Uplift in response to tectonic convergence: The Kyrgyz Tien Shan and Cascadia subduction zone.

摘要

Horizontal contraction at convergent plate boundaries produces uplift at geologic and interseismic time scales. Cenozoic convergence between India and Eurasia has uplifted the high Tien Shan mountains of central Asia and, combined with fluctuations in climate, has produced well preserved flights of river terraces. I correlate uplifted and deformed terraces along and between rivers in the southern Issyk-Kul basin using surveying and geologic mapping. Ages of river and lake sediments from radiocarbon and 10Be cosmogenic radionuclide dating suggest terrace-forming events occurred in response to major glaciations of the source Terskey Range. Terrace geometry and ages show that basal straths may be longitudinally diachronous and rivers can remain atop aggradational deposits for periods >10 ky. Aggradation and subsequent incision may not be closely linked, as widely inferred.The geometries of river terraces and Cenozoic rocks in the southern Issyk-Kul basin constrain the structural process of northward growth of the Terskey Range plateau. My 1:25,000 scale geologic mapping of deformed Cenozoic sediments integrated with previous mapping and geophysical data show that the 5-8 km structural relief along the Terskey rangefront results from thrust faulting and northward tilting across a 15-30 km wide zone. Progressive northward tilting of late Pleistocene fluvial terraces is consistent with the geometry of bedrock relief. I interpret the deformation as crustal-scale fault-propagation, generating a late Pleistocene differential uplift rate of 2 +/- 1 mm/yr.Along the Cascadia subduction zone of western North America, the pattern of historic surface uplift is a consequence of interseismic locking. Analysis of tide gauge and leveling data collected over the past century in Oregon and northernmost California yields a corrected, densified geocentric uplift rate field which varies from 0 to 4 mm/yr with propagated errors for individual benchmarks of &sim0.4 mm/yr. Elastic dislocation modeling of the central subduction zone requires two changes in locking depth to match observed along-strike changes in uplift rate near 45°N and 42.8°N. The along-strike changes in locking on this portion of the Cascadia subduction zone interface appear related to the western and southern extent of the mafic Siletzia block in the forearc.This dissertation includes my co-authored materials.