New Zircon U‐Pb Geochronology of the Post‐kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan‐Red River Shear Zone and Its Geological Implications

Abstract:The Ailao Shan‐Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest. It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian‐Eurasian collision. Diancang Shan (DCS) high‐grade metamorphic complex, located at the northwest extension along the Ailao Shan‐Red River (ASRR) shear zone, is a representative metamorphic complex of the ASRR tectonic belt. Structural and microstructural analysis of sheared rocks in the high‐grade metamorphic rocks reveals that they are coherent with solid‐state high‐temperature ductile deformation, which is attributed to left‐lateral shearing along the ASRR shear zone. New LA‐ICP‐MS zircon U‐Pb geochronological and microstructural studies of the post‐kinematic granitic plutons provide a straightforward time constraint on the termination ductile left‐lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone. It is suggested that the left‐lateral shearing along the ASRR shear zone ended at ca. 21 Ma at relative lower‐temperature or decreasing temperature conditions. During or after the emplacement of the young dikes at ca. 21 Ma, rapid brittle deformation event occurred, which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.