Experimental generation of hybrid silicic melts by reaction of high‐Al basalt with metamorphic rocks

摘要: Melting and crystallization experiments (T = 1000°C; P 0.5, 0.7, 1.0, 1.2, 1.5 GPa) were performed on two hybrid bulk compositions consisting of 50% anhydrous high-Al olivine tholeiite glass (HAOT) metamorphic rock (aluminosilicate-bearing metapelite aluminosilicate-free biotite gneiss). The objective the was to determine phase equilibrium constraints attending assimilation crustal rocks by basaltic melts. Experiments generated 32–38 wt % H2O-undersaturated granitic melt (SiO2 > 70 %). Thermal arguments show that production this amount at chosen experimental conditions is a plausible model for in nature. melts coexisting crystalline assemblages are affected comparable extent pressure composition source. Reaction HAOT with gneiss ≤ 1.0 GPa produces calc-alkaline gabbronoritic cumulates (plag + opx cpx). 0.7 strongly peraluminous resemble S-type granites from Lachlan Fold Belt, noritic ± spi gar). At 1.2 GPa, both source produce leucocratic (<2 FeO MgO TiO2) garnet-rich plagioclase-poor residues (opx cpx gar plag gneiss, metapelite). wide spectrum high-SiO2 can be hybrids formed directly reaction amphibolite-facies rocks. Accumulation complementary mafic deep crust will generate granulites which neither restitic nor products subsolidus dehydration. Mafic share isotopic trace element signatures reflecting inheritance mantle sources.