970–840 Ma magmatic records from the Douling Complex: Insights into Tonian Subduction-Accretionary and collisional processes in the northern Yangtze Block

Tonian subduction-accretionary and collisional records are fundamental for elucidating the tectonic evolution of the northern Yangtze Block. The Douling Complex along the northern margin of the Yangtze Block preserves key Neoproterozoic records. However, due to the limited exposure of Tonian magmatic rocks, the tectonic regime during this period remains ambiguous. In this contribution, we present new geochronological, geochemical, and isotopic data from amphibolites, mica schists, and gneissic diorite–granodiorites from the Douling Complex. The amphibolites yield protolith ages of ca. 970–920 Ma, representing the earliest Neoproterozoic magmatic event identified in the Douling Complex. These amphibolites exhibit tholeiitic affinities, low Th/Nb and Th/Zr ratios, and positive whole-rock Ɛ_Nd(t) values (+3.39 to + 5.12) and zircon Ɛ_Hf(t) values (+3.8 to + 11.1), indicating a depleted mantle source. Two groups are distinguished: Group I (ca. 920 Ma) displays E-MORB affinities and higher TiO₂ contents, and is spatially associated with mica schist, suggesting formation in a subduction-related back-arc basin; Group II (ca. 970 Ma) exhibits N-MORB signatures with lower TiO₂ contents, interpreted as remnants of oceanic crust. The gneissic diorite/granodiorites are dated at ca. 850–840 Ma. The ca. 850 Ma gneissic diorites are characterized by LILE and LREE enrichments, HFSE depletions, and variable zircon Ɛ_Hf(t) values ranging from –4.5 to + 7.7, indicating derivation from partial melting of juvenile crust with recycled components. The ca. 840 Ma gneissic granodiorites exhibit calc-alkaline compositions, low MgO, Ni, and Cr concentrations, and high Sr/Y ratios with TTG-like affinities. Their highly negative zircon Ɛ_Hf(t) values (–15.1 to –12.5) and Neoarchean T_DM2 model ages (2.51–2.67 Ga) imply significant reworking of Archean continental crust in a subduction-related setting. Additionally, amphibolite-facies metamorphism at ca. 821–813 Ma is recorded in unzoned zircon domains, characterized by pronouncedly steep HREE patterns, negligible or slightly negative Eu anomalies, and formation temperatures ranging from 611 to 714 °C. Combined with regional Neoproterozoic data from the northern Yangtze block, we propose a successive of subduction–accretionary and collisional processes occurred along the Bikou–Xiaomoling–Douling suture zone during the Tonian period.