Kinematic model of active deformation in central Asia

Abstract

Abstract. The velocity field of present-day deformation in Central Asia is modelled using a set of four rotating blocks (Siberia, Tarim, Tibet, India) on a spherical earth. A best-fit is inverted on the basis of estimated shorteningrates across the main thrust zones (Himalayas, Tien Shan) and measured slip-rates along the principal strike-slip faults (Altyn Tagh and Karakorum) separating those blocks. The fit to the data implies that nearly all the present convergence between India and Asia can be accounted for by slip-partitioning on these four zones, with as much as 50% absorl:>ed by northeastwards extrusion of Tibet. This suggests that localised deformation governs the present mechanical bepaviour of the Central Asian lithosphere.

Crustal–lithospheric structure and continental extrusion of Tibet

“…Thatcher (2007) produced a similar 11-microplate model for Tibet based upon 349 GPS measurements, and similarly proposed low slip rates of 5-12 mm a À1 for Tibet's major strike-slip faults, in contrast to the large slip rates from earlier studies consisting of larger blocks (e.g. Peltzer & Tapponnier 1988;Avouac & Tapponnier 1993). However, Thatcher (2007) acknowledged systematic misfits that point to internal deformation of the blocks, which he suggested could be smaller blocks within the larger blocks.…”

“…These 'plates', 'microplates' or 'blocks' are bounded by crustal-scale strike-slip faults that extend down to the mantle (Molnar & Tapponnier 1975;Tapponnier & Molnar 1976Tapponnier et al 1982;Avouac & Tapponnier 1993). Tapponnier & Molnar (1976) proposed that the great strike-slip faults correspond to AE and â slip lines radiating out to the NW and NE away from the rigid Indian indenter.…”

“…(c) Plasticine experiments showing plane strain indentation of a rigid Indian indenter into a layered plasticine block with a free boundary on the eastern side, after Tapponnier et al (1982) and Peltzer & Tapponnier (1988). Avouac & Tapponnier (1993) compiled estimated slip rates for all the major faults of Tibet and concluded that the bounding faults all had fast slip rates and large amounts of offsets with as much as 50% of the total convergence absorbed by eastward extrusion of Tibet. However, many of these slip rates rely on poorly dated offset Quaternary features that were assumed to have formed during the last glacial maximum, an assumption that we now know to be incorrect (Brown et al 2005).…”

“…Twentyfour sites were examined using SPOT images, with offsets varying from 50 to 350 m. These offsets, coupled with an assumed postglacial age of formation, allowed Liu (1993) and Avouac & Tapponnier (1993) to infer a rapid slip rate of 32 AE 8 mm a À1 . Despite an accepted offset determination, if their assumed postglacial age were incorrect, then a significant cornerstone of the extrusion hypothesis would be untenable.…”

“…This model has been vigorously promoted by many researchers working both in Tibet (e.g. Tapponnier et al 1982Tapponnier et al , 2001bPeltzer & Tapponnier 1988;Armijo et al 1989;Avouac & Tapponnier 1993) and in SE Asia (Leloup et al , 1995(Leloup et al , 2001Lacassin et al 2004a). …”