Magmatism Of Phanerozoic Granitoids In North Qinling Terrane,china And Its Evolution Regularity

Granite is the most important component of the continental crust,which records the reconstruction and growth of the continental crust.Therefore,the genesis of granites might provide great significance to explore the continental crust structure and composition.And provide an optimal window to unraveling the geodynamic process.In this study,we present zircon U-Pb age,whole-rock Sr-Nd-Pb isotopic and mineral element analysis for the late Mesozoic and Paleozoic granites in the North Qinlng terrane.The main achievements are obtained as follows:(1)The Huichizi and Shangnan plutons are selected from the North Qinling terrane,to explore the genesis and crustal evolution of granites in the Paleozoic North Qinling terrane.New LA-ICPMS zircon U-Pb age dating results indicate that the Huichizi pluton was emplaced at ca 423 ± 7 Ma.Geochemical characteristics indicate that the Huichizi pluton belong to I-type granite.Sr-Nd isotopic data(87Sr/86Sri=0.7050?0.7054;?ENd(t)?2.9?-0.4)indicate that the Huichizi pluton is the product of partial melting of the Neoproterozoic juvenile lower crust.They have relatively high Sr/Y and(La/Yb)N ratios,and not obvious Eu negative anomaly,showing a deep magma source with garnet stability in source area.LA-ICPMS zircon U-Pb age dating results indicate that the Shangnan pluton was emplaced at 424±11 Ma,coeval with Huichizi pluton.According to geochemical characteristics,the Shangnan pluton could divided into two group.The first group samples belong to S-type granites.They have relatively high 87Sr/86Srn ratios(0.7131-0.7158)and low?Nd(t)(-7.1 to-10.5)ratios,implying a plagioclase rich greywacke source,similar to the North Qinling metasedimentary rock;The second group has a relatively low SiO2 content and has Sr-Nd isotopic characteristics similar to the Huichizi pluton(with 87Sr/86Sri=0.7057;#Nd(t)=1.0;TDM2 =1.1 Ga),indicating the contribution of the juvenile continental crust in the source.Combined with the geochemical characteristics and temporal and spatial distribution characteristics of the Paleozoic granites in the North Qinling terrain,we tend to suggest that the Huichizi and Shangnan pluton formed in an extensional environment,and the Neoproterozoic juvenile crust is partially melted to form the Huichizi pluton,then the mafic melt contaminated with metasedimentary rocks to form the Shangnan pluton.(2)The source material is the primary factor to determine the geochemistry of granite.New zircon U-Pb dating and geochemical characteristics of the Muhuguan and Mangling plutons in the North Qinling terrane,it provide an opportunity for exploring the basement material composition and the tectonic evolution of the North Qinling terrane.Monzogranites from the two plutons are characterized by high SiO2 contents(69.3-77.0 wt.%),low Mg numbers(0.21-0.38),enriched light rare-earth elements,Th,U,and Pb,depleted high-field-strength elements,and negative Eu anomalies.The source of the Mangling monzogranite is interpreted to have been deeper than that of the Muhuguan monzogranite,on the basis of its higher Sr/Y,(Dy/Yb)N,and(La/Yb)N ratios and lower SiO2 content.Sr-Nd isotopic compositions indicate similar but heterogeneous magma sources for the two granites:87Sr/86Sri=0.7070-0.7103 and ?Nd(t)?-7.0 to-15.0 for the Muhuguan granite,and 87Sr/86Sri?0.7054-0.7083 and ?Nd(t)=-7.9 to-16.0 for the Mangling granite.The zircon U-Pb age results fall into two groups:(1)syn-magmatic zircons(153 to 140 Ma);and(2)inherited zircons that define five age clusters,namely Neoarchean-Paleoproterozoic(2633-2103 Ma),Paleoproterozoic to Mesoproterozoic(1988-1377 Ma),Neoproterozoic(975-605 Ma),Paleozoic(535-382 Ma),and Late Paleozoic—Early Mesozoic(329-187 Ma).These data are consistent with a derivation of the granites by mixing between melted underplated juvenile crust within the NQT and melts from basement rocks similar to those of the Xiong' er Group within the southern margin of the North China Craton(S-NCC).The involvement of S-NCC material is also supported by the unradiogenic whole-rock Pb isotopic composition of the Muhuguan and Mangling granites,which is similar to that of the S-NCC basement rocks.These results suggest that the widespread Late Jurassic to Early Cretaceous granitoid intrusions within the NQT were generated in an extensional geological setting associated with mantle upwelling.Melts were derived from underthrust S-NCC basement material and juvenile Neoproterozoic basaltic rocks.