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The Admiralty Mountains region forms the northern termination of the northern Victoria Land, Antarctica. Few quantitative data are available to reconstruct the Cenozoic morpho-tectonic evolution of this sector of the Antarctic plate, where the Admiralty Mountains region forms the northern termination of the western shoulder of the Mesozoic–Cenozoic West Antarctica Rift System. In this study we combine new low-temperature thermochronological data (apatite fission-track and (U-Th-Sm)/He analyses) with structural and topography analysis. The regional pattern of the fission-track ages shows a general tendency to older ages (80–60 ​Ma) associated with shortened mean track-lengths in the interior, and younger fission-track ages clustering at 38–26 ​Ma with long mean track-lengths in the coastal region. Differently from other regions of Victoria Land, the younger ages are found as far as 50–70 ​km inland. Single grain apatite (U-Th-Sm)/He ages cluster at 50–30 ​Ma with younger ages in the coastal domain. Topography analysis reveals that the Admiralty Mountains has high local relief, with an area close to the coast, 180 ​km long and 70 ​km large, having the highest local relief of >2500 ​m. This coincides with the location of the youngest fission-track ages. The shape of the area with highest local relief matches the shape of a recently detected low velocity zone beneath the northern TAM, indicating that high topography of the Admiralty Mountains region is likely sustained by a mantle thermal anomaly. We used the obtained constraints on the amount of removed crustal section to reconstruct back-eroded profiles and calculate the erosional load in order to test flexural uplift models. We found that our back-eroded profiles are better reproduced by a constant elastic thickness of intermediate values (Te ​= ​20–30 ​km). This suggests that, beneath the Admiralty Mountains, the elastic properties of the lithosphere are different with respect to other TAM sectors, likely due to a stationary Cenozoic upper mantle thermal anomaly in the region. Image 1 • Fission-track and U–Th/He data indicate a late Eocene-early Oligocene exhumation. • We found an overlap of young thermochronological ages, high topography, high local relief and low seismic velocity zone. • High temperature mantle anomaly is supporting high topography. • Flexural uplift models indicate a constant lithospheric elastic thickness of intermediate values (Te ​= ​20–30 ​km). • Long wavelength flexural uplift profiles explain wider area (towards the interior) of maximum uplift/exhumation. [ABSTRACT FROM AUTHOR]

We present a multidisciplinary provenance study on legacy cores drilled in the 1970s during DSDP Leg 28 at sites 271 and 272, in the central Ross Sea, Antarctica. The two sites combined provide a discontinuous glaciomarine sedimentary record covering 18 myr, from the Middle Miocene to the present day. The two boreholes are located on the continental shelf and near the edge of the Ross Ice Shelf, in the middle of the Ross Sea, at a key site close at 180° longitude that is considered to represent the present confluence between ice flows fed by West Antarctica and East Antarctica. The study employs U Pb dating of detrital zircons and apatites, coupled with apatite fission-track dating and trace element and REE compositions. Based on the sedimentary provenance, our data show a recurrent E -W oscillation of the confluence of the West Antarctica and East Antarctica ice flows, allowing phases of advance and retreat of the West Antarctic Ice Sheet to be inferred. • Provenance of the Middle Miocene to Quaternary glaciomarine sediments of DSDP Site 271 and Site 272 drill core is traced. • U Pb dating of apatites and zircons, fission-track and geochemistry of apatite are coupled for a provenance analysis. • Recurrent provenance from west Antarctica and east Antarctica is detected. • Data show an oscillation of the West Antarctica and East Antarctica flow divide. • Oscillation of the flow divide is interpreted as an evidence of waxing and waning of the West Antarctica Ice Sheet. [ABSTRACT FROM AUTHOR]

Since the early Oligocene, the descent into global colder conditions has led to the stepwise growth of the Antarctic Ice Sheets. However, ocean and air temperatures were not sufficiently cold enough to maintain a large and stable continental ice sheet and associated marine ice shelf, and therefore during the Oligocene to Miocene the glaciation waxed and waned. However there is limited geological evidence for the extent of these early glacial episodes. Here we present a multi-proxy single-grain provenance study on the glaciomarine sediments in DSDP Site 270, from the Central High in the central Ross Sea to determine the extent of such ice volume variations. The Ross Sea embayment is a key region in Antarctica for preserving geological evidence on the early glacial events, because glaciation was synchronous with continuous sea-floor subsidence and uplift of the surrounding mountain ranges. The Central High in the central Ross Sea was drilled by the DSDP project in the 1970s (Site 270) and a sequence of c. 400 m of Oligocene to lower Miocene glaciomarine sediments was recovered, underlain by a few meters of granitic talus breccia and gneissic basement rocks. The sediments evolve from a non-glacial, continental environment to a glaciomarine environment characterized by variable ice-rafted debris content and several diamictite units. Our approach combines information on crystallization ages in the source region (U-Pb detrital zircon dating), medium- and low-temperature thermochronology constraints (detrital apatite U-Pb and fission-track dating on the same grains), information on the source bedrock type (detrital apatite trace element analysis) and petrological analysis of gravel-size clasts. We provide new constraints on the ice sheet evolution since the earliest phases of glaciation, and show a transition from local to regional-scale ice sheets in the central Ross Sea region in the late Oligocene and early Miocene. In addition, our data can identify the source of sediment transported by ice streams to the central Ross Sea from different areas in the Transantarctic Mountains (TAM) and within the West Antarctic Rift System (WARS). In particular, the provenance data show the late Oligocene diamictite strata were sourced from a distant region, likely southern West Antarctica, indicating a substantial continental ice sheet already existed in the late Oligocene. These new data provide robust geological constraints for modeling of ice sheet volumes and ice drainage patterns in the late Oligocene-early Miocene. • Provenance of the Oligocene-early Miocene glaciomarine sediments of DSDP Site 270 drill core is traced. • U- U-Pb dating of apatites and zircons, fission-track and geochemistry of apatite are coupled for a provenance analysis. • Basement rocks of DSDP Site 270 show large affinities with Transantarctic Mountain rocks. • Oligocene diamictite shows detrital U- U-Pb ages suggesting distant sources and the occurrence of a large continental ice sheet. [ABSTRACT FROM AUTHOR]

Abstract: The Cenozoic tectonic reorganization of the West Antarctic Rift System in the Ross Sea region occurred concurrently with a major change in the global climate system and a global reorganization of plate motions. This region thus provides the opportunity to study in detail a range of geological issues dealing with tectonic and climate feedbacks during the late Eocene/early Oligocene greenhouse/icehouse transition at high latitudes. With the aim to decipher tectonic vs. climatic forcing in the ice sheet drainage evolution, a detrital apatite fission track study was carried out throughout the Cenozoic drill-cored stratigraphic succession of the Cape Roberts Project (McMurdo Sound, Victoria Land Basin). Apatite fission-track ages of detrital samples, with depositional ages between 34Ma and 17Ma, were decomposed into statistically significant age populations. Three age peaks were detected, reflecting different bedrock provenance areas: (i) a young peak (P1 between 34Ma and 26Ma) recording the signal of a source area exhumed with a constant denudation rate, but absent in the proximal continental area; and (ii) two peaks, older than 40Ma, that are instead compatible with thermochronological data available from the onshore bedrock. P1 peak testifies a late Oligocene–early Miocene denudation event and traces a southern provenance of a fraction of the sediments filling the Cape Roberts Basin. We propose that this denudation event might have been triggered by renewed N–S transtensional shearing along the western shoulder of Victoria Land Basin, controlling glacial flow pattern and the associated sediment transport. [Copyright &y& Elsevier]

Continental rift systems are commonly characterized by volcanism with parental basaltic magmas sourced from the mantle. Erosion of the rift shoulders and sedimentation in the adjacent basins can affect the stress and thermal fields at depth, thereby affecting partial mantle melting. However, the sensitivity of magmatic activity to such surface forcing is elusive. Geological observations from the western Ross Sea, Antarctica, suggest rift onset in the Cretaceous with a transition from wide-rifting to narrow-rifting at the boundary between the Antarctic craton and the Transantarctic Mountains. Miocene climate cooling during rifting in the western Ross Sea, in addition, leads to an abrupt decrease in sedimentation rate, synchronous to the emplacement of the McMurdo Volcanic Group. This represents the largest alkali province worldwide, extending both inland and offshore of Transantarctic Mountains and western Ross Sea, respectively. Here, we use coupled thermo-mechanical and landscape evolution numerical modeling to quantify melt production in slowly stretching rift basins due to changes in erosion/deposition rates. The model combines visco-elasto-plastic deformation of the lithosphere and underlying mantle during extension, partial rock melting, and linear hillslope diffusion of the surface topography. The parametric study covers a range of slow extension rates, crustal thicknesses, mantle potential temperatures and diffusion coefficients. Numerical simulations successfully reproduce the ∼150–200-km-wide extension of western Ross Sea and Miocene-to-present asthenospheric melt production (McMurdo Volcanic Group). Results further show that slow rifts magmatism is highly sensitive to sediment deposition within the basin, which inhibits mantle decompression melting and delays the crustal breakup. Regional climate-driven sedimentation rate changes are thus likely to have affected the syn -rift magmatic history of the western Ross Sea, Antarctica, supporting the relevance of interactions between surface and deep-seated processes across extensional settings. • Low sedimentation rates enhance decompression rock-melting in continental rift basin. • Syn-extensional magmatism and tectonic deformation in ultra-slow rifts are sensitive to surface processes. • Miocene aridification and sediment starvation affect the lithospheric thermal state and the stress field. • Neogene to Quaternary volcanism in western Ross Sea, Antarctica, is affected by global climate cooling. [ABSTRACT FROM AUTHOR]

Late Paleozoic glacial deposits are widespread in Gondwana. In Antarctica the best outcrops occur in the Central Transantarctic Mountains, Ellsworth Mountains, Pensacola Mountains, and in Southern Victoria Land, whereas they are rare and very scattered in Northern Victoria Land, which represents a linkage sector with Tasmania and eastern Australia. The aim of the present research is to define the stratigraphic setting and the environmental interpretation of a poorly studied Lower Permian glacigenic succession located near Orr Glacier in the Lanterman Range in Northern Victoria Land. It has great importance because it represents the only significant glacigenic succession for this wide area, marking and defining time and modality of a glacial-postglacial transition during the early Permian, a critical time-interval in the paleoenvironmental evolution of southern Gondwana. This succession, named here as the Lanterman Formation, lies directly on to crystalline basement, and is overlain by a thick Permian fluvial succession (Takrouna Formation). The results provided by sedimentological facies analysis and palynological analysis, integrated with a limited petrographic characterization, show a correlation framework between two isolated successions, outlining their stratigraphic architecture and subdivided into a lower glacial portion and an upper postglacial portion. The former, Asselian in age, is dominated by diamictite, sandstone, mudstone with lonestones, and carbonate deposits, suggesting repeated advance and retreat of a terrestrial glacier, with facies associations indicating environmental changes from subglacial to glaciofluvial, to glaciolacustrine. The latter is dominated by lacustrine mudstone with decreasing lonestones upward, thin bedded sandstone, conglomerate and a thick fluvial sandstone and pebbly sandstone succession at the top, signalling the transition to a fluvial system through time. The overall dataset suggests that the late Paleozoic glacigenic deposits of Northern Victoria Land record the evolution from a setting characterized by a terrestrial small ice cap that underwent repeated advances and retreats due to climate cycles in a lacustrine setting, into a postglacial paleoenvironmental scenario with a wide fluvial system draining northwards from Victoria Land towards the Tasmanian Basin. The results contribute to increasing knowledge of the timing and modalities of the Late Paleozoic Ice Age in Gondwana, particularly for polar regions such as Antarctica. [ABSTRACT FROM AUTHOR]