东秦岭西坝花岗岩体及其脉岩的地球化学特征

通过秦岭西坝花岗岩体及邻区脉岩体的岩石学、地球化学研究，探讨了秦岭造山带中生代期间由全面碰撞转入陆内造山的深部动力学过程。研究表明：西坝花岗岩体及花岗斑岩脉具类似于埃达克质岩高Sr(Ba)，低Y和Yb，以及高Sr/Y,La/Yb,Eu异常微弱的地球化学特征，反映其形成于地壳厚度增大的地质背景；闪长玢岩脉代表地壳减薄背景的产物。它们的形成指示秦岭造山带印支晚期到燕山早期地壳增厚，嗣后发生下地壳拆沉的重要转换过程。

Geochemical characteristics and geological significance of Xiba granite,porphyry and porphyrite in East Qinling

Based on the detail studies on the petrology and geochemistry of Xiba granite body and porphyry in East Qinling, the deep dynamical process from final collision to orogeny within continent for the Qinling orogenic belt in the Mesozoic has been discussed. The rocks from Xiba granite and granitic porphyry are geochemically characterized by adakite like rocks with high Sr(Ba) and ratios of Sr/Y, La/Yb as well as low Y, Yb. They are strongly depleted in heavy REE with high ratios La N/Yb N of and slightly negative or positive E u anomaly, indicating that they were melted from materials of the lower crust under the thickening crust resulted from collision between North China and Yangtze plates during the Mesozoic. Of these, the HREE of granitic porphyry are more depleted than that of Xiba granite, showing that the thickness of the crust was much thicker when they formed and being representatives of melted products under the thickening crust of lower crust during the collision between North China and Yangtze plates in the late Indosinian and early Yanshanian. In contrast, the dioritic porphyrite has much different geochemistry, representing the production derived from mantle under the thinning crust due to the delamination resulted from the formation of former magmas. Therefore, the dioritic porphyrite gives a evidence that there was a delamination of lower crust after main collision in Qinling orogeny during early Yanshanian.