Abstract: Enstatites in peridotites from the Vourinos ophiolites, Greece, have exceptionally high Cr/Al ratios, though the pyroxenes are in equilibrium with picotite. Phase-chemistry data yield new empirical relations for the critical effect of Cr on Al solubility, in full agreement with local Cr/Al ratio variations observed in some massifs. These new relations allow application of the single-pyroxene thermobarometer to Cr-rich parageneses and revision of the general method of calculation of pressure and temperature estimates previously suggested for both spinel and garnet facies. The revised method is still based on thermodynamics, but emphasis is given to the fundamental distinction between experimental pure systems and natural complex ones as a result of the observed non-ideality of many solutions dealt with and of the interaction between Al and Cr. The impossibility of extrapolating experimental spinel-facies Al-solubility data for Cr-free systems to natural peridotites, leads to construction of an empirical Al(px) model based on geophysical, petrological and geochemical constraints, such a model yielding realistic estimates. Geotherms constructed fall into three categories, depending on the regional tectonic environment: oceans and continental extension zones, advanced rifting/ridges, and cratonic domains. Typical geotherms so obtained are similar to those proposed earlier (Mercier and Carter, 1975) but with the addition of the new high-temperature rift/ridge type.
Publication Year: 1980
Publication Date: 1980-12-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 230
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