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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. doi: 10.1130/abs/2024AM-402995 

Stable isotope (δ18O, δD, δ11B) ratios of fault surface and shear zone minerals sampled from Marie Byrd Land in the West Antarctic rift system (WARS) provide opportunity to monitor potential fluid transport across multiple levels of the crust during active rifting. In the upper crust, high-angle brittle faults in the southern Ford Ranges display tourmaline-mineralized surfaces at Mt. Douglass, Mt. Dolber, and Lewissohn Nunatak. Tourmaline are strongly aligned with fault striae indicating mineralization during normal-oblique and strike-oblique displacement, with dilatancy allowing fluid infiltration of fault surfaces. Tourmaline’s refractory nature preserves isotopic compositions, which serve as a proxy for fluid sources and water-rock ratios. We compare tourmaline isotopic ratios with those of muscovite and quartz that occupy progressively deeper, kinematically linked fault-shear networks, and high-grade sillimanite-garnet-quartz±biotite associations, with the objective of characterizing potential fluid sources, relative depths of fluid interactions, and eventual estimation of volume of migrated fluids. Tourmaline δ18O values range from 9.1 and 10.4 ± 0.2 ‰ VSMOW (avg.= 9.8 ‰; st.dev. = 0.6), with intrasample reproducibility from 0.9 ‰ to 1.2‰, either as the result of variation in fluid sources or minor fluctuations in temperature during tourmaline formation. Quartz δ18O ratios range from 11.1 to 10.3 ± 0.2 ‰ (avg. =11.0‰; st.dev. = 0.64), with paired ∆Qtz-Tur values lower than quartz calculated to be in equilibrium with tourmaline at 450°C. Calculated qtz-tur temperatures exceed values reasonable for brittle crust (>700°C), indicating tourmaline grew rapidly or quartz has undergone subsolidus reequilibration. Fluids calculated to be in equilibrium with tourmaline at 450°C range from 8.2 to 9.5‰. Tourmaline 40Ar/39Ar geochronology in progress yields Early Cretaceous dates, indicating mineralization coincided with rifting onset. Very rapid development of the WARS and high thermal gradients during ENE- WSW transtension promoted upward movement of fluids in equilibrium with magmatic bodies or dehydrating metamorphic or sedimentary protolith. Tourmaline of Mt. Douglass and Mt. Dolber yield δD values of –60 and –64‰; these values confirm the role of fluids derived from mid crustal sources transported to the upper crust through fault-shear network. 

IODP Expedition 379 to the Amundsen Sea continental rise recovered latest Miocene-Holocene sediments from two sites on a drift in water depths >3900m. Sediments are dominated by clay and silty clay with coarser-grained intervals and ice-rafted detritus (IRD) (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021). Cobble-sized dropstones appear as fall-in, in cores recovered from sediments >5.3 Ma. We consider that abundant IRD and the sparse dropstones melted out of icebergs formed due to Antarctic ice-sheet calving events. We are using petrological and age characteristics of the clasts from the Exp379 sites to fingerprint their bedrock provenance. The results may aid in reconstruction of past changes in icesheet extent and extend knowledge of subglacial bedrock. Mapped onshore geology shows pronounced distinctions in bedrock age between tectonic provinces of West or East Antarctica (e.g. Cox et al. 2020, doi:10.21420/7SH7-6K05; Jordan et al. 2020, doi.org/10.1038/s43017-019-0013-6). This allows us to use geochronology and thermochronology of rock clasts and minerals for tracing their provenance, and ascertain whether IRD deposited at IODP379 drillsites originated from proximal or distal Antarctic sources. We here report zircon and apatite U-Pb dates from four sand samples and five dropstones taken from latest Miocene, early Pliocene, and Plio-Pleistocene-boundary sediments. Additional Hf isotope data, and apatite fission track and 40Ar/39Ar Kfeldspar ages for some of the same samples help to strengthen provenance interpretations. The study revealed three distinct zircon age populations at ca. 100, 175, and 250 Ma. Using Kolmogorov-Smirnov (K-S) statistical tests to compare our new igneous and detrital zircon (DZ) U-Pb results with previously published data, we found strong similarities to West Antarctic bedrock, but low correspondence to prospective sources in East Antarctica, implying a role for icebergs calved from the West Antarctic Ice Sheet (WAIS). The ~100 Ma age resembles plutonic ages from Marie Byrd Land and islands in Pine Island Bay. The ~250 and 175 Ma populations match published mineral dates from shelf sediments in the eastern Amundsen Sea Embayment as well as granite ages from the Antarctic Peninsula and the Ellsworth-Whitmore Mountains (EWM). The different derivation of coarse sediment sources requires changes in iceberg origin through the latest Miocene, early Pliocene, and Plio/Pleistocene, likely the result of changes in WAIS extent. One unique dropstone recovered from Exp379 Site U1533B is green quartz arenite, which yielded mostly 500-625 Ma detrital zircons. In visual appearance and dominant U-Pb age population, it resembles a sandstone dropstone recovered from Exp382 Site U1536 in the Scotia Sea (Hemming et al. 2020, https://gsa.confex.com/gsa/2020AM/meetingapp.cgi/Paper/357276). K-S tests yield high values (P ≥ 0.6), suggesting a common provenance for both dropstones recovered from late Miocene to Pliocene sediments, despite the 3270 km distance separating the sites. Comparisons to published data, in progress, narrow the group of potential on-land sources to exposures in the EWM or isolated ranges at far south latitudes in the Antarctic interior. If both dropstones originated from the same source area, they could signify dramatic shifts in the WAIS grounding line position, and the possibility of the periodic opening of a seaway connecting the Amundsen and Weddell Seas. https://meetingorganizer.copernicus.org/EGU21/EGU21-9151.html 

Abstract New geophysical data from Antarctica's Ross Embayment reveal the structure and subglacial geology of extended continental crust beneath the Ross Ice Shelf. We use airborne magnetic data from the ROSETTA‐Ice Project to locate the contact between magnetic basement and overlying sediments. We delineate a broad, segmented basement high with thin (0–500m) non‐magnetic sedimentary cover which trends northward into the Ross Sea's Central High. Before subsiding in the Oligocene, this feature likely facilitated early glaciation in the region and subsequently acted as a pinning point and ice flow divide. Flanking the high are wide sedimentary basins, up to 3700m deep, which parallel the Ross Sea basins and likely formed during Cretaceous‐Neogene intracontinental extension. NW‐SE basins beneath the Siple Coast grounding zone, by contrast, are narrow, deep, and elongate. They suggest tectonic divergence upon active faults that may localize geothermal heat and/or groundwater flow, both important components of the subglacial system.