Geochemistry and zircon U–Pb ages of the Neoproterozoic Shimian plutons on the western margin of the Yangtze Block, Sichuan Province,Geological Journal

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Geochemistry and zircon U–Pb ages of the Neoproterozoic Shimian plutons on the western margin of the Yangtze Block, Sichuan Province
Geological Journal ( IF 1.4 ) Pub Date : 2020-09-14 , DOI: 10.1002/gj.3969
Qi‐Feng Xie _{1,

2} , Yuan‐Feng Cai ₃ , Ming‐Guo Zhai _{2,

4,

5}

Affiliation

The Shimian Neoproterozoic plutons are located on the western margin of the Yangtze Block and are important for reconstructing the tectonic environment of this region. We present in situ zircon LA–ICP–MS U–Pb geochronological and Hf isotopic analyses for the plutons, as well as whole‐rock major‐ and trace‐element compositions. The monzogranite and syenogranite yield concordant ages of 773.6 ± 5.6 Ma and 812.2 ± 1.8 Ma, respectively, which indicates that they formed during the Tonian of the Neoproterozoic. The samples have very similar geochemistry, with high SiO₂ (71.45–75.46 wt%) and Al₂O₃ (12.38–14.36 wt%) contents. The samples have a geochemical characteristics typical of peraluminous A‐type granites, including high Ga/Al and Rb/Sr ratios and elevated contents of high‐field‐strength elements. The samples also display high Rb/Sr (13.9–23.0) and Rb/Nb (12.5–19.2) ratios. The monzogranite and syenogranite yield positive ε_Hf(t) values (+1.6 to +9.4 and + 5.2 to +9.8, respectively) and T_2DM ages of 1.54–1.22 Ga and 1.51–1.21 Ga, respectively, which indicates that they were derived from partial melting of Mesoproterozoic crust or contamination with upper mantle. We propose that the syenogranite and monzogranite formed in a syn‐orogenic extensional setting during the Tonian period and that continuous subduction was responsible for the Neoproterozoic magmatic activities.

中文翻译：

四川省扬子地块西缘的新元古代什面岩体的地球化学特征和锆石U–Pb年龄

石棉新元古代岩体位于扬子地块的西缘，对于重建该地区的构造环境具有重要意义。我们对岩体以及整个岩石中的主要元素和痕量元素组成进行了原位锆石LA–ICP–MS U–Pb地质年代学和Hf同位素分析。辉长花岗岩和正长花岗岩的一致年龄分别为773.6±5.6 Ma和812.2±1.8 Ma，这表明它们形成于新元古代的统统。样品具有非常相似的地球化学，具有较高的SiO ₂（71.45–75.46 wt％）和Al ₂ O ₃（12.38–14.36 wt％）含量。这些样品具有典型的高铝A型花岗岩的地球化学特征，包括高的Ga / Al和Rb / Sr比以及高场强元素的含量增加。样品还显示出高的Rb / Sr（13.9-23.0）和Rb / Nb（12.5-19.2）比。ε的二长花岗岩和正长花岗岩产量正_的Hf（吨）的值（1.6到9.4和5.2 + 9.8对，分别地）和T _2DM年龄分别为1.54–1.22 Ga和1.51–1.21 Ga，这表明它们是由中元古代地壳的部分熔融或上地幔的污染引起的。我们认为，在Tonian时期，正长花岗岩和共生花岗岩形成于同造山作用的伸展环境中，而连续俯冲是新元古代岩浆活动的原因。

更新日期：2020-09-14

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