ESR dating of fault gouge from the eastern Liupanshan piedmont fault zone
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Gouge is the carrier for information of the fault activity.In this study,fault gouges from the eastern Liupanshan piedmont fault zone were analyzed by ESR method.However,the measured ESR age is much older than that estimated in the field.On the other hand,SEM images of the quartz grains separated from the fault gouge showed a variety of morphologies,which indicate several periods of fault movements.The ESR age estimates failing to represent the latest fault movement suggest that the latest movement may not have zeroed ESR signals significantly for ESR dating and the quartz may be from different periods of the movements.Although there are still many uncertain factors in the ESR dating of fault gouge,it is essential to study systematically in this area.Keywords:
Fault gouge
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Mylonite
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Longgang volcano group is located in Huinan and Jingyu counties of Jilin Province,which occupies the middle segment of the Longgang mountain ranges.The volcanic activity in Quaternary,especially in the early Pleistocene,is very intensive,and as a result,over 2/3 of the total area is covered by Q1p(Xiaoyizishan Group)basalt sheet.The study area of this paper lies in the northeastern part of the Longgang volcano group,where some small-scaled faults are developed and their activity in the Quaternary Period is critical to the potential earthquake risk evaluation for the local engineering.In order to study the activities of these faults,a comprehensive project has been carried out by means of field investigation and application of ESR dating technique to determine the last active time of each fault.However,an inconsistent phenomenon was found in the study area,in which the of fault gouge from ESR dating method is much younger that the of Q1p basalt sheet that covers both fault plane and fault deformed materials.We propose two facts that would be responsible for this contravention.Firstly,the extensive volcanic activity in the study area in Quaternary may produce a significant amount of heat regionally.For example,the temperature of the molten basalt lava is between 1050℃ and 1200℃,which is high enough to cause the effect of annealing and resetting of ESR signals.Consequently,such effect may result in the of fault gouge with ESR dating method younger than the time when this heat event occurred.Secondly,after a fault is formed,chemical weathering will occur at the fault zone,which may result in dissolution on the grain surface of fault gouge.Such effect may significantly increase the amount of annual ESR dose and make the sample of weathered material younger than the un-weathered ones.Therefore,in this study area with extensively volcanic activity,the from fault gouge dated with ESR method should be considered as the upper limit age of the last fault activity rather than the last time when the fault was active.Even though the upper limit age does not represent the of the last activity of a fault,it is very useful in the practice of determining the capable fault for earthquake safety evaluation of large engineering sites.
Fault gouge
Fault plane
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울산광역시 매곡동 일대에서 새롭게 발견된 단층대의 기하학적, 운동학적 특성 및 제4기 단층운동에 대해 알아보고자 야외조사를 통한 지질구조분석을 실시하였다. 그 결과, 퇴적암이 분포하는 첫 번째 조사지점에서는 100 m 내외의 절취사면을 따라 반복층서, 소규모 단층, 단열대, 변형띠대 등이 연속적으로 관찰되고 있어, 이 지점은 대규모 단층의 손상대에 속하는 것으로 해석된다. 한편 주로 화강암 암편으로 구성된 쇄설성 퇴적층이 분포하는 두 번째 조사지점에서는 저각의 경사를 보이는 여러 조의 단층이 서로 분지 또는 결합하는 형태로 발달하고 있어 대규모 역단층이 발달하는 것으로 판단된다. 이 단층의 단층비지 내에 포함된 유기물의 방사성탄소연대에 기초해 추론된 단층의 최후기 운동시기는 33,275 ± 355년 전 이후로 제한된다. 이번 조사에서 확인된 단층대의 손상대 규모, 운동감각, 운동시기 등은 이 단층대가 연구지역 인근의 대규모 신기단층으로 알려진 울산단층 또는 연일구조선과 밀접한 관련이 있음을 시사한다. 따라서 연구지역 일대에 조성 중인 산업단지와 아파트를 비롯한 여러 시설물에 대한 지진 및 지질학적 안정성을 확보하고 이 지역에서의 지질재해에 대비하기 위해서는 보다 정밀한 구조지질학 및 고지진학 관점에서 이 단층에 대한 연구가 필요할 것으로 판단된다. Structural analysis for a large-scale fault in Maegok-dong, Ulsan, was carried out based on filed-works to investigate the geometric and kinematic characteristics of the fault as well as its Quaternary slip. As results, a series of repeated stratigraphy, minor faults, fracture zones, and deformation band clusters are observed over a distance of about 100 m in the first studied site consisting of sedimentary rocks, which may indicate the damage zone of a large-scale fault in this site. In the second site, mainly composed of granitic clastic rocks, a large-scale thrust fault is expected based on low-angle dipping faults showing branched and/or merged patterns. Age of the last slip on this fault was restrained as after 33,275 ± 355 yr BP based on radiocarbon dating for organic material included in the gouge zone. Dimension of fault damage zone, dominant sense of slip, and age of the slip event associated with the fault suggest that these structures have a close relationship with the Ulsan Fault and/or Yeonil Tectonic Line, which are well-known large-scale neotectonic structural features around the study area. Therefore, it is necessary to study the characteristics of the faults in detail based on structural geology and paleoseismology in order to ensure seismic and geologic stability of the buildings under construction, and to prevent geologic hazards in this area.
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Fault gouge
Fault plane
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Much important information referring to fault motion(e.g.,fault activities period,intensity,frequency,and even dynamic background) can be revealed by resolving fault gouge,which is the result of fault motion while extruding or grinding.The field investigation encompassed sample collecting from the Bailong River fault system of the western segment of the Qinling Orogenic Belt(QOB); 44 samples of fault gouges were collected for quartz micro-morphology analysis.These samples were analyzed using field emission scanning electron microscopy.In addition,14 samples were tested for thermo-luminescence dating.The results showed that most of the surface textures of quartz grains are characterized by fish scale,moss-like texture,and stalactite.However,a small amount of orange peel-like fractures and worm-hole-like shaped surface texture were observed.Moreover,a few typical conchoids or subconchoidal fractures in quartz grains can be seen.This implies that the Bailong River Fault was active repeatedly during the Quaternary period,but the main motion period is the Pleistocene.The 14 thermo-luminescence dating values showed two age groups:343.29-184.06 ka and 92.18-13.87 ka.These study data reveal that fault movement started during the Pliocene,occurred frequently in the early-middle period of the Pleistocene,and the peak frequency of the motion was reached in the early Pleistocene.The fault motions were stopped terminated in the early Holocene.The results are significant for the natural disaster risk evaluation in the western segment of the QOB.
Texture (cosmology)
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In order to outline the kinematics and movement history of a new Quaternary fault, Jingwan Fault in Dangjin, West Korea, we analyzed the geometry of the fault zone composed of a few gouge zones, and made ESR dating for fault gouge materials. The striking Jingwan Fault is a normal fault and exhibits a gradual change in dip (gentle in the lower part, steep in the upper part), indicating a listric fault. As for the fault gouge zone, its thickness varies and reaches 2~3 cm in the lower part or between basement rocks, and 20~30 cm in the middle-upper part or between the basement and Quaternary deposit. It is observed in the latter case that more than three gouge zones develop with different colors, and branch out and re-merge, or they are partly superimposed, indicating different movement episodes. The cumulative displacement is estimated to be about 10 m using the geological cross-sections, from which it is inferred that the total length of fault may be about 2.5 km on the basis of the empirical relation between cumulative displacement and fault length. Therefore, a more study would be needed to verify the entire fault length. The results of ESR dating for three gouge samples at different spots along the fault yields ages of , , and , indicating at least two movement episodes. Slickenlines observed on the fault planes indicate a pure dip slip (normal faulting), which suggests that the ENE-WSW trending Jingwan Fault was presumably moved under a NNW-SSE extensional environment.
Fault gouge
Merge (version control)
Detachment fault
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Fault gouge
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Outcrop
Fault gouge
Breccia
Thrust fault
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The microstructures of fault gouge and tectonite in the Huo'erguosi-Manas-Tugulu reverse fault zones along the southern margin of the Junggar basin are studied and twelve samples of gypsum,fault gouge and quartz veins were collected and dated by using the electronic spin resonance(ESR)method.The results show that the gouges underwent at least three deformation stages.Many stick-slip microstructural marks such as slickenside striations and steps appear in gouges and on quartz grains.In addition,many creep deformation marks such as shear slip and oriented arrangement of clay minerals are also found.The results show that the Huo'erguosi-Manas-Tugulu reverse fault zones formed about 1.5 Ma ago and were readjusted at 0.4-1.0 and 0.08-0.12 Ma respectively.The time of faulting is consistent with the time of uplift of the Qinghai-Tibet Plateau,suggesting that the formation of the Huo'erguosi-Manas-Tugulu reverse fault zones on the southern margin of the Junggar basin is closely related to the uplift process of the Qinghai-Tibet Plateau.
Fault gouge
Tectonite
Tarim basin
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Through the geologic drawing of fault zone and microscopic analysis of tectonic rook in the deformation monitoring caves of the Xiannushan fault and the Jiuwanxi fault, the samples of fault mud and calcite were selected and dated age by thermoluminescent (TL). At the same time, the age determination of the Quaternary alluvial deposits on the Xiannushan fault, the Quaternary lake facies sediment lamina and carbonized wood on the bottomland of the Zhouping river on the side of the fault and the clay of landslide zone of the Quaternary as well as the information collection of isotope age date in the past years indicate that the new activity ages of the Xiannushan fault and Jiuwanxi fault accord with the ones of the faults in the Three Gorges Project area, which were about 0.22～0.23Ma as yet. The newest activity age of the Xiannushan fault was about 0.16～0.19 Ma and the Jiuwanxi fault was about 0.14 Ma. The lower limit of the newest activity ages of the Xiannushan fault is 0.14～0.16Ma and the Jiuwanxi fault is 0.13 Ma or so. Since the late Pleistocene, the two faults haven't been active. So the landslide on the Jiuwanxi fault was caused by external force rather than the fault activity.
Fault gouge
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