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首页> 外文期刊>Chinese science bulletin >LA-ICP-MS zircon U-Pb dating for high-pressure basic granulite from North Qinling and its geological significance
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LA-ICP-MS zircon U-Pb dating for high-pressure basic granulite from North Qinling and its geological significance

机译：北秦岭高压碱性花岗石的LA-ICP-MS锆石U-Pb年代测定及其地质意义

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摘要

A combined study of CL imaging, LA-ICP-MS U-Pb dating and trace element analysis were carried out for zircon grains from high-pressure basic granulite at Song-shugou in North Qinling. The zircons display core-rim internal texture. The cores are made up of sector or planar domains, partially displaying weak zoning or misty texture, and have the feature of low content of Th, U, REE, HREE, low Th/U ratio and high (Nd/Yb)N ratio, and the REE pattern typical for zircon coexisting with garnet. These features indicate the metamorphic genesis for the zircon cores. The rims have narrow light margins (<30 mu m in width) around the cores and boundaries between core and rim are rounded or lough-like, indicating that the rims were formed during retrograde metamorphism. U-Pb isotopic data of 24 spots from the cores of 11 zircon grains yield a ~(206)Pb/~(238)U weighted average age of 485 + - 3.3 Ma, which is interpreted as the peak metamorphic age of high-pressure (HP) basic granulite. This age is well consistent within error with that of ultra-high-pressure (UHP) eclogite and its country rock gneiss (507 + - 37 Ma) that occur at the north side of the Qinling Group, possibly indicating the occurrence of two contemporaneous Early-Paleozoic HP to UHP metamorphic rock belts on the north and south sides of the Qinling Group. Combining with the regional geological studies and the distribution of Early-Paleozoic granites related to subduction and collision, the two HP to UHP metamorphic belts may be the products of continental crust bi-directional deep subduction toward Qinling micro-block caused by the subduction and collision of Paleozoic Qinling ocean and Erlangping ocean, respectively.
机译：在北秦岭松树沟，对高压碱性粒粒锆石中的锆石进行了CL成像，LA-ICP-MS U-Pb定年和微量元素分析相结合的研究。锆石显示出核心边缘的内部纹理。核由扇形或平面畴组成，部分显示弱的分区或有雾的质地，并具有低的Th，U，REE，HREE含量，低的Th / U比和高的（Nd / Yb）N比，和锆石与石榴石共存的REE模式。这些特征表明锆石核的变质成因。轮缘在核心周围具有狭窄的光边界（宽度小于30微米），并且核心和轮缘之间的边界呈圆形或波纹状，表明轮缘是在逆行变质作用期间形成的。来自11个锆石晶核的24个点的U-Pb同位素数据得出〜（206）Pb /〜（238）U加权平均年龄485 +-3.3 Ma，这被解释为高压的峰值变质年龄（HP）碱性花岗石。该年龄与秦岭组北侧的超高压榴辉岩及其乡村岩片麻岩（507 +-37 Ma）的年龄基本吻合，可能表明该时期发生了两个同时期的早-秦岭群南北两侧的古生代HP到UHP变质岩带。结合区域地质研究以及与俯冲和碰撞有关的早古生代花岗岩的分布，两条HP-UHP变质带可能是俯冲和碰撞引起的地壳双向深冲向秦岭微区块的产物。古生代秦岭洋和二郎坪洋。

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