Rapid eruption of the Emeishan continental flood basalts: New paleomagnetic and geochronologic constraints
Rapid eruption of the Emeishan continental flood basalts: New paleomagnetic and geochronologic constraints
复制标题
峨眉山大陆溢流玄武岩的快速喷发：新的古地磁和地质年代学约束
DOI：
10.1130/b36132.1
复制
发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Xianqing Jing
中科院分区：
文献类型：
--
作者：
Yingchao Xu;Li;i Zheng;Zhenyu Yang;Ya-Bo Tong;Bin Wang;Wei Yuan;Xianqing Jing
峨眉山大火成岩省喷发的持续时间一直是人们争论的焦点。本文对云南宾川地区大火成岩省的核心区进行了磁性地层学和年代学研究，以确定火山喷发的持续时间。详细的热退磁实验结果显示，11个复合剖面的火山岩中存在两种剩磁分量。低于300 °C分离的低温组分被解释为最近的粘滞剩磁。此外，在400 °C以上的温度下，还发现了可靠的特征剩磁，解除阻塞温度高达580−680 °C，通过了折叠测试，并记录了三个磁区。用高分辨离子探针对基性火山作用末期出露的长英质熔结凝灰岩进行了锆石年龄测定，结果为258.2 ± 0.7Ma（n = 15;加权偏差均方= 1.3）。通过对峨眉山宾川剖面玄武岩的地层学和磁性地层学对比，认为峨眉山大火成岩省基性岩的喷发可明显分为早（反极性亚带）、中（正极性亚带）和晚（反极性亚带）三个阶段，总持续时间小于170万年。（260.8 - 259.1 Ma）。然而，将该年代学与峨眉山大火成岩省周围地区牙形石生物地层学研究结果相结合，并将峨眉山大火成岩省的正-反极性优势序列与地磁极性时间尺度相比较，我们得到的主喷发阶段持续时间短得多，小于0.8百万年。（260.4 - 259.6 Ma）。峨眉山大火成岩省记录中大约四分之三的玄武岩具有正常极性，并在0.4百万年内爆发，而另一个季度主要分布在中心地带，极性相反，持续时间短得多。由于喷发持续时间短，气体挥发物会以高速率释放到大气中，这可能提供了快速喷发和瓜达卢佩末期大灭绝之间的因果关系。在地幔柱喷发之前，可能发生了局部喷发。峨眉山基性岩溢流玄武岩喷发后，在吴家坪早期发生了一次酸性火山喷发，零星分布于峨眉山大火成岩省。
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.