Geology and tectonics of Arakan Yoma - a reappraisal

Author : Nandy, D.R.
Publication : Bulletin of the Geological Society of Malaysia
Page : 137-148
Volume Number : 20
Year : 1987

Bulletin of the Geological Society of Malaysia, Volume 20, August 1986, pp. 137 – 148

Geology and tectonics of Arakan Yoma – A reappraisal


Geological Survey of India, Calcutta


Abstract: The tectono-stratigraphic evolution of the Arakan Yoma Orogen with the Naga and the Chin Hills, positioned between the Sunda arc and the Himalayas, is vital in the framework of convergence of the Indian plate with Asia. The Orogen is flanked to the west by the Assam-Burma Cretaceous-Tertiary turbidite-molasse basin and further west by the Meghalaya (Shillong) Plateau; to the east by the Mesozoic-Cenozoic Central Burman molasse basin and the Shan-Tenasserim block east of the Shan Boundary Fault.

From the above tectono-stratigraphic setting it is surmised that the present site of Naga Hills–Arakan Yoma-Chin Hills has been marked by a meridionally trending spit of land projecting southward from the Angara land during Palaeozoic time forming Archipelagos of islands made of basement rocks, the western slope of which fell away into the Assam-Burma trough having oceanic floor in front of the subducting Indian Plate. On its eastern side, sediments were deposited over a submerged peneplained(?) Pre-Cambrian metamorphic basement volcanic line representing supra Benioff seismic zone volcanic front.

Continuous diastrophism, along a N-S arcuate axis, of the basinal sediments on either side of the Arakan Yoma and gradual upheaval of the same since Eocene indicate that this belt has been under constant and uneven E-W compressive stress due to eastward subduction of the India Plate. The peak of deformation and upheaval had been at the close of Oligocene shaping the mega fabric of the Arakan Yoma tectogene. The Bouguer gravity anomaly contours run parallel to the axis of the sedimentary basin and the fold belts. Maximum negative value contours running adjacent to the flysch trough and the ophiolite belt, 0-anomally contour (positive by contrast) along the volcanic line and the eastward dip of the seismic zone also suggest that the lndian plate has been subducting eastward below the Shan-Tenasserim block since Eocene.

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