Abstract

Upper Mesozoic to lower Eocene ophiolitic rocks occur in two parallel belts along the eastern margin of the Indian plate. The eastern belt passes through central Burma, Sumatra, and Java, and coincides with a zone of gravity highs resulting from steeply dipping mafic rocks. It denotes the locus of the subduction where these ophiolites were accreted just prior to middle Eocene time. In contrast, the western belt, which passes through Nagaland, Manipur, western Burma, and Andaman, is flanked to the east by a negative gravity anomaly zone. In it the ophiolites occur as rootless, subhorizontal bodies, tectonically overlying Eocene-Oligocene flysch sedimentary rocks. They are inferred to be nappes that propagated westward from the eastern belt during late Oligocene terminal collision of the Indian and Eurasian continental blocks.

Ophiolite occurrences in Andaman and Mentawai islands belonging to the western belt are generally linked with active subduction west of the island arc. This subduction began only in late Miocene time, and thus it could not have produced the ophiolites, which had been emplaced on land much earlier.

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