摘要
白马尖花岗岩体是大别山超高压变质带中的重要花岗岩体之一,主要组成岩类为二长花岗岩,成岩年龄为燕山晚期。含铝指数ACNK为0.97～1.01（平均为1.00）。在 Shand指数图解上位于准铝质与过铝质岩石的界线上;在K2O—SiO2图解中处于高钾钙碱系列范围,属碰撞后花岗岩。稀土元素配分型式为富轻稀土中等至强铕负异常的右倾平滑曲线,δEu为0.37～0.65（平均值为0.53）。研究揭示,在花岗岩研究中流行使用的Nb-Y,Rb-Y+Nb和Rb-Hf-Ta图解目前难以准确反映该岩体的侵位构造背景,但却指示了其源区具有古火山岛弧的特征,并反映本区存在一个伸展拉张环境的时期,区内花岗质岩浆上侵的构造环境与中国东部燕山期构造转折的大背景有关。伸展拉张过程造成的地幔上涌不但成为花岗岩类形成的主要条件,也对超高压变质岩的快速折返有重要影响。
Baimajian granitoids in Dabie Ultra High Pressure (UHP) belt are mainly composed of monzogranite. Pertrographical and geochemical characteristics indicate that they were emplaced in the post-collision regime (late Yanshan period). The granitoids belong to the metaluminous -peraluminous transitional type on Shand diagram (ACNK-ANK diagram) (ACNK = 0.97-1.01)), and belong to high-K calc-alkaline series on K2O vs silica diagram. REE pattern diagram shows that they are rich in LREE, with strong negative Eu anomaly (δEu = 0. 37 - 0. 65, average 0. 53). The Nb - Y, Rb - Y + Nb, Rb - Hf - Ta diagrams indicate that the source materials of the Baimajian granitoids were possibly derived from the old island arc, though they cannot exactly reflect the tectonic background of the intrusion activity. Mantle upswelling associaed with extension process during the Yanshanian movement not only created the geotectonic conditions for granitoids formation, but also greatly influenced the fast exhumation of UHP metamorphic rocks in Dabie Mountains.
出处
《高校地质学报》
CAS
CSCD
2002年第3期308-317,共10页
Geological Journal of China Universities
基金
本研究得到国家攀登计划预选项目(项目编号:95-预-39)资助。
