Abstract
The Mesozoic geology of the Zangbo zone in Tibet is closely comparable to that of the zone's continuation through western Burma. Deposition of Triassic turbidites and locally Jurassic sediments on and immediately oceanward of the passive Asian margin was followed by imbrication above subducting ocean floor in the Early Cretaceous. The subducting slab became detached from the downgoing lithosphere and accreted to Asia in the late Lower Cretaceous. Emplacement of the detached slab by southward thrusting over its Triassic flysch cover to form the Zangbo and western Burma ophiolite took place respectively in or after the Cenomanian and before the Albian. Subsidence and deposition of Albian limestones and mudstones in Burma and of the Xigatse flysch in a fore-arc basin in Tibet were followed in both regions by pre-Campanian uplift and Campanian to early Maastrichtian marine deposition. Maastrichtian olistostromes resulted from underthrusting and tectonic burial of poorly consolidated Campanian sediments, their extrusion together with blocks of adjacent older rock, and downslope flow of the extruded melange. Collision of India with Asia in the Eocene was not associated with ophiolite emplacement and in the Zangbo region resulted chiefly in northward-directed thrusting of the Triassic flysch and ophiolite over the Xigatse flysch, with consequent narrowing of the fore-arc basin.
