Indo-Burma passive amalgamation along the Kaladan Fault: Insights from zircon provenance in the Chittagong-Tripura Fold Belt (Bangladesh)

A clear insight of the Indo-Burma amalgamation is required for an understanding of the complex processes of the Indo-Asian collision. Where and when the northeastern part of the Indian subcontinent amalgamated with the Burma plate has not yet been well defined. In order to better understand the tectonic affiliations and evolution of the Indo-Burma Ranges (IBR), we report new detrital zircon U-Pb and Hf isotope data of nine sandstone/siltstone samples (late Miocene- Pliocene) from the Chittagong-Tripura Fold Belt, Bangladesh, which is in the Neogene belt of the IBR. Our results show that the zircon ages of all nine samples have three peaks at <200 Ma, ca. 500 Ma, and 800-1000 Ma. The percentage of young (<200 Ma) zircons increase from the Boka Bil Formation (6.9% to 15.2%) to the Tipam Formation (20.3% to 27.6%). The epsilon(Hf)(t) of most young zircons from the Boka Bil Formation suggest derivation from the Gangdese arc, whereas those from the Tipam Formation show an affinity with the Burma magmatic arc. Therefore, we suggest that the increase of young zircons in the Tipam Formation came from the Burma plate. Comparing provenances of the Paleogene and Neogene belts of the IBR, we suggest that they belong to the Burma plate and Indian subcontinent, respectively, and that the Kaladan Fault, separating these two belts, is the suture between the Indian and Burma terranes. The time of amalgamation is constrained by the ca. 2.5-3.9 Ma boundary between the Boka Bil and Tipam formations, and the eastern Indian promontory likely collided with the Burma plate ca. 11-12 Ma.