北山地区花岗岩类岩石的初步研究

A PRELIMINARY STUDY OF THE GRANITIC ROCKS IN THE BEISHAN AREA

北山地区系指甘肃省西北部及内蒙自治区西部,范围大致为东经92°—101°,北纬40°20＇——42°40＇,西与新疆接壤,面积约100,000km^2。区内广泛分布着花岗岩类岩石以及大量与这类岩类石有关的重要矿产。本文根据目前已有的实际资料对区内花岗岩类岩石进行了初步研究,提出了北山地区花岗岩类的成岩环境、时、空分布规律、岩石类型及其成因类型,并讨论了区内与花岗岩类有关的成矿作用。不妥之处请指正。

The Beishan area is located in the north-western part of Gansu province and the western part of Inner Mongolia, the total area is approximately 100,000 sq km.The granitic rocks covering two-thirds of the magmatic rocks of the Beishan area are poly-cyclic,poly-genetic and can be divided into three rock belts from south to northThey coincide with the orogenic zone and protrude slightly to the north in the western section, the granitic rocks are mainly of the Late Caledonian, the Early-Late Hercynian and the Indosinian-Yenshanian period. the intrusions in the southern and middle rock belts are older, those in the western part are older than in the eastern part.During the granitic rocks intrusion, the petrogenetic temperature is generally higher than 500℃, most are 600-800℃, with a few higher than 1,000℃; the pressure is generally 0. 5 to 5 kb, the emplacement depth is about 1-15 km, the rock types are mainly granodiorite and granite (mainly monzonitic granite) etc; the Rittmann Index is generally lower than 4 and the granitic rocks belong to the calcium-alkali series.variation of the average petrochemical composition and the characteristic value in time and space are regular. Most of the granitic rockbodies are of magmatic origin.The differentiated character is clear, the genetic types of granitic rocks are mainly of the syntexis type and the continental crust-transformation type.The ore deposits in the Beishan area are abundant. The deposits of lead, zinc and copp er etc. are related to the syntexis type while the copper, tungsten, tin and molybdenum ore deposits to the continental crust-transformation type.