嵩山地区新太古宙歪咀山岩体成因及其地质意义
Genesis and Geological Significance of Waijushan Neo-archean Pluton in Songshan Area
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摘要: 嵩山是新太古宙TTG岩石出露的典型地区,新太古宙歪咀山片麻状奥长花岗岩分布于嵩山地区歪咀山一带,岩体呈灰白色,具中粒花岗结构,片麻状构造,局部发育条带状构造.富Na2O(4.08% ~ 5.30%)和SiO2(平均65%),贫Fe、Mg,Na2O/K2O值较高(1.5~3.9),Al2O3含量为14.14%~17.44%,平均为15.33%,>15%,显示为过铝质特征.ΣREE为121×10-6~267×10-6,重稀土亏损,轻重稀土强烈分异,Eu出现微弱负异常,具高的Sr含量,Cr、Yb、Y含量较低,与新生代高硅埃达克岩地球化学特征相似;岩石的Nb、Y、Rb、Th、La和Yb之间的关系特征和岛弧火山岩相似.地球化学特征表明歪咀山岩体是在高压下由俯冲的含水玄武质洋壳部分熔融形成.Abstract: Songshan is the typical area in China, where the neo-archean granitic rocks were well exposed. The Waijushan gneissic trondhjemite is mainly distributed in Waijushan, which shows grayish-white colour, with medium-grained granitic texture, gneissic and banded structures. The Waijushan gneissic trondhjemite has high concentrations of Na2O (4.08%~5.30%) and SiO2 (average 65%), and poor in Fe and Mg, with high ratio of Na2O/K2O (1.5~3.9) and the content of Al2O3 of 14.14%~17.44% (average of 15.33%, larger than 15%), showing the feature of TTG gneiss with peraluminous. It has the similar geochemical characteristics with the high Si Cenozoic adakite, for example, the ΣREE is 121×10-6~267×10-6, the HREE is strongly depleted, and the LREE and HREE are strongly differentiation, with weak negative Eu anomalies, high content of Sr, high ratio of Sr/Y, and low contents of Cr, Yb and Y; It is also similar to island arc volcanics on the relational features among Nb, Y, Rb, Th, La and Yb in the rocks. The geochemical characteristics of the Waijushan pluton shows that it was formed by the partial melting of aqueous basaltic oceanic crust under the high pressure environment during subduction process.
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Key words:
- Neo-archean /
- trondhjemite /
- geological significance /
- Waijushan
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