Reactivation of Neoproterozoic juvenile crust and relict enriched lithospheric mantle in eastern China: contribution to Mesozoic pyroxene diorite in the Tongling district

The Tongling district is a significant tectonic–magmatic–metallogenic region in eastern China. However, the genesis and tectonic setting of its magmatic rocks have long been debated. Historically, research has focused primarily on intermediate–acidic intrusive rocks, while the potential genetic implications of intermediate–mafic intrusions have been overlooked. Here, the Baimangshan pyroxene diorite in the district is investigated through analyses of whole–rock geochemistry, Sr–Nd isotopes, mineral microstructures and geochemistry, and zircon Hf–O isotopes. The results indicate that these rocks are characterized by high-K calc-alkaline series and arc-like characteristics and are enriched in large ion lithophile elements (LILEs) than Ocean Island Basalt (OIB), suggesting that the magma was derived from crust–mantle mixture. Unique mineral textures reflect the injection of high-temperature mafic magmas into acidic magmas. Inherited zircon ages are concentrated between 1000 and 700 Ma, reflecting that the sources include a Neoproterozoic crust. The similarity of zircon εHf(t), two-stage Hf model ages and δ18O values with those of Neoproterozoic magmatic rocks in the Jiangnan Orogen indicate the source rock of crust-derived magma is a Neoproterozoic juvenile crust that has undergone low-T alteration. Apatites have high Cl contents, and their rims have higher SO3, FeO and MgO contents than their cores, suggesting that mantle-derived magma was derived from a subduction-metasomatized enriched mantle. Coupled Nd–Hf isotopes suggest that oceanic crust was formed during the Mesoproterozoic. Zircon Hf–O isotopes suggest the contribution of the Neoproterozoic Cathaysia Oceanic subduction to the sources. Thus, the formation of sources was controlled by the Neoproterozoic subduction, rather than the Mesozoic Paleo-Pacific Plate subduction. This finding reflects the reactivation of the Neoproterozoic materials, with Mesozoic Paleo-Pacific Plate subduction serving as the geodynamic mechanism that reactivated these sources.