Research On Zircon-genisis,Chronology And Material Source Of Crystalline Basement And Supracrustal Rocks In Penglai,Shandong

Jiaodong gold deposits are the largest concentration area of gold metallogenesisin China, in which the most gold deposits are located upon the JiaobeiTerrane.However the forming age, source and tectonic of the Jiaobei Terrane are stillunclear. Hence we have conducted a systematical research of the Jiaobei Terrane inDouYa section, Qixia, where the basement and supracrustal are well exposed wecarried out through petrology, mineralogy, U-Pb chronology and Hf isotope todisclose the tectonic characteristics of the Jiaobei Terrane.We choose trondhjemite in Jiaodong Group, arkose quartzite in Fenzishan Group,granitic dikes intruding the base of Baoshankou Formation and siltstone in FuzikuangFormation to study the morphology of the zircon in these rocks by SE2, Inlens, andAsb detectors of SEM. With EMPA and SEM we found most of the inclusions arequartz, plagioclase, orthoclase, apatite and multiple phase assemblage showing thefeature of igneous zircons or volcanic sedimentary zirconsZircon U-Pb chronology study shows that the age of trondhjemite are2819Maand1865Ma. Taking consider of εHf(t) Value and the model age, we think2819Ma asits main crustal forming age, At1865Ma, another magmatic-thermal event occured.Fenzishan Group arkose quartzites have ages of2807Ma and762Ma, with model agesof1250-2400Ma and2800-3200Ma, indicating an affinity with the Yangtze block.Zircons from the granitic dike intruding the Baoshankou group give ages of125Ma,161Ma,200Ma,230Ma,1800Ma-2000Ma and2450Ma-2550Ma. Therefore, most ofthe important geological events happened in this area can be identified in these ageranges. Fuzikuang Formation of Penglai Group, siltstone have detrital zircon ages of1200-1600Ma and470Ma, where the youngest detrital zircon represents the upperlimit of its sedimentation age, hence the Penglai Group is thought to have sedimentedduring mid-Devonian and Carboniferous. Since Hf model age of zircons showssimilar properties to Yangtz block, we speculate that the sedimentary materials werederived fromYangtz block.Jiaobei Terrance crystalline basement (Fenzishan Group) and the sedimentary cover (Penglai Group) show affinities of Yangtz block, whereas underlying JiaodongGroup displays the evolutionary history of the North China Craton. Especially, acomprehensive record of the evolutionary process in this region has been traced fromthe granitic dike intruding the Baoshankou Formation. We speculate that FenzishanGroup and Penglai Group might have been thrusted above Jiaodong Group of NorthChina block during the collision of North China block and Yangtz block in theMesozoic.