近日，中国科学技术大学郑永飞团队研究了深俯冲大陆地壳无流体与有流体熔融的铁同位素解码。2025年8月21日，《地质学》杂志发表了这一成果。

有流体熔融和无流体熔融是大陆砾岩化学分异的两种主要机制。然而，用传统的地球化学方法解码这些过程仍然具有挑战性。

研究组对中国大别造山带由不同成岩深熔作用机制形成的深熔混辉岩和片麻岩进行了系统的铁同位素分析。黑云母熔融形成混杂岩，Fe³⁺/ΣFe（0.31 ~ 0.44）受限制，δ⁵⁶Fe值（0.06‰~ 0.17‰）均质。而无流体熔融的辉长岩则形成混杂岩和混杂岩片麻岩，其F^e3+/ΣFe（0.26 ~ 0.94）和δ⁵⁶Fe（0.04‰~ 0.61‰）变化剧烈。对部分熔融过程中铁同位素分布的定量模拟表明，在不同的熔融条件下，铁同位素分异受不同矿物组合的控制。

在无流体熔融过程中，反应物云母的Fe³⁺/ΣFe和δ⁵⁶Fe值远高于黑云母，导致互补熔体的δ⁵⁶Fe值较高且呈非均质性。相反，在流体熔融过程中，反应物黑云母和包晶角闪孔具有相似的低Fe³⁺/ΣFe和δ⁵⁶Fe值，导致互补熔体δ⁵⁶Fe值低且均匀。这证实了铁同位素是一种新的陨坑深熔示踪剂，对了解大陆重塑和陨坑内分化至关重要。

附：英文原文

Title: Fe isotope decoding of fluid-absent versus fluid-present melting of deeply subducted continental crust

Author: Er-Lin Zhu, Qiong-Xia Xia, Yi-Xiang Chen, Ren-Xu Chen, Hao-Hong Shu, Zhao-Ya Li, Yong-Fei Zheng

Issue&Volume: 2025-08-21

Abstract: Fluid-present melting and fluid-absent melting are two primary mechanisms for the chemical differentiation of continental crust. However, it is still challenging to decode these processes with conventional geochemical methods. In this study, we present systematic Fe isotope data of anatectic migmatites and gneisses from the Dabie orogen, China, which were formed by different mechanisms of crustal anatexis. Fluid-present melting of biotite generates migmatites with restricted Fe3+/ΣFe (0.310.44) and homogeneous δ56Fe values (0.06‰0.17‰). In contrast, fluid-absent melting of phengite produces migmatites and migmatitic gneisses with dramatic Fe3+/ΣFe (0.260.94) and δ56Fe (0.04‰0.61‰) variations. Quantitative modeling of Fe distribution during partial melting reveals that Fe isotope fractionation is governed by source mineral assemblages under varying melting regimes. During fluid-absent melting, the reactant phengite has much higher Fe3+/ΣFe and δ56Fe values than the peritectic biotite, resulting in high and heterogeneous δ56Fe values in the complementary melt. In contrast, during fluid-present melting, the reactant biotite and peritectic amphibole have similarly low Fe3+/ΣFe and δ56Fe values, leading to low and homogeneous δ56Fe values in the complementary melt. This establishes Fe isotopes as a novel tracer for crustal anatexis, critical for understanding continental reworking and intracrustal differentiation.

DOI: 10.1130/G52997.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52997.1/660735/Fe-isotope-decoding-of-fluid-absent-versus-fluidredirectedFrom=fulltext