Calcite U-Pb Geochronology and Paleomagnetism Reveal Mesozoic Multi-Episodic Remagnetizations From the Penglaitan GSSP Section, South China

Abstract

Carbonate rocks are widely used for paleomagnetic reconstructions of continental block rifting and geodynamic evolution. However, the detection of remagnetization in carbonate rocks is challenging. Uncertainty of remagnetization timing hinders our ability to understand the geomagnetic behavior during critical Phanerozoic transitions, such as the period across the Middle-Permian Guadalupian to Late-Permian Lopingian boundary (GLB). To test whether primary magnetization is preserved, we conducted paleomagnetic, calcite U-Pb geochronological and mineralogical studies at the Penglaitan section in southern China. The rock-magnetic results indicate that magnetite, maghemite and rare hematite are dominant remanence carriers. Calcite U-Pb ages of approximately 126 Ma, 223 Ma and 251 Ma, respectively, are consistent with the timing of three remanent magnetizations (RM1, RM2, RM3). This indicates that calcite U-Pb dating can provide robust support to constrain the age magnetizations. The consistency indicates that RM3 was acquired during the limestone deposition, whereas component RM1 and RM2 were due to early Cretaceous and late-Triassic remagnetization, respectively. In addition, the primary component RM3 was isolated from tuffaceous limestone and yielded a mean direction of D_s/I_s = 195.3°/+5.6° (α_95s = 5.3°, k_s = 22.8, n = 34) after tilt-correction. It defined a reversed magnetozone from the top of conodont Jinogondolella granti Zone to the lower part of the Clarkina dukouensis Zone, straddling the GLB. The calcite U-Pb dating and paleomagnetic results provide new insights into Mesozoic multi-remagnetization in the South China Block and refine the GLB positioned in a reversed magnetozone.