关键词: 北秦岭地体, 晚中生代, 新生地壳再造, 黄花墁岩体, 岩石成因

Abstract: The eastern Qinling orogen documents two magmatic episodes of granitoids in the Late Jurassic and Early Cretaceous. Their geochemical characteristics, being a petrologic probe for the composition and structure of the deep crust, are distinctly different, pointing to the complex magma sources. In this study, we report zircon U-Pb isotopic ages and whole-rock major and trace element contents and Sr-Nd-Pb isotopic compositions of the Huanghuaman pluton exposed in the eastern section of the North Qinling block. Zircon U-Pb ages indicate that the large-volume biotite monzogranite of the Huanghuaman pluton was emplaced during the 119 Ma to 117 Ma interval. The biotite monzogranites are enriched in large ion lithophile elements and light rare earth elements, but depleted in high field-strength elements and heavy rare earth elements, with significantly negative Eu anomalies and belong to the weakly peraluminous high-K calc-alkaline series. They are characterized by high radiogenic Pb isotopic compositions and relatively depleted Nd isotopic composition with initial εNd values of -5.7 to -4.1. These geochemical characteristics are remarkably different from those of the Late Jurassic granitoids within the North Qinling block and L ate Mesozoic granitoids within the southern margin of the North China block. The relatively depleted Nd isotopic composition of the Huanghuaman pluton is similar to those of the coeval Laojunshan in the eastern section and the Early Cretaceous Taibai granite in the western section of the North Qinling block, s uggesting that this block underwent large-scale reworking of the juvenile crust during the Early Cretaceous. The juvenile crustal materials might be derived from the mafic rocks within the North Qinling block or the subducted Neoproterozoic crustal rocks of the Yangtze and/or South Qinling blocks. These Early Cretaceous granitoids have different Nd isotopic compositions from those of the Late Jurassic Mangling and Muhuguan plutons in the North Qinling block, reflecting the compositional diversity of the granitoids that were derived from the deeply underlying, co mplex crustal materials.

Key words: North Qinling, Late Mesozoic, reworking of the juvenile crust, Huanghuaman pluton, petrogenesis