壳源碳酸岩特征、成因及意义  

Characteristics,genesis and implication of crustal-derived carbonatites.

作　　者：苏本勋[1,2] 王静 李晓春 朱明帅 SU BenXun;WANG Jing;LI XiaoChun;ZHU MingShuai(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2022年第12期3747-3759,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42172241);中国科学院青年创新促进会共同资助.

摘　　要：自1999年Lentz David R.重新提出碳酸岩壳源成因以来,已有越来越多壳源成因碳酸岩实例的报道。本文对近二十年来发现的壳源成因碳酸岩的时空分布、产出特征、岩石矿物学特点、地球化学特征以及成因机制进行了总结,对该类碳酸岩成因研究的意义和研究方向进行了展望。壳源碳酸岩在空间上均分布于造山带内部,并以克拉通边缘的造山带为主,在特提斯造山带和中亚造山带中分布最为集中;时代上从元古代到新生代均有发育,不同时代的岩体在地球化学组成上有所差异;其围岩多为经历过高级变质的花岗片麻岩和大理岩组成的混合岩;成分上多为钙质,微量元素具较弱的轻重稀土分异,显著的Eu、Nb、Ta、Zr和Hf负异常及Pb和Sr正异常,Sr-Nd同位素组成介于球粒陨石和大陆地壳演化线之间,C-O同位素介于原生碳酸岩浆与沉积碳酸盐岩之间。这些特征在一定程度上异于克拉通内的碳酸岩,而多与造山带内的碳酸岩相似。实验岩石学工作揭示方解石和白云石在地壳深度、温度低至650℃以及有足够多水参与的情况下可发生部分熔融而形成碳酸盐岩浆,而高级区域变质作用过程中释放的变质流体或热液卤水有助于碳酸盐矿物的部分熔融。这种方式形成的碳酸岩在矿物组合及某些地球化学特征方面与其母岩大理岩、灰岩或白云岩具有相似性。因此,鉴于壳源碳酸岩规模较小且多与其母岩共存,厘定是否发生过部分熔融尚存在一定难度,其成因机制亦存在较多争议。壳源碳酸岩浆的成因机制包括中酸性侵入体引起碳酸盐岩熔融、基性岩浆高温热流引起碳酸盐岩熔融、强烈区域变质作用造成碳酸盐岩部分熔融和大理岩深熔作用。壳源成因碳酸岩的发现对以往碳酸岩成因上的疑惑给出了合理解释,亦对主流的碳酸岩幔源成因观点提出了挑战;对碳酸岩用于反演地幔演化、深There are increasing reports of crustal-derived carbonatites in the world since Lentz David R.revisited the crustal derivation of some carbonatites.This paper focuses on summary of temporal and spatial distribution,occurrence,mineral and rock characteristics,geochemical features,and genetic mechanism of crustal-derived carbonatites reported in last twenty years,and sheds some new outlooks on carbonatite genesis.Crustal-derived carbonatites all occur within orogenic belts,particularly Tethyan Orogenic Belt and Central Asian Orogenic Belt.They span an age range from Proterozoic to Cenozoic with geochemical variations with time.Their country rocks are generally dominated by granitic gneisses and marbles,which had undergone high-grade metamorphism.Geochemically,the crustal-derived carbonatites are mainly calcio-carbonatite and display moderate REE differentiation with negative anomalies of Eu,Nb,Ta,Zr and Hf and positive anomalies of Pb and Sr in trace element patterns.They are plotted between chondrite and continental crust evolution lines in Sr and Nd isotope correlation diagram and between primary mantle-derived carbonatite and limestone in C and O isotope correlation diagram.These features are in some certain distinctive from cratonic carbonatites and resemble much of orogenic carbonatites.Experimental results show that partial melting of calcite and dolomite is feasible at upper crustal pressures and temperatures as low as 650℃if sufficient H 2O is present.Partial melting can be enhanced by infiltration of metamorphic fluids or hydrothermal brines expelled from nearby silicate rocks.The mineral assemblages and geochemical signatures of anatectic carbonatites resemble those of marbles and their limestone or dolostone protoliths.Therefore,establishing that partial melting has occurred may not be straightforward,particularly if melt migration was limited so that the anatectic carbonatite melts did not escape from the(meta)sedimentary source rocks.The genesis of crustal-derived carbonatites is still debated,and th

关 键 词：碳酸岩 壳源 造山带 大理岩 部分熔融 地壳混染 

分 类 号：P588.15[天文地球—岩石学] P595[天文地球—地质学]