中国地质科学院袁学银和北京科技大学钟日晨等报道了了从碳酸盐岩浆到热液卤水的转变。相关论文发表在2023年7月19日出版的《科学进展》杂志上。

研究人员使用热液金刚石压砧和拉曼光谱仪研究了 Na₂CO₃-H₂O 系统在高达 700°C 和 11.0 kbar 下的压力-温度-成分(P-T-X)特性。 他们的研究结果表明，在高P-T条件下，Na₂CO₃ 变得越来越可溶，导致熔体-流体不混溶的消失，以及在地壳深部条件下，从 Na₂CO₃ 熔体到热液的连续转变。

鉴于在高度演化的碳酸盐岩系统中 Na₂CO₃ 的丰富，研究人员认为深部碳酸盐岩中连续的熔体-流体转变导致稀土元素在盐水-熔体中充分富集，形成经济矿体，而在浅部系统中，与同岩浆卤水相比，稀土元素优先分配到碳酸盐岩浆中，并分散到在经历了有限分馏的碳酸盐岩中。

据悉，碳酸盐岩是稀土元素(REEs)最重要的原始来源。虽然碳酸盐矿物的分离结晶导致剩余熔体中挥发物、碱金属和稀土元素的富集，但从碳酸盐岩浆向热液卤水的转变仍不清楚。

附：英文原文 

Title: Transition from carbonatitic magmas to hydrothermal brines: Continuous dilution or fluid exsolution

Author: Xueyin Yuan, Richen Zhong, Xin Xiong, Jing Gao, Yubo Ma

Issue&Volume: 2023-07-19

Abstract: Carbonatites are the most important primary sources for the rare earth elements (REEs). While fractional crystallization of carbonate minerals results in the enrichment of volatiles, alkalis, and REEs in the remaining melts, the transition from carbonatitic magmas to hydrothermal brines remains unclear. Here, we investigated the pressure-temperature-composition (P-T-X) properties of the Na₂CO₃-H₂O system up to 700°C and 11.0 kbar using a hydrothermal diamond anvil cell and a Raman spectrometer. Our results show that Na₂CO₃ becomes increasingly soluble under high P-T conditions, leading to the disappearance of melt-fluid immiscibility and the continuous transition from Na₂CO₃ melts to hydrothermal brines under deep crustal conditions. Given the abundance of Na₂CO₃ in highly evolved carbonatitic systems, we suggest that the continuous melt-fluid transition in deep-seated carbonatites results in REEs being sufficiently concentrated in the brine-melts to form economic ore bodies, whereas in shallow systems, REEs preferentially partition into carbonatitic magmas over synmagmatic brines and disperse in carbonatite rocks that underwent limited fractionation.

DOI: adh0458

Source: https://www.science.org/doi/10.1126/sciadv.adh0458