Contractional and extensional tectonics during the India-Asia collision

This work covers near- and far-field aspects of the India-Asia collision, from the geometry and kinematics of contraction across the Himalaya to the implications of active extension along the Shanxi rift of central China.; Himalayan geology is commonly described via a correlated structural and stratigraphic division. Three units, the Lesser Himalayan Sequence (LHS), the Greater Himalayan Crystalline complex (GHC), and the Tethyan Himalayan Sequence (THS), have a specific structural correlation with two faults, the Main Central thrust (MCT) and the South Tibet detachment (STD) in the central Himalaya. There the MCT places the GHC over the LHS and the STD places the THS over the GHC. This division fails to explain the geology of the western Himalaya where the MCT places the THS directly above the LHS. I investigated the region where the geometry changes with an integrated approach involving field mapping, thermobarometry, U-Pb zircon geochronology, major and trace element geochemistry, Th-Pb monazite geochronology, and 40Ar/ 39Ar thermochronology. This work shows that the change in structural geometry from the central to the western Himalaya results from southward merging of the MCT and STD. This finding, in conjunction with observed alternating shear senses on the STD, is inconsistent with previous Himalayan tectonic models, but is consistent with a tectonic-wedging model.; The Shanxi rift is one of many active east-west extending systems in East Asia. The other systems began extending in the Miocene-Early Pliocene. Synchronous initiation of all active East Asian rift systems would suggest a common dynamic cause for this extension. Low temperature thermochronology demonstrates that two phases of extension occurred in the studied region: (1) an early Cenozoic phase associated with extension to the east, and (2) the development of the Shanxi rift starting in the Late Miocene-Early Pliocene. Thus the start of extension along the Shanxi rift is coeval with the initiation of the other active east-west extensional systems, supporting the common dynamic cause hypothesis.