Supra-subduction zone ophiolites from Inner Mongolia, North China: Implications for the tectonic history of the southeastern Central Asian Orogenic Belt

Abstract

The recently discovered Diyanmiao ophiolite in the eastern part of the Erenhot-Hegenshan ophiolite belt forms part of the southeastern domain of the Central Asian Orogenic Belt (CAOB). The ophiolite suite is composed of the northern Baiyinbulage ophiolite and the southern Naolaiketu ophiolite, each extending for nearly 100km, and a width of around 6km. The suite preserves a well-exposed and a nearly-complete ophiolite stratigraphy, and includes, from bottom to top, harzburgite, bedded gabbro, isotropic gabbros, anorthosite, spilite, pillow basalt, keratophyre, baschtauite, with overlying chert, and plagiogranite veins locally intruding the pillow basalt and gabbro. The pillow basalts possess the geochemical characteristics of Hahajima island arc tholeiite (IAT), indicating that the Diyanmiao ophiolite formed in the incipient arc setting of the supra-subduction zone. LA-ICP-MS U-Pb dating of zircon grains from three gabbro samples yield ages of 361±13Ma, 356.7±3.8Ma and 340±14Ma, indicating an early-Carboniferous age for the Diyanmiao ophiolite. We suggest that the intra-oceanic subduction initiation of the Erenhot-Hegenshan paleo-ocean during the Early Carboniferous resulted in the formation of an incipient arc oceanic crust, and that the Diyanmiao ophiolite represents an important north-dipping subduction event of the paleo Asian oceanic crust beneath the southern margin of the Siberian Plate after Early Carboniferous and Early Permian. Our study provides further insights into the evolution of the Paleo-Asian Ocean and eventual construction of CAOB, the globe's largest Phanerozoic orogen.