南秦岭勉略结合带琵琶寺洋壳蛇绿岩的厘定及其大地构造意义

Geochemistry of the Pipasi ophiolite in the Mianlue suture zone,South Qinling,and its tectonic significance

研究结果表明,康县-琵琶寺-南坪构造带是一个复杂的、含有不同成因岩块的混杂带。该带中分布有蛇绿岩块(古洋壳残片),为典型的洋脊型拉斑玄武岩,具有轻稀土亏损的稀土配分型式、不活动痕量元素及其比值Th/Yb、Ta/Yb、Ti/Y、Ti/Zr等,指示其来源于亏损的软流圈地幔。琵琶寺蛇绿岩与勉县—略阳地区庄科蛇绿岩以及德尔尼蛇绿岩完全可以类比。因此,康县-琵琶寺-南坪蛇绿构造混杂带乃是勉略带向西延伸的组成部分。

The Kangxian-Pipasi-Nanping tectonic belt is a complex mélange zone which includes many tectonic blocks of different origins.The blocks(relict fragments of ancient oceanic crust)therein are typi-cal oceanic ridge basalt and show LREE-depleted REE distribution patterns.The Th /Yb ,Ta/Yb ,Ti/Y and Ti/Zr ratios indicate that they originated from the depleted asthenospheric mantle.The Pipasi ophiolite may be correlated with the Zhuangke ophiolite and Dur'ngoi ophiolite in the Mianxian-Lueyang(Mian-lue)suture zone.Therefore the Kangxian-Pipasi-Nanping tectonic mélange zone is a westward extension of the Mianlue suture zone.