Geochemistry, Sr-Nd-Hf Isotopes and Petrogenesis of Mid-Late Triassic Baizhangzi Granitic Intrusive Rocks in Eastern Hebei-Western Liaoning Province
Xiong Le
Shi Wenjie
Li Huan
Tian Ning
Chen Chong
Zhou Hongzhi
Zhao Shaoqing
Li Pengyu
Abstract：The source of the Mid-Late Triassic adakitic rocks remains controversial in the eastern Hebei-western Liaoning Province in recent years,and there is a lack of petrogenesis studies on the Baizhangzi granitic rocks within this NE-striking uplift.Zircon U-Pb and Hf isotope data,whole rock major and trace element and Sr,Nd isotope data are presented for the Baizhangzi graniticintrusive rocks in this paper.Zircon U-Pb datingyields a weighted mean age of 233±3 Ma.The granitic rocks are featured with the high contentof MgO and Mg#,and low content of Cr,Co,Ni.The granitic intrusive rocks are enriched in largeion lithophile elements,depleted in high-field-strength elements (e.g.Nb,Ta,Ti,P),and display strong positive Pb,Th anomalies and negative Nb,Ta,Ti,P anomalies.Rare earth elements (REE) display right-dipping chondrite-normalized REE patterns,indicating significant fractionation between light REE and heavy REE.The initial 87 Sr/86 Sr ratios and ε Nd (t) values vary from 0.704 45 to 0.705 24 and-7.3 to-1.7,respectively.The ε Hf (t) values of zircons vary from-13.4 to-5.9.It is concluded that the Baizhangzi granitic rocks were derived from partial melting of mafic lower continental crust of the NCC.The high Sr/Y,low Y and negative Nb-Ta anomalies are intrinsic characteristics of the lower continental crust.The Baizhangzi gra nitic rocks have decoupled Nb-Ta characteristics similar to the Archean-Paleoproterozoic TTG suites,which indicates that the Archean-Paleoproterozoic TTG rocks might have been involved in the magma source.The nonradiogenic Sr,scattered Nd-Hf isotopic compositions and low compatible trace element contents also suggest that the granitic rocks were derived from modified lower continental crust.The mafic lower continental crust has experienced modification by basaltic underplating during the Early Mesozoic,which led to formation of some juvenile crust materials.At the same time,melts produced by melting of the lower continental crust induced by basaltic underplating experienced fractional crystallization of plagioclase to some extent and intruded into the supercrust.
Keywords：Baizhangzi granitic intrusive rockseastern Hebei-western LiaoningTriassicmagma sourcesgeochronologygeochemistry
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：16( 207-222 )