INTERNAL STRUCTURE AND GEOCHRONOLOGY OF THE ZHONGBA MICROCONTINENT OF THE WESTERN YARLUNG ZANGBO SUTURE ZONE, AND A 4.13 GA OLD DETRITAL ZIRCON IN TIBETAN PLATEAU

The Zhongba microcontinent in the western part of the Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet is a critical key to the timing and nature of collisional events in the tectonic evolution of the Tibetan–Himalayan orogenic belt. The approximate 70-km-wide ( ~NE–SW direction) Zhongba microcontinent exposes for more than 700 km ( ~NW–SE direction) and tectonically trapped in the middle of two sub-belts of the ophiolites within the western part of the YZSZ. This ribbon continent is composed of Ordovician to Cretaceous biosparite, micrite, shale, meta-sandstone, meta-limestone and schist. The new mesoscale and microscale structural data show a dextral, transtensional deformation along an approximate W–E direction and a contractional deformation following the direction of NE–SW within the Zhongba microcontinent. Here we report in-situ detrital zircon U-Pb age spectrum showing a prominent peak centered in ~999 – 989 Ma, three large peaks around ~595 – 571 Ma, ~1850 – 1750 Ma, ~2600 – 2457 Ma and a small cluster around ~3128 Ma. The zircon U-Pb results provide evidence of age clusters of the Zhongba microcontinent are consistent with the detrital U-Pb age signature of Tethyan Himalaya and northern India. Moreover, the finding of one zircon with the U-Pb age of 4136.09±12 Ma in the Zhongba microcontinent indicates the Jack Hills in the Western Australia is most likely provenance who is responsible for the zircon grains in Hadean ages in the Zhongba microcontinent. Therefore, our data may also prove the sediments in the Zhongba microcontinent were derived from the northern edge of the Indian margin and Western Australia when the India and Australia have not been separated yet.