安徽石台中生代花岗岩类地球化学特征

Geochemical Characteristics of the Mesozoic Granitoids in Shitai area,Anhui Province

安徽石台地区出露的牯牛降(东库)、谭山岩体可划分为4个侵入期次,从早到晚岩性变化趋势为中粒似斑状(二长)花岗岩→中(中粗)粒正长花岗岩→中细粒似斑状(正长)花岗岩→细(微)粒似斑状钾长花岗岩。岩石化学特征显示均为高钾钙碱性系列;微量元素地球化学特征表明,牯牛降(东库)、谭山岩体微量元素总体具相似特征,都富集大部分亲石元素,K/Rb比值低而Rb/Sr比值高;微量元素原始地幔标准化蛛网图总体略显右倾,均具有高Rb低Ba、Sr、Ti的特征。牯牛降(东库)和谭山岩体稀土元素球粒陨石标准化配分模式图均为右倾海鸥型,均具有较强的Eu亏损。研究认为牯牛降(东库)岩体和谭山岩体成岩物质主要来源于上地壳的部分熔融,成岩的地球动力学背景为碰撞造山后挤压收缩向拉张伸展的转变,与中国东部此时发生构造大转折、岩浆活动和成矿作用大爆发基本一致。

Mesozoic granitoids are widely distributed in the Shitai region of Anhui Province. Among the granitoids,Guniujiang（including Dongku） and Tanshan plutons with relatively large exposed areas can be divided into four stages of intrusion, from early to late, their lithologic characters show such a variation： medium-grained quasi-porphyritic（monzonitic） granite→medium to coarse-grained syenogranite→mediumfine grained quasi-porphyritic （syebitic） granite→fine-grained（micrograined） quasi-porphyritic moyite and alkali-feldspar granite. The Guniujiang（including Dongku） and Tanshan plutons have similar lithochemical characteristics, belonging to the high-K calc-alkaline series. They show similar trace-elements geochemical characteristics, being rich in lithophile elements, with higher ratios of Rb/Sr and low ratios of K/Rb. On the primitive mantle-normalized trace-element spidergrams, all of these granitoinds are enriched in large ion lithophile elements as Rb and Th, and depleted in Ba,Sr and Ti. Their chondrite-normalized REE patterns show right-dipping oblique V-shapped patterns, with stronger negative Eu anomalies. Based on pet- rological and geochemical studies, we considered that the lithogenous materials of Guniujiang（including Dongku） and Tanshan granitoid plutons were derived from partial melting of the upper crust, and the geodynamic setting of lithogenesis was the transformation from compression to extension of postcollisional orogenesis, being basically contemporaneous with large-scale tectonic transformation, magmatism and mineralization of eastern China.