Table of Content

20 April 2019, Volume 41 Issue 2

Previous Issue    Next Issue

Research Paper

EXTRACTING FEATURES OF ALLUVIAL FAN AND DISCUSSING LANDFORMS EVOLUTION BASED ON HIGH-RESOLUTION TOPOGRAPHY DATA: TAKING ALLUVIAL FAN OF LAOHUSHAN ALONG HAIYUAN FAULT ZONE AS AN INSTANCE

HAN Long-fei, ZENG Jing, YUAN Zhao-de, SHAO Yan-xiu, WANG Wei, YAO Wen-qian, WANG Peng, LIANG Ou-bo, XU Xin-yue

2019, 41(2):  251-265.  DOI: 10.3969/j.issn.0253-4967.2019.02.001

Asbtract ( )   HTML   PDF (7560KB) ( )  

References | Related Articles | Metrics

Range-front alluvial fan deposition in arid and semiarid environments records vast amounts of climatic and tectonic information. Differentiating and characterizing alluvial fan morphology is an important part in Quaternary alluvial fan research. Traditional method such as field observations is a most important part of deciphering and mapping the alluvial fan. Large-scale automatically mapping of alluvial fan stratigraphy before traditional field observations could provide guidance for mapping alluvial fan morphology, thus improving subsequent field work efficiency. In this research, high-resolution topographic data were used to quantify relief and roughness of alluvial fan within the Laohushan. These data suggest that mean surface roughness plotted against the size of the moving window is characterized by an initial increase in surface roughness with increased window size, but it shows no longer increase as a function of windows size. These data also suggest that alluvial fans in this study site smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces which suggests the evolution process of alluvial fan.
Researchers usually differentiate alluvial morphology by mapping characteristics of fan surface in the field by describing surface clast size, rock varnish accumulation, and desert pavement development and analysis of aerial photographs or satellite imagery. Recently, the emergence of high-resolution topographic data has renewed interest in the quantitative characterization of alluvial and colluvium landforms. Surface morphology that fan surface initially tends to become smoother with increasing age due to the formation of desert pavement and the degradation of bar-and-swale topography and subsequently, landforms become more dissected due to tectonics and climatic change induced increased erosion and channelization of the surface with time is widely used to distinguish alluvial fan types. Those characteristics would reflect various kinds of morphology metrics extracted from high-resolution topographic data. In the arid and semiarid regions of northwestern China, plenty of alluvial fans are preserved completely for lack of artificial reforming, and there exists sparse surface vegetation. In the meantime, range-front alluvial fan displaced by a number of active faults formed a series of dislocated landforms with different offsets which is a major reference mark in fault activity research. In this research, six map units(Qf₆-Qf₁), youngest to oldest, were observed in the study area by mapping performed by identifying geomorphic features in the field that are spatially discernible using hill-shade and digital orthophoto map. Alluvial fan relief and roughness were computed across multiple observation scales(2m×2m to 100m×100m)based on the topographic parameters of altitude difference and standard deviation of slope, curvature and aspect.
In this research, mean relief keeps increasing with increased window size while mean surface roughness is characterized by a rapid increase over wavelengths of 6~15m, representing the typical length scale of bar-and-swale topography. At longer wavelengths, surface roughness values increase by only minor amounts, suggesting the topographic saturation length is 6~15m for those fan surfaces in which saturation length of standard deviation of curvature is less than 8m. Box and whisker plot of surface roughness averaged over 8m² for each alluvial fan unit in the study area suggests that the pattern of surfaces smoothing out with age and then starting to become rougher again as age increases further beyond Qf₄ or Qf₃ unit. The younger alluvial fan is characterized by prominent bar-and-swale while the older alluvial fan is characterized by tributaries headward incision. Cumulative frequency distributions of relief and surface roughness in Figure 8 are determined in an 8m by 8m moving window for the comparison of six alluvial fan units in the northeast piedmont of Laohushan. From these distributions we know that Qf₆ and Qf₁ reflect the prominent relief which is related to bar-and-swale and tributaries headward incision respectively, while Qf₄ and Qf₃ reflect the moderate relief which is related to subdued topography.
Surface roughness, in addition to facilitating the characterization of individual fan units, lends insight to alluvial landform development. We summarize an alluvial landform evolutionary scheme which evolves four stages depending on characteristics of alluvial fan morphology development and features of relief and roughness. The initial stage in this study site is defined as the active alluvial fan channels with bars of coarse cobbles and boulders and swales consisting of finer-grained pebbles and sand which could be reflected by high mean relief and mean roughness values. As time goes, bar-and-swale topography is still present, but an immature pavement, composed of finer grained clasts, has started to form. In the third stage, the bar-and-swale topography on the fan surface is subdued, yet still observable, with clasts ranging from pebbles to cobbles in size and there exists obvious headward tributary incision. Eventually, tributary channels form from erosion by surface runoff. Headward incision of these tributaries wears down the steep walls of channels that are incised through the stable, planar surface, transforming the oldest alluvial landforms into convex hillslopes, leaving only small remnants of the planar surface intact. Those evolutionary character suggests that alluvial fans in this area smooth out with time, however, relief or roughness would be translated to increase at greater wavelength with age until a threshold is crossed.
This research suggests that relief and roughness calculated from high-resolution topographic data of this study site could reflect alluvial fan morphology development and provide constraint data to differentiate alluvial fan unit.

FAULTED LANDFORM AND SLIP RATE OF THE JINGHE SECTION OF THE BOLOKENU-AQIKEKUDUKE FAULT SINCE THE LATE PLEISTOCENE

HU Zong-kai, YANG Xiao-ping, YANG Hai-bo, LI Jun, WU Guo-dong, HUANG Wei-liang

2019, 41(2):  266-280.  DOI: 10.3969/j.issn.0253-4967.2019.02.002

Asbtract ( )   HTML   PDF (13132KB) ( )  

References | Related Articles | Metrics

The Bolokonu-Aqikekuduke fault zone(Bo-A Fault)is the plate convergence boundary between the middle and the northern Tianshan. Bo-A Fault is an inherited right-lateral strike-slip active fault and obliquely cuts the Tianshan Mountains to the northwest. Accurately constrained fault activity and slip rate is crucial for understanding the tectonic deformation mechanism, strain rate distribution and regional seismic hazard. Based on the interpretation of satellite remote sensing images and topographic surveys, this paper divides the alluvial fans in the southeast of Jinghe River into four phases, Fan1, Fan2, Fan3 and Fan4 by geomorphological elevation, water density, depth of cut, etc. This paper interprets gullies and terrace scarps by high-resolution LiDAR topographic data. Right-laterally offset gullies, fault scarps and terrace scarps are distributed in Fan1, Fan2b and Fan3. We have identified a total of 30 right-laterally offset gullies and terrace scarps. Minimum right-lateral displacement is about 6m and the maximum right-lateral displacements are(414±10)m, (91±5)m and(39±1)m on Fan2b, Fan3a and Fan3b. The landform scarp dividing Fan2b and Fan3a is offset right-laterally by (212±11)m. Combining the work done by the predecessors in the northern foothills of the Tianshan Mountains with Guliya ice core climate curve, this paper concludes that the undercut age of alluvial fan are 56~64ka, 35~41ka, 10~14ka in the Tianshan Mountains. The slip rate of Bo-A Fault since the formation of the Fan2b, Fan3a and Fan3b of the alluvial-proluvial fan is 3.3~3.7mm/a, 2.2~2.6mm/a and 2.7~3.9mm/a. The right-lateral strike-slip rate since the late Pleistocene is obtained to be 3.1±0.3mm/a based on high-resolution LiDAR topographic data and Monte Carlo analysis.

DEMARCATION OF THE GEOMORPHOLOGICAL BOUNDARIES OF SOUTHEASTERN TIBET: IMPLICATIONS FOR EXPANSION MECHANISMS OF THE PLATEAU EDGE

WU Gui-ling, ZHU Cheng-yu, WANG Guo-can, ZHANG Pan

2019, 41(2):  281-299.  DOI: 10.3969/j.issn.0253-4967.2019.02.003

Asbtract ( )   HTML   PDF (14714KB) ( )  

References | Related Articles | Metrics

The geomorphologic structure in the southeastern Tibetan Plateau is one of the important indexes for the expansion and deep dynamic process of Tibet. There are two different understandings for the geomorphologic structure in the southeastern Tibetan Plateau, i.e. gradual change and abrupt change. The gradient model suggests a gradual topographic reduction towards southeast which is an important evidence for the lower crust channel flow. The abrupt model considers that the southeast boundary of the plateau shows an abrupt change of topography in a zone of 50~200km wide which is controlled by the Yarlung-Yulong fault system. Here, we describe the morphotectonic feature in detail of the Sichuan-Yunnan block on the southeast edge of the plateau through the digital elevation model(DEM)analysis, further review the structural controls on the geomorphologic structure by combining the tectono-thermochronology analysis, and evaluate the southeastward spreading mode of the plateau.
The topographic arithmetic progression ranking by using the DEM of the Sichuan-Yunnan block reveals three geomorphologic steps gradually lowering from the northwest to southeast. The switching of hypsometric integral(HI)value and the anomaly of SL/K value(where SL is stream length-gradient index and K is altitude of the profile)of river systems all occur on the edge of terraces. The high terrace is located on the north of Muli-Yulong with average elevation~4 200m; the secondary level of terrace extends to the Yanyuan-Lijiang area with average elevation~3 000m; and the third level is the region between the Jinhe-Qinghe and Anninghe with average elevation~1 800m.
Structure investigation reveals that all the topographic boundaries between different terraces are consistent with regional major faults. The Muli thrust fault and Yulong thrust fault control the southeast edge of the high terrace, the Jinhe-Qinghe thrust fault separates the second and third level of terrace. The coincidence between topography boundaries and faults suggests that the formation of the stepped geomorphology on the southeast edge of the plateau were induced by the fault activities, reflecting the fault-controlled southeastward stepped-expanding mode of the plateau.
The fission-track(FT)dating of the granites at the hanging wall of the Yuling-Muli Fault reveals fast uplift during~27~22Ma BP, reflecting the major thrusting along the Yulong-Muli Fault, which is consistent with the early-stage activity (~30~25Ma BP) of the Longmenshan Fault. Therefore, the high terrace was formed during the Oligocene to early Miocene with the thrusting of the Yulong-Muli Fault. Tectono-thermochronology analysis also reveals the major thrusting of the Jinhe-Qinghe Fault occurred during~18~11Ma BP, indicating the middle terrace was formed in the middle Miocene, which also could correspond to the middle Miocene(~15~10Ma BP) activity of the Longmenshan Fault.
Therefore, the thrusting faults controlled stepped terrace geomorphologic structure and the stepwise expanding mode under combined movements of large-scale thrusts and strike-slip faults at the southeast edge of Tibetan Plateau during the late Cenozoic do not support the lower crust channel flow model.

THE MECHANISMS OF ARCUATE STRUCTURES ON THE SOUTH SIDE OF THE ALTYN TAGH FAULT AND THEIR TECTONIC IMPLICATIONS

LI Bing-shuai, YAN Mao-du, ZHANG Wei-lin, YANG Yong-peng, ZHANG Da-wen, CHEN Yi, GUAN Chong

2019, 41(2):  300-319.  DOI: 10.3969/j.issn.0253-4967.2019.02.004

Asbtract ( )   HTML   PDF (6045KB) ( )  

References | Related Articles | Metrics

The giant sinistral Altyn Tagh Fault(ATF)is the northern boundary of the Tibetan Plateau. It has been playing important role in adjusting the India-Eurasia collision and the tectonic evolution of the northeastern Tibetan Plateau. Knowledge of the evolution of the ATF can provide comprehensive understanding of the processes and mechanisms of the deformation of the Tibetan Plateau. However, its timing of commencement, amount of displacement and strike-slip rate, as well as the tectonic evolution of the region are still under debate. South of the ATF, there exist a series of oroclinal-like arcuate structures. Knowledge of whether these curved geometries represent original curvatures or the bending of originally straight/aligned geological units has significant tectonic implications for the evolution of the ATF. The Yingxiongling arcuate belt in the western Qaidam Basin and the northern Qaidam marginal thrust belt(NQMTB)north of the Qaidam Basin are the two typical arcuate thrust belts, where the former has a "7-types" structure, and the latter has a reverse "S-type" structure. Successive Cenozoic sediments are well exposed and magnetostratigraphically dated in both belts.
Paleomagnetic declination has great advantage to reveal vertical-axis rotations of geological bodies since they become magnetized. Recently conducted paleomagnetic rotation studies in different parts of these two thrust belts revealed detailed Cenozoic rotation patterns and magnitudes of the region. By integrating these paleomagnetic rotation results with regional geometric features and lines of geological evidence, we propose that these two arcuate thrust belts were most likely caused by different rotations in different parts of these curvatures, due to the sinistral strike-slip faulting along the ATF, rather than originally curved ones. The Yingxiongling arcuate belt was shaped by the significant counterclockwise(CCW)rotations of its northwestern half(the Akatengnengshan anticline)near the ATF during~16~11Ma BP, while its southeastern half(the Youshashan anticline)had no significant rotations since at least~20Ma BP. The geometry of the NQMTB was developed firstly by remarkable clockwise rotations of its middle part during~33~14Ma BP, and later possibly CCW rotations of its northwestern part during the Middle to Late Miocene, similar to that of the northwestern part of the Yingxiongling arcuate belt. The characteristics of two-stage strike-slip evolution of the ATF since the Early Oligocene were enriched:1)During the Early Oligocene to mid-Miocene, fast strike-slip faulting along the ATF was proposed to accommodate the eastward extrusion of the northern Tibetan Plateau with its sinistral shear confined to the fault itself. While in the NQMTB and farther east area in the Qilian Shan, its sinistral shear was transferred to the interior of the plateau and was accommodated by deformation of differential crustal shortenings and block rotations in these regions. Thus, the displacement along the ATF west of the NQMTB is larger than that east of the NQMTB. 2)Since the mid-late Miocene, sinistral shear of the ATF was widespread distributed within the northern Tibetan Plateau, instead of concentrated to the fault itself. Its sinistral offsets were partially absorbed by the shortening deformation within the Qaidam Basin and the Qilian Shan, leading the offsets along the ATF decreasing to the east. With the sinistral frictional drag of blocks(the Tarim Basin and the Altyn Tagh Range)on the other side during the second stage evolution of the ATF, a transitional zone south of the ATF was likely developed by remarkable CCW rotations during the Middle to Late Miocene, which is probably confined to east of the Tula syncline. Combining the sinistral offsets along the ATF derived from the paleomagnetic rotations during the Early Oligocene to mid-late Miocene and that by piercing points since the Late Miocene, the post Oligocene strike-slip offsets were constrained as at least~350~430km for the reference in the western Qaidam Basin and~380~460km for the reference in the NQMTB, with an average slip rate of at least~10.6~13.9mm/a. The post Early Oligocene offsets are consistent with the widely accepted offsets of~300~500km obtained by piercing point analyses.

LONGITUDINAL PROFILES AND THEIR TECTONIC SIGNIFICANCE OF THE SHIYANGHE RIVER BASIN IN THE EASTERN QILIANSHAN MOUNTAINS

GAO Xiao-dong, XIE Hong, YUAN Dao-yang, SU Qi, SHAO Yan-xiu

2019, 41(2):  320-340.  DOI: 10.3969/j.issn.0253-4967.2019.02.005

Asbtract ( )   HTML   PDF (8309KB) ( )  

References | Related Articles | Metrics

The river system is very sensitive to landscape fluctuations and the pattern of drainage contains the past and present tectonic information and can record the latest even tiny change along the orogenic belt system. Therefore, fluvial geomorphology is always used to describe the shapes of river channels and recognize the different segments of active faults. Qualitative and quantitative geomorphic analyses can provide useful information on detecting active tectonic features and the influence of landscape change and evolution. Quantitative analysis such as analysis of river longitudinal profile and geomorphic indices can help researchers evaluate the relative level of tectonic activity and characterize the geomorphic features of landscape quantitatively.
Our study focuses on the geomorphic analysis of Shiyanghe River Basin which is located in the eastern part of Qilianshan Mountains. The tectonic deformation is very strong since late Cenozoic, and Quaternary active thrust faults, strike-slip faults and active folds are distributed all over the region, indicating that the whole region is suffering from crustal shortening and sinistral shear. In this region, the latest tectonic deformation and tectonic activities have been recorded by its fluvial system.
Based on GIS spatial analysis technology, the longitudinal profiles of seven tributaries(including Gulanghe River, Huangyanghe River, Jintahe River, Zamuhe River, Xiyinghe River, Dongdahe River and Xidahe River)in the Shiyanghe River Basin are extracted by using digital elevation models(DEM)and Matlab script. In channel longitudinal profiles, most tributaries in Shiyanghe River Basin exhibit an increased channel gradient in their midstream and downstream area. This pattern is consistent with the models of transient channel profile which suggests an increase in rock uplift rate or base level fall. The longitudinal profiles of seven tributaries are analyzed synthetically by using the method of bedrock channel erosion model, and the concavity(θ), steepness index(k_sn), as well as the knickpoints information(including distribution, elevation, distance from mouth and drainage area)of seven tributaries are obtained. The result shows that each of the tributaries in the Shiyanghe River Basin at least has one major knickpoint. The comprehensive study of the longitudinal profiles, knickpoints and the lithology of the river basin show that the Gulanghe River, Jintahe River, Zamuhe River, Xiyinghe River, Dongdahe River and Xidahe River all have ‘slope-break’ knickpoints, which suggest that they are in a transient state. The knickpoints represent a transient response to the dynamic surface uplift since late Cenozoic. Therefore, we can conclude that the evolution of fluvial geomorphology in eastern Qilian Mountains is mainly related to tectonic activities. Channel segments upstream of knickpoints exhibit lower concavities(mean θ is 0.458±0.053)and higher channel steepness indices(mean k_sn is 129.09±1.82). In contrast, lower channel segments are more complanate(mean k_sn is 68.162±0.821)and exhibit a higher concavity(mean θ is 0.831±0.147). The distribution of concavity is related to the erosion rate, thence, we can infer that the higher value of concavity in downstream area indicates the higher erosion rate. Because the different steepness index(k_s)and the concavity(θ)below and above the reach of knickpoints indicate that they have different development trends in different channel segments, and the distribution of knickpoints represent the evolution process of the longitudinal section of the tributaries. Using the concavity value of the knickpoint, each lower reach longitudinal profile of tributary is fitted. According to the fitted result, the calculated approximate average erosion volume of the Shiyanghe River Basin is 488m since it formed, and the average erosion volume of the six tributaries, which originated in Gulang nappe, is 508.5m. The total amount of erosion is positively correlated with rock uplift when a river is in transient state. Thence, it concludes that the Gulang nappe has experienced a strong uplift. Furthermore, we obtained the spatial distribution of k_sn values of the whole fluvial system in the Shiyanghe River Basin from calculating and interpolating the k_sn values, and combined the geomorphic parameters results to analyze the tectonic significance of the Shiyanghe River Basin synthetically. The spatial distribution of k_sn values of the Shiyanghe River Basin represent the accommodation of geomorphic landscape to the tectonic force and the manner of channels responding to tectonic forces. In this study, most of the channel gradients obtained from midstream are higher than upstream and downstream and k_sn values in downstream reaches is less than 60m^0.9, the high k_sn values are in the Gulang nappe, reaching over 1 400m^0.9, which indicates that the Gulang nappe has experienced uplift since the Quaternary. Therefore, we conclude that the regional difference of the k_sn is mainly controlled by the uplift rate of bedrocks.
Based on the comprehensive analysis of geomorphic parameters and tectonic background, we conclude that the geomorphic evolution of the Shiyanghe River Basin is in a non-equilibrium state, and the tectonic deformation is the main factor affecting the geomorphic evolution of the eastern Qilianshan Mountains and controlling the present tectonic pattern, geomorphic development and evolution history of the study area.
According to the river longitudinal profiles and modeling analysis, this study indicates that the quantitative geomorphic analyses can provide useful and effective information on detecting active tectonic features and the influence of landscape change and evolution, and the geomorphic indices are useful and appropriate tools to analyze the coupling of tectonic and geomorphy.

GEOMORPHIC FEATURES AND LATE QUATERNARY SLIP RATE OF THE SOUTHERN ZONGWULONG SHAN FAULT

DONG Jin-yuan, LI Chuan-you, ZHENG Wen-jun, LI Tao, LI Xin-nan, ZHANG Pei-zhen, REN Guang-xue, DONG Shao-peng, LIU Jin-rui

2019, 41(2):  341-362.  DOI: 10.3969/j.issn.0253-4967.2019.02.006

Asbtract ( )   HTML   PDF (19068KB) ( )  

References | Related Articles | Metrics

With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin.

APPLICATION OF SEMIAUTOMATIC EXTRACTION OF FLUVIAL TERRACES BASED ON R LANGUAGE-AN EXAMPLE FROM THE YELLOW RIVER TERRACES AT MIJIA SHAN

YAO Wen-qian, LIU-ZENG Jing, Michael Oskin, HAN Long-fei, LI Xue, WANG Heng, XU Xin-yue, LI Zhan-fei, ZHANG Jin-yu

2019, 41(2):  363-376.  DOI: 10.3969/j.issn.0253-4967.2019.02.007

Asbtract ( )   HTML   PDF (6746KB) ( )  

References | Related Articles | Metrics

The generation, abandonment and preservation of terraces formed in active tectonic areas are important to the analysis of the role of the tectonics and climate along the temporal variations, so it appears significant as how to use the effective quantitative methods to extract and accurately depict these terraces. The increasingly convenient acquisition of high-precision topographic data has greatly promoted the advancement of quantitative research in geoscience, making it possible to analyze mid-micro-geomorphic features on a large scale, especially by studying the temporal and spatial evolution of tectonic deformation through accurate capture of micro-geomorphic features. Over the past decade, the rapid development of LiDAR(Light Detection and Ranging)technology has provided unprecedented opportunity to access high-precision topographic data(up to centimeter in vertical and horizontal directions). However, its relatively high cost and relatively complex data processing techniques limit its widespread application in the field of earth sciences. In recent years, with the continuous innovation and advancement of topographic measurement technology, the three-dimensional structure of motion reconstruction technology(Structure from Motion, SfM)has gradually been introduced into the field of digital topographic photogrammetry due to its rapid advantage in providing quick, convenient and cost-effective methods for obtaining high-density geospatial point data. This method thus shows great potential for providing high resolution topographic data with comparable resolution and precision. Therefore, with the acquisition of more and more high-resolution terrain data in recent years, it is an important development trend to explore automated or semi-automated quantitative geomorphological analysis methods. R language, as an excellent programming language, has not been used in the geology and geomorphology, although is widely applied in medicine and meteorology based on its powerful capability of statistician and graphic visualization. In this paper, we focus on the Yellow River multi-terraces formed to the east of the Mijia Shan, which belongs to the Jingtai-Hasi Shan segment of the Haiyuan Fault. With the analysis and visualization of the high-resolution topographic data collected from the SfM in the environment of the R language, we implement the semiautomatic classification and mapping of the Yellow River multi-terraces. The method identifies 20 terraces with different elevation. Our results also imply that the younger terraces have better continuity and elongation, and the older terraces have more deformation, which can be demonstrated from their gradually notable semi-parabolic shape. Besides this, it also suggests the diverse evolution stages of the Yellow River terraces. Our study indicates that R language is expected to become an efficient tool of statistics and visualization of the high-resolution topographic data.

THE DELINEATION OF THREE-DIMENSIONAL SHALLOW GEOMETRY OF ACTIVE FAULT BASED ON TLS AND GPR: A CASE STUDY OF AN NORMAL FAULT ON THE NORTH MARGIN OF MAOYABA BASIN IN LITANG, WESTERN SICHUAN PROVINCE

ZHANG Di, WU Zhong-hai, LI Jia-cun, LIU Shao-tang, MA Dan, LU Yan

2019, 41(2):  377-399.  DOI: 10.3969/j.issn.0253-4967.2019.02.008

Asbtract ( )   HTML   PDF (12867KB) ( )  

References | Related Articles | Metrics

It is crucial to reveal the surface traces and activity of active faults by obtaining high-precision microtopography and three-dimensional shallow geometry. However, limited by the traditional geological investigation methods in the field and geological condition factors, the measurement method on microtopography and shallow geometry of active fault is badly insufficient. In this study, the TLS and GPR are firstly used comprehensively to delineate the microtopography and shallow geometry of the normal fault scarp on the north margin of Maoyaba Basin in Litang. Firstly, the vertical displacements of two landforms produced by the latest two periods of normal faulting and the two-dimensional GPR profiles are obtained separately. Secondly, the three-dimensional measurement method of active fault based on TLS and GPR is preliminarily established. On this basis, three-dimensional model of fault scarp and three-dimensional images of subsurface geometry are also obtained. These data all reveal a graben structure at normal fault scarps. Thirdly, the fusion and interpretation of three-dimensional data from the surface and subsurface are realized. The study results show:1)the vertical displacements of the T₁ and T₂ terraces by the normal fault movement is 1.4m and 5.7m, the GPR profile shows a typical fault structure and indicates the existence of small graben structure with a maximum width of about 40m in the shallow layer, which further proves that it is a normal fault. 2)the shallow geometry of the normal fault scarp can be more graphically displayed by the three-dimensional radar images, and it also makes the geometry structure of the fault more comprehensive. The precise location and strike of faults F₁ and F₂ on the horizontal surface are also determined in the three-dimensional radar images, which further proves the existence of small graben structure, indicating the extensional deformation characteristics in the subsurface of the fault scarps. Furthermore, the distribution of small graben structure on the surface and subsurface is defined more precisely. 3)the integrated display of microgeomorphology and shallow geometry of normal fault scarp is realized based on the three-dimensional point cloud and GPR data. The fusion of the point cloud and GPR data has obvious advantages, for the spatial structure, morphological and spectral features from the point cloud can improve the recognition and interpretation accuracy of GPR images. The interpreted results of the GPR profiles could minimize the transformation of the surface topography by the external environment at the most extent, restore the original geomorphology, relocate the position and trend of faults on the surface and constrain the width of deformation zones under the surface, the geological structure, and the fault dislocation, etc.
In a word, the TLS and GPR can quickly and efficiently provide the spatial data with multi-level and multi-visual for non-destructive inspection of the microgeomorphology and shallow structure for the active fault in a wide range, and for the detection of active fault in the complex geological environments, and it is helpful to improve the accuracy and understanding of the investigation and research on microtopography and shallow geometry of active faults. What's more, it also offers important data and method for more comprehensive identification and understanding of the distribution, deformation features, the behaviors of active faults and multi-period paleoseismicity. Therefore, to continuously explore and improve this method will significantly enhance and expand the practicability and application prospects of the method in the quantitative and elaborate studies of active faults.

IDENTIFICATION OF PALEO-EARTHQUAKES OF LUOYUNSHAN PIEDMONT FAULT BY QUANTITATIVE MORPHOLOGY OF LIMESTONE FAULT SURFACES

ZOU Jun-jie, HE Hong-lin, SHI Feng, WEI Zhan-yu, SU Peng, YAN Xiao-bing

2019, 41(2):  400-418.  DOI: 10.3969/j.issn.0253-4967.2019.02.009

Asbtract ( )   HTML   PDF (7234KB) ( )  

References | Related Articles | Metrics

The quantitative analysis of morphologic characteristics of bedrock fault surface is a useful approach to study faulting history and identify paleo-earthquake. It is an effective complement to trenching technique, specially to identifying paleo-earthquakes in a bedrock area where the trenching technique cannot be applied. This paper focuses on the Luoyunshan piedmont fault, which is an active normal fault extending along the eastern boundary of the Shanxi Graben, China. There are a lot of fault scarps along the fault zone, which supply plentiful samples to be selected to our research, that is, to study faulting history and identify paleo-earthquakes in bedrock area by the quantitative analysis of morphologic characteristics of fault surfaces. In this paper, we calculate the 2D fractal dimension of two bedrock fault surfaces on the Luoyunshan piedmont fault in the Shanxi Graben, China using the isotropic empirical variance function, which is a popular method in fractal geometry. Results indicate that the fractal dimension varies systematically with height above the base of the fault surface exposures, indicating segmentation of the fault surface morphology. The 2D fractal dimension on a fault surface shows a ‘stair-like’ vertical segmentation, which is consistent with the weathering band and suggests that those fault surfaces are outcropped due to periodic faulting earthquakes. However, compared to the results of gneiss obtained by the former researchers, the characteristic fractal value of limestone shows an opposite evolution trend. 1)The paleo-earthquake study of the bedrock fault surface can be used as a supplementary method to study the activity history of faults in specific geomorphological regions. It can be used to fill the gaps in the exploration of the paleo-earthquake method in the bedrock area, and then broaden the study of active faults in space and scope. The quantitative analysis of bedrock fault surface morphology is an effective method to study faulting history and identify paleo-earthquake. The quantitative feature analysis method of the bedrock fault surface is a cost-effective method for the study of paleo-earthquakes in the bedrock fault surface. The number of weathered bands and band height can be identified by the segment number and segment height of the characteristic fractal dimension, and then the paleoearthquake events and the co-seismic displacement can be determined; 2)The exposure of the fault surface of the Luoyunshan bedrock is affected and controlled by both fault activity and erosion. A strong fault activity(ruptured earthquake)forms a segment of fault surface which is equivalent to the vertical co-seismic displacement of the earthquake. After the segment is cropped out, it suffers from the same effect of weathering and erosion, and thus this segment has approximately the same fractal dimension. Multiple severe fault activities(ruptured earthquake)form multiple fault surface topography. The long-term erosion under weak hydrodynamic conditions at the base of the fault cliff between two adjacent fault activities(intermittent period)will form a gradual slow-connect region where the fractal dimension gradually changes with the height of the fault surface. Based on the segmentation of quantitative morphology of the two fault surfaces on the Luoyunshan piedmont fault, we identified four earthquake events. Two sets of co-seismic displacement of about 3m and 1m on the fault are obtained; 3)The relationship between the fault surface morphology parameters and the time is described as follows:The fractal dimension of the limestone area decreases with the increase of the exposure time, which reflects the gradual smoothing characteristics after exposed. The phenomenon is opposite to the evolution of the geological features of gneiss faults acquired by the predecessors on the Huoshan piedmont fault; 4)Lithology plays an important role in morphology evolution of fault surface and the two opposite evolution trends of the characteristic fractal value on limestone and gneiss show that the weathering mechanism of limestone is different from that of the gneiss.

APPLICATION OF TOPOGRAPHIC SLOPE AND ELEVATION VARIATION COEFFICIENT IN IDENTIFYING THE MOTUO ACTIVE FAULT ZONE

YANG Xiao-ping, WANG Ping, LI Xiao-feng, XIE Chao, ZHOU Ben-gang, HUANG Xiong-nan

2019, 41(2):  419-435.  DOI: 10.3969/j.issn.0253-4967.2019.02.010

Asbtract ( )   HTML   PDF (17652KB) ( )  

References | Related Articles | Metrics

The eastern Himalaya syntaxis is located at the southeastern end of the Qinghai-Tibet Plateau and is the area where the Eurasian plate collides and converges with the Indian plate. The Namjabawa is the highest peak in the eastern section of the Himalayas, and the Yarlung Zangbo River gorge is around the Namjabawa Peak. The NE-striking Aniqiao Fault with right-lateral strike-slip is the eastern boundary fault of the Namjabawa syntaxis. Motuo Fault is in the east of and parallel to the Aniqiao Fault, distributing along the valley of the Yarlung Zangbo River. The section of Yarlung Zangbo River valley at the eastern side of the Namjabawa area is located in the southern foothills of the Himalayas and belongs to the subtropical humid climate zone with dense tropical rainforest vegetation. Dense vegetation, large terrain elevation difference, strong endogenetic and exogenic forces, and abundant valley deposition bring enormous difficulty to the research on active faults in this area.
Since 1990s, surface morphology can be quantitatively expressed by digital elevation models as the rapid development of remote sensing technology. Geomorphic types and their characteristics can be quantified by geomorphological parameters which are extracted from DEM data, describing geomorphologic evolution and tectonic activity. But to date, researches based on quantitative geomorphic parameters are mainly focus on the differential uplift of regional blocks. In the study and mapping of active faults, surface traces of active faults are acquired by visual interpretation of remote sensing images. It has not been reported to identify the location of active faults via the change of quantitative geomorphic parameters. The distribution map of topographic elevation variation coefficient is suitable to reflect the regional erosion cutting and topographic relief, and the places with higher topographic elevation variation coefficient are more strongly eroded. In this paper, we attempt to identify the active faults and explore their distribution in the Yarlung Zangbo Gorge in the east of the Namjabawa Peak based on the application of two quantitative geomorphic parameters, namely, the topographic slope and the elevation variation coefficient.
Using the DEM data of 30m resolution, two quantitative geomorphic parameters of topographic slope and elevation variation coefficient in Namjabawa and its surrounding areas were obtained on the ArcGIS software platform. On the topographic slope distribution map, the slope of the eastern and western banks of the Yarlung Zangbo River near Motuo is steep with a slope angle of more than 30°. Under the background of steep terrain, there are gentle slope belts of 5°~25° distributing intermittently and NE-striking. On the distribution map of topographic elevation variation coefficient, the elevation variation coefficient of the Yarlung Zangbo River near Motuo is greater than 0.9. On the background of the high topographic fluctuation area, it develops gently topographic undulating belts with elevation variation coefficient of 0.2~0.9. The belts are intermittently distributed and northeastern trending. Through the field geological and geomorphological investigation and trench excavation, it is found that the abnormal strips of the above-mentioned geomorphological parameters are the locations where the active faults pass. The above results show that the quantitative analysis of the topographic slope and the coefficient of variation of elevation can help us find active faults in areas with large terrain slope, serious vegetation coverage and high denudation intensity.

FIRST REPORT OF BERO ZECO ACTIVE FAULT IN GÊRZÊ, NORTHERN TIBET

HA Guang-hao, WU Zhong-hai, MA Feng-shan, ZENG Qing-li, ZHANG Lu-qing, GAI Hai-long

2019, 41(2):  436-446.  DOI: 10.3969/j.issn.0253-4967.2019.02.011

Asbtract ( )   HTML   PDF (4826KB) ( )  

References | Related Articles | Metrics

In the interior of the Tibetan Plateau, the active tectonics are primarily marked by conjugate strike slip faults and north-trending rifts, which represent the E-W extension since late Cenozoic of the plateau. The conjugate faults are mainly composed of NE-trending left-lateral strike-slip faults in Qiangtang terrane and NW-trending right-lateral strike-slip faults in Lhasa terrane. While, the rifts mainly strike N, NNW and NNE within southern Tibet. However, it is still a debate on the deformational style and specific adjustment mechanism of E-W extension. One of key reasons causing this debate is the lack of detailed investigation of these active faults, especially within the northwestern plateau. Recently, we found a 20km long, NNW-trending active fault at Bero Zeco in northwestern Tibet. This fault is presented as fault sag ponds, channel offsets and fault scarps. Displacement of channels and geomorphic features suggested that the Bero Zeco Fault(BZF)is a dextral strike-slip fault with a small amount of normal slip component, which may result from the E-W extensional deformation in the interior of Tibet. BZF strikes N330°~340°W, as shown on the satellite image. The main Quaternary strata in the studied area are two stages alluvial fans around the Bero Zeco. From the satellite images, the old alluvial fans were cut by the lake shoreline leaving many of lake terraces. And the young fans cut across the lake terraces and the old fans. By contrasting to the "Paleo-Qiangtang Huge Lake" since late Quaternary, these old alluvial fans could be late Pleistocene with age ranging from 40ka to 50ka. And the young fans could be Holocene. The sag ponds along the BZF are distributed in the late Pleistocene alluvial fans. Also, the BZF displaced the late Pleistocene fans without traces within Holocene fans, suggesting that the BZF is a late Pleistocene active fault. The fault scarps are gentler with the slope angle of around 10° and the vertical offset is about 2m by field measurement. Reconstruction of the offset of channels suggested that the accumulated dextral offset could be about 44m on the late Pleistocene alluvial fans. Therefore, we infer that the dextral slip-rate could be around 1mm/a showing a low-rate deformation characteristic. The angle between the strike of BZF and principal compressive stress axis(σ₁)is around 30°, which is significantly different to the other faults within the conjugate strike-slip fault zones that is 60°~75°. Now, the deformation mechanisms on these conjugate faults are mainly proposed in the studies of obtuse angle between the faults and σ₁, which is likely not applicable for the BZF. We infer that the BZF could be the northward prolongation of the north-trending rifts based on the geometry. This difference suggests that the conjugate strike-slip faults may be formed by two different groups:one is obtuse angle, which is related to block extrusion or shear zones in Lhasa and Qiangtang terranes possibly; the other is acute angle, which may represent the characteristics of new-born fractures. And more studies are needed on their deformation mechanisms.

BURIAL AND EXHUMATION OF THE XIGAZE FORE-ARC BASIN FROM LOW TEMPERATURE THERMOCHRONOLOGICAL EVIDENCE

GE Yu-kui, ZENG Jing, ZHANG Jin-yu, LI Ya-lin

2019, 41(2):  447-466.  DOI: 10.3969/j.issn.0253-4967.2019.02.012

Asbtract ( )   HTML   PDF (6861KB) ( )  

References | Related Articles | Metrics

The Xigaze fore-arc basin is adjacent to the Indian plate and Eurasia collision zone. Understanding the erosion history of the Xigaze fore-arc basin is significant for realizing the impact of the orogenic belt due to the collision between the Indian plate and the Eurasian plate. The different uplift patterns of the plateau will form different denudation characteristics. If all part of Tibet Plateau uplifted at the same time, the erosion rate of exterior Tibet Plateau will be much larger than the interior plateau due to the active tectonic action, relief, and outflow system at the edge. If the plateau grows from the inside to the outside or from the north to south sides, the strong erosion zone will gradually change along the tectonic active zone that expands to the outward, north, or south sides. Therefore, the different uplift patterns are likely to retain corresponding evidence on the erosion information. The Xigaze fore-arc basin is adjacent to the Yarlung Zangbo suture zone. Its burial, deformation and erosion history during or after the collision between the Indian plate and Eurasia are very important to understand the influence of plateau uplift on erosion.
In this study, we use the apatite fission track(AFT)ages and zircon and apatite(U-Th)/He(ZHe and AHe)ages, combined with the published low-temperature thermochronological age to explore the thermal evolution process of the Xigaze fore-arc basin. The samples' elevation is in the range of 3 860~4 070m. All zircon and apatite samples were dated by the external detector method, using low~U mica sheets as external detectors for fission track ages. A Zeiss Axioskop microscope(1 250×, dry)and FT Stage 4.04 system at the Fission Track Laboratory of the University of Waikato in New Zealand were used to carry out fission track counting. We crushed our samples finely, and then used standard heavy liquid and magnetic separation with additional handpicking methods to select zircon and apatite grains.
The new results show that the ZHe age of the sample M7-01 is(27.06±2.55)Ma(Table 2), and the corresponding AHe age is(9.25±0.76)Ma. The ZHe and AHe ages are significantly smaller than the stratigraphic age, indicating suffering from annealing reset(Table 3). The fission apatite fission track ages are between(74.1±7.8)Ma and(18.7±2.9)Ma, which are less than the corresponding stratigraphic age. The maximum AFT age is(74.1±7.8)Ma, and the minimum AFT age is(18.7±2.9)Ma. There is a significant north~south difference in the apatite fission track ages of the Xigaze fore-arc basin. The apatite fission track ages of the south part are 74~44Ma, the corresponding exhumation rate is 0.03~0.1km/Ma, and the denudation is less than 2km; the apatite fission track ages of the north part range from 27 to 15Ma and the ablation rate is 0.09~0.29km/Ma, but it lacks the exhumation information of the early Cenozoic. The apatite(U-Th)/He age indicates that the north~south Xigaze fore-arc basin has a consistent exhumation history after 15Ma.
The results of low temperature thermochronology show that exhumation histories are different between the northern and southern Xigaze fore-arc basin. From 70 to 60Ma, the southern Xigaze fore-arc basin has been maintained in the depth of 0~6km in the near surface, and has not been eroded or buried beyond this depth. The denudation is less than the north. The low-temperature thermochronological data of the northern part only record the exhumation history after 30Ma because of the young low-temperature thermochronological data. During early Early Miocene, the rapid erosion in the northern part of Xigaze fore-arc basin may be related to the river incision of the paleo-Yarlungzangbo River. The impact of Great Count Thrust on regional erosion is limited. The AHe data shows that the exhumation history of the north-south Xigaze fore-arc basin are consistent after 15Ma. In addition, the low-temperature thermochronological data of the northern Xigaze fore-arc basin constrains geographic range of the Kailas conglomerate during the late Oligocene~Miocene along the Yarlung Zangbo suture zone. The Kailas Basin only develops in the narrow, elongated zone between the fore-arc basin and the Gangdese orogenic belt.
The southern part of the Xigaze fore-arc basin has been uplifted from the sea level to the plateau at an altitude of 4.2km, despite the collision of the Indian plate with the Eurasian continent and the late fault activity, but the plateau has been slowly denuded since the early Cenozoic. The rise did not directly contribute to the accelerated erosion in the area, which is inconsistent with the assumption that rapid erosion means that the orogenic belt begins to rise.

STUDY ON QUATERNARY MAGNETIC STRATIGRAPHY IN WUHAN AREA, CHINA

ZHANG Yu-fen, LI Chang-an, YANG Wei, ZHAO Ju-xing, YU Jun, XIONG Zhi-qiu

2019, 41(2):  467-480.  DOI: 10.3969/j.issn.0253-4967.2019.02.013

Asbtract ( )   HTML   PDF (3792KB) ( )  

References | Related Articles | Metrics

With the lateral and vertical expansion of cities, urban geology becomes critical for urban construction. Wuhan City, as one of the largest cities in China, was chosen by China Geological Survey as pilot city to study multiple elements of urban geological survey. 90% of Wuhan area is covered by Quaternary strata, which means that most of the city is built on Quaternary sediments. The study of Quaternary stratigraphic structure of Wuhan area is a crucial groundwork for the urban geological survey of Wuhan. Due to the badly lagging of research on Quaternary stratigraphy of Wuhan area, this study selects four boreholes from hundreds of cores in this area in the project of Wuhan Urban Geological Survey for magnetic stratigraphic study and paleomagnetic analysis. This work mainly focuses on the borehole SK2 which possesses well-developed strata and is representative for magnetic strata division. Wuhan is located in the eastern Jianghan Basin where the Quaternary sediment has a fluctuant bottom edge, forming a half-graben shape boundary in large scale, as revealed by a large amount of boreholes. The borehole SK2 is located in the western Dongxi Lake depression. SK2 reveals continuous deep Quaternary sediment except for a short gap of late Pleistocen-early Holcene. Moreover, the grain size of drill core is generally smaller than other cores nearby, which is more suitable for paleomagnetic study.
In this study, we collected 117 samples with an interval of 0.25~0.30m from relative fine grain layers in the borehole for paleomagnetic study. Demagnetization and sample measurement were conducted in State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, CAS. By comparing with other well dated cores nearby, Wuhan's Quaternary magnetic stratigraphic chronology framework is initially established. Our data show that:1)the Brunhes-Matsuyama boundary(B/M)of borehole SK2 is clear, locating at 29.6m, and sediment at 1.2~29.6m belongs to Bmnhes normal polarity chron; 2)Two polarity drifts at 9.3~9.6m and 14.1~15.0m are observed in Brunhes. These samples collected from the Xiashu Loess yield two polarity drifts, which can be compared with the Xiashu Loess at Nanjing. The comparison between Xiashu Loess from borehole SK2 and that at Nanjing suggests that negative polarity drift at 14.1~15.0m is the Blake reverse polarity subchron(0.104~0.128Ma BP)and the polarity drifts at 9.3~9.6m(0.07~0.08Ma BP)is Norwegian-Greenland Sea reversal-polarity subchron; 3)Three polarity drifts were observed in Matsuyama, which is comparable with the borehole at Zhoulao and the borehole R25 in the center of the Jianghan Basin. They are at 38.2~39.8m(Jaramillo:0.99~1.07Ma BP), 66.5~71.9m(Olduvai:1.77~1.95Ma BP)and 75.8m(Reunion:2.01Ma BP); 4)Based on the forementioned paleomagnetic data, the depositional age structure of this borehole is:1.2~14.1m(late Pleistocene), 15~29.6m(middle Pleistocene)and 29.6~78.8m(early Pleistocene); 5)Our data show that deposition rate increased during 1.47~1.57Ma BP(54.9~61.3m)and 1.07~1.21Ma BP(39.8~47.3m)because they are fluvial sediments. This study builds the Quaternary stratigraphy and timescale for Wuhan area for the first time. However, because of the complex Quaternary sediment type in Wuhan area and the coarse sediment in the Matuyama, more comprehensive study is needed in the future to test whether our Quaternary stratigraphy and timescale is the best.

THE DEFORMATION OF THE 2008 ZHONGBA EARTHQUAKES AND THE TECTONIC MOVEMENT REVEALED

QIU Jiang-tao, LIU Lei, LIU Chuan-jin, WANG Jin-shuo

2019, 41(2):  481-498.  DOI: 10.3969/j.issn.0253-4967.2019.02.014

Asbtract ( )   HTML   PDF (7555KB) ( )  

References | Related Articles | Metrics

On August 25, 2008, an M_W6.7 earthquake struck Zhongba County, central Lhasa block. Subsequently, an aftershock of M_W6.0 occurred on September 25. The rupture caused by this earthquake is rather complicated. There are some differences in focal positions and fault parameters given by different institutions. In addition, a deeper understanding of the tectonic significance of this earthquake is also needed.
Firstly, we use interferometric synthetic aperture radar data collected by the environmental satellite(ENVISAT)of European Space Agency and the advanced land observing satellite(ALOS)of Japan Aerospace Exploration Agency to obtain eight coseismic deformation fields covering the whole epicenter region based on InSAR technology. Because the terrain in the earthquake area fluctuates greatly and there are many objects with low coherence(eg. lake), we choose 30-resolution SRTM DEM data as reference DEM, the more robust Goldstein as filtering method, and Delaunay Minimum Cost Flow as phase unwrapping method. The interferograms show that the surface deformation caused by this earthquake is about 50km long and is divided into two lobes, north and south. The shape of the deformation in the north is similar to that of Palung Co Lake, and the maximum signal is hidden by the lake. The deformation in the south has two centers, located at two ridges respectively. The aftershock also caused two minor deformations at the east and north of Palung Co Lake.
Secondly, we use uniform sampling method to downsample 8 interferograms, and set the sampling interval of near-field data to be much smaller than that of far-field region, to ensure the observation data characteristic and sampling density of the main deformation region. In order to better invert the rupture slip distribution of the main shock, we subtract the influence of aftershock deformation. Finally, 6 data sets for the main shock deformation are obtained. Smoothness of sliding distribution is applied to restrict the sliding amount of adjacent fault slices. The best-fit solution shows that at least two ruptures in the south and north are caused by the earthquake, mainly of normal dip-slip and partial sinistral strike-slip by Okada uniform elastic half-space dislocation model and SDM method. The northern rupture is related to the Palung Co Fault with NE strike, with the maximum deformation of -13.0cm and the maximum slip of 0.52m in the depth of~12km, and the southern rupture deformation is obviously strongly related to topography, with the maximum deformation of -38.7cm and the maximum slip of 1.15m in the depth of~14km. The maximum slip is located at(30.81°N, 83.45°E), between the positions determined by GCMT and NEIC. The results also show that normal fault earthquakes may play an important role in the uplift of Tibet Plateau.
Thirdly, we use 15 images obtained between 2008 and 2010 from ENVISAT to obtain the post-earthquake time series deformation to further understand the tectonic background of the earthquake using SBAS-InSAR technology. 54 pairs of good interferences are screened out for processing, of which 30 pairs were unwrapped by Delaunay MCF method. The velocity accuracy threshold is set to 2mm/a to ensure reliable estimation of deformation velocity value. After two step SBAS inversions, the time series of deformation after the earthquake is obtained, thereby revealing that the post-earthquake deformation is not obvious on both sides of the fault but in the denudation and deposition area. This shows that no obvious common phenomena such as afterslip or creep are found after the earthquake. From the three cumulative deformation profiles, it can be seen that the regional deformation is mainly denudation and subsidence related to topography and geomorphology, and the deformations of adjacent subsidence and uplift regions are basically the same. The result shows that the graben structure in Lhasa block is mainly vertical deformation caused by terrain difference. In order to explain this result, we processed GPS data from 1991 to 2015 and obtained the principal strain rate in the western region of Lhasa block. The result shows that the east-west extension in Lhasa block is obvious but uneven. The strain is mainly stretching or squeezing perpendicular to deep and large faults, and the strain decreases near the grabens. The tensile strain near the Palung Co fault graben is~2.4×10⁸/a. This also shows that estimates of the tectonic activity based on geomorphology may be underestimated on some normal faults that have not been mapped or have no clear large-scale surface expression in the Tibet Plateau.
This study combines multi-orbit InSAR data to constrain the focal mechanism solution of the Zhongba earthquake, proving that abundant interferometric results can complement each other, which is helpful to analyze the deformation distribution caused by the earthquake more clearly and completely, especially in the absence of surface rupture.

Special Review

A REVIEW OF MOUNTAIN-BASIN COUPLING OF JIANGHAN AND DONGTING BASINS WITH THEIR SURROUNDING MOUNTAINS

LIN Xu, ZENG Jing

2019, 41(2):  499-520.  DOI: 10.3969/j.issn.0253-4967.2019.02.015

Asbtract ( )   HTML   PDF (4420KB) ( )  

References | Related Articles | Metrics

Sedimentary basin and orogenic belt are two important components of continental structure with internal genetic links. The study of the basin-mountain coupling can reconstruct and restore the coupling relationships between the deep lithosphere process, near-surface structure and climate change over time. The Jianghan-Dongting Basin locates in the middle reaches of the Yangtze River, presenting a clear basin and mountain boundary with the Qinling-Dabie Shan to the north, the Mufu Shan to the southeast, the Wuling Shan to the southwest, and the E'xi Mountain to the west, respectively.
The Meso-Cenozoic Jianghan-Dongting Basin was affected by the subduction and collision of the Pacific plate and the Indian Ocean plate on the Eurasian continent, resulting in multiple tectonic evolution processes. There are some big rivers pouring into the Jianghan-Dongting Basin, such as the Yangtze River, Hanjiang River, Ba River, Xiangjiang River, and Yuanjiang River, etc. to serve as the material transport belts linking between the orogenic belt denudation and basin deposition. Therefore, the Jianghan-Dongting Basin has become a multi-source sedimentary basin, which makes it a natural laboratory to explore the geological processes from source to sink. Because the low-temperature thermochronology(e.g. fission-track and(U-Th)/He)can record the recent uplift time of mountains, they are widely used on the bedrock samples and the detrital synorogenic sediments in basins to constrain the surface uplift time of the orogenic belt. Hence, in the first parts of the paper we summarize and sort out the research results of basin-mountain coupling process in the Jianghan-Dongting Basin, evaluate the research results, identify the existing problems, and propose new research directions. After that, we introduce the applications of low-temperature thermochronology on the bedrock within the orogenic belt, basin and river sediments, combined with the actual situation of Jianghan-Dongting Basin, and put forward a new research breakthrough point. It is found that the Jianghan-Dongting Basin is very suitable for the study of low-temperature thermalchronology on detrital minerals. However, it should combine the low-temperature thermochronology results of both orogenic belt and river sediments with the provenance analysis on the same target minerals, building the connection between the exhumation and provenance information on the orogenic belt, thus providing the detailed evolution of mountain-basin coupling process.

PROGRESS OF DETRITAL ZIRCON CHRONOLOGY IN SEDIMENT PROVENANCE STUDIES IN THE YANGTZE RIVER BASIN

LI Ya-wei, LI Chang-an, ZHANG Yu-fen, LIN Xu, WANG Jie-tao, SUN Xi-lin, WEI Chuan-yi, GUO Ru-jun, LENG Yong-hui

2019, 41(2):  521-544.  DOI: 10.3969/j.issn.0253-4967.2019.02.016

Asbtract ( )   HTML   PDF (7497KB) ( )  

References | Related Articles | Metrics

Evolution of the Yangtze River in East Asia is closely linked to the evolving topography following India-Eurasia collision and plays an important role in connecting the Tibetan plateau and the marginal sea, which is of great significance for understanding the evolution of modern Asian landform pattern and exploring the response of river development to tectonic uplift and monsoon evolution. Thus, many methods have been performed to reconstruct the evolution history of the Yangtze River, but there are still some disputes about the age of the Yangtze River, which has been strongly debated for over a century with estimates ranging from late Cretaceous to late Pleistocene. At present, sediment provenance tracing is one of the most important methods for studying the Yangtze River drainage evolution, for the provenance tracers could effectively represent the source area information and the various dating methods would provide reliable chronology framework. Previous studies showed that the zircon high closure temperature, wide distribution in fluvial sediment, and convenient sampling and analyzing made the zircon U-Pb dating a unique indicator recording the source area information. However, the Yangtze River drains a large basin and runs through different geological blocks with complicated lithology, as well as the abundant thermal historical events, leading to the zircon U-Pb dating a challenge work in tracing the sediment source within the Yangtze River Basin. In this study, based on the combination of previous research data and the "source to sink" system, the limitations and disadvantages of the detrital zircon U-Pb dating in the studies of sediment provenance tracing of the Yangtze River Basin were re-analyzed and re-discussed. Considering the evolving process of the large river system, some key areas and diagnostic information carrier, including bedrock and fluvial sediments deposited in present day or geo-history, would provide significant constraints on the evolution process. The former records the original information of the source region, and the latter reserves the practical information preserved in the downstream sink.
As for the Yangtze River Basin, the limitation and disadvantages of the detrital zircon U-Pb dating in tracing sediment provenance are showed as follows:Firstly, six major tectonic units in the source region shows four similar age peaks, which closely corresponds to the previously identified synchronous major granitoid magmatic episodes. Five similar age peaks obviously exist in the sediment of the downstream sink both in the modern fluvial sediment and the geo-historical deposits such as outcrops and basin sediments. Thus, detrital zircon U-Pb chronology is indistinguishable from source to sink, making it unreliable in provenance tracing of the Yangtze River. Secondly, comparing with the detrital zircon spectra of tributary downstream and the upper reaches, all the tributaries below the Three Gores, the running-through of which is regarded as the symbol of the establishment of the modern Yangtze River system, could make up the similar spectra with the modern river sediments. Moreover, Sichuan Basin and Jianghan Basin, which is the last basin and first basin in western and eastern of the Three Gorges, are crucial basins for recording the incision information. However, sediment in these two basins show the similar spectra with five major age peaks from early Jurassic to late Cretaceous, which means the detrital zircon U-Pb chronology could not efficiently record the capture information no matter in spatial scale or time scale. In addition, the same results are also shown in Neogene gravel layer both in Jianghan Basin and Nanjing area. In summary, we propose that the similarity of the detrital zircon age spectra exists widely in Yangtze River system, and this greatly restricts the application of detrital zircon chronology in provenance tracing in the Yangtze River Basin, and the combination of multi-index and multi-method will shed new light in the future studies of provenance tracing within Yangtze River drainage system.