桐柏北部二朗坪蛇绿岩片中花岗岩:地球化学、成因及对地壳深部物质的指示

GRANITOIDS IN ERLANGPING OPHIOLITE FRAGMENT FROM NORTHERN TONGBAI AREA,CHINA:GEOCHEMISTRY, PETROGENESIS AND DEEP CRUSTAL NATURE

本文对产于桐柏北部二朗坪蛇绿岩片中加里东期桃园岩体和燕山期梁湾岩体花岗岩进行了系统的主量元素、微量元素和Ｓｒ－ Ｎｄ－ Ｐｂ 同位素地球化学研究。研究表明，桃园花岗岩与二朗坪基性岩具有相同的岩浆来源，两者均来自于亏损地幔源区，其中桃园花岗岩浆来自于基性岩浆的分异结晶，是与蛇绿岩共生的岩浆侵入单元，形成于与洋壳消减作用有关的弧后盆地环境，从而支持了二朗坪蛇绿岩属弧后盆地型蛇绿岩的认识。梁湾花岗岩的岩浆物质来自于南部（南秦岭）陆壳物质的部分熔融，指示在桐柏北部（北秦岭）的深部地壳中含有南秦岭陆壳物质，从而进一步证明了早期南秦岭陆壳向北俯冲叠置于北秦岭块体之下的认识。

This paper reports major elements, trace elements and Pb-Sr-Nd isotopes of Caledonian Taoyuan and Yanshanian Lianwan granites, which are distributed in Erlianping ophiolite fragment, northern Tongbai area. The results show that the geochemical characteristics of the Taoyuan granites are different from those of the Lianwan granites. The Taoyuan granitic magma was derived from depleted mantle similar to the Erlianping basic volcanic magma, both of which are the magma intrusion unit and the extrusion unit in ophiolite association, respectively. The Taoyuan granites were formed in back-arc basin related to ocean plate subduction. This supports the understanding that the tectonic setting of the Erlianping ophiolite was the back-arc basin. The Lianwan granitic magma was derived from the partial melting of South Qinling basement. Therefore, the deep crust of the northern Tongbai contains the crust material of South Qinling, which further confirms the underthrusting of the South Qinling continental crust beneath the North Qinling block in early period.