碳酸岩的特征、分类及其成因分析

Basic characteristics and genetic analysis of carbonate rocks

碳酸岩是世界上轻稀土元素和Nb等战略金属元素的主要来源,对技术发展至关重要,具有重要研究意义和经济价值。碳酸岩源于交代富集地幔且受地壳同化混染影响小,被认为是揭示地幔地球化学的“探针岩石”。因此,碳酸岩受到国内外地质学家广泛重视,但目前关于碳酸岩的成因机制存在不同的认识。本文简要总结了碳酸岩的构造背景、基本特征、地球化学特征及碳酸岩分类,重点介绍了幔源与壳源碳酸岩的成因机制及二者的判别特征。幔源碳酸岩形成机制有3种:(1)地幔低程度部分熔融;(2)从富CO_(2)碱性硅酸盐岩浆中以液态不混溶的形式分离;(3)富CO_(2)硅酸盐岩浆分离结晶。壳源碳酸岩主要由中酸性岩浆侵入、幔源基性岩浆上侵等引起的含碳酸盐矿物的表壳部分熔融形成。

Carbonatite is the main source of light rare earth elements and Nb and other strategic metal elements in the world,which is of great importance to technological development and has important research significance and economic value.Carbonates are derived from the metasomatic enriched mantle and are not affected by crustal assimilation and contamination,so they are considered as"probe rocks"to reveal mantle geochemistry.Therefore,carbonate rocks have been widely paid attention to by geologists at home and abroad,but there are different understandings about the genetic mechanism of carbonate rocks.This paper briefly summarizes the tectonic setting,basic characteristics,geochemical characteristics and classification of carbonates,and focuses on the genetic mechanism and discriminative characteristics of mantle and crust carbonates.There are three kinds of formation mechanisms of mantle-derived carbonates:①low-degree partial melting of mantle;②Separated from CO_(2)rich alkaline silicate magma in liquid immiscible form;③Separation crystallization of CO_(2)-rich silicate magma.There are four kinds of formation mechanisms of carbonate rocks:①intermediate-acid magmatic intrusion limestone;②marble remelting;③Strong regional metamorphism;Upwelling of high-temperature mantle-derived basic magma.