Chronology and geochemical characteristics of trachytes in the Tiaojishan Formation,Xuanhua Basin,northwestern Hebei Province,and their geological implications
The Tiaojishan Formation in northwestern Hebei Province is home to volcanic-sedimentary strata.Due to the lack of fossil organisms,insufficient isotopic dating data,and outdated dating methods,the formation epochs of these strata have been controversial.To accurately determine their formation epochs and examine their regional geotectonic setting,this study conducted a detailed field in-vestigation of the lithologic assemblage of the Tiaojishan Formation in the Xuanhua Basin.Petrological,petrogeochemical,and high-precision isotopic dating studies were conducted on the trachytic volcanic rocks in the upper segment of the formation,obtaining the LA-ICP-MS-based zircon U-Pb isotopic ages,which were 161.1±1.2 Ma and 162.5±1.3Ma.As indicated by the petrological and petro-geochemical characteristics,these trachytic volcanic rocks belong to the shoshonite series,exhibiting enriched light rare earth ele-ments,relatively enriched elements including Rb,K,Th,Ce,Zr,and Hf,and relatively depleted Ba,Nb,Sr,P,and Ti.According to the comparison of principal parameters and graphical discrimination,the magma originated primarily from the melting of continental crustal materials and formed in the tectonic setting of compressional continental margin volcanic arcs.The comprehensive research re-veals that the Tiaojishan Formation formed primarily during the Middle Jurassic and continued to the Late Jurassic,and the trachytic volcanic rocks in its upper segment formed in the intraplate compressional tectonic setting.The results of this study provide new data for the division and correlation of Mesozoic volcanic-sedimentary strata and the analysis of their formation environment.
万方数据
维普
