Chronology and petrogenesis of the Hejiazhuang granitoid pluton and its constraints on the Early Triassic tectonic evolution of the South Qinling Belt

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• 作者：PengTao Yang (1) (2)
  ShuWen Liu (1)
  QiuGen Li (1)
  ZongQi Wang (3)
  Fan Zhang (1)
  Wei Wang (1)
  
• 关键词：granodiorites in Hejiazhuang pluton ; zircon U ; Pb ; Hf isotopic systematics ; petrogenesis and tectonic setting ; evolution of South Qinling Tectonic Belt
• 刊名：Science China Earth Sciences
• 出版年：2014
• 出版时间：February 2014
• 年：2014
• 卷：57
• 期：2
• 页码：232-246
• 全文大小：1,177 KB
• 作者单位：PengTao Yang (1) (2)
  ShuWen Liu (1)
  QiuGen Li (1)
  ZongQi Wang (3)
  Fan Zhang (1)
  Wei Wang (1)
  
  1. Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing, 100871, China
  2. Key Laboratory of Crustal Dynamics, Institute of Crastal Dynamics, China Earthquake Administration, Beijing, 100085, China
  3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China
  
• ISSN：1869-1897

文摘

The Hejiazhuang pluton is located in the South Qinling Tectonic Belt (SQTB) in the north side of the Mianxian-Lueyang Suture Zone, and consists dominantly of granodiorites. LA-ICP-MS zircon U-Pb dating and Lu-Hf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at ?48 Ma, and show a large variation in zircon ?Hf(t) values from ?.8 to 8.8. These granodiorite samples are attributed to high-K to mid-K calc-alkaline series, and characterized by high SiO2 (66.6%-0.0%), Al2O3 (15.04%-6.10%) and Na2O (3.74%-.33%) concentrations, with high Mg# (54.2-1.7). All samples have high Sr (627-51 ppm), Cr (55-73 ppm) and Ni (17.2-82 ppm), but low Y (5.42-.41 ppm) and Yb (0.59-.74 ppm) concentrations with high Sr/Y ratios (84.90-20.66). They also display highly fractionated REE patterns with (La/Yb)N ratios of 18.9-4.0 and positive Eu anomalies (δEu=1.10-.22) in the chondrite-normalized REE patterns. In the primitive mantle normalized spidergrams, these samples exhibit enrichment in LILEs but depletion in Nb, Ta, P and Ti. These geochemical features indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments, and the melts were polluted by the mantle wedge materials during their ascent. The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at ?48 Ma ago, and the SQTB was still under subduction tectonic setting in the Early Triassic.