HR: 09:30h
AN: T41G-07    [Abstracts]
TI: Synfolial Metamorphic Veins Distribution At Belt scale : Evidences For Local Equilibrium As First Order Mechanism For Veins Mineralization During Metamorphism
AU: * Goffe, B
EM: goffe@ens.fr
AF: Geologie ENS, rue lhomond, Paris, 75005 France
AU: Agard, P
EM: agard@hermes.lgs.jussieu.fr
AF: Tectonique, P6 Univ., place Jussieu, Paris, 75005 France
AU: Bousquet, R
EM: romain@geo.uni-potsdam.de
AF: Potsdam Univ., Inst. fur Geowissenschaften , Potsdam, D-14476 Germany
AU: Verlaguet, A
EM: Verlaguet@ens.fr
AF: Geologie ENS, rue lhomond, Paris, 75005 France
AB: In the W and SW part of the Alps, HP-LT metamorphism is particularly well expressed. HP-LT conditions range from the greenschist facies to Ultra High Pressure conditions defining 8 metamorphic units wrapped around the Western Alpine arc. The metamorphic imprint at the belt scale is consistent with the geometry of the Western alpine arc, i.e. the PT metamorphic conditions increase from the external to the internal part of the arc in the inward movement of the subducting slab. Alpine metasediments, Stephanian to Eocene in age, are characterized by a large abundance of syntectonic (synfolial) metamorphic veins. These veins opened in various protoliths (pelitic-schists, calcschists, meta-conglomerates, metaflyschs, meta-evaporites, meta-argilites and metabauxites) are mineralized by HP-LT metamorphic mineral assemblages. Study of more than 3000 syntectonic veins in metasediments distributed through all the metamorphic domains of the W Alps shows that the veins mineralogy is systematically related to the metamorphic imprint and equilibrated with the surrounding metasediments recording both the local metamorphic conditions and geochemistry. In the lowest grade greenschist facies, the first metamorphic minerals (rectorite +/-pyrophyllite) appear only in veins in metapelites. In blueschists domains the synfolial veins are widespread. Their mineralogy varies according to the protolith (lawsonite in metavolcanic, Fe/Mg carpholite in metapelites, jadeite in meta-evaporites, chloritoid-diaspore-pyrophyllite-cookeite in metabauxites). Although veins are comparably scarcier in eclogite domains, kyanite- or jadeite- bearing veins in metapelites, and omphacite-bearing veins in metagabbros are ubiquitous. Mainly, synfolial veins record the prograde PT path but late veins generations, sometime opened through earlier ones, record the retrograde path and are mineralized by greenschist facies assemblages corresponding to the local chemical system. Observations, analyses and experiments suggest that local equilibrium maintained through metamorphic reactions and reaction paths is the main mechanism that controls mineralization in spaces opened by tectonic movements.
DE: 1012 Reactions and phase equilibria (3612, 8412)
DE: 3612 Reactions and phase equilibria (1012, 8412)
SC: Tectonophysics [T]
MN: Fall Meeting 2005