滇西来利山花岗岩年代学、地球化学特征及其壳源部分熔融成因

Petrological, geochemical and geochronological features of Lailishan ganitoids in western Yunnan and their genesis of partial melting of crustal soure

与锡矿有关的花岗岩成因一直是地学界关注的焦点。来利山花岗岩位于云南省腾冲—梁河地区(花岗岩带上),构造上属于腾梁花岗岩带。该花岗岩带总体呈北北东向带状展布,构成冈底斯的南延部分。来利山岩体主要由似斑状黑云母二长花岗岩和中粗粒黑云母正长花岗岩组成。本次工作在前人研究的基础上对来利山花岗岩进行了岩石学、地球化学和年代学研究,获得二长花岗岩(14L-4)锆石LA-ICP-MS U-Pb年龄为(52.34±0.68)Ma(MSWD=1.4,n=26)。地球化学数据显示二长花岗岩相对富铝(Al2O3=14.70%~15.27%)、碱(K2O+Na2O=8.07%~8.50%)、钙(Ca O=1.64%~2.56%)、REE、Ba。铝饱和度(A/CNK)为0.97~1.12,平均为1.04,属偏铝质到弱过铝质岩石。正长花岗岩相对富硅(Si O2=74.57%~76.69%)、Rb,强烈亏损Ba、Sr、P、Ti、Eu,铝饱和度(A/CNK)为1.05~1.18,平均为1.09,属弱过铝质岩石。两类花岗岩系同源岩浆于不同阶段侵位形成,二者在矿物学、地球化学、年代学等方面表现出良好的演化关系,均显示S型花岗岩的特征。其形成与印度大陆和亚洲大陆碰撞过程中地壳物质部分熔融有关。

Granites genetically related to tin ore deposits always constitute the focus of geological studies.The Lailishan granitoids are located in the Tengchong-Lianghe area of western Yunnan and belong tectonically to Tengliang granitoids.These granites extend in NNE direction as a belt,connected with Gangdise belt on the north.The Lailishan granitoids are mainly composed of porphyaceous biotite monzogranite and medium to coarse-grained biotite syenogranite.Based on the data available,the authors conducted petrological,geochemical and geochronological studies of the Lailisahn granitoids.The zircon LA-ICP-MS U-Pb age of the monzogranite(14L-4)is52.34±0.68Ma(MSWD=1.4,n=26).Geochemically,the monzogranite is relatively rich in Al(Al2O3=14.70%-15.27%),alkalis(K2O+Na2O=8.07%-8.50%),Ca(CaO=1.64%-2.56%),REE,and Ba.The ASI values range from0.97to1.12,1.04on average,indicating that monzogranite is from metaluminous to weakly peraluminous.The syenogranite is relatively rich in Si(SiO2=74.57%-76.69%)and Rb,and strongly depleted in Ba,Sr,P,Ti,and Eu.The ASI values range from1.05to1.18,1.09on average,indicating weakly peraluminous features.The monzogranite and syenogranite originated from the same magma reservoir but emplaced at different stages;the evolution of them in mineralogy,geochemistry and chronology was obvious,suggesting S-type granites.It is therefore held that the Lailishan granitoids originated from crust partial melting in deep crust during main Indian-Euro-Asian collision period,responding to the interaction between the Indian-Euro-Asian continents.