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 SiO_(2)(72.34-76.53 wt.%),Al_(2)O_(3)(12.45-14.65 wt.%),and A/CNK(1.07-1.16),but depleted Sr,Nb,and Ta contents.They exhibit positiveε_(Nd)(t)andε_(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 SiO_(2)(47.06-53.49 wt.%)and K_2O(0.04-0.99 wt.%)contents,and demonstrate slight light rare earth element(REE)depletion in the chondritenormalized REE diagrams.They have high zirconε_(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.