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    扬子地块西缘Grenville期花岗岩的厘定及其地质意义

    The identification of the Grenvillian granite on the western margin of the Yangtze Block and its geological implications

    • 摘要: 提要:本文在扬子地块西缘的米易垭口地区,从原划分的冷竹关组地层中厘定出一变质变形的侵入体,岩性为二长花岗岩,具有高硅、富钾特征。该岩体具有较高的Rb/Sr(2.66~10.5)和Rb/Zr(0.43~1.12);有明显的Ba、Sr、P、Nb、Ta和Ti的负异常;87Sr/86Sr为1.209549;εNd(t,1.0Ga)=-0.89,具有壳源碰撞花岗岩的特征。锆石SHRIMP U-Pb年龄测试结果表明该岩体形成于(1014±8)Ma左右,应为扬子地块与华夏地块在Grenville期碰撞拼贴时的产物。本文的研究表明江南造山带向西可能一直延伸到扬子西缘的会理攀枝花一带,而不是经黔滇向南转折。

       

      Abstract: Abstract:A deformed and metamorphosed monzogranite intrusion was ruled off from the Lengzhuguan Formation at Yakou Town, Miyi County, which is situated on the western margin of the Yangtze Block. The intrusion is high in SiO2 and K2O and shows obvious negative anomalies of Ba, Sr, P, Nb, Ta and Ti in the mantle-normalized trace element spidergram. In addition, the rock has high Rb/Sr (2.66~10.5) and Rb/Zr (0.43~1.12) ratios, and the 87Sr/86Sr and εNd (t,1.0 Ga) values are 1.209549 and -0.89, respectively, suggesting a crust-derived collisional granite. The zircon SHRIMP data give a granite crystallization age of ca 1014±8 Ma. It is proposed that the Huoshangou granite might have resulted form the collision between the Yangtze Block and the Cathysia Block during the Grenvillian event. It can also be deduced that the Jiangnan orogenic belt can probably extend westward to Huili-Panzhihua area on the western margin of the Yangtze Block instead of turning southward from the Guizhou-Yunnan area.

       

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