Deep Structure of the Northeast Tibetan Collision Zone: INDEPTH IV The Himalaya-Tibet Collision Zone

The Himalayan Mountain Belt and adjacent Tibetan Plateau (Figure 1) remain the world’s foremost natural laboratory for investigation of continental collisional tectonics. The continuing debate over how the Asian continent has responded to the embedding of the Indian subcontinent has variously revolved around concepts such as distributed shortening (e.g. Dewey and Burke, 1973), wholesale continental underthrusting (e.g. Argand, 1924; Powell and Conaghan, 1973; Ni and Barazangi, 1984), indentor tectonics (Tapponnier and Molnar, 1976), orogenic collapse (Tapponnier et al., 1986); delamination (e.g. England and Houseman, 1989); and ductile flow in the lower crust (e.g. Zhao and Morgan, 1985; Clark and Royden, 2000; Beaumont et al., 2001). Intrinsic to most, if not all, of these concepts is the degree of subduction of the Indian plate beneath the southern margin of Asia (see DeCelles et al., 2002, and Chemenda et al., 2000, for recent takes on this issue). Subduction of Asian continental crust beneath the Tibetan Plateau along its northern margin has received less attention, but is a common theme of several recent analyses (Willet and Beaumont, 1994; Tapponnier et al., 2001; Kind et al., 2002). It is this northern margin, and the large-scale geotectonic issues involved, which are the focus of the current proposal.