Estimation of Displacement and Extension due to Reverse Drag of Normal Faults: Forward Method

In the case of reverse drag of normal faulting, the displacement and horizontal extension are determined based on the established equations for the three mechanisms: rigid body, vertical shear and inclined shear. There are three sub-cases of basal detachment for the rigid body model: horizontal detachment, antithetic detachment and synthetic detachment. For the rigid body model, the established equations indicate that the total displacement on the synthetic base (Dt2) is the largest, that on the horizontal base (Dt1) is moderate, and that on the antithetic base (Dt3) is the smallest. On the other hand, the value of (Dt1) is larger than the displacement for the vertical shear (Dt4). The value of (Dt1) is larger than or less than the displacement for the inclined shear (Dt5) depending on the original fault dip δ0, bedding angle θ, and the angle of shear direction β. For all original parameters, the value of Dt5 is less than the value of Dt4. Also, by comparing three rotation mechanisms, we find that the inclined shear produces largest extension, the rigid body model with horizontal detachment produces the smallest extension, and the vertical shear model produces moderate extension.

Sandbox Modeling of the Fault-increment Pattern in Extensional Basins

Three series of sandbox modeling experiments were performed to study the fault-increment pattern in extensional basins. Experimental results showed that the tectonic action mode of boundaries and the shape of major boundary faults control the formation and evolution of faults in extensional basins. In the process of extensional deformation, the increase in the number and length of faults was episodic, and every ＇episode＇ experienced three periods, strain-accumulation period, quick fault-increment period and strain-adjustment period. The more complex the shape of the boundary fault, the higher the strain increment each ＇episode＇ experienced. Different extensional modes resulted in different fault-increment patterns. The horizontal detachment extensional mode has the ＇linear＇ style of fault-increment pattern, while the extensional mode controlled by a listric fault has the ＇stepwise＇ style of fault-increment pattern, and the extensional mode controlled by a ramp-flat boundary fault has the ＇stepwise-linear＇ style of fault-increment pattern. These fault-increment patterns given above could provide a theoretical method of fault interpretation and fracture prediction in extensional basins.

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

The spatio-temporal characteristics of acoustic emission (AE) during the deformation of rock samples with compressional and extensional en-echelon faults have been studied. The results show that the pre-existing structure can significantly influence the patterns of AE spatial distribution. With increasing of differential stress, AE events firstly cluster around the two ends of pre-existing faults inside the jog and then along the line joining the two ends. The biggish AE events often occur around one end repeatedly. The image of AE clusters indicates the direction and the area of the fracture propagation. The direction of the macroscopic fracture in extensional and compressional jogs is perpendicular and parallel to the direction of axial stress, respectively. The weakening process before the fracturing of jog area is remarkable, and one of the typical precursors for the instability is that the cumulative frequency of AE events increases exponentially. After the fracturing of the jog the frequency and releasing strain energy of AE events decrease gradually. During the friction period, there is no precursory increasing of AE activity before the big stick-slip events. The change of b value in jog shows a typical change of decreasing tendentiously returning quickly before the instability. The decrease of b value occurs in the process of stress increasing and sometime goes down to the weakening stage, and the quick increase b values appears in a short time just before the instability. The comparative analysis shows that the difference in b value due to the different structures is larger than b value variation caused by increase of the differential stress. For the same sample, the temporal sequence of AE is strongly affected by the mechanical state, and the high loading velocity corresponds to the high release rate of strain energy and low b value. Due to its lower failure strength, the broken area is sensitive to small changes in differential stress. Therefore, it offers a potential explanation for the phenomena of precursory window or sensitive point and separation of seismic source and precursors.

Improved Geometric Model of Extensional Fault–bend Folding

Extensional fault-bend folds, also called rollovers, are one of the most common structures in extensional settings. Numerous studies have shown that oblique simple shear is the most appropriate mechanism for quantitative modeling of geometric relations between normal faults and the strata in their hanging walls. However, the oblique simple shear has a rather serious issue derived from the shear direction, particularly above convex bends. We use geometric and experimental methods to study the deformation of extensional fault-bend folds on convex bends. The results indicate that whether the fault bends are concave or convex, the shear direction of the hanging wall dips toward the main fault. On this basis, we improve the previous geometric model by changing the shear direction above the convex bends. To illustrate basin history, our model highlights the importance of the outer limit of folding instead of the growth axial. Moreover, we propose a new expression for the expansion index that is applicable to the condition of no deposition on the footwall. This model is validated by modeling a natural structure of the East China Sea Basin.

Extensional Tectonic System of Erlian Fault Basin Groupand Its Deep Background

The Erlian fault basin group, a typical Basin and Range type fault basin group, was formed during Late Jurassic to Early Cretaceous, in which there are rich coal, oil and gas resources. In the present paper the abundant geological and petroleum information accumulated in process of industry oil and gas exploration and development of the Erlian basin group is comprehensively analyzed, the structures related to formation of basin are systematically studied, and the complete extensional tectonic system of this basin under conditions of wide rift setting and low extensional ratio is revealed by contrasting study with Basin and Range Province of the western America. Based on the above studies and achievements of the former workers, the deep background of the basin development is treated.

Analysis Method for Predicting Strain in Interior Beds and Sub-Resolution Faults from Area Balance Theory in Extensional Basins

Extensional basins include mainly grabens and half grabens displaced along alower detachment. Based on area balance theory, there is a linear relationship between a height ofregional and the lower detachment h on the outside of the basin and 'lost area S' from the regionalin the basin. The pre-growth beds above lower detachment are of the same extensional displacement sothat an 'S-h diagram' can be used to determine the depth to lower detachment and to calculate thetotal extensional displacement of the beds above the lower detachment. The extensional displacementis dominated by the heave of various scale normal faults. The displacement of obvious faults can beimmediately figured out from the measured bed-length. The requisite extension calculated by areabalance is the layer-parallel strain, which could be accommodated by displacement on sub-resolutionfaults. Accordingly, the layer-parallel strain can help us predict the magnitude and distribution ofsub-resolution faults on the basis of analysis of the structural style and rheological behavior.

Quantitative evaluation of lateral sealing of extensional fault by an integral mathematical-geological model

To evaluate the lateral sealing mechanism of extensional fault based on the pressure difference between fault and reservoir, an integral mathematical-geological model of diagenetic time on diagenetic pressure considering the influence of diagenetic time on the diagenetic pressure and diagenetic degree of fault rock has been established to quantitatively calculate the lateral sealing ability of extensional fault. By calculating the time integral of the vertical stress and horizontal in-situ stress on the fault rock and surrounding rock, the burial depth of the surrounding rock with the same clay content and diagenesis degree as the target fault rock was worked out. In combination with the statistical correlation of clay content, burial depth and displacement pressure of rock in the study area, the displacement pressure of target fault rock was calculated quantitatively. The calculated displacement pressure was compared with that of the target reservoir to quantitatively evaluate lateral sealing state and ability of the extensional fault. The method presented in this work was used to evaluate the sealing of F_(1), F_(2) and F_(3) faults in No.1 structure of Nanpu Sag, and the results were compared with those from fault-reservoir displacement pressure differential methods without considering the diagenetic time and simple considering the diagenetic time. It is found that the results calculated by the integral mathematical-geological model are the closest to the actual underground situation, the errors between the hydrocarbon column height predicted by this method and the actual column height were 0–8 m only, proving that this model is more feasible and credible.

Extensional tectonics and sedimentary response of the Early—Middle Cambrian passive continental margin,Tarim Basin,Northwest China

The fact that several half-grabens and normal faults developed in the Lower--Middle Cambrian of Tazhong （central Tarim Basin） and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three- pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform -- slope -- bathyal facies sedimentation of mainly limestone-dolomite-gypsum rock-saline rock-red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults.

Application of extension method to fault diagnosis of transformer

A novel extension diagnosis method was proposed for enhancing the diagnosis ability of the conventional dissolved gas analysis. Based on the extension theory a matter-element model was established for qualitatively and quantitatively describing the fault diagnosis problem of power transformers. The degree of relation based on the dependent functions was employed to determine the nature and the grade of the faults in a transformer system. And the proposed method was verified with the experimental data. The results show that accuracy rate of the diagnosis method exceeds 90% and two kinds of faults can be detected at the same time.

Study and Application of Case-based Extension Fault Diagnosis for Chemical Process

In chemical processes, fault diagnosis is relatively difficult due to the incomplete prior-knowledge and unpredictable production changes. To solve the problem, a case-based extension fault diagnosis (CEFD) method is proposed combining with extension theory, in which the basic-element model is used for the unified and deep fault description, the distance concept is applied to quantify the correlation degree between the new fault and the original fault cases, and the extension transformation is used to expand and obtain the solution of unknown faults. With the application in Tennessee Eastman process, the result indicates that CEFD method has a flexible fault representation, objective fault retrieve performance and good ability for fault study, providing a new way for diagnosing production faults accurately.

Dislocation configuration evolution during extension twinning and its influence on precipitation behavior in AZ80 wrought magnesium alloy

Thermomechanical treatment T10(extension twinning+aging treatment)can largely enhance the precipitation strengthening effect of magnesium alloys.In this study,dislocation structure evolution and precipitation behavior during T10 treatment of an AZ80 extruded bar were analyzed mainly by two-beam diffraction in TEM.At a compressive strain of 1%in the extrusion direction(ED),a typical dislocation configuration,including basal I1 stacking faults(SFs)and<c+a>dislocations,has been established in extension twins.As the strain reaches 7%,the volume fraction of extension twins increases to more than 90%at which point high dense I1 SFs and<c+a>dislocations occur.After aging for 2 h at 150℃for the 7%strained sample,masses of basal I1 SFs and<c+a>dislocations remain in the extension twins and can act as effective nucleation sites and solute fast-diffusion channels for continuous precipitates.Consequently,the precipitates in extension twins become highly dense.

渤东凹陷新生代伸展-走滑叠合断裂时空差异演化模式及控藏效应

以三维地震精细解释为基础,通过构造剖面恢复,系统分析了渤东凹陷新生代伸展-走滑叠合断裂的时空差异演化特征及控藏作用。研究结果表明:(1)渤东凹陷新生代广泛发育以NNE向为主干、NE向为派生、NW向为叠加的伸展-走滑叠合断裂体系,可划分为强伸展-弱走滑断裂和强走滑-弱伸展断裂2类;整体具有深浅分层、南北分段的特征,纵向上,古近系主要发育强伸展-弱走滑断裂,断裂大而稀,新近系—第四系主要发育强走滑-弱伸展断裂,断裂小而密;平面上,同一断裂在不同段的构造组合样式存在差异。(2)研究区新生代伸展-走滑叠合断裂的演化主要表现为北部断裂活动强度“早强晚弱”,中部断裂继承性持续发育,南部断裂活动强度“早弱晚强”;演化模式分为初始断陷(孔店组—沙四段沉积期)、强烈断陷(沙三段—东营组沉积期)和走滑坳陷(馆陶组—平原组沉积期)3个阶段,初始断陷阶段,NNE—NE向强伸展与弱走滑叠合,NE向强伸展-弱走滑断裂为主控,NW向先存断裂活化,分割凹陷;强烈断陷阶段,NNE—NE向强伸展与弱走滑叠合,NNE向强伸展-弱走滑断裂变为主控,NW向断裂活动减弱或停止;走滑坳陷阶段,NNE向强走滑与弱伸展叠合,断裂不控制沉积,但对地层展布具有调整作用。(3)研究区伸展-走滑叠合断裂的发育演化与油气成藏密切相关,整体具有“早期伸展控源、晚期走滑控运、多期叠加控圈”的特征,东部斜坡带是油气运聚的有利区。

岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics):华北克拉通东部早白垩世岩石圈减薄与破坏机理

华北克拉通岩石圈减薄和破坏机理长期以来存在争议,基于岩石学、岩石地球的化学分析研究突出强调深部过程的重要性。前人提出了两种重要模式:包括以拆沉作用为代表的top-down tectonics模型和以热-机械侵蚀与化学侵蚀,或地幔置换、交代作用的bottom-up tectonics模型。然而,对于这两种模式而言尚存在许多无法合理解释的问题,比如在此深部过程中,区域性岩石圈伸展有多大的贡献?地壳伸展构造是作为深部过程的响应,还是同为岩石圈伸展的产物?本文基于早白垩世东亚地区(尤其是华北克拉通东部地区)伸展构造与岩浆活动的综合分析,揭示出华北克拉通东部不同地区伸展构造变形与岩浆活动之间的时、空和成因关系有一定的差异。但整体上看,岩石圈伸展起着主导作用,控制着岩浆上侵和就位,在拆离断层下盘侵入形成各种规模的花岗质为主的侵入体,或于上盘喷发形成火山-沉积岩盆地。在伸展构造发育的不同阶段,可以有伸展早期、伸展期及伸展期后的岩浆活动。岩浆活动的强度及岩浆源区特点有显著的时空变化。一方面,在同一地区不同演化阶段其源区有很大的差异。表现为主体上是早期以古老下地壳源为主,随着壳/幔伸展作用演化,逐渐向混合源或独立幔源的演化。同时,不同地区岩浆源区的变化规律也显著不同。以胶辽地区为例,胶东整体上是壳幔混合源区对于岩浆演化有重要贡献;而辽东地区具有显著的源区演化特点:从剪切早期古老下地壳源区为主,并伴有幔源物质加入,剪切期古老下地壳为主,到剪切晚期和剪切期后以新生下地壳为主。本文认为岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics),可以合理地解释华北克拉通及邻区早白垩世构造-岩浆活动性。在该模型中,遭受伸展的华北克拉通岩石圈发生壳-幔拆离作用。在岩石圈伸展作用期间,地壳层次的拆离作用与岩石圈地幔层次上的拆离作用可以是耦合的或者是解耦的,从而导致华北克拉通岩石圈减薄过程中在地壳尺度上的拆离作用与变质核杂岩的剥露有三种不同的类型:同岩浆活动型伸展(C型:Co-magmatism mode extension)、无岩浆活动型伸展(A型:Amagmatism mode extension)和多阶段混合型(M型:Multi-mode extension)。

A Novel Three-stage Tectonic Model for Mississippi Valleytype Zn-Pb Deposits in Orogenic Fold-and-Thrust Belts

Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood. This study, through a comprehensive review of MVT deposits across global fold-and-thrust belts, introduces a novel model elucidating the mineralization process in the context of tectonic belt evolution. It is demonstrated that during the stage Ⅰ, regional compression is introduced by early stages of plate convergence, causing the folding and thrusting and creating structural or lithological traps such as evaporite diapirs and unconformity-related carbonate dissolution-collapse structures. Thereafter, in stage Ⅱ, hydrocarbons begin to migrate and accumulate within these traps, where reduced sulfur is generated through thermochemical or bacterial sulfate reduction concurrent with or preceding Zn-Pb mineralization. In the subsequent stage Ⅲ, as plate convergence persists, the regional stress transitions from compression to transpression or extension. Under these conditions, steeply-dipping extensional faults are generated, facilitating the ascent of metalliferous brines into early-formed structural or lithological traps. Precipitation of Zn and Pb sulfides occurs through the mixing of Zn-Pb-transporting fluids with pre-existing reduced sulfur or by interaction with hydrocarbons.

Miocene Tectonic Evolution from Dextral-Slip Thrusting to Extension in the Nyainqentanglha Region of the Tibetan Plateau

Dextral-slip in the Nyainqentanglha region of Tibet resulted in oblique underthrusting and granite generation in the Early to Middle Miocene, but by the end of the epoch uplift and extensional faulting dominated. The east-west dextral-slip Gangdise fault system merges eastward into the northeast-trending, southeast-dipping Nyainqentanglha thrust system that swings eastward farther north into the dextral-slip North Damxung shear zone and Jiali faults. These faults were took shape by the Early Miocene, and the large Nyainqentanglha granitic batholith formed along the thrust system in 18.3-11.0 Ma as the western block drove under the eastern one. The dextral-slip movement ended at -11 Ma and the batholith rose, as marked by gravitational shearing at 8.6-8.3 Ma, and a new fault system developed. Northwest-trending dextral-slip faults formed to the northwest of the raisen batholith, whereas the northeast-trending South Damxung thrust faults with some sinistral-slip formed to the southeast. The latter are replaced farther to the east by the west-northwest-trending Lhtinzhub thrust faults with dextral-slip. This relatively local uplift that left adjacent Eocene and Miocene deposits preserved was followed by a regional uplift and the initiation of a system of generally north-south grabens in the Late Miocene at -6.5 Ma. The regional uplift of the southern Tibetan Plateau thus appears to have occurred between 8.3 Ma and 6.5 Ma. The Gulu, DamxungYangbajain and Angan graben systems that pass east of the Nyainqentanglha Mountains are locally controlled by the earlier northeast-trending faults. These grabens dominate the subsequent tectonic movement and are still very active as northwest-trending dextral-slip faults northwest of the mountains. The Miocene is a time of great tectonic change that ushered in the modern tectonic regime.

Multistage Extension and Age Dating of the Xiaoqinling Metamorphic Core Complex,Central China

Abstract There are two extensional systems in the Xiaoqinling metamorphic core complex (XMCC). One is the detachment fault system developed along the peripheries of the XMCC, which extended in an ESE-WNW direction and whose upper plate moved towards the WNW. The other extensional system includes the retrograde shear zones and normal faults developed within the XMCC, which represent the collapse of the XMCC. Ar-Ar and K-Ar dating shows that the extension of the detachment fault system continued from 135 to 123 Ma, i.e. in the late stage of its evolution at about 127 Ma. The collapse represented by the extensional system within the XMCC was operative during 120–106 Ma, and its main activity occurred about 116 Ma ago. These suggest that the XMCC experienced two extensional stages in its evolution, i.e., the syn-orogenic regional extension and post-orogenic collapse extension.

K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China: Implications for Crustal Extension

Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province. Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively.

Normal Faulting Type Earthquake Activities in the Tibetan Plateau and Its Tectonic Implication

This paper analyzes various earthquake fault types, mechanism solutions, stress field as well as other geophysical data to study the crust movement in the Tibetan plateau and its tectonic implications. The results show that a lot of normal faulting type earthquakes concentrate in the central Tibetan plateau. Many of them are nearly perfect normal fault events. The strikes of the fault planes of the normal faulting earthquakes are almost in the N-S direction based on the analyses of the equal area projection diagrams of fault plane solutions. It implies that the dislocation slip vectors of the normal faulting type events have quite great components in the E-W direction. The extension is probably an eastward extensional motion, mainly a tectonic active regime in the altitudes of the plateau. The tensional stress in the E-W or WNW-ESE direction predominates the earthquake occurrence in the normal event region of the central plateau. A number of thrust fault and strike-slip fault type earthquakes with strong compressive stress nearly in the NNE-SSW direction occurred on the edges of the plateau. The eastward extensional motion in the Tibetan plateau is attributable to the eastward movement of materials in the upper mantle based on_seismo-tomographic results. The eastward extensional motion in the Tibetan plateau may be related to the eastward extrusion of hotter mantle materials beneath the east boundary of the plateau. The northward motion of the Tibetan plateau shortened in the N-S direction probably encounters strong obstructions at the western and northern margins. Extensional motions from the relaxation of the topography and/or gravitational collapse in the altitudes of the plateau occur hardly in the N-S direction. The obstruction for the plateau to move eastward is rather weak.

Submarine canyons on the north of Chiwei Island:influenced by recent extension of the southern Okinawa Trough

Based on new multibeam bathymetric data and about 300 km long single seismic profiles, three topographic units were identified： the canyons, fractural valley and submarine terrace on the north of Chiwei Island where is a structural transition zone between the southern trough and the middle trough. The Chiwei Canyon and the North Chiwei Canyon are two of the largest canyons in the East China Sea （ECS） slope. Topographic features and architectures of them are described. The study shows that both of them are originated along faults. The evolution and spatial distribution of topographic units in the study area are controlled mainly by three groups of faults which were formed and reactive in the recent extensional phase of Okinawa Trough. The Chiwei Canyon was initia- ted during the middle Pleistocene and guided by F4 that is a N--S trending fault on the slope and F1, a large NW--SE trending fault on the trough. The pathway migration from the remnant channel to the present one of Chiwei Canyon is the result of uplift of tilted fault block that is coupled to the recent extension movements of the southern trough. The submarine terrace is detached from the ECS slope by the NEE -trending fault. The North Chiwei Canyon, developing during the late Pleistocene, is guided by FS, a N-S trending fault, diverted and blocked by the submarine terrace.

Oblique extension of pre-existing structures and its control on oil accumulation in eastern Bohai Sea

Based on 3D seismic data, the evolution mechanism and characteristics of faults were investigated to reveal the structural origin and its control on differential hydrocarbon accumulation through comprehensive analyses, including structure style analysis, fault activity analysis, analogue modelling and comparison among the wells. The complex fault system with differently trending faults resulted from strike-slip and rifting in Paleogene was partly activated, developed successively and stretched obliquely by the near-NS extensional stress field in Neogene. In the area little affected by pre-existing faults, new faults nearly perpendicular to the extension direction developed. The structural development in the study area was not caused by transpressional strike slip. Under the oblique extension effect of pre-existing faults, if the angle between the strike of pre-existing fault and the extensional direction is different, the strike-slip and extensional stresses are different in ratio. The larger the angle between the two is, the stronger the extensional component, the poorer the sealing ability of the fault, and the stronger the oil and gas migration capacity will be. Conversely, the smaller the angle between the two is, the stronger the strike-slip component, the better the sealing ability of the fault, and the poorer the oil and gas migration capacity will be. The accumulation condition analysis results considering the fault trend are in good agreement with the oil and gas shows in wells drilled in this area.