Age,Mechanism and Direction of Eash Qinling—Dabieshan Lithosphere Delamination——Petrological Evidence and Stipulation

Throughy studies of P-T-t paths and decompressive retrograde metamorphic textures of metamorphic rocks in the East Qinling-Dabieshan region,the authors determined the Mesozoic crust rapid uplifting age,and then inferred that in the East Qinling-Dabieshan region lithosphere delamination occurred from T3 to J1.The Yanshanian granites produced by delamination are developed well in the East Qinling-Dabieshan region.But due to the Gondwana plate effect,magmatism in the region caused by delamination lagged until J3 when the northern Tibet terrane and the Eurasian plate completely amalgamated.Additionally,due to western Pacific plate subducting underneath the Eurasian plate,in the East Qinling-Dabieshan region the stress state was transformed from compression to extension.So in the region from J3 to K2 magmatism was most intensive,and liberalization was also relatively strong.Geophysical data reflect that in the East Qinling-Dabieshan region the asthenosphere rose to the shallow level,the Moho is flat with no mountain root,and the crustal thickness is less than 40 km on average. These features agree with those of collisional orogenes in which delamination has occurred.Through contrastin differences in surface and interior depth between east and west Qinling we believe that elamination proceeded from east to west.

Age, mechanism and direction of East Qinling-Dabieshan lithosphere delamination — petrological evidence and stipulation

Through studies ofP-T-t paths and decompressive retrograde metamorphic textures of metamorphic rocks in the East Qinling-Dabieshan region, the authors determined the Mesozoic crust rapid uplifting age, and then inferred that in the East Qinling-Dabieshan region lithosphere delamination occurred from T₃ to J₁. The Yanshanian granites produced by delamination are developed well in the East Qinling-Dabieshan region. But due to the Gondwana plate effect, magmatism in the region caused by delamination lagged until J₃ when the northern Tibet terrane and the Eurasian plate completely amalgamated. Additionally, due to western Pacific plate subducting underneath the Eurasian plate, in the East Qinling-Dabieshan region the stress state was transformed from compression to extension. So in the region from J₃ to K₂ magmatism was most intensive, and liberalization was also relatively strong. Geophysical data reflect that in the East Qinling-Dabieshan region the asthenosphere rose to the shallow level, the Moho is flat with no mountain root, and the crustal thickness is less than 40 km on average. These features agree with those of collisional orogenes in which delamination has occurred. Through contrasting differences in surface and interior depth between east and west Qinling we believe that delamination proceeded from east to west.