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Doctoral thesis
English

Halogens as Tracers of Magma Degassing at Crustal Depths

Contributors

Miranda, Mara Camille

Directors

Zajacz, Zoltan

Number of pages

179

Imprimatur date

2026-08-21

Defense date

2025-05-13

Abstract

The release of fluids from magmas at crustal depths is an essential process for the formation of magmatic-hydrothermal ore deposits. However, magma degassing in transcrustal magmatic systems in arc settings is complex due to the various depth, melt compositions and the interconnected state of magma reservoirs within the crust. This thesis investigates the partition coefficient () of chlorine, bromine, and iodine between silicate melts and aqueous fluids to improve our understanding of magma degassing, fluid migration, and the formation of magmatic-hydrothermal ore deposits. High-pressure and high-temperature experiments were performed to quantify the effects of fluid salinity, pressure, temperature, and melt composition, on the of halogens. The results demonstrate that fluid salinity, pressure, and melt composition exert the strongest controls on halogen partitioning, with Br and I partitioning more strongly into fluids than Cl. New empirical equations were developed to determine halogen partitioning over a wide range of magmatic conditions and incorporated into numerical models of magma degassing in transcrustal magmatic systems. These models show that Br/Cl and I/Cl ratios in melts and exsolved fluids are sensitive proxies to trace crystallization-driven degassing, decompression, and fluid fluxing. This study provides tools to reconstruct volatile evolution in crustal magma reservoirs and constrain processes responsible for magmatic-hydrothermal ore formation.

Keywords

  • Halogen partitioning
  • Chlorine
  • Bromine
  • Iodine
  • Magma degassing
  • Fluid-melt partitioning
  • Experimental geochemistry
  • Magmatic-hydrothermal ore deposits
  • Volatile exsolution
  • Numerical modelling
  • Transcrustal magmatic systems

UNIGE affiliation entities

UNIGE research groups

Citation (ISO format)

MIRANDA, Mara Camille. Halogens as Tracers of Magma Degassing at Crustal Depths. Thèse, 2026. doi: 10.13097/archive-ouverte/unige:196133

Main files (1)

Thesis
18/03/2029

Secondary files (1)

Imprimatur

Identifiers

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Technical informations

Creation

18/09/2026 09:05:12

First validation

29/09/2026 09:10:09

Update

29/09/2026 09:10:09

Status update

29/09/2026 09:10:09

Last indexation

29/09/2026 09:10:11
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