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  • 1. Badenszki, Eszter
    et al.
    Daly, J Stephen
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kronz, Andreas
    Upton, Brian G J
    Horstwood, Matthew S A
    Age and Origin of Deep Crustal Meta-igneous Xenoliths from the Scottish Midland Valley: Vestiges of an Early Palaeozoic Arc and ‘Newer Granite’ Magmatism2019Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 60, nr 8, s. 1543-1574Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Deep crustal felsic xenoliths from classic Scottish Midland Valley localities, carried to the surface by Permo-Carboniferous magmatism, are shown for the first time to include metaigneous varieties with dioritic and tonalitic protoliths. Four hypotheses regarding their origin have been evaluated: (1) Precambrian basement; (2) Permo-Carboniferous underplating; (3) ‘Newer Granite’ magmatism; (4) Ordovician arc magmatism. U–Pb zircon dating results rule out the Precambrian basement and Permo-Carboniferous underplating hypotheses, but establish that the meta-igneous xenoliths represent both ‘Newer Granite’ and Ordovician (to possibly Silurian) arc magmatism. The metadiorite xenoliths are shown to have protolith ages of c. 415 Ma with εHft zircon values ranging from +0·1 to +11·1. These are interpreted to represent unexposed ‘Newer Granite’ plutons, based on age, mineralogical, isotopic and geochemical data. This shows that Devonian ‘Newer Granite’ magmatism had a greater impact on the Midland Valley and Southern Uplands crust than previously realized. Clinopyroxene–plagioclase–quartz barometry on the metadiorites from the east and west of the Midland Valley yielded a similar pressure range of c. 5–10 kbar, and a metadiorite from the east yielded a minimum two-feldspar temperature estimate of c. 793–816°C. These results indicate that the metadiorites once resided in the middle–lower crust. In contrast, two metatonalite xenoliths have a Late Ordovician protolith age (c. 453 Ma), with zircon εHft values of +7·8 to +9·0. These are interpreted as samples of a buried Late Ordovician magmatic arc situated within the Midland Valley. Inherited zircons with similar Late Ordovician ages and εHft=453 values (+1·6 to +10·8) are present in the metadiorites, suggesting that the Devonian ‘Newer Granites’ intruded within or through this Late Ordovician Midland Valley arc. A younger protolith age of c. 430 Ma from one of the metatonalites suggests that arc activity continued until Silurian times. This validates the long-standing ‘arc collision’ hypothesis for the development of the Caledonian Orogen. Based on U–Pb zircon dating, the metatonalite and metadiorite xenoliths have both experienced metamorphism between c. 400 and c. 391 Ma, probably linked to the Acadian Orogeny. An older phase of metamorphism at c. 411 Ma was possibly triggered by the combined effects of heating owing to the emplacement of the ‘Newer Granite’ plutons and the overthrusting of the Southern Uplands terrane onto the southern margin of the Midland Valley terrane.

  • 2. Grange, M.
    et al.
    Scharer, U.
    Merle, Renaud E.
    Naturhistoriska riksmuseet.
    Girardeau, J.
    Cornen, G.
    Plume–Lithosphere Interaction during Migration of Cretaceous Alkaline Magmatism in SW Portugal: Evidence from U–Pb Ages and Pb–Sr–Hf Isotopes2010Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 51, nr 5, s. 1143-1170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large massifs of alkaline rocks are exposed along ∼250 km of the Atlantic coast of Portugal. Their origin is still poorly understood, including the precise timing of their emplacement and their relationships with the well-constrained alkaline magmatic rocks that occur 200–1000 km offshore. To elucidate the precise timing and origin of the alkaline magmatism in this region, magmatic rocks from the three major alkaline massifs (Sintra, Sines, and Monchique) and an isolated diorite intrusion (Ribamar, north of Sintra) have been dated by the U–Pb method on titanite and zircon and characterized based on their Pb, Sr, and Hf isotopic compositions obtained on feldspar and zircon. From north to south, the resulting ages are: 88·3 ± 0·5 Ma (95% confidence level) for Ribamar, 83·4 ± 0·7, 82·0 ± 0·7, 81·7 ± 0·4, and 80·1 ± 1·0 Ma for the Sintra complex, 77·2 ± 0·6, 77·2 ± 0·4, and 76·1 ± 1·3 Ma for the Sines massif, and 70·0 ± 2·9 and 68·8 ± 1·0 Ma for the Monchique complex. Initial isotopic compositions of Pb in feldspars are in the range of 18·522–19·299 for 206Pb/204Pb, 15·555–16·007 for 207Pb/204Pb, and 38·480–39·330 for 208Pb/204Pb. Initial 87Sr/86Sr of feldspars varies between 0·70274 and 0·70481 and initial Hf isotope ratios yield εHfi values between +3·7 and +9·6. These results, together with major, trace, and rare earth element analyses, show that the ages, (207Pb/204Pb)i, and (87Sr/86Sr)i increase northward, whereas the alkaline affinity, (206Pb/204Pb)i, and εHfi increase southward, substantiating a north–south trend of geochemical and age variation. The isotopic composition of the studied rocks can be explained by partial melting of a sub-lithospheric mantle source with an enriched DMM (Depleted MORB Mantle) signature and subsequent contamination by the metasomatized Iberian subcontinental lithospheric mantle (SCLM). The north–south age trend is in agreement with the motion of the Iberian plate between 88 and 60 Ma. The spatial and temporal variations in the isotopic signatures are explained by differences in the contribution of the two source components. The sub-lithospheric mantle-derived magmas are more contaminated by the SCLM in the northern part of the alignment, compared with the southern part of the studied region, where the rocks have isotopic signatures closer to those of enriched sub-lithospheric mantle. Our data are incorporated into a geodynamical model that explains the overall distribution of alkaline magmatism in this part of the eastern Central Atlantic, and provide new constraints on the occurrence of alkaline magmatism along the Iberian margin and the NW African plate. The spatial distribution of the magmatism is directly correlated with the motion of the Iberian plate above a deep-rooted thermal anomaly (mantle plume) that has caused magmatism since the Cretaceous.

  • 3. Marzoli, Andrea
    et al.
    Bertrand, Hervé
    Youbi, Nasrrddine
    Callegaro, Sara
    Merle, Renaud
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Reisberg, Laurie
    Chiaradia, Massimo
    Brownlee, Sarah I
    Jourdan, Fred
    Zanetti, Alberto
    Davies, Joshua H F L
    Cuppone, Tiberio
    Mahmoudi, Abdelkader
    Medina, Fida
    Renne, Paul R
    Bellieni, Giuliano
    Crivellari, Stefano
    El Hachimi, Hind
    Bensalah, Mohamed Khalil
    Meyzen, Christine M
    Tegner, Christian
    The Central Atlantic Magmatic Province (CAMP) in Morocco2019Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 60, nr 5, s. 945-996Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Central Atlantic Magmatic Province (CAMP) is a large igneous province (LIP) composed of basic dykes, sills, layered intrusions and lava flows emplaced before Pangea break-up and currently distributed on the four continents surrounding the Atlantic Ocean. One of the oldest, best preserved and most complete sub-provinces of the CAMP is located in Morocco. Geochemical, geochronologic, petrographic and magnetostratigraphic data obtained in previous studies allowed identification of four strato-chemical magmatic units, i.e. the Lower, Intermediate, Upper and Recurrent units. For this study, we completed a detailed sampling of the CAMP in Morocco, from the Anti Atlas in the south to the Meseta in the north. We provide a complete mineralogical, petrologic (major and trace elements on whole-rocks and minerals), geochronologic (40Ar/39Ar and U–Pb ages) and geochemical set of data (including Sr–Nd–Pb–Os isotope systematics) for basaltic and basaltic–andesitic lava flow piles and for their presumed feeder dykes and sills. Combined with field observations, these data suggest a very rapid (<0·3 Ma) emplacement of over 95% of the preserved magmatic rocks. In particular, new and previously published data for the Lower to Upper unit samples yielded indistinguishable 40Ar/39Ar (mean age = 201·2 ± 0·8 Ma) and U–Pb ages (201·57 ± 0·04 Ma), suggesting emplacement coincident with the main phase of the end-Triassic biotic turnover (c.201·5 to 201·3 Ma). Eruptions are suggested to have been pulsed with rates in excess of 10 km3/year during five main volcanic pulses, each pulse possibly lasting only a few centuries. Such high eruption rates reinforce the likelihood that CAMP magmatism triggered the end-Triassic climate change and mass extinction. Only the Recurrent unit may have been younger but by no more than 1 Ma. Whole-rock and mineral geochemistry constrain the petrogenesis of the CAMP basalts. The Moroccan magmas evolved in mid-crustal reservoirs (7–20 km deep) where most of the differentiation occurred. However, a previous stage of crystallization probably occurred at even greater depths. The four units cannot be linked by closed-system fractional crystallization processes, but require distinct parental magmas and/or distinct crustal assimilation processes. EC-AFC modeling shows that limited crustal assimilation (maximum c.5–8% assimilation of e.g. Eburnean or Pan-African granites) could explain some, but not all the observed geochemical variations. Intermediate unit magmas are apparently the most contaminated and may have been derived from parental magmas similar to the Upper basalts (as attested by indistinguishable trace element contents in the augites analysed for these units). Chemical differences between Central High Atlas and Middle Atlas samples in the Intermediate unit could be explained by distinct crustal contaminants (lower crustal rocks or Pan-African granites for the former and Eburnean granites for the latter). The CAMP units in Morocco are likely derived from 5–10% melting of enriched peridotite sources. The differences observed in REE ratios for the four units are attributed to variations in both source mineralogy and melting degree. In particular, the Lower basalts require a garnet peridotite source, while the Upper basalts were probably formed from a shallower melting region straddling the garnet–spinel transition. Recurrent basalts instead are relatively shallow-level melts generated mainly from spinel peridotites. Sr–Nd–Pb–Os isotopic ratios in the CAMP units from Morocco are similar to those of other CAMP sub-provinces and suggest a significant enrichment of the mantle-source regions by subducted crustal components. The enriched signature is attributed to involvement of about 5–10% recycled crustal materials introduced into an ambient depleted or PREMA-type mantle, while involvement of mantle-plume components like those sampled by present-day Central Atlantic Ocean Island Basalts (OIB, e.g. Cape Verde and Canary Islands) is not supported by the observed compositions. Only Recurrent basalts may possibly reflect a Central Atlantic plume-like signature similar to the Common or FOZO components.

  • 4.
    Merle, Renaud E.
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Marzoli, Andrea
    Reisberg, Laurie
    Bertrand, Hervé
    Nemchin, Alexander
    Chiaradia, Massimo
    Callegaro, Sara
    Jourdan, Fred
    Bellieni, Giuliano
    Kontak, Dan
    Puffer, John
    McHone, J. Gregory
    Sr, Nd, Pb and Os Isotope Systematics of CAMP Tholeiites from Eastern North America (ENA): Evidence of a Subduction-enriched Mantle Source2013Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 55, nr 1, s. 133-180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Central Atlantic Magmatic Province (CAMP) is one of the largest igneous provinces on Earth, with an areal extent exceeding 107 km2. Here we document the geochemical characteristics of CAMP basalts from Triassic–Jurassic basins in northeastern USA and Nova Scotia (Canada). The CAMP rocks occur as lava flows, sills and dykes. All of our analysed samples show chemical characteristics typical of CAMP basalts with low titanium content, which include enrichment in the most incompatible elements and negative Nb anomalies. All the basalts also show enriched Sr–Nd–Pb initial (t = 201 Ma) isotopic compositions (206Pb/204Pbini. = 18·155–18·691, 207Pb/204Pbini. = 15·616–15·668, 208Pb/204Pbini. = 38·160–38·616, 143Nd/144Ndini. = 0·512169–0·512499). On the basis of stratigraphy, rare earth element (REE) chemistry and Sr–Nd–Pb isotope composition, three chemical groups are defined. The Hook Mountain group, with the lowest La/Yb ratios, initial 206Pb/204Pbini. >18·5 and 143Nd/144Ndini. > 0·51238, comprises all the lastest and upper stratigraphic units. The Preakness group, with intermediate La/Yb ratios, 206Pb/204Pbini. > 18·5 and 0·51233 > 143Nd/144Ndini. > 0·51225, comprises the intermediate units. The Orange Mountain group has the highest La/Yb ratios and 143Nd/144Ndini. < 0·51235 and involves all the earliest and stratigraphically lowest units, including the entire North Mountain basalts from Nova Scotia. In this last group, three sub-groups may be distinguished: the Rapidan sill, which has 206Pb/204Pbini. higher than 18·5, the Shelburne sub-group, which has 143Nd/144Ndini. < 0·51225, and the remaining Orange Mt samples. With the exception of one sample, the Eastern North America (ENA) CAMP basalts display initial 187Os/188Os ratios in the range of mantle-derived magmas (<0·15). Simple modelling shows that the composition of the ENA CAMP basalts cannot plausibly be explained solely by crustal contamination of oceanic island basalt (OIB), mid-ocean ridge basalt (MORB) or oceanic plateau basalt (OPB) magmas. Mixing of such magma compositions with sub-continental lithospheric mantle (SCLM)-derived melts followed by crustal contamination, by either assimilation–fractional crystallization (AFC) or assimilation through turbulent ascent (ATA) processes is somewhat more successful. However, this latter scenario does not reproduce the REE and isotopic composition of the ENA CAMP in a fully satisfactory manner. Alternatively, we propose a model in which asthenospheric mantle overlying a subducted slab (i.e. mantle wedge) was enriched during Cambrian to Devonian subduction by sedimentary material, isotopically equivalent to Proterozoic–Lower Paleozoic crustal rocks. Subsequently, after subduction ceased, the isotopic composition of this mantle evolved by radioactive decay for another 170 Myr until the CAMP magmatic event. Varying amounts and compositions of the incorporated sedimentary component coupled with radiogenic ingrowth over time can account for the main geochemical characteristics of the ENA CAMP (enriched incompatible element patterns, negative Nb anomalies, enriched Sr–Nd–Pb isotopic composition) and the differences between the three chemical groups.

  • 5.
    Merle, Renaud
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Marzoli, A.
    Aka, F. T.
    Chiaradia, J. M.
    Reisberg, L.
    Castorina, F.
    Jourdan, F.
    Renne, P. R.
    N’ni, J.
    Nyobe, J. B.
    Mt Bambouto Volcano, Cameroon Line: Mantle Source and Differentiation of Within-plate Alkaline Rocks2017Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 58, nr 5, s. 933-962Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Late Cretaceous–Quaternary Cameroon Volcanic Line (CVL) is a 1600 km long chain of volcanoes that straddles the continent–ocean boundary and extends from the Gulf of Guinea to the interior of the African continent. The magmatic activity started at 70 Ma and has continued until the present. The products of this magmatic activity are distinctive in terms of petrology and isotope geochemistry, the variety of volcanic rocks ranging from ultrabasic, alkaline to sub-alkaline lavas to highly evolved alkaline lavas with isotopic compositions indicating complex combinations of both sub-lithospheric (HIMU, EM, DMM) and lithospheric components (sub-continental lithospheric mantle and crust). We conducted a petrological and geochemical study of a set of volcanic rocks, sampled from the rim and interior of the Miocene Mt Bambouto caldera, one of the 12 main volcanic centres of the CVL. The rocks were analysed for their whole-rock major and trace element contents, 40Ar/39Ar ages and whole-rock Sr–Nd–Pb–Os isotopic compositions. Phonolites and quartz-trachytes of the Mt Bambouto caldera are derived by fractional crystallization of highly alkaline and moderately alkaline parental basic magmas, respectively. Assimilation of the shallow crust has affected both alkaline and subalkaline magmas, suggesting that the petrogenesis of the differentiated rocks cannot be explained by crustal contamination alone. Only minor amounts (usually less than 5%) of assimilation of upper crustal silicic rocks from the local Pan-African basement are required to produce the most differentiated compositions. The rocks with the highest crustal contribution are Q-normative trachytes from peripheral cones, as well as one Ne-trachyte. Mt Bambouto basic–ultrabasic rocks, including basanites and alkali-basalts with high 187Os/188Osi, might have experienced some crustal contamination, but it must have been a limited process. Some Mt Bambouto ultrabasic to basic rocks show large ion lithophile element enrichment, notably of Sr, Ba and P compared with Zr. These samples also have relatively radiogenic Sr and unradiogenic Pb isotopic compositions. Such compositions are similar to those of the high-Sr group identified by previous studies. Most of the basic rocks do not show such characteristics and are identified as a low-Sr group. We interpret the geochemical characteristics of the high-Sr group as resulting from the partial melting of a depleted mantle (DMM-like) peridotite source containing pyroxenite veins that had interacted with carbonatitic fluids. To test this hypothesis, we used a new modelling approach based on Monte Carlo simulation; this method has the advantage of deciphering how different mantle components interacted through time. Our modelling confirms the plausibility of a three-component source. In addition, it suggests that the carbonatitic fluid first mixed with the pyroxenititic component and the resulting melt interacted with a DMM-like mantle. Both high-Sr and low-Sr groups can be produced by such a mixing scenario but with a stronger contribution of the carbonatitic fluid for the high-Sr group. At the time of melting, these source components could have been located in a metasomatized region of the sublithospheric mantle (uppermost section of the asthenosphere) or in the sub-continental lithospheric mantle.

  • 6. Neumann, E.-R.
    et al.
    Abu El-Rus, M.A:
    Tiepolo, M.
    Ottolini, L.
    Vannucci, R.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Serpentinization and deserpentinization reactions in the upper mantle beneath Fuerteventura revealed by peridotite xenoliths with fibrous orthopyroxene and mottled olivine.2015Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 56, s. 3-31Artikel i tidskrift (Refereegranskat)
    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.                  

  • 7.
    O’Driscoll, Brian
    et al.
    Department of Earth and Environmental Sciences, University of Manchester, Oxford Road, M13 9PL, UK.
    Leuthold, Julien
    Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland.
    Lenaz, Davide
    Dipartimento di Matematica e Geoscienze, Università degli Studi di Trieste, Trieste, I-34127, Italy.
    Skogby, Henrik
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Day, James M
    Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA.
    Adetunji, Jacob
    School Environmental Sciences, University of Derby, Kedleston Road, Derby DE22 1GB, UK.
    Melt Percolation, Melt-Rock Reaction and Oxygen Fugacity in Supra-Subduction Zone Mantle and Lower Crust from the Leka Ophiolite Complex, Norway2021Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 62, nr 11, s. 1-26, artikel-id egab078Artikel i tidskrift (Refereegranskat)
  • 8. Oostingh, K. F.
    et al.
    Jourdan, F.
    Merle, Renaud E.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Chiaradia, M.
    Spatio-temporal Geochemical Evolution of the SE Australian Upper Mantle Deciphered from the Sr, Nd and Pb Isotope Compositions of Cenozoic Intraplate Volcanic Rocks2016Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 57, nr 8, s. 1509-1530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intraplate basaltic volcanic rocks ranging in age from Late Cretaceous to Holocene are distributed across southeastern Australia in Victoria and eastern South Australia. They comprise four provinces differentiated on the basis of age and spatial distribution. The youngest of these (<4·6 Ma) is the Newer Volcanic Province (NVP), which incorporates lava flows, scoria cones and maars, distributed across western and central Victoria into South Australia. The oldest eruptive rocks belong to the 95–19 Ma Older Volcanic Province, which comprises basaltic lava flows and shallow intrusions distributed across eastern and central Victoria. When examined within the broader framework of geochemical data available for Cretaceous to Cenozoic intraplate volcanism in southeastern Australia, new major, minor and trace element and Sr, Nd and Pb isotope analyses of volcanic rocks from the NVP suggest that their parental magmas originated from a distinctively different mantle source compared with that of the Older Volcanics. We propose that the magmas represented by the Older Volcanics originated from low degrees of partial melting of a mixed source of Indian mid-ocean ridge basalt (MORB)-source mantle and calcio-carbonatite metasomatized sub-continental lithospheric mantle (SCLM), followed by up to 20% fractional crystallization. The magmas of the youngest (<500 ka) suite of the NVP (the Newer Cones) were generated by up to 13% partial melting of a garnet-rich source, followed by similar degrees of fractional crystallization. We also suggest that the temporally intermediate Euroa Volcanics (∼7 Ma) reflect chemical evolution from the source of the Older Volcanics to that of the Newer Cones. Furthermore, energy-constrained recharge, assimilation and fractional crystallization (EC-RA x FC) modelling suggests that the Sr isotope signature of the ∼4·6–1 Ma Newer Plains component of the NVP can be explained by up to 5% upper crustal assimilation. On the basis of these results and data from the literature for mantle xenoliths, we propose a geodynamic model involving decompression melting of metasomatized veins at the base of the SCLM generating the Older Volcanics and modifying the ambient asthenosphere of Indian MORB isotope character. This was followed by thermal erosion and entrainment of the resulting depleted SCLM into the modified Indian MORB-source asthenospheric mantle, generating the Newer Cones. Such a model is in agreement with recent geophysical observations in the area suggesting edge-driven convection with shear-driven upwelling as a potential geodynamic model resulting in temporal upwelling in the region.

  • 9.
    Rämö, O Tapani
    et al.
    Geology and Geophysics Research Program Department of Geosciences and Geography, , P.O. Box 64, FI-00014 University of Helsinki, Finland.
    Andersen, Tom
    University of Oslo Department of Geosciences, , Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, N-0318 Oslo, Norway;University of Johannesburg Department of Geology, , PO Box 524, Auckland Park, 2006, Johannesburg, South Africa.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Timing and Petrogenesis of the Permo-Carboniferous Larvik Plutonic Complex, Oslo Rift, Norway: New Insights from U–Pb, Lu-Hf, and O Isotopes in Zircon2022Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 63, nr 12Artikel i tidskrift (Refereegranskat)
  • 10. Schaltegger, U
    et al.
    Nowak, A
    Ulianov, A
    Fisher, C M
    Gerdes, A
    Spikings, R
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bindeman, I
    Hanchar, J M
    Duff, J
    Vervoort, J D
    Sheldrake, T
    Caricchi, L
    Brack, P
    Müntener, O
    Zircon Petrochronology and 40Ar/39Ar Thermochronology of the Adamello Intrusive Suite, N. Italy: Monitoring the Growth and Decay of an Incrementally Assembled Magmatic System2019Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 60, nr 4, s. 701-722Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Adamello intrusive suite is a composite batholith in Northern Italy, with an estimated 2000 km3 volume, assembled incrementally over a time span of 10 to 12 million years. The history of crystallization has been studied in detail through laser ablation ICP-MS and SIMS U–Pb geochronology of zircon, which records prolonged crystallization of each of the different intrusive units at mid-crustal levels between 43·47 and 33·16 Ma. The magmas were episodically extracted from this storage area and ascended to the final intrusion level at ∼6 km paleo-depth. Each batch of melt cooled very rapidly down to the ambient temperature of 250°C, evidenced by distinct cooling paths recorded by amphibole, biotite and K-feldspar 40Ar/39Ar dates. The magma source area was moving from SW to NE with time, causing increasing thermal maturity in the mid-crustal reservoir. The resulting temporal trend of higher degrees of crustal assimiliation in the course of the evolution of the magmatic system can be traced through Hf and O isotopes in zircon. Rough estimates of magma emplacement rates (‘magma flux’) yield very low values in the range of 10-4 km3/yr, typical of mid-to-upper crustal plutons and increase with time. Although we cannot discern a decrease of magma flux from our own data, we anticipate that a dramatic decrease of magma flux between 33 and 31 Ma along the northern contact lead to cessation of magma emplacement.

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  • 11. Ware, Bryant D
    et al.
    Jourdan, Fred
    Merle, Renaud
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Chiaradia, Massimo
    Hodges, Kyle
    The Kalkarindji Large Igneous Province, Australia: Petrogenesis of the Oldest and Most Compositionally Homogenous Province of the Phanerozoic2018Ingår i: Journal of Petrology, ISSN 0022-3530, E-ISSN 1460-2415, Vol. 59, nr 4, s. 635-665Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kalkarindji Large Igneous Province (LIP) is a Middle Cambrian (511 Ma) continental flood basalt (CFB) province located in northern and central–west Australia that has been linked to an extinction event at the Early–Middle Cambrian boundary. The extent of this LIP has been estimated at about 2·1 x 106 km2, with exposures in Western Australia, Northern Territory, Queensland and South Australia. Major and trace element datasets reveal geochemical characteristics typical for continental flood basalts (CFBs) including: tholeiitic affinity; an enrichment in incompatible elements, in particular, large-ion lithophile elements (LILE); enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) relative to N-MORB; negative Nb and Ta anomalies in normalized extended element patterns. Here we present the first comprehensive geochemical investigation of the Kalkarindji CFB province. The Kalkarindji CFBs are geochemically homogeneous, low-Ti basaltic andesites, with a nearly complete lack of basalts as defined using a total-alkalis vs silica diagram. All of the rocks analysed for Sr, Nd, Pb isotopic ratios display enriched initial (t = 511 Ma) isotopic compositions (143Nd/144Ni = 0·511928–0·511981; 87Sr/86Sri = 0·70917–0·71029; 206Pb/204Pbi = 18·105–18·843; 207Pb/204Pbi = 15·726–15·805; 208Pb/204Pbi = 38·374–39·208). Crustal assimilation models are interpreted to suggest that the geochemical characteristics, as well as the homogenous composition across the entire province, cannot be explained by continental crust contamination. Therefore, the enriched isotopic ratios (particularly the extremely high 207Pb/204Pbi and elevated 208Pb/204Pbi for moderate 206Pb/204Pbi), coupled with relative depletions in Nb and Ta concentrations, indicate the involvement of an ancient enriched lithospheric-like component in the genesis of the Kalkarindji CFB. We propose a model in which the source region was affected by an enrichment event at around 2·5 Ga (possibly through the addition of subducted sediments). Decompression melting and mantle warming (focused by edge driven convection) allowed melting of the fertile mantle to generate the Kalkarindji CFB province at c. 511 Ma.

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