The Timing of Collision Between Asia and the West Burma Terrane, and the Development of the Indo‐Burman Ranges

Abstract

The West Burma Terrane (WBT) is a small terrane bounded to the east by the Asian Sibumasu Block and to the west by the Indo‐Burman Ranges (IBR), the latter being an exhumed accretionary prism that formed during subduction of Indian oceanic lithosphere beneath Asia. Understanding the geological history of the WBT is important for reconstruction of the closure history of the Tethys Ocean and India‐Asia collision. Currently there are major discrepancies in the proposed timings of collision between the WBT with both India and Asia; whether the WBT collided with India or Asia first is debated, and proposed timings of collisions stretch from the Mesozoic to the Cenozoic. We undertook a multi‐technique provenance study involving petrography, detrital zircon U‐Pb and Hf analyses, rutile U‐Pb analyses and Sr‐Nd bulk rock analyses on sediments of the Central Myanmar Basins of the WBT. We determined that the first arrival of Asian material into the basin occurred after the earliest late Eocene and by the early Oligocene, thus placing a minimum constraint on the timing of WBT‐Asia collision. Our low temperature thermochronological study of the IBR records two periods of exhumation, in the early‐middle Eocene, and at the Oligo‐Miocene boundary. The Eocene event may be associated with the collision of the WBT with India. The later event at the Oligo‐Miocene boundary may be associated with changes in wedge dynamics resulting from increased sediment supply to the system; however a number of other possible causes provide equally plausible explanations for both events.

Plain Language Summary

Closure of the ancient Tethys Ocean by collision of various continental fragments culminated in the formation of the Himalayan mountain belt. A knowledge of the timing of collision of the various terranes is important to reconstruct the geological history of the region. The timing of the collision of the West Burma Terrane with both India and Asia is debated. We show that material eroded from Asia is first recorded in the Central Myanmar Basin of the West Burma Terrane after the earliest late Eocene and by the early Oligocene, providing a minimum time of docking of these continental fragments. We show two periods of exhumation of the exhumed accretionary prism of the Indo‐Burman Ranges, in the early‐middle Eocene and at the Oligo‐Miocene boundary. These events may be associated with the collision of the West Burma Terrane and India, and changes in wedge dynamics, respectively, but other causes are equally plausible.

Key Points

• First arrival of Asian detritus into the Central Myanmar Basin occurred after the earliest late Eocene and by the early Oligocene, thus constraining the time of WBT‐Asia collision

• Our low temperature thermochronological study of the Indo‐Burman Ranges indicates exhumation in the early‐mid Eocene and around the Oligo‐Miocene boundary