Paleomagnetic Constraints of the Lower Triassic Strata in South Qinling Belt: Evidence for a Discrete Terrane Between the North and South China Blocks

Abstract

AbstractThe paleoposition of the South Qinling Belt is a crucial key to understanding the collisional process between the North and South China blocks. In order to identify the paleogeography of the South Qinling Belt during the Early Triassic and its correlation to the North and the South China blocks, combined paleomagnetic studies have been conducted on the Lower Triassic sedimentary rocks in the South Qinling Belt. After systematic thermal demagnetization, a high‐temperature characteristic remanence was isolated from 133 specimen embracing 22 sites with a mean direction of D = 330.5°, I = 27.7° (α95 = 2.5°). The positive fold and reversal tests suggest that the characteristic remanence was acquired during deposition. This characteristic remanence corresponds to a mean paleopole at φp = 7.2°E, λp = 62.5°N (A95 = 2.4°), indicating a paleolatitude of ~23.6°N for the South Qinling Belt. These new data are in concordance with the coeval paleomagnetic pole of the North China Block but are distinctly different from that of the South China Block with ~10.0° paleolatitude and ~73.6°declination differences. Together with the regional geology, our new data suggest that the South Qinling Belt had amalgamated with the North China Block along the Shangdan Suture by the Early Triassic times; however, it was still separated from the South China Block by the Mianlue Ocean up to the Early Triassic. The final collision between the North and South China blocks resulted from a ~73.6° clockwise rotation of the South China Block relative to the South Qinling Belt along the Mianlue Suture during the Late Triassic.