Experimental Petrological Study of Carbonatite and Its Significances on the Earth Deep Carbon Cycle

详细信息   

• 责任者：Song Wenlei (School of Earth and Space Sciences ; Peking University ; Beijing 100871 ; China) ; Xu Cheng
• 刊名：Geological Review
• 出版年：2012
• 卷期：58(4)
• 关键词：碳酸岩 ; carbonatites ; 火成岩 ; igneous rocks ; 碳循环 ; carbon cycle
• 页码：p.726-744
• 图表：illus., 2 tables, 161 refs.
• 分类号：0801
• issnNo：ISSN0371-5736
• isbnNo：CN11-1952/P

摘要

Carbonatites are rare mantle-derived rocks on the Earth＇s surface. Experimental studies have shown that near-solidus melts （ extremely low degree melting, usually 〈 1% ） formed in a carbonated peridotite and crustal cyclic materials such as carbonated eclogite and pelite at pressures of more than 3 GPa have carbonatite compositions. Note that of all the major subducted rock types, carbonated pelites have the lowest melting point, and are by far the most enrichment in recycling CO2, alkalis and incompatible elements. Carbonatite could also be fromed as products of fractional crystallization or liquid immiscibility of carbonated silica-undersaturated magmas such as nephelinite explaining their field relationships between carbonatites and associated silicate rocks. More generally, it has been also shown that a very low degree of melting produces a carbonatitic liquid whereas a high degree of melting produces kimberlitic like or even basaltic like melts. Due to their low density and viscosity and highly reactive nature, carbonatite melts and fluids are considered to be one of the most important metasomatic agents in the lithospheric mantle and cause mantle inhomogeneties. Experimental study of various carbonate silicate mineral assemblages shows that a significant amount of carbonates can be transported to the deep mantle without decarbonation during melting beneath the island arcs and those carbonates in the deep mantle likely induces the formation of carbonatitic melts, this points out that the the subduction of crustal carbonate rocks be likely to have play an very important role in the genesis of the carbonatite. However, some questions such as the initial composition of carbonatites, the evolution of the magma, the role of mantle metasomatism and how carbon returns back to surface are still topics of considerable debate. There are many carbonatites in China, so enhance the Geological and geochemical combined with the high P-T experiments study of carbonatites will test current theories about carbonatite genesis and supply new scientific clues to some major geological events due to their special petrogenesis background.