FORMATION AND TECTONIC SIGNIFICANCE OF THE MAIN PHASE FOLIATION OF THE JIAYUQIAO SCHISTOSE FORMATION COMPLEX IN EASTERN TIBET

The Jiayuqiao schistose formation complex in eastern Tibet consists dominantly of quartz schist, albite schist and muscovite schist and the shear planes strike 320° and the corresponding Flinn parameter K is 2.13 on the average, implying that the main phase deformation is a compound of simple shear and contraction. The differential stress value estimated by quartz dislocation density is 149.5 MPa and the formation temperature of muscovite is 383.27 ℃. The ages of the main phase deformation determined by the 40 Ar/ 39 Ar method are （164.7±1.33） Ma （muscovite） to （166.27±0.99） Ma （hornblende）. The above mentioned data indicate that the main phase deformation was synchronous with the exhumation of the Jiayuqiao metamorphic complex and took place essentially at the same time as the Early Middle Jurassic oceanic crust spreading of the Bangong Co Nujiang suture zone.