Change search
Refine search result
456789 301 - 350 of 429
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 301. 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.                  

  • 302. Ng, S.W.P.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Tam, P.Y.
    Jayasingha, P.
    Wong, J.P.-M.
    Denyszyn, S.
    Yiu, J.S.-Y.
    Chang, S.-C.
    Ca. 820-640 Ma SIMS U-Pb age signal in the peripheral Vijayan Complex, Sri Lanka: Identifying magmatic pulses in the assembly of Gondwana.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 294, p. 244-256Article in journal (Refereed)
    Abstract [en]

    Sri Lanka comprises three roughly north-south trending amphibolite- to granulite-facies lithotectonic complexes, from west to east the Highland Complex, the Wanni Complex, and the Vijayan Complex. These terranes were correlated with other East Gondwana continental terranes with similar lithologies forming at similar ages. The Wanni Complex and the Vijayan Complex have been interpreted as volcanic arc terranes brought together by a double-sided subduction. The Highland Complex represents the metamorphosed accretionary prism within the suture when the Wanni and Vijayan Complexes were juxtaposing against each other. In contrast to the Wanni and Highland Complexes, the Vijayan Complex has yielded only a few geochronological data with satisfactory precision. Previous studies suggested that the Vijayan Complex comprises ∼1100–924 Ma granitic gneisses, which were metamorphosed during ∼590–456 Ma. More recently, ∼772–617 Ma mafic intrusions have been identified. This study divides the Vijayan granitic gneisses and the associated melt products geochemically into a low-Nb series and a more primitive high-Nb series. Our SIMS U-Pb zircon data suggested that both series have protolith magmatic ages of ∼1062–935 Ma, and metamorphic ages of ∼580–521 Ma, which is consistent with previous work. However, some of the Vijayan granitic gneisses and granitic anatectic melt products at the Highland-Vijayan tectonic mixed zone preserve an additional Tonian-Cryogenian (∼820–630 Ma) age signal. This age signal suggested that felsic magmatism also occurred when mafic granulites were emplaced along the Highland-Vijayan boundary, which is broadly coeval with to the bimodal magmatism occurring along the Highland-Wanni boundary. This study also suggests that charnockitisation in the Vijayan Complex occurred at 562 ± 6 Ma during the Neoproterozoic regional metamorphism. The Tonian-Cryogenian signal preserved in the Highland-Vijayan tectonic mixed zone can also be found in the alkaline intrusion hosted by the Namuno Terrane and the Lurio Belt in Mozambique. This indicates a relationship between the Vijayan granitic gneisses and the Lurio foreland metagranitic basement, while the Namuno Terrane and the Lurio Belt are correlated with the Highland-Vijayan tectonic mixed zone. The ages and the isotope signatures of these granitic bodies further suggest a genetic relationship of these granitic bodies with various magmatic intrusions in East Antarctica.

  • 303. 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.

  • 304.
    Nilsson, E.J. Charlotta
    et al.
    Lunds Universitet.
    Kristiansson, Per
    Lunds Universitet.
    Ros, Linus
    Lunds Universitet.
    De La Rosa, Nathaly
    Lunds Universitet.
    Elfman, Mikael
    Lunds Universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Pallon, Jan
    Lunds Universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    A nuclear geochemical analysis system for boron quantification using a focused ion beam2017In: Journal of Radioanalytical and Nuclear Chemistry, ISSN 0236-5731, E-ISSN 1588-2780, Vol. 311, p. 355-364Article in journal (Refereed)
    Abstract [en]

    Ion beam analysis has for decades been used as a tool for geochemical analysis of trace elements using both X-rays (particle induced X-ray emission) and nuclear reaction analysis. With the geoanalytical setup at the Lund Ion Beam Analysis Facility, the boron content in geological samples with a spatial resolution of 1 µm is determined through nuclear reaction analysis. In the newly upgraded setup, a single detector has been replaced by a double sided silicon strip detector with 2048 segments. After optimization, boron content in geological samples as low as 1µg g-1 can be measured.

  • 305.
    Ning, Wenxin
    et al.
    Department of Geology Lund University.
    Andersson, Per S
    Swedish Museum of Natural History, Department of Geology.
    Ghosh, Anupam
    Dept. of Geol. Sciences Jadavpur University India.
    Khan, Mansoor
    Department of Geology Lund University.
    Filipsson, Helena
    Department of Geology Lund University.
    Quantitative salinity reconstructions of the Baltic Sea during the mid-Holocene2017In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 46, no 1, p. 100-110Article in journal (Refereed)
  • 306. 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.

  • 307. Nord, Anders
    et al.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Isotopes in cultural heritage: present and future possibilities2018In: Heritage Science, E-ISSN 2050-7445, Vol. 6, no 25, p. 1-13Article in journal (Refereed)
  • 308. Nord, Anders
    et al.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Tronner, Kate
    Björling Olausson, Karin
    Lead isotope data for provenancing mediaeval pigments in Swedish mural paintings2015In: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674, Vol. 16, p. 856-861Article in journal (Refereed)
  • 309. Nord, Anders
    et al.
    Lundmark, Elin
    Asp, Mia
    Tronner, Kate
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Pigmentanalys av 1100-talsmålningarna i Torpa kyrka, Kungsör2017In: Fornvännen, ISSN 0015-7813, E-ISSN 1404-9430, Vol. 2017, no 2, p. 73-79Article in journal (Refereed)
  • 310. Nord, Anders
    et al.
    Tronner, Kate
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Gustafsson Belzacq, Marianne
    Pigment traces on medieval stonework in Goland´s churches - examination of seven 12th century baptismal fonts and a limestone pew2016In: Fornvännen, ISSN 0015-7813, E-ISSN 1404-9430, no 1, p. 17-26Article in journal (Refereed)
  • 311. Nord, Anders
    et al.
    Tronner, Kate
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Strandberg Zerpe, Birgitta
    Analysis of mediaeval Swedish paintings influenced by Russian-Byzanthine art2016In: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674Article in journal (Refereed)
  • 312. Nord, Anders
    et al.
    Tronner, Kate
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Strandberg Zerpe, Birgitta
    Analysis of mediaeval Swedish paintings influenced by Russian-Byzantine art2017In: Journal of Cultural Heritage, ISSN 1296-2074, E-ISSN 1778-3674, Vol. 23, p. 162-169Article in journal (Refereed)
  • 313.
    Nyquist, Susanne
    et al.
    Stockholms universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    An EELS study of near edge structures of the oxygen K-edge in spinels2014In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 41, p. 255-265Article in journal (Refereed)
  • 314.
    Nysten, Per
    et al.
    Sveriges geologiska undersökning.
    Persson, Stefan
    Sveriges geologiska undersökning.
    Triumf, Carl-Axel
    Sveriges geologiska undersökning.
    Persson, Per-Olof
    Swedish Museum of Natural History, Department of Geology.
    Hellström, Fredrik
    Sveriges geologiska undersökning.
    Morris, George
    Sveriges geologiska undersökning.
    U-Pb zircon dating of granodiorite from the Muddus structure, northern Sweden.2018Report (Other academic)
    Abstract [en]

    A Svecofennian granodiorite forming the core of the Muddus structure, has been dated to 1889±5 Ma. This is interpreted as the igneous crystallisation age of the rock. The geophysical signature and geological composition of this structure is also discussed.

  • 315.
    Nyström, Jan Olov
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Henríquez, Fernando
    Naranjo, José A.
    Naslund, H. Richard
    Magnetite spherules in pyroclastic iron ore at El Laco, Chile2016In: American Mineralogist, ISSN 0003-004X, Vol. 101, no 3, p. 587-595Article in journal (Refereed)
  • 316. 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)
  • 317. Panieri, G.
    et al.
    Lepland, A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wirth, R.
    Raanes, M.P.
    James, R.H.
    Graves, C.A.
    Crémière, A.
    Schneider, A.
    Diagenetic Mg-calcite overgrowths on foraminiferal tests in the vicinity of methane seeps.2017In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 458, p. 203-212Article in journal (Refereed)
    Abstract [en]

    Methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera. Here, we present structural, geochemical, and stable carbon isotope data from single foraminiferal calcite tests and authigenic Mg-calcite overgrowths in a sediment core recovered from an area of active methane seepage in western Svalbard at ca. 340 m water depth. The foraminifera are from intervals in the core where conventional bulk foraminiferal δ13C values are as low as −11.3 ‰. Mg/Ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain Mg-rich interlayers with Mg/Ca up to 220 mmol/mol. Transmission electron microscopy (TEM) of the contact point between the biogenic calcite and authigenic Mg-calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation. Secondary ion mass spectrometry (SIMS) analyses reveal that the Mg-rich layers are strongly depleted δ13C (δ13C as low as −34.1 ‰). These very low δ13C values indicate that the authigenic Mg-calcite precipitated from pore waters containing methane-derived dissolved inorganic carbon at the depth of the sulfate–methane transition zone (SMTZ). As the depth of the SMTZ can be located several meters below the sediment-seawater interface, interpretation of low foraminiferal δ13C values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care.

  • 318.
    Panikorovskii, Taras
    et al.
    Saint-Petersburg State University, Russia.
    Shilovskikh, Vladimir
    Saint-Petersburg State University, Russia.
    Avdontseva, Evgenia
    Saint-Petersburg State University, Russia.
    Zolotarev, Andrey
    Saint-Petersburg State University.
    Pekov, Igor
    Moscow State University, Russia.
    Britvin, Sergey
    Saint-Petersburg State University, Russia.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Krivovichev, Sergey
    Saint-Petersburg State University, Russia.
    Cyprine, Ca19Cu2+(Al,Mg,Mn)12Si18O69(OH)9, a new vesuvianite-group mineral from the Wessels mine, South Africa 2017In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 29, no 2, p. 295-306Article in journal (Refereed)
  • 319.
    Perchiazzi, Natale
    et al.
    Università di Pisa, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vignola, Pietro
    CNR, Milano, Italy.
    Demitri, Nicola
    ELETTRA, Trieste, Italy.
    Crystal-chemical study of ecdemite from Harstigen, a new natural member of the layered lead oxyhalides group2019In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 31, no 3, p. 609-617Article in journal (Refereed)
  • 320.
    Perchiazzi, Natale
    et al.
    Università di Pisa, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Vignola, Pietro
    CNR, Milano, Italy.
    Demitri, Nicola
    ELETTRA, Trieste, Italy.
    Gabrielsonite revisited: crystal-structure determination and redefinition of chemical formula2018In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 30, no 6, p. 1173-1180Article in journal (Refereed)
    Abstract [en]

    A reinvestigation of gabrielsonite from the holotype specimen from Långban, central Sweden, using single-crystal synchrotron X-ray diffraction, electron-microprobe techniques and Fourier-transform infrared (FTIR) spectroscopy, Raman and Mössbauer spectroscopies show that the mineral is an anhydrous Fe3+-bearing arsenite and not a hydrous Fe2+-bearing arsenate, as originally proposed. The revised ideal chemical formula of gabrielsonite is PbFe3(As3+O3)O. The mineral is related to the descloizite supergroup, but it differs through the valencies of the non-Pb cations Fe (M3+ vs. M2+) and As (3+ vs. 4+) and through lower coordination of Pb (4 vs. 7–8) and As (3 vs. 4). The redefinition of gabrielsonite (proposal 17-G) has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association.

  • 321. 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.

  • 322. 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.

  • 323.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology. University of Western Australia.
    A new 3.59 Ga magmatic suite and a chondritic source to the east Pilbara Craton2019In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, p. 51-70Article in journal (Refereed)
    Abstract [en]

    The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greenstone terrains on Earth, and is inferred to have developed on an older (> 3.8 Ga), possibly Hadean, continental substrate. Such ancient crust has, however, never been identified in outcrop. Here, we show that metamorphosed gabbroic, leucogabbroic and anorthositic rocks of the South Daltons area, in the western part of the Shaw Granitic Complex, formed at 3.59–3.58 Ga and were intruded by granitic magma at 3.44 Ga. The 3.59–3.58 Ga gabbroic rocks, here named the Mount Webber Gabbro, represent the oldest, unambiguous igneous rock emplacement in the Pilbara Craton and significantly predate the oldest volcanic activity of the 3.53–3.23 Ga Pilbara Supergroup within the East Pilbara Terrane. We interpret the Mount Webber Gabbro samples to represent fragments of a dismembered layered mafic intrusion. Mantle-like zircon δ18O and Hf isotope signatures indicate derivation from a chondritic to near chondritic mantle at ~3.59 Ga, and do not support the existence of a>3.8 Ga basement to the East Pilbara Terrane. These results strengthen the notion of an approximately chondritic>3.5 Ga mantle beneath the Pilbara Craton, and provide further evidence that recent estimates of Archean stabilised continental volumes, based on the assumption of crust extraction from a global, convecting depleted mantle reservoir, may be overestimated.

  • 324.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology. University of Western Australia.
    Kristinsdottir, Bara (Contributor)
    Kemp, Anthony (Contributor)
    Whitehouse, Martin (Contributor)
    Swedish Museum of Natural History, Department of Geology.
    Birimian crustal growth in the West African Craton: U-Pb, O and Lu-Hf isotope constraints from detrital zircon in major rivers2018In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, no 479, p. 259-271Article in journal (Refereed)
    Abstract [en]

    Combined U-Pb, O and Lu-Hf isotope analyses of detrital zircon grains from five major rivers in Ghana are used to investigate the growth and evolution of the Birimian terrane of the West African Craton. The majority of the analysed zircon yields supra-chondritic εHf values, suggesting derivation from primarily juvenile host magmas. Zircon grains from the Birim River in southwestern Ghana deviate from the generally juvenile trend, where the sub-chondritic εHf but mantle-like δ18O of the 2.15 Ga population suggest reworking of ancient, but unweathered, meta-igneous crust. Hf-O isotope data from detrital zircons of the remaining rivers are consistent with sequential crust generation between ca. 2.2 and 2.1 Ga. Oxygen isotope data suggest that the contribution from Archaean sedimentary material to felsic magmas was below 30%, and in most cases below 10%. Zircon with strongly positive εHf values and elevated δ18O indicate rapid reworking of juvenile crust within southern Ghana. An increase towards heavier oxygen isotope signatures over time suggests a maturing arc system with rapid recycling of juvenile supracrustal material during the evolution of the Birimian terrane.

  • 325.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology. University of Western Australia.
    Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes2017In: Geoscience Frontiers, ISSN 1674-9871Article in journal (Refereed)
    Abstract [en]

    Located in the southeastern parts of the Baoulé Mossi domain of the West African Craton, the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny. Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern, western and southeastern Ghana. Sub-chondritic Eps-Hf-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana. As a conservative estimate 71% of all analysed zircon grains spanning in age from 2220 Ma to 2130 Ma require contribution from a reworked Archaean source, contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust. A minimum Eps-Hf-value of 10.5 at 2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source. Combined with previously reported heavy zircon Delta-18O signatures from Birimian river zircon in Ghana, our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one, or possibly in between two Archaean aged cratons.

  • 326.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology. University of Western Australia.
    Gerdes, Axel (Contributor)
    Extensive reworking of Archaean crust within the Birimian terrane in Ghana as revealed by combined zircon U-Pb and Lu-Hf isotopes2018In: Geoscience Frontiers, Vol. 9, p. 173-189Article in journal (Refereed)
    Abstract [en]

    Located in the southeastern parts of the Baoulé Mossi domain of the West African Craton, the Birimian terrane in Ghana is known to consist of predominantly juvenile crust emplaced during the Eburnean orogeny. Here we present novel coupled zircon U-Pb and Lu-Hf isotope data from nine Birimian granitoids intruding different domains from northwestern, western and southeastern Ghana. Sub-chondritic Eps-Hf-values indicating reworking of Archaean crust are recorded in zircon from both northwestern and southeastern Ghana. As a conservative estimate 71% of all analysed zircon grains spanning in age from 2220 Ma to 2130 Ma require contribution from a reworked Archaean source, contradicting the common belief that the Birimian terrane consist of predominantly juvenile crust. A minimum Eps-Hf-value of 10.5 at 2139 Ma suggests a Palaeoarchaean to late Mseoarchaean component as the contributing ancient source. Combined with previously reported heavy zircon delta-18O signatures from Birimian river zircon in Ghana, our new data suggests reworking of Archaean aged sediments during subduction initiated crustal growth in the vicinity of one, or possibly in between two Archaean aged cratons.

  • 327.
    Petersson, Andreas
    Swedish Museum of Natural History, Department of Geology. University of Western Australia.
    Scherstén, Anders (Contributor)
    Lund University.
    Gerdes, Axel (Contributor)
    Goethe University.
    Næraa, Tomas (Contributor)
    Lund University.
    Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U–Pb and Lu–Hf isotopes2017In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 284–285, p. 122-131Article in journal (Refereed)
    Abstract [en]

    Constraints on the composition of the depleted mantle Sm–Nd and Lu–Hf crust formation ages have a long history of scientific debate. When calculating mantle extraction ages, and constructing crustal growth models, a linear evolution of incompatible trace elements in a depleted mantle since > 4 Ga is routinely used. Mantle depletion however varies regionally and over time and subduction of sediments and oceanic crust renders a mantle-wedge variously enriched relative to a modelled depleted mantle.

    Here we show that primitive mantle-derived subduction related gabbroic intrusions from southern Fennoscandia have Hf isotope compositions that are enriched relative to a MORB-like linear depleted mantle evolution curve. Extrapolation of primitive Paleoproterozoic gabbro suites enables the construction of a regional mantle evolution curve, providing improved constraints on model ages, crustal residence times and the fraction of juvenile versus reworked continental crust. Convergent margins are assumed to be one of the main sites of continental crust growth, and using an overly depleted mantle source yield model ages that are too old, and hence cumulative crustal growth models show too much crust generation early in the Earth's history. The approach of using the Hf isotope composition of zircon from primitive subduction related gabbroic intrusions as a proxy for mantle Hf isotope composition, piloted in this study, can be applied to other convergent margins.

  • 328. Pidgeon, R.T.
    et al.
    Nemchin, A.A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    The effect of weathering on U-Th-Pb and oxygen isotope systems of ancient zircons from the Jack Hills, Western Australia.2017In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 197, p. 142-166Article in journal (Refereed)
    Abstract [en]

    We report the result of a SIMS U–Th–Pb and O–OH study of 44 ancient zircons from the Jack Hills in Western Australia with ages ranging from 4.3 Ga to 3.3 Ga. We have investigated the behaviour of oxygen isotopes and water in the grains by determining δ18O and OH values at a number of locations on the polished surfaces of each grain. We have divided the zircons into five groups on the basis of their U–Th–Pb and OH-oxygen isotopic behaviour. The first group has concordant U–Th–Pb ages, minimal common Pb, δ18O values consistent with zircons derived from mantle source rocks and no detectable OH content. U–Th–Pb systems in zircons from Groups 2, 3 and 4 vary from concordant to extremely discordant where influenced by cracks. Discordia intercepts with concordia at approximately zero Ma age are interpreted as disturbance of the zircon U–Th–Pb systems by weathering solutions during the extensive, deep weathering that has affected the Archean Yilgarn Craton of Western Australia since at least the Permian. Weathering solutions entering cracks have resulted in an influx of Th and U. δ18O values of Group 2 grains fall approximately within the “mantle” range and OH is within background levels or slightly elevated. δ18O values of Group 3 grains are characterised by an initial trend of decreasing δ18O with increasing OH content. With further increase in OH this trend reverses and δ18O becomes heavier with increasing OH. Group 4 grains have a distinct trend of increasing δ18O with increasing OH. These trends are explained in terms of the reaction of percolating water with the metamict zircon structure and appear to be independent of analytical overlap with cracks. Group five zircons are characterised by U–Pb systems that appear to consist of more than one age but show only minor U–Pb discordance. Nevertheless trends in δ18O versus OH in this group of grains resemble trends seen in the other groups. The observed trends of δ18O with OH in the Jack Hills zircons are similar to those reported in a previous study of zircons from an Archean granite from south-western Australia.

  • 329. Pogge von Strandmann, Philip AE
    et al.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Murphy, Melissa J
    Lithium isotope behaviour during weathering in the Ganges Alluvial Plain2017In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 198, p. 17-31Article in journal (Refereed)
    Abstract [en]

    The Ganges river system is responsible for the transportation of a large flux of dissolved materials derived from Himalayan weathering to the oceans. Silicate weathering-driven cooling resulting from uplift of the Himalayas has been proposed to be a key player in Cenozoic climate variation. This study has analysed Li isotope (d7Li) ratios from over 50 Ganges river waters and sediments, in order to trace silicate weathering processes. Sediments have d7Li of $0‰, identical to bulk continental crust, however suspended sediment depth profiles do not display variations associated with grain size that have been observed in other large river systems. Dissolved d7Li are low ($11‰) in the Ganges headwaters, but reach a constant value of 21 ± 1.6‰ within a relatively short distance downstream, which is then maintained for almost 2000 km to the Ganges mouth. Given that Li isotopes are controlled by the ratio of primary mineral dissolution to secondary mineral formation, this suggests that the Ganges floodplain is at steady-state in terms of these processes for most of its length. Low d7Li in the mountainous regions suggest silicate weathering is therefore at its most congruent where uplift and fresh silicate exposure rates are high. However, there is no correlation between d7Li and the silicate weathering rate in these rivers, suggesting that Li isotopes can- not be used as a weathering-rate tracer, although they do inform on weathering congruency and intensity. The close-to- constant d7Li values for the final 2000 km of Ganges flow also suggest that once the size of the alluvial plain reached more than $500 km (the flow distance after which riverine d7Li stops varying), the Ganges exerted little influence on the changing Cenozoic seawater d7Li, because riverine d7Li attained a near steady-state composition. 

  • 330. Pokharel, Rasesh
    et al.
    Gerrits, Ruben
    Schuessler, Jan
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Sobotka, Roman
    Gorbushina, Anna
    von Blanckenburg, Friedhelm
    Magnesium Stable Isotope Fractionation on a Cellular Level Explored by Cyanobacteria and Black Fungi with Implications for Higher Plants2018In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, p. 12216-12224Article in journal (Refereed)
    Abstract [en]

    In a controlled growth experiment we found that the cyanobacterium Nostoc punctiforme has a bulk cell 26Mg/24Mg ratio (expressed as δ26Mg) that is −0.27‰ lower than the growth solution at a pH of ca. 5.9. This contrasts with a recently published δ26Mg value that was 0.65‰ higher than growth solution for the black fungus Knufia petricola at similar laboratory conditions, interpreted to reflect loss of 24Mg during cell growth. By a mass balance model constrained by δ26Mg in chlorophyll extract we inferred the δ26 Mg value of the main Mg compartments in a cyanobacteria cell: free cytosolic Mg (−2.64‰), chlorophyll (1.85‰), and the nonchlorophyll-bonded Mg compartments like ATP and ribosomes (−0.64‰). The lower δ26Mg found in Nostoc punctiformewould thus result from the absence of significant Mg efflux during cell growth in combination with either (a) discrimination against 26Mg during uptake by desolvation of Mg or transport across protein channels or (b) discrimination against 24Mg in the membrane transporter during efflux. The model predicts the preferential incorporation of 26Mg in cells and plant organs low in Mg and the absence of isotope fractionation in those high in Mg, corroborated by a compilation of Mg isotope ratios from fungi, bacteria, and higher plants.

  • 331. Qu, Y
    et al.
    Wang, J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engdahl, A.
    Wang, G.
    McCloughlin, N.
    Carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the Ediacaran Doushantuo Formation.2017In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 290, p. 184-196Article in journal (Refereed)
    Abstract [en]

    The Ediacaran Doushantuo Formation (DST) is renowned for exceptionally preserved Precambrian fossils including metazoans. Some of these fossils, particularly microfossils such as multicellular algae and acanthomorphic acritarchs, are preserved in DST chert nodules. To better understand the geomicrobiological processes that contributed to the authigenic formation of DST chert nodules and facilitated exceptional fossil preservation, we analyzed organic matter in these chert nodules and the surrounding matrix (calcareous mudstone) using multiple in-situ techniques: confocal laser Raman spectroscopy, micro-Fourier transform infrared spectroscopy (FTIR), and secondary ion mass spectroscopy (SIMS). We found strong ultrastructural, chemical, and isotopic heterogeneities in the organic matter as indicated by the Raman spectral parameter I-1350/1600 ranging from 0.49 to 0.88, the infrared spectral index R3/2 from 0.12 to 0.90, and an estimated δ13Corg-SIMS range of 44‰ (V-PDB). These micron-scale heterogeneities imply that the organic matter preserved in the DST chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem, including eukaryotic and/or prokaryotic photoautotrophs, as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains. Thus, the microbial ecosystems in Ediacaran ocean waters and sediments were more complex than previously thought, and these microbial processes controlled dynamic micro-environments in DST sediments where chert nodules were formed and fossils were mineralized. The results also show that variations in the relative abundances, activities, and interactions of co-existing microorganisms in DST sediments may have modulated δ13Corg shifts, causing local decoupling between δ13Corg and δ13Ccarb as measured in bulk samples.

  • 332. Qu, Yuangao
    et al.
    Lepland, Aivo
    van Zuilen, Mark A.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Črne, Alenka E.
    Fallick, Anthony E.
    Sample-scale carbon isotopic variability and diverse biomass in the Paleoproterozoic Zaonega Formation, Russia2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 315, p. 222-231Article in journal (Refereed)
    Abstract [en]

    The stratigraphic record of organic matter in the c. 1.97 Ga Zaonega Formation (ZF), Onega Basin, northwestern Russia, exhibits a distinct negative δ13C excursion (δ13Corg from −25 to −40‰ VPDB), which was previously interpreted either to reflect a disturbance in the global carbon cycle after the Great Oxidation Event, or to have been caused by an increase in basinal methanotrophic activity. In order to assess the nature of primary biomass and the effects of post-depositional alteration, we here report the sample-scale carbon isotopic characteristics of organic matter in two drill cores from the ZF, covering 500 m of stratigraphy, by using secondary ion mass spectrometry (SIMS). The results confirm that the organic matter has to a large extent preserved the primary isotopic signatures, whereas secondary effects are limited (<4‰). The sample-scale isotopic heterogeneity, defined as the difference between the maximum and minimum δ13C values obtained by SIMS from every individual sample, increases from typically <5‰ in the lower part of stratigraphy to systematically larger values (up to 11‰) in the upper part, which coincides with the decreasing trend of δ13Corg of bulk samples from −25 to −40‰. Samples with either relatively high (c. −25‰) or low (c. −40‰) δ13Corg values have small sample-scale isotopic heterogeneities, while samples with intermediate δ13Corg values (between −25 and −40‰) have significantly larger heterogeneities. These observations imply the co-existence of photoautotrophic and methanotrophic biomass during deposition of the upper part of the stratigraphy. Our study provides insight into the carbon isotopic characteristics of organic matter and suggests that the negative excursion of δ13Corg in the ZF is induced by a methanotrophic microbial ecosystem sustained by seepage of thermogenic methane during the deposition of the ZF and contemporaneous igneous activities.

  • 333. Qu, Yuangao
    et al.
    Zhu, Shixing
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Engdahl, Anders
    McLoughlin, Nicola
    Carbonaceous biosignatures of the earliest putative macroscopic multicellular eukaryotes from 1630 Ma Tuanshanzi Formation, north China2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 304, p. 99-109Article in journal (Refereed)
    Abstract [en]

    The Paleo- and Mesoproterozoic fossil record of multicellular eukaryotes is scarce but extremely important in studying the evolution of life in the Precambrian Era. Typically, fossils heralded as ‘multicellular eukaryotes’ that are older than the Ediacaran are met with controversy. To confront such debates, we investigate the chemical, isotopic, and molecular structural characteristics of organic matter from carbonaceous compressions in the 1630 Ma Tuanshanzi Formation in northern China, some of the earliest putative macroscopic multicellular eukaryote fossils (Zhu and Chen, 1995). The large-size and relative complexity of these fossils and similar remains from the 1.56 Ga Gaoyuzhuang Formation have led to their interpretation as eukaryotes. Raman spectral parameters give an estimated peak-metamorphic temperature TMax in the range of 202–286 °C, confirming the good preservation of the organic remains. Two-dimensional Raman maps of the carbonaceous compressions show ultrastructural variations that suggest diverse subcellular compounds being consistent with multicellular eukaryotes. The organic matter has carbon isotopic composition δ13Corg-SIMS between −45.3 and −32.2‰, and a branching index of carbon chain measured by the micro-FTIR spectral parameter R3/2 between 0.17 and 0.31. Together with their large-size and morphology, the isotopic, geochemical and ultrastructural data supports an interpretation of the Tuanshanzi Formation carbonaceous compressions as derived from phototrophic, multicellular eukaryotic algae. Our data support the early evolution of macroscopic multicellular eukaryotes in the sulfidic and low-oxygen conditions that prevailed in the Paleo- and Mesoproterozoic oceans.

  • 334. 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)
  • 335.
    Reznitskii, Leonid
    et al.
    Russian Academy of Science, Irkutsk, Russia.
    Clark, Christine M.
    University of Manitoba, Winnipeg, Canada.
    Hawthorne, Frank C.
    University of Manitoba, Winnipeg, Canada.
    Grice, Joel D.
    Canadian Museum of Natural History, Ottawa, Canada.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Sapienza Università di Roma, Rome, Italy.
    Chromo-­alumino-­povondraite,  NaCr3(Al4Mg2)(Si6O18)(BO3)3(OH)3O,  a  new  mineral  species   of  the  tourmaline  supergroup2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 1767-1773Article in journal (Refereed)
  • 336. Riley, T.
    et al.
    Flowerdew, M.J.
    Curtis, M.J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks.2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 244, p. 59-73Article in journal (Refereed)
    Abstract [en]

    New geochronology from a thick (> 800 m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178 ± 1 Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~ 170 Ma) of the Antarctic Peninsula. The geochemistry of other rare, but broadly contemporaneous, basaltic successions of the Antarctic Peninsula, along with Cretaceous-age mafic dykes, are used to interpret the influences of lithospheric and asthenospheric mantle sources during the Mesozoic. Two significant high magmatic addition rate events occurred along the Antarctic Peninsula continental margin at 170 and 110 Ma and can be correlated to events along the South American Cordillera. These ‘flare-up’ events are characterised by extensive silicic (mostly ignimbrite) volcanism of the Chon Aike Province (V2 event: 170 Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110 Ma). The 170 Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110 Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the ‘flare-up’ event at 170 Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170 Ma event indicates that extensive lithospheric thinning had occurred, which allowed the ascent of depleted mafic melts. The thinning was the direct result of widespread lower crustal/upper lithospheric melting associated with the silicic volcanism. In the southern Antarctic Peninsula, the lithosphere remained over thickened until the emplacement of the major batholiths of the Lassiter Coast intrusive suite at 110 Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.

  • 337. Riley, Teal R.
    et al.
    Burton-Johnson, Alex
    Flowerdew, Michael J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Episodicity within a mid-Cretaceous magmatic flare-up in West Antarctica: U-Pb ages of the Lassiter Coast intrusive suite, Antarctic Peninsula, and correlations along the Gondwana margin2018In: Geological Society of America Bulletin, ISSN 0016-7606, E-ISSN 1943-2674, Vol. 130, no 7-8, p. 1177-1196Article in journal (Refereed)
    Abstract [en]

    Long-lived continental margin arcs are characterized by episodes of large-volume magmatism (or flare-ups) that can persist for ∼30 m.y. before steady-state arc conditions resume. Flare-up events are characterized by the emplacement of large-volume granodiorite-tonalite batholiths and sometimes associated rhyodacitic ignimbrites. One of the major flare-up events of the West Gondwana margin occurred during the mid-Cretaceous and was temporally and spatially associated with widespread deformation and Pacific plate reorganization. New U-Pb geochronology from the Lassiter Coast intrusive suite in the southern Antarctic Peninsula identifies a major magmatic event in the interval 130–102 Ma that was characterized by three distinct peaks in granitoid emplacement at 130–126 Ma, 118–113 Ma, and 108–102 Ma, with clear lulls in between. Mid-Cretaceous magmatism from elsewhere in West Antarctica, Patagonia, and New Zealand also featured marked episodicity during the mid-Cretaceous and recorded remarkable continuity along the West Gondwana margin. The three distinct magmatic events represent second-order episodicity relative to the primary episodicity that occurred on a cordillera scale and is a feature of the North and South American Pacific margin. Flare-up events require the development of a highly fusible, lower-crustal layer resulting from the continued underplating of hydrous mineralogies in the melt-fertile lower crust as a result of long-lived subduction. However, the actual trigger for melting is likely to result from external, potentially tectonic factors, e.g., rifting, plate reorganization, continental breakup, or mantle plumes.

  • 338. Riley, T.R.
    et al.
    Flowerdew, M.J.
    Pankhurst, R.J.
    Leat, P.T.
    Millar, I.L.
    Fanning, C.M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    A revised geochronology of Thurston Island, West Antarctica, and correlations along the proto-Pacific margin of Gondwana.2017In: Antarctic Science, ISSN 0954-1020, E-ISSN 1365-2079, Vol. 29, p. 47-60Article in journal (Refereed)
    Abstract [en]

    The continental margin of Gondwana preserves a record of long-lived magmatism from the Andean Cordillera to Australia. The crustal blocks of West Antarctica form part of this margin, with Palaeozoic–Mesozoic magmatism particularly well preserved in the Antarctic Peninsula and Marie Byrd Land. Magmatic events on the intervening Thurston Island crustal block are poorly defined, which has hindered accurate correlations along the margin. Six samples are dated here using U-Pb geochronology and cover the geological history on Thurston Island. The basement gneisses from Morgan Inlet have a protolith age of 349±2 Ma and correlate closely with the Devonian–Carboniferous magmatism of Marie Byrd Land and New Zealand. Triassic (240–220 Ma) magmatism is identified at two sites on Thurston Island, with Hf isotopes indicating magma extraction from Mesoproterozoic-age lower crust. Several sites on Thurston Island preserve rhyolitic tuffs that have been dated at 182 Ma and are likely to correlate with the successions in the Antarctic Peninsula, particularly given the pre-break-up position of the Thurston Island crustal block. Silicic volcanism was widespread in Patagonia and the Antarctic Peninsula at ~ 183 Ma forming the extensive Chon Aike Province. The most extensive episode of magmatism along the active margin took place during the mid-Cretaceous. This Cordillera ‘flare-up’ event of the Gondwana margin is also developed on Thurston Island with granitoid magmatism dated in the interval 110–100 Ma.

  • 339. Riley, T.R.
    et al.
    Flowerdew, M.J.
    Pankhust, R.J.
    Curtis, M.L.
    Fanning, C.M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Early Jurassic magmatism on the Antarctic Peninsula and potential correlation with the Subcordilleran plutonic belt of Patagonia.2017In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 174, p. 365-376Article in journal (Refereed)
    Abstract [en]

    Early Jurassic silicic volcanic rocks of the Chon Aike Province (V1: 187 – 182 Ma) are 30 recognised from many localities in the southern Antarctic Peninsula and northeast Patagonia and are 31 essentially coeval with the extensive Karoo (182 Ma) and Ferrar (183 Ma) large igneous provinces of 32 pre-breakup Gondwana. Until recently, plutonic rocks of this age were considered either rare or 33 absent from the Antarctic Peninsula batholith, which was thought to have been mainly constructed 34 during the Middle Jurassic and the mid-Cretaceous. New U-Pb zircon geochronology from the 35 Antarctic Peninsula and recently published U-Pb ages from elsewhere on the Peninsula and 36 Patagonia are used to demonstrate the more widespread nature of Early Jurassic plutonism. Eight 37 samples are dated here from the central and southern Antarctic Peninsula. They are all moderately 38 to strongly foliated granitoids (tonalite, granite, granodiorite) and locally represent the crystalline 39 basement. They yield ages in the range 188 – 181 Ma, and overlap with published ages of 185 – 180 40 Ma from granitoids from elsewhere on the Antarctic Peninsula and from the Subcordilleran plutonic 41 belt of Patagonia (185 – 181 Ma). Whilst Early Jurassic plutons of the Subcordilleran plutonic belt of 42 Patagonia are directly related to subduction processes along the proto-Pacific margin of Gondwana, 43 coeval volcanic rocks of the Chon Aike Province are interpreted to be directly associated with 44 extension and plume activity during the initial stages of Gondwana break-up. This indicates that 45 subduction was ongoing when Chon Aike Province volcanism started. The Early Jurassic plutonism on 46 the Antarctic Peninsula is transitional between subduction-related and break-up related 47 magamatism.

  • 340. Robinson, Frank
    et al.
    Pease, Victoria
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Preliminary detrital zircon signatures from the southern Asir terrane, Saudi Arabia: A link to Yemen or the Nubian Shield?2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 311, p. 247-261Article in journal (Refereed)
    Abstract [en]

    The Arabian Shield comprises early Neoproterozoic to Cambrian (∼850–530 Ma) tectonostratigraphic terranes formed by the closure and accretion of juvenile volcanic arcs and back-arc basins associated with Gondwana assembly. Unlike the Nubian Shield which preserves crustal isotopic signatures, the Arabian Shield is distinctly juvenile with the exception of the Paleoproterozoic (∼1800–1670 Ma) Khida subterrane in Saudi Arabia and the terranes of Yemen. This study presents the first combined zircon U-Pb, O and Hf isotope data of metavolcanic and metasedimentary rocks from southwestern most Saudi Arabia, near the Yemen border – a region thought to contain some of the oldest (>815 Ma) lithologies in Saudi Arabia, including the Atura Formation and the Tayyah Belt. One volcaniclastic metasediment sample from the Atura Formation yields zircon U-Pb age peaks of 741, 672, 646 Ma (n = 131), δ18O(V-SMOW) ranging from 4.6 to 8.3‰ and ɛHf (t) from +7.7 to +12.5. Two samples from the Tayyah Belt include an older metasandstone and a late intruding granitic dyke which provides a minimum age for the Tayyah Belt. The former yields two significant U-Pb peaks of 812 (n = 8) and 999 (n = 6) Ma, δ18O and ɛHf (t) values ranging from 4.4 to 9.6‰ and −10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [±1.7] Ma (n = 29), δ18O ranging from 5.7 to 6.6‰, and ɛHf (t) of +5.9 to +9.6. The zircon age and juvenile Hf signatures from the Atura Formation are consistent with the synorogenic phase in the Shield. Sedimentation was likely associated with arc volcanism during the previously documented eastward phase of accretion at ∼740–640 Ma and the closure of the Mozambique Ocean. In contrast, the data from the texturally more mature Tayyah Belt metasediment indicate a more distal, and more evolved crustal input at the time of sediment deposition which is unusual for the Saudi Arabian Shield. Consequently, the Tayyah metasediments are likely sourced from areas with greater continental affinity, such as the cratonic basement and/or reworked crust of the Sahara metacraton in NE Africa.

  • 341. Roerdink, D.L.
    et al.
    Mason, P.R.D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Brouwer, F.M.
    Reworking of atmospheric sulfur in a Paleoarchean hydrothermal system at Londozi, Barberton Greenstone Belt, Swaziland2016In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 280, p. 195-204Article in journal (Refereed)
    Abstract [en]

    Anomalous fractionation of the minor isotopes of sulfur (Δ33S, Δ36S) in Archean pyrite is thought to reflect photochemical reactions in an anoxic atmosphere, with most samples falling along a reference array with Δ36S/Δ33S ≈ −1. Small deviations from this array record microbial sulfate reduction or changes in atmospheric source reactions. Here, we argue that reworking of atmospheric sulfur with distinct minor sulfur isotope ratios (Δ36S/Δ33S ≠ −1) produced additional variability in sulfide Δ33S and Δ36S-values in a 3.52 Ga hydrothermal barite deposit at Londozi, Barberton Greenstone Belt, Swaziland. In situ measurement of the four stable sulfur isotopes in pyrite revealed Δ36S–Δ33S relationships and a Δ36S/Δ33S trend (−3.2 ± 0.4), which is significantly different from the co-variation between Δ36S and Δ33S in the co-existing barite that reflects ambient Paleoarchean seawater sulfate. This argues against biological or thermochemical sulfate reduction at the time of barite deposition, and requires incorporation of sulfide generated in a chemically distinct atmosphere before 3.52 Ga. We propose a model that combines reworking of this sulfur by hydrothermal leaching, deep mixing with juvenile sulfur and surface mixing with biogenic sulfide to explain the observed variation in δ34S, Δ33S and Δ36S. These interactions between abiotic and biological processes in the Londozi hydrothermal system complicate the interpretation of biosignatures based on deviations in Δ33S and Δ36S from the Archean reference array.

  • 342. Rose-Koga, E.F.
    et al.
    Koga, K.T.
    Moreira, M.
    Vlastélic, I.
    Jackson, M.G.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Shimizu, N.
    Habib, N.
    Geochemical systematics of Pb isotopes, fluorine, and sulfur in melt inclusions from São Miguel, Azores.2017In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 485, p. 22-37Article in journal (Refereed)
    Abstract [en]

    Pb isotopic measurements in olivine-hosted melt inclusions of ocean island basalts (OIBs) from São Miguel, Azores, reflect the high 207Pb/204Pb and 208Pb/204Pb at a given 206Pb/204Pb of their host lavas. The data are consistent with mixing between two endmembers: the first (the Central Group) has relatively high 208Pb/206Pb and is similar to the component sampled by Graciosa and Faial, and the second is a radiogenic endmember (with low 208Pb/206Pb) that we refer to as the Nordeste component. F and Cl concentrations measured in the same melt inclusions from São Miguel represent parental abundances unmodified by crustal assimilation. Based on undegassed F and Cl concentrations, the source beneath São Miguel is volatile-rich. Pb-isotope composition of the melt inclusions correlates positively with S concentration: we attribute this correlation to the dissolution of oceanic crust sulfides in the S-undersaturated basaltic melt of the Nordeste component. These blebs were then assimilated by the São Miguel magma and the magma droplets were later trapped in olivines.

    When comparing melt inclusions from worldwide OIBs representing mantle endmembers, we find an overall negative correlation between F/Nd and 208Pb/206Pb for volcanic glasses and melt inclusions. The high F/Nd (up to 40) endmember is represented by HIMU melt inclusions and the low F/Nd (down to 14) by EM1 Pitcairn glasses. São Miguel melt inclusions have an intermediate F/Nd of 23.1 ± 3.4.

  • 343. Rose-Koga, Estelle F.
    et al.
    Koga, Kenneth
    Hamada, Morisha
    Hélouis, Thomas
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Shimizu, Nobumichi
    Volatile (F and Cl) concentrations in Iwate olivine-hosted melt inclusions indicating low-temperature subduction2014In: Earth Planets and Space, ISSN 1343-8832, E-ISSN 1880-5981, Vol. 66Article in journal (Refereed)
    Abstract [en]

    Investigation of olivine-hosted melt inclusions provides information about the abundance of volatile elements thatare often lost during subaerial eruptions of lavas. We have measured the abundances of H2O, CO2, F, Cl, and S as well as Pb isotopes in 29 melt inclusions in the scoria of the 1686 eruption of the Iwate volcano, a frontal-arc volcano in the northeast Japan arc. Pb Isotope compositions identify that Iwate magma is derived from a mixture of depleted mantle, subducted basalt, and sediment. Systematics of F in comparison to MORB and other arc magma indicates that (1) the slab surface temperature must be among the lowest on Earth and (2) hydrous minerals, such as amphibole, humites, and/or mica, must be present as residual phases during the dehydration of the slab.

  • 344. Roszjar, J.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Srinivasan, G.
    Mezger, K.
    Scherer, E.E.
    Van Orman, J.A.
    Bischoff, A.
    Prolonged magmatism on 4 Vesta inferred from Hf–W analyses of eucrite zircon2016In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 452, p. 216-226Article in journal (Refereed)
    Abstract [en]

    The asteroid 4 Vesta is the second most massive planetesimal in the Solar System and a rare example of a planetary object that possibly can be linked to a specific group of differentiated meteorites, the howardite–eucrite–diogenite suite. The 182Hf–182W chronometry of individual zircon grains from six basaltic eucrites revealed distinct growth episodes ranging from 4532 −11/+6 Ma−11/+6 Ma to 4565.0±0.9 Ma4565.0±0.9 Ma and constrains the early thermal history of 4 Vesta, indicating that its mantle generated basaltic melts for at least 35 million years (Myr). Initially, the energy needed for melting was provided by decay of short-lived isotopes, mostly 26Al. The long duration of magmatism despite the short lifetime of 26Al implies that the asteroid must have accreted within the first ∼4 Myr of Solar System formation, similar to the formation of iron meteorite parent bodies, and that its interior must have been thermally well insulated by an early-formed crust that prevented heat loss.

  • 345. Roszjar, Julia
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Bischoff, Addi
    Meteoritic zircon – Occurrence and chemical characteristics2014In: Chemie der Erde, ISSN 0009-2819, E-ISSN 1611-5864, Vol. 74, no 3, p. 453-469Article in journal (Refereed)
  • 346.
    Rosén, Per-Olov
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Alling, Vanja
    Norwegian Environment Agency.
    Mörth, Carl-Magnus
    Department of Geological Sciences Stockholm University.
    Björk, Göran
    Department of Oceanography Göteborg University.
    Semiletov, Igor
    International Arctic Research Center University of Alaska.
    Porcelli, Don
    Department of Earth Sciences Oxford University.
    Ice export from the Laptev and East Siberian Sea derived from δ18O values2015In: Journal of Geophysical Research - Oceans, ISSN 2169-9275, E-ISSN 2169-9291, ISSN 2169-9275, Vol. 120, no 9, p. 5997-6007, article id 10.1002/2015JC010866Article in journal (Refereed)
  • 347. Rydland Pedersen, L.-E.
    et al.
    Staudigel, H.
    McLoughlin, N.
    Strauss, H.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    A multiple sulfur isotope study through the volcanic section of the Troodos ophiolite.2017In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 468, p. 49-62Article in journal (Refereed)
    Abstract [en]

    Multiple S isotope systematics (δ34S and Δ33S) and high resolution in-situ S isotope measurements offer new perspectives on the study of biological and abiotic cycling of sulfur in hydrothermal systems. We applied these techniques to the Tethyian Troodos ophiolite (91 Ma) from Cyprus, one of the best-preserved remnants of oceanic crust in the world, using materials from deep drill cores and surface sampling. We focused on the volcanic section of the ophiolite, including the hydrothermal massive sulfide deposit at Agrokipia, which represents a fossil zone of high-temperature fluid upwelling, and the Akaki river section which displays a range of lower temperature alteration types.

    The δ34S and Δ33S values of bulk and SIMS (secondary ion mass spectrometry) analyses from the Agrokipia sulfide deposits show that the sulfide minerals are largely derived from thermochemical reduction of entrained seawater sulfate and leached H2S from the “root zone” of hydrothermal upwelling. The contributions of these two sources can vary substantially within individual sulfide grains, indicating a very dynamic mixing between these sulfur sources. Microbial reworking of the sulfide mound is recorded in a sample with very elevated Δ33S values (0.22‰).

    The Akaki and Agrokipia volcanics experienced low temperature sulfur loss and removal of heavier sulfur isotopes due to partial oxidation by microbes. While some intervals gained sulfur, and have δ34S and Δ33S values indicative of microbial sulfate reduction. REE-data of vein quartz containing pyrite with δ34S = ~− 21‰ implies local ephemeral hydrothermal upwelling in the lower Akaki volcanics, possibly associated with the late stage boninitic magmatic activity in the Troodos ophiolite, suggesting that microbial sulfate reduction in oceanic crust may continue for 10–15 Ma in crustal sections with prolonged igneous activity such as Troodos.

  • 348. Saji, N. S.
    et al.
    Larsen, K.
    Wielandt, D.
    Schiller, M.
    Costa, M. M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Rosing, M. T.
    Bizzarro, M.
    Hadean geodynamics inferred from time-varying 142Nd/144Nd in the early Earth rock record2018In: Geochemical Perspectives Letters, Vol. 7, p. 43-48Article in journal (Refereed)
    Abstract [en]

    Tracking the secular evolution of 142Nd/144Nd anomalies is important towards understanding the crust-mantle dynamics in the early Earth. Excessive scatter in the published data, however, precludes identifying the fine structure of 142Nd/144Nd evolution as the expected variability is on the order of few parts per million. We report ultra-high precision 142Nd/144Nd data for Eoarchean and Palaeoarchean rocks from the Isua Supracrustal Belt (SW Greenland) that show a well-resolved 142Nd/144Nd temporal variability suggesting progressive convective homogenisation of the Hadean Isua depleted mantle. This temporally decreasing 142Nd/144Nd signal provides a direct measure of early mantle dynamics, defining a stirring timescale of <250 Myr consistent with vigorous convective stirring in the early mantle. The 142Nd/144Nd evolution suggests protracted crustal residence times of ~1000-2000 Myr, inconsistent with modern-style plate tectonics in the Archean. In contrast, a stagnant-lid regime punctuated by episodes of mantle overturns accounts for the long life-time estimated here for the Hadean proto-crust.

  • 349. Salifu, Musah
    et al.
    Aiglsperger, T.
    Hällström, Lina
    Martinsson, Olof
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Ingri, Johan
    Dold, B.
    Alakangas, Lena
    Strontium (87Sr/86Sr) isotopes: A tracer for geochemical processes in mineralogically-complex mine wastes2018In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 99, p. 42-54Article in journal (Refereed)
  • 350. Sallstedt, E.
    et al.
    Karhu, J.A.
    Pitkänen, P.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Biogenic processes in crystalline bedrock fractures indicated by carbon isotope signatures of secondary calcite.2016In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 67, p. 30-41Article in journal (Refereed)
    Abstract [en]

    Variation in 13C/12C-isotope ratios of fracture filling calcite was analyzed in situ to investigate carbon sources and cycling in fractured bedrock. The study was conducted by separating sections of fracture fillings, and analyzing the 13C/12C-ratios with secondary ion mass spectrometry (SIMS). Specifically, the study was aimed at fillings where previously published sulfur isotope data indicated the occurrence of bacterial sulfate reduction. The results showed that the δ13C values of calcite were highly variable, ranging from −53.8‰ to +31.6‰ (VPDB). The analysis also showed high variations within single fillings of up to 39‰. The analyzed calcite fillings were mostly associated with two calcite groups, of which Group 3 represents possible Paleozoic fluid circulation, based on comparison with similar dated coatings within the Baltic Shield and the succeeding Group 1–2 fillings represent late-stage, low temperature mineralization and are possibly late Paleozoic to Quaternary in age. Both generations were associated with pyrite with δ34S values indicative of bacterial sulfate reduction. The δ13C values of calcite, however, were indicative of geochemical environments which were distinct for these generations. The δ13C values of Group 3 calcite varied from −22.1‰ to +11‰, with a distinct peak at −16‰ to −12‰. Furthermore, there were no observable depth dependent trends in the δ13C values of Group 3 calcite. The δ13C values of Group 3 calcite were indicative of organic matter degradation and methanogenesis. In contrast to the Group 3 fillings, the δ13C values of Group 1–2 calcite were highly variable, ranging from −53.8‰ to +31.6‰ and they showed systematic variation with depth. The near surface environment of <30 m (bsl) was characterized by δ13C values indicative of degradation of surface derived organic matter, with δ13C values ranging from −30.3‰ to −5.5‰. The intermediate depth of 34–54 m showed evidence of localized methanotrophic activity seen as anomalously 13C depleted calcite, having δ13C values as low as −53.8‰. At depths of ∼60–400 m, positive δ13C values of up to +31.6‰ in late-stage calcite of Group 1–2 indicated methanogenesis. In comparison, high CH4 concentrations in present day groundwaters are found at depths of >300 m. One sample at a depth of 111 m showed a transition from methanogenetic conditions (calcite bearing methanogenetic signature) to sulfate reducing (precipitation of pyrite on calcite surface), however, the timing of this transition is so far unclear. The results from this study gives indications of the complex nature of sulfur and carbon cycling in fractured crystalline environments and highlights the usefulness of in situ stable isotope analysis.

456789 301 - 350 of 429
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf