Early Mesozoic ferroan (A-type) and magnesian granitoids in eastern South China

tracing the influence of flat-slab subduction at the western Pacific margin

Kong Yang Zhu*, Zheng Xiang Li, Xi Sheng Xu, Simon A. Wilde, Han Lin Chen

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Zircon U-Pb ages, Hf isotopes andwhole-rock geochemical data are used to constrain the petrogenesis of the Late Triassic-Early Jurassic granitoids in southeastern China and their tectonic settings. The 225 Ma Qiuwang and 178 Ma Xiepu granites at Ningbo, Zhejiang Province, have εHf(t) values of -15.7 to -9.9 and -17.6 to -13.4, respectively. They are both ilmenite-series granitoids derived from the Paleoproterozoic basement of the Cathaysia Block in South China. The Late Triassic Qiuwang granite is strongly peraluminous with high zircon saturation temperatures (850-900 °C), and high Gd/Yb (2.7-4.8) and Ga/Al ratios (3.7-4.6 × 10-4). In contrast, the Early Jurassic Xiepu granite is weakly peraluminous with low zircon saturation temperatures (~670 °C), low Gd/Yb (1.0-1.1) and high Ga/Al ratios (2.4-2.6 × 10-4). The Qiuwang granite records higher melting temperatures and pressures than the younger Xiepu granite, reflecting a change in the tectonic regime from collisional tectonics to orogenic collapse. A regional review indicates that Triassic flat-slab subduction along the western Pacific may have led to thickening of the continental crust and metasomatism-oxidation of the continental lithosphere in the regions relatively close to the trench, where Cordilleran-type magnesian granitoids were generated. However, contemporaneous magnesian granitoids were produced in the thickened crust away from the trench, where the source rocks have uniformly moderate oxygen fugacities and metasomatism-oxidation was insignificant. Such Early Mesozoic "A-type" granitoids in the coastal region of South China are related to water-deficient and reduced melting conditions rather than an anorogenic tectonic setting.

Original languageEnglish
Pages (from-to)371-381
Number of pages11
JournalLithos
Volume240-243
DOIs
Publication statusPublished - Jan 2016
Externally publishedYes

Keywords

  • Early Mesozoic
  • Ferroan and magnesian granitoids
  • Flat-slab subduction
  • South China

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