| Deformation within the Pamir and Tian Shan in Central Asia has been ongoing during the Cenozoic as a result of the Indo-Eurasian collision. The timing and rates of deformation along the NE Pamir margin have been largely unconstrained until recently. This dissertation presents a synthesis of new structural mapping, stratigraphy, magnetostratigraphy, cosmogenic radionuclide (TCN) burial and depth profile dating, optically stimulated luminescence (OSL) dating, and topographic surveys of deformed Quaternary surfaces, to understand the tectonic evolution of the NE Pamir margin since ~20 Ma. Two geochronologic techniques, OSL and TCN, are applied to determine the timing and slip/shortening rates of faults and folds in the Pamir and Tian Shan forelands. Deformed fluvial terraces crossing active structures record Late Quaternary deformation. Traditionally, silt quartz has been used to date fluvial terraces using OSL. However, OSL dating on fine-sand, in conjunction with appropriate age models, yielded stratigraphically consistent ages that also agree with TCN depth profile ages whereas silt ages overestimate the terrace age by ≥50%. Commonly, coarse-grained basin fills and syntectonic growth strata adjacent to growing structures may be difficult to date. Eight new 26Al/10Be cosmogenic burial ages on syntectonic growth strata and basin fills, in conjunction with magnetostratigraphic sections, provide new initiation ages and shortening rates for several key structures in the region. Modeling of post-burial nuclide production suggests burial ages may be perturbed up to 60% due to Late Quaternary incision of rivers, whereas synburial production is negligible in these rapidly accumulating basins. The new ages document the basinward growth and eastward propagation of deformation of the Pamir and Tian Shan. Piggyback basin sediments in the hanging wall of the frontal fault of the Pamir record coeval deformation since ~10 Ma. Deformation propagated northward and eastward into the Tarim Basin as the collision with the Tian Shan progressed. Similar to the Tian Shan, coeval deformation on hinterland and basinward structures appeared to play an important role in accommodating shortening along the NE Pamir margin. During the Late Quaternary, much of the deformation is accommodated on the frontal faults, with shortening rates 6-8 mm/a, consistent with the current geodetic rate. |
