HR: 09:05h
AN: T31E-05    [Abstracts]
TI: Tertiary Deformation in the Kashgar Basin, Southern Margin of the Tian Shan, China
AU: * Heermance, R V
EM: richard@crustal.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, 1006 Webb Hall, Santa Barbara, CA 93106 United States
AU: Chen, J
EM: chenjie@eq-igl.ac.cn
AF: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Seismological Bureau, P.O. Box 9803, Beijing, 100029 China
AU: Scharer, K
EM: kscharer@darkwing.uoregon.edu
AF: Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403 United States
AU: Burbank, D
EM: burbank@crustal.ucsb.edu
AF: University of California, Santa Barbara, Department of Geological Sciences, 1006 Webb Hall, Santa Barbara, CA 93106 United States
AB: The northwest corner of the Tarim Platform, near the town of Kashgar, China, is an actively deforming fold-and-thrust belt related to uplift of the Tian Shan. Mapping of 5000 km$^{2}$ in the area north of Kashgar city and west of the Kepintage thrust zone indicates at least 15 km of shortening has occurred since the Miocene. Shortening is accomodated along 5 major structures that extend $>$60 km ~east-west along strike. These structures, from north to south, are the basin-bounding Tuotergongbaizi fault(TF), the Kepintage-Yishilakekalawuer fault (KYTF), the Keketamu syncline-anticline pair (KEK), the Atushi-Talanghe (AT) anticline, and the Kashi (K) anticline. Smaller-displacement imbricate faults and small-wavelength folds occur throughout the region associated with these major structures. Scharer et al (in press) document 7 km of shortening in the AT and K anticlines. Our new values add at least 8 km of shortening accomodated in the TF, KYTF, and KEK structures for a total of $>$15 km in the region. Uplifted and deformed fluvial terraces are observed along the AT, K, and KYTF, indicating that deformation is active and occurring throughout the fold-and thrust belt, not only in the southern foreland. In the north the TF and KYTF are south-vergent faults that juxtapose Paleozoic basement with Tertiary sediments. The KEK anticline is a south vergent fault-propagation-fold, but the AT and K are detachment structures that display both north and south vergence. Detachment horizons are likely gypsum-rich Miocene layers near the base of the ($>$5 km thick) Tertiary section. The TF cuts poorly sorted, debris-flow facies conglomerate in its footwall. The conglomerate changes facies southward, toward the foreland, to well-sorted fluvial deposits. New magnetostratigraphy reveals the the basal age of the conglomerate becomes younger towards the south, from $\sim$5.2 Ma 10 km south of the fault, to $<$2 Ma 20 km south of the fault. These observations imply significant erosional topography along the TF prior to 5.2 Ma, and progradation of a conglomerate wedge into the basin. Our shortening estimates for this area since the latest Miocene imply minimum long-term shortening rates of $\sim$3mm/year, or less than half of the present-day shortening rates (7-10 mm/year) determined by GPS measurements across the region.
DE: 8102 Continental contractional orogenic belts
DE: 1208 Crustal movements--intraplate (8110)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting