花岗岩构造岩浆组合

On Granitic Tectono-Magmatic Assemblages

花岗岩的构造岩浆组合主要反映花岗岩的岩浆类型与大地构造环境之间的成因联系。从全球范围来看,结合中国的地质实际,花岗岩的构造岩浆组合可以区分为5种主要类型:(1)洋壳俯冲消减型,如太平洋两岸的大陆边缘;(2)陆—陆碰撞型,如喜马拉雅—冈底斯碰撞造山带;(3)陆缘伸展型,如中国东南部伸展型大陆边缘、北美西部盆岭省;(4)陆内断裂拗陷型,如长江中下游断裂拗陷、钱塘江—信江断裂拗陷;(5)裂谷型,如东非裂谷、攀西裂谷。通过钙碱指数(CA)和铝饱和指数(ASI)的计算,可以大体获知花岗岩的岩浆类型。造山带花岗岩的时空演变规律是:俯冲型→碰撞型→伸展型。亦可表述为:前碰撞花岗岩→同碰撞花岗岩→后碰撞花岗岩。但不能一概而论,只有在对不同造山带花岗岩的具体情况进行认真分析对比之后,才能对花岗岩的构造岩浆组合作出判断。

Granitic tectono-magmatic assemblages mainly reflect the genetic connections between the magma types of granites and tectonic environments. Viewing from the global scope, particularly looking at the situation in China, the granitic teetono-magmatic assemblages could be divided into five major types： （1） oceanic crust subduction type, such as continental margins on both sides of the Pacific Ocean; （2） continent continent collision type, e.g., the Himalaya-Gangdise collisional belt; （3） extensional continental margin type, such as the Southeast China extensional margin and the Basin and Range Province, USA; （4） inland faulted depression type, such as the Lower Yangtze faulted depression and the Qiantan-Xinjiang faulted depression; （5） rift type, such as the Eastern African Rift and the Panxi Rift of China. By calculating the calc-alkali index （CA） and alumina saturation index （ASI）, the magma types of the granites can be roughly determined. The temporal and spatial evolution of orogenic granitic belt shows certain kind of regularities： subduction type granites→ collision type granites → extensional type granites. Or, it may be described as： precollision granites → syncollision granites → postcollision granites. However, instead of giving general assumptions, we should carefully examine and analyze actual cases and conditions before reaching a conclusion.