The Tectonic Significance Of The Early Permian Volcanic Rocks In The North Margin Of North China Block

There is a wide support that the Paleo-Asian Ocean was closed along the Solonker suture in the Late Permian to Early Triassic.However,the late-stage processing of the Paleo-Asian Ocean still keeps controversial.The Late Paleozoic volcanic rocks are widely exposed in the northern margin of the North China craton and the southeastern Central Asian Orogenic Belt.In order to constrain the petrogenesis,tectonic setting of Late Paleozoic volcanic rocks and to address the late stage tectonic evolution of the Paleo-Asian Ocean,we have carried out the analysis of the petrology,geochronology,and geochemistry data of these Late Paleozoic volcanic rocks.We present new zircon U-Pb ages,geochemical data on the Late Paleozoic volcanic rocks of the Suji and Dahongshan formations,which are exposed in the Plate Marginal Orogenic Belt along the northern Margin of the North China craton.The Suji and Dahongshan formations present the main rock association with basaltic andesite,andesite,dacite,rhyolite,and tuff.New zircon U-Pb dating results suggest that the volcanic rocks formed during 280-261 Ma and 276-267 Ma,respectively.These volcanic rocks belong to the low-K tholeiitic to high-K calc-alkaline series and are characterised by highly enriched LREEs,K,Rb,Ba;depleted Nb,Ta,Ti;and highly negative Eu anomalies,very similar to that of the continental arc magmatism.In order to explore the evolution of the Central Asian Orogenic Belt accreted in the northern margin of the North China craton,we compared the Suji and Dahongshan formations volcanic rocks with the Dashizhai Formation volcanic rocks(311-274 Ma)exposed from the Central Asia orogenic belt,suggesting that the Paleo-Asian Ocean may have experienced two important cycles/epochs,of which we name respectively them “the older Paleo-Asian ocean” and “the younger Paleo-Asian ocean”,and propose the following tectonic evolution during the Late Paleozoic:(1)The older Paleo-Asian ocean closed via the soft collision between the Northern orogen and Southern orogen before the Late Carboniferous.(2)The younger Paleo-Asian ocean opened in the Late Carboniferous to Early Permian as the new ocean along the closed location of the older Paleo-Asian Ocean.(3)Southern subduction of the younger Paleo-Asian ocean beneath the northern Margin of the North China craton led to the development of the Plate Marginal Orogenic Belt along the northern margin of the North China craton and accommodated final closure of the younger Paleo-Asian ocean during the re-collision between the Northern orogen and Southern orogen during the Early Permian to Middle Triassic.