Carbonatites are igneous rocks formed in the crust by fractional crystallization of carbonate-rich parental melts that are mostly mantle derived. They dominantly consist of carbonate minerals such as calcite, dolomite, and ankerite, as well as minor phosphates, oxides, and silicates. They are emplaced in continental intraplate settings such as cratonic interiors and margins, as well as rift zones, and rarely on oceanic islands. Carbonatites are cumulate rocks, which are formed by physical separation and accumulation of crystals that crystallize from a melt, and their parental melts form by either ( a) direct partial melting of carbonate-bearing, metasomatized, lithospheric mantle producing alkali-bearing calciodolomitic melts or ( b) silicate-carbonate liquid immiscibility following fractional crystallization of carbonate-bearing, silica-undersaturated magmas such as nephelinites, melilitites, or lamprophyres. Their emplacement into the crust is usually accompanied by fenitization, alkali metasomatism of wallrock caused by fluids expelled from the crystallizing carbonatite.Carbonatites are major hosts of deposits of the rare earth elements and niobium, and the vast majority of the global production of these commodities is from carbonatites. ▪ Carbonatites are igneous rocks formed from carbonate-rich magmas, which ultimately formed in Earth's upper mantle. ▪ Carbonatites are associated with economic deposits of metals such as the rare earth elements and niobium, which are essential in high-tech applications. ▪ There are more than 600 carbonatites in the geological record but only one currently active carbonatite volcano, Oldoinyo Lengai in Tanzania.

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碳酸岩：分类、来源、演化和定位

碳酸岩是地壳中由富含碳酸盐的母体熔体分步结晶而形成的火成岩，这些母体熔体主要来自地幔。它们主要由碳酸盐矿物组成，例如方解石、白云石和铁白云石，以及少量磷酸盐、氧化物和硅酸盐。它们位于大陆板内环境中，例如克拉通内部和边缘以及裂谷带，很少位于海洋岛屿上。碳酸岩是堆积岩，是通过从熔体中结晶的晶体的物理分离和积累而形成的，其母体熔体是通过以下两种方式形成的：（a）含碳酸盐、交代化的岩石圈地幔直接部分熔融，产生含碱钙白云岩熔体或(b) 含碳酸盐、二氧化硅不饱和岩浆（例如霞石、黄长石或煌斑岩）分步结晶后的硅酸盐-碳酸盐液体不混溶性。它们进入地壳通常伴随着铁硝化作用，即由结晶碳酸岩排出的流体引起的围岩碱交代作用。碳酸岩是稀土元素和铌矿床的主要宿主，这些商品的全球产量绝大多数是来自碳酸岩。 ▪ 碳酸岩是由富含碳酸盐的岩浆形成的火成岩，最终形成于地球的上地幔中。 ▪ 碳酸岩与稀土元素和铌等金属的经济矿藏有关，这些金属对于高科技应用至关重要。 ▪ 地质记录中存在超过 600 处碳酸岩，但目前只有一处活跃的碳酸岩火山，即位于坦桑尼亚的 Oldoinyo Lengai。