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Alpine-Himalayan Orogens |
United Nations Development Project, B.P. 862, Niamey, Republic of Niger
Burma is the only section of the Tertiary orogen of the Far East which is entirely above sea level and hence available for investigation over its full width. It has been intermittently studied over many years, particularly in relation to petroleum exploration, yet remains rather fragmentarily documented in the intensively folded complex in the west and the Basement shield in the east. It is an area of critical interest in relation to plate movements and the history of the Indian Ocean. The description includes the marginal tectonic zones which lie in East Bengal and India.
Segments: three segments, each approximately 400 km in N-S extent, are utilized to describe the Burma Tertiary orogen. From north to south they are the Naga Hills, Chin Hills and Arakan Yoma segments. The Naga Hills are narrow (average width of orogen—250 km). The rocks there contain ophiolites but exotic blocks are absent from the Flysch and the Miocene strata lack exotics and have a generally thinner, less complex sequence than further south. The Chin Hills are wide (700 km). Ophiolites are absent but exotic blocks are present in the Flysch and unknown in Miocene strata. In the narrow (300 km exposed above sea level) Arakan Yoma segment ophiolites are absent but exotic blocks are present in both the Flysch and in Miocene strata.
The nature of the outer (western) and inner (eastern) margins of the orogen varies considerably. The east margin varies from broadly gradational (> 3 km) to indefinite (due to structural or
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