The four types of subsolidus assemblages in silicate-water systems are: I, water-absent; assemblage of anhydrous minerals with no vapor phase. Type , water-deficient and vapor-absent; assemblage of minerals including hydrous minerals, with no vapor phase. Type III, water-deficient and vapor-present; an assemblage minerals, with or without hydrous minerals, with a vapor phase; there is water present to saturate the liquid when the crystalline assemblage is melted at the existing pressure. Type IV, water-excess; an assemblage of and vapor with at least enough water to saturate the liquid when the crystalline is completely melted at the existing pressure. Water-deficient systems types II and III are significant for magma generation and crystallization; there are experimental results. Water-deficient phase relationships can be estimated by between available experimental data for systems of types I and IV. magmas are generated in type I, II, or III systems. The first liquid produced type III systems is H_20-saturated, and the first liquid in type II systems H_2O-undersaturated. It appears that the normal product of partial fusion of many crustal rocks is a H_2O-undersaturated granite liquid in a crystal mush, that liquids of intermediate composition are not generated because temperatures are too high. Phase relationships are depicted for granodiorite in a pressure-temperature- diagram.
No takes yet. Share an insight, caveat, or question.
Robertson et al. (1971) studied this question.