Skip to main content

Research Repository

Advanced Search

Multi-stage subduction-related metasomatism recorded in whiteschists from the Dora-Maira Massif, Western Alps

Harris, Benedict J R; De Hoog, Jan C M; Halama, Ralf; Schertl, Hans-Peter; Chen, Yi-Xiang


Benedict J R Harris

Jan C M De Hoog

Hans-Peter Schertl

Yi-Xiang Chen



Whiteschists from the Dora-Maira massif (Western Alps, Italy) are Mg and K-rich metasomatised granites which experienced ultra-high pressure metamorphism and fluid-rock interaction during Alpine continental subduction. The sources and timing of fluid infiltration are a source of significant debate. In this study we present boron (B) isotopes and other fluid-mobile trace element (FME) concentrations in various generations of phengite from whiteschists and their country rock protoliths to investigate the sources and timing of metasomatic fluid influx. Reconstructed bulk rock concentrations based on modal data and mineral compositions indicate that significant amounts B and other FME were added to the rock during prograde metamorphism, but that this fluid influx postdates the main Mg metasomatic event. High B concentrations (150–350 µg/g) and light δ11B values (-16 to -4 ‰) recorded in phengite point to a B-rich sediment-derived fluid as the main source of B in the whiteschists. Further redistribution of FME during metamorphism was associated with breakdown of hydrous minerals such as talc, phlogopite and ellenbergerite. The source of the Mg-rich fluids cannot be constrained based on the B data in phengite, since its signature was overprinted by the later main B metasomatic event. Rare tourmaline-bearing whiteschists record additional information about B processes. Tourmaline δ11B values (-6 to +1 ‰) are in isotopic equilibrium with similar fluids to those recorded in most phengite, but phengites in tourmaline-bearing samples records anomalous B isotope compositions that reflect later redistribution of B. This study demonstrates the utility of in situ analyses in unravelling complex fluid-rock interaction histories, where whole rock analyses make it difficult to distinguish between different stages of fluid-rock interaction. Polymetasomatism may result in decoupling of different isotopic systems, thus complicating their interpretation. The Dora-Maira whiteschists interacted with multiple generations of fluids during subduction and therefore may represent a long-lived fluid pathway.

Journal Article Type Article
Acceptance Date Sep 11, 2023
Online Publication Date Oct 16, 2023
Publication Date Nov 1, 2023
Deposit Date Sep 12, 2023
Publicly Available Date Oct 26, 2023
Journal Contributions to Mineralogy and Petrology
Print ISSN 0010-7999
Publisher Springer Verlag
Peer Reviewed Peer Reviewed
Volume 178
Issue 11
Article Number 76
Keywords Subduction metasomatism, Ultra-high-pressure metamorphism, Whiteschist, Fluid–rock interaction, Boron isotopes
Publisher URL


Multi-stage subduction-related metasomatism recorded in whiteschists from the Dora-Maira Massif, Western Alps (4.2 Mb)

Copyright Statement
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit

You might also like

Downloadable Citations