Zircon U-Pb-Hf Isotopes, Whole-Rock Geochemistry and Sr-Nd Isotopes of Early Neoproterozoic Intrusion in the Erguna Block, NE China: Petrogenesis and Tectonic Implications

The early crustal evolution of microcontinental fragments in the Central Asian Orogenic Belt remains poorly constrained. Among these fragments, the Erguna Block records extensive Neoproterozoic magmatism that provides key constraints on its tectono-magmatic development in relation to the Rodinia supercontinent cycle. To furthering constrain the Neoproterozoic magmatic evolution of the Erguna Block, an integrated investigation combining petrography, zircon U-Pb and Lu-Hf isotopic analyses, whole-rock geochemistry, and Sr-Nd isotope data was carried out on the newly recognized Fengshuishan intrusion in northern Alongshan. Zircon U-Pb ages of 810 ± 5 Ma and 807 ± 4 Ma were obtained from granitic samples, while the dioritic sample gave an age of 773 ± 2 Ma, representing a major Neoproterozoic magmatic episode. The 810–807 Ma granites show positive zircon εHf(t) (+0.09 to +12.1) and whole-rock εNd(t) (+0.50 to +1.77), suggesting derivation mainly from partial melting of Mesoproterozoic juvenile crust with minor contribution from mantle-derived materials. In contrast, ca. 773 Ma gabbroic diorite exhibits εHf(t) values of −1.23 to +4.3 and an εNd(t) value of +1.33, implying a contribution from an enriched mantle source. These Fengshuishan igneous rocks show A-type geochemical signatures, enriched in Rb, Th, and Pb but depleted in Ba, Sr, and Eu. Integrating these data with regional geological evidence, we infer that the Fengshuishan intrusion formed in an intraplate extensional regime, recording an important phase of crust–mantle interaction during the Neoproterozoic. These results expand the record of Neoproterozoic igneous rocks in the Erguna Block and offer new constraints on its role within the Rodinia supercontinent.