HR: 1340h
AN: T23D-1634    [Abstracts]
TI: The Role of Inherited Strike-Slip Faults in the Growth of the Northern Tian Shan
AU: * Selander, J
EM: selander@unc.edu
AF: Department of Geological Sciences, University of North Carolina at Chapel Hill, Mitchell Hall 104 South Road CB# 3315, Chapel Hill, NC 27599, United States
AU: Oskin, M
EM: oskin@email.unc.edu
AF: Department of Geological Sciences, University of North Carolina at Chapel Hill, Mitchell Hall 104 South Road CB# 3315, Chapel Hill, NC 27599, United States
AU: Ormukov, C
EM: ormukov@rambler.ru
AF: Krygyz Institute of Seismology, Asanbay 52/1, Bishkek, 720060, Kyrgyzstan
AU: Abdrakhmatov, K
EM: kanab52@rambler.ru
AF: Krygyz Institute of Seismology, Asanbay 52/1, Bishkek, 720060, Kyrgyzstan
AB: We document the role of inherited strike-slip faults in the northward propagation of the Tian Shan orogen. The Kungey and Zailiskey Ranges (KZR), located along the border of Kyrgyzstan and Kazakhstan, are cored by the ENE-striking Kemin-Chilik fault. This fault is an inherited structure with >30 km of sinistral displacement of Paleozoic basement terranes. Stratigraphic observations show that prior to Neogene reactivation, this region was overlain by a wedge of fluvial sediment derived from more southerly portions of the Tian Shan. The onset of uplift adjacent to the Kemin-Chilik fault is recorded by a transition from distally derived metamorphic clasts to locally derived grus and a reversal of paleocurrent directions. Upward-coarsening records outward propagation and growth of the KZR. We find that deformation is partitioned into sinistral slip on the Kemin-Chilik fault and reverse-oblique slip on a surrounding network of steeply dipping faults. Structural relief on members of this fault network is well-recorded by deformation of a planar unconformity that separates Neogene strata from Paleozoic basement. This unconformity is preserved as a geomorphic surface up to high elevations of the KZR. Activity of fault systems surrounding the KZR is consistent with the long-term pattern of outward growth. We measured fault slip-rates from displaced fluvial terraces in ten different locations surrounding the KZR. These terraces were correlated to a very well-preserved chronosequence at the Toru-Aygir River in the southern Kungey range. Cosmogenic 10Be dating of this sequences yields terrace ages of 85.6 +/- 7.6 ka, 126.4 +/- 10.8 ka, and 139.9 +/- 6.5 ka. Fault slip rates on range-bounding faults vary from 0.07 +/- 0.02 mm/yr to 0.37 +/- 0.04 mm/yr on thrust faults and 1.1 +/- 0.2 mm/yr to 1.5 +/- 0.2 mm/yr on strike-slip faults. Overall, the growth of the KZR surrounding the Kemin-Chilik fault is suggestive of a mega-flower structure with deformation distributed across a network of simultaneously active strike-slip and oblique-slip faults.
DE: 8002 Continental neotectonics (8107)
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8104 Continental margins: convergent
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: 2007 Fall Meeting