New paleomagnetic investigations of the Emeishan basalts in NE Yunnan, southwestern China: Constraints on eruption history

Paleomagnetic and magnetostratigraphic investigations have been conducted on two consecutive sections of the Emeishan trap at Shuimo (SM) and Dadi (DD) in northeastern Yunnan province, southwestern China. Rock magnetic analysis indicates that the magnetic carrier of the basalts is dominantly low-Ti magnetite. Stepwise thermal demagnetization isolates a stable characteristic remanent magnetization (ChRM) at high temperatures (400-585 degrees C). The ChRMs (301/323) at SM section are northeasterly upward of normal polarity, with a mean direction of D-s/l(s) = 11.0/-5.2 degrees (N = 12, k = 53.7, alpha(95) = 6.0 degrees). At DD section, the ChRMs are southwesterly downward of reversed polarity, with a mean direction of 205.9/10.0 degrees (N = 5, k= 78.4, alpha(95) = 8.7 degrees). The ChRMs from the basaltic gravels from the overlying conglomerate layer in late Permian Xuanwei Formation at DD section pass the conglomerate test, suggesting the primary nature of magnetization. Together with other magnetostratigraphic studies (e.g., N-R pattern) of the Emeishan basalts and the known radiometric ages (ca 260 Ma), it suggests that the eruption period of the Emeishan large igneous province is less than 3 Myr. (C) 2012 Elsevier Ltd. All rights reserved.