钦-杭缝合带锡田合江口SP花岗岩地质地球化学特征及其对比研究

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF SP GRANITES IN HEJIANGKOU DEPOSIT OF XITIAN ORE FIELD AND THEIR CONTRACTION WITH PLUTON OF QINHANG SUTURE ZONE

合江口锡多金属矿位于锡田矿田内,钦-杭缝合带之中。矿区内花岗岩体主要呈隐伏状产出,其主岩基为斑状二云母花岗岩,晚期侵入体为白云母花岗岩,岩石中含有原生白云母、堇青石、电气石等矿物。地球化学特征具有高硅(>67%),高铝(A/CNK≥1.1),高钾,分异指数高,固结指数低,里特曼指数小于3,低铁镁(总量<5%),富Rb,Th,Nd,Gd,K,亏损Ba,Nb,Sr,P,Ti,δEu负异常明显、高δO18(>9.5‰)等特点,与高钾钙碱性SP花岗岩吻合。合江口隐伏花岗岩体与钦-杭缝合带上的成矿主岩体在岩相学特征、地球化学分类上均一致。其岩浆来源均为地壳物质重熔的产物,源岩中以砂质岩占优势,泥质岩也占有一定比例。但其大地构造背景却反映出两种截然不同的形式,早期主要表现为挤压向拉张转换环境,而晚期则为拉伸减薄环境。

Hejiangkou Tin poly-metal deposit occurred in the Xitian ore field, Qinhang suture zone. The buried pluton consists of porphyritic two-mica granite and late stage muscovite granite. Primary muscovite, cordierite, tourmaline and other primary alumina are the major mineral compo- sitions in the granites. Geochemistry analysis of the granite indicated that the major elements are characterized by high-silica （〉67%）,alumina （A/CNK≥1.1）, high potassium,high differentia- tion index,low consolidation index,tow Rittmann index （less than 3） and low total iron magnesi- um （〈5%）,and the trace element is rich in Rb,Th,Nd,Gd,K,deplete in Ba,Nb,Sr,P,Ti,with negative anomalies of 3Eu and isotopic 30TM over 9.5%. It is typical of high-K calc-alkaline granite SP. The petrological and geochemical characteristics of Hejiangkou granites were similar to those of Qinhang suture zone. The magma sources were resulted from the remelting of crust rocks dom- inated by sandstones and some argillaceous rocks. However, the granites reflect two distinct tec- tonic settings,early compressive stress environment and late stretching environment.