花岗质岩石中微粒交生体的成因研究

在一些花岗质片麻岩中,经常看到分布在长石颗粒周围的细小矿物集合体——微粒交生体。电子探针分析结果表明,微粒交生体主要由钠长石、钾长石和石英组成,其标准矿物平均成分相当于An-Ab-Or体系的“低限熔点”成分。显然,微粒交生体是花岗质片麻岩经部分熔融产生的“低限熔体”的结晶产物。太古宙高级区一些晚构造钾质花岗岩的矿物,化学特征与微粒交生体类似。这意味着在塑性变形过程中产生和聚集的“低限熔体”最终可以形成大规模钾质花岗岩。

STUDY OF THE ORIGIN OF MICRO-INTERGROWTH OCCURRED IN THE GRANITOID ROCKS

A mineral aggregate or micro-intergrowth made of fine grains often appears in the interstice or periphery of the feldspar grains within the rocks which underwent ductile shear or plastic deformation. At present, it is generally believed that the micro-intergrowth would be products of recrystallization and the occurrence of the micrc-intergrowth shows that the rocks not only suffered from the plastic deformation under stress, but the anatexis could also be caused by increasing temperature and pressure. Therefore, the micro-intergrowth is the prcducts of crystallization of intergranular melt. According to the texture the micro-intergrowth can be divided into the following types:granular, sutured, myrmekitic, graphic and the quartz intergrowth with deformational riband and undulatory extinction. Judging from micro-electron prbe analyses, the micro-intergrowth is mainly made of albite, potasium feldspar and quartz,and the average composition of the normal mineral corresponds to that of "Iower-limit melting point"of Q-An-Ab-Or-H_2O system.The occurrence of the microintergrowth demonstrates that the "lower-limit melt" could be migrated and concentrated into the fissure, fold bend and other places with released stress forming the veins during the plastic deiormation. The mineralogy and chemistry of the serokinematic potash granites in the areas of Archean high-grade metamorphism (e.g. Qin Huandao granites of East Hebei Province) are similar to those of the micro-intergrowth. This means that the "lower-limit melt" produced and accumulated during the plastic deformation could finally form a large scale potash granitic rock.