Abstract | The 85E Ridge is a buried ridge in the Bay of Bengal. It is unusual in that it has a
negative Free air anomaly. It owes its existence to the long mid Cretaceous jump of
a part of the spreading center in the Enderby Basin (off Antarctica) to a location on
the Indian continent as the Rajmahal and Sylhet Traps. Because the entire
spreading center did not jump but only a part jumped, the two parts have to be
connected mostly by a strike slip fault. This fault would lie in part in the Indian
continent and in part in the already opened ocean. Strike slip faults, by definition,
have zero width and the oceanic Bengal Basin would lie immediately adjacent to the
continental Indian platform. However, as seismic refraction studies extending from
the Indian platform to the Bengal Basin have shown, there is about a 150 km wide
gap between the two. This gap has a negative gravity anomaly, which continues
south into the ocean as the buried 85E ridge. Seismic reflection studies reveal the
shallow structure of the 85E ridge but do not explain its origin, nor why it has a
negative gravity anomaly. We offer some speculations about the peculiar nature of this strike slip (transform) fault. |