Uranium, rare metals, and granulite-facies metamorphism

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During granulite-facies metamorphism of metasedimentary rocks by the infiltration of carbonic fluids.the disappearance of hydrated minerals leads to the liberation of aqueous fluids.These fluids arc strongly enriched in Fand CI,and a series of Large-lon-Lithophile(LIL) elements and rare metals.resulting in their depletion in granulites.To sum up the fate of these elements,we focus on three domains representing different crustal levels and showing distinct behaviours with respect to these elements.The Lapland metasedimentary granulites illustrate the behaviour of the LI1.E and rare metals during lower crustal metamorphism.There is no change in Ba.moderate loss in Kb,and extreme depletion in Cs,Li,and Sn.F and CI contents are also very low compared to the protoliths or average upper continental crust.Biotite and amphibole breakdown leads to the incorporation of their partitioning into a fluid or a melt.The Tranomaro metasomatized marbles recrystallizing under granulite-facies conditions represent a demonstrative example of fluid transfer from granulite-facies supiacrustals to traps represented by regional scale skarns.Such fluids may be at the origin of the incompatible element enrichment detected in leucosomes of migmatites from St Malo in Brittany(France) and Black Hills in South Dakota.The northern French Massif Centra]provides us with an example of a potential association between incompatible element enrichment of granitic melts and granulite-facies metamorphism.U- and Fenriched fine-grained granites are emplaced along a crustal scale shear zone active during the emplacement within the St Sylvestre peraluminous leucogranitic complex.We propose that during granulite-facies metamorphism dominated by carbonic waves in a deep segment of the continental crust,these shear zones control:(i) the percolation of F-,LILE-,rare metal-rich fluids liberated primarily by the breakdown of biotite;(ii) the enhancement of partial melting by F-rich fluids at intermediate crustal levels with the generation of F-,LILE-,rare metal-rich granitic melts;(iii) their transfer through the crust with protracted fractionation facilitated by their low viscosity due to high F-Li contents;and finally(iv)their emplacement as rare metal intrusions at shallow crust levels. During the infiltration of carbonic fluids. The disappearance of hydrated minerals leads to the liberation of aqueous fluids. These fluids arc strongly enriched in Fand CI, and a series of Large-lon-Lithophile (LIL) elements and rare metals.resulting in their depletion in these elements, we focus on three domains representing different crustal levels and showing distinct behaviors with respect to these elements. Lapland metasedimentary granulites illustrate the behavior of the LI1. E and rare metals during lower crustal metamorphism. Here is no change in Ba. Moderate loss in Kb, and extreme depletion in Cs, Li, and Sn. F and CI contents are also very low compared to the protoliths or average upper continental crust. Biotite and amphibole breakdown leads to the incorporation of their partitioning into a fluid or a melt. The Tranomaro metasomatized marbles recrystallizing under granulite-facies conditions represent a demonstrative example of fluid transfer from granulite-facies supiacrustals to traps represented by regional scale skarns. Chuch fluids may be at the origin of the incompatible element enrichment detected in leucosomes of migmatites from St Malo in Brittany (France) and Black Hills in South Dakota. The northern French Massif Centra] provides us with an example of a potential association between incompatible element enrichment of granitic melts and granulite-facies metamorphism. U- and Fenriched fine-grained granites are emplaced along a crustal scale shear zone active during the emplacement within the St Sylvestre peraluminous leucogranitic complex. We propose that during granulite-facies metamorphism dominated by carbonic waves in a deep segment of the continental crust, these shear zones control: (i) the percolation of F-, LILE-, rare metal-rich fluids liberated primarily by the breakdown of biotite; (ii) the enhancement of partial melting by F-rich fluids at intermediate crustal levels with the generation of F-, LILE-, rare metal-rich granitic melts; (iii) their transfer through the crust with protracted fractionation facilitated by their low viscosity due to high F-Li contents; and finally (iv) their emplacement as rare metal intrusions at shallow crust levels.
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