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Three independent net-transfer reactions determine compositional and modal changes for green-schist-, blueschist-, and amphibolite-facies metamorphism of marie rocks, as different paths are followed though pressure, temperature, and [a.sub.[H.sub.2.]O] space. For natural terrains, only one [a.sub.[H.sub.2.]O]--dependent reaction is chosen, whereas to interpret experimental studies, where [H.sub.2]O is in excess, there is an advantage to choosing two dehydration reactions. Published experimental studies on the greenschist to amphibolite transition and thermodynamic calculation in simple systems and with pseudosections, show that reactions involving [Al.sub.2][Mg.sub-1] [Si.sub.-1] in amphibole and chlorite predominate, that Fe[Mg.sub.-1] exchange and [Al.sub.2][Mg.sub-1][Si.sub.-1] are strongly coupled, and that all reactions and, in particular, the stability of chlorite are affected by [Fe.sup.3+]/[Fe.sub.total]. Modal spaces for marie schist are constRucted for different sets of independent reactions, and permit correlation of mineral mode with directions of change of pressure and temperature. These can be used to deduce field gradients in these variables in natural terrains, when only modal change data are available and when compositional and thermodynamic data are limited.

Research on eclogite facies rock in Switzerland's Zermatt-Saas zone indicates that veins found in the rock are local segregation phenomena, rather than eo-Alpine subduction zone fluid dehydration channels.

In the proposed model, weak zones of rheologically homogeneous crust, continually compressed between rigid lithospheric indenting plates, can be exhumed upward by extrusion. The rate of exhumation is governed by the rate of convergence of approaching plates and by the width of the weak deformable zone. Modeled extrusion results in near-isothermal decompression during the rapid elevation history in narrow orogenic belts for realistic plate velocities. Such pressure-temperature-time paths exhibit distinct collapsed geochronologies and record maximum metamorphic temperatures ([T.sub.max]) at the maximum burial depth ([P.sub.max]).

Experiments performed with CMASH and natural plagioclase-bearing amphibolites reveal that I-type granites and other similar magmatic rocks are formed by the melting of amphibolites after continental collision. The continental collision occurs with basalt input into the magmatic arcs or thickened crust. The collision is also accompanied by basalt addition in surroundings where the lithosphere is heated during extension. The CMASH experiments reveal that zoisite, talc and hydrous minerals are stable at temperatures higher than that of the H2O-saturated solidus.

Discusses the dehydration of amphibolite as a source for I-type granites and several other types of magmatic rocks. Stability of hydrous minerals in basaltic compositions; CMAS as a system to model the metamorphism of ultramafic rocks; Phase relations and compositions; Disappearance of quarts in water-saturated melts from amphibolites.