Magnetostratigraphic constraints on two‐stage eruptions of the Emeishan continental flood basalts

Abstract

[1] Temporal and spatial variations of high and low contents of Ti basalts in the Permian Emeishan large igneous province (ELIP) of southwest China and Vietnam are crucial for modeling of continental basalt formation and the nature of mantle-lithosphere interaction. A combined geochemical and magnetostratigraphic study was carried out at Yanyuan in the inner zone of the ELIP. Geochemical results indicate that the basalts are low-Ti (LT) basalts (Ti/Y ∼ 484.2-511.4) in the Luomapu section and high-Ti (HT) basalts (Ti/Y ∼ 558.2-658.9) in the Gongmushan section. Systematic paleomagnetic sampling and stepwise thermal demagnetization demonstrate that the higher temperature component shows two distinct characteristic remanent magnetizations with northeasterly upward and SWW downward directions. These results indicate a simple magnetostratigraphic normal and reversed polarity pattern from the lower and upper parts of the section, respectively. By comparing with available magnetostratigraphic and paleomagnetic data carried out in the ELIP, these results imply that the eruption of the Emeishan basalts can be divided into early (normal polarity subchron) and late (reversal subchron) stages. The early stage included LT basalts in the inner zone and most of the HT basalts in the intermediate and outer zones, and the late stage contained a part of LT and HT basalts in the upper parts of the sections in the inner zone and a few in the intermediate zone of the ELIP. Correlating with available Middle-Late Permian magnetostratigraphy and the Permian magnetic time scale, the new magnetic polarity sequence result suggests that the ELIP formed over a very short time interval (<1 Myr).

LA-ICPMS zircons U/Pb dating of Permo-Triassic and Cretaceous magmatisms in Northern Vietnam – Geodynamical implications

“…It can be considered as a product of the Permo-Triassic intra-plate magmatism of North Vietnam (Wang et al, 2007a;Hoa et al, 2008;Polyakov et al, 2009;Shelepaev et al, 2010). Nevertheless, the duration of the ELIP in the South China is strongly debated: some authors (Ali et al, 2002;Zheng et al, 2010;Shellnutt et al, in press) consider that this magmatic event is extremely short in time between 260 and 257 Ma while other authors Zhong et al, 2007Zhong et al, , 2009Shellnutt and Zhou, 2008) propose a longer duration around 10 Ma. Either this magmatism is continuous up to around 250 Ma or the magmatism post-257 Ma would be related to the collision between the Sibumasu and Indochina Blocks (Shellnutt et al, 2011) during the closure of the Paleotethys ocean (Late Permian/Early Triassic) (Lepvrier et al, 2004).…”

CA-TIMS zircon U–Pb dating of felsic ignimbrite from the Binchuan section: Implications for the termination age of Emeishan large igneous province

“…magnetostratigraphic data and field observations indicate that the whole volcanic sequence formed within 1-2 m.y. (Ali et al, 2002;Zheng et al, 2010).…”

Voluminous silicic eruptions during late Permian Emeishan igneous province and link to climate cooling

“…2). Accessory minerals include chlorite, magnetite and Emeishan province (He et al, 2007;Wignall et al, 2009;Zheng et al, 2010;Zhong et al, 176 2014). The zircons show two groups of chondrite-normalized rare earth element (REE) 177 patterns based on the presence or absence of light REE enrichment (La > 2 ppm) (Fig.…”