Physicochemical parameters of formation of ore melts and fluid phase in magma chambers under the mid-oceanic ridges

Thermodynamic parameters of magmatic mineralization in MORE from slowly and quickly spreaded mid-oceanic ridges are estimated with KOMAGMAT 3.0 software. Liquidus crystallization of MORE in the central part of the Mid-Atlantic Ridge corresponds to T= 1170-1300 degrees C. For MORE subliquids dissolution, T-liq = 1208-1280 degrees C and T-sol= 1148-1167 degrees C under P from 0.25 to 8.5 kb. For the Kleft sector of the Juan-de-Fuca Ridge, the temperature values are correspondingly 1175-1195 and 1150-1165 degrees C under P = 0.25-4 kb. The composition of magmatic fluids separated from magmas during the crystallization of MORE in shallow and intermediate magmatic chambers depends on the intensity of the retrograde boiling of the melt. The composition of the gas mixture was estimated with chromatographic and X-ray spectrographic techniques from inclusions in glassy basalts, and then was calculated with Selector-2.30 software. The following was concluded: (I) two specific temperature intervals with different physicochemical parameters of the magmatic fluid, conditionally named "sulfidic" and "haloidal" occur; (2) the composition of the magmatic fluid strongly depends on the mass value of the degassing volatiles; (3) the evolution path of the fluid depends on the relative content of sulfur and chlorine in the system; (4) almost complete sublimation of metal and silicon compounds from the fluid occurs at 950-600 degrees C; (5) low-temperature essentially aqueous condensates of the magmatic fluids contain high contents of methane and manganese. The composition of the bubbling fluids that causes the dissolution of the basic melt relates to the "haloidal" trend of the evolution of magmatic fluids. These fluids move along fissure zones around the magma-conducting structures. They locally melt fissure walls in the serpentinized ultrabasic rocks and in altered gabbroids of the "exfoliation series" belonging to the anomaleous crust section at the crest of the Mid-Atlantic Ridge.