HR: 1340h
AN: V23C-1558    [Abstracts]
TI: Constraints on Mesozoic and Tertiary Brittle Faulting in the Southern East Gobi Fault Zone, Southeastern Mongolia
AU: * Taylor, J P
EM: jtaylo03@syr.edu
AF: Syracuse University, Dept. of Earth Sciences, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Webb, L E
AF: Syracuse University, Dept. of Earth Sciences, 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Johnson, C L
AF: University of Utah, Dept. of Geology and Geophysics, 135 S. 1460 E, Room 719, Salt Lake City, UT 84112, United States
AU: Heumann, M J
AF: University of Utah, Dept. of Geology and Geophysics, 135 S. 1460 E, Room 719, Salt Lake City, UT 84112, United States
AB: The East Gobi Fault Zone (EGFZ) is a NE trending structural corridor in southeastern Mongolia. Following the Paleozoic amalgamation of Central Asia from numerous arc terranes and microcontinents, the EGFZ records a protracted history of Mesozoic-Cenozoic intracontinental deformation and basin development. Several workers have proposed a common Mesozoic and/or Cenozoic strike-slip history for the EGFZ and the Altyn Tagh fault; however this correlation has remained largely untested due to a lack of field-based studies in southeastern Mongolia. This study presents the preliminary results of ongoing work that examines the structural history of the EGFZ. Analysis of fault-slip data collected during field studies in the southern EGFZ identified multiple generations of brittle faults. Faults were broken down into subsets on the basis of crosscutting/overprinting and kinematic relationships. Subsets I and II were the oldest identified but presently their relative timing is unknown. Both subsets crosscut Upper Permian to Lower Triassic(?) strata. Faults in subset I are locally crosscut/overprinted by normal faults inferred to have originated during previously documented Late Jurassic-Early Cretaceous NW-SE extension. (1) Subset I mainly consists of NE-ENE striking sinistral faults and NW-WNW striking dextral faults. Inversion of this subset suggests it was produced during regional N-S directed shortening and E-W directed extension. (2) Subset II contains SSW dipping thrust faults with a top-to-the-NE sense of shear, consistent with regional NE-SW directed shortening. (3) Subset III consists of NE striking dextral faults, NW striking sinistral faults, and E or W dipping thrust faults. Faults within this subset were observed crosscutting Lower Cretaceous strata and overprinting normal faults inferred to be related to Late Jurassic-Early Cretaceous extension. Inversion of this subset indicates that it is associated with E-W directed shortening. (4) Subset IV consists of N-NE striking sinistral faults and W-NW striking dextral faults. Faults within this subset were observed crosscutting Lower Cretaceous strata. Inversion of this subset indicates formation during regional N-S directed shortening and E-W directed extension. Subset I confirms the presence of Mesozoic NE-striking sinistral faults in the southern EGFZ. Future work will explore any links between this subset and early Mesozoic sinistral shear documented in the northern EGFZ. The timing, orientation, and shear-sense of the faults within subset II are similar to pre-extensional fabrics observed nearby at the Yagan-Onch Hayrhan metamorphic core complex, suggesting this deformation may be related to the emplacement of large carbonate klippe in the region. Future work will investigate any correlations between this phase of deformation and Middle-Late Jurassic thrusting documented in the Noyon Uul and Beishan regions. Subset III is interpreted as the southern continuation of deformation associated with middle-Late Cretaceous transpression in the EGFZ. Subset IV represents the continuation of the Tertiary NE-striking sinistral faults previously documented in the northern EGFZ. This extends the trace of Tertiary sinistral faulting in the EGFZ to the southern border of Mongolia, in close proximity to the Alxa fault zone.
DE: 8010 Fractures and faults
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8110 Continental tectonics: general (0905)
DE: 9320 Asia
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting