新疆西南天山霍什布拉克碱长花岗岩体岩石学及地球化学特征——岩石成因及其构造与成矿意义

Petrology and geochemistry of the Huoshibulake alkali feldspar granite pluton in Southwest Tianshan Mountains,Xinjiang:implications for petrogenesis,tectonic setting and mineralization

位于中国西南天山南缘的霍什布拉克岩体,由碱长花岗岩和碱长花岗斑岩组成。岩石化学成分比较均一,具有富SiO2、Al2O3,贫Fe2O3T、MgO、TiO2、P2O5等特点。AR-SiO2图解中,样品均落入碱性区间,在A/CNK-A/NK图解中,样品主要为准铝质。微量元素总体表现为高场强元素(HFSE)相对于大离子亲石元素的富集以及高场强元素P、Ti和大离子亲石元素Sr、Ba的明显亏损。稀土元素中轻稀土元素相对于重稀土元素富集,Eu的负异常十分明显。岩体含副矿物萤石,并具有高FeOT/MgO、低CaO等特征,10000Ga/Al的比值和Zr+Ni+Sr+Y的含量亦较高,岩石学和地球化学特征表明它为典型的A1型花岗岩,是铁镁质下地壳在低压条件下部分熔融的产物。岩体具有极低的Ti含量是由于源区部分熔融过程中大量磁铁矿的残留所致,而较高的Nb-Ta含量则与岩浆中富含F有关。岩体产出于板内环境,在构造岩体的形成上受到塔里木板块内部裂谷体系的影响。岩体对霍什布拉克铅锌矿成矿意义不大,但具有Sn元素的成矿潜力。

Located in the south margin of the Chinese Southwest Tianshan area,the Huoshibulake alkali feldspar granite pluton is composed mainly of alkali feldspar granite with a small amount of alkali feldspar granite porphyry.All samples from the pluton are characterized by high values of SiO2 and Al2O3 and low values of Fe2O3T,MgO,TiO2,P2O5.All samples are of alkaline affinities based on AR versus SiO2 diagram,and chiefly fall into the metaluminous area in the A/CNK versus A/NK diagram.The primitive mantle normalized trace element diagrams are characterized by the enrichment of the HFSE relative to the LILE,and negative anomalies of Sr,Ba,P,Ti.The samples exhibit a relative enrichment of LREE as well as strong negative anomalies of Eu,contain fluorite and have high ratios of FeOT/MgO and low values of CaO.The alkali feldspar granite pluton is also characterized by high 10 000 Ga/Al ratios and Zr＋Ni＋Sr＋Y values.Petrology and geochemistry of the pluton show that it belongs to typical A1-type granite,and is a product of the partial melting of the mafic lower crust in an intraplate environment.The low content of Ti results from a large quantity of residual magnetite minerals in the source area,and the high Nb-Ta value is caused by the enrichment of F in magmas.The tectonic setting is affected by the rift system within the Tarim Block.The pluton is rather insignificant in the study of the genesis of the Huoshibulake Pb-Zn deposit but displays Sn mineralization potential.