安徽周王地区早白垩世侵入岩年代学、地球化学特征及成因分析

CHRONOLOGY, GEOCHEMICAL CHARACTERISTICS AND GENETIC ANALYSIS OF EARLY CRETACEOUS INTRUSIVE ROCKS IN THE ZHOUWANG AREA, ANHUI PROVICE

安徽宣城周王地区出露一套中酸性侵入岩,主要为花岗斑岩、花岗闪长斑岩等。本文对该套侵入岩进行了详细的主量元素、微量元素以及锆石U-Pb年代学研究。主量元素组成上,该套侵入岩具富硅(61.26%~68.08%)、富钾(2.7%~4.89%)、贫镁(1.07%~1.69%)的特征,属于准-过铝质(A/CNK=0.95~1.5)的高钾钙碱性系列岩石。微量元素方面,轻重稀土元素分馏明显[((La/Yb)_N=9.14~10.63)],具中等-弱的负铕异常(δEu=0.69~0.8),大离子亲石元素富集,高场强元素明显亏损,表现出壳源的特征。LA-ICP-MS锆石U-Pb定年结果显示侵入岩形成于早白垩世。结合区域地质研究成果,认为该套岩石具有类似岛弧岩浆岩的特征,其形成与太平洋板块对欧亚大陆的俯冲碰撞密切相关。

A set of intermediate-acid intrusive rocks, mainly of granite porphyry and granodiorite porphyry, outcrop in the Zhouwang area of Xuancheng, Anhui Province. In this paper, major elements, trace elements and zircon U-Pb chronology of the intrusive rocks were studied in detail. For the major elements, the intrusive rocks are characterized by high silicon(61.26% ~68.08%), high potassium(2.7% ~4.89%), and low magnesium(1.07% ~1.69%), belonging to quasi-peraluminous(A/CNK=0.95~1.5) rock series with high potassium, calcium and alkali. In terms of trace elements, the fractionation of light and heavy rare earth elements is obvious [(La/Yb)N=9.14~10.63)], with moderate to weak negative europium anomaly(Eu=0.69~0.8), rich in big-ion lithophile elements, obviously deficient in high field-strength elements, showing the characteristics of crustal source.The LA-ICP-MS U-Pb dating of zircon shows that the intrusive rocks were formed in the early Cretaceous. By referring to the results of regional geology, it is argued that the rocks are similar to island arc magmatic rocks and their formation is closely related to the subduction and collision of the Pacific plate toward Eurasia.