东秦岭造山带南部宁陕花岗岩体群的地球化学及其构造环境研究

GEOCHEMICAL STUDY ON NINGSHAN GRANITIC PLUTON GROUPS IN THE SOUTH OF EAST QINLING OROGEN AND ITS TECTONIC ENVIRONMENT

本文详细研究了东秦岭造山带南部宁陕花岗岩体群的地质特征、岩石学、矿物学和地球化学特征.宁陕岩体群为钙碱性-碱性系列的花岗岩基,主要副矿物为钛铁矿、磷灰石、锆石和独居石,其黑云母为铁质黑云母,SiO_2和碱质含量都较高,除V,Sc,Sr和Bi等元素之外的大多数元素出现亏损;稀土元素负Eu异常较为明显,其组成模式为右倾“V”形曲线;δ^(18)O较高,而初始锶比值相对较低.因此,宁陕岩体群花岗岩为S型花岗岩.作者用多元统计分析和图解法将本岩体群花岗岩与世界著名造山带花岗岩的地球化学特征进行了对比研究,认为本岩体群花岗岩为陆-陆碰撞型花岗岩,是扬子板块与华北板块在晚古生代期间发生对接碰撞的产物.

The geological characteristics, petrology, mineralogy and geochemistry of Ningshan granitic pluton groups in the south of east Qinling Orogen are dealt with in this paper. The pluton group is calc-alkaline to alkaline granitic batholiths, whose accessory minerals are mainly ilmenite, apatite, zircon and monazite, and biotites are magnesium-rechened. The contents of SiO_2, K_2O and Na_2O in the granitic rocks are high, and most elements except V, Sc, Sr and Bi are depleted. The nagative Eu anomaly of REE in the granitic rocks is clear; the δ^(18)O values are very high and initial strontium ratio low. So Ningshan granitic pluton group is S-type granites. Geomathematics and diagrams are used to compare Ningshan granitic plutons with those in worldwide famous orogens. It is suggested that the granites from the group are collision-type granites, which are originated by the collision of the Yangtze Plate with the North China Plate during late Palaeozoic.