榴辉岩的研究意义及其新进展

SIGNIFICANCE OF THE STUDY OF ECLOGITES AND ITS NEW ACHIEVEMENTS

榴辉岩是由石榴石一单斜辉石组成、具玄武质成分的、在下地壳或上地幔高压条件下结晶(或重结晶)的一种岩石.其研究意义表现在岩石学、矿物学、地球化学和地球物理学等多方面. 在70年代,高温高压实验就已证明玄武岩一榴辉岩的相转变面并不是Moho不连续面.近几年来,在榴辉岩的研究中又取得了不少新的进展, 其中包括1)榴辉岩的产状与成因之间并没有直接的对立关系,其产状也不仅仅三种;榴辉岩可以在很高的水压条件下形成,水压远小于总压可以存在,但并不总是必须的;3)由洋壳变质的榴辉岩是古板块边界的标志,而且记录了汇聚型造山作用的历史,以及地热梯度随时间的变化;4)有些榴辉岩的形成过程是相当复杂的,不能用简单的成因模式加以注释;5)金伯利岩中的榴辉岩包体既可以在地幔内形成,也可以在地壳内形成.

Eclogites are garnet-clinopyroxene rocks with basaltic bulk compositions that crystallized ( or recrystallized ) at relatively high pressure in the lower crust or upper mantle. Kyanite, rutile, clinozoisite, quartz, amphibole or spinel are commonly associated as varietal or accessory phases. The significance in the study of eclogites finds experession in many other areas, such as petrology, mineralogy geochemistry and geophysics. In the 1970's, many high-T and high-p experimental investigations showed that the Moho-discontinuity in stable continental regions is not responsible for the gabbro-eclogite transformation. In recent years, new achievements obtained in the study of eclogites, demunstrate that the occurrences of eclogites are not direcely related to the origin of eclogites, eclogites could have formed at very high H2O pressures, and that PH2o much lower than ptotal may have occurred but was not generally necessary、 The study also shows that eclo-gite representing the metamorphic ocean crust is a mark of old suture line, and has recorded a history of subduction metamorphism and a change of geothermal gradient with time; that forming processes of some eclogites are very complex, can not be explained by a simple origin model and that eclogite xenoliths in kim-berlite can be formed both in the mantle and the crust.