Tectonic Characteristics Of Mesozoic Dykes And Their Relationship With Gold Mineralization In Qingchengzi Area,Liaodong Peninsula

The Liaodong Peninsula in the northeastern margin of the North China Craton has experienced multiple tectonics episodes,magmatic emplacement and gold mineralization during the Mesozoic with gold mineralization closely related to magmatism.The Qingchengzi area in the northern Liaodong Peninsula is an important gold ore concentration area,with widely developed Mesozoic dykes of different tectonic stages.The study of these dykes in the area has great significance for understanding regional tectonic nature and gold mineralization.This study aims to analyze the structural characteristics,genesis and the relationship with gold mineralization of Mesozoic dykes in the Qingchengzi area based on previous studies,combining with our field geological surveys,petrological and geochemical analysis,structural observation and zircon U-Pb geochronology analysis.Based on field geological investigation and zircon U-Pb geochronological dating,at least three stages of the Mesozoic dykes emplacement events have been identified in the Qingchengzi area:(1)the widely developed granitic dykes striking in NE and EW with emplaced age at 217-224Ma(Late Triassic).Outcrop scale and microstructural observation reveal that the dykes are syn-tectonic emplacement.These dykes have geochemical composition of high Sr,low Y,and Yb element content,indicating characteristics of typical adakitic rocks.Together with Sr-Nd isotopic composition,these dykes were derived from the melting of a thickened lower crust,revealing that they might been form in the background of the transition from compression to extension at the later stage of the collision of the North China and South China plates;(2)Early Jurassic quartzite dykes,gabbro dykes and diorite dykes were emplaced at ?190Ma,which might been formed in the background of subduction of the Paleo-Pacific plate underneath the Eurasian plate;(3)The Early Cretaceous dykes were mainly produced at 126-130Ma,including lamprophyre dykes intruded into Xiaotongjiapuzi gold deposit at ?130Ma along an extensional fault,indicating extensional tectonic setting resulted by the subduction and retreat of the Paleo-Pacific plate.The dykes have very close relationship in emplacement time,space and genesis with gold veins in Qingchengzi area.The mineralized dykes in the core of Caohekou compound syncline are sub-parallel to gold veins with similar emplaced mechanism dominated by the Late Triassic EW trending thrust fault and interlayer sliding fracture zone.Multi-stages mineralization in Qingchengzi area include main period produced by the Late Triassic compressional tectonics,and re-enrichment of the gold resulted by the Early Cretaceous tectonic-magmatism.Therefore,the widely developed Mesozoic dykes in the area might be an important sign for gold deposit prospecting.