THE SYSTEM MgO—SiO2—H2O

Concentrically zoned ultramafic pods from the Haast schist zone, South Island, New Zealand

“…(1) and serpentine + magnesite ~ 2 forsterite + 2H 2 0 + CO 2 (2) Experimentally determined reaction temperatures for (1) are 490-500 o c at 2 kbar with X eo2 0'005 to 0'060 (Bowen & Tuttle 1949;Yoder 1966;Johannes 1969). For reaction (2) equilibrium temperatures range from 410°-500°c at 4 kbar with X 002 0'005-0'04 (Johannes 1969).…”

Petrology and geochemistry of selected talc-bearing ultramafic rocks and adjacent country rocks in north-central Vermont

“…In either case, the geologic evidence is conclusive that the ultramafic rocks were at low temperatures comparable with those of the schist (the temperature of the upper limit of the greenschist facies) when emplaced. This evidence, taken in conjunction with the experimental data of Bowen and Tuttle (1949) and supported by contact relations and by structural features in the serpentinite (shear polyhedrons; see p. 24, 71), demands the conclusion that the ultramafic rocks were intruded in the solid state.…”

“…A particularly great advantage which the present study has had over earlier ones and this statement applies as well to other phases of the problem of ultramafic rocks, not just to steatitization is in the availability of the results of experimental investigation of the system MgO-SiO2-H2O (Bowen and Tuttle, 1949). These experimental data, and the clear analysis in that paper of the geologic implications of the experimental results, have made possible more precise evaluation of the geologic and petrologic relations, and more informed judgment on conflicting or opposing claims.…”

“…The mode of origin subscribed to in this report (p. 88-89) for the serpentinite places it outside the realm of strictly regional metamorphism. The experimental evidence (Bowen and Tuttle, 1949) places the temperature of serpentinization at less than 500° C., and the geologic relations indicate that, at the time of emplacement, the serpentinite was not appreciably hotter than the enclosing schist (lower boundary of the epidote-amphibolite facies), but chere is not a direct relationship between serpentinization and the regional metamorphism of the rocks adjacent to the ultramafic bodies. Steatitization, on the other hand, appears, on the basis of all the available evidence, to belong to the episode of regional metamorphism.…”

“…Benson (1918) reviews and summarizes the pertinent geologic literature prior to 1918, and analyzes (1926) the tectonic conditions accompanying the intrusion of ultramafic rocks. Bowen (1927;1947), Bowen and Schairer (1936) Bowen and Tuttle (1949), Hess (1938), and Bain (1936) review current opinion and have made recent contributions to the problem.…”