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Article Dans Une Revue Geoscience Frontiers Année : 2014

From granulite fluids to quartz-carbonate megashear zones: The gold rush

Résumé

At peak granulite-facies metamorphic conditions, lower continental crust is arguably fluxed by largeamounts of two key low water activity fluids: (i) high-density CO2 and/or (ii) concentrated saline solutions.These fluids are either internally-derived, generated by mineral reactions or dehydration meltingor, notably for CO2, externally-derived, issued from the underlying mantle. Postmetamorphic evolutionresults in complete disappearance of these fluids, except for minute remnants preserved in minerals asfluid inclusions. Two major processes are involved: (i) at peak conditions, granitoid magmas form,migrate upward, and crystallize as shallow intrusions in the upper crust (mineralized porphyry types orreduced intrusions); (ii) during the rapid decompression which almost systematically follows a period ofpost-peak isobaric cooling, especially for ultrahigh-temperature granulites (anticlockwise P-T paths),quartz-carbonate megashear zones are formed by repeated periods of seismic activity. Seismic activitymay continue until all free fluids have disappeared, resulting in the ultramylonites and pseudotachylitesthat are found in many granulite domes. A great majority of vein-type Au deposits worldwide occur inthe above-mentioned settings or nearby. We suggest that the Au has been scavenged by the granulitefluids, then redistributed and concentrated during the formation of veins and related phenomena

Dates et versions

hal-01087547 , version 1 (26-11-2014)

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Bin Fu, Jacques L.R. Touret. From granulite fluids to quartz-carbonate megashear zones: The gold rush. Geoscience Frontiers, 2014, 5 (5), pp.747 - 758. ⟨10.1016/j.gsf.2014.03.013⟩. ⟨hal-01087547⟩
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