The Geochemical Characteristics And The Facies Research Of The Volcanic Rocks In Deren Formation Of Pinggang Basin

Based on petrology,geochemistry and geochronology researches of the volcanics from the Deren Formation locating in the Pinggang basin of north Liaoning province,petrogenesis,formation age,and tectonic setting have been discussed respectively.Furthermore,this paper also discusses the timing and mechanism of lithosphere thining of the North China Craton.Then,the relationship between the volcanic phase and reservoir has been discussed through the research of volcanic lithology phase and reservoir space types' subdivision.The LA-ICP-MS zircon U-Pb dating indicates that rhyolites from the Deren Formation formed at Early Cretaceous,with the age of 117.0±1.2Ma.Meanwhile,two age groups of captured zircons from dacitic breccia crystal and lithic tuffs(245.8±3.4Ma and 167±8.5Ma,respectively)represent the formation time of the basement rocks.In addition,these volcanic rocks are enriched in large ion lithophile elements(e.g.K,Rb,and Ba),and depleted in high field strength elements(e.g.Nb,Ta,Zr,Hf,Y,and Yb).Besides,the characteristics of of LREEs' enrichment and HREEs ' depletion show a right-trend REE patterns.In summary,the magma of these volcanics derived from remelting of the basement under a volcanic arc of active continental margins environment.The Early Cretaceous granite-porphyry and alkali-feldspar granites are the A type granite,which present an extensional environment during Post-Orogenic stage.Major changes from positive to negative of landform occurred at the period of 117~127 Ma.Extensional basins and metamorphic core complexes are widespread in the North China Craton,and the magma may be affected by mantle contamination during remelting of basement rocks.All of these suggest the occurring of the lithosphere thinning,and the initial timing at 127.0±4Ma belonged to Early Cretaceous,and the delamination is the most likely thinning mechanism.The lithofacies of these volcanic can be divided into flowing facies,erupting facies,volcano-sedimentary facies,volcanic cent facies,and subvolcanic facies.Meanwhile,the reservoir space can be divided into three types and ten subtypes.The different volcanic facies have different reservoir space.The volcanic erupting facies and flowing facies are well reservoires of the study area.