Abstract:

Up to now, no paleomagnetic data has been reported on the Bayankala folded belt, which is an upside-down triangle area located among the Yangze, North China, Tarim, and Qiangtang-Changdu blocks. The paleomagnetic study on Songpan-Aba continental block is to provide with quantitative data for its localization during geological history and to be a basis for oil and gas resources evaluation. The sampling spots are around the four micro-blocks such as the southern structural belt(Motianling area and Ruo'ergai area), and the central structural belt(Taohe area) of west Qinling structural zone , the Markang composite syncline belt of the Bayankala structural zone(Bayankala folded zone). The sampling is centered around the Triassic rocks. There are 57 sampling spots and 376 core samples in all. By the analysis and calculation of the measured data of the core samples, the paleomagnetic pole location for the Taohe, Bayankala, Motianling, and Ruo'ergai blocks(with the later two blocks located between the former two blocks)has been acquired. These micro-blocks are located at north latitude 49.5° to 58.5° and east longitude 191.4° to 202.9°. The paleo-latitude of the Taohe and the Bayankala micro-blocks in Late Triassic is the same as north 26.2°, which indicates that the four micro-blocks separated by the faults had combined to be a larger block in Late Triassic. The variation in the paleo-latitude during Triassic for the Taohe and the Bayankala micro-blocks shows the north 13.4° and north 11.3° of the two blocks respectively in Early Triassic have changed to the same north 26.2° in Late Triassic. Meanwhile, the two blocks have anticlockwise rotated approximately 40° and 16° respectively from Early Triassic to Late Triassic with their northward movement.

Key words: paleomagnetism, plate kinematics, Triassic, Songpan-Aba continental block, Bayankala folded belt