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Sedimentary records can illuminate relationships between the climate, topography, and glaciation of West Antarctica by revealing its Cenozoic topographic and paleoenvironmental history. Eocene fluvial drainage patterns have previously been inferred using geochemical provenance data from an ~44– to 34–million year deltaic sandstone recovered from the Amundsen Sea Embayment. One interpretation holds that a low-relief, low-lying West Antarctic landscape supported a >1500-kilometer transcontinental river system. Alternatively, higher-relief topography in central West Antarctica formed a drainage divide between the Ross and Amundsen seas. Here, zircon U-Pb data from Amundsen Sea Embayment sediments are examined alongside known regional bedrock provenance signatures. These analyses suggest that all observed provenance indicators in the Eocene sandstone derive from West Antarctic rocks. This implies that a local river system flowed off a West Antarctic drainage divide, helping constrain the mid-Late Eocene evolution of West Antarctic topography with implications for the history of rifting and the characteristics of sediments infilling interior basins. 

In 2019, International Ocean Discovery Program (IODP) expeditions to offshore West Antarctica recovered deep ocean sediment cores in the outer Amundsen Sea (Exp. 379) and Dove Basin (Exp. 382). These cores are characterized by numerous ice-rafted detritus (IRD) intervals, including dropstone cobbles released by icebergs calved from past glaciers/ice streams that incised the subglacial bedrock of West Antarctica. We selected nine dropstones from latest Miocene through mid-Pliocene sediment from IODP Sites U1532C, U1533B (Exp. 379) and U1536E (Exp. 382), comprising sandstone, diorite, granitoid, basalt, and rhyolite, for petrologic characterization and multi-method geo-thermochronology. Dating methods applied include U-Pb zircon (UPbZ) geochronology, and apatite fission-track (AFT) and (U-Th)/He (AHe) low-temperature thermochronology, to reveal dates and rates of geologic events with bearing on their crustal provenance and source region bedrock thermal history. Comparison to published data reveal dropstones to be of both local and distant origin. Notable discoveries are: 1) From U1536E, a ~1200 Ma [U-PbZ] diorite cobble, with ca. 130 Ma AFT and 65-50 Ma AHe ages that most resembles cratonic crust of Queen Maud Land (East Antarctica). 2) Three granitoid rocks from U1533B with ca. 174-179 Ma (UPbZ) ages. The only known rocks of similar age and lithology in West Antarctica are described in the Whitmore Mountains (WM). AFT ages of 114 Ma, 91 Ma, and 81 Ma may thus provide the first thermochronology data from the WM. 3) A 27±1 Ma (UPbZ) diorite of from U1533B records 25.6 Ma AFT and 10.6 Ma AHe ages, suggesting origins in the western Antarctic Peninsula. 4) Two very similar distinctive green quartz arenite dropstones were recovered from latest Miocene core at U1533B and U1536E, locations separated by 3270 km. Multivariate statistical comparison of their UPbZ age populations with published data indicates a common provenance in the Ellsworth Mountains (Antarctic interior). When placed within geotectonic and paleoclimate context, discoveries from IRD-dropstones promise to advance understanding of crustal and landscape evolution of evolution of glaciated continents, variations in icesheet extent during warm periods, and ocean/atmospheric current circulation. 

The Cenozoic tectonic history of Marie Byrd Land (MBL), West Antarctica, is dominated by uplift of the MBL dome, a ~800 by ~300 km topographic swell thought to be supported by a hot mantle anomaly, and normal faulting accompanying extension of the West Antarctic rift system (WARS). Additionally, glaciation beginning at 34 – 20 Ma resulted in deeply incised glacial troughs with up to 5km of relief. This study investigates the timing, magnitude, and spatial relationships of these tectonic and erosional events by determining a regional exhumation history of western MBL through thermo-kinematic modeling of low-temperature thermochronologic data. New apatite (U-Th)/He (AHe) analyses include ages between 46 – 63 Ma, significantly younger than previously determined ages between 80 – 100 Ma. 3D thermo-kinematic modeling reveals focused glacial incision alone is incapable of producing this young population of AHe ages, indicating additional exhumation processes have been at work since ~80 Ma. Differential exhumation across western MBL is required to produce the range of observed AHe ages, with laterally variable exhumation ranging from little to none on the Edward VII Peninsula to ~0.04 km/myr in the eastern Ford Ranges. This spatial pattern is consistent with enhanced exhumation related to uplift of the MBL dome in the eastern Ford Ranges, with this effect diminishing westward to the Edward VII Peninsula. A sharp change in exhumation rate in the western Ford Ranges suggests recent motion on inferred normal faults consistent with WARS extension and down-dropping of the Edward VII Peninsula. Models based on available bedrock data provide little insight into the timing and magnitude of glacial incision due to the present inability to directly sample bedrock in deep glacial troughs. However, model predictions of bedrock low-temperature age distributions within glacial troughs are useful as a point of comparison for detrital age distributions. New detrital AHe ages from Sulzberger Bay, offshore western MBL, range from 49 – >100 Ma and are consistent with model age distributions. These model results support a complex, spatially heterogeneous exhumation history for western MBL tied to its position between the MBL dome and the WARS and provide insight into the impact of glacial incision across the regional landscape. 

Marie Byrd Land (MBL), West Antarctica, is poorly studied geologically due to its ice cover and remoteness. As a result, the timing and magnitude of tectonic and erosional events, such as the tectonic uplift of the Marie Byrd Land dome and the incision of the DeVicq Glacial Trough, are debated. When faced with problems difficult to study and solve through in-person field work, it becomes necessary to turn to modeling. Pecube is a thermo-kinematic modeling program that uses topographic and crustal thermal data to calculate thermochronologic ages across a landscape. Thermochronology uses radiometric dating of mineral systems that are sensitive to specific temperatures and can be used to track cooling related to the tectonic and exhumation history of a region. Model predictions can be compared to observed ages to test the viability of tectonic or geomorphic scenarios. Observed ages used here include dates derived from apatite fission track analysis (AFT; closure temperature ~ 110 °C) and apatite (U-Th)/He dating (AHe; closure temperature ~ 60 °C) of detrital material recovered from offshore MBL that presumably originated from the DeVicq Trough region of MBL. Ongoing modeling efforts will determine how closely calculated bedrock ages compare to new detrital AHe ages, ranging from 23.5-82.8 Ma, and AFT ages, ranging from 49.7-83.6 Ma. These ages broadly correspond to late breakup of Gondwana (~100-85Ma), erosion during and after the uplift of the Marie Byrd Land dome (~30Ma), and glacial incision (beginning at 34 or 20Ma). In light of these new data, alterations were made to existing Pecube models for the DeVicq Trough region to rule out and narrow down the timings and rates possible for both glacial incision at the DeVicq Glacial Trough and exhumation of the Marie Byrd Land dome. Preliminary results suggest that varying glacial incision start time between 34 and 20 Ma, dates proposed for the initiation of the West Antarctic Ice Sheet, does not change resulting bedrock ages significantly. However, varying background exhumation rates results in ages that are broadly consistent with observed ages. Ongoing modeling efforts seek to refine this range further to give insight on the exhumation history and tectonic processes of this region. 

Abstract The Antarctic ice sheet blankets >99% of the continent and limits our ability to study how subglacial geology and topography have evolved through time. Ice-rafted dropstones derived from the Antarctic subglacial continental interior at different times during the late Cenozoic provide valuable thermal history proxies to understand this geologic history. We applied multiple thermochronometers covering a range of closure temperatures (60–800 °C) to 10 dropstones collected during Integrated Ocean Drilling Program (IODP) Expedition 318 in order to explore the subglacial geology and thermal and exhumation history of the Wilkes Subglacial Basin. The Wilkes Subglacial Basin is a key target for study because ice-sheet models show it was an area of ice-sheet retreat that significantly contributed to sea-level rise during past warm periods. Depositional ages of dropstones range from early Oligocene to late Pleistocene and have zircon U-Pb or 40Ar/39Ar ages indicating sources from the Mertz shear zone, Adélie craton, Ferrar large igneous province, and Millen schist belt. Dropstones from the Mertz shear zone and Adélie craton experienced three cooling periods (1700–1500 Ma; 500–280 Ma; 34–0 Ma) and two periods of extremely slow cooling rates (1500–500 Ma; 280–34 Ma). Low-temperature thermochronometers from seven of the dropstones record cooling during the Paleozoic, potentially recording the Ross or Pan-African orogenies, and during the Mesozoic, potentially recording late Paleozoic to Mesozoic rifting. These dropstones then resided within ~500 m of the surface since the late Paleozoic and early Mesozoic. In contrast, two dropstones deposited during the mid-Pliocene, one from the Mertz shear zone and one from Adélie craton, show evidence for localized post-Eocene glacial erosion of ≥2 km. 

Large-scale geological structures have controlled the long-term development of the bed and thus the flow of the West Antarctic Ice Sheet (WAIS). However, complete ice cover has obscured the age and exact positions of faults and geological boundaries beneath Thwaites Glacier and Pine Island Glacier, two major WAIS outlets in the Amundsen Sea sector. Here, we characterize the only rock outcrop between these two glaciers, which was exposed by the retreat of slow-flowing coastal ice in the early 2010s to form the new Sif Island. The island comprises granite, zircon U-Pb dated to ~177–174 Ma and characterized by initial ɛ_Nd,⁸⁷Sr/⁸⁶Sr and ɛ_Hfisotope compositions of -2.3, 0.7061 and -1.3, respectively. These characteristics resemble Thurston Island/Antarctic Peninsula crustal block rocks, strongly suggesting that the Sif Island granite belongs to this province and placing the crustal block's boundary with the Marie Byrd Land province under Thwaites Glacier or its eastern shear margin. Low-temperature thermochronological data reveal that the granite underwent rapid cooling following emplacement, rapidly cooled again at ~100–90 Ma and then remained close to the Earth's surface until present. These data help date vertical displacement across the major tectonic structure beneath Pine Island Glacier to the Late Cretaceous. 

Abstract Lateral movement of lithospheric fragments along strike-slip faults in response to collision (escape tectonics) has characterized convergent settings since the onset of plate tectonics and is a mechanism for the formation of new plates. The Anatolian plate was created by the sequential connection of strike-slip faults following ≥10 m.y. of distributed deformation that ultimately localized into plate-bounding faults. Thermochronology data and seismic images of lithosphere structure near the East Anatolian fault zone (EAFZ) provide insights into the development of the new plate and escape system. Low-temperature thermochronology ages of rocks in and near the EAFZ are significantly younger than in other fault zones in the region, e.g., apatite (U-Th)/He: 11–1 Ma versus 27–13 Ma. Young apatite (U-Th)/He ages and thermal history modeling record thermal resetting along the EAFZ over the past ~5 m.y. and are interpreted to indicate thermal activity triggered by strike-slip faulting in the EAFZ as it formed as a through-going, lithosphere-scale structure. The mechanism for EAFZ formation may be discerned from S-wave velocity images from the Continental Dynamics–Central Anatolian Tectonics (CD-CAT) seismic experiment. These images indicate that thin but strong Arabian lithospheric mantle extends ~50–150 km north beneath Anatolian crust and would have been located near the present surficial location of the Bitlis-Zagros suture zone (co-located with the EAFZ in our study area) at ca. 5 Ma. Underthrusting of strong Arabian lithosphere facilitated localization of the EAFZ and thus was a fundamental control on the formation of the Anatolian plate and escape system. 

West Antarctica hosts an unusually high geothermal gradient supported by hot, low-viscosity mantle which likely enhanced the lithospheric response to West Antarctic Ice Sheet [WAIS] cycles of growth and increased the sensitivity of thermochronometers to landscape evolution. Thus a valuable record of glacial landscape change might be recovered from apatite fission track [AFT 80-130°C range] and (U-Th)/He [AHe; 50-90°C]dating, provided that landscape evolution can be distinguished from tectonic signals, including the effects of faults. This study utilizes AFT-AHe thermochronology and thermo-kinematic Pecube modeling to investigate interactions between the hot geotherm, glacial erosion, and inferred crustal structures in the Ford Ranges and the DeVicq Glacier trough in Marie Byrd Land (MBL). The Ford Ranges host glacial troughs (up to 3km relief) dissecting a low-relief erosional surface. Previous work suggests a majority of bedrock exhumation and cooling occurred at/by 80 Ma. However, new data hint at renewed exhumation linked to glacial incision since WAIS formation at 34 or 20 Ma. Prior (U-Th)/He zircon dates from exposures of crystalline bedrock span 90 – 67 Ma. New AHe bedrock dates are 41 to 26 Ma, while two glacial erratics (presumed to be eroded from walls or floor of glacial troughs) yielded AHe dates of 37 Ma and 16 Ma. The DeVicq Glacier trough (>3.5km relief) likely coincides with a regional fault but lacks temperature-time information compared to other regions. The structure may have accommodated motion between elevated central MBL and the subdued crust of the Ford Ranges. We are acquiring AHe and AFT for onshore and offshore samples to compare uplift and exhumation rates for bedrock flanking DeVicq trough. Our new Pecube models test a series of thermal, tectonic, and landscape evolution scenarios against a suite of thermochronologic data, allowing us to assess the timing of glacial incision and WAIS initiation in the FordRanges, and to seek evidence of an inferred tectonic boundary at DeVicq Trough. Modeling efforts will be aided by new AHe analyses from ongoing work. These models combine topographic, tectonic, thermal, and key thermochronologic datasets to produce new insight into the unique cryosphere-lithosphere interactions affecting landscape change in West Antarctica.