| 火成碳酸岩的实验岩石学研究及对地球深部碳循环的意义 |
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| 引用本文： | 宋文磊,许成,刘琼,王林均,吴敏,曾亮.火成碳酸岩的实验岩石学研究及对地球深部碳循环的意义[J].地质论评,2012,58(4):726-744. |
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| 作者姓名： | 宋文磊 许成 刘琼 王林均 吴敏 曾亮 |
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| 作者单位： | 1. 北京大学地球与空间科学学院,北京,100871
2. 中国科学院地球化学研究所地球深部物质与流体作用地球化学研究室,贵阳,550002;中国科学院研究生院,北京,100049 |
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| 基金项目： | 本文为国家自然科学基金资助项目（编号40973040,41173033）的成果。 |
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| 摘 要： | 火成碳酸岩是地表出露较少的幔源岩石之一。实验岩石学研究表明碳酸盐化的橄榄岩和循环的地壳物质(如碳酸盐化榴辉岩或泥质岩)的低程度(<1%)部分熔融均可以产生碳酸岩质的熔体,其中碳酸盐化泥质岩具有最低的熔融温度且更加富碱质、CO2和不相容元素;富CO2的霞石质等硅酸盐岩浆也可以通过不混溶或分离结晶作用产生碳酸岩,用于解释碳酸岩在空间中常与碱性硅酸岩的共生关系。由于碳酸岩熔体具有极低的粘度和高的活性,形成后在上升过程中会将二辉橄榄岩转变为异剥橄榄岩,是引起地幔交代作用和地幔地球化学不均一性的重要介质之一。实验表明在俯冲作用过程中,大多数的碳酸盐在位于岛弧之下的含水熔融并不分解而是被带入到深部地幔并且稳定存在,含碳地幔的熔融又会形成碳酸岩质的熔体,这说明俯冲循环物质可能对碳酸岩的成因也起着重要的作用。然而,对于碳酸岩的初始熔体成分、岩浆演化、地幔交代作用、成矿特征以及碳从地球深部返回到地表的途径和过程等都存在着很大的争议。我国火成碳酸岩出露相对较多,分布广泛,因此,加强我国碳酸岩以及伴生硅酸岩的成因研究,同时开展与碳酸岩相关的实验岩石学工作,不仅可以检验现有的成因理论,而且有助于提高我国对火成碳酸岩的研究水平;由于其特殊的成因背景,还可为许多存在很大争议的重大地质事件提供新的科学依据。
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| 关 键 词： | 火成碳酸岩 部分熔融 液态不混溶 分离结晶 地幔交代 碳循环 |
Experimental Petrological Study of Carbonatite and Its Significances on the Earth Deep Carbon Cycle |
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| SONG Wenlei
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XU Cheng
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LIU Qiong
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WANG Linjun
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WU Min
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ZENG Liang.Experimental Petrological Study of Carbonatite and Its Significances on the Earth Deep Carbon Cycle[J].Geological Review,2012,58(4):726-744. |
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| Authors: | SONG Wenlei XU Cheng LIU Qiong WANG Linjun WU Min ZENG Liang |
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| Institution: | 1)1) School of Earth and Space Sciences,Peking University,Beijing,100871;2) Institute of Geochemistry,Chinese Academy of Sciences,Guiyang,550002;3) Graduate School,Chinese Academy of Sciences,Beijing,100039 |
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| Abstract: | 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. |
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| Keywords: | carbonatite partial melting liquid immiscibility fractional crystallization mantle metasomatism carbon cycle |
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