Advances in Earth Science
• Articles •
1,2,M. J. Le Bas
Yang Xueming,Yang Xiaoyong,M. J. Le Bas. GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF CARBONATITES AND THEIR IMPLICATION FOR TECTONIC SETTINGS[J]. Advances in Earth Science, 1998, 13(5): 457-466.
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 CO2 saturated 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.