Geologic Features And Tectonic Significance Of Early Cretaceous Hekou Groups And Pliocene Linxia Groups Sediment Stratum At Xunhua Area In The Qinghai Province

The sediments in the basin can effective tracer mountains provenance and uplift history.Basin sedimentary record is an important information records of orogenic belt tectonic thermal event and uplift and denudation,is another shortcut to research and inversion the orogeny of orogenic belts.This thesis mainly study the Early cretaceous Hekou groups and the neogene Lixia groups,focus on the sedimentary petrology,rock geochemistry and the characteristics of detrital zircon U-Pb isotope chronology to discuss the basin sedimentary characteristics,material source,and basin properties,determine its ancient tectonic environment,which can provide detailed information for the West qinling-South qilian junction geological evolution form late Mesozoic to Cenozoic.Until now,some new points have been achieve as follows:1?The study on petrographic shows that Hekou groups main types of sandstone is lithic sandstone and the matrix content between 10-20%,which have higher maturity.It can be divided into two lithologic members,based on the differences of sedimentary rock assemblages and sedimentary environment.Under section is the coarse clastic rock section,belongs to the alluvial fan sedimentary system.Above section is sandy conglomerate,sandstone,mudstone rhythm interval,belongs to the braided river sedimentary system.Linxia groups can be divided into four lithological member,which can reflects the lake sedimentary,salt water lake-brackish water lakes,meandering river delta and meandering river sedimentary environment characteristics of the deposit.2?Hekou groups sandstone detrital component statistics show that tectonic setting is mainly for the cycle again orogenic belt and mixed area,source mainly from cycle again orogenic belt and a few form mixed orogenic belt.Characteristics of the main elements shows its tectonic background of provenance,mainly form continental island arc and active continental margin.Rare earth and trace elements characteristics showed that sediment provenance mainly form felsic rocks at the same time contains ancient sediments.3?LA-ICP-MS detrital zircon U-Pb age spectrum reveal that Hekou groups of samples with 217~260Ma,the peak age of 249 Ma,270~371Ma,401~506Ma,the peak age of 480 Ma,606~931Ma and 842 Ma peak age,1054 ~ 1546 Ma,1658~2710Ma,the peak age of 1658 Ma six age groups,respectively corresponding to the early Triassic,late Paleozoic,early Paleozoic,the neoproterozoic,middle Proterozoic,and late paleoproterozoic to new archean early 6 evolution stage of the information age.Combined with characteristics of Hekou groups of detrital zircon age and researched regional geological features,the most important province of Hekou groups is the north of West Qiling Triassic magmatite,and Qilian orogenic belt in palaeozoic period of magmatic rocks and old metamorphic basement.4?Comprehensive the above information,show that Sedimentary basin prototype of early Cretaceous Hekou groups which Widely distributed in Qinghai xunhua area is extensional fault basin which is formed in Indian plate subduction northward basement strike-slip displacement.Pliocene Linxia groups formed in intermountain basin during the Lajishan and Jishishan uplift,which was influenced by the Indian plate and Asia plate collision.