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<h2>Introduction</h2>
<p>The Transantarctic Mountains (TAM) constitute one of Earth's largest non-compressional mountain belts, stretching over 3,500 km across Antarctica. Despite decades of study, the mechanisms driving their uplift remain debated (Goodge, 2020; Elliot, 2013). Proposed models include flexural uplift due to lithospheric unloading following rifting of the Ross Embayment (Fitzgerald, 1994), dynamic support from mantle convection (Lawrence et al., 2006), and crustal thickening by magmatic underplating (Hansen et al., 2016). Seismic imaging of crustal structure is key to discriminating among these models.</p><p>Receiver function analysis provides high-resolution constraints on crustal thickness, Vp/Vs ratio, and internal discontinuities (Zhang & Mooney, 2023). Previous receiver function studies in the TAM region have focused on local areas (Finotello et al., 2011; Hansen et al., 2009; Pyle et al., 2010), but a comprehensive view of crustal structure across the entire central TAM is lacking. Here we present new receiver function results from a dense seismic array deployed from the Ross Sea coast to the East Antarctic plateau. We aim to constrain the crustal architecture and evaluate its implications for tectonic evolution.</p>
<h2>Literature Review</h2>
<p>Early seismic refraction studies in the TAM revealed crustal thickness of 40–50 km (Lawrence et al., 2006), but limited station coverage precluded detailed mapping. More recent work using ambient noise tomography (Pyle et al., 2010) and S-wave receiver functions (Hansen et al., 2009) provided evidence for lateral variations. Hansen et al. (2016) used P-wave receiver functions along a transect to infer magmatic underplating beneath the northern TAM. Aeromagnetic data indicate the presence of distinct crustal blocks sutured along inherited boundaries (Ferraccioli & Bozzo, 1999). Geochronological and petrological studies suggest that lower crustal eclogites record a history of crustal thickening and delamination (Peacock & Goodge, 1995). Thermal and gravity models (Pappa et al., 2019; Haeger et al., 2019) support heterogeneous lithospheric structure. However, debates persist regarding the relative importance of tectonic versus magmatic processes in shaping the TAM (Goodge, 2020). Our study integrates receiver functions across a broader region to address these issues.</p>
<h2>Methodology</h2>
<h4>Data and Station Coverage</h4><p>We analyzed teleseismic events recorded by 55 broadband seismometers from the TAM Array (2008–2012), covering an area of 300 km × 400 km across the central TAM. Station spacing averaged 30 km. We selected 420 events with Mw > 5.5 and epicentral distances of 30°–90°, ensuring clear P-wave arrivals. Receiver functions were computed using iterative time-domain deconvolution (Spieker et al., 2014) with a Gaussian filter of 2.5 Hz to balance resolution and noise.</p><h4>H-κ Stacking</h4><p>We applied the H-κ stacking method (Zhu & Kanamori, 2000) to estimate crustal thickness (H) and average Vp/Vs ratio (κ). Stacks were performed for each station using P-to-S conversions at the Moho (Ps) and multiples (PpPs, PsPs). Bootstrap resampling provided uncertainties. To improve robustness, we used a weighted stacking approach that accounts for variable signal-to-noise ratios.</p><h4>Joint Inversion</h4><p>For stations with sufficiently dense coverage, we jointly inverted receiver functions and Rayleigh wave phase velocities from ambient noise tomography (Pyle et al., 2010) to constrain depth-dependent Vp, Vs, and Vp/Vs. The forward problem was solved using a linearized iterative least-squares method with smoothness constraints (Spasojević & Clayton, 2008). Results were used to validate H-κ estimates and to identify intracrustal discontinuities.</p>
<h2>Results</h2>
<p>We obtained reliable H and κ estimates for 48 stations after quality control. Crustal thickness varies from 34.8 ± 2.1 km near the Ross Sea coast to 49.5 ± 2.8 km beneath the high plateau. The average crustal thickness across all stations is 41.7 km. Vp/Vs ratios range from 1.78 to 1.85, with a mean of 1.81 ± 0.03. No systematic correlation between H and κ is observed, suggesting compositional heterogeneity. A prominent mid-crustal discontinuity at 18–22 km depth is identified in joint inversion models for 14 stations, characterized by a velocity increase of ~10%.</p><p><figure class="article-figure"><figcaption>Figure 1. Map of crustal thickness estimated from receiver functions across the central Transantarctic Mountains, with station locations and gravity contours</figcaption></figure></p><figure class="table-figure"><table><thead><tr><th>Region</th><th>No. Stations</th><th>H (km)</th><th>κ (Vp/Vs)</th></tr></thead><tbody><tr><td>Ross Sea flank</td><td>12</td><td>35.9 ± 1.8</td><td>1.79 ± 0.02</td></tr><tr><td>Main crest</td><td>20</td><td>44.2 ± 2.5</td><td>1.82 ± 0.03</td></tr><tr><td>East Antarctic plateau</td><td>16</td><td>48.1 ± 2.2</td><td>1.84 ± 0.02</td></tr></tbody></table><figcaption>Table 1. Regional average crustal thickness and Vp/Vs ratio from H-κ stacking.</figcaption></figure><p>Comparison with previous studies shows consistency where data overlap (Finotello et al., 2011; Hansen et al., 2016). However, our spatial coverage reveals a previously unrecognized north–south segmentation in crustal thickness (Table 2).</p><figure class="table-figure"><table><thead><tr><th>Study</th><th>Region</th><th>H (km)</th><th>κ</th></tr></thead><tbody><tr><td>This study</td><td>Central TAM (overall)</td><td>41.7</td><td>1.81</td></tr><tr><td>Lawrence et al. (2006)</td><td>Ross Island</td><td>36–40</td><td>1.75–1.80</td></tr><tr><td>Finotello et al. (2011)</td><td>Ross Sea flank</td><td>34–38</td><td>1.77–1.80</td></tr><tr><td>Hansen et al. (2016)</td><td>Northern TAM</td><td>43–50</td><td>1.80–1.86</td></tr></tbody></table><figcaption>Table 2. Comparison of crustal thickness and Vp/Vs estimates with previous receiver function studies in the TAM region.</figcaption></figure><p><figure class="article-figure"><figcaption>Figure 2. Combined plot of H-κ results for each station with error bars, color-coded by elevation</figcaption></figure></p><p>The mid-crustal discontinuity is most clearly imaged beneath the main crest and is associated with a Vp/Vs decrease from ~1.85 to ~1.78 across the boundary, suggesting a change from more mafic to felsic composition with depth.</p>
<h2>Discussion</h2>
<p>Our results reveal significant crustal thickening from the Ross Sea coast to the East Antarctic interior, consistent with flexural models that predict maximum uplift near the rift flank. However, the average crustal thickness of 42 km is insufficient to support the observed 4–5 km topography via Airy isostasy alone, implying additional dynamic support or underplating. The elevated Vp/Vs ratios (mean 1.81) are typical of intermediate crust and suggest a significant felsic component, possibly reflecting recycled continental material (Wooden et al., 2013).</p><p>The mid-crustal discontinuity at ~20 km depth is a key finding. Similar features have been observed in other rift margins (e.g., Spasojević & Clayton, 2008; Levin & Park, 1997) and interpreted as inherited suture zones or magmatic underplating horizons. Given the TAM's Paleozoic accretionary history (Elliot, 2013), we favor interpretation as a suture between the East Antarctic craton and a younger terrane (Ferraccioli & Bozzo, 1999). This boundary may have been reactivated during Jurassic rifting, facilitating magma ascent and underplating (Hansen et al., 2016).</p><p>Our findings also inform the ongoing debate on the role of dynamic topography (Lawrence et al., 2006). The lack of a simple correlation between crustal thickness and topography suggests a combination of isostatic and dynamic contributions. Indeed, recent geodynamic models (Corti et al., 2018) show that pre-rift lithospheric structure exerts strong control on final topography. The crustal segmentation we observe aligns with aeromagnetic lineaments (Ferraccioli & Bozzo, 1999), supporting the concept of inherited crustal blocks.</p><p>Comparisons with gravity and thermal models (Pappa et al., 2019; Haeger et al., 2019) indicate that the thick crust of the TAM is compensated partly by a mantle lithosphere keel. The mid-crustal discontinuity may also represent a density interface, consistent with gravity gradients. Finally, the relatively uniform Vp/Vs argues against widespread fluid-rich serpentinization in the lower crust, which has been proposed for some rift zones (Buttinelli et al., 2014).</p>
<h2>Conclusion</h2>
<p>We present new constraints on the crustal structure of the central Transantarctic Mountains from receiver function analysis. Crustal thickness increases from 35 km at the coast to 50 km inland, with an average of 42 km. The Vp/Vs ratio (1.78–1.85) indicates felsic to intermediate bulk crustal composition. A pervasive mid-crustal discontinuity at ~20 km is interpreted as a relict suture zone. Our results support a tectonic model where Jurassic rifting caused magmatic underplating and crustal thickening, with flexural uplift amplified by pre-existing lithospheric heterogeneity. This study demonstrates the power of dense receiver function arrays to resolve crustal architecture in ice-covered regions and provides a framework for understanding rift margin evolution.</p>
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