P-T paths from anatectic pelites

Article Abstract:

A study was conducted to analyze a petrogenetic grid for partial melting of pelitic rocks in the NCKFMASH system. The grid is based on the premise that only water available for melting is through a dehydration reaction. It supports discontinuous and continuous Fe-Mg reactions. The grid promotes the identification of abundant matrix K-feldspar if rocks are heated at less than 3.8 kbar and that abundant retrograde muscovite should be observed if rocks are cooled greater than 3.8 kbar.

Petrogenesis, Biotite

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Uncertainties in differential thermodynamic (Gibbs' method) P-T paths

Article Abstract:

An analysis describing uncertainties in differential thermodynamics with Gibbs equation applications is presented. The presence of these uncertainties in P-T paths shows errors emanating from parameters which include initial pressure, initial composition, change of composition, endmember entropy and endmember volume. It is shown that the differential thermodynamic method presents a precise technique for measuring metamorphic heating and thickening.

Thermodynamics, Gibbs' equation

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Modeling of prograde mineral sigma18O changes in metamorphic systems

Article Abstract:

A mathematical model was developed to compute for changes in the oxygen isotope composition of minerals in metamorphic systems. The isopleths of garnet oxygen isotope compositions, as applied to continuous reactions, were independent of pressure conditions and spaced at 0.1% per 10-20 degrees Centigrade. For nearly discontinuous reactions, the isopleths were very similar to endmember reaction boundaries and were more temperature dependent.

Oxygen, Oxygen isotopes, Metamorphism (Geology)

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