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Department of Earth and Environmental Sciences

Faculty of Science

K. Andrew Gustajtis
ES_John_Doe_210H-214W

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M. Sc. Thesis

An Experimental Hydrothermal Study of Basalt-Seawater Interaction in the Temperature Range 2o - 180o and Pressures up to 1 Kilobar.

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Recent evidence indicates that along active mid-ocean spreading centers seawater circulates through the porous, newly generated basaltic crust, as a result of uneven heating from beneath. This circulation alters both chemically and physically the nature of the basaltic sea floor. To examine the chemical consequences of such a circulation, a unique hydrothermal system was designed and built. The system permitted to simulate the flow of seawater through the basalt, across a temperature range of 2o to 180oC, and under pressures of up to 1 kbar. Presented in this thesis are the chemical results of both the seawater and the basalt analyses for ten different experimental runs, which varied both in temperature and total duration (48-624 hours). These results not only substantiate the already available information from both naturally altered basalt sample studies, as well as other similar experimental investigation, but also introduce new evidence of the importance of such a circulation phenomenon on marine chemical mass-balance.

The major chemical trends reported in this study include:

  1. the drop of pH and total alkalinity of the seawater at higher temperatures.
  2. the leaching of calcium, potassium, iron and manganese from the basalt, especially at temperatures greater than 100oC.
  3. the removal from the flowing seawater of magnesium and strontium at temperatures greater than 75oC.
  4. potassium and magnesium behave in directly opposite ways at below 25oC potassium is removed from the flowing seawater by the basalt, while the seawater leaches the magnesium into solution, the exact reverse occurs at temperatures greater than 80oC.
  5. the precipitation of anhydrite at temperatures greater than 140oC.
  6. the formation of a series of alteration minerals which included pyrite, pyrrhotite, geothite, hematite, montmorillonite-saponite clay minerals, halloysite and possibly some zeolites.

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Supervisors: Fab Aumento