湖南邓阜仙印支晚期二云母花岗岩年代学、地球化学特征及其意义

Chronology and geochemical characteristics of Late Indosinian Dengfuxian two-mica granite in eastern Hunan Province,China,and its significance

邓阜仙花岗岩体位于湖南省东部,是印支期-燕山期多期次多阶段侵入的复式岩体。本文对邓阜仙岩体中部的两件二云母花岗岩样品进行了锆石LA-ICP-MS U-Pb测年,得到的锆石U-Pb年龄为222.9±1.6Ma和224.3±2.4Ma,首次证实了邓阜仙岩体存在有印支晚期二云母花岗岩。印支晚期二云母花岗岩具有高硅、高碱、强过铝质的特征,富集Cs、Rb、U、Pb而亏损Ba、Sr、Ti等元素,与华南己发现的其他印支期强过铝质花岗岩类似。花岗岩较高的(87Sr/86Sr)i值(0.721463~0.728115)、较低的εNd(t)值(-11.68^-11.33)以及1.92~1.95Ga的Nd模式年龄说明其主要起源于区内古元古代地壳的部分熔融。邓阜仙印支晚期二云母花岗岩与华南印支期强过铝质花岗岩的成岩时间一致,根据区域地质特征及花岗岩地球化学特征,认为其形成于后造山伸展的构造环境。邓阜仙钨矿与区内燕山期花岗岩有密切的成因联系。印支晚期二云母花岗岩具有较高的钨含量,属于富钨岩体,可能为燕山期的钨成矿作用提供了物质基础。

Dengfuxian granite is an Indosinian-Yanshanian multi-stage complex batholiths located in eastern Hunan Province, South China. Zircon LA-ICP-MS U-Pb dating of the Dengfuxian two-mica granite has been carried out. The results show that two samples have zircon U-Pb ages of 222.91.6Ma and 224.32.4Ma, respectively, demonstrating firstly the occurrence of the Late Indosinian two-mica granite in Dengfuxian batholiths. This Late Indosinian two-mica granite is strongly peraluminous with high Si and alkali contents. It is enriched in Cs, Rb, U and Pb, but depleted in Ba, Sr and Ti, and shows the similar geochemical characteristics to Indosinian strongly peraluminous granites in South China. The samples have high （87Sr/86Sr）i values （0.721463~0.728115）, low εNd（t） values （-11.68^-11.33） and Nd model ages of 1.92~1.95Ga. It is proposed that the Late Indosinian Dengfuxian two-mica granite would be derived from partial melting of the Paleoproterozoic crustal materials. The intrusive time of the granite is consistent with those of the Indosinian strongly peraluminous granites in South China. Based on the geochemical characteristics and regional geological features, it is considered that the late Indosinian Dengfuxian two-mica granite was formed in a post-collision extensional tectonic environment. The mineralization of the Dengfuxian tungsten deposit is genetically related to the Yanshanian granite. The Late Indosinian two-mica granite has a high content of tungsten, and might provide metals for later Yanshanian tungsten mineralization.