Carboniferous ridge subduction in the Xingmeng Orogenic Belt: Constraints from geochronological, geochemical, and Sr-Nd-Hf isotopic analysis of strongly peraluminous granites and gabbro-diorites in the Xilinhot micro-continent

The Xingmeng Orogenic Belt evolved through a long-lived orogeny involving multiple episodes of subduction and accretion. However, there is a debate on its tectonic evolution during the Late Paleozoic. Here, we report geochemical, geochronological, and isotopic data from strongly peraluminous granites and gabbro-diorites from the Sunidzuoqi-Xilinhot region. Zircon U-Pb ages suggest that the intrusive rocks were emplaced during the Early Carboniferous (333-322 Ma). The granites exhibit geochemical characteristics similar to S-type granites, with high SiO₂ (72.34-76.53 wt.%), Al₂O₃ (12.45-14.65 wt.%), and A/CNK (1.07-1.16), but depleted Sr, Nb, and Ta contents. They exhibit positive ε_Nd(t) and ε_Hf(t) values (-0.3 to 2.8 and 2.7-5.7, respectively) and young Nd and Hf model ages (T_DM2(Nd)=853-1110 Ma and T_DM2(Hf)=975-1184 Ma), suggesting that they may be the partial melting products of heterogeneous sources with variable proportions of pelite, psammite, and metabasaltic rocks. The meta-gabbro-diorites from the Maihantaolegai pluton have low SiO₂ (47.06-53.49 wt.%) and K₂O (0.04-0.99 wt.%) contents, and demonstrate slight light rare earth element (REE) depletion in the chondrite-normalized REE diagrams. They have high zircon ε_Hf(t) values (14.41-17.34) and young Hf model ages (T_DM2(Hf)=230-418 Ma), indicating a more depleted mantle source. The variations of the Sm/Yb and La/Sm ratios can thus be used to assess the melting degree of the mantle source from 5% to 20%, suggesting a quite shallow mantle melting zone. We propose that the petrogenesis and distribution of the strongly peraluminous granites and gabbro-diorites, as well as the tectonic architecture of the region, can be explained by a ridge subduction model. Based on these results, and previous studies, we suggest a southward ridge subduction model for the Sunidzuoqi-Xilinhot region.