碳酸岩是研究地幔组成和深部演化的重要岩石类型之一，与稀土和稀有金属成矿关系密切，一直是国际地学研究的热点。碳酸岩常产于裂谷环境，近年来越来越多的碳酸岩在造山带被发现，并常伴生（超）大型的稀土矿床。蒙古国南部碰撞造山作用广泛发育，区域内出露大量中生代碳酸岩，其中大部分碳酸岩与稀土成矿密切相关，但关于碳酸岩及相关稀土矿床的成因仍缺乏系统研究。本申请选择蒙古国南部Lugiin Gol和Ulgii Khiid两处富REE碳酸岩为研究对象，通过系统的矿物学、岩石学、年代学、流体-熔融包裹体、地球化学和矿床地质研究工作，查明碳酸岩及相关稀土矿体中矿物的共生组合，结晶顺序及成分；厘定碳酸岩的成岩成矿年代；探究REE在碳酸岩演化过程中迁移和富集成矿作用；揭示碳酸岩母源岩浆性质及地幔源区特征，以及碳酸岩成岩成矿作用的大地构造背景，为区域构造演化提供约束，以期完善碳酸岩成岩成矿理论。

Mantle-derived carbonatite plays important role in studying composition and evolution of the mantle. The carbonatite is also rich in rare earth and rare metal mineral resources, render carbonatites always as research focus worldwide. Most of the presently known carbonatite intrusions generally occur in anorogenic settings related to intracontinental rifting. Whereas more and more carbonatites emplaced in orogenic setting have been discovered in recent years, with most of them host large REE deposits. For example, a number of Mesozoic carbonatite intrusions have been discovered in Southern Mongolia where the crust has experienced intensive and episodic tectonic and magmatic processes as a result of convergent orogenies. REE mineralization was closely associated with these carbonatite complexes. However, there is lack of systematic and detailed studies of petrogenesis and metallogenesis for these carbonatites. In this proposal, we choose the representative Lugiin Gol and Ulgii Khiid REE-rich carbonatite intrusions for a systematic petrological, mineralogical, geochemical, fluid-inclusion and geochronological study. We plan to investigate mineralogical assemblage, crystallization sequence and geochemical composition of major minerals, determine rock- and ore-forming ages of the carbonatite intrusions and related REE deposits with high-precision radiometric methods, and understand migration and enrichment mechanisms of the REEs during the evolution of carbonatitic magmas. We also propose to use C-O-Sr-Nd isotopic tracers to analyze the carbonatites and to constrain characteristics of their mantle source. A major objective is to determine the tectonic background of petrogenesis and metallogenesis of carbonatites. We believe the proposed study would enhance our understanding of petrogenesis and REE metallogenesis of carbonatites and constrain the geotectonic evolution in the region.