湖北七尖峰花岗岩成因类型初探——兼论花岗岩类某些成岩机制

A Primary Approach to the Genetic Types of Qijianfeng Granite in Hubei Province——Concurrent Views on Some Petrogenetic Mechanism of Granitoid

花岗岩是大陆陆壳主要的组成部分,与之有关的矿产十分丰富,故长期以来,一直是岩石学者研究的重点。自Chappell和White（1974）在研究了澳大利亚东南部莱克兰（Lachlan）地区褶皱带的花岗岩之后,提出了＂S＂型和＂I＂型的分类。＂S＂型即地壳表面经历风化、搬运和沉积作用,而后由超变质作用形成的花岗岩类。＂I＂型,即直接从火成成因的先成岩派生出来的花岗岩类[1]。之后,

Within the metamorphosed rocks of Proterozoic Erathem-Archaeozoic Erathem in Tongbai-Dabie Mt. area, Northern Hubei Province, there distributed considerable granites of Yanshan Period ; among which Qijianfeng granite is a representative rock mass. According to the geological features, the constituents of rock-forming minerals and accessory minerals, the petrological geochemistry and the compositions of minor elements and their evolution behaviour, the partition features of rare earth elements in rocks as well as the isotopic dating data and the correlation with some rock masses at home and abroad, the authors obtain some conclusions as follows ：（1）Qijianfeng granite is rich in accessory minerals of magnetite ＋ sphene but poor in ilmenite ; the plagioclase degree of order = 0.2 ~ 0.8 ; the lower limit of potash-feldspar triclinity = 0.22 ; the range of forming temperature of biotite and quartz = 730 - 1 060℃ ; the Rittmann＇s index of rock series = 2.59 - 2.99 ; A/CNK 〈 1.1 ; FM value 〉 0.38 ; K2O/Na2O 〈 1 ; ∑Ree = 101 - 159 × 10 -6; there is no depletion of 8δu;∑Ce/：∑Y 〉5; La/Yb 〉 10; by C. I. P. W . , the typical mineral of corundum 〈1; the distribution curve of rare earth is right-inclined and smooth; and the initial ratio of isotope Sr87/Sr88 〈0. 7100. According to the data mentioned a- bove, it may be correlated with syntectic type ganite （corresponding to ＂I＂-type granite） but it is different from remehed type granite （approximate to ＂S＂-type granite）. （2）Based on the Qijianfeng granite being a composite batholith, some quartz inclusions containing glass substances, none of rounded minerals, high content of Cr, Ni and Co within biotite, obvious contacts between granite and country rocks and the contacts between one granite and another granites, the distri- bution curve of rare earth of magrnatic type granite is correlated with that of metasomatic type granite again. The result of the study shows that the mantle substances joined the processes during the formation of granites; so, Qijianfeng granite does not belong to the migmatized granite （i. e. rnetasomatic type granite）. （3）This paper suggests that during the Yangtze movment, the partial elevation of mantle and the rise of heat flow caused the melting of some substances in lower crust and the intruding of the materials along the fractures. During the Yanshanian movement, the fractures activized again and caused the mantle or lower crustal substances to melt and intrude along the fractures once again. This is the ge- netic mechanism of Qijianfeng granite. （4）In recent years, some precious metal resources of Au and Ag have been prospected in the west of gently inclined position within Qijianfeng granite. Obviously, the genesis of these mineral deposits related ＇ to＇ the granite.