天水渭北地区变质花岗岩类岩石学特征及其地质时代

天水渭北地区地处祁连与北秦岭造山带结合部位。通过详细的岩石学特征、接触关系、形变及变质特征研究证实,尽管岩体有较强烈的变质和变形作用,但岩体内保留有清晰的原生岩浆组构,岩体与围岩有清楚的侵入关系,因而从变质地层中识别和解体出来众多的变质花岗岩类。主要成岩期及代表性岩类有:晚元古代为片麻状正长花岗岩—二长花岗岩—花岗闪长岩,同位素年龄为953.4～1 450 Ma;震旦纪为片理化石英二长岩—石英闪长岩,同位素年龄为547 Ma。识别和解体出的这些变质花岗岩类,为进一步研究祁连和北秦岭两大构造单元的岩浆事件和构造演化提供了十分重要的信息。

Petrologic Feature of Meta-Granitioids and Their Geological Ages in Weibei Area, Tianshui, Gansu Province

Weibei area is located in the joint of the Qilian and North Qinling orogenic belts.From detailed studies on the petrology,contact relation,deformation,metamorphism and so on,it is confirmed that although the granitoids had been strongly metamorphosed and deformed,they still contain clear primary fabrics.There are clear intrusive contact relations between the granitoids and their country rocks.So the meta-granitoids can be recognized and separated from the metamorphic sequences.They are grouped as the Mesoproterozoic-Neoproterozoic gneissoid granite-monzogranite-granodiorite,with their isotope ages of 953.4Ma to 1450Ma,and the Sinian schistostose quartz monzogranite diorite.This offers important information for the study of magmatic event and tectonic environment in the area.