Hydrothermal systems hosted in peridotites at slow-spreading ridges. Modeling phase transformations and material balance: Upwelling limb of the hydrothermal cell

Abstract

The research was centered on the estimation of geochemical and mineralogical effects related to the transport of hydrothermal fluid to the seafloor surface in the upwelling limb of a hydrothermal system hosted in peridotites at slow-spreading mid-oceanic ridges. The three variants of the location of the root zone of the circulation cell considered in this research were as follows: (1) shallow-depth, with T = 107°C, P = 1.14 kbar; (2) moderate low depths, with T = 151°C, P = 1.4 kbar; and (3) deep, with T = 500°C, P = 4 kbar. The modeling results demonstrate that ore material is accumulated in the discharge zones of serpentinite-related hydrothermal systems only at a high temperature of the fluid in the discharge zone of the upwelling limb of the circulation cell. The root zones at hydrothermal fields that meet this condition should be situated at a significant depth in the crustal section. It was also established that a significant volume of ore material involved in hydrothermal material exchange between the peridotites and fluid is redeposited in the downwelling limb of the hydrothermal system and gives rise to disseminated ore mineralization, which is typical of many serpentinized abyssal peridotites. The activity of moderately low-temperature and low-temperature hydrothermal systems in peridotites does not concentrate ore material in the discharge zone, and no hydrothermal edifices can grow at such systems.