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Article Dans Une Revue Journal of Petrology Année : 2009

An experimental determination of the effect of bulk composition on phase relationships in metasediments at near-solidus conditions

F. Ferri
  • Fonction : Auteur
S. Poli
  • Fonction : Auteur

Résumé

Phase relationships in metapelites were experimentally investigated in the model system CaO-K2O-FeO-MgO-Al(2)O(3)-SiO(2)-H(2)O on four synthetic compositions differing in their K(2)O content and K(2)O/Al(2)O(3) ratio. Experiments were carried out at pressures ranging from 0.8 to 1.4 GPa and temperatures from 620 to 740 degrees C under different fluid-buffered conditions. The stability of the assemblage garnet-biotite-staurolite/Al(2)SiO(5) at the investigated conditions largely controls the absence of muscovite in K-poor compositions. At 1.2 GPa and 700 degrees C staurolite is present with garnet + biotite + muscovite, replaced by Al(2)SiO(5) at lower pressures through the reaction staurolite + muscovite + quartz garnet + biotite + Al(2)SiO(5) + H(2)O. In K-poor bulk compositions, garnet + biotite + staurolite + gedrite coexist up to 730 degrees C. A compositional reversal of the Mg-Fe partitioning between garnet and staurolite is observed with decreasing pressure and is responsible for the singular equilibrium staurolite + quartz = Al(2)SiO(5) + garnet + H(2)O that governs the high-temperature breakdown of staurolite. Melting is found to depend both on bulk composition and on fluid speciation. The wet solidus is represented by the reaction muscovite + anorthite + garnet + quartz + H(2)O = melt + biotite + Al(2)SiO(5). Even though staurolite is never recovered at supersolidus conditions, the large pressure-temperature stability field of staurolite + muscovite and of staurolite + gedrite suggests that staurolite can be directly involved in melt production through fluid-present or fluid-absent reactions.

Domaines

Géochimie

Dates et versions

hal-00413551 , version 1 (04-09-2009)

Identifiants

Citer

F. Ferri, S. Poli, D. Vielzeuf. An experimental determination of the effect of bulk composition on phase relationships in metasediments at near-solidus conditions. Journal of Petrology, 2009, 50 (5), pp.909-931. ⟨10.1093/petrology/egp026⟩. ⟨hal-00413551⟩
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