Browsing by Author "Wiens, Douglas A."
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Item Rayleigh wave constraints on the structure and tectonic history of the Gamburtsev Subglacial Mountains, East Antarctica(American Geophysical Union, 2013-05-10) Heeszel, David S.; Wiens, Douglas A.; Nyblade, Andrew A.; Hansen, Samantha E.; Kanao, Masaki; An, Meijan; Zhao, Yue; Washington University (WUSTL); University of California System; University of California San Diego; Scripps Institution of Oceanography; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Alabama Tuscaloosa; Research Organization of Information & Systems (ROIS); National Institute of Polar Research (NIPR) - Japan; Chinese Academy of Geological SciencesThe Gamburtsev Subglacial Mountains (GSM), located near the center of East Antarctica, remain one of the most enigmatic mountain ranges on Earth. A lack of direct geologic samples renders their tectonic history almost totally unconstrained. We utilize teleseismic Rayleigh wave data from a 2 year deployment of broadband seismic stations across the region to image shear velocity structure and analyze the lithospheric age of the GSM and surrounding regions. We solve for 2-D phase velocities and invert these results for 3-D shear velocity structure. We perform a Monte Carlo simulation to improve constraints of crustal thickness and shear velocity structure. Beneath the core of the GSM, we find crustal thickness in excess of 55km. Mantle shear velocities remain faster than global average models to a depth of approximately 250km, indicating a thick lithospheric root. Thinner crust and slower upper mantle velocities are observed beneath the Lambert Rift System and the Polar Subglacial Basin. When compared with phase velocity curves corresponding to specific tectonothermal ages elsewhere in the world, average phase velocity results for the GSM are consistent with regions of Archean-Paleoproterozoic origin. Combined with radiometric ages of detrital zircons found offshore, these results indicate a region of old crust that has undergone repeated periods of uplift and erosion, most recently during the Mesozoic breakup of Gondwana. Lower crustal seismic velocities imply a moderately dense lower crust beneath the core of the GSM, but with lower density than suggested by recent gravity models.Item Upper mantle seismic structure beneath central East Antarctica from body wave tomography: Implications for the origin of the Gamburtsev Subglacial Mountains(American Geophysical Union, 2013-04-17) Lloyd, Andrew J.; Nyblade, Andrew A.; Wiens, Douglas A.; Shore, Patrick J.; Hansen, Samantha E.; Kanao, Masaki; Zhao, Dapeng; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; Washington University (WUSTL); University of Alabama Tuscaloosa; Research Organization of Information & Systems (ROIS); National Institute of Polar Research (NIPR) - Japan; Tohoku UniversityThe Gamburtsev Subglacial Mountains (GSM), located near the center of East Antarctica, are the highest feature within the East Antarctic highlands and have been investigated seismically for the first time during the 2007/2008 International Polar Year by the Gamburtsev Mountains Seismic Experiment. Using data from a network of 26 broadband seismic stations and body wave tomography, the P and S wave velocity structure of the upper mantle beneath the GSM and adjacent regions has been examined. Tomographic images produced from teleseismic P and S phases reveal several large-scale, small amplitude anomalies (Vp=1.0%, Vs=2.0%) in the upper 250 km of the mantle. The lateral distributions of these large-scale anomalies are similar in both the P and S wave velocity models and resolution tests show that they are well resolved. Velocity anomalies indicate slower, thinner lithosphere beneath the likely Meso- or Neoproterozoic Polar Subglacial Basin and faster, thicker lithosphere beneath the likely Archean/Paleoproterozoic East Antarctic highlands. Within the region of faster, thicker lithosphere, a lower amplitude (Vp=0.5%, Vs=1.0%) slow to fast velocity pattern is observed beneath the western flank of the GSM, suggesting a suture between two lithospheric blocks possibly of similar age. These findings point to a Precambrian origin for the high topography of the GSM, corroborating other studies invoking a long-lived highland landscape in central East Antarctica, as opposed to uplift caused by Permian/Cretaceous rifting or Cenozoic magmatism. The longevity of the GSM makes them geologically unusual; however, plausible analogs exist, such as the 550 Ma Petermann Ranges in central Australia. Additional uplift may have occurred by the reactivation of pre-existing faults, for example, during the Carboniferous-Permian collision of Gondwana and Laurussia.Item Using S wave receiver functions to estimate crustal structure beneath ice sheets: An application to the Transantarctic Mountains and East Antarctic craton(American Geophysical Union, 2009) Hansen, Samantha E.; Julia, Jordi; Nyblade, Andrew A.; Pyle, Moira L.; Wiens, Douglas A.; Anandakrishnan, Sridhar; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; Washington University (WUSTL); University of Alabama TuscaloosaFor seismic stations deployed on ice sheets, determining crustal structure using P wave receiver functions can be difficult since ice reverberations may mask P-to-S (Ps) conversions from the crust-mantle boundary (Moho). In this study, we assess the usefulness of S wave receiver functions (SRFs), which are not affected by ice multiples, for investigating crustal structure beneath ice sheets by analyzing broadband seismic data recorded across the Transantarctic Mountains (TAMs) and the East Antarctic (EA) craton. Clear S-to-P (Sp) conversions from the Moho are obtained using standard SRF processing methods and are easier to interpret than the corresponding Ps conversion on PRFs. When the Sp-S times are modeled together with 16-20 s Rayleigh wave group velocities, we obtain Moho depth estimates of similar to 40-45 km for the EA craton, consistent with average Precambrian crustal thickness found globally but similar to 9 km thicker than previously reported estimates. A somewhat thinner crust (similar to 35-40 km) is obtained beneath the TAMs, suggesting that crustal buoyancy is at most a minor contributor to the uplift of the mountain range in this region.