Primary rare earth element enrichment in carbonatites: Evidence from melt inclusions in Ulgii Khiid carbonatite, Mongolia
Primary rare earth element enrichment in carbonatites: Evidence from melt inclusions in Ulgii Khiid carbonatite, Mongolia
复制标题
碳酸岩中原生稀土元素的富集：来自蒙古 Ulgii Khiid 碳酸岩熔体包裹体的证据
DOI：
10.1016/j.oregeorev.2019.103294
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发表时间：
2020-02-01
影响因子：
3.3
通讯作者：
Wei, Chunwan
中科院分区：
文献类型：
--
作者：
Feng, Meng;Song, Wenlei;Wei, Chunwan
碳酸岩富含稀土元素，是世界上最重要的稀土资源。然而，机制，集中这些元素在碳酸岩岩浆过程中仍然受到很大的限制。在这里，我们报告的磷灰石托管熔融包裹体的发生从乌尔吉Khiid碳酸岩，蒙古，并使用这些重建稀土元素的浓度和模式的演化，早期，原生碳酸岩岩浆。熔体包裹体由方解石、透辉石、金云母、磁铁矿、黄铁矿、独居石、黄铁矿和磷酸盐玻璃等多种多晶子矿物组合组成。加热淬火实验表明，包裹体的均匀化温度高于1200 ℃，并产生三个不混溶的液相（即，磷酸盐-、硅酸盐-和铁-硅酸盐-熔体）。磷酸盐熔体的稀土元素含量远高于硅酸盐熔体。因此，我们认为，熔融包裹体捕获的稀土，磷和硅酸盐丰富的碳酸盐熔体通过碳酸盐-硅酸盐液体不可渗透性产生。在这一过程中，稀土元素和磷优先纳入碳酸盐熔体。随着随后的稀土和磷贫碳酸盐和硅酸盐矿物的晶体分馏，分离的碳酸盐熔体变得P-REE饱和，形成稀土矿物和不混溶的富稀土磷酸盐熔体。磷酸盐熔体在不混溶过程中对稀土元素具有高效富集作用，对富磷碳酸岩岩浆中稀土元素收支起着至关重要的控制作用。
Carbonatites are abundant in the rare earth elements (REE), and they host the most important REE resources in the world. However, the mechanisms that concentrate these elements during carbonatitic magmatic processes are still poorly constrained. Here, we report the occurrence of apatite-hosted melt inclusions from the Ulgii Khiid carbonatites, Mongolia, and use these to reconstruct the evolution of REE concentrations and patterns in early, primary carbonatite magma. The melt inclusions consist of a varied polycrystalline assemblage of daughter minerals, including calcite, diopside, phlogopite, magnetite, pyrite, monazite, parisite, and a phosphate glass which is remarkably enriched in REE. Heating-quenching experiments show that the homogenization temperatures of the inclusions are above 1200 degrees C and produce three immiscible liquid phases (i.e., phosphate-, silicate-, and Fe-silicate-melt). The phosphate melt has much higher REE content than the silicate melts. We, therefore, suggest that the melt inclusions trapped a REE-, P- and silicate-enriched carbonate melt produced via carbonate-silicate liquid immiscibility. During this process, both REE and P preferentially incorporated into the carbonate melt. With subsequent crystal fractionation of REE- and P-poor carbonate and silicate minerals, the separated carbonatitic melt becomes P-REE-saturated, forming REE minerals and an immiscible REE-rich phosphate melt. The phosphate melt is highly efficient at concentrating REE during the immiscibility process and plays a crucial role in controlling the REE budget in the P-rich carbonatite magmas.