The origin and tectonic implications of the ca. 406 Ma magmatic activity in the western Yangtze Block, South China

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
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Abstract

In this study, we report for the first time a new gabbro diorite, forming in an intraplate extensional environment during the Early Devonian, in the Shimian of the western margin of the Yangtze Block. Zircon SIMS U–Pb dating indicates that the gabbro diorite formed at ca. 406 Ma. This gabbro diorite belongs to low-K tholeiite and has enriched in Rb, Ba, K, Pb, negative anomalies of Nb, Ta, depletion of flat LREE patterns, negative εHf(t) (−1.1 to −11.7), and high δ18O (8.83 ± 0.21‰) ratios, showing that the magma formed by partial melting of N-MROB-type mantle and indicating that the magma underwent crustal contamination during emplacement. The magma is formed in the extensional environment, which provides evidence for the extensional environment in the western margin of the Yangtze. The geochemical characteristics and emplacement time of the rocks are similar to those in the early Paleozoic post-orogenic mafic rocks in South China, suggesting that the gabbro diorite may be influenced by the early Paleozoic orogeny in South China.

Abstract Image

华南西部扬子地块约 406 Ma 岩浆活动的起源及构造影响华南西部扬子地块约 406 Ma 岩浆活动的起源及其对构造的影响
在这项研究中,我们首次报告了一个新的辉长闪长岩,它形成于早泥盆世的板内延伸环境中,位于扬子地块西缘的石门地区。锆石SIMS U-Pb年代测定表明,辉长闪长岩形成于约406Ma。406 Ma。该辉长岩属于低K透辉岩,具有Rb、Ba、K、Pb富集,Nb、Ta负异常,LREE平面贫化,εHf(t)负(-1.1~-11.7),δ18O比值高(8.83±0.21‰)等特征,表明该岩浆是由N-MROB型地幔部分熔融形成的,也表明该岩浆在成岩过程中受到了地壳的污染。岩浆是在伸展环境中形成的,这为长江西缘的伸展环境提供了证据。岩石的地球化学特征和成岩时间与华南早古生代后成因黑云母岩相似,表明辉长闪长岩可能受到华南早古生代造山运动的影响。
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来源期刊
Solid Earth Sciences
Solid Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.60
自引率
5.00%
发文量
20
审稿时长
103 days
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