Geological Characteristics Of The Mesoproterozoic Changcheng System And South Shoushan Granitic Pegmatite In Xingcheng Area,Western Liaoning

The Mesoproterozoic Changcheng System deposition is widely developed in the North China Craton,The stratigraphic division of rocks and the determination of the sedimentary age are of great significance in the study of the Early Cambrian geologic evolution of the Craton.The study area selected in this paper is Xingcheng-Huludao,Liaoxi Area,which is located at the eastern margin of the Yanliao Aulacogen of North China Craton.In this paper,a section of the Mesoproterozoic Changcheng System in Wanghai Temple of Huludao,Liaoxi is measured.The lithostratigraphic features are basically consistent with the western section of the Xingcheng-Huludao area.This paper summarizes the characteristics of rock stratigraphy in the Changcheng Section of the region.At the bottom of the Changzhougou Formation,a layer of conglomerate is developed,and the grain size is thinner and the thickness is gradually thinned,which is on behalf of transgressive cycle;The string stability of the Chuanlinggou Formation is mainly composed of dark tapers;The calcareous sandstone that is the lowest of the Tuanshanzi Formation contains magnetite,the middle is rich in calcareous sandstone,and the top contains stromatolites and karst weathering;Two kinds of conglomerates are developed in the lower part of the Dahongyu Formation,one is the complex constitutive breccia,which is speculated as a tsunami rock and the other is a quartz sandstone conglomerate with the same composition as the cement.The quartz sandstone is developed above the conglomerate,with tuffy siltstone?The granitic pegmatite at south of Shoushan in Xingcheng studied petrography,LA-ICP-MS zircon U-Pb geochronology and geochemistry,aimed to reveal the formation age and adjacent to the Neoarchean granite in Suizhong area and its tectonic setting.Dating results reveal that the pegmatite were formed at 2486±8Ma?NSWD=3.1?.Compared with biotite granite,the pegmatite shows similar characteristics with respect to major elements,trace elements and rare elements.These samples are characterized by high silica?Si O2=77.28% 77.9%?,alkali-rich?K₂O+Na₂O=5.5%⁵.69%?,peraluminous?A /CNK =2.53².54?and shoshonitic.The SiO₂-K₂O discrimination diagrams belongs to shoshonite series.They have low rare elements contents(? REE=33.1×10^-641.01 ×10^-6),and enriches light REE relative to high ones.The pegmatite is related to the revolution of the biotite monzogranite.In this paper,four tuffaceous siltstone samples are picked to study the detrital zircon U-Pb chronology,which aims to reveal the Precambrian,especially the Proterozoic to the Paleoproterozoic geological events.The results reveal that:U-Pb age peaks of Sample Chd are ²473Ma and ²575Ma,In addition,there are 2009 Ma, 2195 Ma, 2755 Ma, 3373 Ma weaker peaks;Sample PWH6 gives a 2556 Ma major age peak;The age peaks of PWH10 focus on ²199Ma and ²468Ma;Sample PWH25 gives 2071 Ma, 2226 Ma and 2510 Ma three age peaks,and gives the minimum age of 1822 Ma.The records of the Archean to Mesoproterozoic geological events preserved by different age debris zircons are conducive to the study of the ancient geologic evolution of the North China Craton.