Late Cenozoic exhumation history of the Gaoligong and Chongshan shear zones (SE Tibet)

Abstract

The Gaoligong, Chongshan, and Ailaoshan-Red River shear zones (GLSZ, CSSZ, and ALRRSZ) are interpreted as the boundary structures, accommodating Cenozoic block or sub-block extrusion and rotation in the southeastern Tibetan Plateau. Their orogenic processes and landscape evolution have significant implications for understanding the geodynamics of intracontinental deformation. In this study, we present new low-temperature thermochronologic data from the GLSZ and CSSZ, and quantitative analyses of fluvial longitudinal profiles along the Salween valley which lies between the shear zones in order to examine their exhumation histories. The results reveal that the GLSZ and CSSZ experienced two phases of exhumation in the late Cenozoic. The first episode of rapid cooling commenced in the early Miocene caused by transpressional movements along the shear zones. The nearly contemporaneous shearing between the GLSZ and CCSZ continued until ~11 Ma. The northward migration of the tectonic events along the Mogok metamorphic belt and GLSZ, and synchronous dextral displacement along the Jiali fault indicate the dominant role of the north advancing eastern Himalayan syntaxis on the surrounding structures. The second phase of rapid exhumation, albeit of lower magnitude, occurred in the late Miocene-early Pliocene. During this interval, the tributaries along the GLSZ and CSSZ may have formed lower steep channels, compared to the upper relatively low-gradient segments. The tributary transient response could result from temporal changes in uplift or adjustments of the trunk channel to climatic change. Different drivers for the two exhumation events may reflect distinct stages of plateau growth characterized by different crustal deformation patterns