Discovery of the Late Carboniferous adakite in the Erenhot-Hegenshan suture zone and intra-oceanic subduction of the Paleo-Asian Ocean

The Ehenaobaotu tonalite is outcropped in the northern part of the Meilaotewula SSZ-type ophiolite of the Erenhot-Hegenshan suture zone in Xi Ujimqin Banner of Inner Mongolia. Based on the study of petrology, geochemistry and zircon LA-ICP-MS U-Pb geochronology, the genetic type and tectonic setting of the tonalite were determined, and the final closure time and subduction process of the Erenhot-Hegenshan ocean basin of the Paleo-Asian Ocean were discussed. The tonalite is characterized by high SiO₂, Al₂O₃, Na₂O, Sr and low K₂O, Y contents, enrichment of Rb, Ba, Sr large ion lithophile elements and LREE, and depletion of Nb, Ta, Ti, P high field strength elements and HREE. There is no pronounced Eu anomaly. The lithological and geochemical characteristics show that the Ehenaobaotu pluton is a high Si adakite (HSA) formed in island arc, and was derived from patial melting of the intra-oceanic subductingd oceanic crust and sediment and subsequently reaction with overlying mantle wedge peridotite. Its U-Pb LA-ICP-MS dating yields (305.6±1.5) Ma and suggests that the Ehenaobaotu pluton was formed during Late Carboniferous. Combined with the study of spatio-temporal evloution of the Carboniferous ophiolites and Carboniferous-Permian island arc magmatic rocks in the Erenhot-Hegenshan suture, it is assumed that the Erenhot-Hegenshan oceanic basin of the Paleo-Asian Ocean was in the process of oceanic subduction characterized by intra-oceanic subduction during the Carboniferous-Early Permian.