关键词: A型花岗岩, 地球化学, 锆石U-Pb定年, 造山后伸展, 义敦岛弧带

Abstract: The Yidun island arc is a significant component of Sanjiang Tethys composite orogenic belt. This paper presents zircon
U-Pb age, whole-rock geochemistry and Sr-Nd-Pb isotopic data for the Haizishan granite from the Yidun island arc, aiming to explore
its petrogenesis and geological significance. Zircon U-Pb dating results show that the Haizishan granite pluton was crystallized at 93.7±
1.1 Ma (MSWD=2.1, 2σ), indicating it was produced during early period of Late Cretaceous. The Haizishan granite is characterized by
high SiO2 and alkali, with A/CNK values of 1.04-1.12, showing a weakly peraluminous affinity. REEs of the granites are characterized
by significant negative Eu anomalies with Eu/Eu* values of 0.05-0.32. The granitic rocks are enriched in Rb, Th, U, Ta, Pb but
depleted in Ba, Sr. The εNd(t) values of the granites range from -4.8 to -3.4, with two-stage model age of 0.91-1.00 Ga. In combination
with their Pb isotopic characteristics and the chemical signatures of low CaO/Na2O and high Al2O3/TiO2 ratios, it is suggested that the
Haizishan granite was originated from partial melting of argillaceous rocks with addition of minor mantle component. Based on a
synthesis of their geochemistry, isotope characteristics and geological setting, we suggest that the Haizishan granite can be genetically
grouped into A-type granites which were generated by partial melting of argillaceous rocks with minor involvement of mantle
components in a post-collisional extension tectonic setting induced by upwelling of asthenosphere mantle.

Key words: A-type granite, geochemistry, zircon U-Pb dating, post-collisional extension, Yidun island arc belt