We present a new 1:500 000 geological map of Alexander Island of West Antarctica. The map, combined with recent detrital zircon analysis, defines an updated chronostratigraphy for the Fossil Bluff Group, a Late Jurassic-Cretaceous forearc succession > 8 km in thickness that represents one of the most complete forearc successions globally. The forearc succession overlies and is in faulted contact with the LeMay Group, a late Permian basement accretionary complex that forms part of an extensive array of late Permian accretionary complexes in West Gondwana. The LeMay Group is intruded and overlain by a succession of Late Cretaceous-Palaeogene intermediate to silicic volcanic rocks and granitoid plutons. The uppermost unit on Alexander Island is an episode of Neogene to Quaternary basaltic volcanism associated with ridge-trench collisions and slab window development.

Detrital zircon U-Pb and Lu-Hf data from the youngest (late Permian) sedimentary succession of the Falkland/Malvinas Islands are used to constrain the depositional age, provenance and palaeogeography, and to test the Natal Embayment model for the Falkland/Malvinas Islands microplate. The late Permian was a period of extensive magmatism and sediment recycling along the accretionary margin of West Gondwana. Deposition into retro-arc foreland basins was widespread across South Africa, Antarctica, South America and the Falklands Islands, forming thick successions of fluvial, deltaic and shallow marine units. Our analysis links the late Permian (c. 260 Ma) Bay of Harbours Formation of the Falkland/Malvinas Islands with deltaic/fluvial volcaniclastic units from the Karoo Basin of South Africa, the Theron Mountains of East Antarctica and the sandstones of the Ellsworth Mountains and southern Antarctic Peninsula. These units all have a shared provenance from the Antarctic sector of the West Gondwana margin. Although the detrital zircon age profiles of the Falkland/Malvinas Islands sedimentary units overlap with those from the accretionary and volcanic complexes of Patagonia, the Lu-Hf isotope compositions are clearly distinct, indicating that there was no direct link between the late Permian successions of the Falkland/Malvinas Islands (epsilon(Hf) -3 to +3) to the volcano-sedimentary successions of southern South America (epsilon(Hf) less than -5).

The Fossil Bluff Group of eastern Alexander Island records the exceptional preservation of more than 8 km of Mesozoic sedimentary rocks deposited into an accretionary forearc basin that developed unconformably above a late Paleozoic accretionary complex, and in proximity to a continental margin arc during a prolonged phase of enhanced magmatism. Through the Mesozoic, the Fossil Bluff Group evolved from a trench-slope environment to a forearc basin sourced from the continental margin arc. During this period, the Antarctic Peninsula's convergent margin was characterized by episodes of magmatic flare-ups that developed during tectonic compression, crustal thickening, extension, and uplift. U -Pb and Lu -Hf detrital zircon data are used to determine the provenance of the forearc succession and as a monitor of arc magmatic tempos during the late Mesozoic. The magmatic record in the adjacent arc is poorly preserved or partially absent, but the sedimentary record of the forearc basin preserves a largely uninterrupted record of arc magmatism that can be studied with detrital zircon geochronology and geochemistry. The basal succession of the Fossil Bluff Group is sourced from the adjacent accretionary complex, but thereafter it is strongly controlled by the proximal arc in western Palmer Land and is characterized by a mixed arc/recycled signature during episodes of renewed sedimentation. However, the main phases of deposition during the Early Jurassic (ca. 180 Ma), Early Cretaceous (141-131 Ma), and mid-Cretaceous (125-102 Ma) are dominated by arc-only sources. The Lu -Hf isotopic record supports a transition from convergence to extension and a return to convergence during the Mesozoic, which is consistent with accretionary orogens from elsewhere along the West Gondwanan margin. The provenance record during the depositional history of the basin points overwhelmingly to an autochthonous origin; as such, models for parts of the western province of the Antarctic Peninsula being allochthonous are unsupported.

Abstract The NW–SE-trending Pai-Khoi fold–thrust belt links the Permian Uralian Orogen in the Polar Urals with the early Mesozoic fold belt on Novaya Zemlya. An interpretation of structural lineaments present in southern Novaya Zemlya suggests that the NW–SE-trending fold belt in southernmost Novaya Zemlya may have formed contemporaneously with parallel sinistral strike-slip faults. Analysis of regional-scale geological maps of the adjacent Pai-Khoi fold–thrust belt reveals large-scale structural relationships indicative of sinistral shear along the fold–thrust belt, including the presence of left-stepping en echelon folds within the Kara Shale Allochthon. This interpretation is corroborated by a field study of the allochthon-bounding Main Pai-Khoi Thrust, which reveals a consistently oblique tectonic stretching lineation, pitching 56° towards the east, suggesting tectonic displacement towards the west. It is therefore proposed that the Pai-Khoi fold–thrust belt is best described as a zone of sinistral inclined transpression. The interpretation of the Pai-Khoi fold–thrust belt as a zone of sinistral transpression has important implications for the interpretation of this tectonic boundary. This is reflected in a new structural cross-section through southernmost Novaya Zemlya, which is characterized by thick-skinned tectonics and steep strike-slip faults. These faults may link at depth with the Baidaratsky Fault.

New geochronology from a thick (>800m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178±1Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~170Ma) 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 110Ma 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: 170Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110Ma). The 170Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the ‘flare-up’ event at 170Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170Ma 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 110Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.

Changes in penguin abundance and distribution can be used to understand the response of species to climate change and fisheries pressures, and as a gauge of ecosystem health. Traditionally, population estimates have involved direct counts, but remote sensing and digital mapping methodologies can provide us with alternative techniques for assessing the size and distribution of penguin populations. Here, we demonstrate the use of a field-based digital mapping system (DMS), combining a handheld geographic information system with integrated geographical positioning system as a method for: (a) assessing penguin colony area and (b) ground-truthing colony area as derived from satellite imagery. Work took place at Signy Island, South Orkneys, where colonies of the three congeneric pygoscelid penguins: Adélie Pygoscelis adeliae, chinstrap P. antarctica and gentoo P. papua were surveyed. Colony areas were derived by mapping colony boundaries using the DMS with visual counts of the number of nesting birds made concurrently. Area was found to be a good predictor for number of nests for all three species of penguin. Using a maximum likelihood multivariate classification of remotely sensed satellite imagery (QuickBird2, 18 January 2010; Digital Globe ID: 01001000B90AD00), we were able to identify penguin colonies from the spectral signature of guano and differentiate between colonies of Adélie and chinstrap penguins. The area classified (all species combined) from satellite imagery versus area from DMS data was closely related (R 2 = 0.88). Combining these techniques gives a simple and transferrable methodology for examining penguin distribution and abundance at local and regional scales.

New structural and geochronological data from the Eastern Palmer Land Shear Zone, in the vicinity of Beaumont Glacier, provide the first evidence of dated structural control on emplacement of the 119-95 Ma, >13000 km(2) Cretaceous Lassiter Coast Intrusive Suite, during the accretionary mid-Cretaceous Palmer Land Event orogeny. A previously undated >100 m thick dyke-like quartz tonalite intrusion was emplaced at 116.5 +/- 1.5 Ma (Ar-Ar biotite cooling age) along a NW-SE axis, coeval with NW-SE compressional deformation, and possibly controlled by sinistral transpression along the Beaumont Glacier shear zone. The quartz tonalite preserves two styles of deformation and was probably progressively deformed by normal-sinistral shearing during magmatic cooling with initial deformation of mafic enclaves in the dyke interior and final formation of proto-mylonite to mylonite on the dyke margin. The quartz tonalite cuts folding associated with Phase 1 of the Palmer Land Event, indicating that this folding is older than 116 Ma, extending the onset of Phase 1 back in time. Mylonite on the quartz tonalite sheet margin was subsequently thermally reset at c. 107 Ma (Ar-Ar biotite method), during a peak in Lassiter Coast Intrusive Suite magmatism.

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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 trending folds and a coaxial penetrative cleavage displaying a predominantly NE-SW stretching lineationDetailed structural studies of the Cooper Bay to Cape Valisel 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 D-2 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. Crown Copyright (C) 2010 Published by Elsevier Ltd All rights reserved.

Jurassic dykes of western Dronning Maud Land (Antarctica) form a minor component of the Karoo large igneous province. Ail extensive local dyke swarm intrudes Neoproterozoic gneisses and Jurassic syenite plutons oil the margins of the Jutulstraumen palaeo rift in the Svedrupfjella region. The dykes were intruded in three distinct episodes (similar to 204, similar to 176 and similar to 170 Ma). The 204 Ma dykes are overwhelmingly low-Ti, olivine tholeiites including some primitive (pieritic) compositions (MgO >12 wt.%; Fe2O3 >12 wt.%; Cr >1000 ppm; Ni >600 ppm). This 204 Ma event precedes the main Karoo volcanic event by similar to 25 Ma, so any correlations to the wider province are difficult to make. However, it may record the earliest phase of rill activity along the Jutulstraumen. The 176 Ma dyke event is more intimately associated with the two syenite plutons. The dykes are alkaline (basanite/tephrite) and were small-degree melts from an enriched, locally derived Source and underwent at least some degree of interaction with a syenitic contaminant. This similar to 176 Ma dyke event is widespread elsewhere in the Karoo (southern Africa and Dronning Maud Land). Later-stage (170 Ma) felsic (phonolite-comendite) dykes intrude the 176 Ma basanite-tephrite suite and represent the last phase of magmatic activity in the region.

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 178–175Ma, alkaline, Straumsvola dyke swarm that predominantly intrudes a nepheline syenite pluton; and the 206–204Ma, 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 178–175Ma, supporting a mantle plume origin for the Karoo large igneous province.

U-Pb detrital zircon geochronology from the upper Cambrian to Devonian part of the Ellsworth Mountains succession, Antarctica, yields dominant late Mesoproterozoic and late Neoproterozoic-Cambrian age populations that are consistent with a provenance from within Gondwana. III isotope compositions reveal a source predominantly within west Gondwana and identify a change in provenance up-stratigraphy that coincides with the change of sedimentation setting from active rift to passive margin, which has been independently determined by stratigraphic, structural, and geochemical arguments. For the Late Cambrian Frasier Ridge Formation, late Mesoproterozoic grains have positive epsilon(Hf) values, suggesting derivation from juvenile crust, and late Neoproterozoic-Cambrian grains have epsilon(Hf) values greater than -5, consistent with remelting of similar juvenile late Mesoproterozoic crust during the Pan African-Ross orogenies. Provenance during rifting was from proximal sources from within west Gondwana, most likely, southernmost Africa and basement to the Ellsworth-Whitmore Mountains block. At higher stratigraphic levels where deposition occurred along a passive margin, in the early Ordovician Mount Twiss Member and middle Devonian Mount Wyatt Earp Formation, late Neoproterozoic-Cambrian grains have epsilon(Hf) values less than -5; this means that early Mesoproterozoic-Archean crust was remelted to generate these zircons. Provenance was from a more expansive source region within west Gondwana, and probably included the Kaapvaal and Congo cratons of south and west Africa. Isolated outcrops of sedimentary rock of uncertain age at Mount Woollard and the Whitmore Mountains have detrital zircon signatures similar to the Frasier Ridge Formation, suggesting correlation with these Late Cambrian deposits. Sedimentary rock from the Stewart Hills contains some late Mesoproterozoic grains with lower epsilon(Hf) values than the previously mentioned samples. This suggests that the Stewart Hills sample has a provenance from within east Gondwana and was possibly deposited on the East Antarctic craton prior to the Ross orogeny and is not part of the displaced Ellsworth-Whitmore Mountains crustal block.

The Cooper Bay Dislocation Zone (CBDZ) represents a major NW-SE trending tectonic boundary within the island of South Georgia that juxtaposes components of a Middle Jurassic to mid-Cretaceous island-arc and back-arc- basin system. New detailed structural data from the southern end of the dislocation zone reveal that earliest displacement along the boundary appears to have been associated with dip-slip reverse shear, characterised by widespread proto- to meso-mylonitic granitic rocks within the basement assemblage exposed to the southwest of the shear zone. Along the northeast margin, highly sheared and mylonitised metasedimentary and metabasic rocks reveal sinistral strike-slip kinematics and a sub-horizontal mineral lineation. Narrow zones of sinistral shear are locally superimposed within the basement rocks along the SW margin, that together with the presence of brittle sinistral faults suggest that the strike-slip component of deformation postdates the dip-slip. Comparison with the tectonic history of the Rocas Verdas Marginal Basin, Fuegian Andes, suggests that the sinistral shear event preserved along the CBDZ maybe be related to Late Cretaceous, main Andean orogenic transpression, although a Cenozoic event cannot to ruled out. Citation: Curtis, M.L. (2007), Main Andean sinistral shear along the Cooper Bay Dislocation Zone, South Georgia?, in Antarctica: A Keystone in a Changing World - Online Proceedings of the 10 th

The Jurassic Karoo large igneous province (LIP) of Antarctica, and its conjugate margin in southern Africa, is critical for investigating important questions about the relationship of basaltic LIPs to mantle plumes. Detailed aerogeophysical, structural, anisotropy of magnetic susceptibility (AMS), geochronological and geochemical investigations completed under the British Antarctic Survey's MAMOG project have provided some of the answers. Across most of the area, magma volumes were small compared to those in southern Africa. Jurassic dikes intruding the Archean craton are sparse and the Jutulstraumen trough, a Jurassic rift, is interpreted, from aerogeophysical data, as largely amagmatic. The largest volumes of magma were emplaced along the margin of the craton and close to the Africa-Antarctica rift. Although dikes were emplaced by both vertical and horizontal flow, overwhelmingly magmas in Dronning Maud Land were locally derived, and not emplaced laterally from distant sources. Basaltic magmatism was protracted in Dronning Maud Land (several dike emplacement episodes between ~206 and 175 Ma), and the small magma volumes resulted in highly diverse magma compositions, including picrites and ferropicrites interpreted to have been derived from hot mantle in a mantle plume. The protracted magmatism before the locally ~177 Ma flood lava eruptions, and evidence for a radiating dike swarm, favor a model of mantle plume incubation for 20-30 million years before flood lava eruption.

A suite of mafic dykes from the Underberg region of southern KwaZulu-Natal (South Africa) were intruded at 178 Ma, coincident in age with the major Okavango Dyke Swarm of Botswana, and also coincident with minor Karoo-related intrusions of the northern and central Lebombo. The dykes are all low-Ti-Zr tholeiites, they trend NW-SE and are presumed to continue into the Karoo central area of the Lesotho Highlands. In many respects, the Underberg dykes are similar to the majority of the low-Ti-Zr volcanic and subvolcanic intrusions of the Karoo; however, their 87Sr/86Sr and Nd isotope ratios are either ‘Ferrar-like’ (87Sr/86Sr 0·710; Nd < -3) or transitional between Karoo low-Ti-Zr and Ferrar low-Ti magmas. A potential Ferrar source for at least some of the Underberg dykes is supported by anisotropy of magnetic susceptibility analyses of the dyke suite, which demonstrate absolute flow direction from the SE to the NW, consistent with Gondwana reconstructions. The role of crustal contamination and combined fractional crystallization is also demonstrated to have played a key role in the petrogenesis of the Underberg dykes, involving a local upper crust contaminant. However, the composition of the ‘Ferrar-like’ dykes cannot be easily explained by AFC processes, but they do demonstrate that melting of a lithospheric mantle source enriched to a small degree by subduction-derived fluid was also important.