Paleomagnetic Reconstruction of the Early Triassic Paleogeographic Position of the South Yellow Sea and Its Geological Significance

Most studies on the Early Triassic paleomagnetism of the Yangtze Block (YB) have concentrated on the Western to Middle parts, but the South Yellow Sea (SYS) in the Eastern YB (EYB) is relatively lacking. To ascertain the paleogeographic position of the SYS, we isolated the characteristic remanent magnetization (ChRM) direction from 46 standard core samples and characterized the magnetic mineral compositions of 70 fragmentary samples. These samples were all derived from continuous full-core drilling in the Lower Triassic Qinglong Formation within the CSDP-2 Well. We also reconstruct the paleomagnetic directions by utilizing published Early Triassic paleomagnetic pole data individually from the YB and North China Block (NCB). The experimental results show that the CSDP-2 Well was at 15.9° N (+2.9°/−3.2°) in the Early Triassic after paleomagnetic inclination correction. Taking the CSDP–2 Well as the reference point, published data indicated that the YB was at 19.4° N ± 1.2° and the NCB was at 13.7° N ± 2.7° in the Early Triassic. On the basis of previous knowledge and the paleomagnetic data, we think that the YB and NCB collided before the Triassic and further confirm the reliability of the scissor-like collisional model which was initially in the East and later in the West. In addition, we consider that the crust of the EYB may have moved northward 389.2 ± 166.8 km since the Early Triassic. These results have implications for reconstructing paleogeographic position of the SYS and some details of collisional process between two blocks.