Petrogenesis of two types of Late Triassic granite from the Guandimiao Complex, southern Hunan Province, China

作者：Zhao, Zengxia; Miao, Baihu; Xu, Zhaowen^*; Lu, Jianjun^*; Liu, Lei; Zuo, Changhu; Lu, Rui; Wang, Hao

来源：Lithos, 2017, 282: 403-419.

DOI：10.1016/j.lithos.2017.02.021

• Zircon dating
• Source rocks
• Peraluminous and metaluminous granites
• Microgranular enclaves
• Guandimiao Complex

Two types of Late Triassic granite are found in the Guandimiao Complex of the South China Block (SCB). Here, we present new LA-ICP-MS zircon U-Pb ages as well as geochemical and Sr-Nd-Pb-Hf isotopic data in order to elucidate the genesis of these granites. The Guandimiao Complex, located in southern Hunan Province, consists dominantly of the Shizhucliao two-mica alkali feldspar granite and the Jingtou hornblende-bearing biotite monzogranite. The latter contains abundant microgranular enclaves. Zircon U-Pb isotopic analyses show that the microgranular enclaves and the two types of granite were all emplaced during the Late Triassic (226-220 Ma). The Shizhucliao peraluminous granite has high (Sr-87/Sr-86)(i) ratios (0.72173-0.72485), enriched epsilon(Nd)(t) and epsilon(Hf)(t) values (-9.6 to -9.4 and -10.5 to -5.5, respectively), and Pb isotopic compositions similar to those of the metamorphic basement of the Cathaysia Block (part of the SCB), implying derivation from the crust The granite's low molar CaO/(MgO + FeOT) ratios and high molar Al2O3/(MgO + FeOT) ratios indicate a metasedimentary source. The Jingtou metaluminous granite exhibits epsilon(Hf)(t) values (-10.0 to -5.6) that are similar to those of the Shizhugiao granite, but it has lower (Sr-87/Sr-86); ratios (0.71326-0.71454) and higher epsilon(Nd)(t) values (-72 to -6.6). Its high ratios of molar CaO/(MgO + FeOT) and low ratios of molar Al2O3/(MgO + FeOT) suggest an amphibolitic source. The microgranular enclaves contain acicular apatite and are more mafic than their hosts. The combined textural, geochemical, and isotopic data indicate that the enclaves in the Jingtou granite originated from a more mafic crust-derived melt that was injected into the host felsic melt. The geochemical signatures indicate that the microgranular enclaves and the two types of coeval granite that constitute the Guandimiao Complex were derived from different source rocks. The Late Triassic granites in the SCB were emplaced in an extensional post-orogenic setting and related to underplating of mantle-derived magma.

• 出版日期2017-6
• 单位南京大学; 内生金属矿床成矿机制研究国家重点实验室; 国家海洋局第二海洋研究所; 江苏省地质调查研究院; 桂林理工大学