Record details

Title
    Phase equilibria constraints on melting of stromatic migmatites from Ronda (S. Spain): insights on the formation of peritectic garnet
Author
    Acosta-Vigil, Antonio
    Bartoli, Omar
    Cesare, Bernardo
    Tajčmanová, Lucie
Language
    anglicky
Publication type
    článek v periodiku
Source title - serial
    Journal of Metamorphic Geology
Vol./nr.
    Roč. 31, č. 7
Pages
    14
Year
    2013
Thesaurus term
    melt inclusions, nanogranites, peritectic garnet, phase equilibria modelling with graphite, Ronda migmatites
Keyword
    Constraints
    Equilibria
    Formation
    Garnet
    Insights
    Melting
    Migmatites
    Peritectic
    Phase
    Ronda
    Spain
    Stromatic
Abstract (in english)
   Stromatic metatexites occurring structurally below the contact with the Ronda peridotite (Ojén nappe, Betic Cordillera, S Spain) are characterized by the mineral assemblage Qtz+Pl+Kfs+Bt+Sil+Grt+Ap+Gr+Ilm. Garnet occurs in low modal amount (2-5 vol.%). Very rare muscovite is present as armoured inclusions, indicating prograde exhaustion. Microstructural evidence of melting in the migmatites includes pseudomorphs after melt films and nanogranite and glassy inclusions hosted in garnet cores. The latter microstructure demonstrates that garnet crystallized in the presence of melt. Re-melted nanogranites and preserved glassy inclusions show leucogranitic compositions. Phase equilibria modelling of the stromatic migmatite in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2-O2-C (MnNCaKFMASHOC) system with graphite-saturated fluid shows P-T conditions of equilibration of 4.5-5 kbar, 660-700 °C. These results are consistent with the complete experimental re-melting of nanogranites at 700 °C and indi
   cate that nanogranites represent the anatectic melt generated immediately after entering supersolidus conditions. The P-T estimate for garnet and melt development does not, however, overlap with the low-temperature tip of the pure melt field in the phase diagram calculated for the composition of preserved glassy inclusions in garnet in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O (NCKFMASH) system. A comparison of measured melt compositions formed immediately beyond the solidus with results of phase equilibria modelling points to the systematic underestimation of FeO, MgO and CaO in the calculated melt. These discrepancies are present also when calculated melts are compared with low-T natural and experimental melts from the literature. Under such conditions, the available melt model does not perform well.
Contributor
    Česká geologická služba
Contributor code
    ČGS (RIV)
Source format
    R
Import date
    15. 10. 2014