Experimentally derived thermochemical data for pargasite and reinvestigation of its stability with quartz in the system Na2O-CaO-MgO-Al2O3-SiO2-H2O

Article Abstract:

Stability analysis of pargasite in the presence of excess quartz in the system Na2O-CaO-MgO-Al2O3-SiO2-H2O reveals the presence of two distinct mineral assemblage regimes. The supersolidus region contains tremolitic amphibole + melt + quartz, while the subsolidus comprises Al-rich amphibole + plagioclase + enstatite + quartz. Derived compositional reversals for three equilibria indicate a continuous change of amphibole composition from pargasite to tremolite with increasing temperature. A site-mixing model for pargasitic amphiboles and thermochemical data for the equilibria are given.

Observations, Geochemistry, Quartz, Amphiboles

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Reinvestigation of fayalite + anorhite = garnet

Article Abstract:

A study was conducted to evaluate the reaction combining fayalite and anorhite to produce garnet (GAF). The study assumes that the reaction of fayalite (Fe2SiO4) plus anorhite (CaAl2Si2O8) to garnet (CaFe2Al2Si3O12) serves as the foundation for granulite geobarometers. Results show that discrepancies between calculated and experimentally determined GAF slopes remain unless certain excess entropy levels condition Ca-Fe mixing.

Composition, Granulite, Garnet

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Compositions of minerals and melts

Article Abstract:

The chemical compositions of the products from the partial melting of quartz-rich metagreywacke are studied. These include biotite, plagioclase, orthopyroxene, garnet, cordierite, hercynite, staurolite, gedrite, oxide and glass at 100-1000 MPa and 780-1025 degrees Centigrade. It is shown that metagreywackes are fertile at pressures of 300-700 MPa and less fertile at pressures exceeding 800 MPa.

Magmatism, Rocks, Igneous, Igneous rocks

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