Zircon U-Pb Age, Sr-Nd-Hf Isotopic Characteristics of Baiyinhushuo Adakite in Inner Mongolia: Implications for Tectonic Evolution

Abstract

The petrogenesis and geodynamic implications of the Early Paleozoic adakitic rocks in the east of Inner Mongolia remain topics of debate. This study presents new petrology data through zircon U-Pb age and Lu-Hf isotopic composition, whole-rock major-trace element geochemistry, and Sr-Nd isotopes from adakitic rocks. The zircon U-Pb dating results demonstrate that the formation age is 242.8 ± 1.0 Ma, which is the product of Early Triassic magmatism. Petrology and geochemical study have shown that the granodiorite have high SiO2 (66.93~69.40%), Al2O3 (15.37~15.43%), and MgO (1.35~1.55%), with LREE enrichment and HREE deficit, and they have high Sr, low Y, and high Sr/Y ratios, showing typical signatures of adakitic rocks. The εHf(t) values of zircon vary between +11.3 and +13.8, with low whole-rock (87Sr/86Sr)i (0.703382) and positive εNd(t) values, and the average Mg# of the rock is 56.14, suggesting that adakite derived from partial melting of MORB materials and magma interaction with the mantle. Comprehensive analysis suggests that during the Late Permian to Early Triassic, the subducted slab of the Paleo-Asian Ocean broke off, and the residual oceanic slab preserved in the mantle beneath the subduction zone underwent partial melting, generating adakitic magma.

Keywords

• Paleo-Asian Ocean
• adakite
• zircon chronology
• Sr-Nd isotope
• subducted slab