Journal Article

The Mg‐Fe Isotope Compositions and Geochemical Effects of Supercritical Fluids: Constraints From an Ultrahigh‐Pressure Eclogite‐Vein System in the Dabie Orogen

Chen, Tie‐Nan, Pan, Zheng‐Hua, Zheng, Yong‐Fei, Chen, Ren‐Xu, Sun, Guo‐Chao, Gan, Xue‐Jing

2025

Overview

Supercritical fluids are ideal media for mass transfer from the subducting slab into the mantle wedge. However, little is known about the Mg‐Fe isotope compositions of supercritical fluids in subduction zones. Here, we present the Mg‐Fe isotope data for a coesite‐bearing eclogite‐vein system, which is closely associated with supercritical fluids, from the Dabie Orogen in China. The results reveal the geochemical effects of supercritical fluids under subarc conditions. The eclogites close to the eclogitic vein formed by supercritical fluids have not only lighter Mg isotope compositions for whole‐rock but also higher δ26Mg and δ56Fe values in separate minerals than those distant from the vein. The ultrahigh‐pressure eclogitic vein has δ26Mg values of +0.17 to +0.23‰ and δ56Fe values of +0.26 to +0.35‰. These observations indicate that vein‐forming supercritical fluids have heavy Mg‐Fe isotope compositions and are produced by the contributions of omphacite from eclogite during the dissolution‐precipitation process. The supercritical fluids released from eclogite at subarc depths are recovered to have high δ26Mg values of +0.30 to +0.37‰ and δ56Fe values of +0.34 to +0.49‰ and thus can contribute to arc lavas with heavy Mg‐Fe isotopic compositions. On the basis of the mixing modeling between subduction zone fluids and mantle wedge peridotites, we propose that the supercritical fluids have an effect on the mantle wedge to drive it to incorporate slightly heavier Fe isotopes.

• Publisher: John Wiley & Sons, Inc
• Subject: Aqueous solutions / Exhumation / Fluids / Geochemistry / Iron / Isotope composition / Isotopes / Mass transfer / Subduction / Subduction zones / Veins (geology)