赞皇杂岩翁城地区长城系常州沟组砂岩碎屑锆石U-Pb-Hf同位素研究OA北大核心CSTPCD

The Changzhougou Formation is one of the oldest sedimentary cover on the Archean-Paleoproterozoic metamorphic basement of the North China Craton.The analysis for the U-Pb geochronology and Hf isotopes of the detrital zircons from the Changzhougou Formation is of great significance for exploring the formation age and source characteristics of the Changcheng System as well as the basement evolution.In this study,LA-ICP-MS(laser abla-tion inductively coupled plasma mass spectrometry)and LA-MC-ICP-MS(laser ablation multiple inductively cou-pled plasma mass spectrometry)were employed to analyze detrital zircon U-Pb ages and rare earth element composi-tions and Lu-Hf isotopic compositions of samples from the Changzhougou Formation of the Changcheng System in the Wengcheng area,Zanhuang Complex,respectively.The main peak ages of detrital zircons in two sandstone samples is 2 500 Ma,and the detrital material of the quartz sandstones is mainly derived from the late Neoarchean metamor-phic basement in the North China Craton,and the 207Pb/206Pb age of youngest detrital zircon is 1 822 Ma,combi-ning with the 1 850～1 800 Ma metamorphic ages which was recorded by the Zanhuang metamorphic basement and the 1 635 Ma age of magmatic zircon from the volcanic rocks in the upper Dahongyu Formation,further define that the initial depositional timing of Changzhougou Formation of Changcheng System in the Zanhuang Complex is later than 1 800～1 635 Ma.The εHf(t)values of the detrital zircon from one quartz sandstone sample vary from-6.8 to+5.2,and the corresponding two-stage model peak age is 2 820 Ma.Combined with the published Hf isotope re-sults of 2 900～2 700 Ma magmatic zircons and detrital zircons from the Zanhuang Complex,it is further indicated that 2 900～2 700 Ma is the most important period of crustal growth in the Zanhuang Complex.Integrating with the published sedimentary and new geochronological data of the Changzhougou Formation of the central and southern parts of the Taihangshan area,it is speculated that the Changzhougou Formation in Wengcheng area was deposited in the continental rift basin.