Petrogenesis of Early Cretaceous volcanic rocks in the Tuoyun Basin, western Central Asian Orogenic Belt: Implications for crust–mantle interaction

Abstract

The petrogenesis of continental intraplate basalts has been widely debated, primarily due to the uncertainties surrounding their thermal state and the role of recycled materials. Herein, we focus on the Early Cretaceous basalts from the Tuoyun Meso-Cenozoic volcanic basin, located in the western Central Asian Orogenic Belt. The samples are porphyritic, with phenocrysts predominantly composed of olivine, clinopyroxene, and plagioclase. Primitive mantle-normalized incompatible trace element patterns and chondrite-normalized rare earth element patterns show a strong ocean island basalt affinity. The Zn/Fe, Mn/Zn, and Fe/Mn ratios in olivine suggest a mixed source of peridotite and pyroxenite. This is further supported by trends in the whole-rock CaO–MgO compositions, FeO/MnO ratios (42.1–106.5), and FCKANTMS values (0.52–0.82). Additionally, the basalts exhibit significantly lighter Mg and heavier Zn isotopic compositions compared to the normal mantle, suggesting the involvement of recycled sedimentary carbonates. However, the olivine SIMS in situ oxygen isotopes show reveal that the Early Cretaceous basalts in the Tuoyun Basin have normal mantle oxygen isotope compositions, with δ¹⁸O_V-SMOW values ranging from 5.12 ‰ to 5.76 ‰. Moreover, the absence of typical carbonate signatures, such as negative anomalies in Zr, Hf, and Ti in the trace elemental spider diagram, indicates that carbonates did not participate in the partial melting of the mantle source. The decoupling of O and Mg–Zn isotopic signatures suggests that recycled carbonates may have decomposed during subduction. Overall, this study implies that the formation of intraplate basalts may be significantly influenced by recycled oceanic crust derived from ancient subducted slabs.