Evidence for variable upper mantle temperature and crustal thickness in and near the Australian-Antarctic Discordance

Details Evidence for variable upper mantle temperature and crustal thickness in and near the Australian-Antarctic Discordance Evidence for variable upper mantle temperature and crustal thickness in and near the Australian-Antarctic Discordance

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994e%26psl.128..135w&link_type=abstract

Earth and Planetary Science Letters (ISSN 0012-821X), vol. 128, no. 3-4, p. 135-153

Computer Science

Numerical Analysis

22

Antarctic Regions, Australia, Bathymeters, Earth Crust, Earth Mantle, Geochemistry, Geotemperature, Gravitational Effects, Mathematical Models, Mid-Ocean Ridges, Seismology, Variations, Anomalies, Density (Mass/Volume), Gravity Gradient Satellites, Indian Ocean, Numerical Analysis, Pacific Ocean, Thermal Diffusivity, Viscosity

Scientific paper

The Southeast Indian Ridge (SEIR) in and near the Australian-Antarctic Discordance (AAD) exhibits, at a constant spreading rate, almost the full range of the many geophysical and geochemical parameters characteristic of the 'slow' Mid-Atlantic Ridge and 'fast' East Pacific Rise. We use satellite-derived gravity data, in combination with SeaMARC II bathymetry in and near the AAD, to examine regional density variations in the upper mantle beneath the AAD. Through three-dimensional gravity analysis, we found that at least two end-member models satisfy the gravity observations: regional crustal thickness variations of at least 3 km along the SEIR near the AAD or a temperature anomaly of the order of 150 C in the upper mantle beneath the SEIR. These new observations, combined with other geophysical and geochemical characteristics of the Australian-Antartic Discordance, provide further evidence that the temperature structure of a mid-ocean ridge is a controlling factor, in addition to spreading rate, in the crustal accretionary process. Numerical models of mantle flow beneath mid-ocean ridges offer one means of investigating the dynamic effect of a variable upper mantle temperature on the accretionary process. Our results indicate that temperature is important, especially at intermediate and slower spreading rates, where thermal effects can dominate mantle flow beneath a mid-ocean ridge and result in increasing crustal production with decreasing spreading rate. At the constant, intermediate spreading rate of 37 mm/yr, characteristic of the SEIR in and near the AAD, our numerical models show that significant crustal thinning (2-4 km) can occur with relatively small variations in upper mantle temperature, all else being equal. Thus, combined with our end-member gravity models, these observations and results suggest that both anomalously cool upper mantle and thin crust exist beneath the AAD.

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