腾冲地区与锡矿床有关的花岗岩地球化学特征及类型判别

Geochemical Characteristics and Classification of Granites Related to Tin Deposits in the Tengchong Area,Southwest China

腾冲地区自东向西依次发育早白垩世（K。）东河花岗岩带（143．O～111．7Ma）、晚白垩世（K：）古永花岗岩带（84．3～65．9Ma）和早第三纪（E1-2）槟榔江花岗岩带（66．4～41．2Ma）。通过对与锡成矿关系密切的槟榔江花岗岩带中来利山花岗岩和古永花岗岩带中小龙河、水城花岗岩的岩相学、元素地球化学研究发现：花岗岩SiO：含量高，全碱（ALK）=8．17oA～8．15％，K2O／Na2O〉1，修改后的钙碱指数（MALI）=7．25～8．34，属高钾钙碱性一碱钙性系列；来利山花岗岩A／CNK=1．02～1．04，为弱过铝质花岗岩，小龙河和水城花岗岩A／CNK≤1．0，为准铝质花岗岩；这些花岗岩的形成与腾冲地块和保山地块碰撞有关，其中来利山花岗岩FeO／（FeO＋MgO）=0．61～0．67，相对富Mg，但铁镁含量低，源于（含）泥质岩石，为形成于后碰撞造山伸展阶段的s型花岗岩；小龙河和水城花岗岩Fe0／（FeO＋MgO）=0．88～O．94，相对富Fe，源于无水硅酸盐大陆地壳，为形成于后碰撞造山阶段A型花岗岩中的A2亚型花岗岩。研究确定了腾冲地区与锡矿床有关的来利山、小龙河、水城花岗岩的成因类型、源区特征和构造背景，并表明不同花岗岩带发育不同类型的花岗岩。

The Early Cretaceous （K1） Donghe granitoid belt （143.0-111.7Ma）, Late Cretaceous （K1） Guyong granitoid belt （84.3-65.9Ma） and Paleogene （E1-2） Binlangjiang granitoid belt （66.4-41.2Ma） extend from east to west in the Tengchong area. Based on petrography and element geochemistry of the Lailishan granite from Binlangjiang granitoid belt and Xiaolonghe as well as Shuicheng granites from Guyong granitoid belt which are closely related to tin deposits, this study shows that., these granites are riched in SiO2 and belong to potassic calc-alkalic to alkali-calcic series which total alkali （ALK） are 8. 17~ 8.15%, K20/Na2O〉1 and modified alkali-lime index （MALI） are 7.25-8.34; Lailishan granite＇s A/ CNK is 1.02 - 1. 04 and appears weakly peraluminous whereas Xiaolonghe and Shuicheng granites＇ A/ CNK are lower than 1. 0 and appear to be metaluminous; these granites were related to the collision between Tengchong and Baoshan blocks for Lailishan granite, FeO/（FeO-k MgO） = 0. 61 - 0. 67, relatively Mg enriched but low in ferromagnesian and referred to pelitic or semi-pelitic rocks sources as well as post-collision extension S-type granite~ while for Xiaolonghe and Shuicheng granites, FeO/（FeO ＋ MgO） =0.88-0.94, relatively Fe enriched and referred to anhydrous silicates continental crust sources as well as post-collision A2-subtype of A-type granites. This study defined genetic types, source characteristics and tectonic settings of Lailishan, Xiaolonghe and Shuicheng granites which are related to tin deposits, and pointed that different granitoid belts developed different granites.