Petrogenesis of the Dongfeng granite and its dioritic enclave: Implications for the Triassic magmatism in the Songpan−Ganzi Orogenic Belt

The Songpan−Ganzi Orogenic Belt has emerged as a prominent Li−polymetallic metallogenic belt in China, characterized by polymetallic mineralization intricately associated with granitic magmatism during the Late Triassic to Early Jurassic period. The complicated magma evolution has resulted in the geochemical diversity of these granites. Enclaves play an important role in the formation of granite. However, it is still enigmatic about the role played by enclaves in the formation of granite within the Songpan−Ganzi Orogenic Belt, as well as their contribution to Li in the magmatic system. The Dongfeng pluton, located in the eastern part of the Songpan−Ganzi Orogenic Belt, is a typical granitoid that contains numerous enclaves. Zircon U−Pb dating yielded crystallization ages of 211.8 ± 1.0 Ma for the biotite granite and 210.5 ± 1.1 Ma for the dioritic enclave. The biotite granite is characterized by high−Si and prealuminous, alongside low Rb content, Rb/Sr and Rb/Ba ratios. Furthermore, it displays negative zircon ε_Hf(t) values ranging from −10.2 to −5.9, notably high (⁸⁷Sr/⁸⁶Sr)_i ratios between 0.7117 and 0.7118, and negative ε_Nd(t) values of −9.7 to −9.3. These features suggest that the parental magma derived from the partial melting of meta−sediments within the upper to middle crust. These dioritic enclaves display high concentrations of Mg, Ca, Cr and Ni, and relatively slightly depleted zircon Hf isotopes (ε_Hf(t) = −9.6 to −1.3) and whole−rock Nd isotopes (ε_Nd(t) = −9.5 to −8.8), as well as lower radiogenic Sr isotopes ((⁸⁷Sr/⁸⁶Sr)_i = 0.7108~0.7113). This indicates a lower crustal source that had undergone modifications by asthenospheric mantle materials. The pronounced variations in An values from core to rim of the plagioclase phenocrysts from the biotite granite and dioritic enclaves provides compelling evidence for mixing process involving felsic and mafic magmas. The dioritic enclaves exhibit a low Li content (26×10⁻⁶~52×10⁻⁶), reflecting that the lithium deposits in the Songpan−Ganzi Orogenic Belt are not contributed by the lower crust or deeper mantle materials.