Multiscale Seismic Tomography Of The Upper Mantle Beneath The Western Ordos And Its Surrounding Area

The geographical location in the Ordos and its adjacent areas is rather special.The study of this area is of great significance to the uplifted mechanism of the northeastern edge of the Tibet Plateau.Therefore,this area has attracted much attention of scholars.Since 1960 s,with the continuous enrichment of geology,geophysics and geochemistry,the study of this area has also been lucubrated.There are obvious differences in construction,tectonic geomorphology,basement depth,and anisotropy between the north and south regions of Ordos region.Because of the lack of the data of deep structures,many researchers have a lot of controversy about the causes of this difference.The deep structure of Ordos block also affects the relationship between the Alashan block and the North China Craton(ncc),the traditional research believes that Alashan block is a part of the North China Craton,in recent years,with the study on geology and geochemistry of the deepening,some scholars believe that the Alashan block and the North China Craton do not belong to the same block.For this moment,there is also a lack of deep geophysical evidence to this issue.The Himalaya project 678 seismic stations in scientific detection array and 26 fixed stations with 9641 earthquakes recorded a total of about 16000 teleseismic P wave travel time data,using multi-scale tomography imaging method based on sparse constraint,the Ordos western margin and its adjacent areas of the upper mantle within the depth of 800 km P wave velocity structure get.The results show that there is a tectonic boundary of lithosphere depth between the Alashan block and the Ordos basin at 104°E,indicating that the Alashan block and Ordos belong to different geotectonic units.At 38°N,Ordos plots at the western margin of the north and south there are obviously differences within the scope of the lithosphere velocity,southern Ordos mantle depth of 200km-300 km shows high velocity anomaly,and northern Ordos of the upper mantle shows large area of low velocity anomaly.According to the results of this paper can be further inferred,due to the Tibetan Plateau,the Alashan block to the northeast and push the lithospheric detachment of the upper mantle caused by disturbance caused by upwelling mantle upwelling of hot material,the transformation of the Ordos northwestern margin area of lithosphere,and the area of lithospheric thinning.Mantle upwelling may also be the deep dynamic factor of the 104°E boundary zone and the 38 °N tectonic belt of the northern latitude.