中央海嶺の熱水系

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タイトル別名
  • Hydrothermal Circulation System along Mid-Ocean Ridges ODP/DSDP Hole 504B, Cyprus CY2A
  • チュウオウ カイレイ ノ ネッスイ ジュンカンケイ ODP DSDP Hole

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説明

DSDP/ODP Hole 504 B was drilled into 6 Ma crust, about 200 km south of the Costa Rica Rift, penetrating 1.55 km into a section that can be divided into four zones-Zone I: oxic submarine weathering; Zone II: anoxic alteration; Zones III and IV: hydrothermal alteration to greenschist facies. In Zone III there is intense veining of pillow basalts.<BR>Cyprus CY2A is located near Agrokipia deposits and cored into 90 Ma crust. The alteration is divided into four zones-Zone I: low-grade alteration; Zone II: silicified hydrothermal alteration; Zone III: propylitic alteration; Zone IV: lower greenschist facies alteration.<BR>Both drill cores were located at discharge zones in hydrothermal circulation systems. So the alteration characteristics of both cores were similar. Alteration temperatures of hydrothermally altered rocks were 200-350°C in Hole 504 B and 200-<300°C in CY2A. Boiling didn't occur in both cores. The hydrothermally altered rocks from both cores were formed under low seawater/rock ratio (1-5). The estimated isotopic and/or chemical compositions of hydrothermal solutions are within the range of those of endmember hydrothermal solutions from present seafloor hydrothermal fields.<BR>At least 2km3 of magma would be needed for the formation of 6 million tons of sulfide deposit if magma supplies heat energy to make hydrothermal solutions during the cooling from 1200°C to 350°C.

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  • 地学雑誌

    地学雑誌 98 (3), 204-211, 1989

    公益社団法人 東京地学協会

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