HR: 09:50h
AN: T31E-08    [Abstracts]
TI: Sedimentary Basin Evolution in the Context of Polyphase Intracontinental Deformation: New Insights From Southeastern Mongolia
AU: * Johnson, C L
EM: cjohnson@mines.utah.edu
AF: Dept of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Webb, L E
EM: lewebb@syr.edu
AF: Dept of Earth Sciences, Syracuse University, Syracuse, NY 13244
AU: Minjin, C
EM: minjin@must.edu.mn
AF: School of Geology, Mongolian University of Science and Technology, Ulaanbaatar, 210646 Mongolia
AU: Sersmaa, G
EM: sers@must.edu.mn
AF: School of Geology, Mongolian University of Science and Technology, Ulaanbaatar, 210646 Mongolia
AU: Affolter, M
EM: qfl247@netscape.net
AF: Dept of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112 United States
AU: Manchuk, N
EM: minjin@must.edu.mn
AF: School of Geology, Mongolian University of Science and Technology, Ulaanbaatar, 210646 Mongolia
AB: At least four major intracontinental deformation events have punctuated the geologic evolution of SE Mongolia since Late Paleozoic time. Much of the structural deformation was concentrated along the northeast-trending East Gobi Fault Zone (EGFZ), which we have studied in multiple localities along its 250 km (minimum) length. Our structural and geochronologic studies, described in more detail in a companion abstract by Webb et al. (2004), define a general tectonic framework of Late Triassic sinistral shear, Late Jurassic-Early Cretaceous extension, mid-Cretaceous transpression and basin inversion, and Cenozoic compression and strike-slip faulting. Perhaps the best-known phase of basin development in this area is Late Jurassic-Early Cretaceous rifting which formed multiple NE-SW-trending grabens, as well as a metamorphic core complex. This rifting event, in which most structures of the EGFZ were active as a series of high angle normal faults, postdates motion on a Late Triassic sinistral shear zone. As a result of Early Mesozoic sinistral shear, Paleozoic basins may have been dismembered and offset by some 100s of km prior to late Mesozoic rifting. Similarly, we have new evidence for mid-Cretaceous and Cenozoic transpression along the EGFZ following the rifting event. Postrift reactivation of the EGFZ may have coincided with Cenozoic activity along the Altyn Tagh fault zone, and suggests that motion along these faults may have been linked for at least part of their histories. Multi-phase reactivation of the EGFZ has important implications for evolution of sedimentary basins that formed along it, as well as for other regions subject to intracontinental deformation. Such implications include the importance of inherited shear zones, particularly in areas where basement is extremely heterogeneous, as a controlling factor in the development of polyphase sedimentary basins. This work also emphasizes the need for careful analysis of offset piercing points in order to accommodate accurate paleogeographic reconstructions of the basin.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting