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

SHRIMP zircon U-Pb age and Nd isotopic study on

the Nyainqêntanglha Group in Tibet

作者：HU;Daogong;WU;Zhenhan;JIANG;Wan;SHI;Yuruo;YE;Peish 作者机构：

Institute;of;Geomechanics,;Chinese;Academy;of;Geological;Sciences,;Beijing;100081,;China;Institute;of;Geomechanics,;Chinese;Academy;of;Geological;Sciences,;Beijing;100081,;China;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;Institute;of;Geomechanics,;Chinese;Academy;of;Geological;Sciences,;Beijing;100081,;China;Institute;of;Geomechanics,;Chinese;Academy;of;Geological;Sciences,;Beijing;100081,;China 来源：中国科学 年：2005 卷：000 期：009

页码：P.1377-1386 页数：10 中图分类：N 正文语种：CHI 关键词：

Nyainqêntanglha;Group,;SHRIMP;dating,;Nd;isotope,;Neoproterozoic,;Tibet.

摘要：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±9 Ma of zircons from the trondhjemite imposes a constraint on maximum protolith age, and minimum formation age of the Nyainqêntanglha Group is constrained by U-Pb age of 748±8 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 developed 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 207Pb/206Pb ages from 947 to 1766 Ma. The positive εNd( 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.