HR: 0830h
AN: V21D-0549    [PDF]
TI: Sub-seafloor hydrothermal alteration of oceanic crust of the Oman ophiolite - Interaction with global environmental change -
AU: * Kawahata, H
EM: h.kawahata@aist.go.jp
AU: Nohara, M
EM: m.nohara@aist.go.jp
AB: The chemical change of rocks during hydrothermal alteration was investigated in a complete section through the Wadi Fizh oceanic crust in the Oman ophiolite was investigated in order to evaluate seawater-rock interaction through the oceanic crust. 20 elements analyzed in this study are classified into 6 groups: Group 1 (Ca, P, Al), Group 2 (Mg, Ni, Co, Cr), Group 3 (Fe, Ti, Na, Mn, Zn, Y), Group 4 (K, Rb, Ba), Group 5 (Li, Cd) and Group 6 (other elements such as Sr, Cu). The degree of alteration is assessed by 87Sr/86Sr ratios of rocks and the abundance of secondary minerals. Heavy metals (Cu, Zn, Ni, Cr, Co and Cd) and phosphorus were leached from the lower oceanic crust during amphibolite facies ($>$ 450u$^C$) alteration. Even if the scavenging and/or removal by hydrous Fe and Mn oxides is taken into consideration, the alteration of ophiolite complex, as a whole, works as a source of phosphorus to the ocean during the mid-Cretaceous. This period is characterized by deposition of black shales and oil generation caused by superplume activity. Although such carbon should have been supplied directly by mantle outgassing, nutrients such as phosphorus and silica required for the production of marine organic matter would have been supplied from enhanced hydrothermal activity.
DE: 1615 Biogeochemical processes (4805)
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4832 Hydrothermal systems
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting