| The Ordos Basin is located in the west part of the North China Craton,and its formation is closely connected to the evolution of Xing'an Mongolian orogenic belt.The provenance analysis of the Early-Middle Jurrasic clastic rocks in the Ordos Basin could provide a significant for the research of basin-range evolution in the North Chian Craton.In this paper,we took the sedimentary strata of the Middle-Lower Jurrasic in the northestern part of the Ordos Basin.Based on Sedimentology and Petrology,combined with detrital zircon U-Pb chronology and Hf isotope analysis,the provenance for the Jurassic clasitic rocks in this study has been identified.Finally,combined with the reginal geological data,we also discussed about the features of basin-range evolution in the studied area during the Late Paleozoic to Middle Jurassic.The Middle-Lower Jurrasic strata in the northestern part of the Ordos Basin are composed mainly of debris-arkosic sandstones and feldspar lithic sandstones.The sandstone grains are mainly subrounded to angular with low maturity in composition and low textural maturity,showing a feature of near sources for deposition.Based on the statistics observation under microscope,the samples are composed of quartzs of 43%-79%,feldspars of 6%-32% and lithic fragments of 10%-33%.Among them,lithic fragments are mainly metamorphic lithics,with few sedimentary lithics and volcanic lithics.The feature of detrital grains indicates that the parent rocks were mainly metamorphic rocks,and could be formed in the multi-recycle orogenic belt environment.The three clastic rock samples of Early-Middle Jurraric in Ordos Basin share the similarity of morphological characteristics of zircons and zircon U-Pb age distribution.The cathodoluminescence images and the high Th/U ratios(>0.1)shows that the detrital zircons is mainly magmatic origin.The histograms and probability curves for detrital zircon ages of three samples in the Shenmu shown that the three samples have similar peak age value ranges,which are occurred at 2586~2306Ma,2006~1628Ma and 327~241Ma.And the Hf isotope decay manle model age of the samples have demonstrated that the crustal accretion period was between 2677~2365Ma,during when 92% of zircon directly originated from the mantle-origin rocks.By comparing the age of the magmatic rocks and and detrital zircon ages of the strata around the Ordos Basin,we conclude that the main provenance for the clastic rocks is mainly from the Daqing and Yin mountains,and the Jining Area also had provided some detritus.Based on the detrital zircon age characteristics of the Early-Middle Jurrasic clastic rocks at Shenmu,and published magma activity ages,it is inducted that the collisional age of the Mongonia landmass and North China landmass was constrained in the Middle Permian.During Middle-Late Trassic,the studied areas were affected by the asthenosphere and mantle-originated matters,and the lithosphere extentional broke,which led the Ordos Basin into the extensional basin phase.During Early-Middle Jurrasic(early Yanshanian),the northern part of the Ordos Basin was quiet,and provided stable detitus supply for the studied areas. |
PDF Full Text Request