Welcome to visit Geoscience!

Geoscience ›› 2019, Vol. 33 ›› Issue (03): 487-500.DOI: 10.19657/j.geoscience.1000-8527.2019.03.03

• Ore Deposits and Petrology • Previous Articles     Next Articles

Zircon U-Pb Age,Geochemical and Tectonic Significance of Early Cretaceous Namtso Rhyolite in Tibet,China

WEI Yongfeng1,2(), XIAO Qianru2, LI Youbo1,2, LUO Wei1,2, RAN Jie1, LIN Meiying1   

  1. 1. Regional Geological Survey Party,Sichuan Bureau of Geology and Mineral Resources Development,Shuangliu,Sichuan 610213,China
    2. College of Earth Sciences,Chengdu University of Technology,Chengdu,Sichuan 610059,China
  • Received:2018-03-21 Revised:2018-11-30 Online:2019-06-23 Published:2019-06-24
  • Contact: XIAO Qianru

Abstract:

The Namtso rhyolite is located in the southern margin of the North Gangdese Belt. It belongs to the Woronggou Formation and overlies the Middle-Late Jurassic Lagongtang Formation along an angular unconformity.The rhyolite is LA-ICP-MS zircon U-Pb dated to be Early Cretaceous(120-112 Ma). The rocks are characterized by high SiO2, Al2O3 and K2O, and low TiO2, MgO and CaO, A/CNK=0.94-1.91(average 1.16). The rhyolite is high-K calc-alkaline and peraluminous. The chondrite-normalized patterns show a gently right-inclining ((La/Yb)N=1.49 to 11.08) “V” shape and weakly negative Eu anomalies(δEu= 0.12 to 0.55). The elements of Rb, K, Th, Ta, Ce, Zr and Hf are enriched, while Nb and Ba, Sr, P and Ti are strongly depleted, suggesting a crustal inheritance. The geochemistry can be compared with the Duoni Group felsic volcanic rocks. The Namtso rhyolite does not have the characteristics of typical island arc rhyolites, but mimics those of collisional felsic volcanic rocks. We considered that during the middle Early Cretaceous(ca.120 Ma), a major tectonic event may have occurred in the North Gangdese Belt, i.e., subduction of Neo-Tethys Ocean in the Bangong Lake and Nujiang River region had ended, and the continent-continent collision in the Gangdese and Qiangtang region had begun. During the collision, the lower crust may have thickened and partially melted, forming the Namtso rhyolite.

Key words: zircon U-Pb age, Early Cretaceous, rhyolite, Woronggou Formation, Namtso, North Gangdese belt, Tibet, China

CLC Number: