近日，巴西地质调查局Carlos E. Ganade团队报道了进变质石榴石在地壳早期熔融阶段发生溶解。相关论文发表在2025年12月24日出版的《地质学》杂志上。

学界普遍认为，石榴石在进变质作用和部分熔融过程中稳定性及体积会增加。然而，早期形成的亚固相线石榴石在熔融开始时究竟会持续存在还是发生分解，仍是一个悬而未决的问题。

研究组通过整合三维X射线断层扫描技术，并对变泥质岩变质序列中经中心切面的石榴石进行高分辨率主微量元素分布制图，追踪了石榴石从亚固相线-超固相线转变至熔融温度（约770°C）的响应过程。与实验及相平衡预测相反，石榴石在部分熔融开始时发生广泛溶解，体积损失超过40%。熔体渗流在石榴石内部形成孔洞网络，使晶体内部与反应性基质相连，显著缩短了熔体-晶体界面处的晶内扩散路径。

这一过程导致石榴石被消耗，并在温度过低、无法发生大颗粒晶内扩散的条件下，引起主微量元素重新分配。该研究结果解释了长期以来关于固相线以上石榴石渐进生长预测与混合岩、麻粒岩中石榴石边部熔体包裹体稀缺之间的矛盾。随着部分熔融的开始，亚固相线石榴石发生反应，成为残留地壳中一个具有渗透性的重稀土元素和钇（HREE-Y）储库。

附：英文原文

Title: Melting the myth: Prograde garnet dissolves during early crustal melting

Author: Lucas R. Tesser, Pierre Lanari, Jacob B. Forshaw, Thorsten A. Markmann, Mathias Hueck, Benita Putlitz, Noralinde de Leijer, Cauê R. Cioffi, Miguel A.S. Basei, Carlos E. Ganade

Issue&Volume: 2025-12-24

Abstract: Garnet is widely thought to increase in stability and volume during prograde metamorphism and partial melting. Yet, whether early-formed subsolidus garnet persists or breaks down when melting begins remains an open question. Here, we integrate 3-D X-ray tomography with high-resolution major- and trace-element mapping of centrally sectioned garnets across a metapelitic metamorphic sequence to track their response from the subsolidus-suprasolidus transition to melting temperatures up to ～770 °C. Contrary to experimental and phase equilibrium predictions, garnet undergoes extensive dissolution at the onset of partial melting, losing >40% of its volume. Melt percolation creates internal cavity networks within garnet, connecting crystal interiors to the reactive matrix, markedly shortening intracrystalline diffusion pathways at the melt-crystal interface. This process leads to the consumption of garnet and results in major- and trace-element redistribution at temperatures too low for intracrystalline diffusion in larger grains. Our findings reconcile the long-standing discrepancy between predicted progressive garnet growth above the solidus and the scarcity of melt inclusions in garnet rims in migmatites and granulites. As partial melting begins, subsolidus garnet reacts and becomes a permeable heavy rare earth elements and yttrium (HREE-Y) reservoir in the residual crust.

DOI: 10.1130/G54000.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G54000.1/723759/Melting-the-myth-Prograde-garnet-dissolves-during