秦岭造山带丹凤变质岛弧火山岩系的岩石组合与地球化学特征

ROCK ASSOCIATION AND GEOCHEMISTRY OF THE DANFENG META-VOLCANICS IN THE QINLING OROGENIC BELT: ITS FORMATION SETTING AND MECHANISM AND TECTONIC IMPLICATIONS

本文通过对秦岭造山带内的早古生代丹凤交火山岩系岩石组合和地球化学特征的研究,探讨了该变火山岩系的形成环境和构造意义,指出丹凤变火山岩系为秦岭古洋内弧地壳的构造残片。

The Danfeng meta-volcanics that are located in the major suture zone of the Qinling oro-genic belt are crucial to an understanding of the tectonic evolution of the belt during the Pha-nerozoic, but there still exists much controversy about its formation setting and tectonic em-placement. On the basis of large-scale mapping and multidisciplinary investigations and fromits rock association and geochemistry, the formation setting and mechanism as well as the tec-tonic significance of this meta-volcanic complex is discussed. It is suggested that the Danfengmeta-volcanic complex exhibits no pseudo-stratified structure charocteristic of ophiolites, but thestructure of predominantly mafic supercrust rocks from the petrological and geochemical charac-ters, the orogenic belt was formed in an intra-oceanic arc seting during the Early Paleozoic, i.e.,in a back-arc environment, as represented by the Erliangping Ophiolite to the north. And it wasformed in a process of vertical (non-extensional) thickening of the intra-oceanic arc crust. Evi-dence shows that there had existed an ocean to the south of northern Qinling tectonic belt during,at least, the Early Paleozoic, which then becamearrow because of plate subduction.