Geochronology, geochemistry and Hf isotopic compositions of late Silurian granodiorites in the Shaolang River metallogenic belt: Implications for magmatism and tectonic evolution

The Shaolang River metallogenic belt in Inner Mongolia is one of the main lead-zinc polymetallic belt on the northern margin of the North China Plate. The granodiorites, which are closely coexisting with lead-zinc veins in deposit, are extensively developed. Previous geochronological research results show that the dikes and veins in the metallogenic belt belong to the products of magmatic hydrothermal activity in the middle Yan-shanian, so the genesis of the metallogenic belt deposit is generally considered to be a hydrothermal vein type deposit related to sub-volcanic dikes. We obtained zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions of granodiorites, which are widely distributed in the deposit and were considered to be closely connected with the genesis of the deposits. The zircon U-Pb ages are 419.4 +/- 1.4 Ma and 424.5 +/- 4.1 Ma for the granodiorites, respectively, and they formed in the late Silurian. The geological and geo-chemical data indicate that the granodiorites are consistent with the geochemical char-acteristics of typical adakite. All epsilon Hf(t) values of the granodiorites are minus, on the zircon Hf isotope age diagram, epsilon Hf(t) are below the evolution curve of chondrite. The two-stage model ages (tDM2) are 2.45 similar to 2.79 Ga and 1.87 similar to 2.29 Ga, respectively, showing rock-forming materials mainly derived from the Paleoproterozoic and earlier crustal partial melting, and there may have been mantle-derived magma underplating of the lower crust. Combining with the previous regional research, it is concluded that the granodiorites were formed during the extinction of the island arc under the background of subduction of the Paleo-Asian Ocean and North China Craton. Because of the 125 -170 Ma metallogenic age, we concluded that the granodiorites in the ore areas have no obvious relationship with the deposit genesis. However, it provided the advan-tageous space for the formation of the lead-zinc veins, it can be regarded as an impor-tant prospecting indicator in metallogenic belt.