Continental crust subduction and collision along Shangdan Tectonic Belt of East Qinling, China——Evidence from Pb, Nd and Sr isotopes of granitoids

Abstract

The East Qinling orogenic belt can be divided into North and South Qinling erogenic belts by the Shangdan fault. The granitoids, especially the late Paleozoic - early Mesozoic granitoids, are widely distributed in North Qinling and South Qinling orogenic belts. Pb, Nd and Sr isotopic compositions and some trace element ratios for the collision-type granitoids were measured. The data are used to evaluate the granitic magma source and to probe the chemical composition of deep crust where the granitic intrusions were emplaced. The studies indicate that the South Qinling collision-type granitoids came from the South Qinling middle-lower crust and the North Qinling collision-type granitic batholiths were also derived from the South Qinling middle-lower crust rather than from the North Qinling block itself. These results provide direct evidence for the South Qinling continental crust underplating beneath the North Qinling block in the continent-continent interaction stage of the East Qinling orogenic belt.