Heat Flow measurements along a 14 Ma isochron paralleling the South-East Indian Ridge between 90°E and 130°E
Abstract
New heat flow data were obtained during the MD120-ANTAUS expedition of R/V Marion Dufresne (Oct. 12th - Nov. 7th 2000), along a profile paralleling the Southeast Indian Ridge, between 90o and 130oE, on 14 Ma old sea floor. The prime objective of the cruise was to quantify the temperature anomalies within the earth upper mantle associated with the Australian-Antarctic Discordance (AAD), an anomalously deep section of the Mid-Ocean Ridge that is often attributed to a mantle ``cold spot''. The second objective was to collect sediment cores from the southern ocean in order to study past climate changes. Despite rough weather and bad seas, a total of 25 thermal measurements was obtained, using 9 autonomous digital temperature probes fitted on a 18 m-long, 13 cm-diameter, gravity corer. Full penetration of 18 m was regularly achieved. In order to quantify water advection, sediment samples sealed in copper tubes will be analyzed to determine the 3He/4He isotope ratio, used as a tracer of hydrothermal activity (with the assumption that if water has circulated within the crust, then the 3He/4He isotopic signature is expected to be that of the crust and upper mantle). The data are highly variable and the measured heat flow is everywhere less than the theoretical heat flow predicted by conductive lithospheric models, probably because of advective heat transport linked to hydrothermal circulation, which is most certainly still active on 14 Ma old crust. Within the deep AAD region, the thermal gradient in the sediments departs from linearity as it approaches the water/sediment interface, probably because of step-changes in the bottom water temperature. The AAD is a major passageway for deep water formed around Antarctica (AABW: Antarctic Deep Bottom Water), and our data reveal 0.05 to 0.08oC temperature fluctuations of this deep water mass. The average heat flow is lower inside the AAD than outside, but this could be the result of differing sedimentation in the two regions that induce differences in hydrothermal activity. We suggest that variations in hydrothermal crustal cooling induced by the eastward decrease in sedimentation may partly explain the large variations in subsidence rate that have been documented along the South-East Indian Ridge between 90oE and 140oE (e. g. Hayes and Kane, JGR, 99, 19679-19692, 1994).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T32C..06G
- Keywords:
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- 3015 Heat flow (benthic) and hydrothermal processes;
- 3022 Marine sediments: processes and transport;
- 3035 Midocean ridge processes;
- 3040 Plate tectonics (8150;
- 8155;
- 8157;
- 8158)