Basin analysis and apatite fission-track thermochronology of the Jurassic-Paleogene southwest Tarim Basin, NW China.

摘要

The evolution of the southwest Tarim basin in northwest China reflects a continuum of orogenic activity from the Jurassic through the Cenozoic, although the stratigraphic record is punctuated with discrete events chronologically-linked with accretionary tectonism to the south. This record is documented by basin analysis, synthesizing original stratigraphic, facies, paleocurrent, and petrographic observations from the outcrop belts with data, primarily on marine paleontology and subsurface geometry, taken from the literature. The basin evolved from Early-Middle Jurassic transtension through Late Jurassic-Early Cretaceous transpression and Paleogene compression to the present Neogene system of partitioned deformation, with both transpression and compression. Jurassic coarse clastic sedimentation was associated with transtension on north-northwest trending right-lateral strike-slip faults. These faults are located on the western margin of the Jurassic pull-apart basin, along the Kunlun Shan and on the eastern side of the basin, in the Tian Shan. The former is active today as the Karakorum fau the latter as the Talas-Ferghana fault. The location of the eastern margin of the Neogene Pamir Plateau is determined by the pre-Neogene structures.;Around the margins of the western Tarim basin, major basin-vergent thrusting has uplifted and exhumed Jurassic to Neogene sedimentary sections; this presumably reflects the propagation of Himalayan compression into the area. Apatite fission-track thermochronologic data were collected from sections. Most sections yield strongly but not completely annealed sample ages which may be interpreted using radial plots of single grain fission-track ages. Overall, the fission-track record is dominated by Late Oligocene to Middle Miocene exhumation and cooling.;Sandstone petrographic studies of these Jurassic through Paleogene sections show little variation in modal compositions either within a stratigraphic section or between sections. Compositions are similar to Mesozoic sandstones from north Tarim (Hendrix, 1992) and modern sands from both north and southwest Tarim (Graham et al., 1993). This consistency suggests that the pre-Mesozoic tectonic inheritance of the margins of the Tarim basin controls the composition of the Mesozoic through modern sandstones, rather than specific tectonic events which occurred synchronous with depositional.;