HR: 1330h
AN: T12D-0500    [PDF]
TI: Hydrothermal circulation and subsidence of ocean basins : a case study from the South-East Indian Ocean
AU: * Louis, G B
EM: geli@ifremer.fr
AF: Ifremer, Centre de Brest, BP 70, Plouzane, 29280 France
AU: Jean, F
EM: franch@univ-brest.fr
AF: IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AU: James, C R
EM: jrc@ldeo.columbia.edu
AF: LDEO, Columbia University, Palisades, NY 10964 United States
AU: Cinthia, L
EM: clabails@ifremer.fr
AF: Ifremer, Centre de Brest, BP 70, Plouzane, 29280 France
AU: Delphine, A
EM:
AF: IUEM, Place Nicolas Copernic, Plouzane, 29280 France
AB: The South-East Indian Ridge (SEIR) flanks between 105$\deg$E and 130$\deg$E are characterized by anomalously low subsidence rates, less than about 280 m/ sqrt(Ma) [Hayes and Kane, JGR, 1994]. While individual estimates of the upper mantle temperature variations below the SEIR axis may vary significantly from one study to the other, all geophysical (axial morphology, seismology and geoid) and geochemical (major and trace elements systematics) evidence is compatible with variations of less than about 100$\deg$C. Such a temperature anomaly is not sufficient to fully explain the observed anomalously low subsidence rates, using the present available models for the thermal evolution of the lithosphere. Ad hoc explanations, such as, for instance, variations in mantle thermal parameters cannot be readily rejected, but are not completely satisfactory because they cannot be supported by direct estimates. In contrast, of direct evidence is the lack of sedimentation that characterizes the flanks of the SEIR and the fact, recognized from heat flow data, that in absence of sediment cover, seawater penetrates into the ocean crust and plays a key role in the mechanisms of heat transfer through the seafloor. Although it is now widely accepted that seawater may penetrate massively into poorly sedimented off-axis crust, the contribution of water circulation to the seafloor subsidence rate has only been considered so far near crestal areas, but not at the scale of tens of millions years. We thus propose a simple model which assumes, at first approximation, that seawater penetrates into highly permeable off-axis crust to a depth H below the seafloor and maintains the temperature equal to Tc at that depth (Note : H may depend on age crust). Assuming that hydrothermal circulation is active over large periods (of tens of Ma, for instance), the subsidence rate is controlled by Tm-Tc. The model thus predicts that variations in the hydrothermal regime, by affecting Tc, may affect the subsidence rate. Estimates for the best fitting values of Tc and H are proposed and discussed. Agreement with re-assessed subsidence estimates a posteriori supports the model hypothesis, suggesting that in absence of sedimentation sealing the upper crust, anomalously low temperatures could be forced for tens of millions of years, down to the base of the layer penetrated by the diffusive seawater circulation.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3015 Heat flow (benthic) and hydrothermal processes
DE: 3022 Marine sediments--processes and transport
DE: 8030 Microstructures
DE: 8035 Pluton emplacement
SC: Tectonophysics [T]
MN: 2003 Fall Meeting