碳酸岩的地质地球化学特征及其大地构造意义

doi:10.11867/j.issn.1001-8166.1998.05.0457

地球科学进展 ›› 1998, Vol. 13 ›› Issue (5): 457 -466. doi: 10.11867/j.issn.1001-8166.1998.05.0457

杨学明 ^1,2，杨晓勇 ^1,2，Ｍ.Ｊ.Le Bas ³

1.中国科技大学地球和空间科学系合肥 230026；2.第三世界科学院中国科学技术大学地球科学和天文学高级研究中心合肥 230026；3.Department of Geology, University of Leicester, Leicester LEI 7RH, U. K.

收稿日期:1997-12-19 修回日期:1998-05-29 出版日期:1998-10-01
通讯作者: 杨学明
基金资助:
中国科学院留学经费择优支持回国工作基金、国家教委科研基金和中国科技大学青年科学基金资助。

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF CARBONATITES AND THEIR IMPLICATION FOR TECTONIC SETTINGS

Yang Xueming ^1,2,Yang Xiaoyong ^1,2,M. J. Le Bas ³

1.Department of Earth and Space Sciences, University of Science and T chnology of China, Hefei 230026; 2.The Advanced Research Center for Earth Science and Astronomy, The Third World Academy of Science, USTC, Heifei 230026; 3.Department of Geology, University of Leicester, Leicester LE1 7RH, U. K.

Received:1997-12-19 Revised:1998-05-29 Online:1998-10-01 Published:1998-10-01

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从已知碳酸岩的地质产状、岩石学特征、Nd-Sr-Pb-O-C同位素及痕量元素地球化学特征数据，结合高温高压实验岩石学资料，论述了其地幔源区的物质成分、交代过程软流圈地幔部分熔融机制和碳酸岩岩浆的演化模型。碳酸岩既可以产生于拉张岩石圈构造背景，也能够产生于挤压而派生的引张岩石圈构造背景。前者以产于裂谷环境、与硅酸不饱和过碱性岩构成环状碳酸岩—碱性杂岩为特征，主要由起源于软流圈地幔的霞石质超基性—基性岩浆经液态不混溶作用而形成；后者产于碰撞造山过程中派生的引张岩石圈断裂带，以单一的透镜状、条带状和似层状碳酸岩体为标志，直接由导源岩石圈富集地幔的低程度部分熔融作用而产生的碳酸岩浆侵入或喷发所形成。

关键词: 碳酸岩, 霓长岩, 同位素和痕量元素地球化学, 岩石圈引张构造环境, 地幔交代作用, 热地幔柱

This contribution reviews on the chemical compositions of the mantle sources of carbonatites, mantle metasomatism, mechanisms of partical melting in asthemospheric mantle and the evolution models for carbonatite magmas based on the occurrences, petrologic characteristics and Nd-Sr-Pb isotope and trace element data of the known carbonatites in the world and experiment petrologic data. Carbonatite could not only be produced in extentional tectonic setting in lithosphere, such as continental rift, but also be formed in locally derivative spreading setting on a compressive tectonic background. The former is characterized by association with peralkaline rocks forming ring complexes and mainly is derived from the asthenospheric mantle as a nephelinitic ultrabasicbasic magmas and then through liquid immicibility, but the later is characterized by its occurrence as a single lens and banded carbonatitic intrusion and/or extrusion along extentional lithospheric fractures resulted from continental collsion and in such case carbonatite could directly be produced by very small partial melting of the lithospheric mantle.
There are three cabonatite origin processes that probably happen above a mantle plume or different parts of a mantle plume, which are not mutually exclusive.①Partial melting of CO₂saturated asthenoshere mantle atca. 100 km depth to produce Na-Mg-rich carbonatite magma,no associated silicate rocks.②Fractional crystallization of carbonate-bearing undersaturated silicate magmas(nephelinitic/melilititic) produced by partial melting of sthenospheric mantle at intersection of the geotherm with a volatile-poor solidus. ③Liquid immiscibility of a carbonaterich silicate magma(nephelinitc/ melilititic) produced by partial melting of asthenosheric mantle at intersection of the geothern with a volatile-richer solidus.

Key words: Carbonatite, Fenite, Isotope and trace element geochemistry, Extentional tectonic setting in lithosphere, Mantle metasomatism, Plume.

中图分类号:

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