Geochemistry, zircon U–Pb and Lu–Hf isotopes of an Early Cretaceous intrusive suite in northeastern Jiangxi Province, South China Block: Implications for petrogenesis, crust/mantle interactions and geodynamic processes

Abstract

Abstract The Early Cretaceous Tieshan intrusive suite, in northeastern Jiangxi Province along the northern margin of the Eastern Cathaysia Block, is composed of diabase porphyrites, monzodiorites, syenite porphyries, quartz monzonites, monzogranites and granite porphyries. LA–ICPMS zircon U–Pb isotopic analyses reveal that this intrusive complex was emplaced between 142 Ma and 117 Ma. The ~ 135 Ma diabase porphyrites, monzodiorites, and syenite porphyries are characterized by low to moderate SiO2 and MgO contents, with high K2O and total alkaline contents. These rocks exhibit slightly to strongly fractionated REE patterns and upper crust-like multi-element patterns with depletions of Nb, Ta and Ti, and show strongly negative eHf (t) values of − 9.0 to − 11.8. All these patterns are identical to those of the Caiyuan syenites, Huangtuling gabbros in the east, and Lengshuikeng trachyandesites and quartz syenites in the west. These geochemical and zircon Lu–Hf isotopic features indicate that their magmatic precursors were generated by 0.2%–2% partial melting of a phlogopite-bearing enriched subcontinental lithospheric mantle source that was metasomatized by sediments. The ~ 117 Ma quartz monzonite has slightly higher eHf (t) values (− 5.6 to − 8.7) like those of the Honggong syenites, indicating an interaction between the asthenosphere and the lithosphere. The ~ 142–134 Ma granite porphyries and monzogranites are characterized by high SiO2 levels but low concentrations of refractory elements, and show enrichment of LREEs and LILEs, with variable negative anomalies of Nb, Ta, Ti, Sr, P and Ba in multi-element diagrams normalized by primitive mantle. The monzogranite exhibits strongly negative eHf (t) values of − 10.5 to − 13.3 and TDM2 (Hf) values of 1849–2023 Ma, and the granite porphyries display relatively wide eHf (t) values of − 7.2 to − 13.4 and TDM2 (Hf) values of 1645–2043 Ma, indicating that these monzogranites and granite porphyries are highly fractionated granites derived from partial melting of the Paleoproterozoic basement with involvement of enriched mantle-derived magmas or juvenile components, and the primary magma experienced fractionation of K-feldspar, plagioclase, monazite, allanite and zircon during magma ascent and emplacement. The Tieshan intrusive suite, together with the Caiyuan syenites, Huangtuling gabbros, and Lengshuikeng trachyandesites and quartz syenites, forms a highly enriched shoshonitic rock belt in the northeastern margin of the Cathaysia Block. Integrating with previously published data, we propose that the subducted Paleo-Pacific plate extended into the central South China Block in the Middle Jurassic, and experienced slab rollback during the Early Cretaceous.