SHRIMP zircon U-Pb age and Nd isotopic study on the Nyainqêntanglha Group in Tibet

• Published in: Science China. Earth sciences Vol. 48; no. 9; pp. 1377 - 1386
• Main Authors: Hu, Daogong, Wu, Zhenhan, Jiang, Wan, Shi, Yuruo, Ye, Peisheng, Liu, Qisheng
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.09.2005; Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China%Institute of Geology, Chinese Academy of Geological Sciences, Beijing SHRIMP Centre, Beijing 100037, China
• Subjects: Backscattering; Basements; Cathodoluminescence; Constraints; Continental margins; Geochronometry; Geology; Granite; Lead; Oceanic crust; Plate tectonics; Radiometric dating; Rocks; Tectonics; Zircon; Nd isotope; Nyainqêntanglha Group; SHRIMP dating; Tibet; Neoproterozoic
• ISSN: 1006-9313; 1674-7313; 1862-2801; 1869-1897
• DOI: 10.1360/04yd0183

The Nyainqêntanglha Group is traditionally viewed as the oldest metamorphic basement in the Lhasa block, but its formation age and tectonic setting remain debate. Zircons extracted from the metamorphic sequence of volcanics and intrusions of the Nyainqêntanglha Group, 10 km west of Nam Co in northern Lhasa block, have been investigated by cathodoluminescence (CL), backscattered (BSE) and dated by ion microprobe (SHRIMP). We conclude that the U-Pb age of 787 ê9 Ma of zircons from the trondhjemite imposes a constraint on maxi-mum protolith age, and minimum formation age of the Nyainqêntanglha Group is constrained by U-Pb age of 748 ê8 Ma of zircons from the granite. The formation age of the Nyainqêntanglha Group is consistent with sedimentary age of Greater Himalayan rocks, showing that they devel-oped coevally in an arc-basin tectonic setting of Neoproterozoic active continental margin along the northern margin of the India shield. The inherited zircons from the tholetiite and granite give older 207 Pb/206 Pb ages from 947 to 1766 Ma. The positive å Nd(t) value indicates that the mafic rocks were derived from the depleted mantle, but contaminated by the older continental crustal material. Integrated Nd model age and U-Pb age data provide excellent evidence for the existence of Mesoproterozoic basement in the Lhasa block during Neoproterozoic time.