The Shotori mountain range is located along the northern terminus of the Nayband fault on the eastern and western domains of the Tabas and Lut blocks,respectively.This range with NNW-SSE trending and approximately 120...The Shotori mountain range is located along the northern terminus of the Nayband fault on the eastern and western domains of the Tabas and Lut blocks,respectively.This range with NNW-SSE trending and approximately 120 km long includes a series of thrust faults approaching the right-lateral strike-slip Nayband fault.Since the Shotori range has experienced various geological events since the Triassic,our investigations suggest that the basement of the Central Iranian subcontinent of the Shotori range contains the early Triassic deep sedimentary with normal faults which confirms Triassic tensional tectonic stress regime in the region.After the middle Triassic,the mountain range has experienced thrust and strike-slip regimes.Therefore,in this study,we reconstruct the stress regimes for different geological periods using fault-slip data.The inversion of faultslip data reveals drastic temporal changes in the maximum stress regime(σ1)over the Triassic,Jurassic,Cretaceous,Paleogene,Neogen,and Quaternary.The reconstruction of the stress field based on the age and direction of fault movement reveals that the direction of the maximum horizontal stress axis(σ1)under a tensional stress regime was approximately N129°in the Early Triassic.This stress regime is the cause of thinning and subsidence of the Shotori sedimentary basin.During the middle Triassic,theσ1 direction was about N81°and the upper Triassic,theσ1 direction was almost N115°.The middle Triassic and upper Triassic stress states exhibited two distinct strike-slip and compressive stress regimes.This stress regime led to the uplift of the Shotori sedimentary basin.During the Jurassic,the direction of the maximum horizontal stress axis(σ1)was~NW-SE under a compressive stress regime.During the Triassic,theσ1 direction was~N-S.This stress regime led to the formation of the high topography of the Shotori Mountain Range.In the Late Cretaceous,the direction of the maximum horizontal stress axis(σ1)under the extensional stress regime was~NE-SW.This stress regime led to the uplift of the Paleogen Dacite in eastern Iran.During the Neogene,theσ1 direction was~N60°.The Quaternary tectonic regime is strike-slip and theσ1 direction is~N50°,consistent with the current convergence direction of the Arabia–Eurasia plates.Our paleostress analysis reveals four recognized stress in this area,which includes compressional,transtensional,transpressional,and strike-slip regimes.Our findings indicated that the crustal diversity of the tectonic regimes was responsible for the formation of various geological structures,such as folds,faults by different mechanisms,and the present-day configuration of the Shotori sedimentary basin.展开更多
In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Ma...In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Magnetic Susceptibility (AMS) and paleostress?have been used. Paleomagnetism is the characteristics of magnetic rocks. Some issues in associated with the past places of continental and oceanic plates can be solved. AMS is one of the paleomagnetism methods that pay to measurement of parameters (which are reflector of the magnetic fabrics rocks). It is presenting an ellipsoid with three-axis perpendicular to each other that defines magnetic ellipsoid. In this regard, the number of 12 stations in different rocks (Jurassic to Quaternary) in the southern region of Ardebil sampling was conducted. In this connection, the study of magnetic fabrics has shown an elliptical magnetic susceptibility with the prolate shape. For the separation of paleostress phases in the Khalkhal area using the analysis of the paleostress based on the study of heterogeneous fault-slip data and sliding lineaments. Firstly, data were picked from 10 stations, and after their analysis, the elliptical shape (prolate) has been determinated. The shape of the ellipsoid, based on AMS and paleostress methods and their results show that in both methods the shape of the stress field is prolate.展开更多
Brittle structures in rock of different ages can be used to establish the tectonic evolution of an orogenic belt through paleostress calculations. Micangshan is located at the southern margin of the Qinling orogenic b...Brittle structures in rock of different ages can be used to establish the tectonic evolution of an orogenic belt through paleostress calculations. Micangshan is located at the southern margin of the Qinling orogenic belt, between the SE-trending Longmenshan fold-and-thrust belt and the arcuate Dabashan thrust-and-fold belt. Structural observations revealed that the dominant structures are reverse and strike-slip faults and folds with E-W and NE-SE trends. To increase knowledge of the tectonic evolution of the Micangshan anticlinorium, faults, joints, veins, and folds were measured at more than eighty sites. On the basis of structural analysis, it emerged that the multiphase paleostress fields became established after the oblique collision between the North and South China plates. The earliest stress field with N-S compression was established during the Micangshan uplift associated with the E-W trending faults and folds. Subsequently, a N-S extension occurred when the Qinling orogenic belt collapsed. Then NW-SE compression developed, with NE trending faults and folds forming in relation to Longmenshan thrusting toward southwest on the eastern margin of the Tibetan plateau. With the development of the arcuate Dabashan orogenic belt, the compression stress orientation of the Micangshan anticlinorium altered from NE-SW to E-W.展开更多
The Salmas geothermal field is located in NW Iran. Subduction of Neo-Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic-Arc. Fractures and faults in the convergent zone have ...The Salmas geothermal field is located in NW Iran. Subduction of Neo-Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic-Arc. Fractures and faults in the convergent zone have created path-ways for the circulation of geothermal fluid. Fracture concentration in the Salmas geothermal field has been characterized using of the fractal method and creation of a fracture density map that shows the highest concentration in the central part of the study area. The permeability of fractures has been evaluated by analyzing their orientation in respect to the paleostress axes. Also, the fractal analyzing result indicates the maximum fractal dimension（1.96） is around the thermal spring outlet. Paleostress analyzing revealed that in the central part of the study area, σ1 axes orientation is S90°W/10° and the σ2 dip is near to the vertical in this stress field, where strike slip faults can be propagated. In the SE part near the recharge of the thermal springs, the σ3 plunge increases to 70？ and σ1 orientation is N15°E/20°, in this local tectonic regime thrust fault developed. Fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs in the Salmas geothermal field. Regarding the paleostress data fracture with N-S direction such as the F1 fault zone（parallel to the σ1 axes）, a suitable pathway for deep circulation of geothermal fluid flow has been created.展开更多
Field investigation shows that the boundary between the Kuqa Basin and the Tianshan Mountains can be divided into two sections with the Yanbulak area as the di-viding point. In the western section, the Mesozoic strata...Field investigation shows that the boundary between the Kuqa Basin and the Tianshan Mountains can be divided into two sections with the Yanbulak area as the di-viding point. In the western section, the Mesozoic strata overlie unconformably on the Paleozoic rocks. The ba-sin-dipping faults developed in both Mesozoic and Paleozoic rocks. The eastern section is characterized by basin-dipping normal faults separating the Paleozoic strata and Tertiary. The brittle structural analysis was carried out along the ba-sin-range boundary. 360 measurements of striations have been obtained at a total of 25 sites. Paleostress reconstruction indicates that the basin-range boundary was in an exten-sional condition, with some superimposed strike-slip, during the Late Tertiary. The extension could be explained by the vertical block uplift of the Tianshan Mountains.展开更多
磁组构通常指磁化率各向异性,即AMS(Anisotropy of Magnetic Susceptibility),是一种重要的岩石组构,是弱变形沉积岩地区灵敏的应变指示计.近年来,AMS在造山带及前陆地区的广泛应用为构造变形研究提供了极大的帮助,同时提升了该方法的...磁组构通常指磁化率各向异性,即AMS(Anisotropy of Magnetic Susceptibility),是一种重要的岩石组构,是弱变形沉积岩地区灵敏的应变指示计.近年来,AMS在造山带及前陆地区的广泛应用为构造变形研究提供了极大的帮助,同时提升了该方法的理论认识.本文在研读最新相关文献与著作的基础上,结合笔者及研究团队在龙门山地区获得的磁组构研究成果,综述了磁组构在沉积岩地区构造变形研究中的应用进展,并基于现有的研究认识对关键问题进行讨论,提出以下几点认识:(1)磁性矿物分析是AMS研究的关键,应结合多种岩石磁学实验及光学与电子显微构造研究手段展开详细的磁性矿物学分析;(2)磁化率椭球与应变椭球的对应主轴在绝大多数情况下相互平行,但在不同期次、不同种类复杂的磁性矿物组成,或者多期次构造变形的影响下,AMS与应变的关系相对复杂,应比对高场和低温AMS及非磁滞剩磁各向异性(AARM)测试结果,获得不同矿物的优选定向特征,并对获得的组构进行分期;(3)AMS可以揭示造山带及其前陆地区的构造演化历史,并且是分析断层相关褶皱的有限应变特征和变形机制的重要方法,同时也是厘定断裂带变形性状和期次及运动学分析的有效手段;(4)磁组构形成于成岩作用早期或构造变形的最早阶段,能很好地记录褶皱和逆冲作用之前的平行层缩短变形,因此可以揭示同沉积阶段的古构造应力方向.后期足够强烈的构造变形能局部改造或彻底掩盖先存AMS记录,构造流体有关的同构造期结晶矿物或先存矿物的重结晶导致的再定向被认为是其根本原因;(5)斜交磁线理是一种特殊的磁组构类型,反映了区域构造叠加或多期构造变形作用或隐伏斜向逆冲等可能的构造过程,有必要结合多方面的地质证据对其成因作出合理解释.展开更多
文摘The Shotori mountain range is located along the northern terminus of the Nayband fault on the eastern and western domains of the Tabas and Lut blocks,respectively.This range with NNW-SSE trending and approximately 120 km long includes a series of thrust faults approaching the right-lateral strike-slip Nayband fault.Since the Shotori range has experienced various geological events since the Triassic,our investigations suggest that the basement of the Central Iranian subcontinent of the Shotori range contains the early Triassic deep sedimentary with normal faults which confirms Triassic tensional tectonic stress regime in the region.After the middle Triassic,the mountain range has experienced thrust and strike-slip regimes.Therefore,in this study,we reconstruct the stress regimes for different geological periods using fault-slip data.The inversion of faultslip data reveals drastic temporal changes in the maximum stress regime(σ1)over the Triassic,Jurassic,Cretaceous,Paleogene,Neogen,and Quaternary.The reconstruction of the stress field based on the age and direction of fault movement reveals that the direction of the maximum horizontal stress axis(σ1)under a tensional stress regime was approximately N129°in the Early Triassic.This stress regime is the cause of thinning and subsidence of the Shotori sedimentary basin.During the middle Triassic,theσ1 direction was about N81°and the upper Triassic,theσ1 direction was almost N115°.The middle Triassic and upper Triassic stress states exhibited two distinct strike-slip and compressive stress regimes.This stress regime led to the uplift of the Shotori sedimentary basin.During the Jurassic,the direction of the maximum horizontal stress axis(σ1)was~NW-SE under a compressive stress regime.During the Triassic,theσ1 direction was~N-S.This stress regime led to the formation of the high topography of the Shotori Mountain Range.In the Late Cretaceous,the direction of the maximum horizontal stress axis(σ1)under the extensional stress regime was~NE-SW.This stress regime led to the uplift of the Paleogen Dacite in eastern Iran.During the Neogene,theσ1 direction was~N60°.The Quaternary tectonic regime is strike-slip and theσ1 direction is~N50°,consistent with the current convergence direction of the Arabia–Eurasia plates.Our paleostress analysis reveals four recognized stress in this area,which includes compressional,transtensional,transpressional,and strike-slip regimes.Our findings indicated that the crustal diversity of the tectonic regimes was responsible for the formation of various geological structures,such as folds,faults by different mechanisms,and the present-day configuration of the Shotori sedimentary basin.
文摘In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Magnetic Susceptibility (AMS) and paleostress?have been used. Paleomagnetism is the characteristics of magnetic rocks. Some issues in associated with the past places of continental and oceanic plates can be solved. AMS is one of the paleomagnetism methods that pay to measurement of parameters (which are reflector of the magnetic fabrics rocks). It is presenting an ellipsoid with three-axis perpendicular to each other that defines magnetic ellipsoid. In this regard, the number of 12 stations in different rocks (Jurassic to Quaternary) in the southern region of Ardebil sampling was conducted. In this connection, the study of magnetic fabrics has shown an elliptical magnetic susceptibility with the prolate shape. For the separation of paleostress phases in the Khalkhal area using the analysis of the paleostress based on the study of heterogeneous fault-slip data and sliding lineaments. Firstly, data were picked from 10 stations, and after their analysis, the elliptical shape (prolate) has been determinated. The shape of the ellipsoid, based on AMS and paleostress methods and their results show that in both methods the shape of the stress field is prolate.
基金the China Geological Survey Program (Grant No.1212011220748 and 1212011220761)the Project of the National Natural Science Foudation of China (Grant No.40802049)
文摘Brittle structures in rock of different ages can be used to establish the tectonic evolution of an orogenic belt through paleostress calculations. Micangshan is located at the southern margin of the Qinling orogenic belt, between the SE-trending Longmenshan fold-and-thrust belt and the arcuate Dabashan thrust-and-fold belt. Structural observations revealed that the dominant structures are reverse and strike-slip faults and folds with E-W and NE-SE trends. To increase knowledge of the tectonic evolution of the Micangshan anticlinorium, faults, joints, veins, and folds were measured at more than eighty sites. On the basis of structural analysis, it emerged that the multiphase paleostress fields became established after the oblique collision between the North and South China plates. The earliest stress field with N-S compression was established during the Micangshan uplift associated with the E-W trending faults and folds. Subsequently, a N-S extension occurred when the Qinling orogenic belt collapsed. Then NW-SE compression developed, with NE trending faults and folds forming in relation to Longmenshan thrusting toward southwest on the eastern margin of the Tibetan plateau. With the development of the arcuate Dabashan orogenic belt, the compression stress orientation of the Micangshan anticlinorium altered from NE-SW to E-W.
基金supported financially by Urmia Universitythe Renewable Energy Department of the Niroo Research Institute(NRI)
文摘The Salmas geothermal field is located in NW Iran. Subduction of Neo-Tethys oceanic crust beneath the Iranian microcontinent caused to propagation of the magmatic-Arc. Fractures and faults in the convergent zone have created path-ways for the circulation of geothermal fluid. Fracture concentration in the Salmas geothermal field has been characterized using of the fractal method and creation of a fracture density map that shows the highest concentration in the central part of the study area. The permeability of fractures has been evaluated by analyzing their orientation in respect to the paleostress axes. Also, the fractal analyzing result indicates the maximum fractal dimension（1.96） is around the thermal spring outlet. Paleostress analyzing revealed that in the central part of the study area, σ1 axes orientation is S90°W/10° and the σ2 dip is near to the vertical in this stress field, where strike slip faults can be propagated. In the SE part near the recharge of the thermal springs, the σ3 plunge increases to 70？ and σ1 orientation is N15°E/20°, in this local tectonic regime thrust fault developed. Fractures have an important role in the circulation of fluid and the fractal dimension increases near the thermal springs in the Salmas geothermal field. Regarding the paleostress data fracture with N-S direction such as the F1 fault zone（parallel to the σ1 axes）, a suitable pathway for deep circulation of geothermal fluid flow has been created.
文摘Field investigation shows that the boundary between the Kuqa Basin and the Tianshan Mountains can be divided into two sections with the Yanbulak area as the di-viding point. In the western section, the Mesozoic strata overlie unconformably on the Paleozoic rocks. The ba-sin-dipping faults developed in both Mesozoic and Paleozoic rocks. The eastern section is characterized by basin-dipping normal faults separating the Paleozoic strata and Tertiary. The brittle structural analysis was carried out along the ba-sin-range boundary. 360 measurements of striations have been obtained at a total of 25 sites. Paleostress reconstruction indicates that the basin-range boundary was in an exten-sional condition, with some superimposed strike-slip, during the Late Tertiary. The extension could be explained by the vertical block uplift of the Tianshan Mountains.
文摘磁组构通常指磁化率各向异性,即AMS(Anisotropy of Magnetic Susceptibility),是一种重要的岩石组构,是弱变形沉积岩地区灵敏的应变指示计.近年来,AMS在造山带及前陆地区的广泛应用为构造变形研究提供了极大的帮助,同时提升了该方法的理论认识.本文在研读最新相关文献与著作的基础上,结合笔者及研究团队在龙门山地区获得的磁组构研究成果,综述了磁组构在沉积岩地区构造变形研究中的应用进展,并基于现有的研究认识对关键问题进行讨论,提出以下几点认识:(1)磁性矿物分析是AMS研究的关键,应结合多种岩石磁学实验及光学与电子显微构造研究手段展开详细的磁性矿物学分析;(2)磁化率椭球与应变椭球的对应主轴在绝大多数情况下相互平行,但在不同期次、不同种类复杂的磁性矿物组成,或者多期次构造变形的影响下,AMS与应变的关系相对复杂,应比对高场和低温AMS及非磁滞剩磁各向异性(AARM)测试结果,获得不同矿物的优选定向特征,并对获得的组构进行分期;(3)AMS可以揭示造山带及其前陆地区的构造演化历史,并且是分析断层相关褶皱的有限应变特征和变形机制的重要方法,同时也是厘定断裂带变形性状和期次及运动学分析的有效手段;(4)磁组构形成于成岩作用早期或构造变形的最早阶段,能很好地记录褶皱和逆冲作用之前的平行层缩短变形,因此可以揭示同沉积阶段的古构造应力方向.后期足够强烈的构造变形能局部改造或彻底掩盖先存AMS记录,构造流体有关的同构造期结晶矿物或先存矿物的重结晶导致的再定向被认为是其根本原因;(5)斜交磁线理是一种特殊的磁组构类型,反映了区域构造叠加或多期构造变形作用或隐伏斜向逆冲等可能的构造过程,有必要结合多方面的地质证据对其成因作出合理解释.
