As part of the 8th Turkish Antarctic Expedition (TAE-IV) and Turkey-Ecuador Bilateral Cooperation, field studies were conducted on Dee and Cecilia Islands, two small islets situated between Robert and Greenwich Islands in the South Shetland Archipelago (Western Antarctica). This study explores the geological characteristics and petrography of gabbroic intrusions on these islands, offering insights into their emplacement depths.

The geological setting of these islands is formed from volcanic and intrusive rocks, with a minor presence of sedimentary rocks distributed throughout the landmass of the islands. Volcanic rocks primarily consist of basaltic lavas, while sedimentary rocks are represented by conglomerates. The Burro Peaks (Dee Island) and Cecilia (Cecilia Island) gabbroic intrusions share a broadly similar mineralogical composition—dominated by plagioclase, orthopyroxene, and olivine with minor opaque minerals—but exhibit different textural and structural characteristics. The Burro Peaks Intrusion is distinguished by its fine-grained, holocrystalline porphyritic texture and orthogonal cooling joints, indicative of rapid cooling at shallow crustal levels. Disequilibrium textures such as sieve-textured plagioclase, embayed crystals, and multiple generations of plagioclase are in line with this shallow-level emplacement. In contrast, the Cecilia Intrusion displays a coarser-grained holocrystalline granular texture, predominantly one-dimensional joints, and euhedral to subhedral crystals with minimal zoning or reaction rims, pointing to slower cooling at relatively deeper levels. Basaltic lavas on both islands share a similar mineralogical composition with the gabbros but are texturally distinct, exhibiting phaneritic to hemicrystalline-porphyritic textures with pilotaxitic to intersertal groundmass. On Cecilia Island, basaltic lavas overlie the intrusion in the western part, while the contact relationship between lavas and the Burro Peaks Intrusion is unclear in the field.

The field and petrographical data collectively suggest that the Burro Peaks and Cecilia intrusions were emplaced at different crustal levels. The similar compositions of the intrusions and lavas, along with their spatial relationships, support the hypothesis that they may have originated from a common magmatic system but were emplaced at varying depths rather than through separate magmatic events. However, geochronology and geothermobarometry studies are planned as future work to test this hypothesis further and elucidate the interplay with tectonic events within the framework of the South Shetland Arc.

How to cite: Ünal, A.: Preliminary Results on the Geology and Petrography of the Burro Peaks and Cecilia Intrusions, South Shetland Islands (Antarctica): Constraints for Different Emplacement Depths, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10432, https://doi.org/10.5194/egusphere-egu25-10432, 2025.

The ancient landmass of East Antarctica was assembled through multiple cycles of tectonic supercontinent assembly and breakup. Sparse geological exposures around the periphery of the continent, set in the context of plate reconstructions, provide clues to the nature of those assembled lithospheric domains and their boundaries. However, many boundary locations are obscured by ice, and cryptic domains (i.e. with no exposure) are likely in the East Antarctic interior. 

This presentation takes a step towards better constraints on the architecture and character of the crust and upper mantle components of the lithosphere. The study makes use of seismic and multivariate geophysical inputs, introducing new data from recent field campaigns such as the CAD (Casey-Davis) deployment with co-located seismic and GNSS instruments.

We place new constraints on parameters such as bulk geological composition, crustal thickness and Moho character to enable the refinement of previous low-resolution 3D models of East Antarctica. We outline how the spatial heterogeneity of these properties might (a) shape the ice sheet from below and (b) impact the dynamics of the Earth’s response to ice mass change.

Metrics calculated to appraise the spatial variation in uncertainty of the above properties show that significant knowledge gaps remain.  Targeted data collection might be achieved through collaboration between National Antarctic Programs, newly invigorated by making use of independent logistics providers. We welcome discussions that might further improve solid Earth datasets to inform Earth-ice interactions in East Antarctica.

How to cite: Reading, A., Stål, T., Askey-Doran, N., Kelly, I., Magyar, J., Kupis, S., King, M., and Halpin, J.: Crust and Uppermost Mantle Heterogeneity in East Antarctica, and Potential Impacts on Earth-ice Interactions., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-134, https://doi.org/10.5194/egusphere-egu25-134, 2025.

Approximately 17% of the modern Greenland Ice Sheet is drained via the Northeast Greenland Ice Stream (NEGIS), which extends ~600 km into the interior of the ice sheet. The NEGIS is generally thought to be topographically unconstrained, as the onset of fast flowing ice is not confined to or channeled by a distinct valley.

In our study, we investigate the subglacial topography along the length of the NEGIS, from its onset to its divergence into its outlet glaciers, in order to ascertain the characteristics of the subglacial conditions beneath the ice stream. We analyse airborne radio-echo sounding surveys collected using the AWI airborne ultra-wideband radar system during 2018 and 2022, alongside selected survey lines from Operation IceBridge. We use the metrics of hypsometry, topographic roughness, and valley morphometry, to elucidate three geomorphologically distinct regions over which the NEGIS flows.

The region at the onset of the NEGIS exhibits very low small-scale roughness, low relief, and a lack of valleys, indicating a likely sedimentary basin. Downstream of this, the subglacial environment changes, increasing in small-scale roughness following a topographic step. Here, two major overdeepened troughs control the ice flow. As the ice stream starts to diverge, the subglacial topography evolves again into smaller, more alpine-like valleys, akin to the eastern subglacial highlands which previously hosted Pliocene ice caps. The differences in these geomorphological regimes underlying the NEGIS are likely to be attributable to changing geological provinces, which in this area are poorly constrained. In addition, whilst these regimes appear to have little effect on the location of the onset of the ice stream and its shear margins, the subglacial topography downstream has a distinct impact on ice stream geometry by channeling or reinforcing ice flow direction. In contrast to the fact that the NEGIS is generally thought of as topographically unconstrained, this study indicates that topography is in fact influencing the ice stream. We will also present first results on quantifying this effect, through the derivation of 3-dimensional mass flux balance and its relation to topography.

This study provides new insights into the subglacial environment along the NEGIS, which, despite the acquisition of large amounts of bed elevation data in recent years, has yet to be fully characterised. Furthermore, it emphasises the highly variable conditions which can affect and facilitate fast ice flow, indicating that no one single process controls the ice stream.

How to cite: Carter, C., Franke, S., Paxman, G., Jamieson, S., Bentley, M., Jansen, D., Paden, J., and Eisen, O.: Diverse geomorphological regimes underlie the Northeast Greenland Ice Stream, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1350, https://doi.org/10.5194/egusphere-egu25-1350, 2025.

The Discovery Deep Basin, located beneath the Ross Ice Shelf, adjacent to the Trans-Antarctic Mountains and south of Minna Bluff, is the deepest (>1500 m water depth) shelfal basin in the Ross Sea.  Its tectonic origin and sedimentary and glacial evolution are poorly constrained, and direct investigations are hindered by the ice cover of the Ross Ice Shelf. Understanding of bathymetry and seafloor geology in the region is based on limited surface investigations and inversions of regional airborne geophysical datasets. However, its proximity to outflow glaciers from East Antarctica and great depth mean that it is likely to contain sedimentary records of past glacial cycles and environmental change.

We present the results of two seasons of explosive-source seismic exploration of the basin in the summers of 2021/22 and 2023/24, for which the primary objectives were to identify the basin’s deepest point, obtain high-resolution imagery of seafloor sediment accumulations, and constrain subsurface structure and stratigraphy. More than 65 km of seismic reflection imaging was complemented by surface collected gravity data. These data provide localised coverage of the sub-ice-shelf ocean and sediments in a region where ROSETTA-Ice airborne-gravity data identified a regional gravity low. During the first season, data were collected using explosive charges frozen into 25-m-deep hot-water-drilled holes that are recorded by 96 conventional geophones buried in the firn with a 10-m spacing; the shot spacing was 240 m. During the second season, data were collected using  surface-detonated Cordtex detonating cord sources (10 m lengths at 10 g/m) recorded by a 300-m-long 96-geophone snow streamer with a 60 m shot spacing. Both seismic reflection data sets were processed into seismic images using GLOBE Claritas.

Processed seismic data show a gently dipping layered seafloor lying beneath the ocean cavity with a maximum depth of 1650 m and at least 200 m of layered and dipping sedimentary strata containing several mappable unconformities and distinct geological structures (e.g., a regional anticline and several faults). Given its depth and substantial sediment accumulation, this site may offer one of the highest resolution climate records in Antarctica. The study also provides a critical bathymetric tie for regionally inverted airborne gravity data (Tinto et al., 2019; Tankersley et al., 2022) by confirming a greater basin depth than previously modelled and relocating the deepest point of Discovery Deep towards the NW. These findings will contribute to an improved understanding of RIS basin geodynamics, ice sheet stability, ocean currents, and tectonic activity and emphasise the importance of future exploration drilling to refine our knowledge of past climate conditions.

How to cite: Gorman, A., Oliver, W., Hansen, O., Bowman, H., Black, J., Keller, E., Carter, C., Tankersley, M., Horgan, H., and Dunbar, G.: Using seismic and gravity data to examine the seafloor geology in the vicinity of the Discovery Deep shelfal basin, Ross Ice Shelf, Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14493, https://doi.org/10.5194/egusphere-egu25-14493, 2025.

Sub-ice-shelf bathymetry exerts a primary control on the stability of ice shelves by guiding melt-inducing water masses and through pinning points that resist the flow of the overriding ice. Collecting sub-ice-shelf bathymetry data using active source seismic surveying or direct observations is inefficient, and often impractical. Gravity methods provide a pragmatic alternative, by which observed variations in Earth’s gravitational field are used to estimate the underlying bathymetry. We utilize a new open-source gravity inversion algorithm (Invert4Geom) developed specifically for modeling sub-ice-shelf bathymetry and estimating the spatially variable uncertainty in the results. Here we test the inversion on a suite of models created with real bathymetric data from Antarctica's Ross Sea. These tests enable 1) determination of the best practices for conducting bathymetric inversions, 2) recognition of the limitations of the inversion and uncertainty quantification, and 3) identification of where community efforts should be focused for the future of determination of Antarctica’s sub-ice-shelf bathymetry. We find that estimating and removing the regional component of gravity prior to the inversion is the largest source of error in the resulting bathymetry model, but this error can be greatly reduced with additional bathymetry constraints. Additionally, we explore the effectiveness of inversions with varying levels of data noise, spacing, and strengths of the regional gravity field.

How to cite: Tankersley, M., Horgan, H., Caratori Tontini, F., and Tinto, K.: Gravity inversion for sub-ice shelf bathymetry; best practises, uncertainty estimates, and open-source software, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12769, https://doi.org/10.5194/egusphere-egu25-12769, 2025.

Magnetic data collection in Antarctica is commonly carried out using airborne platforms, which allow to cover large spatial areas. Airborne surveys in Antarctica have been conducted since the 1950s as part of international and collaborative efforts. A challenge in creating a homogenous magnetic data compilation for Antarctica arises from heterogeneity in data collection through the decades, for example from different flight lines spacing, different observation height and long time period between surveys. Traditional data processing is performed manually or semi-automated which is time consuming due to the factors described above.

Equivalent source technique is a powerful tool to automate the data processing to combine irregular airborne surveys on different observation heights and time periods. The magnetic field data from different airborne surveys can be represented by a set of equivalent sources that accurately reproduce the input data. The magnetic forward response of the equivalent sources can be calculated at any height making upward / downward continuation obsolete and allowing a uniform observation height between surveys. Furthermore, the magnetic field can be calculated on a regular grid, removing irregular flight lines from airborne data compilations. Combining the equivalent source method with despiking-, wavelet filtering-, IGRF/DGRF correction- and weighted distance base station correction routines allow a fully automated processing workflow to create a harmonised magnetic compilation containing irregular airborne surveys with decreased noise.

We present a test case in East Antarctica to highlight the potential of an automated processing workflow to harmonise magnetic airborne data without biases arising from manual processing. Here, we utilise ICECAP data (2009-2017) and RAE data (1956-1960) as well as the ADMAP data compilation grid as prior. The next step is to use ADMAP line data to create a fully automated homogeneous continent wide Antarctic magnetic data compilation under the SCAR ADMAP working group umbrella.

How to cite: Lowe, M., Szwillus, W., Aitken, A., Lösing, M., Li, L., Eagles, G., and Ebbing, J.: Equivalent source inversion to homogenise magnetic airborne surveys in Antarctica flown on irregular flight lines, line spacing, heights and decades., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5645, https://doi.org/10.5194/egusphere-egu25-5645, 2025.

Subglacial bed-type (bedrock or sediment) is a significant control on fast glacier-motion. Geophysical techniques provide a relatively efficient means to explore variations in bed type. The GHOST project collected a range of geophysical datasets to explore variability in bed type beneath Thwaite glacier including active source seismic and radar measurements. Over the course of two seasons an array of ~ 200 Magseis Fairfield ZLand 3C nodal seismometers were deployed on Thwaites. The primary goal of this array was to record glacier generated seismicity to explore subglacial dynamics via subglacial stick-slip events and ice dynamics via crevasses generated seismicity. We explore the potential use of this seismic array to image bed type using passive source seismic methods. We will present initial results using two complimentary methods. First, we use the receiver function method, which leverages the recording of earthquakes to identify converted waves that are produced by significant material boundaries, such as those that occur at the ice-bed interface or between sediment-bedrock interfaces. Second, we explore the use of ambient-noise seismic-imaging to measure seismic surface waves traveling across the network. We then use these surface-wave measurements to measure phase velocities which can then be used to identify the presence of large sedimentary layers. We will present initial results of spatial variability in sedimentary structure across our study area and how these are related to variations in basal conditions and flow-speed of Thwaites Glacier.  Finally, we  will show how these data can be used to extract information about sediment properties that can be linked interpreted in terms of physical properties that influence ice sheet flow speed such as porosity.        

How to cite: Winberry, J. P., Stevens, N., Willet, A., Zak, J., Zoet, L., and Anandakrisnan, S. and the ITGC GHOST Team: Passive Seismic Imaging of Subglacial Conditions on Thwaites Glacier , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13970, https://doi.org/10.5194/egusphere-egu25-13970, 2025.

Sub-ice shelf pinning points provide buttressing to the Antarctic Ice Sheet, which regulates sea-level rise by reducing ice discharge across the grounding line. Satellite-derived ice rises or rumples have been identified on Antarctic ice shelves as sub-ice-shelf pinning points where the ice-shelf bottom is anchored to the seafloor, and they have been used to extend the ice-shelf thickness change record back to 1973 (Miles & Bingham, 2024). We use combined analysis of Landsat imagery with aerogravity-derived bathymetry to present a history of intermittent grounding of the Venable Ice Shelf on a seafloor high since ~1935. We interpret crevasse patterns in satellite imagery over this former pinning point as evidence of mid-twentieth-century ice-shelf thinning in the Bellingshausen Sea sector, allowing us to extend the ice-shelf thickness record beyond the satellite era. Investigation of additional Antarctic ice shelves with similar analysis reveals other paleo-pinning points, which can extend the ice-shelf thickness record beyond the satellite era in key locations.

How to cite: Locke, C. and Tinto, K.: Mid-twentieth Century Bellingshausen Sea Sector Ice-shelf Thinning Identified from Venable Ice Shelf Grounding History, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14295, https://doi.org/10.5194/egusphere-egu25-14295, 2025.

Understanding the Solid Earth structure beneath ice shelves and glaciers is essential for predicting their interaction with ocean circulation and the evolution of Polar Regions. This study focuses on the innovative use of airborne gravimetric data collected during transit flights to improve bathymetric and tectonic models in Antarctica and the surrounding regions.

We first present a detailed bathymetric model of the Cook Ice Shelf, Ninnis Glacier Tongue, and the surrounding continental shelf edge derived from airborne gravity inversion. This model improves our understanding of water pathways connecting the continental shelf to the ice shelves, a critical factor for analyzing basal melt processes. Localized basins (~1400 m deep) beneath the ice shelves and shallow areas (~200 m) near Cape Freshfield were identified, with seafloor depths near grounding lines exceeding the observed depths of modified Circumpolar Deep Water (< 350 m). For the first time, transit flight gravity anomalies were used to propose a new position for the continental shelf edge (~27 km north of its currently mapped location), challenging previous assumptions about the extent of the Cook Shelf Depression.

Building on this work, we explore further applications of transit flight gravity data in tectonic studies of the region between South America and Antarctica, encompassing the South American, Scotia, Shetland and Antarctic plates. These datasets, compared with satellite-derived gravity models and ship-based data, are evaluated for their potential to refine bathymetric grids and address gaps in tectonic understanding. Preliminary results suggest that airborne gravimetry, with appropriate filtering and leveling, can provide valuable insights into regions where traditional methods face limitations, such as beneath ice shelves or in sparsely surveyed areas.

Our ongoing efforts focus on optimizing data processing to enhance resolution and combining these results with existing tectonic models. By addressing questions such as the resolution achievable for gravity-based bathymetric inversions and the integration of sparse data into robust models, this research seeks to expand the applicability of transit flight data. These insights will contribute to understanding the lithospheric structure and plate interactions in the Southern Ocean, bridging gaps in knowledge critical for both solid-earth and cryospheric studies.

This work exemplifies the importance of integrating novel data sources, such as transit flight gravimetric data, into comprehensive models that connect the solid Earth and ice dynamics. By doing so, we aim to improve the understanding of tectonic and subglacial processes that influence the evolution of Polar Regions.

How to cite: Constantino, R. and Tinto, K.: From the Antarctic Continental Shelf to Plate Boundaries: Applications of Airborne Gravity Data from Transit Flights, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16908, https://doi.org/10.5194/egusphere-egu25-16908, 2025.

Subglacial digital elevation models (DEMs) are a critical boundary condition in glaciological modeling for hypothesis testing. Interpreting the results of this glaciological modeling requires careful consideration of statistical methods, data integrity, and error quantification when generating the bed DEMs used as a constraining boundary condition.  Here we use various DEMs to model ice flow over a suite of hypothesized geothermal anomalies, at Thwaites/Haynes Glaciers, West Antarctica, described in Bott et al. 2023 & 2024, to assess the impact of DEM selection on hypothesis testing for these potential melt anomalies.

Commonly used DEMs (e.g. Bedmap 2 and BedMachine), while robust on a continental level, do not in general represent the finer-scale variation in bed topography, which has a significant impact on ice dynamics from the ice divide all the way to the grounding line. 

Bedmap 2 uses a thin plate spline algorithm with iterative finite difference interpolation, producing a smooth interpolation of subglacial topography. This method has merit in providing a general topographic shape; however, the smaller-scale basal roughness is virtually erased, and notable inaccuracies exist in areas of high topographic relief, such as the edges of deep troughs and subglacial valleys. 

BedMachine, constrained by its mass-balance ice flow model must, by nature, assume where basal ice is sliding vs. where ice is frozen to the bed. This creates inherent circular logic in modeling, whereby one cannot constrain basal melt and basal sliding using BedMachine’s topography - since the thermodynamic state of basal ice has already been assumed by the DEM’s mass-balance model. 

To combat these issues, novel geostatistical and machine-learning methods for generating high-fidelity DEMs, which incorporate simulations of smaller-scale basal roughness, have been developed by Goff et al. 2014, Graham et al. 2017, and Dr. Emma MacKie at the University of Florida’s Gator Glaciology Lab. But all methods, regardless of their sophistication, come with assumptions, biases, and uncertainties. And with Bedmap 3 and BedMachine 4 not far from becoming publicly available, the selection of DEMs has never been wider. Here we use the potential for basal melting beneath Haynes/Thwaites Glaciers as a framework for understanding how underlying assumptions, methodologies, and uncertainties associated with the spectrum of bounding DEMs impact our confidence in the hypothesis tests based on this ice sheet modeling. 

Here we focus on the Thwaites/Haynes Glacier System of West Antarctica, which has two properties that make it ideal for assessing the impact of bed DEMs on ice sheet modeling results. 1) The presence of a trough-dominated basal morphology, characterized by heterogeneous geothermal flux provides ample conditions for testing the spatial distribution of basal sliding vs. plastic flow. And 2) a richness of volcaniclastic internal reflection horizons to be used as indicators of mass losses from basal melting through time. 

How to cite: Bott, J., Blankenship, D., Young, D., and Yan, S.: Why Assumptions & Uncertainties in Bed DEMs Matter: A Geothermal Example from Haynes Glacier, West Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14386, https://doi.org/10.5194/egusphere-egu25-14386, 2025.

Understanding the spatial variability of geothermal heat flow (GHF) in Greenland is critical for predicting ice sheet dynamics. However, the scarcity of direct observations complicates GHF predictions and most samples of thermal parameters are from its coasts, which requires some form of extrapolation or modelling to predict these under the Greenland ice sheet.

Finland, in turn has a uniquely dense coverage of radiogenic heat production (RHP) measurements. Here, the RHP data reveal a significant spatial variability, which can be correlated with tectonic age units. However, RHP also exhibits variability within the units, which we find to be describable as a random field with two correlation lengths of <10 and c. 50 km as well as substantial white noise variability. If we decimate the Finish data to a strip at the Finish coast and inland border, the statistical distribution (mean and standard deviation) for each unit is almost identical to the whole data set. Hence, using the limited data for Greenland to predict thermal parameters under the ice is justified, if the subglacial geology was known.

Subglacial geology is, however, not well known for Greenland and we test two geological maps. Using conditional simulation, we extrapolate RHP from coastal rock samples, assuming the statistical properties are valid for the whole units. Based on the Finish data, we treat the within-unit variability using a random field with a spatial length scale of 50 km and an amplitude equal to 10% of total standard deviation. We choose to neglect the smaller-scale variations, as they are likely not affecting surface heat flow, due to the smoothing effect of heat diffusion.

Our results show that both geological maps predict significantly different GHF values of up to 20 mW/m² differences within the local spots in the interior of Greenland with a similar unit wide GHF. In northern Greenland and at the transition between southern and central Greenland larger scale differences of about 30 mW/m² can be found, which come from the different structure of the units of both maps and thus significantly different mean RHP values. This underlines the need for reliable geological maps to constrain the distribution of RHP.

How to cite: Szwillus, W., Freienstein, J., Ebbing, J., and Zimmer, M.: Learning from Finland: The role of geology and Radiogenic Heat Production to predict subglacial heat flow in Greenland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16800, https://doi.org/10.5194/egusphere-egu25-16800, 2025.

Active deglaciation results in faster solid earth deformation rates than predicted by models that are used on longer glacial-cycle timescales. We test the hypothesis that the discrepancy can be explained by transient mantle viscosities.

In mechanical experiments on mantle rocks, steady-state viscous flow is preceded by transient creep during and after changes in stress. Transient deformation following stress changes initially occurs at fast rates and decays while the rock viscosity gradually increases. New efforts in microphysical modelling, calibrated against experimental deformation, provide a novel flow law that captures both transient as well as steady-state viscous behaviour. The flow law describes dislocation creep, where interactions between dislocations lead to internal stresses that counteract loading. We complement the flow law by a model that describes the evolution of these internal stresses with progressive deformation, and thereby allows for variable viscosity. We use this flow law in numerical models to study stress history-dependent glacial isostatic adjustment (GIA). First, we investigate the relevance of this flow law for GIA, using a simple 1D model. For typical loads induced by ice-mass changes, we predict that the asthenospheric viscosity may temporarily reduce by 1 to 2 orders of magnitude compared to the long-term, steady-state viscosities.

Second, we study the contribution of transient dislocation creep to present-day GIA by using regional 3D finite element models. We focus on the Amundsen Sea Embayment in Antarctica, and test whether transient rheology can provide a better fit to GNSS time series than steady-state mantle rheology. Satellite altimetry and firn models provide a spatio-temporal view of ice load changes for the last three decades, and we test the sensitivity to ice load changes in the pre-observational era.

Recent studies demonstrate that feedback between vertical velocities of bedrock and ice-sheet evolution, and the speed of grounding line retreat, depends strongly on mantle viscosity. As transient rheology affects effective viscosity when ice loads change, transient rheology may be an important factor to consider in ice sheet-bedrock motion interactions.

How to cite: van Calcar, C., Broerse, T., Iannidi, I., Breithaupt, T., Wallis, D., Willen, M., Riva, R., van der Wal, W., and Govers, R.: Present-day deglaciation driving transient upper-mantle deformation: modelling fast uplift rates in the Amundsen Sea Embayment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20938, https://doi.org/10.5194/egusphere-egu25-20938, 2025.

The geotectonic evolution of the Antarctic Peninsula (AP), one of the most important parts of the West Antarctic mosaic, began before the breakup of the Gondwana continent during the Triassic. The geotectonic events that formed the AP continued after the breakup. Horseshoe Island, located near the center of the AP, contains crystalline records of these geological events. This study presents the magmatic stratigraphy of Horseshoe Island was reconstructed using the LA-ICP-MS U-Pb ages of zircon crystals from plutonic rocks of the island, collected during the Turkish Antarctic Science Expedition-VII (2023). The obtained ages are matched to the plutonic units mapped thoroughly by Matthews (1983) as follows. Old to young: U-Pb zircon analyses of rocks from the Antarctic Peninsula Metamorphic Complex, which consists of metamorphic rocks ranging in grade from meta-granites to gneisses, yielded mean ages ranging from 211.5 ± 1 Ma to 175.1 ± 0.5 Ma (MSWD=0.1-13). The light-colored, medium-grained Homing Head Granites, which surface south of Homing Head along the northern slopes of Mount Searle, yielded ages ranging from 108.83 ± 0.47 Ma to 106.19 ± 0.46 Ma (MSWD=0.3-1.1). The age of the myrmecitic textured brick-red coloured Gaul Cove Granites within the Andean Plutonic Series is between 106.9 ± 0.4 Ma and 103.4 ± 0.7 Ma. The coarse-grained Mite Diorite observed in a narrow area south of Lystad Bay yielded an age of 91.0 ± 0.2 My. The Sally Cove gabbro, observed on the southern slopes of Sally Cove, the northernmost of the rocky islands in Lystad Bay and in a narrow area on the beach where the Turkish Scientific Research Station is located on the island gave ages ranging from 73.4 ± 0.5 Ma to 72.0 ± 0.4 Ma. In the west of the island, U-Pb ages ranging from 74.6 ± 1.1 Ma to 72.78 ± 0.99 Ma were obtained from zircons from the coarse-grained pink-coloured Beacon Point Granites, which cut the gabbros and surface along the northern slopes of Lystad Bay. Jurassic and Cretaceous plutons of island have I-type geochemical character. The isotopic compositions of I_Sr, ε_Nd(t) and ε_Hf(t) indicate that the Homing Head Granodiorite, Gaul Cove Granite, and the Upper Beacon Head Quartz Monzonite were formed by partial melting of crustal sedimentary rocks. The Mite Diorite and Sally Cove Gabbro are hybrid magmas formed by amphibolitic mafic lower crust dominated and lithospheric mantle contribution. When geochemical data are evaluated in tectonic discrimination diagrams, Sally Cove Gabbro and Beacon Head Quartz Monzonite have the characteristics of rocks formed in intraplate environments, while Homing Head Granodiorite, Gaul Cove Granite and Mite Diorite have the characteristics of rocks formed in subduction environments.

This study was carried out under the auspices of the Presidency of the Republic of Turkey, Ministry of Industry and Technology of the Republic of Turkey and in coordination with TÜBİTAK MAM Polar Research Institute (KARE) and supported by TÜBİTAK grants 122Y192 and 122G261.

How to cite: Kandemir, R., Karslı, O., Moghadam, H. S., Şen, C., Uysal, İ., Bak, T., Yalçınkaya Bay, Ş., and Erturaç, M. K.: Geochemistry and Geochronology of Horseshoe Island (Antarctic Peninsula) Igneous Rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14819, https://doi.org/10.5194/egusphere-egu25-14819, 2025.

Geological fieldwork was conducted on Nelson Island (South Shetland Islands, West Antarctica) during January and February 2023, with logistical support provided by the Czech Antarctic Research Center and in-kind assistance from TÜBİTAK MAM Polar Research Institute. This study presents the petrography and preliminary crystal size distribution (CSD) results of the volcanic rocks from the Nelson Island-Stansburry Peninsula.

Nelson Island is situated in the northwestern region of the Antarctic Peninsula, within the South Shetland Islands. The dominant lithologies in the study area are volcanic and intrusive rocks, with a minor presence of sedimentary rocks distributed throughout the ice-free areas. The volcanic rocks are primarily basalt/basaltic andesite lavas, accompanied by associated pyroclastic rocks. Petrographic analyses reveal that the lavas are predominantly composed of plagioclase and orthopyroxene crystals, with occasional olivine. Plagioclases occur as phenocrysts and microlites, with phenocrysts exhibiting labradorite composition (An_50–70). The basaltic lavas display phaneritic to hemicrystalline-porphyritic textures, with pilotaxitic to intersertal groundmass. Disequilibrium textures, such as sieve-textured plagioclase, multiple generations of plagioclase, and embayed pyroxenes and plagioclases, are prominent.

To understand magma chamber processes, the crystal size distributions (CSD) of two basalt samples from Nelson Island were analyzed. A total of 400 crystals were measured, yielding average results indicating a relatively short magma residence time of 10.6 years and a population density (​n₀) of 19.7 mm⁻⁴. These results produce a concave-up trend in the population density versus size diagram. Petrographic and CSD data collectively highlight dynamic disequilibrium crystallization conditions, likely influenced by variations in temperature and pressure within the magmatic system. Future petrological and geothermobarometric analyses will refine these interpretations, providing deeper insights into the evolution and magma chamber processes of Eocene magmatism in the South Shetland Islands.

How to cite: Bayram, G., Ünal, A., and Altunkaynak, Ş.: Preliminary Results from Petrography and Crystal Size Distribution (CSD) Analysis of Lavas from Nelson Island, South Shetland Islands (Antarctica), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18684, https://doi.org/10.5194/egusphere-egu25-18684, 2025.