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首页> 外文期刊>Journal of Asian earth sciences >Petrogenesis and geodynamic implications of Neoproterozoic gabbro-diorites, adakitic granites, and A-type granites in the southwestern margin of the Yangtze Block, South China
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Petrogenesis and geodynamic implications of Neoproterozoic gabbro-diorites, adakitic granites, and A-type granites in the southwestern margin of the Yangtze Block, South China

机译：中国扬子地块西南缘新元古代辉长闪长岩，adakitic花岗岩和A型花岗岩的岩石成因及其地球动力学意义

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The occurrence of A-type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone. This paper presents a comprehensive study of zircon U-Pb-Hf isotopes and whole rock geochemistry on the Neoproterozoic gabbro-diorites, biotite granites, and K-feldspar granites in the southwestern margin of the Yangtze Block, South China. Zircon U-Pb dating of three distinctive intrusions yield concordant ages of 810 +/- 4 2.0 Ma for gabbro-diorites, 800.3 +/- 2.1 Ma for biotite granites, and 749.1 +/- 2.0 Ma for K-feldspar granites. The gabbro-diorites are sodic and calc-alkaline rocks with low SiO2 (52.62-53.87 wt%), medium MgO (2.67-3.41 wt%), high Fe2O3T (7.18-7.49 wt%) and CaO (5.68-7.50 wt%) contents. They display high Th/Zr and Rb/Y ratios but low Nb/Zr and Nb/Y ratios. Together with their positive whole-rock epsilon Nd(t) (+1.0 to +1.5) and zircon epsilon(Hf)(t) values (+3.66 to +8.18), we suggest that these gabbro-diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction-related fluids. The biotite granites display relatively high Sr contents (335-395 ppm), Sr/Y ratios (38.9-54.3), low Y (7.04-9.71 ppm) and Yb contents (0.78-1.08 ppm), resembling the adakitic granites. Their low Mg-# (36-41) values, Cr (2.94-3.59 ppm) and Ni (1.32-1.55 ppm) contents as well as positive eNd(t) (+0.5 to +0.6) and eHf (t) values (+1.62 to +8.07) indicate that they were formed by partial melting of thickened juvenile mafic lower crust, probably within the existence of garnet. The K-feldspar granites have high SiO2 (76.61-77.14 wt%) and alkalis (Na2O + K2O = 8.55-9.69 wt%) contents, high 10,000* Ga/Al (2.56-2.80) ratios and differentiation index (95.3-96.9), indicating the affinity to highly fractionated A-type granites. We suggest that these A-type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant. Taking into account previous studies from the western Yangtze Block, South China, we propose that the gabbro-diorites, adakitic granites and A-type granites in this study were formed in persistent subduction process during the Neoproterozoic.
机译：继花岗岩之后的A型花岗岩的出现可以为俯冲带的构造演化提供独特的见解。本文对中国扬子地块西南缘的新元古代辉长岩闪长岩，黑云母花岗岩和钾长石花岗岩进行了锆石U-Pb-Hf同位素和全岩石地球化学的综合研究。锆石U-Pb测年的三个不同侵入年龄，辉长岩闪长岩的一致年龄为810 +/- 4 2.0 Ma，黑云母花岗岩的年龄为800.3 +/- 2.1 Ma，钾长石花岗岩的年龄为749.1 +/- 2.0 Ma。辉长岩闪长岩是苏打和钙碱性岩石，具有低SiO2（52.62-53.87 wt％），中等MgO（2.67-3.41 wt％），高Fe2O3T（7.18-7.49 wt％）和CaO（5.68-7.50 wt％）内容。它们显示出高的Th / Zr和Rb / Y比，但低的Nb / Zr和Nb / Y比。加上它们的正全岩石epsilon Nd（t）（+1.0至+1.5）和锆石epsilon（Hf）（t）值（+3.66至+8.18），我们建议这些辉长岩闪长岩是部分熔融的产物俯冲相关流体改良的枯竭岩石圈地幔。黑云母花岗岩显示出相对较高的Sr含量（335-395 ppm），Sr / Y比（38.9-54.3），低Y（7.04-9.71 ppm）和Yb含量（0.78-1.08 ppm），与Adakitic花岗岩相似。它们的低Mg-＃（36-41）值，Cr（2.94-3.59 ppm）和Ni（1.32-1.55 ppm）含量以及正eNd（t）（+0.5至+0.6）和eHf（t）值（ +1.62至+8.07）表示它们是由加厚的镁铁质下部地壳的部分融化形成的，可能在石榴石的存在下。钾长石花岗岩的SiO2（76.61-77.14 wt％）和碱金属（Na2O + K2O = 8.55-9.69 wt％）含量高，10,000 * Ga / Al（2.56-2.80）比例高，分化指数（95.3-96.9） ，表明对高度分级的A型花岗岩具有亲和力。我们认为，这些A型花岗岩主要是由于低压条件下长英质地壳岩石的部分熔融而产生的，随后大量的分步结晶意义重大。考虑到以前从华南西部扬子地块进行的研究，我们认为本次研究中的辉闪闪长闪闪岩，阿达克纪花岗岩和A型花岗岩是在新元古代一直持续俯冲过程中形成的。

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