A Burma terrane related to India: Evidence from the U-Pb zircons in Late Cretaceous-Paleogene sediments from the Myanmar Central Basins
Résumé
Recent paleomagnetic data from Myanmar demonstrate that the Burma Terrane (BT)
underwent an impressive northward translation alongside India in the Cenozoic
(Westerweel et al., 2019, 10.1038/s41561-019-0443-2).
Thick sedimentary basins, filled during the Cenozoic, characterize the geology of the BT
and were first considered as the receptacle for the erosion products of the India-Asia
collision (Métivier et al., 1999; 10.1046/j.1365-246X.1999.00802.x). More local sources
have however been proposed for the infill of the Eocene Myanmar basins often
presented as forearc and backarc basins of an Andean-type magmatic arc along the
western margin of Sibumasu with uplifted parts of Eastern Myanmar e.g. Mogok
Metamorphics and Shan Plateau as additional sediment sources (Licht et al., 2013,
10.1144/jgs2012-126, Licht et al. 2016, 10.1111/bre.12108; Cai et al., 2019,
10.1046/j.1365-246X.1999.00802.x; Najman et al., 2020,
10.1016/j.epsl.2019.115948). However, the Late Eocene equatorial position of the BT
implies that the Myanmar sedimentary basins were far away from a potential source in
eastern Myanmar and challenges all these previous interpretations. We review the
numerous studies on detrital zircons (>5000 zircons) from the Late Cretaceous -
Paleogene sediments of the Myanmar central basins. While the age spectrum is
dominated by a mid-Cretaceous peak compatible with the main magmatic event along
the Myanmar magmatic arc or the Gangdese arc, more than 40% of the zircons from
sediments of the Central Basins have pre-Cretaceous ages. There is a clear correlation
in the distribution of these ages with those from the Triassic turbidites of the Pane
Chaung Fm. of the Indo-Burman ranges (Yao et al. 2017, 10.1016/j.tecto.2017.09.016)
and the Triassic sediments from the Tethyan Himalaya. This observation clearly
supports a paleogeography where the Burma terrane is on the India plate and linked to
Greater India during the Paleogene.
The large northward motion of the BT likely also impeded active subduction below
Myanmar during the Paleogene. Filling of the BT sedimentary basins is clearly
controlled by Cenozoic tectonics north of the BT due to the collision of India first with
the trans-Tethyan arc and then with Asia.
Paleoenvironments of Myanmar need to be reinterpreted using the new paleogeography.