Marine sedimentary rocks drilled on the southeastern margin of the South Orkney microcontinent in Antarctica (Ocean Drilling Program Leg 113 Site 696) were deposited between ∼36.5 Ma to 33.6 Ma, across the Eocene–Oligocene climate... more
Marine sedimentary rocks drilled on the southeastern margin of the South Orkney microcontinent in Antarctica (Ocean Drilling Program Leg 113 Site 696) were deposited between ∼36.5 Ma to 33.6 Ma, across the Eocene–Oligocene climate transition. The recovered rocks contain abundant grains exhibiting mechanical features diagnostic of iceberg-rafted debris. Sand provenance based on a multi-proxy approach that included petrographic analysis of over 275,000 grains, detrital zircon geochronology and apatite thermochronometry rule out local sources (Antarctic Peninsula or the South Orkney Islands) for the material. Instead the ice-transported grains show a clear provenance from the southern Weddell Sea region, extending from the Ellsworth–Whitmore Mountains of West Antarctica to the coastal region of Dronning Maud Land in East Antarctica. This study provides the first evidence for a continuity of widespread glacier calving along the coastline of the southern Weddell Sea embayment at least 2.5 million yrs before the prominent oxygen isotope event at 34–33.5 Ma that is considered to mark the onset of widespread glaciation of the Antarctic continent.
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Page 1. Lithospheric mantle domains beneath Antarctica PT LEAT 1, AA DEAN 1, IL MILLAR 2, SP KELLEY 3, APM VAUGHAN 1 & TR RILEY 1 1British Antarctic Survey, High Cross, Madingley Road, Cambridge... more
Page 1. Lithospheric mantle domains beneath Antarctica PT LEAT 1, AA DEAN 1, IL MILLAR 2, SP KELLEY 3, APM VAUGHAN 1 & TR RILEY 1 1British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK (e-mail: p. leat@bas, ac. ...
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... at least 3 km thick, and facies analysis indicates deposition as submarine fans along a continental margin (Smellie, Roberts & Hirons, 1996 ... 5.e. Jason Peninsula 5.e.1 Occurrence Jason... more
... at least 3 km thick, and facies analysis indicates deposition as submarine fans along a continental margin (Smellie, Roberts & Hirons, 1996 ... 5.e. Jason Peninsula 5.e.1 Occurrence Jason Peninsula, with an area of approximately 3000 km 2 , extends eastward from Graham Land ...
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The island of South Georgia exposes remnants of a Late Jurassic to Early Cretaceous Andean magmatic arc and marginal basin system that was compressively deformed during the mid-Cretaceous main Andean Orogeny forming widespread NW-SE... more
The island of South Georgia exposes remnants of a Late Jurassic to Early Cretaceous Andean magmatic arc and marginal basin system that was compressively deformed during the mid-Cretaceous main Andean Orogeny forming widespread NW-SE trending folds and a coaxial penetrative cleavage displaying a predominantly NE-SW stretching lineation.Detailed structural studies of the Cooper Bay to Cape Vahsel area of South Georgia reveal that intense, mid-Cretaceous, polyphase deformation was strongly influenced by sinistral strike-slip shear parallel to the NW-SE regional structural grain, and along a major pre-existing fault, which we interpret as the partitioned wrench component of bulk transpressional deformation. The relationship between fold axial plane orientation and interlimb angle of widely distributed mesoscale folds is consistent with counter-clockwise rotation and fold appression as a result of sinistral simple shear deformation, suggesting kinematic strain partitioning of the wrench component was on the whole highly efficient. Locally, the modification of steep tectonic anisotropies to shallow inclinations during D2 deformation induced imperfect or inefficient partitioning with fold arrays exhibiting fold appression characteristic of a transpressional deformation path.Our partitioned transpression model for main Andean deformation of South Georgia fits well with tectonic interpretations of the Cordillera Darwin, Patagonia.
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... 1). Precise UPb dating of zircons from the Mount Poster Formation have yielded ages of 188 ± 3 Ma, and 189 ± 3 Ma from Mount Peterson and the Sweeney Mountains (Fig. ... The Latady Formation The Latady Formation of the Orville Coast,... more
... 1). Precise UPb dating of zircons from the Mount Poster Formation have yielded ages of 188 ± 3 Ma, and 189 ± 3 Ma from Mount Peterson and the Sweeney Mountains (Fig. ... The Latady Formation The Latady Formation of the Orville Coast, eastern Ellsworth Land (Fig. ...
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The Mesozoic dyke swarms of Western Dronning Maud Land, Antarctica, form a minor intrusive component of the Karoo large igneous province. Five-hundred and sixty one dykes were recorded intruding Neoproterozoic gneisses and Middle Jurassic... more
The Mesozoic dyke swarms of Western Dronning Maud Land, Antarctica, form a minor intrusive component of the Karoo large igneous province. Five-hundred and sixty one dykes were recorded intruding Neoproterozoic gneisses and Middle Jurassic syenite plutons. 40Ar/39Ar geochronology data reveal two temporally distinct components: the 178–175 Ma, alkaline, Straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton; and the 206–204 Ma, tholeiitic, Jutulrøra dyke swarm found throughout the study area. The Straumsvola swarm exhibits highly variably dyke trends that display a restricted opening direction, interpreted to be the result of high magma pressure equal to the maximum principal stress. The Jutulrøra swarm displays a fan of dyke trends, with dyke thickness and spacing increasing away from the inferred point of fan convergence. Anisotropy of magnetic susceptibility measurements reveal vertical magma transport within both dyke swarms in the Straumsvola area, with the southern/outer exposures of the Jutulrøra swarm exhibiting lateral magma transport. Although associated with a long-lived, local igneous centre comparison of palaeostress estimates for the Straumsvola dyke swarm and contemporaneous dykes in Ahlmannryggen and Vestfjella, indicates the presence of a regional scale radial stress system in western Dronning Maud Land between 178–175 Ma, supporting a mantle plume origin for the Karoo large igneous province.
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... PT LEAT 1 , TR RILEY 1 , CD WAREHAM 1 ,4 , I. L MILLAR 2 , SP KELLEY 3 & BC STOREY 1 ,5. 1 1 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK (e-mail:... more
... PT LEAT 1 , TR RILEY 1 , CD WAREHAM 1 ,4 , I. L MILLAR 2 , SP KELLEY 3 & BC STOREY 1 ,5. 1 1 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK (e-mail: p.leat@bas.ac.uk) 2 2 British Antarctic Survey, c/o NERC Isotope Geoscience Laboratory ...
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Ultramafic lamprophyre (UML) dykes from the Ferrar Province (Pensacola Mountains) of Antarctica preserve trace element and isotope signatures similar to Bouvet volcanic rocks, which are considered to reflect the palaeo composition of the... more
Ultramafic lamprophyre (UML) dykes from the Ferrar Province (Pensacola Mountains) of Antarctica preserve trace element and isotope signatures similar to Bouvet volcanic rocks, which are considered to reflect the palaeo composition of the Bouvet mantle plume. We report Sr, Nd, Pb, and Os isotope compositions for three ultramafic lamprophyre dykes emplaced at 183.2±2.2 Ma, coincident with the main Karoo–Ferrar magmatic event. The ultramafic lamprophyre dykes are characterized by high Ti, Cr, Ni, Nb/La, LaN/YbN, and Mg# values, and are the most primitive rocks of the Ferrar Province. The dykes have initial (183 Ma) 87Sr/86Sr ratios of 0.7044–0.7055, εNd of 4.6–4.8, 208Pb/204Pb of 39.6–40.3, and 187Os/188Os of 0.120–0.146 and contrast markedly with even the most primitive rocks of the Ferrar and Karoo provinces. The trace element and isotope characteristics have affinities to ocean island basalt (OIB) and the highly radiogenic character of 208Pb/204Pb and 206Pb/204Pb bear closest resemblance to Bouvet, which has previously been postulated as the plume responsible for the Ferrar Province. The ultramafic lamprophyres are believed to be the result of melting enriched Bouvet mantle plume material and represent one of the mantle end members in the Karoo–Ferrar province.
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ABSTRACT
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U–Pb SHRIMP ages are reported for three rhyolite flows from the Lebombo rift region of the Karoo volcanic province. Two flows are interbedded with the Sabie River Basalt Formation and a third sample is from the overlying rhyolitic Jozini... more
U–Pb SHRIMP ages are reported for three rhyolite flows from the Lebombo rift region of the Karoo volcanic province. Two flows are interbedded with the Sabie River Basalt Formation and a third sample is from the overlying rhyolitic Jozini Formation. The interbedded ...
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The Chon-Aike Province of southern South America is unusual among Jurassic igneous provinces associ-ated with the initial stages of Gondwana break-up, in that it is dominantly silicic. The broadly contempora-neous Karoo, Dronning Maud... more
The Chon-Aike Province of southern South America is unusual among Jurassic igneous provinces associ-ated with the initial stages of Gondwana break-up, in that it is dominantly silicic. The broadly contempora-neous Karoo, Dronning Maud Land and Ferrar provinces of South Africa ...
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The field occurrence, age, classification and geochemistry of the Mesozoic volcanic rocks of Patagonia and West Antarctica are reviewed, using published and new information. Dominated by rhyolitic ignimbrites, which form a bimodal... more
The field occurrence, age, classification and geochemistry of the Mesozoic volcanic rocks of Patagonia and West Antarctica are reviewed, using published and new information. Dominated by rhyolitic ignimbrites, which form a bimodal association with minor mafic and intermediate lavas, these constitute one of the largest silicic igneous provinces known, equivalent in size to many mafic LIPs. Diachronism is recognized between the Early–Middle Jurassic volcanism of eastern Patagonia (Marifil and Chon Aike formations) and the Middle Jurassic–earliest Cretaceous volcanism of the Andean Cordillera (El Quemado, Ibañez and Tobı́fera formations). This is accompanied by a change in geochemical characteristics, from relatively high-Zr and -Nb types in the east to subalkaline arc-related rocks in the west, although the predominance of rhyolites remains a constant factor. All of the associated mafic rocks are well fractionated compared to direct mantle derivatives. Petrogenetic models favour partial melting of immature lower crust as a result of the intrusion of basaltic magmas, possibly with some hybridisation of the liquids and subsequent fractionation by crystal settling or solidification and remelting. The formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas, which are thus rare in the province.
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Rare basaltic volcanic rocks from the northern Antarctic Peninsula (Jason Peninsula) are established as marginally predating a silicic large igneous province, which developed along the proto-Pacific margin of Gondwana. 40Ar–39Ar... more
Rare basaltic volcanic rocks from the northern Antarctic Peninsula (Jason Peninsula) are established as marginally predating a silicic large igneous province, which developed along the proto-Pacific margin of Gondwana. 40Ar–39Ar geochronology reported here has dated the basalts in the interval, 175–168 Ma, which overlaps with the dates previously obtained on the silicic volcanic rocks, 171–168 Ma.The basalts are evolved with low Mg#, Cr and Ni, indicating they have undergone significant fractional crystallisation from mantle-derived melts. Their trace elements (high Th/Yb) and isotope ratios (positive εSr and low εNd) indicate that they are derived from lithospheric mantle, which has been significantly modified by subduction-derived fluids and sediments.Cretaceous age (126–106 Ma) primitive mafic dykes from the Antarctic Peninsula are also interpreted as partial melts of the subduction-modified mantle, and together with the Middle Jurassic basalts are used to monitor the Antarctic Peninsula lithosphere. The shift from lithosphere-derived (Jurassic) to asthenosphere-derived (Cretaceous) partial melts in the northern Antarctic Peninsula is attributed to thinning of the lithosphere, which was a consequence of the voluminous silicic volcanism of the Middle Jurassic, coupled with regional extension. The chemistry, chronology and rarity of the basalts are consistent with the model proposed for the voluminous silicic volcanism.
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Page 1. Antarctic Science 13 (2): 99-110 (2001) © Antarctic Science Printed in the United Kingdom Review Age of pre-break-up Gondwana magmatism TEAL R. RILEY1 and KIM B. KNIGHT2 ■» 'British Antarctic Survey,... more
Page 1. Antarctic Science 13 (2): 99-110 (2001) © Antarctic Science Printed in the United Kingdom Review Age of pre-break-up Gondwana magmatism TEAL R. RILEY1 and KIM B. KNIGHT2 ■» 'British Antarctic Survey, Natural ...
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The Ellsworth Mountains of West Antarctica represent part of a displaced terrane once situated along the palaeo-Pacific margin of Gondwana, prior to supercontinent break-up, adjacent to South Africa and the Weddell Sea coast of East... more
The Ellsworth Mountains of West Antarctica represent part of a displaced terrane once situated along the palaeo-Pacific margin of Gondwana, prior to supercontinent break-up, adjacent to South Africa and the Weddell Sea coast of East Antarctica. Middle Cambrian sedimentary rocks of the southern Ellsworth Mountains host locally thick volcanic and subvolcanic rocks forming five igneous centres. Geochemically, most of the igneous samples are mafic, with a subordinate suite of evolved types. The mafic suite is geochemically varied, ranging from MORB (mid-ocean ridge basalt)-like compositions to shoshonitic and lamprophyric (e.g. LaN/YbN = 0.95 to 15.2), with εNdi values ranging from +5.2 to −2.0, correlating with Ti/Y. They are interpreted as representing melts derived from more than one mantle source, with the MORB-like rocks being derived from a depleted mantle source, and the more enriched compositions representing partial melting of lithospheric mantle. Silicic rocks contain melt contributions from Late Proterozoic crust, which is inferred to form the basement of the Ellsworth Mountains. We interpret these igneous rocks as having been formed in a continental rift environment, with MORB-like basalts erupted near the rift axis, and melts from lithospheric mantle emplaced on the rift shoulder. Such an interpretation is consistent with the sedimentary host-rock palaeogeography and contemporaneous structures. This Middle Cambrian rift event is correlated spatially and temporally with rift-related sedimentary rocks in South Africa. It is currently unclear what rifted off the southern African–Weddell Sea sector of the Gondwana palaeo-Pacific margin at that time.
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CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 8RU, United Kingdom 32 Avenue of the Americas, New York, NY 10013–2473, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, 28014 Madrid,... more
CAMBRIDGE UNIVERSITY PRESS The Edinburgh Building, Cambridge CB2 8RU, United Kingdom 32 Avenue of the Americas, New York, NY 10013–2473, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa ... Cambridge Journals Online For further information about this journal please go to the journal web site at: journals.cambridge.org/geo ... ORIGINAL ARTICLES U–Pb and 40Ar–39Ar geochronology of the Baiyunshan gneiss (central ...