摘要
A sequence of terrigenous siliciclastic rocks crop out at Baxiandun, Qingdao, near the Mesozoic collisional boundary between North China block （NCB） and South China block （SCB）. These low-grade metamorphosed siliciclastic rocks are dominated by greywacke with shale, man- ganiferous fine-grained sandstone, arkose and conglomerate layers. There are two basic interpreta- tions about the formation of these rocks. One considered that this sequence was formed within NCB, and is part of the Cretaceous Laiyang Group and Qingshan Group fluvial facies and volcanic debris facies, as shown on the Shandong Regional Geological Map. Another opinion suggested that these rocks represent turbidity depositional systems in the slope and the basin facies was mainly deposited in Ordovician. Based on field observation, petrological analysis, and most importantly, geochemical results in this study, the sedimentary strata at Baxiandun Section mainly consist of siltstone, sand- stone and mudstone lithologies. They are dominated by deepwater debris and turbidity deposits in the slope and base of a lake. The U-Pb detrital zircon dating of the rocks at the Baxiandun Section indicates that the source rocks are very complex and their ages are varied from Archean to Early Cretaceous. The youngest age of the terrigenous detritus could represent the age of the sedimentary strata. Therefore, we infer that the sedimentary rocks belong to Early Cretaceous deepwater lacus- trine sedimentary sequences and have multiple sources origined from the erosion of the Sulu UHP orogen and South China block margin.
A sequence of terrigenous siliciclastic rocks crop out at Baxiandun, Qingdao, near the Mesozoic collisional boundary between North China block （NCB） and South China block （SCB）. These low-grade metamorphosed siliciclastic rocks are dominated by greywacke with shale, man- ganiferous fine-grained sandstone, arkose and conglomerate layers. There are two basic interpreta- tions about the formation of these rocks. One considered that this sequence was formed within NCB, and is part of the Cretaceous Laiyang Group and Qingshan Group fluvial facies and volcanic debris facies, as shown on the Shandong Regional Geological Map. Another opinion suggested that these rocks represent turbidity depositional systems in the slope and the basin facies was mainly deposited in Ordovician. Based on field observation, petrological analysis, and most importantly, geochemical results in this study, the sedimentary strata at Baxiandun Section mainly consist of siltstone, sand- stone and mudstone lithologies. They are dominated by deepwater debris and turbidity deposits in the slope and base of a lake. The U-Pb detrital zircon dating of the rocks at the Baxiandun Section indicates that the source rocks are very complex and their ages are varied from Archean to Early Cretaceous. The youngest age of the terrigenous detritus could represent the age of the sedimentary strata. Therefore, we infer that the sedimentary rocks belong to Early Cretaceous deepwater lacus- trine sedimentary sequences and have multiple sources origined from the erosion of the Sulu UHP orogen and South China block margin.
基金
supported by the Fundamental Research Program of the Ministry of Sciences and Technology, China (No. 2009CB219401)
the Knowledge Innovation Project of the Chinese Academy of Sciences (No. KZCX3-SW-229)
