A phase equilibrium investigation of selected source controls on the composition of melt batches generated by sequential melting of an average metapelite
Published:April 21, 2020
Matthew J. Mayne, Gary Stevens, Jean-François Moyen, 2020. "A phase equilibrium investigation of selected source controls on the composition of melt batches generated by sequential melting of an average metapelite", Post-Archean Granitic Rocks: Petrogenetic Processes and Tectonic Environments, V. Janoušek, B. Bonin, W. J. Collins, F. Farina, P. Bowden
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The ability of Rcrust software to conduct path-dependent phase equilibrium modelling with automated changing bulk compositions allows for a phase equilibrium approach to investigate an array of source controls for their effect on the bulk compositions of melts produced by sequential melting events. The following source controls of the rock system are considered: (1) initial magnesium and iron content; (2) initial sodium and calcium content; (3) pressure–temperature path followed by the system; and (4) threshold by which melt extractions in the system are triggered. These source controls are investigated in a water-restricted system and a water-in-excess system. The permutation of these cases resulted in 128 different modelled pressure–temperature bulk composition paths investigating the melting of an average pelite composition. The resultant melt compositions are compared to that of a natural granite dataset and provide a good fit for the incompatible elements Na2O and K2O with the allowance that granites most likely form as magmas consisting of melt and ferromagnesian-rich crystals. The fluid state of the system is shown to have the strongest control on melt compositions, with the pressure–temperature path having subordinate control on the volume and composition of melts produced.
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Post-Archean Granitic Rocks: Petrogenetic Processes and Tectonic Environments
CONTAINS OPEN ACCESS
Granites (sensu lato) represent the dominant rock-type forming the upper–middle continental crust but their origin remains a matter of long-standing controversy. The granites may result from fractionation of mantle-derived basaltic magmas, or partial melting of different crustal protoliths at contrasting P–T conditions, either water-fluxed or fluid-absent. Consequently, many different mechanisms have been proposed to explain the compositional variability of granites ranging from whole igneous suites down to mineral scale. This book presents an overview of the state of the art, and envisages future avenues towards a better understanding of granite petrogenesis. The volume focuses on the following topics:
compositional variability of granitic rocks generated in contrasting geodynamic settings during the Proterozoic to Phanerozoic Periods;
main permissible mechanisms producing subduction-related granites;
crustal anatexis of different protoliths and the role of water in granite petrogenesis; and
new theoretical and analytical tools available for modelling whole-rock geochemistry in order to decipher the sources and evolution of granitic suites.