The Late Paleozoic Tectonic Evolution Of The Central Great Xing'an Range,NE China

The central Great Xing'an Range,NE China,is a key tectonic unit in the eastern segment of the Central Asian Orogenic Belt(CAOB).This region records a complicated tectonic evolution during the Paleozoic and is therefore important for understanding the regional geological history.However,few studies have examined the geology of the region.Based on new findings and existing data,this paper presents the petrology,geochronology,geochemistry,paleogeography,and paleontology of the Paleozoic rocks of the central Great Xing'an Range with the aim of reconstructing the regional geological history and establishing a tectonic model.The Xing'an block records several magmatic events that produced rhyolite,andesite,and basalt during the Late Devonian(379–359 Ma).The composition and geochemistry of the magmatic rocks indicate a subduction setting related to westward subduction of the Nenjiang oceanic crust beneath the Xing'an block.Coeval granites(366–360 Ma)with A-type affinities are exposed at the western margin of the Songnen block and indicate an extensional setting.Early Carboniferous subduction-related magmatic rocks are widespread in the Xing'an and Songnen blocks,and suggest bi-directional subduction.A middle Carboniferous(~320 Ma)S-type granite in the Moguqi area suggests a collision setting relating to the amalgamation of the Xing'an and Songnen blocks.Middle late Carboniferous rhyolite(312 Ma)of the Baoligaomiao Formation in the Moguqi area shows a typical A-type signature,indicating an extensional setting.Latest Carboniferous granodiorite(301 Ma)and meta-grabbro(300 Ma)in the Jalaid Banner area comprise a suite of bimodal volcanic rocks that indicate extension and rifting.An early Permian A-type rhyolite(292 Ma)in the Moguqi area suggests a rift basin system.The widely distributed terrestrial facies of the Baoligaomiao Formation indicate the Nenjiang Ocean had closed at this time.The laterally inter-layered marine and continental facies strata of the Gegenaobao Formation suggest a transgression,as do early and middle Permian marine strata,including the Dashizhai and Zhesi formations.An ophiolitic mélange in the Ulanhot area records the reopening of a limited ocean basin in the region,and widespread terrestrial facies of the Linxi Formation indicate a regression and the end of rifting and basin development.A tectonic model of the Paleozoic evolution of the central Great Xing'an Range is proposed,as follows.Westward subduction of the Nenjiang oceanic crust during the Late Devonian(379–360 Ma);bi-directional subduction during the early Carboniferous(346–320 Ma);collision of the Xing'an and Songnen blocks and the formation of the Hegenshan–Heihe suture,which extended along the entire Heihe–Nenjiang–Moguqi– Hegenshan–Erenhot belt,during the middle Carboniferous(~320 Ma);post-collisional extension during the middle to late Carboniferous(320–300 Ma);rifting and basin development during the early to middle Permian(300–260 Ma);and finally terrestrial sedimentation and the end of rifting and basin development during the late Permian(260–250 Ma).