Zircon U-Pb geochronology of the Konggar granitoid and migmatite: Constraints on the Oligo-Miocene tectono-thermal evolution of the Xianshuihe fault zone, East Tibet

- SHRIMP zircon U-Pb dating of the migmatite along the Xianshuihe Fault zone.
- Deciphering an Oligocene metamorphic event along this fault zone.
- Confirming episodic emplacements of the Konggar granitic pluton at 18-12 Ma.
- Addressing the onset time (about 12-10 Ma) of the sinistral strike-slip faulting.

The Konggar massif, about 120 km long and 13 - 18 km wide, developed along the eastern segment of the Xianshuihe fault zone in East Tibet. It consists of two rock units: the Konggar granitic pluton and an elongate migmatite zone about 70 km long and 1 - 3 km wide. A metamorphic event was well recorded by the growth rims of zircons in the migmatite, their SHRIMP U-Pb dating of two rock samples taken from leucosome and melanosome yields respectively the ages of ca. 31.75 Ma and ca. 26.9 Ma. The SHRIMP U-Pb dating of zircons from two rock samples of the granitic pluton yields respectively the crystalline ages of 17.35 Ma and 14.4 Ma. These new data, together with the previously zircon U-Pb ages, the mica Ar-Ar dating ages and whole rock Rb-Sr age of the granitoid, allows to constraining the tectono-thermal evolution history of the Xianshuihe fault zone. It is inferred that this fault zone suffered along its eastern segment from high temperature metamorphism and migmatization during the Oligocene (in 32 - 27 Ma), which was followed by magma intrusion during the Miocene (in 18 - 12 Ma); sinistral shearing began to occur at about 10 Ma and continues to present-day.