摘要
本文简要概述了近年在西阿尔卑斯、挪威西部、我国中东部及苏联一些地区超高压变质岩石的最新研究成果,指出柯石英及其向石英转变而形成的张裂结构是鉴别这一超高压变质作用的主要标志.指示超高压变质条件的其它矿物及矿物组合的尚有镁十字石、ellenberserite、硬玉十蓝晶石、滑石十蓝晶石和滑石十多硅白云母等,金刚石代表更极端的高压条件.超高压变质作用的边界压力>2.SGPa,温度约700~840C,代表一个近于7℃/km的极低的地热梯度,其退化轨还为压力和温度同时降低.超高压变质岩石严格地产出于陆内造山带,表明它们是在大陆与大陆碰撞过程中由深俯冲作用形成的,其俯冲深度可超过90km,使柯石英得以保存的快速构造抬升可能是连续俯冲一仰冲的结果.
The recent study of ultra-high-pressure metamorphic rocks from the Western Alps, the Western-Norway Gneiss Region, the eastern-central China and some areas in USSR is summarized briefly in this paper. Coesite as well as its expansion fracture textures formed during conversion of co-esite into quartz are proposed to be the indicator of ultra-high-pressure metamorphism. The other minerals and mineral assemblages symbolizing ultra-high-pressure include Mg-staurolite, ellenbergerite, jadeite-kynite.talc- kynite and talc - phengite. Diamond represents extremely high-pressure condition. Ultra-high-pressure metamorphism formed at the pressure of more than 2. 8GPa and the temperature from 700 to 840 ℃ requires an abnormally low geothermal gradient, about 7℃/km. The pressures decrease together with temperatures during retrograde metamorphism. Ultra-high-pressure rocks totally restricted within major intracontinental orogenic belts suggest that they may be produced by subduction to depths of more than 90km during continent-continent collision. The rapid tectonic uplift for preservation of coesite may be due to continuous subduction-obduction. The occurrences of ultra-high-pressure rocks in orogenic belts in different areas and at different ages in the world suggest that this type of metamorphism is widely spread other than rare. Obviously.it is important for geologists to study these typical rocks in detail and establish a tectonometamorphic model for ultra-high-pressure metamorphism.
出处
《地质科技情报》
CAS
CSCD
北大核心
1991年第1期17-23,共7页
Geological Science and Technology Information
