Hydrothermal alteration of upper oceanic crust formed at a fast-spreading ridge: mineral, chemical, and isotopic evidence from ODP Site 801

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• 作者：Alt ; Jeffrey C. ; Teagle ; Damon A.H.
• 关键词：Ocean Drilling Program ; Site 801 ; Hydrothermal systems ; Midocean ridge ; Isotope geochemistry
• 刊名：Chemical Geology
• 出版年：2003
• 出版时间：November 28, 2003
• 年：2003
• 卷：201
• 期：3-4
• 页码：191-211
• 全文大小：852 K

文摘

ODP Hole 801C penetrates >400 m into 170-Ma oceanic basement formed at a fast-spreading ridge. Most basalts are slightly (10–20 % ) recrystallized to saponite, calcite, minor celadonite and iron oxyhydroxides, and trace pyrite. Temperatures estimated from oxygen isotope data for secondary minerals are 5–100 °C, increasing downward. At the earliest stage, dark celadonitic alteration halos formed along fractures and celadonite, and quartz and chalcedony formed in veins from low-temperature (<100 °C) hydrothermal fluids. Iron oxyhydroxides subsequently formed in alteration halos along fractures where seawater circulated, and saponite and pyrite developed in the host rock and in zones of restricted seawater flow under more reducing conditions. Chemical changes include variably elevated K, Rb, Cs, and H₂O; local increases in Fe^T, Ba, Th, and U; and local losses of Mg and Ni.