Abstract
Several profiles of the negative gravity anomaly over the submerged 85o E ridge in the Bay of Bengal of the Indian Ocean have been interpreted in two dimension and results are combined together to give a detailed picture of its morphology and thickness of surrounding sediments. The observed negative gravity anomaly has been explained as the combined effect due to the positive mass anomaly caused by the replacement of sediments by high dense igneous rocks of the ridge, and the negative mass anomaly caused by replacing the high dense upper mantle material by the oceanic crust, which has been bended and sunk into the upper mantle due to the pressure exerted by the ridge. Downward migration of the oceanic crust has been also calculated assuming that the oceanic crust is behaving as a thin infinite elastic plate resting on inviscid fluid half space and is found to closely agree with the results of the gravity study. Both studies indicate that the thickness of the ridge vary from 11 km to 16 km while the oceanic crust has undergone a depression of 9 km to 14 km.
Highlights
INTRODUCTION$VH[SODLQHGDERYHJUDYLW\DQRPDOLHVRYHUWKHo E Ridge have WZR VRXUFH UHJLRQV7KH ¿UVW LV WKH SDUW RI WKH ULGJH ZKLFK LV EXULHG LQVLGH ORZ GHQVH VHGLPHQWV DQGWKHVHFRQGLVWKHSDUWRIWKHRFHDQLFFUXVWZKLFKKDV migrated downward into the high dense upper mantle due WRWKHSUHVVXUHH[HUWHGE\WKHULGJH7KH¿UVWSURGXFHVD positive anomaly while the second produces a negative anomaly
Interpretation of gravity anomalies provides a relatively inexpensive way of revealing the shallow crustal structure of the Earth
Low dense sediments in sedimentary basins surrounded by high dense country URFNVJLYHULVHWRQHJDWLYHDQRPDOLHVZKLOHKLJKGHQVH igneous intrusions emplaced in an environment of relatively low dense country rocks give rise to positive anomalies
Summary
$VH[SODLQHGDERYHJUDYLW\DQRPDOLHVRYHUWKHo E Ridge have WZR VRXUFH UHJLRQV7KH ¿UVW LV WKH SDUW RI WKH ULGJH ZKLFK LV EXULHG LQVLGH ORZ GHQVH VHGLPHQWV DQGWKHVHFRQGLVWKHSDUWRIWKHRFHDQLFFUXVWZKLFKKDV migrated downward into the high dense upper mantle due WRWKHSUHVVXUHH[HUWHGE\WKHULGJH7KH¿UVWSURGXFHVD positive anomaly while the second produces a negative anomaly. In this interpretation of gravity DQRPDOLHVERWK these sources have to be considered. Two dimensional LQWHUSUHWDWLRQ RI JUDYLW\ DQRPDOLHV LV VXI¿FLHQW LQ WKLV case as the anomaly is a linear feature indicating that it is GXHWRDERG\ZLWKRQHKRUL]RQWDOGLPHQVLRQWKDWLVPXFK larger than the other
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