Superimposed tectono-metamorphic episodes of Jurassic and Eocene age in the jadeite uplift, Myanmar, as revealed by 40Ar/39Ar dating

The Myanmar jadeite uplift forms an important link between the Indo-Burma Range and the Tagaung–Myitkyina Belt. Two contrasting ages of Jurassic (152.4 ± 1.5 Ma of glaucophane from blueschist) and Eocene (44.8 ± 1.1 and 45.0 ± 1.3 Ma of phengitic muscovites from quartz schists in the uplift) were yielded using 40Ar/39Ar dating. The Jurassic age of the glaucophane, even older than the forming age of the jadeitite from recent relevant literatures, and for the reason of possible excess argon involved, is interpreted as the lower limit of the subduction age. Previous studies correlated this subduction with the Woyla intra-oceanic arc, or the Incertus Arc to the west. The Eocene ages of phengitic muscovites are interpreted as the time of an intra-continental shearing deformation event, against the timing of HP/LT metamorphism as previously suggested. Combined with other studies, it is suggested that the Tagaung–Myitkyina Belt and the Indo-Burma Range belonged to a single belt, which has been separated by the Sagaing Fault, leaving the jadeite uplift straddling along the fault between the Belt and the Range. We propose a rapid exhumation model for the Myanmar jadeitite at ~ 45 Ma, coeval with onset of the Sagaing Fault.