U-Pb age and geochemical characteristics of quartz diorite in Early Carboniferous from Langshan area of Inner Mongolia, and its implication for subduction of Paleo-Asian Ocean

The Late Paleozoic magmatites are distributed in the west of Inner Mongolian Langshan Mountain, with the formation concentrated in Early Carboniferous and Late Permian.The quartz diorite body of Early Carboniferous strata are outcropped in the west of Chaogewenduer Town.LA-ICP-MS zircon U-Pb age shows that the ²⁰⁶Pb/²³⁸U weighted average age of quartz diorite is 337.4±6.6 Ma.The characteristics of quartz diorite exhibit that the amphibole is the main dark mineral, characterized by enrichment in TFeO(TFeO=4.18%~6.95%) and Na₂O (Na₂O=3.11%~4.07%), high Na₂O/K₂O (Na₂O/K₂O 1.27~2.50), being calc alkaline series, enrichment in LILE (K, Rb, Ba), depletion in Nb, Ta, P and Ti, enrichment in LREE, and depletion in HREE as well as negligible Eu anomalies, which reflects the geochemical characteristics of magmatic arc.Th/Yb-Ta/Yb discriminant diagram shows the samples plot in the area of the continental margin arc.The geochemical characteristics of quartz diorite shows that the tectonic setting of Langshan area belonged to the continental margin arc in Early Carboniferous, the existence of the southward subduction of the paleo-Asian Ocean, and that, compared with the Early Carboniferous quartz diorite in Xiwuqi area of the northern orogenic belt, their geochemical characteristics are basically the same.Therefore, the paleo-Asian Ocean underwent bidirectional subduction in Early Carboniferous and formed the rock type dominated by quartz diorite.