| The Mianluening region is located in the eastern part of the Bikou micro-block,with a relatively complete sequence of Nanhua sedimentary strata exposed,which records the Nanhua sedimentary characteristics,tectonic evolution,and basin-mountain coupling information in the study area and adjacent areas.Although the predecessors have done a lot of research work on the Nanhua System in the study area,they only divided it into the Nantuo Formation in general,and they have not been able to establish a complete sequence of the Nanhua System.The discovery and establishment of a complete Nanhua stratigraphic sequence in this area,ascertaining the sedimentary characteristics and paleo-sedimentary environment of the research object,and analyzing the material source area and the geotectonic attributes of the Nanhua system are not only conducive to the establishment of the Mianluening area system The stratigraphic sequence can also enrich regional basic geological data in the Mianluening region,and has important research value for the Neoproterozoic tectonic evolution of the Bikou microblock and adjacent areas.This article takes the plate tectonics and continental dynamics theory as the guiding ideology,adopts the methods of stratigraphic division and regional comparison,gravel analysis and clastic skeleton composition statistics,sandstone rock geochemistry,detrital zircon and volcanic rock chronology,etc.,to compare the Mianluening region A systematic analysis of the sedimentary strata of the Nanhua System in Hongyangou,we have achieved the following results and understandings:(1)On the basis of field observations,the lithology,rock combination and sedimentary structure characteristics of the Nanhua-Sinian system in Hongyangou have been identified,combined with regional stratigraphic correlation,the Nanhua system has been divided into four lithostratigraphic units: The Lower Chang'an,Gucheng,Datangpo and Upper Nantuo Formations,the Sinian is divided into the Lower Doushantuo Formation and the Upper Dengying Formation,and a complete Nanhua-Sinian stratigraphic sequence has been initially established in this area..In addition,the study of the sedimentary characteristics and sedimentary environment of the Nanhua System shows that the main body of the Nanhua System is a combination of glacial water turbidity current deposition and clastic current deposition.(2)Statistical analysis of the gravels of the Nantuo Formation shows that the roundness of the gravels is good,mostly sub-circular to round,and the gravel composition is complex,mainly sandstone and quartzite,and the long axis of the gravel is mainly southward,indicating that the ancient current should be from south to north.The overall characteristics of the Nanhua System sandstone detrital skeleton is that the content of debris is the largest,followed by feldspar and relatively less quartz.From bottom to top,the content of quartz increases,and the content of feldspar and cuttings decreases.Its provenance mainly comes from arc magmatic rocks.In addition,whole-rock geochemical testing and analysis of Nanhua system sandstones,sandstones are mainly composed of aluminum-rich feldspar minerals,secondly silicon-rich quartz minerals,and also contain a small amount of iron-rich minerals.Mainly from the felsic acid magmatic rock of the upper crust.(3)The zircon age study of the volcanic interbedded layer(andesite)in the lower part of the Chang'an Formation shows that the formation age of the andesite is 763±20 Ma.Combining the layer relationship in the stratigraphic sequence and the isotope dating data of the Doushantuo Formation in the region,it is believed that The sedimentary age of the Nanhua System in Hongyangou is roughly 780Ma?635Ma.The ages of detrital zircons from the lower feldspar sandstone of the Nantuo Formation can be divided into two groups: the late Neoproterozoic age group(750?800Ma)and the early and middle Neoproterozoic age group(820?920Ma).The age of the youngest detrital zircons It is 750 Ma.Comprehensive studies suggest that the Nanhua system has multiple sources,mainly from the interior of the Bikou microblock on the northwestern margin of the Yangtze Plate and the Longmenshan tectonic belt on the south side,and the Hannan-Micangshan microblock in the Neoproterozoic.Acidic magmatic rock,and the magmatic rock exposed in the Mianlue structural belt on the north side may also provide a small amount of provenance for this formation.(4)A comprehensive analysis of the provenance and tectonic environment of the Nanhua System has been carried out.It is believed that the chemical weathering in the provenance area of the Nanhua System is relatively weak,the paleo-climate is cold and dry,and it has experienced a relatively low degree of sediment recirculation during the transportation process.The main body of the provenance area should be composed of intermediate-acid magmatic rocks.Based on the results of previous studies,it is believed that the Hongyangou Nanhua System may be the sedimentary caprock in the intracontinental rift environment at the margin of the plate. |
PDF Full Text Request