The Xuelongshan high strain zone: Cenozoic structural evolution and implications for fault linkages and deformation along the Ailao Shan–Red River shear zone

Abstract

New structural, geometric, petrographic, and U–Pb zircon data constrain the kinematics of the Xuelongshan high strain zone, northermost parts of the Ailao Shan–Red River shear zone. In the Xuelongshan range, mylonitic foliation mainly trends NW–SE. On steep foliation and flatted foliation, mineral stretching lineation is various, from gentle to steep, and ductile shear senses indicate a left–lateral, top–to–the–northwest shear movement on the eastern limb, and a left–lateral, top–to–the–southeast shear on the western limb of the range. These dome-related ductile geometries and kinematics, namely D1 deformation, represent regional high-temperature metamorphism due to crustal thickening. The superimposed sinistral strike–slip shearing of D2 deformation occurred locally along the earlier domal fabrics. Metamorphism, migmatization, and the emplacement of leucogranitic veins associated with partial melting were syntectonic with the regional–scale upright antiform. LA–ICP–MS U–Pb dating of zircons reveals the late Permian–Triassic and Oligocene thermal events. The latter event (ca. 33–26 Ma or possibly earlier) from the leucogranitic veins corresponds to the regional metamorphism during crustal thickening along the Xuelongshan. These data indicate that the Jiali–Xuelongshan–Diancangshan–Ailao Shan high strain zones can belong to a system around the Eastern Himalayan Syntaxis (EHS), and that the Xuelongshan zone played a role in linking other segments between the Tibet to Indochina in Cenozoic.