Nikubuchi peridotite body in the sanbagawa metamorphic belt; thermal history of the ‘Al-pyroxene-rich suite’ peridotite body in high pressure metamorphic terrain |
| |
| Authors: | Kazumi Yokoyama |
| |
| Institution: | (1) Department of Geology, Texas A&M University, 77843 College Station, TX, USA;(2) Present address: Battelle Laboratories, 505 King Ave., 43201 Columbus, Ohio, USA |
| |
| Abstract: | Oceanic tholeiite glass has been reacted with natural seawater at 25°–500° C, 1 kbar, with both low (5) and high (50) water/rock mass ratios. Initial experiments were conducted at constant temperatures between 100° C and 500° C (100° intervals) in order to characterize the mineralogy and chemical exchange trends for both water/rock ratios. However, the primary purpose of this investigation was to study the chemical and mineralogical changes that may take place as reacted seawater cools as it traverses a temperature gradient before exiting onto the seafloor, as may happen in some submarine hydrothermal systems. Consequently, a series of cooling or  temperature gradient experiments were performed in which seawater that had reacted with basalt at 500° C was cooled to 25° C in a step-wise fashion; mineralogy and fluid chemistry were determined at 100 degree intervals during cooling.For all of the experiments, the elemental exchange trends were the same. With respect to the initial sea-water, Fe, Mn, Ca, Si and H+ increased while Na and Mg decreased. However, the extent of the exchange depended heavily on the temperature and water/rock ratio. During cooling, fluid compositions in the temperature gradient runs generally approached those of the constant temperature experiments. Even though fluid compositions were very similar at 500° C for both water/rock ratios, the high water/rock ratio systems were more efficient in leaching transition metals from the rock and maintained substantial concentrations in solution during cooling, even to temperatures as low as 25° C. The Fe/Mn ratio in the fluid, however, was quite different for the two water/rock ratios; consequently, the effective water/rock ratio appears to be one parameter that can control the Fe/Mn ratio in exiting hydrothermal fluids and may influence the Fe/Mn ratio in metal-rich sediments.Alteration minerals produced in these seawater/ basalt experiments are very similar to those found at submarine springs on the East Pacific Rise, 21° N. Iron sulfides, pyrite and pyrrhotite, precipitated during cooling for both water/rock ratios, demonstrating the ore-forming potential of submarine hydrothermal systems. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
