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Fluids driving the evolution of the continental crust: influence of pathway networks, fluxes, and time scales.

Periodic Reporting for period 1 - FluidNET (Fluids driving the evolution of the continental crust: influence of pathway networks, fluxes, and time scales.)

Reporting period: 2021-01-01 to 2022-12-31

Today human society is facing unprecedented challenges: the impact of human actions on the environment is increasing, with global warming and depletion of resources. The new EU commission has announced an ambitious programme, ‘The EU Green Deal’, with an energy transition away from fossil fuels to renewable sources. For this, the demand for metals necessary for generation, storage and transport of energy will grow strongly. The FluidNET consortium has created a strong new industry-academia collaboration of 8 beneficiaries, of which 6 academic, 1 natural history museum and 1 industry partner, and strong industry participation. The charter of FluidNET is to constrain the fluid rock interaction processes that underlie the genesis of critical metal ores and to train early stage researchers (ESRs) in the skills to address and manage the growing demand for metal resources.

FluidNET partners noted the current absence of research initiatives designed to bring together as yet disparate research fields of nano- and micro-chemistry and crustal scale fluid assisted mass transport, chemical and physical constraints for ore formation processes and in particular the timescales over which such pro-cesses operate. FluidNET will structure the EU research effort in these fields by bringing together a new and diverse, cross-disciplinary team of academic and industry leaders to deliver new training paths for the next generation of science leaders. Our global field leader industry Partner Organisations BHP (ores) and ThermoFisher Scientific (analytical equipment), as well as a range of resource and geothermal energy consultancy firms have all actively contributed to the design of the FluidNET research goals and training programmes. FluidNET’s integrating approach will develop crucial new knowledge necessary to help society reach EU Green Deal goals and UN Sustainable Development Goals including SDG#7 and SDG#13. See Figure 1. Overview of FluidNET Work Package structure.
WP1 – Upper crust: We has sampled quartz veins in a skarn deposit (Serifos, Greece), in slates the coastline of Almograve, Portugal and a section from slates to high grade gneisses in the Agly Massif to understand crustal fluid flow. We focused jointly in WP1's and 5 on on the development of numerically consistent models of fluid mixing in fracture networks, with the capacity to estimate porosity and permeability changes. These models can further be adapted by other ESRs in the consortium. We have started to estimate the composition of the fluids trapped in fluid inclusions in quartz veins along with 40Ar/39Ar dating in the crushed samples and by experimental data.
WP2 – Middle crust: We focus on mid-crustal levels where ductile processes dominate in the most common rock types (quartz- and feldspar-rich rocks), where hydrous fluids alternate between subcritical and supercritical (depending on ambient T), and where sub-solidus conditions prevail, with the exception of crystallizing magmas and adjacent thin contact aureoles; WP2 is concerned with the emplacement level of granitoid magmas. Constraints on the time- and length scales of fluid flow are emerging.
WP3 - Lower crust: In WP3, we focus on those crustal levels where supersolidus conditions prevail in mica-rich lithologies and where regional-scale partial melting takes place. In terms of rock types this involves mainly migmatites and granulites. Before and after peak temperatures, subsolidus conditions have generally prevailed, which implies that deep crustal levels commonly show a sequence in time from early fluid-dominated via melt-dominated to late fluid-dominated processes. As such, these rocks show a high level of complexity that requires a multitude of approaches to unravel the full sequence of events.
WP4 - Improving the Toolbox; using, developing and improving cutting edge laboratory techniques This WP focuses on the acquisition of data using analytical methods examining natural materials obtained in WP 1 to 3 and those acquired through experiments. We are focusing targeting the source of the fluids by the use of halogens in fluid inclusions or the isotopic signatures, the reactivity of phases to fluid infiltration, timescales of fluid flow and outcrop scale drone photogrammetry to examine the distribution of veins. We utilize micro-chemical analysis, and triple halogen microanalysis for the provenance of the fluid inclusions, and hydrothermal experiments to demonstrate the formation of mineral phases associated with porosity development. We are determining the temperature and pressures under which fluids were trapped inside a crystal by microthermometry. We are using step-wise crushing, single-grain fusion, in-situ dating of solids 40Ar/39Ar geochronology and noble gas geochemistry to evaluate fluid mobility timescales.
WP5 – Modelling and validation: We focus on data utilization using numerical, database or observational and experimental methods. As stated above for WP1, we focused jointly in WP1's and 5 on the development of numerically consistent models of fluid mixing in fracture networks, with the capacity to estimate porosity and permeability changes. These models can further be adapted by other ESRs in the consortium.
Our research programme has multiple integrated and innovative targets. The integrated research program will tread new ground by integrating field observations, micro-geochemical approaches and macroscopic fluid flow models.
Our key strength is that we link novel analytical approaches to unlocking the geological fluid flow record:
-dating fluid inclusions via 40Ar/39Ar stepwise crushing of the host minerals (VUA), noble gas tracing of fluid sources (OU),
-molecular speciation and thermobarometry (UniMib),
-nano-scale AFM analyses and modelling (WWU),
-in situ X-ray tomography and electron microscopy (UU), as well as
-micro-scale trace element and
-triple halogen geochemistry (RWTH).
The progressive utilization, refinement and combination of this unique range of state-of-the-art methods in we pioneer a new step in fluid rock interaction studies. We bring together knowledge of crustal processes in the upper, middle and lower crustal domains. Our methodologies will constrain when, where, why, how and how fast fluids are released and transported, how they react in the crust, and quantify the amount of metals those fluids may carry. The strong meaningful contribution of industry in the network ensures cross fertilization with ideas and short-tracking of novel applications.

Our focus is to integrate fluid provenance, length scale and time scale constraints into a new model combining chemical-physical aspects of crustal fluid flow, linking chemical reactions to physical processes across multiple temporal and spatial scales. Currently our knowledge lacks the temporal information necessary to test model predictions the synchronicity of fluid infiltration. We aim to validate such models and apply them to a series of well characterized case histories.
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