Periodic Reporting for period 3 - PROMOTING (PROgrade metamorphism MOdeling: a new petrochronological and compuTING framework)
Période du rapport: 2023-06-01 au 2024-11-30
The main objective of PROMOTING is to quantify the fluxes of aqueous fluids and silicate melts released during prograde metamorphism in the Earth's interior and to model fluid pathways. Understanding the behaviour of these fluids is crucial as they play an important role in earthquake generation, arc magmatism, continental crustal growth and global geochemical cycles. However, the task is challenging because direct observation in metamorphic environments is impossible and (indirect) geophysical observations do not have the necessary spatial resolution. In addition, the presence of fluid in the grain boundary network of a metamorphic rock is important as it acts as a catalyst, reducing the kinetic barriers to mineral dissolution and growth. The presence of fluid is often invisible when the rock is dried and exhumed to the surface. The only evidence is preserved in the isotopic composition of minerals and the textures of dissolution-precipitation.
The aim of PROMOTING is to develop new analytical tools, modelling frameworks and computer programs to track and simulate fluid-rock interaction processes and fluid flows in the lithosphere. The project focuses on the quantification of (1) aqueous fluid fluxes, e.g. during oceanic subduction, using natural examples from the Alps and the Cyclades, and (2) silicate melt fluxes, e.g. during partial melting of continental crust, using the El Oro Massif in Ecuador as a natural case study. Estimates from the natural record are critical to quantify key model parameters such as permeability under conditions where they cannot be estimated experimentally. The study of the collected samples requires advanced surface analysis and 3D characterisation of grain shapes and textures. To achieve this goal, several data analysis and reduction techniques are being developed in PROMOTING. In addition, new computational models will be developed to simulate prograde metamorphism: (1) a multi-rock petro-geochemical model including a rock failure model to simulate fluid extraction and (2) a multi-phase reactive flow model to simulate melt generation and migration including chemical advection.
The aim of PROMOTING is to develop new analytical tools, modelling frameworks and computer programs to track and simulate fluid-rock interaction processes and fluid flows in the lithosphere. The project focuses on the quantification of (1) aqueous fluid fluxes, e.g. during oceanic subduction, using natural examples from the Alps and the Cyclades, and (2) silicate melt fluxes, e.g. during partial melting of continental crust, using the El Oro Massif in Ecuador as a natural case study. Estimates from the natural record are critical to quantify key model parameters such as permeability under conditions where they cannot be estimated experimentally. The study of the collected samples requires advanced surface analysis and 3D characterisation of grain shapes and textures. To achieve this goal, several data analysis and reduction techniques are being developed in PROMOTING. In addition, new computational models will be developed to simulate prograde metamorphism: (1) a multi-rock petro-geochemical model including a rock failure model to simulate fluid extraction and (2) a multi-phase reactive flow model to simulate melt generation and migration including chemical advection.
The work carried out since the beginning of the PROMOTING project along the three axes of "new analytical developments", "application to the study of natural rocks", "development of new modelling programmes" is reported below.
a. Analytical developments:
(a1) An advanced analytical technique for quantitative compositional mapping of LA-ICPMS was developed and implemented in the open source software XMapTools, which is already available for public use (https://github.com/xmaptools(s’ouvre dans une nouvelle fenêtre)). New tools for the classification of complex datasets have also been developed and implemented. The method and application examples of element mobility during partial melting have been published in Markmann et al. (2024).
(a2) A new machine learning strategy and a program, garNET, have been developed for the classification of tomography data and the automated identification of grain shapes in 3D. This technique has been used to localise in key samples where garnet has been spatially dissolved by interacting with an aqueous fluid at high pressure conditions. This new technique has significant potential to easily distinguish in any sample whether the metamorphic fluid responsible for garnet dissolution has flowed along channels or pervasively through the grain boundary network. The work has been published in Hartmeier et al. (2024).
b. Applications: Several case studies were selected to study (b1) aqueous fluid flows (b2) and the consequences of fluid-rock interaction processes on the rock record, and (b3) melt flows.
(b1) Several localities in the western Alps (Lago di Cignana, Zermatt) and in the Cyclades (Syros) were selected for further investigation along the theme of "fluid flows in subduction zones". Key samples and geological data were collected during several field campaigns at the different sites. The samples were analysed in the laboratory and are analysed by EPMA, LA-ICPMS and SIMS. A proof-of-concept study was published (Bovay et al. 2021) demonstrating that in-situ oxygen isotope analyses can be used to quantify critical parameters of fluid flow during high-pressure metamorphism. A second paper was published for the Lago di Cignana site (Rubatto et al. 2023).
(b2) The possible consequences of element redistribution by aqueous fluid during prograde metamorphism were investigated using a bulk rock composition database for pelites (Forshaw & Pattison, 2022) and a newly created bulk rock composition database for metabasites (Forshaw et al., 2024).
(b3) Key samples and geological data were collected from the El Oro metamorphic complex in southern Ecuador during a field campaign in 2022 and analysed in the laboratory in 2023 and 2024. Geochronological and isotopic data were obtained and several manuscripts are in preparation.
c. Modeling programs:
(c1) A thermodynamic model for aqueous speciation calculation is in development to be implemented in a Gibbs energy minimizer. This program will be the first to perform accurate speciation calculations in metamorphic environments.
(c2) A multi-rock petro-geochemical model containing a rock-failure model for simulating fluid extraction has been developed and is submitted for publication. We are currently working on a new approach of energy calculation for systems with metastable relics to better consider the possible kinetic barriers for mineral re-equilibration in petrological models.
(c3) A multi-phase flow model has been developed and is now tested with several advection algorithms to ensure an optimal quantification of element transport by a fluid phase such as melt. This work has been published in Dominguez et al. (2024).
a. Analytical developments:
(a1) An advanced analytical technique for quantitative compositional mapping of LA-ICPMS was developed and implemented in the open source software XMapTools, which is already available for public use (https://github.com/xmaptools(s’ouvre dans une nouvelle fenêtre)). New tools for the classification of complex datasets have also been developed and implemented. The method and application examples of element mobility during partial melting have been published in Markmann et al. (2024).
(a2) A new machine learning strategy and a program, garNET, have been developed for the classification of tomography data and the automated identification of grain shapes in 3D. This technique has been used to localise in key samples where garnet has been spatially dissolved by interacting with an aqueous fluid at high pressure conditions. This new technique has significant potential to easily distinguish in any sample whether the metamorphic fluid responsible for garnet dissolution has flowed along channels or pervasively through the grain boundary network. The work has been published in Hartmeier et al. (2024).
b. Applications: Several case studies were selected to study (b1) aqueous fluid flows (b2) and the consequences of fluid-rock interaction processes on the rock record, and (b3) melt flows.
(b1) Several localities in the western Alps (Lago di Cignana, Zermatt) and in the Cyclades (Syros) were selected for further investigation along the theme of "fluid flows in subduction zones". Key samples and geological data were collected during several field campaigns at the different sites. The samples were analysed in the laboratory and are analysed by EPMA, LA-ICPMS and SIMS. A proof-of-concept study was published (Bovay et al. 2021) demonstrating that in-situ oxygen isotope analyses can be used to quantify critical parameters of fluid flow during high-pressure metamorphism. A second paper was published for the Lago di Cignana site (Rubatto et al. 2023).
(b2) The possible consequences of element redistribution by aqueous fluid during prograde metamorphism were investigated using a bulk rock composition database for pelites (Forshaw & Pattison, 2022) and a newly created bulk rock composition database for metabasites (Forshaw et al., 2024).
(b3) Key samples and geological data were collected from the El Oro metamorphic complex in southern Ecuador during a field campaign in 2022 and analysed in the laboratory in 2023 and 2024. Geochronological and isotopic data were obtained and several manuscripts are in preparation.
c. Modeling programs:
(c1) A thermodynamic model for aqueous speciation calculation is in development to be implemented in a Gibbs energy minimizer. This program will be the first to perform accurate speciation calculations in metamorphic environments.
(c2) A multi-rock petro-geochemical model containing a rock-failure model for simulating fluid extraction has been developed and is submitted for publication. We are currently working on a new approach of energy calculation for systems with metastable relics to better consider the possible kinetic barriers for mineral re-equilibration in petrological models.
(c3) A multi-phase flow model has been developed and is now tested with several advection algorithms to ensure an optimal quantification of element transport by a fluid phase such as melt. This work has been published in Dominguez et al. (2024).
The newly developed methodologies have already proved to be crucial in producing preliminary results that go beyond the state of the art. The following results are expected by the end of the project
- The determination of fluid fluxes and permeability values for different rock types in different subduction systems (e.g. cold, warm, recent, old subduction environments) using both modelling and estimates from natural rocks.
- The simulation of element transport by aqueous fluid during prograde metamorphism to quantify open system behaviour and possible consequences for element cycling.
- The quantification of melt production and fluxes during partial melting of the continental crust using new modelling techniques and estimates from natural rocks.
- A new method and case study to constrain ultrafast mineral growth caused by fluid flow in dry rocks during regional metamorphism.
- The determination of fluid fluxes and permeability values for different rock types in different subduction systems (e.g. cold, warm, recent, old subduction environments) using both modelling and estimates from natural rocks.
- The simulation of element transport by aqueous fluid during prograde metamorphism to quantify open system behaviour and possible consequences for element cycling.
- The quantification of melt production and fluxes during partial melting of the continental crust using new modelling techniques and estimates from natural rocks.
- A new method and case study to constrain ultrafast mineral growth caused by fluid flow in dry rocks during regional metamorphism.