Geochronology and Hf Isotope Study of Pegmatite in the Xiaoqinling Area of NW China： Implication for Petrogenesis and Regional Metamorphism

• Published in: Journal of earth science (Wuhan, China) Vol. 26; no. 3; pp. 295 - 305
• Main Authors: Zhao, Haixiang, Jiang, Shaoyong, Dai, Baozhang, Ma, Liang, Li, Jianwei
• Format: Journal Article
• Language: English
• Published: Wuhan China University of Geosciences 01.06.2015; Springer Nature B.V; School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China%State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China%State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China
• Subjects: Ablation; Biogeosciences; Cratons; Crystallization; Earth and Environmental Science; Earth Sciences; Geochemistry; Geochronology; Geochronometry; Geological time; Geology; Geotechnical Engineering & Applied Earth Sciences; Hf同位素; Inductively coupled plasma mass spectrometry; Isotope studies; Isotopes; Laser ablation; Lasers; Lava; Lead; Magma; Mantle; Mass spectrometry; Mass spectroscopy; Melting; Metamorphic rocks; Metamorphism; Metamorphism (geology); Minerals; Pegmatite; Petrogenesis; Petrography; Petrology; Radiometric dating; Regions; Rock; Thorium; Uranium; Zircon; 中国西北; 区域变质作用; 小秦岭地区; 年代学; 电感耦合等离子体质谱; 花岗伟晶岩; 锆石U-Pb年龄; China; pegmatite; metamorphism; zircon U-Pb dating; Hf isotope; Xiaoqinling
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-015-0537-8

In this study, we carried out petrography, zircon U-Pb geochronology and Hf isotopic analyses on a granitic pegmatite dyke in the Xiaoqinling area in southern margin of the North China Craton（NCC）. Our study suggests that the pegmatite dyke likely crystallized from a volatile-rich pegmatitic magma. Different from most other pegmatite elsewhere, zircon from this pegmatite dyke does not contain unusually high U and Th concentrations and suffered no evident radioactive damage, therefore we successfully obtained a zircon U-Pb dating using laser ablation-inductively coupled plasma-mass spectrometry（LA-ICP-MS）, which yields an average 207Pb/206 Pb age of 1 814±6 Ma, representing the intrusive age of the granitic pegmatite dyke. Zircon εHf（t） values are between-8.3 and-3.0, corresponding to Hf depleted mantle model ages from 2 649 to 2 991 Ma with an average of 2 881 Ma. These data indicate that this granitic pegmatite dyke may have been derived from partial melting of Meso-Neoarchean metamorphic rocks from the Xiaoqinling basement. Granitic pegmatite magma may have emplaced within the Taihua Group wall rocks during the last stage of the middle to high grade metamorphism. Furthermore, according to the petrographic observation, the 1.81 Ga pegmatite dyke and the 1 800–1 750 Ma Xiong’er Group rocks were not undergone middle to high grade metamorphism, indicating 1.81 Ga as the termination of the latest regional metamorphism in the southern margin of the NCC.