EVIDENCE OF HOLOCENE ACTIVITY OF NALATI FAULT ZONE WITHIN THE TIANSHAN
The Tianshan orogenic belt,extending across the Euro-Asian plates,is one of the most signi-ficant intracontinental orogenic belts globally.Spanning over 2500km,it traverses China,Kazak-hstan,Kyrgyzstan,and Uzbekistan from east to west.The belt has been continuously uplifted due to the collision of the India-Eurasia plate during the Cenozoic era.The Tianshan is divided into three segments:North Tianshan,Middle Tianshan,and South Tianshan.The crust in this tectonic region is being shortened in the north-south direction,and a series of NEE-trending or NWW-trending strike-slip faults have developed to accommodate the deformation.The Nalati fault zone serves as the collision suture between the Central Tianshan block and the Tarim block and marks the boundary between Central and South Tianshan.This fault zone trends NEE and extends southwest into Kyrgyzstan,connecting to the Nikolayev line.Its eastern segment is located north of the Dayouludusi basin.The north-south shortening rate is approximately 2.0mm/a,and the horizontal strike-slip rate is about 2.9mm/a.Reports indicate a north-south shortening rate of 0.8-1.1mm/a since the late Quaternary,suggesting it is a significant Holocene active fault zone.However,research on this fault zone's activity is limited,with most studies focused on its eastern segment.Research on other sections remains scarce.This study focuses on the middle segment of the Nalati fault zone in Tekes county,Ili Prefecture.The Tekes section trends ENE,starting from Qiongkushitai village in the east,passing through Kalatuori,Ayakeaqia,and Kalawenkeer,and reaching Burili in the west,spanning approximately 55km.Methods employed include remote sensing image interpretation,field geological investigation,UAV aerial surveys,trench excavation,Radiocarbon-14 dating,and semi-automatic horizontal dislocation measurement.The main findings are as follows:1) The linear geomorphological features of the Tekes segment are prominent,with typical fault geomorphological signs such as fault cliffs,triangles,scarps,bulges,gate ridges,passes,guanmen mountains,and left-lateral dislocation ridges and gullies widely observed.;2 ) Small Unmanned Aerial Vehicle Mapping and LaDiCaoz semi-automatic dislocation measurement and analysis indicate a minimum horizontal displacement of approximately 3.4m;3) Faults are developed in the Proterozoic and Paleozoic strata.A trench 4m long and 1.6m wide excavated at a series of fault reverse scarps revealed a sedimentary event of the sag pond at the hillside,indicating at least four paleo-earthquake events;4 ) To date the paleo-earthquake events,we collected 11 sediment samples for Radiocarbon-14 dating at the BETA Analytic laboratory.Results show that the sample at a depth of 2m is about(7.06±0.03) ka BP,and the latest colluvial wedge is about(1.67±0.03) ka BP;5)Using OxCal age correction,the ages of the four paleo-earthquake events were determined at a 95.4% confidence level:event E1 occurred between 2757BC and 413AD,event E2 between 3581BC and 429BC,event E3 between 4702BC and 3932BC,and event E4 between 5742BC and 5230BC.In summary,we propose that the middle segment of the Nalati fault zone has been active since the Holocene.
万方数据
维普
