Experimental study on hydrothermal alteration of dacite collected from the Hatoma knoll, Okinawa Trough, Japan
Abstract
The Okinawa Trough is a back-arc basin located between the southern part of Japan offshore and Taiwan North. Hemipelagic sediments supplied from the continents covered at the bottom of the trough. Vigorous hydrothermal activity exists with rifting. The Hatoma Knoll (the depth 1500 m) is one of the active hydrothermal fields located in the southern part of the trough. The measured highest temperature of the vent fluid was 301 °C. The rocks were sampled by manned research submersible ship "Shinkai 2000" in 2000. During the dive program, 25 hydrothermal fluid samples were collected and their chemical compositions were analyzed (Nakano et al., 2001). As a result, it was revealed that the compositions of the hydrothermal vent fluids are strongly influenced by the dacitic rock presumably in a reaction zone. In this presentation, we will show the results of experimental study on hydrothermal alteration dacite sample collected from the Hatoma Knoll. The sample was obtained near the hydrothermal area with ROV "Hyper-Dolphin" during the NT11-20 cruise in 2011. The experiment simulating water/rock reaction was conducted at 300 °C and 325 bars for more than 2,200 hours using the dacite sample and synthetic seawater. The reaction cell is made of a gold tube with a titanium head, which is pressurized in an autoclave. The chemical components of reacted fluid and altered dacite were measured with pH meter, ion chromatograph, ICP-AES, gas chromatograph, and XRD. We also observed thin section of the samples before and after the experiment under microscope. The major element concentrations of the reacted fluid were comparable with those of the natural hydrothermal fluids in the Hatoma Knoll in an order of magnitude except for Mn. As a result of XRD analysis, there was no significant difference in mineral assemblage between the starting material and the experimental product.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMOS13A1703M
- Keywords:
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- 1034 GEOCHEMISTRY / Hydrothermal systems;
- 3000 MARINE GEOLOGY AND GEOPHYSICS