Pamir

One major thrust of our research in the Chinese Pamir has been the establishment of the exhumation pattern along the Kongur Extensional System (KES), a major normal fault system within the eastern Pamir. My colleagues Ed Sobel and Rasmus Thiede (a post-doc on the project) led this part of the project, collecting samples for (U-Th)/He, Fission-track and 40Ar/39Ar dating. We established the pattern of exhumation in the KES footwall (Thiede et al., 2013) and the timing of strike-slip faulting in the region using geomorphic criteria combined with thermochronology (Sobel et al., 2011). Our research also took us in an unexpected direction, leading us to hypothesize oceanic-style subduction and upper plate extension in the Pamir as a whole (Sobel et al., 2013). In this context, the KES is a tear fault above the subducting slab. These data established a baseline of exhumation against which the influence of glacial erosion could be tested.

We also spent a large effort in constraining the glacial and landsliding history of this region. I worked with a student of Lewis Owen, Yeong Bae Seong, in his interpretation of the geomorphology and glacial history of the central part of the KES, where two high, bedrock peaks, Muztagh Ata and Kongur Shan, lie in the footwall of the fault (Seong et al., 2009). One of my own students, Benjamin Kirby, completed an MSc thesis examining a sequence of terraces intercalated with glacial moraines along the northern part of the fault system. I was involved in establishing a Quaternary geochronology along the southern end of the KES as well (Owen et al., 2012). I also trained and supported a Chinese student, Yuan Zhoade, in his efforts to date large landslides in the hanging wall valley (Yuan et al., 2012; 2013).

My colleagues and I investigated the larger-scale tectonic geomorphology and erosion and depositional history of the Pamir as well with detrital work. I supervised a student in the field, John Bershaw, who conducted zircon provenance work in the Chinese Pamir (Bershaw et al., 2012). My colleague from my Argentina work, Barbara Carrapa, works in the Tajikistan Pamir, and we collaborated, investigating differences in erosion and climate on the eastern and western Pamir with detrital thermochronology (Carrapa et al., 2014c).

A major aspect of my research in the Pamir has been attempting to link the tectonic and glacial stories. I mapped and dated terraces intercalated with glacial moraines in the northern part of the study area, establishing a glacial chronology that markedly contrasts with that in the southern area. I also developed novel techniques for quantifying and analysing glacial morphology. I extracted morphologic data for 156 glaciers in the footwall of the KES. We observed a pronounced asymmetry in glacial ELA, area, debris cover and headwall relief that we interpreted to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers on the upwind, fault-controlled side of the range. This asymmetry results from the transfer of moisture deeply into the range as wind-blown or avalanched snow, and from limitations imposed on glacial area on the upwind side of the range by the geometry of the KES. We also establish that the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) likely reflects lithologic control (i.e. the location of crustal gneiss domes), and the formation of peaks which rise above the ELA and escape the glacial buzzsaw (Schoenbohm et al., 2014).

A final part of my research in the Chinese Pamir, in collaboration with Alex Robinson (U Houston) and Lewis Owen (U Cincinnati) has been into the Karakoram and the Karakax-Altyn Tagh faults, two of the largest faults that cut the Tibetan plateau, which converge and nearly intersect in the Pamir. It is unknown whether these are long-lived features in the plateau which continue to accommodate continental extrusion today or are second order, transient features which have not overlapped temporally or interacted kinematically. This project is primarily founded on field structural and geomorphic mapping and dating of Quaternary landforms. This work has resulted in one paper on the glacial chronology in the Tashkorgan Valley (Owen et al., 2012), and an additional manuscript focused on the structural interpretation is in review (Robinson et al., in review). Our results show that the Karakoram fault has not been active for at least the past 150 thousand years, and perhaps longer. These results are controversial, as the Karakoram fault has been implicated as a major force in the recent evolution of the Tibetan Plateau (Valli et al., 2007).

Bershaw, J., Garzione, C.N., Schoenbohm, L.M., Gehrels, G., and Li, T., 2011, Journal of Asian Earth Sciences, v. 44, p. 136-148.
Carrapa, B., Cosca, M., Mustapha, F.S., Schoenbohm, L.M., Sobel, E.R., DeCelles, P.G., Russell, J., and Goodman, P., 2014c, Lithosphere, doi:10.1130/L360.1.
Owen, L.A., Chen, J., Hedrick, K.A., Caffee, M.W., Robinson, A.C., Schoenbohm, L.M., Yuan, Z.-D., Li, W.-Q., Imrecke, D.B., and Liu, J.-F., 2012, Quaternary Science Reviews, v. 47, p. 56-72.
Robinson, A.C., Owen, L.A., Chen, J., Schoenbohm, L.M., Hedrick, K.A., Blisniuk, K., Sharp, W.D., Imrecke, D.B., Li, W.-Q., and Yuan, Z.-D., Caffee, M.W., Mertz-Kraus, R.,  in review, EPSL.
Schoenbohm, L.M., Jie., C., Stutz, J., Sobel, E.R., Thiede, R.C., Kirby, B., and Strecker, M.R., 2014, Geomorphology, v. 221, p. 1-17.
Seong, Y.B., Owen, L.A., Yi, C.-L., Finkel, R.C., and Schoenbohm, L.M., 2009, Geomorphology, v. 103, p. 227-250.
Sobel, E.R., Schoenbohm, L.M., Chen, J., Thiede, R., Stockli, D.R., Sudo, M., and Strecker, M.R., 2011, EPSL, v. 304, p. 369-378.
Sobel, E.R., Chen, J., Schoenbohm, L.M., Thiede, R., Stockli, D.F. Sudo, M., and Strecker, M.R., 2013, EPSL, v. 363, p. 204-218.
Theide, R.C., Sobel, E.R., Chen, J., Schoenbohm, L.M., Stockli, D.F., Sudo, M., and Strecker, M.R., 2013, Tectonics, v. 32, p. 763-779.
Valli, F., Arnaud, N., Leloup, P.H., Sobel, E.R., Maheo, Gwéltaz, Lacassin, R., Guillot, S., Li, H.-B., Tapponnier, P., and Xu, Z.-Q., 2007, Tectonics, v. 26, TC4004.
Yuan, Z.-D., Chen, J., Li, W.-Q., Owen, L.A., and Schoenbohm, L.M., 2012, Quaternary Sciences, v. 32, p. 409-416. (In Chinese).
Yuan, Z.-D., Chen, J., Owen, L.A., Hedrick, K.A., Caffee, M.W., Li, W.-Q., Schoenbohm, L.M., and Robinson, A.C., 2013, Geomorphology, v. 182, p. 49-65.