云南瓦渣钨矿区老君山花岗岩体的SHRIMP锆石U-Pb定年、地球化学特征及成因探讨

SHRIMP zircon U-Pb dating and geochemical characteristics of Laojunshan granite intrusion from the Wazha tungsten deposit,Yunnan Province and their implications for petrogenesis

云南省瓦渣钨矿区位于老君山花岗岩体的东北接触带,属于滇东南-桂西白垩纪钨锡多金属成矿区中的组成部分。该矿床与矿区西部大面积分布的老君山第一期中粗粒二云二长花岗岩在时间和成因上有着密切联系。本文通过SHRIMP锆石U-Pb测年、岩石主量元素、微量元素和稀土元素的系统研究,进而探讨该花岗岩的形成年龄和动力学背景、岩石物质来源以及形成温度和压力。研究表明,与瓦渣钨矿床有关的中粗粒二云二长花岗岩属于高钾钙碱性岩系,为强过铝质S型花岗岩。岩体形成时代为83.3±1.5Ma,属于晚白垩世,形成于岩石圈伸展环境,其源岩为富粘土的泥质来源,其形成温度为875～900℃,压力约为7×108Pa,相当于深度为26km。

The Wazha tungsten deposit in Yunnan Province is located in the northeast contact zone of Laojunshan granite intrusion and belongs to the southeastern Yunnan-western Guangxi tungsten-tin polymetallic metallogenic area in Cretaceous age. The tungsten deposit displays close temporal and genetic relationship with the granites occurring in the Wazha tungsten ore district,which are recognized to be the first phase of Laojunshan granites-medium-coarse two mica monzonitic granites. In this paper we applied SHRIMP zircon U-Pb dating and major,trace and rare earth element analysis to the granites,in order to clarify the rock-forming age,dynamic background,source rocks and formation temperature and pressure of the granites. The granites are high-K calc-alkaline series and are proposed to be strongly-peraluminous S-type granites. The crystallization age of the intrusion was determined to be 83.3±1.5Ma. They may emplaced within the lithospheric extensional period and Were derived from the remelt of clay-enriched argillaceous rocks. The formation temperature of granite magma was from 875℃ to 900℃,the estimated pressure was about 7×108 pa,indicating that they were formed at depth of 26km.