摘要
中生代花岗质岩石在华南分布广泛, 且常与W-Sn、Pb-Zn 等金属矿床具有紧密的时空联系, 而湖南水口山花岗闪长岩是与Pb-Zn 成矿作用有关的典型代表.与华南改造型花岗岩相比, 水口山花岗闪长岩及其成矿作用的研究程度较低.本文系统研究了该花岗闪长岩的岩相学特征、主元素、微量元素和Sr-Nd 同位素组成, 重点讨论了其岩石成因类型、物质来源及形成的构造环境.研究结果表明, 水口山花岗闪长岩为贫SiO2、富碱、富铁镁、准铝质-弱过铝质的高钾钙碱性岩; 表现出轻稀土元素富集, 轻重稀土分馏强烈, 弱负Eu 异常; 不相容元素Ba、Ta、Nb、Sr、Ti 亏损, 而Rb、Th、U、K、LREE 相对富集的特征.岩体的（87Sr/86Sr）i比值为0.707364-0.711380, εNd（t）值为–6.61-–2.40, 具明显的亏损地幔和华南上地壳混合特征.水口山花岗闪长岩的矿物组成、元素地球化学和同位素地球化学特征均表明, 该岩体为同熔型花岗岩.该岩体是在晚中生代由太平洋板块向欧亚大陆板块俯冲诱发的华南板块伸展-减薄构造环境下, 玄武质岩浆上涌, 底侵中下地壳, 与中上地壳混合形成的燕山早期高钾钙碱性花岗岩.
Mesozoic granitoids occur extensively in South China, and are generally associated with W-Sn deposits and Pb-Zn deposits temporally and spatially. The Shuikoushan pluton is a typical granodiorite related with Pb-Zn hydrothermal mineralization. However, the petrogenesis of this pluton and its relevant mineralization are poorly constrained. The petrological and geochemical (major elements, trace elements and Sr-Nd isotopes) characteristics, together with the genetic type, magma source and formation tectonic background, of the Shuikoushan pluton are documented and discussed in this study. The rocks from the Shuikoushan pluton display low SiO2 contents, high K2O+Na2O contents, indicating that they are metaluminous to weakly peraluminous, belonging to the high potassium calc-alkaline series. They are characterized by LREE-enrichment, remarkable fractionation between LREE and HREE, and weak negative Eu anomalies. In addition, they are enriched in Rb, Th, U, K and LREE, but depleted in Ba, Ta, Nb, Sr and Ti. The initial 87Sr/86Sr and εNd(t) values for the pluton range between 0.707364~0.711380 and –6.61~ –2.40, respectively, displaying an obvious mixing between the depleted mantle and the upper crust of South China. All petrographical and geochemical evidences reveal that the Shuikoushan granodiorite is of the syntexis type. The granodiorites can be interpreted as being resulted from anorogenic magmatism, which is mixed with upwelling mantle-derived and upper crust magmas in response to the lithosphere extension and crust thinning due to Mesozoic subduction beneath South China Block.
出处
《地球化学》
CAS
CSCD
北大核心
2015年第2期131-144,共14页
Geochimica
基金
国家重点基础研究发展计划(2012CB416705)
关键词
花岗闪长岩
地球化学特征
同熔型花岗岩
水口山矿田
granodiorite
geochemistry
syntexis type granite
Shuikoushan orefield,South China
