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Contrasting Timescales of Volatile Degassing from Hydrous Magmas in Porphyry Copper Systems

Yulia Gruzdeva 1,2, Philipp Weis1,2

  • Affiliations:  1GFZ German Research Centre for Geosciences, Potsdam, Germany; 2Institute of Geosciences, University of Potsdam, Germany

  • Presentation type: Talk

  • Presentation time: Tuesday 16:00 - 16:15, Room S160

  • Programme No: 4.1.6

  • Theme 4 > Session 1

Abstract

The timing and duration of volatile generation from crystallizing magmas and fluid release across the magmatic-hydrothermal interface are complex processes governed by non-linear, dynamic interactions between magmas, rocks, and fluids. The interplay of these processes can lead to the formation of ore deposits or trigger volcanic eruptions. To investigate and quantify these mechanisms, we developed a novel coupled model for magmatic-hydrothermal systems with a consistent formulation for fluid generation and transport with viscous magma flow and porous fluid flow. Our simulations use an up-scaled description of volatile release from reservoir to host rock and realistic magma properties from published experimental and modelling works. The results suggest that the cooling of hydrous magmas can involve distinct phases of volatile release, each with its unique timescale and implications for magmatic and hydrothermal processes during the development of porphyry copper systems. Magma convection with bubble suspension in melt-dominated states leads to homogenization, delaying fluid release and promoting a rapid evolution towards a mush state. The onset of volatile release can be near-explosive, with tube-flow outburst events lasting less than 100 years for high initial water contents, potentially forming hydrothermal breccias and vein stockworks or triggering eruptions. This initial event can be followed by sustained fluid release at moderate rates due to volatile flushing caused by magma convection. Subsequent continuous fluid release from concentric tube rings by radial cooling of non-convecting magma mush lasts <100 kyr. Our simulation results show how voluminous water-rich upper-crustal magma reservoirs can form large porphyry deposits.