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《ADVANCE IN EARTH SCIENCES》 1998-05
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GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF CARBONATITES AND THEIR IMPLICATION FOR TECTONIC SETTINGS

YANG Xue ming YANG Xiao yong (Department of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026) (The Advanced Research Center for Earth Science and Astronomy, The Third World Academy of S  
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 CO 2 saturated asthenoshere mantle at ca.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 asthenospheric mantle at intersection of the geotherm with a volatile poor solidus.③Liquid immiscibility of a carbonaterich silicate magma(nephelinitic/melilititic)produced by partial melting of asthenosheric mantle at intersection of the geothern with a volatile richer solidus.
【Fund】: 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 中国科技大学青年科学基金
【CateGory Index】: P588.15,P597
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