中祁连党河南山碱性系列岩浆岩-埃达克岩成因及其对俯冲带壳幔相互作用的启示

碱性系列岩浆岩和埃达克岩是通常产生于汇聚板块边缘的特殊岩石类型,记录了俯冲物质与地幔橄榄岩相互作用的过程.笔者对中祁连南缘党河南山地区贾公台杂岩体和鸡叫沟岩体进行了岩石学、地球化学和锆石U-Pb年代学研究.LA-ICP-MS锆石U-Pb定年表明,鸡叫沟岩体中的二长闪长岩形成于(467±4.7)Ma,贾公台岩体花岗闪长岩...

Petrogenesis of Magmatic Rocks and Adakite of Alkaline Series from Danghenanshan Area in Central Qilian Belt:Implications for Crust-Mantle Interaction in Subduction Zone

Magmatic rocks and adakite of alkaline series,often at the convergent plate boundaries,witness the interaction process between subduction material and mantle peridotite.This investigation of zircon U-Pb dating and whole-rock geochemistry of the Jiagongtai and Jijiaogou plutons in the western Central Qilian belt provides new insights into crust-mantle interaction in subduction zone.LA-ICP-MS zircon dating shows that monzodiorite of the Jijiaogou pluton and granodiorite of the Jiagongtai pluton formed at about(467±4.7)Ma and(445±4.3)Ma,respectively.The compositions of Jijiaogou pluton are alkaline series with the characteristics of shoshonite.The different rock types of Jijiaogou pluton have similar trace element patterns and are enriched in Sr、Nb、LILE and LREE,which shows residual rutile in the magma source.The Jijiaogou alkaline series rocks are generated from hybrid alkali-rich subduction sediments and mantle peridotite at the sub-arc mantle wedge.The Jiagongtai granodiorite is medium potassium calc-alkaline series,with Na2O/K2O greater than 2.5;the samples show the characteristics of high Sr(>400×10^-6),low Y(<7×10^-6),high ratios of Sr/Y(>70)and La/Yb(>22).The Jiagongtai pluton represents high-SiO2 adakite,formed by partial melting of the subducted oceanic crust under eclogite-facies condition,and left garnet residue in the source.The alkaline magma and adakite in Danghenanshan indicate the characteristic of deep melting of subducted materials(greater than 50~100 km)and intense crust-mantle interaction in the source.It further indicates that subducted sediments and oceanic crust can provide a direct material source for the formation of arc magma,and the interaction between subduction material and mantle peridotite may be one of the ways of arc crust growth.