Provenance of Late Permian volcanic ash beds in South China: Implications for the age of Emeishan volcanism and its linkage to climate cooling
Provenance of Late Permian volcanic ash beds in South China: Implications for the age of Emeishan volcanism and its linkage to climate cooling
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DOI：
10.1016/j.lithos.2018.06.009
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发表时间：
2018-08
期刊：
影响因子：
3.5
通讯作者：
Hu Huang;Peter A. Cawood;Mingcai Hou;S. Ni;Jianghai Yang;Yuansheng Du;Huaguo Wen
中科院分区：
文献类型：
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作者：
Hu Huang;Peter A. Cawood;Mingcai Hou;S. Ni;Jianghai Yang;Yuansheng Du;Huaguo Wen
上思县上二叠统火山灰的全岩地球化学、锆石微量元素、单键铅和Hf同位素资料表明，火山灰的物源从峨眉山大火成岩省(LIP)向汇聚的板块边缘岩浆弧转变。下部地层样品表现出高的Al_2O_3/TiO_2比值，强烈的Eu负异常，高场强元素没有亏损。这些火山灰中的锆石年龄约为260 Ma，与宾川峨眉山火山序列最上部的板内型岩浆和长英质火成岩具有地球化学亲和力。这些特征，再加上锆石中相对较高的εHf(T)值和较低的Th/Nb比值，暗示了与峨眉山唇有关的晚期长英质火山成因。上四的上层地层样品中Nb和Ti明显亏损，从火山灰中分离出的锆石在化学上与弧相关/造山岩中的锆石相似，表明为岩浆弧源。结合已公布的这些火山灰层的高精度CA-TIMS数据，峨眉山火山活动可以被限制在大约260-257.8 Ma之间。峨眉山火山活动的时代与乌家坪纪气候降温事件相一致，支持这两种现象之间的潜在联系。
Whole-rock geochemistry and zircon trace element, Usingle bondPb and Hf isotopic data for Upper Permian volcanic ash at Shangsi show a significant change in source from the Emeishan Large Igneous Province (LIP) to a convergent plate margin magmatic arc. The lower stratigraphic samples display high Al2O3/TiO2ratios, strong negative Eu anomalies, and no depletion in high field strength elements. Zircons with ages of ca. 260 Ma from these ashes have a geochemical affinity to within-plate-type magmas and with felsic ignimbrites from the uppermost part of the Emeishan volcanic succession at Binchuan. These features, combined with relatively high εHf(t) values and low Th/Nb ratios in the zircons, imply a late-stage felsic volcanic origin related to Emeishan LIP. The upper stratigraphic samples at Shangsi display significant depletion in Nb and Ti; zircons separated from these volcanic ashes are chemically similar to those from arc-related/orogenic rocks, indicative of a magmatic arc source. Combined with published high-precision CA-TIMS data for these volcanic ash layers, the Emeishan volcanism can be constrained to between ca. 260–257.8 Ma. The age of Emeishan volcanism is consistent with the Wuchiapingian climate cooling event, supporting a potential linkage between these two phenomena.