黄河口河流沙碎屑沉积物锆石U-Pb年龄及地质意义

陆缘碎屑沉积(物)岩是来自物源区物质的天然混合物,保存了源区不同地质作用过程形成产物的重要信息,可以为揭示盆地沉积、区域构造和地壳增长和演化以及古大陆再造等方面提供重要证据。对采集自山东东营黄河口河流沙的碎屑锆石进行了U-Pb年龄分析,并结合河流沙碎屑矿物粒度分析及重砂矿物组成特征,确定黄河口河流沙主体粒度为10～280μm,重砂矿物主要为角闪石、赤-褐铁矿、石榴子石、绿帘石、磁铁矿等。黄河口碎屑锆石以岩浆成因锆石为主,其U-Pb年龄呈多峰特征,最大U-Pb谐和年龄为3.65 Ga,意味着华北克拉通其他地区也有>3.6 Ga的地壳物质存在;近2.7 Ga的碎屑锆石反映鲁西地区该期岩浆活动产物的贡献。锆石U-Pb年龄主体分布于206～440 Ma、843～1 239 Ma、1 476～2 714 Ma等几个阶段,并以～2.5 Ga、～1.8 Ga和400 Ma为峰期,其中～2.5 Ga与～1.8 Ga的峰期反映华北板块的物质贡献,而400 Ma峰期与1 000～800 Ma的年龄代表源自苏鲁造山带的物质。结合已有的研究资料,认为黄河流域2.5～1.8 Ga为主要的大陆地壳增生阶段,该阶段形成地壳应占当今流域地壳的60%以上。

Zircon U-Pb Ages of Clastic Sediment from the Outfall of the Yellow River and Their Geological Significance

Terrigenous clastic sedimentary rocks(sediments) are natural mixture of their provenance materials,preserving important information of different processes on their provenances,which can usually be used as key clues of processes of basin sedimentation,regional tectonic,crustal growth and evolution,and reconstruction of ancient continent.Zircon U-Pb age studies of river sand from the outfall of the Yellow River in Dongying,Shandong Province,together with grain size analysis of detrital components and constituent of heavy minerals,show that the main size of river sand in the outfall of the Yellow River ranges from 10 to 280 μm.Heavy minerals are composed of hornblende,hematite-limonite,garnet,epidote,magnetite,etc.Detrital zircons in the outfall of the Yellow River are igneous origin with multiple populations of ages.The maximum concordant U-Pb age is～3.65 Ga,which reflects the existence of over 3.6 Ga crustal material in the other areas apart from Anshan,Liaoning Province and eastern Hebei Province.Zircon ages mainly distribute in 206-440 Ma,843-1,239 Ma,1,476-2,714 Ma,peakings at ～2.5 Ga,～1.8 Ga and 400 Ma.The two peaks of around ～2.5 Ga and ～1.8 Ga show contribution of the North China Block.The 400 Ma peak and ages between 1,000 and 800 Ma represent input materials that came from the Su-Lu Orogenic Belt.Together with previous studies,2.5-1.8 Ga should be the main growth stage of continent for the provenance crust of the Yellow River's draining area,and over 60% crust was formed at that time.