北山中部地区闪长岩-花岗岩类成因及构造背景

北山中部地区中酸性侵入岩以海西中晚期为主,加里东晚期次之。岩石类型有辉长岩、闪长岩、花岗闪长岩、斜长花岗岩和花岗岩类。岩浆活动分为3个旋回6期,其中海西中期第2,3期和海西晚期岩浆活动员为强烈。研究区岩体多呈岩株、岩枝和岩基产出,围岩普遍发育混合岩化和同化混染,岩石具花岗结构,块状-(巨)斑状构造。岩石化学成分为钙碱性系列,闪长岩分异程度低,斜长花岗岩和花岗闪长岩分异程度中等,花岗岩类相对较高。加里东晚期和海西晚期花岗岩类属S(海西)型花岗岩类,海西中期闪长岩、花岗闪长岩和斜长花岗岩类则属I型(科迪勒拉),闪长岩属交代(花岗岩化)成因,花岗闪长岩-花岗岩类属岩浆成因。加里东晚期花岗岩是中-晚志留世北山地区哈萨克斯坦板块向南俯冲使上地壳局部熔融的结果;海西中期闪长岩是混合岩化(花岗岩化)的产物;花岗闪长岩和斜长花岗岩是裂谷扩张阶段上地慢部分熔融的结果;而海西晚期花岗岩是裂谷萎缩和闭合阶段地壳局部熔融的结果。

The origin and tectonic settings of diorite granitoid in the centre of Beishan Region of Gansu

The Beishan Region is located at the junction of Tarim-SK (Sino-Korea) plate and Hazakstan plate. In its centre, there are two kinds of calc-alkalic intermediate-acid intrusive rocks: the I and S types. These intrusive rocks belong to the late Caledonian and mid-late Hercynian magmatism which can be classified into 3 cycles including 6 stages: late Caledonian (the rocks are granite and plagiogranite), middle Hercynian which can be farther sorted into 3 stages (the rocks of the first stage is diorite, the second stage is granodiorite and the third is plagiogranite) and late Hercynian (the rocks are granite, plagiogranite and moyite). The diorite is less differentiated index (DI less than 50) than plagiogranite, and granite is most (DI more than 75). Of them the diorite, granodiorite and plagiogranite is I type granites. The late Caledonian rocks formed by crustal partial melting caused by Hazakstan plate subduct to Tarim-SK(sino-korea) plate at Silurian. The genesis of diorite is migmagmtizationally during Carboniferous metamorphism in Beishan Region. The genesis of granodiorite and plagiogranite is that upper mantle melt partially resulted from rift expanding in the middle of Hercynian in Beishan Region. The rocks of late Hercynian is formed during the period of rift close in Beishan by the crustal partial melting.