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  • 1
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    Chrono- and lithostratigraphy of a Mesozoic-Tertiary fore- to intra-arc basin: Adelaide Island, Antarctic Peninsula (2012)
    Cambridge University Press
    Details
    Publication Date: 2012-09-01
    Description: The Mesozoic fore-arc of the Antarctic Peninsula is exposed along its west coast. On Adelaide Island, a 2–3 km succession of turbiditic coarse sandstones and volcanic rocks is exposed. Four U–Pb (zircon) ages are presented here that, in combination with a new stratigraphy, have permitted a robust chrono- and lithostratigraphy to be constructed, which in turn has allowed tentative correlations to be made with the Fossil Bluff Group of Alexander Island, where the ‘type’ fore-arc sequences are described. The lithostratigraphy of Adelaide Island includes the definition of five volcanic/sedimentary formations. The oldest formation is the Buchia Buttress Formation (149.5 ± 1.6 Ma) and is correlated with the Himalia Ridge Formation of Alexander Island. The sandstone–conglomerate dominated succession of the Milestone Bluff Formation (113.9 ± 1.2 Ma) is tentatively correlated with the Pluto Glacier Formation of Alexander Island. Three dominantly volcanic formations are recognized on Adelaide Island, akin to the volcanic rocks of the Alexander Island Volcanic Group; the Mount Liotard Formation is formed of 2 km of basaltic andesite lavas, whilst the Bond Nunatak Formation is also dominated by basaltic andesite lavas, but interbedded with volcaniclastic rocks. The Reptile Ridge Formation has been dated at 67.6 ± 0.7 Ma and is characterized by hydrothermally altered rhyolitic crystal-lithic tuffs. Tentative correlations between Adelaide Island and Alexander Island preclude the two areas forming part of distinct terranes as has been suggested previously, and a proximal source for volcaniclastic sediments also indicates an exotic terrane origin is unlikely.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 2
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    U–Pb ion-microprobe zircon geochronology from the basement inliers of eastern Graham Land, Antarctic Peninsula (2012)
    Geological Society of London
    Details
    Publication Date: 2012-07-01
    Description: New geological mapping combined with U–Pb ion microprobe zircon geochronology on the isolated but locally extensive exposures of crystalline basement inliers of eastern Graham Land has greatly improved our understanding of the region’s early crustal evolution and has allowed a more thorough evaluation of Patagonia–Antarctic Peninsula connections prior to Gondwana break-up. At Eden Glacier, diorite gneisses yield Early Ordovician protolith ages of 487 ± 3 and 485 ± 3 Ma and represent the oldest in situ rocks recorded on the Antarctic Peninsula, and indicate a significant spatial extension of Famatinian-age magmatism of Patagonia. Zircon overgrowths in the Early Ordovician protoliths and granitic leucosomes developed within them record two phases of Permian metamorphism at c. 275 and c. 257 Ma, coincident in part with diorite plutonism of the area at 272 ± 2 Ma. At Adie Inlet, granitic leucosomes from paragneiss have been dated at 276 ± 3 Ma, and these are in turn cut by 257 ± 3 Ma xenolith-rich diorite gneiss. The diorite intruded during a second phase of deformation, which folded the paragneiss leucosomes into tight folds. This whole assembly is cut by intensely brecciated megacrystic granodiorite, which yielded a 259 ± 3 Ma age. South of Cabinet Inlet a very different sequence of events is evident, with Triassic magmatism at c. 236 Ma extensive along the Joerg Peninsula. Migmatitic leucosomes are dated at c. 224 Ma and magmatism and deformation events apparently continued to c. 209 Ma at Cape Casey. Our data indicate that the Devonian and Carboniferous magmatism at Target Hill, considered to represent the ‘classic’ basement complex of the Antarctic Peninsula, is not representative regionally. The Target Hill crustal block contains a major break along Cabinet Inlet; to the north, Ordovician and Permian protoliths were variably migmatized during two episodes of Permian deformation and metamorphism, whereas to the south, Triassic protoliths and Triassic metamorphism are encountered.Supplementary material: U–Pb isotopic data are available at http://www.geolsoc.org.uk/SUP18526.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 3
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    Evidence for hydrothermal alteration and source regions for the Kiruna iron oxide-apatite ore (northern Sweden) from zircon Hf and O isotopes (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-05-13
    Description: Zircon grains from the Kiruna iron oxide–apatite (IOA) ore bodies in northern Sweden are distinct in their hafnium and oxygen isotopic ratios compared to zircon grains from adjacent metavolcanic host rocks and related intrusions. Here, we combine these two isotopic systems on previously dated zircon grains to improve our understanding of these ore deposits with a long-debated origin. Contrasting theories for the formation of the Kiruna iron ores suggest either (1) emplacement through immiscible silicate–iron oxide melts or (2) transportation and deposition of iron by hydrothermal fluids. Zircon from the metavolcanic host rocks and intrusions have oxygen isotopic ratios ( 18 O ~3) that lie below typical magmatic compositions, which is evidence that roof rocks altered by meteoric water were digested into the magma. In contrast, the ores show an influence of a fluid that is higher in 18 O (~7). Based on these findings, we propose the involvement of episodic magmatic-hydrothermal fluids in the ore genesis of the Kiruna iron ore deposits: (1) the first episode related to a deep-seated magmatism and to regional-scale metasomatic alteration, and (2) a later fluid event related to shallow intrusions and responsible for the ore formation. Distinct differences in the Hf isotopic ratios for host rocks and intrusions ( Hfi = –6 to –10, Archean crust) and ore ( Hfi = –5 to +3, depleted mantle) further allow us to screen possible fluid sources for their involvement in the ore process.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    The Pb isotopic evolution of the Martian mantle constrained by initial Pb in Martian meteorites (2015)
    Wiley
    Details
    Publication Date: 2015-11-22
    Description: The Pb isotopic compositions of maskelynite and pyroxene grains were measured in ALH84001 and three enriched Shergottites (Zagami, RBT04262, and LAR12011) by Secondary Ion Mass Spectrometry (SIMS). A maskelynite-pyroxene isochron for ALH84001 defines a crystallization age of 4089±73 Ma (2σ). The initial Pb isotopic composition of each meteorite was measured in multiple maskelynite grains. ALH84001 has the least radiogenic initial Pb isotopic composition of any Martian meteorite measured to date (i.e., 206 Pb/ 204 Pb=10.07±0.17, 2σ). Assuming an age of reservoir formation for ALH84001 and the enriched Shergottites of 4513 Ma (Borg et al., 2003, Lapen et al., 2010), a two stage Pb isotopic model has been constructed. This model links ALH84001 and the enriched Shergottites by their similar μ-value ( 238 U/ 204 Pb) of 4.1-4.6 from 4.51 Ga to 4.1 Ga and 0.17 Ga, respectively. The model employed here is dependent on a chondritic μ-value (~1.2) from 4567–4513 Ma, which implies core segregation had little to no effect on the μ-value(s) of the Martian mantle. The proposed Pb isotopic model here can be used to calculate ages that are in agreement with Rb-Sr, Lu-Hf and Sm-Nd ages previously determined in the meteorites and confirm the young (~170 Ma) ages of the enriched Shergottites and ancient, 〉4 Ga, age of ALH84001.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    The early geological history of the Moon inferred from ancient lunar meteorite Miller Range 13317 (2019)
    Details
    Publication Date: 2019
    Description: Abstract Miller Range (MIL) 13317 is a heterogeneous basalt‐bearing lunar regolith breccia that provides insights into the early magmatic history of the Moon. MIL 13317 is formed from a mixture of material with clasts having an affinity to Apollo ferroan anorthosites and basaltic volcanic rocks. Noble gas data indicate that MIL 13317 was consolidated into a breccia between 2610 ± 780 Ma and 1570 ± 470 Ma where it experienced a complex near‐surface irradiation history for ~835 ± 84 Myr, at an average depth of ~30 cm. The fusion crust has an intermediate composition (Al2O3 15.9 wt%; FeO 12.3 wt%) with an added incompatible trace element (Th 5.4 ppm) chemical component. Taking the fusion crust to be indicative of the bulk sample composition, this implies that MIL 13317 originated from a regolith that is associated with a mare‐highland boundary that is KREEP‐rich (i.e., K, rare earth elements, and P). A comparison of bulk chemical data from MIL 13317 with remote sensing data from the Lunar Prospector orbiter suggests that MIL 13317 likely originated from the northwest region of Oceanus Procellarum, east of Mare Nubium, or at the eastern edge of Mare Frigoris. All these potential source areas are on the near side of the Moon, indicating a close association with the Procellarum KREEP Terrane. Basalt clasts in MIL 13317 are from a very low‐Ti to low‐Ti (between 0.14 and 0.32 wt%) source region. The similar mineral fractionation trends of the different basalt clasts in the sample suggest they are comagmatic in origin. Zircon‐bearing phases and Ca‐phosphate grains in basalt clasts and matrix grains yield 207Pb/206Pb ages between 4344 ± 4 and 4333 ± 5 Ma. These ancient 207Pb/206Pb ages indicate that the meteorite has sampled a range of Pre‐Nectarian volcanic rocks that are poorly represented in the Apollo, Luna, and lunar meteorite collections. As such, MIL 13317 adds to the growing evidence that basaltic volcanic activity on the Moon started as early as ~4340 Ma, before the main period of lunar mare basalt volcanism at ~3850 Ma.
    Print ISSN: 1086-9379
    Electronic ISSN: 1945-5100
    Topics: Geosciences , Physics
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  • 6
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    Record of the ancient martian hydrosphere and atmosphere preserved in zircon from a martian meteorite (2014)
    Springer Nature
    Details
    Publication Date: 2014-08-29
    Description: Nature Geoscience 7, 638 (2014). doi:10.1038/ngeo2231 Authors: A. A. Nemchin, M. Humayun, M. J. Whitehouse, R. H. Hewins, J-P. Lorand, A. Kennedy, M. Grange, B. Zanda, C. Fieni & D. Deldicque Mars exhibits ample evidence for an ancient surface hydrosphere. The oxygen isotope compositions of carbonate minerals and alteration products in martian meteorites suggest that this ancient hydrosphere was not in isotopic equilibrium with the martian lithosphere. Martian meteorite NWA 7533 is composed of regolith breccia from the heavily cratered terrains of ancient Mars and contains zircon grains for which U–Pb ages have been reported. Here we report variations between the oxygen isotopic compositions of four zircon grains from NWA 7533. We propose that these variations can be explained if the mantle melts from which the zircon crystallized approximately 4.43 Gyr ago had assimiliated 17O-enriched regolith materials, and that some of the zircon grains, while in a metamict state, were later altered by low-temperature fluids near the surface less than 1.7 Gyr ago. Enrichment of the martian regolith in 17O before the zircon crystallized, presumably through exchange with the 17O-enriched atmosphere or hydrosphere during surface alteration, suggests that the thick primary atmosphere of Mars was lost within the first 120 Myr after accretion. We conclude that the observed variation of 17O anomalies in zircon from NWA 7533 points to prolonged interaction between the martian regolith, atmosphere and hydrosphere.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 7
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    Metasomatic origin of quartz-pyroxene rock, Akilia, Greenland, and implications for Earth's earliest life (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-05-25
    Description: A quartz-pyroxene rock interpreted as a banded iron formation (BIF) from the island of Akilia, southwest Greenland, contains (13)C-depleted graphite that has been claimed as evidence for the oldest (〉3850 million years ago) life on Earth. Field relationships on Akilia document multiple intense deformation events that have resulted in parallel transposition of Early Archean rocks and significant boudinage, the tails of which commonly form the banding in the quartz-pyroxene rock. Geochemical data possess distinct characteristics consistent with an ultramafic igneous, not BIF, protolith for this lithology and the adjacent schists. Later metasomatic silica and iron introduction have merely resulted in a rock that superficially resembles a BIF. An ultramafic igneous origin invalidates claims that the carbon isotopic composition of graphite inclusions represents evidence for life at the time of crystallization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Fedo, Christopher M -- Whitehouse, Martin J -- New York, N.Y. -- Science. 2002 May 24;296(5572):1448-52.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Environmental Sciences, George Washington University, Washington, DC 20052, USA. cfedo@gwu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12029129" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon Isotopes ; Crystallization ; *Earth (Planet) ; Elements ; Fossils ; *Geologic Sediments/chemistry ; Graphite/analysis ; Greenland ; Iron/analysis ; *Life ; *Minerals/analysis ; *Quartz/analysis ; Time ; Trace Elements/analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    A light carbon reservoir recorded in zircon-hosted diamond from the Jack Hills (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-07-04
    Description: The recent discovery of diamond-graphite inclusions in the Earth's oldest zircon grains (formed up to 4,252 Myr ago) from the Jack Hills metasediments in Western Australia provides a unique opportunity to investigate Earth's earliest known carbon reservoir. Here we report ion microprobe analyses of the carbon isotope composition of these diamond-graphite inclusions. The observed delta(13)C(PDB) values (expressed using the PeeDee Belemnite standard) range between -5 per mil and -58 per mil with a median of -31 per mil. This extends beyond typical mantle values of around -6 per mil to values observed in metamorphic and some eclogitic diamonds that are interpreted to reflect deep subduction of low-delta(13)C(PDB) biogenic surface carbon. Low delta(13)C(PDB) values may also be produced by inorganic chemical reactions, and therefore are not unambiguous evidence for life on Earth as early as 4,250 Myr ago. Regardless, our results suggest that a low-delta(13)C(PDB) reservoir may have existed on the early Earth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Nemchin, Alexander A -- Whitehouse, Martin J -- Menneken, Martina -- Geisler, Thorsten -- Pidgeon, Robert T -- Wilde, Simon A -- England -- Nature. 2008 Jul 3;454(7200):92-5. doi: 10.1038/nature07102.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Applied Geology, Western Australian School of Mines, Curtin University of Technology, Bentley, Western Australia 6102, Australia. nemchina@kalg.curtin.edu.au〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18596808" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 9
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    The crystallization age of eucrite zircon (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-07-21
    Description: Eucrites are a group of meteorites that represent the first planetary igneous activity following metal-silicate differentiation on an early planetesimal, similar to Asteroid 4 Vesta, and, thus, help date geophysical processes occurring on such bodies in the early solar system. Using the short-lived radionuclide (182)Hf as a relative chronometer, we demonstrate that eucrite zircon crystallized quickly within 6.8 million years of metal-silicate differentiation. This implies that mantle differentiation on the eucrite parent body occurred during a period when internal heat from the decay of (26)Al and (60)Fe was still available. Later metamorphism of eucrites took place at least 8.9 million years after the zircons crystallized and was likely caused by heating from impacts, or by burial under hot material excavated by impacts, rather than from lava flows. Thus, the timing of eucrite formation and of mantle differentiation is constrained.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Srinivasan, G -- Whitehouse, M J -- Weber, I -- Yamaguchi, A -- New York, N.Y. -- Science. 2007 Jul 20;317(5836):345-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geology, University of Toronto, Toronto, ON, Canada, M5S 3B1. srini@geology.utoronto.ca〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17641194" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    Pinpointing the source of a lunar meteorite: implications for the evolution of the Moon (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-08-03
    Description: The lunar meteorite Sayh al Uhaymir 169 consists of an impact melt breccia extremely enriched with potassium, rare earth elements, and phosphorus [thorium, 32.7 parts per million (ppm); uranium, 8.6 ppm; potassium oxide, 0.54 weight percent], and adherent regolith. The isotope systematics of the meteorite record four lunar impact events at 3909 +/- 13 million years ago (Ma), approximately 2800 Ma, approximately 200 Ma, and 〈0.34 Ma, and collision with Earth sometime after 9.7 +/- 1.3 thousand years ago. With these data, we can link the impact-melt breccia to Imbrium and pinpoint the source region of the meteorite to the Lalande impact crater.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gnos, Edwin -- Hofmann, Beda A -- Al-Kathiri, Ali -- Lorenzetti, Silvio -- Eugster, Otto -- Whitehouse, Martin J -- Villa, Igor M -- Jull, A J Timothy -- Eikenberg, Jost -- Spettel, Bernhard -- Krahenbuhl, Urs -- Franchi, Ian A -- Greenwood, Richard C -- New York, N.Y. -- Science. 2004 Jul 30;305(5684):657-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut fur Geologie, Universitat Bern, Baltzerstrasse 1, CH-3012 Bern, Switzerland. gnos@geo.unibe.ch〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/15286369" target="_blank"〉PubMed〈/a〉
    Keywords: Crystallization ; Elements ; *Evolution, Planetary ; Isotopes ; Lead ; Metals, Rare Earth/analysis ; *Meteoroids ; *Moon ; Phosphorus/analysis ; Potassium/analysis ; Thorium/analysis ; Uranium/analysis
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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