Tectonic Geomorphology Along The Gyaring Co Fault In Central Tibet

The continuous collision between India plate and Eurasian plate started from~50–65 Ma,resulting in rapid uplift and gradual expansion of the Tibet Plateau,and formed a series of Late Cenozoic tectonic deformation.On the northeastern margin of the Tibetan Plateau and the southeastern margin of the plateau,the terrace is mainly accomodated through the shortening and the strike slip deformation to and adjust the convergence of India plate and Eurasian plate.In the interior of the Tibetan Plateau,remote sensing image interpretation and geological survey reveal a series of Late Cenozoic strike slip faults and rift system under a continuous tectonic collision environment.The GPS velocity field also reveals that the modern deformation in the Tibetan Plateau is dominated by East-West extension and North-South shortening.There are~20 mm/yr east-west extension and~10 mm/yr near north-south shortening in the whole interior of Tibetan Plateau.Therefore,large scale strike slip fault and normal fault systems are widely developed within the Tibetan Plateau.Thus they play a crucial role in accommodate the stress and strain produced by the collision between India and Eurasia.So,what is the deformation model of the late Cenozoic extensional strike slip structure in the central Tibet? Two endnumber models are under disputing: rigid block and continuous deformation.The rigid block model suggest the echelon dextral strike slip fault system in the sounthern BangongNujiang suture zone(BNS)constitute the Karakorum Jiali fault zone(KJFZ).The KJFZ is regarded as the southern boundary of east extrusion,the slip rate is as high as 10–20 mm/yr,and form the escape tectonic with the Kunlun fault and Karakorum fault,and they accommodate at least 30% of convergence between India and Eurasia plate.On the contrary,the continuous deformation model suggests that the sinistral strike slip fault system and the dextral strike slip fault intersect at BNS,and constitute a V type conjugate strike slip fault system,the overall slip rate is low(5 to 6 mm/yr).To sum up,no matter what kind of deformation mode is,the basic research data,such as abundant geological structure,deformation observation and seismicity,are the key information to understand the deformation in the central Tibet.Due to the limitation of natural conditions,the lack of detailed and reliable geological research on strike slip fault and normal fault system is still a lack of quantitative parameters or the reliability is very low,which makes the understanding of relationship between the strike-slip faults and normal faults.Is there a decoupling between them in the upper crust? Is there a regional kinematics and dynamics relationship between them? This is also the main reason for the gap in the understanding of the deformation models in the central Tibet.In order to construct and perfect the geometric of the tectonic activity in the interior of the plateau,this paper discussed the dynamic mode of the deformation in the interior of the Tibetan Plateau.In this paper,the right-lateral slip fault of the Gyaring Co fault is selected as the research objective in the central Tibet.The main fault and the surrounding area are the key research areas,and the investigation of the tectonic and geomorphology and the analysis of the tectonic geomorphology parameters are carried out systematically.The main results and understanding are as follows:(1)The preliminary interpretation and staging of the Quaternary major landform evolution in the study area were carried out.Geomorphology and geochronology work was carried out on the typical landforms by using optically stimulated luminescence(OSL)dating,and the basic framework of late Quaternary landform evolution in the Gyaring Co fault zone was determined.The shrinkage of Gyaring Co generally in the late Quaternary.There was a high level of Gyaring Co in the late Quaternary,a small expansion in the late LGM and Early Holocene,respectively.The abandoned alluvial fans completed their deposition at~60–130 ka,~16–19 ka and~2–3 ka,respectively.The terraces were cut at~70–80 ka,~50 ka,~40 ka and~17 ka,respectively.The rapid decline of lake water in the Gyaring Co fault zone since the Quaternary had important control over the terraces of the river.In addition,there is a significant difference between the distribution of the alluvial fan on the north and south sides of the Gyaring Co fault zone and the depth of the cut in corresponding terrace,which indicates that there may be a continuous uplifting of the southern side of the Gyaring Co fault since the late Quaternary.(2)The main active fault scarps,geological profiles,small extensional basins,large fault triangles and asymmetric tectonic valleys together reveal that the Gyaring Co fault perform the extensional strike slip in the long term geological history.The east Quba trench suggset that the central segment of the Gyaring Co fault occurred at least 3 paleo-earthquake since~60 ka and the latest event occurred in the~2–3 ka.Detail tectonic geomorphology mapping at Quba-Kong Co,Aerqingsang,Shanong,Aruo and Nacha suggest the horizontal slip rate of Gyaring Co fault is low(0.5–3 mm/yr)and the vertical slip is very weak(<0.15 mm/yr).From the spatial distribution,fault slip rate decreasing to both Southeast and North West at Aerqingsang,which indicates the Aerqingsang fault strand may be the most active segment,but the range of change is very limited;Late Quaternary slip rate for the central segment of the Gyaring Co fault is basically stable in~2–3 mm/yr,and the slip rate of Southern segment stable at a lower range of~0.5 to 1 mm/yr.Despite the InSAR data have revealed the current slip rate of Gyaring Co fault is far greater than the geological slip rate,this paper suggest InSAR rate of Gyaring Co fault was over estimated based on the relative stable slip rate and latest earthquake.This view is support by the Beng Co fault which share consistent geodetic and geological slip rate.Thus the difference between geological and geodetic slip rates is very likely due to the sparse geodetic data along the Gyaring Co fault.This highlight the need for more new constraints on geodetic slip rates along the Gyaring Co fault and other strikeslip faults in central Tibet.(3)Based on ASTER GDEM data,Google Earth images(Landsat and GeoEye)and field work.This paper acquired basic geomorphic parameters of 153 sub-basin(such as grade,relief,average slope,area)and Hypsometric Index(HI)value and curve.Statistical results show significant differences in scale(area and river network grade)in north and south sides of the fault.Southern drainage basins relief,slope,HI value are higher than the northern basins,and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity.Along the strike of the Gyaring Co fault,average slope,and HI value are showing general increasing trending and hypsometric curves become convex from west to east.By comparing and analyzing the lithology and rainfall conditions,indicate that they have little influence on the basic parameters and HI value of drainage basins.Therefore,basin topographic differences between northern and southern side of fault and profile changes reveal the Gyaring Co fault has experienced differential uplift since the late Cenozoic.Southern side has greater uplift compared to the north side,and the uplift increased from NW to SE,indicating normal faulting of the Gyaring Co fault may enhanced by the southern Xainza rift.(4)The tectonic geomorphology,regional tectonic and strike-slip related-basin theory indicate that extensional strike-slip is the kinematic mechanism for the formation of the asymmetrical basin along the Gyaring Co fault.The Gyaring Co fault and the Xainza rift is kinematically related and jointly shape the E-W asymmetric geometry of the basin in the Gyaring Co fault zone.In addition,the early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and late further rapid uplift on the GangdiseNyainqentanglha Mountain and Xainza-Dinggye rift might contribute to the N-S asymmetrical development of the Gyaring Co fault zonal drainage basin.(5)By combing the geometric and kinematic tectonic activity in the interior of the Tibetan Plateau,the deformation of the strike-slip faults and normal faults were suggested dispersed in the interior of the plateau with low slip rates.The strike-slip faults are kinematically linked to the acceleration of~N-trending rifts since Pliocene and their exhibit comparable slip rate since their inception of strike-slip faults and accommodate convergence between India and Asia by slow outward spreading in the interior Tibetan Plateau.