Gravity anomalies, flexure of axial lithosphere, and along-axis asthenospheric flow beneath the Southeast Indian Ridge

Details Gravity anomalies, flexure of axial lithosphere, and along-axis asthenospheric flow beneath the Southeast Indian Ridge Gravity anomalies, flexure of axial lithosphere, and along-axis asthenospheric flow beneath the Southeast Indian Ridge

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998e%26psl.156..253w&link_type=abstract

Earth and Planetary Science Letters, Volume 156, Issue 3-4, p. 253-266.

Physics

2

Scientific paper

Mantle Bouguer and residual gravity anomaly patterns consistent with two- and three-dimensional mantle flow and/or crustal thickness variability, are observed juxtaposed within the five first-order segments of the Southeast Indian Ridge (SEIR) surveyed between 98° and 112°E. Within each segment `bull's-eye' or `triangular' patterns of mantle Bouguer and residual gravity anomalies, consistent with focused mantle upwelling and/or three-dimensional crustal thickness patterns, occur systematically toward the western ends of segments which adjoin significant left-stepping offsets in the ridge axis. The eastern ends of these segments and those that abut smaller, right-stepping transforms display a more two-dimensional anomaly character. Axial morphology also varies along strike; axial highs coincide with focused gravity anomalies, while rifted highs occur elsewhere. These observations imply that more magmatically robust extension, more vigorous mantle upwelling, and/or thicker crust characterize the western parts of those segments adjacent to significant ridge offsets. These trends are mirrored east of the deepest portions of the Australian-Antarctic Discordance (AAD), where more vigorous upwelling is located toward the eastern end of segment B5. In addition to the usual interpretations in terms of crustal thickness and/or mantle temperature, we suggest that the systematics of topographic style and gravity anomaly character provide further evidence for along-axis asthenospheric flow beneath the SEIR. In western portions of segments between 98° and 112°E, sub-axial flow toward the AAD causes asthenosphere to be drawn from beneath older lithosphere to the west, thereby increasing the region of mantle upwelling and melting supplying the `upstream' portion of the ridge axis.

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