Burma Terrane Collision and Northward Indentation in the Eastern Himalayas Recorded in the Eocene‐Miocene Chindwin Basin (Myanmar)

Abstract

The Burma Terrane (Myanmar) played an important role in the India-Asia collision and moved over 2,000 km northward on the Indian Plate during the Cenozoic, before colliding with the Asian margin. However, the timing of this collision and its correlation to regional uplift phases, sedimentary provenance, and basin development remain poorly constrained. We report sedimentological, paleomagnetic, and geochronological data from the late Eocene to early Miocene strata of the Chindwin Basin in the Burmese forearc, constraining the paleogeographic evolution of the Burma Terrane and the Eastern Himalayan orogen. Our results highlight two unconformities of late Eocene-middle Oligocene and latest Oligocene-early Miocene age, revealing a two-stage interaction of the Burma Terrane with the Asian margin during its northward translation. The first unconformity follows rapid~0.6 m/ky subsidence in the Burmese forearc, as shown by magnetostratigraphy. The transition to a fluvial depositional environment and the occurrence of reworked sediments at this first unconformity likely records the commencing collision of India and the northern extent of the Burma Terrane with the Asian margin. The second unconformity shows drastic changes in magnetic properties, mineralogy, and provenance, with high-grade metamorphic grains and early Miocene apatite U-Pb and fission-track ages indicating that it is coeval to a major deformation phase in Myanmar and the Eastern Himalayan orogen. It likely records the indentation of the Burma Terrane into the Eastern Himalayan collision zone, forming the modern Eastern Himalayan Syntaxis.

Crustal Clockwise Rotation of the Southeastern Edge of the Tibetan Plateau Since the Late Oligocene

“…This process recorded the northward moving of the West Burma Block and the northward migration of extremely intense compression between the West Burma Block and southeastern Tibetan Plateau and its edge. The drastic changes in magnetic properties, mineralogy and provenance, with high‐grade metamorphic grains and early Miocene apatite U‐Pb and fission track ages of the Burmese forearc also likely recorded the indentation of the West Burma Block into the Eastern Himalayan orogenic belt, forming the EHS, since the latest Oligocene‐early Miocene age (Westerweel et al., 2020). These results consistently indicate that the Indian Plate and West Burma Block began to indent into the Eastern Himalayan orogenic belt to form the EHS since ∼28‐26 Ma (Figure 6b).…”

Fossil woods from the lower Miocene of Myanmar (Natma Formation): paleoenvironmental and biogeographic implications

“…The age of the Natma Formation is constrained by the age of geological units higher and lower in the Chindwin Basin stratigraphy. The Letkat Formation has yielded detrital zircons and apatite ages as young as 20-17 Ma, indicating a lower Miocene age or younger (Wang et al 2014;Licht et al 2019;Westerweel et al, 2020). The base of the Irrawaddy Formation, also named Mingin Gravels in the Chindwin Basin, has yielded fossil mammals (Tetralophodon cf.…”

“…There is ~1.5 km of sediment thickness (Shwethamin Formation) between the top of the Natma Formation and the base of the Mingin Gravels, implying some significant time lag between both units. Based on these constraints, the Natma Formation is attributed to the upper lower Miocene to lowermost middle Miocene (Westerweel et al, 2020).…”

“…The Natma Formation reflects deposition from a paleo-drainage flowing southward into the Minbu Basin and the Andaman Sea further South, by contrast to the Pondaung Formation, which was opened to the Bengal Bay (Licht et al 2019). Though no specific study has focused on the provenance of the Natma Formation, Westerweel et al (2020) propose the Indo-Burman Ranges, the Wuntho Popa Arc in central Myanmar, and the eastern Himalayan Syntaxis further north as potential sources for the underlying unit, the Letkat Formation.…”

“…studies have shown that central Myanmar river drainages experienced significant restructuring during the Oligocene based on changes of sedimentary provenance in nearby basins (Licht et al 2016;Zhang et al 2019;Westerweel et al 2020). None of these studies specifically addressed the provenance history of the Natma Formation, but they showed no evidence for long-distance sediment transport into Myanmar, far outside the modern drainage basin of central Myanmar.…”