian meteorite2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, p. 638-642Article in journal (Refereed)
    Abstract [en]

    Mars exhibits ample evidence for an ancient surfacehydrosphere. The oxygen isotope compositions of carbonateminerals and alteration products in martian meteoritessuggest that this ancient hydrosphere was not in isotopicequilibrium with the martian lithosphere1–4. Martian meteoriteNWA 7533 is composed of regolith breccia from the heavilycratered terrains of ancient Mars and contains zircon grainsfor which U–Pb ages have been reported5. Here we reportvariations between the oxygen isotopic compositions offour zircon grains from NWA 7533. We propose that thesevariations can be explained if the mantle melts from whichthe zircon crystallized approximately 4.43Gyr ago hadassimiliated 17O-enriched regolith materials, and that someof the zircon grains, while in a metamict state, were lateraltered by low-temperature fluids near the surface less than1.7Gyr ago. Enrichment of the martian regolith in 17O beforethe zircon crystallized, presumably through exchange withthe 17O-enriched atmosphere or hydrosphere during surfacealteration, suggests that the thick primary atmosphere ofMars was lost within the first 120Myr after accretion. Weconclude that the observed variation of 17O anomalies in zirconfrom NWA 7533 points to prolonged interaction between themartian regolith, atmosphere and hydrosphere.

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  • 42. Neumann, E.-R.
    et al.
    Abu El-Rus, M.A:
    Tiepolo, M.
    Ottolini, L.
    Vannucci, R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Serpentinization and deserpentinization reactions in the upper mantle beneath Fuerteventura revealed by peridotite xenoliths with fibrous orthopyroxene and mottled olivine.2015In: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 56, p. 3-31Article in journal (Refereed)
    Abstract [en]

    Mantle xenoliths collected from Fuerteventura, one of the easternmost Canary Islands, exhibit a complex evolutionary history comprising events of depletion, serpentinization, dehydration and melt metasomatism. Each of these events left imprints on both the texture and chemistry of the xenoliths. Extensive partial melting is shown by complete lack of primary clinopyroxene, the ultra-refractory trace element composition of orthopyroxene porphyroclasts, and low heavy rare earth element contents as compared with abyssal peridotites sampled along mid-ocean ridges and oceanic fracture zones, in the xenoliths least affected by later metasomatism. In many xenoliths the original orthopyroxene porphyroclasts and some olivines are replaced by fibrous aggregates of orthopyroxene and/or large, deformed olivine porphyroclasts with mottled rims with stringy glass and fluid inclusions. Such features are very rare in ocean island xenoliths. Unusually high H2O and Cl concentrations, together with very high H2O/Ce and Cl/K ratios in interstitial glasses, suggest that the fibrous orthopyroxene formed by local serpentinization by hot seawater. The volume increase accompanying the serpentinization caused extensive fracturing of adjacent olivine porphyroclasts. The most likely scenario for local mantle invasion by hydrous fluids is along deep faults and fractures caused by tectonic movements along the continent–ocean transition during the early phases of the opening of the Atlantic Ocean. The peridotites were later (probably during the Canary Islands magmatism) dehydrated, causing the serpentine minerals to be replaced by porous domains of fibrous orthopyroxene. Hydrous fluids released by the deserpentinization escaped into neighbouring and overlying rocks leaving trails of fluid inclusions along fractures and grain boundaries causing mottled rims and zones in olivine porphyroclasts. During the Canary Islands magmatism the upper mantle beneath Fuerteventura was also infiltrated by enriched silicate magmas that caused different degrees of Fe–Ti-metasomatism. A higher degree of melt metasomatism in rocks with fibrous orthopyroxene and mottled olivine than in the massive harzburgites strongly suggests that the sublithospheric Canarian magmas reused serpentinized extensional faults during their rise to the surface. The strongest degree of melt metasomatism appears to have resulted in the formation of lherzolites, wehrlites, and dunites.                  

  • 43. Ng, S.W.-P.
    et al.
    Chung, S.-L.
    Robb, L.J.
    Searle, M.P.
    Ghani, A.A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Oliver, G.J.H.
    Sone, M.
    Gardiner, N.J.
    Roselee, M.H.
    Petrogenesis of Malaysian granitoids in the Southeast Asian Tin Belt: Part 1. Geochemical and Sr-Nd isotopic characteristics.2015In: Geological Society of America Bulletin, ISSN 0016-7606, E-ISSN 1943-2674, Vol. 127, p. 1209-1237Article in journal (Refereed)
    Abstract [en]

    The Malaysian granitoids of the Southeast Asian tin belt have been traditionally divided into a Permian to Late Triassic “I-type”–dominated arc-related Eastern province (Indochina terrane) and a Late Triassic “S-type”–dominated collision-related Main Range province (Sibumasu terrane), separated by the Bentong-Raub Paleo-Tethyan suture that closed in the Late Triassic. The present study, however, shows that this model is oversimplified and that the direct application of Chappell and White’s (1974) I- and S-type classification cannot account for many of the characteristics shared by Malaysian granitoids. Despite being commonly hornblende bearing, as is typical for I-type granites, the roof zones of the Eastern province granites are hornblende free. In addition, the Main Range province granitoids contain insignificant primary muscovite, and are dominated by biotite granites, mineralogically similar to many of the plutons of the Eastern province. In general, the Malaysian granitoids from both provinces are more enriched in high field strength elements than typical Cordilleran I- and S-type granitoids. The mineralogy and geochemistry of the Eastern province granitoids, and their relationship with contemporaneous volcanics, confirm their I-type nature. The bulk liquid lines of descent of both granitic provinces largely overlap with one another. Sr-Nd isotopic data further demonstrate that the Malaysian granitoids, especially those of the Main Range, were hybridized melts derived from two “end-member” source regions, one of which is isotopically similar to the Kontum orthoamphibolites and the other akin to the Kontum paragneisses of the Indochina block. However, there are differences in the source rocks for the two provinces, and it is suggested in this paper that these are related to differing proportions of igneous and sedimentary protoliths. The incorporation of sedimentary-sourced melts in the Eastern province is insignificant, which allowed the granites in this belt to maintain their I-type nature. The presence of minor primary tin mineralization in the Eastern province compared to the much more significant tin endowment in the Main Range is considered to reflect the incorporation of a smaller proportion of sedimentary protolith in the melt products of the former.                  

  • 44. Ng, S.W.--P.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Searle, M.P.
    Robb, L.J.
    Ghani, A.A.
    Chung, S.-L.
    Oliver, G.J.H.
    Sone, M.
    Gardiner, N.J.
    Roselee, M.H.
    Petrogenesis of Malaysian granitoids in the Southeast Asian Tin Belt: Part 2. U-Pb zircon geochronology and tectonic model.2015In: Geological Society of America Bulletin, ISSN 0016-7606, E-ISSN 1943-2674, Vol. 127, p. 1238-1258Article in journal (Refereed)
    Abstract [en]

    In our complementary geochemical study (Part 1), the Malaysian granitoids of the Southeast Asian tin belt were divided into a Middle Permian to Late Triassic I-type–dominated Eastern province (Indochina terrane) and a Triassic to Early Jurassic transitional I/S-type Main Range province (Sibumasu terrane), separated by the Bentong-Raub suture zone which closed in the Late Triassic. Previous geochronology has relied on only a few U-Pb zircon ages together with K-Ar and whole rock Rb-Sr ages that may not accurately record true magmatic ages. We present 39 new high-precision U-Pb zircon ion microprobe ages from granitoids and volcanics across the Malay Peninsula. Our results show that ages from the Eastern province granitoids span 289–220 Ma, with those from the Main Range province granitoids being entirely Late Triassic, spanning 227–201 Ma. A general westerly younging magmatic trend across the Malay Peninsula is considered to reflect steepening and roll-back of the Bentong-Raub subduction zone during progressive closure of Paleo-Tethys. The youngest ages of subduction-related granites in the Eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the Paleo-Tethyan suture zone. Our petrogenetic and U-Pb zircon age data support models that relate the Eastern province granites to pre-collisional Andean-type magmatism and the western Main Range province granites to syn- and post-collisional crustal melting of Sibumasu crust during the Late Triassic. Tin mineralization was mainly associated with the latter phase of magmatism. Two alternative tectonic models are discussed to explain the Triassic evolution of the Malay Peninsula. The first involves a second Late Triassic to Jurassic or Early Cretaceous east-dipping subduction zone west of Sibumasu where subduction-related hornblende and biotite–bearing granites along Sibumasu are paired with Main Range crustal-melt tin-bearing granites, analogous to the Bolivia Cordilleran tin-bearing granite belt. The second model involves westward underthrusting of Indochina beneath the West Malaya Main Range province, resulting in crustal thickening and formation of tin-bearing granites of the Main Ranges. Cretaceous granitoids are also present locally in Singapore (Ubin diorite), on Tioman Island, in the Noring pluton, of the Stong complex (Eastern Province), and along the Sibumasu terrane in southwest Thailand and Burma (Myanmar), reflecting localized crustal melting.                  

  • 45. Nikogosian, I.K.
    et al.
    Ersoy, Ö.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Mason, P.R.D.
    de Hoog, J.C.M.
    Wortel, R.
    van Bergen, M.J.
    Multiple subduction imprints in the mantle below Italy detected in a single lava flow.2016In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 449, p. 12-19Article in journal (Refereed)
    Abstract [en]

    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western–Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  • 46. Niu, D.J.
    et al.
    Renock, D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Leone, J.
    Rowe, H.
    Landis, J.D.
    Hamren, K.
    Symcox, C.W.
    Sharma, M.
    A relict sulfate-methane transition zone in the mid-Devonian Marcellus Shale.2016In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 182, p. 73-87Article in journal (Refereed)
    Abstract [en]

    A barium-enriched interval of Marcellus Shale (Middle Devonian Oatka Creek Formation) from a core in Chenango County, NY contains ∼100 μm diameter ellipsoidal grains with variable mineralogical compositions between pure barite and pure pyrite endmembers. Petrographic characterization and in-situ sulfur isotope analysis by Secondary Ion Mass Spectrometry (SIMS) was performed to better understand the diagenetic conditions under which these grains form and are preserved in the shale. Textural relationships suggest partial to complete pseudomorphic replacement of ellipsoidal barite by pyrite. Spatially, the ellipsoidal grains are concentrated in discrete layers parallel to original bedding and intervals within these layers often contain grains with similar degrees of replacement. The fraction of barite replaced by pyrite between these intervals can vary significantly, which is remarkable considering these intervals are separated by stratigraphic distances on the order of mm to cm in the shale (depths equivalent to deposition over 10’s–1000’s of years).

    The mean δ34S of barite and pyrite in ellipsoidal grains is 63.3 ± 3.6‰ and 2.2 ± 3.0‰, respectively, indicating that the grains are authigenic. Mass balance calculations based on density and stoichiometric differences between barite and pyrite indicate that reduction of sulfate from barite alone cannot be the sole source of sulfur in the replaced grains: only ∼23% of sulfur in pyrite comes from the dissolution of barite while the remainder derives from an additional source with δ34S = −17.6 ± 1.3‰. We suggest that pseudomorphic replacement of barite led first to the formation of greigite (Fe3S4), where one mole of sulfur was provided by barite and the other three moles of sulfur were contributed by FeS(aq); the latter formed by reaction of Fe2 + with sulfide from microbial sulfate reduction. Transformation of greigite to pyrite occurred via the sulfur addition and/or iron loss pathways. These observations suggest the following mechanism for the replacement of barite by pyrite in the ellipsoidal barite grains: (1) burial of authigenic barite below the sulfate–methane transition zone (SMTZ), and (2) partial to complete dissolution of the grain and concomitant precipitation of greigite (and its subsequent transformation to pyrite) in the presence of pore water depleted in sulfate and enriched in FeS(aq) and polysulfides. We suggest that closely-spaced intervals containing different barite to pyrite ratios may reflect fine-scale temporal shifts or fluctuations in the position of the SMTZ due to variable rates of methanogenesis and/or sedimentation during diagenesis.

  • 47. Næraa, Tomas
    et al.
    Kemp, Anthony
    Scherstén, Anders
    Rehnström, Emma
    Rosing, Minik
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    A lower crustal mafic source for the ca. 2550 Ma Qôrqut Granite Complex in southern West Greenland2014In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 192-195, p. 291-304Article in journal (Refereed)
  • 48. Petersson, A.
    et al.
    Scherstén, A.
    Andersson, J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Baronoski, M.T.
    Zircon U-Pb, Hf and O isotope constraints on growth versus reworking of continental crust in the subsurface Grenville orogen, Ohio, USA.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 265, p. 313-327Article in journal (Refereed)
    Abstract [en]

    Combined U-Pb, O and Hf isotope data in zircon allows discrimination between juvenile and reworked crust, and is therefore a useful tool for understanding formation and evolution of the continental crust. The crustal evolution of basement rocks in central North America (Laurentia) is poorly constrained, as it is almost entirely overlain by Palaeozoic cover. In order to improve our understanding of the evolution of this region we present U-Pb, O and Hf isotope data from zircon in drill-core samples from the subsurface basement of Ohio. The Hf isotope data suggests juvenile crust formation at similar to 1650 Ma followed by continued reworking of a single reservoir. This similar to 1650 Ma reservoir was tapped at similar to 1450 Ma during the formation of the Granite-Rhyolite Province and subsequently reworked again during the Grenvillian orogeny. The similar to 1650 Ma crust formation model age for the suite of samples along with the presence of similar to 1650 Ma magmatic rocks suggests an eastward extension of the Mazatzal Province (or Mazatzal-like crust) and makes it a possible protolith to the subsurface basement of Ohio and surrounding Mesoproterozoic (i.e. Grenville-age) rocks. The eastward extension of this similar to 1650 Ma crustal reservoir into Ohio requires a revision of the crustal boundary defined by Nd isotopic data to be located further east, now overlapping with the Grenville front magnetic lineament in Ohio. In fact, the easternmost sample in this study is derived from a more depleted reservoir. This limits the extent of >1.5 Ga basement in subsurface Ohio and constrains the location of the crustal boundary. Further, syn-orogenic magmatism at similar to 1050 Ma suggests a potential extrapolation of the Interior Magmatic Belt into Ohio. Oxygen isotopic data in zircon suggests that during Grenvillian metamorphism, zircon recrystallisation occurred in the presence of heavy delta O-18 fluids resulting in zircon with elevated delta O-18 values.

  • 49. Petersson, A.
    et al.
    Scherstén, A.
    Bingen, B.
    Gerdes, A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Mesoproterozoic continental growth: U-Pb-Hf-O zircon record in the Idefjorden Terrane, Sveconorwegian Orogen.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 261, p. 75-95Article in journal (Refereed)
    Abstract [eo]

    The Idefjorden Terrane of the Sveconorwegian Orogen, Fennoscandia, is known to be an area of comparatively juvenile Mesoproterozoic continental growth. Here we provide an improved model of crustal growth based on new coupled zircon U-Pb-O-Lu-Hf isotopic data on thirteen samples of mafic to intermediate plutonic rocks from different domains of the Idefjorden Terrane. The new data support a retreating volcanic arc system, with shorter pulses of accretion. A gradual increase of radiogenic Hf (mean slif from 3.5 to 5.4) in plutonic rocks intruded between ca. 1630 Ma and 1560 Ma reflects an increase in juvenile mantle-derived magma in the genesis of the plutonic suites. This trend is consistent with development of an extensional back-arc rift geotectonic setting, accommodating deposition of the Stora Le-Marstrand greywacke dominated metasediment sequence. Combined isotopic information and the detrital zircon record of the Stora Le-Marstrand Formation support the interpretation that the Idefjorden Terrane was separated from the Fennoscandian Shield before the Sveconorwegian Orogeny.

  • 50. Rantakokko, Nina
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Pease, Victoria
    Windley, Brian
    Neoproterozoic evolution of the eastern Arabian basement based on a refined geochronology of the Marbat region, Sultanate of Oman2014In: Geological Society Special Publication, ISSN 0305-8719, E-ISSN 2041-4927, Vol. 392, p. 107-127Article in journal (Refereed)
12 1 - 50 of 72
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