蛇纹岩体中的硬玉岩与异剥钙榴岩

Relationship between jadeitite and rodingite in serpentinite complex.

硬玉岩是一种稀少的岩类,常以构造岩包体和脉体的型式产出在蛇纹岩中。本文着重介绍与蛇纹岩化过程密切相关的硬玉岩。这类硬玉岩总是出现在洋壳俯冲碰撞带中,常常与蓝片岩、偶尔也与榴辉岩伴生。通过研究硬玉岩的矿物组合、化学成分和结构构造,综合世界各地硬玉岩产状,可将硬玉岩从广义的变质成因上分为三类,即:在蛇纹岩体中、或其它岩类包体中由交代作用形成的硬玉岩脉体;蛇纹岩中的构造岩成因岩石包体经固相变质作用后形成的块状硬玉岩:以及介于上述两者之间,由变质和交代的共同作用形成的硬玉岩。此外,还对交代成因的硬玉岩在蛇纹岩化过程中与异剥钙榴岩化作用的关系从流体及其化学成分演化的角度进行了分析和研究。提出了在海底和俯冲带上板片的构造背景下硬玉岩形成的模式。

Jadeitite is a well known but rare rock type that is found only in a few places in the world. Jadeites are always found in the subduction and subsequent continental collision zone, associated frequently with blueschist facies and occasionally with eclogite facies. Based on the investigation of mineral assemblages, bulk chemical composition, microscope textures and the occurrences of the distribution of jadeitites worldwide, three types of jadeitite have been classified in the text. These, which all occur in tectonic rock inclusions in serpentinite body, are jadeitite veins produced from metasomatic process along the fractures in the serpentinites; massive jadeitites resulted from metamorphic process, and jadeitites formed from mixing processes of metasomatism and metamorphism. In addition, the paper highlights the relationship between jadeitites and rodingites during serpentinization by studying chemical characteristics and evolution of the fluid for forming these two rocks, and proposes a model for the formation of jadeitite in ocean-floor and in the super subduction zone (SSZ) background.