Mantle origin of the Emeishan large igneous province (South China) from the analysis of residual gravity anomalies
Mantle origin of the Emeishan large igneous province (South China) from the analysis of residual gravity anomalies
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DOI：
10.1016/j.lithos.2014.02.008
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发表时间：
2014-09
期刊：
影响因子：
3.5
通讯作者：
Yangfan Deng;Zhongjie Zhang;W. Mooney;J. Badal;W. Fan;Q. Zhong
中科院分区：
文献类型：
--
作者：
Yangfan Deng;Zhongjie Zhang;W. Mooney;J. Badal;W. Fan;Q. Zhong
尽管对峨眉山大火成岩省进行了大量的地质和地球化学研究，但该大火成岩省的深部成因仍然缺乏约束。本文结合华南地区近几十年来的深地震测深剖面、深地震反射剖面和各种宽频带地震观测资料，研究了华南地区的剩余重力异常及其与峨眉山大地震的关系。我们的分析包括消除相关的重力效应，由于：（1）沉积物，（2）结晶基底，（3）上地壳的起伏，（4）莫霍面和（5）地幔盖。由此产生的剩余重力异常在峨眉山LIP和周围地区达到最大值的+ 150 mGal，并逐渐减少，从这个内部带的距离。利用共轭梯度法建立了一个由圆柱形正密度异常组成的岩石圈模型，该模型能很好地拟合观测到的剩余重力异常。峨眉山LIP的反演密度异常在内带为+ 0.06 g/cm 3，在外带为+ 0.03 g/cm 3左右。观测到的正剩余重力和相应的高密度可以归因于大规模岩浆侵入产生的镁铁质/超镁铁质岩石和冷却的围岩。因此，考虑到二叠纪峨眉山LIP，我们的剩余重力和密度模型提供了证据，形成的地幔柱上涌。
Despite numerous geologic and geochemical studies conducted on the Emeishan Large Igneous Province (LIP) in SW China, the deep origin of this LIP is still poorly constrained. Here we investigate the residual gravity anomaly in South China, and its relationship to the Emeishan LIP, in conjunction with deep seismic sounding profiles, deep seismic reflection surveys and a variety of broadband seismic observations performed in South China during the past few decades. Our analysis includes the removal of related gravitational effects due to: (1) the sediments, (2) the crystalline basement, undulations of (3) the upper crust, (4) the Moho and (5) the mantle lid. The resultant residual gravity anomaly in the Emeishan LIP and surrounding region reaches a maximum value of + 150 mGal and decreases gradually with distance from this inner zone. With the conjugate gradient method, we develop a lithospheric model consisting of a cylindrical-shaped positive density anomaly that provides a good fit to the observed residual gravity anomaly. The inverted density anomaly of the Emeishan LIP is + 0.06 g/cm3in the inner zone and decreases to about + 0.03 g/cm3in the outer zone. The observed positive residual gravity and the corresponding high density can be attributed to mafic/ultramafic rocks and cooled surrounding rocks generated by large scale magmatic intrusion. Hence, taking account of the Permian Emeishan LIP, our residual gravity and density model provide evidence for the formation by an upwelling of a mantle plume.