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J4 ›› 2012, Vol. 18 ›› Issue (1): 133-149.

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Petrogenesis of Indosinian High Ba-Sr Granites in Laoniushan Batholith, Shaanxi Province and Their Tectonic Implications

Wang Yanfen, Shao Yi, Jiang Shaoyong, Zhang Zunzhong, Hu Jian, Xiao E, Dal Baozhang, Li Haiyong   

  1. 1. East China Mineral Exploration and Development Bureau for Non-Ferrous, Nanjing 210007, China;
    2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;
    3. State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093, China
  • Received:2011-04-29 Revised:2011-05-03 Online:2012-03-20 Published:2012-03-20
  • Contact: Shao Yi, Research Fellow; E-mail: shaoyi@china-ece.com
  • About author:Wang Yanfen, Assistant Research Fellow. E-mail: wangyfnj@126.com

Abstract:

       The Laoniushan complex granitic batholith occurs in Xiaoqinling orogen along the southern margin of the North China
Craton. Zircon LA-ICP-MS U-Pb dating yields an age of 207.9±0.72 Ma for the Kangping pluton, which is the early-stage
granites in Laoniushan batholith, indicating that they were generated from the Early Mesozoic magmatism. These granites are characterized by metaluminous, high silica and total alkalinity with high FeO*/(FeO*+MgO) ratios, LILEs (especially Sr and Ba) and LREEs, low HREEs and Y contents, and insignificant Eu anomalies, similar to the high Ba-Sr granites. In comparison to the typical slab-derived adakites, the Kangping granites have low compatible elements (such as Cr, Ni) and high K2O contents with high-K calc-alkaline features, and display insignificant fractionation of HREEs. During the diagenetic processes, the geochemical behaviors of these granites were mainly constrained by the fractional crystallization of amphibole (clinopyroxene), plagioclase (K-feldspar), and minor garnet. Element and isotope compositions suggest that the sources of the Kangping granites in Laoniushan complex batholith are the mixture of the ancient basement materials of Taihua Group and small amounts of enriched lithospheric mantle metasomatised by fluid/melt that was derived from pelagic sediments-bearing subducted slab. These granites were generated by partial melting of the lowest part of the crust due to the subducted slab break-off during the post-collision extensional stage of the continental collision and orogenic processes.

Key words: High Ba-Sr granite, Post-collision, Xiaoqinling orogen, Laoniushan, Shaanxi Province

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