New Paleomagnetic results from the Beiya porphyry-skarn gold–polymetallic deposit at the Western Dali faulted-block: Implications for the Cenozoic tectonic rotation of the Chuan-Dian Fragment, Southeastern Tibetan Plateau

摘要

The Chuan-Dian Fragment (CDF), in the southeastern Tibetan Plateau, is crucially important for understanding the intra–continental deformation behavior of the blocks between the stable Yangtze craton and the Indian Plate after the Indian-Asian collision. The Beiya porphyry-skarn gold–polymetallic deposit at the northwestern part of the fragment may provide an important paleomagnetic result for understanding the deformation behavior of the CDF. The paleomagnetic study of mineralized and intrusive rocks from the ~35?Ma Beiya deposit reveals a high temperature component with site–mean direction of D?=?337.6°,I?=?32.6°,k?=?74.8, with α95?=?4.4°. Our results show that the Beiya deposit experienced 21.5°?±?3.1° of anticlockwise rotation relative to the stable part of the South China Block since ~35?Ma. The stable part of the Dali faulted-block is deduced to have experienced ~20° clockwise rotation based on a comparison of the fold-axis strike of Triassic strata between the Beiya deposit and surrounding stable area. A best-fit linear regression of the fold-axis strike direction and the tectonic rotation at each sampling site reveals that differential tectonic rotation occurred, accompanied by the horizontal deflection of strata within the CDF.