Volcanism of the Nanpu Sag in the Bohai Bay Basin, Eastern China: Geochemistry, petrogenesis, and implications for tectonic setting
Volcanism of the Nanpu Sag in the Bohai Bay Basin, Eastern China: Geochemistry, petrogenesis, and implications for tectonic setting
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中国东部渤海湾盆地南堡凹陷火山活动：地球化学、岩石成因及其对构造环境的影响
DOI：
10.1016/j.jseaes.2010.03.003
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发表时间：
2010-08-10
影响因子：
3
通讯作者：
Huang, Hongxiang
中科院分区：
文献类型：
--
作者：
Dong, Yuexia;Xiao, Long;Huang, Hongxiang
最近发现的南堡大油田位于中国东部渤海湾盆地西北部。广泛的钻探和地球物理研究揭示了始新世至中新世基性火山岩的广泛存在。根据地层的限制，三个火山作用周期已被确认。岩石学和地球化学研究表明，这些镁铁质岩石大多数是碱性玄武岩。一些玄武岩经历了分离结晶，主要是单斜辉石和FeTi氧化物。所有样品的微量元素模式与洋岛玄武岩（OIB）相似。Sr和Nd同位素分析表明，Sr-87/Sr-86（i）值在0.703577 ~ 0.708160之间，Sr-87/Sr-86（t）值在0.7 ~ 6.8之间。Pb同位素分析得出Pb-206/Pb-204比值为17.43 ~ 19.19，Pb-207/Pb-204比值为15.43 ~ 15.67，Pb-208/Pb-204比值为37.35 ~ 38.64。微量元素和同位素特征表明南堡凹陷玄武岩类似于洋岛玄武岩，可能有陆下岩石圈地幔的贡献，考虑到渤海湾盆地广泛存在同时代的玄武质火山活动，具有可比的地球化学特征，我们采用软流圈地幔幕式上涌熔融的成因模式。古老的陆下岩石圈地幔与新的软流圈幔源熔体发生了相互作用。华北地区古老的软流圈地幔向新的、肥沃的软流圈地幔的置换仍在进行中。早期岩浆来自地幔深部，部分熔融程度高于晚期岩浆。熔融柱的向上迁移支持了伸展体制下活动的软流圈地幔上涌或地幔柱引起的岩浆活动。(C)2010爱思唯尔有限公司版权所有。
The recently discovered large Nanpu Oilfield is located in the NW part of the Bohai Bay Basin, eastern China. Extensive drilling and geophysical research have revealed widespread occurrence of Eocene to Miocene mafic volcanic rocks. On the basis of stratigraphic constraints, three cycles of volcanism have been recognised. Petrological and geochemical studies of drill core samples indicate that most of these mafic rocks are alkaline basalts. Some basalts experienced fractional crystallization, dominated by clinopyroxene and FeTi oxides. All samples have trace elements patterns similar to oceanic island basalts (OIB). Sr and Nd isotopic analyses show that Sr-87/Sr-86(i) values range from 0.703577 to 0.708160 and epsilon Nd(t) varies from 0.7 to 6.8. Pb isotope analyses yield Pb ratios ranging from 17.43 to 19.19 for Pb-206/Pb-204, from 15.43 to 15.67 for Pb-207/Pb-204 and from 37.35 to 38.64 for Pb-208/Pb-204. The trace element and isotopic characteristics indicate that the Nanpu Sag basalts are similar to oceanic island basalts possibly with some contributions of subcontinental lithospheric mantle.Considering that there is widespread and coeval basaltic volcanism in the Bohai Bay Basin, which has comparable geochemistry, we adopt a model of episodic upwelling and melting of asthenospheric mantle for the origin of these basalts. The old subcontinental lithospheric mantle had interacted with new asthenospheric mantle-derived melts. The replacement of old North China Craton mantle to new and fertile asthenospheric mantle is still ongoing. Early-stage magmas were generated from deeper in the mantle with a higher degree of partial melting than late stage magma. The upward migration of the melting column supported active asthenosphere mantle upwelling or mantle plume induced magmatism under an extensional regime. (C) 2010 Elsevier Ltd. All rights reserved.