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. In this study, petrology, zircon U–Pb age and Lu–Hf isotopic composition, whole-rock geochemistry and Sr–Nd isotopes from adakitic rocks. Zircon U–Pb dating results demonstrate that the formation age is 242.8±1.0Ma, 247Ma，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%), 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 a low whole-rock (87Sr/86Sr)i ( 0.703382 )and positive εNd(t) values, the average Mg# of the rock is 56.14, suggesting that adakite derived from partial melting of MORB, 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.