Paleomagnetic Secular Variation Constraints on the Rapid Eruption of the Emeishan Continental Flood Basalts in Southwestern China and Northern Vietnam

Abstract

Estimating the duration of magma eruptions using isotopic dating methods is difficult because of the intrinsic errors of the technique regarding the dated materials (such as zircon). However, the long‐term variation of the geomagnetic field recorded by lava flows can be used to estimate the net duration of an eruption sequence. The Emeishan basalts at Dongchuan, with a thickness of 630 m, yielded a reliable characteristic remanent magnetization of normal polarity and which passed the fold test (Tauxe & Watson, 1994, https://doi.org/10.1016/0012-821X(94)90006-X). Stratigraphic and magnetostratigraphic correlations of the Emeishan basalts in the Dongchuan section with other sections indicate that the eruption of the Emeishan basalts at Dongchuan spans the entire normal polarity zone in the early stage of the Emeishan large igneous province. A flow‐by‐flow analysis of geomagnetic directions of the Emeishan basalts at Dongchuan indicates that four directional groups and fifteen individual lava directions were recorded, with a net duration (excluding quiescent intervals) of no more than 3100 years. The averaged site directions from the Emeishan basalts with normal polarity conforming to a geocentric axial dipole direction indicate that this interval is longer than 104–105 years. In addition, a magnetostratigraphic study indicates that the normal polarity interval recorded by the Emeishan basalts was shorter than 2–20 × 104 years. Thus, the total duration of the normal polarity stage of the Emeishan large igneous province was roughly 105 years. There is a possible relationship between the rapid eruption and the Late Capitanian mass extinction (259.8 ± 0.4 Ma, Henderson et al., 2012).

Paleomagnetic Evidence for Inverse Correspondence between the Relative Contribution of the Axial Dipole Field and CMB Heat Flux for the Past 270 Myr

“…As discussed by some authors (e.g., ref. 43,44 ), datasets that provide A95 > A95 max may contain additional scatter contributors, whereas A95 < A95 min could be considered as an indicator for an EMF spot-reading record. It was noticed that four of the select datasets (datasets # 2, 8, 10 and 15) provided A95 values that fall out of the A95 min /A95 max range, and hence were not considered for the paleomagnetic data processing and the subsequent Model G curve fitting for the IHMP.…”

The life cycle of large igneous provinces

“…As geochronologic precision surpasses ±0.05%, variations in time-averaged volcanic output within the main phase have emerged, although hiatus durations are controversial 146,149,150,153 . Variations in the intensity of volcanic activity also find support from palaeomagnetic records [154][155][156] and coeval records of sedimentary Hg (refs 5,157-159 ), which leverage the role of volcanoes as a dominant source of environmental Hg to reconstruct province-scale activity intensity from sedimentary records.…”

Pangea B and the Late Paleozoic Ice Age

“…1E). The reversal in trends coincides with: 1) the emplacement of the Emeishan flood basalt province at~260 Ma (Xu et al, 2018) virtually at the equator on the South China Block (Huang and Opdyke, 1998) and which remained within the equatorial humid belt for the rest of the Late Permian (Fig. 11); and 2) drift into the equatorial humid belt of the Cimmerian continental blocks that rifted off the northern margin of Gondwana in the Early Permian (Fig.…”