Rapid eruption of the Emeishan continental flood basalts: New paleomagnetic and geochronologic constraints

Author:

Xu Yingchao12,Zheng Liandi3,Yang Zhenyu4,Tong Ya-Bo5,Wang Bin6,Yuan Wei7,Jing Xianqing4

Affiliation:

1. College of Geography and Tourism, Huanggang Normal College, Huanggang 438000, China

2. Environmental Magnetism Laboratory, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China

3. SINOPEC Geophysical Research Institute, Nanjing 211103, China

4. College of Resources, Environment and Tourism, Capital Normal University, 105 Xi San Huan Bei Road, Haidian District, Beijing 100048, China

5. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China

6. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, Shanxi, China

7. State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China

Abstract

The duration of the eruption of the Emeishan large igneous province is hotly debated. We conducted a magnetostratigraphic and geochronological study of the core area of the large igneous province in the Binchuan area of Yunnan Province, southwestern China, in order to constrain the duration of the eruption. The results of detailed thermal demagnetization experiments revealed two remanent magnetic components from the volcanic rocks of 11 composite sections. A low-temperature component separated below 300 °C is interpreted as a recent viscous remanence. Additionally, reliable characteristic remanent magnetizations were revealed above 400 °C, with unblocking temperatures up to 580−680 °C, which passed the fold test and record three magnetozones. Zircons from the felsic ignimbrites exposed in the final stage of the mafic volcanism are dated to 258.2 ± 0.7 Ma (n = 15; mean square of weighted deviates = 1.3) by sensitive high-resolution ion microprobe. Stratigraphic and magnetostratigraphic correlations of the Emeishan basalts in the Binchuan sections indicate that the eruption of the mafic rocks of the Emeishan large igneous province can be clearly divided into early (reverse polarity subzone), middle (normal polarity subzone), and late (reverse polarity subzone) stages, with a total duration of less than 1.7 m.y. (260.8−259.1 Ma). However, by combining this chronology with previously reported conodont biostratigraphic results from locations around the Emeishan large igneous province, and comparing the dominant normal-reverse polarity sequence in the Emeishan large igneous province with the geomagnetic polarity time scale, we obtain a much shorter duration of the main eruptive stage of <0.8 m.y. (260.4−259.6 Ma). About three quarters of the basalts of the Emeishan large igneous province record have a normal polarity and erupted within 0.4 m.y., while the other quarter, mainly distributed in the central zone, shows a reverse polarity and much shorter duration. Given the short duration of the eruption, gas volatiles would have been released into the atmosphere at high rates, which might provide a causal link between the rapid eruption and the end-Guadalupian mass extinction. Before the mantle plume eruption, localized eruptions probably occurred. After eruption of the mafic Emeishan flood basalts, an acid volcanic eruption occurred in the early Wuchiapingian, which was sporadically distributed in the Emeishan large igneous province.

Publisher

Geological Society of America

Subject

Geology

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