Abstract

Correlation of late Mesozoic mafic and ophiolitic rocks suggests that in the late Lower Cretaceous a northeasterly-facing mafic arc was emplaced onto southeast Borneo, western Sumatra, western Myanmar (Burma) then 1100 km south of its present position, the Mogok belt of Myanmar and the Denqen–Bangong Co ophiolite zone in Tibet, all then situated on the southwestern margin of Asia. Reversal in tectonic polarity and eastward subduction generated a late Cretaceous magmatic arc in western Myanmar and Sumatra, and its continuation through the Mogok belt into the Gandise batholith of Tibet. Magmatism, interrupted in the latest Cretaceous, probably resumed in the western Myanmar–Tibet and Sumatra arc segments in the early Palaeogene. It was again interrupted in the Mid-Eocene when an east-vergent ophiolite nappe overrode the Indo-Burman Ranges, deforming Lower Eocene turbidites derived from the magmatic arc to the east. Following renewed northward and eastward subduction of ocean floor in the latest Eocene, India collided with northern Myanmar, and with Tibet along a suture south of the Jurassic–Triassic flysch and adjacent Yarlung ophiolite. In the Mogok segment of the late Cretaceous arc, crust thickened in the early Cretaceous orogeny underwent extension to form a metamorphic core complex as Myanmar, west of the Sagaing Fault moved northward. More than half of this northward movement preceded the well-documented 450 km of post-early Miocene dextral displacement on the Sagaing Fault and related spreading in the Andaman Sea. Generation of late Cretaceous to early Eocene I- and S-type granites in and east of the Mogok belt was related either to crustal shortening, or more probably, to subsequent extension in the Mogok belt.

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