Zircon U-Pb Ages of A Felsic Vein in Ultrahigh-Pressure Eclogite from North Qinling Terrane and Their Geological Implications
He Yu
Zhao Yujie
Zhang Wenxiang
Wang Hao
Zhou Guangyan
Wu Yuanbao
Abstract：The Early Paleozoic high pressure (HP) to ultrahigh pressure (UHP) metamorphism in the North Qinling (NQ) terrane preserves the oldest UHP record in the whole Qirding-Tongbai-Hong'an-Dabie-Sulu orogenic belt and thus registers the first accretionary collision process between the South China block (SCB) and the North China block (NCB).However,its evolution processes remain the subject of heated debate.This paper presents an integrated study of CL image,trace elements,and U-Pb age of zircons from a felsic vein within a UHP eclogite outcrop from the Guanpo area,NQ terrane.Zircons from the vein are euhedral in shape,displaying oscillatory,planar or no zoning,high U but low Th contents resulting in low Th/U ratios,indicating that they precipitated from hydrous melts responsible for the vein formation.In addition,these metamorphic zircons are characterized by low LREE contents,relatively high HREE patterns,and significant negative Eu anomalies,suggesting the hydrous melts formed during the amphibolite-facies retrogression.The weighted mean 206 pb/238 U age of 494±10 Ma of these zircons is similar to the age of the peak UHP metamorphism (490.4±5.8 Ma) of the NQ unit,within the analytical error.Based on the above observations,we suggest that the NQ terrane underwent fast exhumation after deep subduction in the Early Paleozoic,and released hydrous melts derived from partial melting during exhumation,which was triggered by the significant amphibolite-faices retrogression.
Keywords：North Qinlingfelsic veinzircon U-Pb agezircon trace elementfast exhumationgeochemistrygeochronology
Publication Date：2018-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：12( 389-400 )