TECTONIC EVOLUTION OF THE WESTERN KUNLUN AND KARAKORAM MOUNTAINS—SOME NEW OBSERVATIONS FROM A MULTI-DISCIPLINARY GEOSCIENTIFIC TRANSECT (MGT) IN NW TIBET

New results from deep seismic sounding reveal that the Tarim block (basin) was subducted, with gently dipping, to the W.Kunlun Mts. The depths of Moho from north to south are 50km in S.Tarim to 65km in the W. Kunlun Mts. A low velocity and low resistivity layer occurs at the depth of 15～30km, which may be the decollement in the upper crust. A “delamination Crack" might have been formed in the lower crust\|mantle lid, causing the intrusion of alkaline magma along the southern margin of the W. Kunlun Mts. A detailed research for forming and evolving of the Kudi ophiolite in the central part of the W. Kunlun Mts.,which has been given the age of 700～450Ma by using the Re\|Os isotopic dating, and the Radiolarits in chert intercalated with pillow lava are determined to be the late Ordovician to Silurian. Until now we did not find any complete ophiolite suite except Kudi ophiolite. So we suggest that there was no “vast protero\|ocean", and a “limited oceanic basin" exists only during the late Proterozoic to Early Paleozoic, which might have been subducted in Silurian\|Devonian and formed the oldest suture in the north of the Tibet plateau.A suture zone consisting of H. P/T metamorphic blueschist, ophiolitic melange and olistostrome in the north\|western Tibet has been revealed recently, which may extend to NW. connecting with MKT in N. Pakistan.A study of the Fission track thermochronology indicates that the W.Kunlun Mts. has been undergone a pulsatory uplift since 20～18Ma,and a rapid uplift after 3Ma.A model of collision between the Indo\|Pakistan subcontinent\|N.Tibet and the Eurasian blocks of Tarim has been illustrated.