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 °C). The ChRMs (301/323) at SM section are northeasterly upward of normal polarity, with a mean direction of Ds/Is = 11.0/−5.2° (N = 12, k = 53.7, α95 = 6.0°). At DD section, the ChRMs are southwesterly downward of reversed polarity, with a mean direction of 205.9/10.0° (N = 5, k = 78.4, α95 = 8.7°). 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.

► We present new paleomagnetic results from the SM and DD basaltic sections.
► Rock magnetic analysis shows low-Ti magnetite as dominant magnetic carriers.
► A normal to reversed polarity sequence is determined.
► The polarity sequence suggests a short eruption of Emeishan basalts.