Structure kinematics of a transtensional basin:An example from the Linnan Subsag,Bohai Bay basin,Eastern China

The Linnan subsag is a petroliferous, secondary tectonic unit of the Huimin sag that is located in the western part of the Jiyang depression in the Bohai Bay basin, eastern China. In this study, the authors calculated basin extensional rate and slipping displacement of boundary faults in the dip and strike directions, using seismic and drilling data. The evolution of the Linnan transtensional basin from the Eogene through the Quaternary is quantitatively described, and a dynamic model is established. The Linshan and Xiakou boundary faults of the Linnan subsag are used as a case study to describe a method to calculate the strike and dip slipping displacements of active faults under oblique extension. The results quantitatively illustrate the behavior of the Linnan subsag boundary faults over time. The Linnan subsag transtensional basin experienced four stages of evolution: weak extension during the Kongdian Formation, rapid extension and fault depression during the fourth member of the Shahejie Formation,intensive transtension and fault depression during the third member of the Shahejie Formation-Dongying Formation, and weakening fault depression during the Guantao Formation-Pingyuan Formation.The results of this study provide further understanding of the processes of petroleum migration and accumulation in the region.     

Neotectonic transpressional intraplate deformation in eastern Eurasia: Insights from active fault systems in the southeastern Korean Peninsula

Transpression occurs in response to oblique convergence across a deformation zone in intraplate regions and plate boundaries. The Korean Peninsula is located at an intraplate region of the eastern Eurasian Plate and has been deformed under the ENE–WSW maximum horizontal compression since the late Pliocene. In this study, we analyzed short-term instrumental seismic (focal mechanism) and long-term paleoseismic (Quaternary fault outcrop) data to decipher the neotectonic crustal deformation pattern in the southeastern Korean Peninsula. Available (paleo-)seismic data acquired from an NNE–SSW trending deformation zone between the Yangsan and Ulleung fault zones indicate spatial partitioning of crustal deformation by NNW–SSE to NNE–SSW striking reverse faults and NNE–SSW striking strike-slip faults, supporting a strike-slip partitioned transpression model. The instantaneous and finite neotectonic strains, estimated from the focal mechanism and Quaternary outcrop data, respectively, show discrepancies in their axes, which can be attributed to the switching between extensional and intermediate axes of finite strain during the accumulation of wrench-dominated transpression. Notably, some major faults, including the Yangsan and Ulsan fault zones, are relatively misoriented to slip under the current stress condition but, paradoxically, have more (paleo-)seismic records indicating their role in accommodating the neotectonic transpressional strain. We propose that fluids, heat flow, and lithospheric structure are potential factors affecting the reactivation of the relatively misoriented major faults. Our findings provide insights into the accommodation pattern of strain associated with the neotectonic crustal extrusion in an intraplate region of the eastern Eurasian Plate in response to the collision of the Indian Plate and the subduction of the Pacific/Philippine Sea Plates.     

The space problem of caldera resurgence: an example from Ischia Island, Italy

A space problem can arise in a resurgent caldera when the resurgent block is non-cylindrical, such as, for example, when it is bounded by inward- or outward-dipping faults. Ischia caldera (Italy) is an excellent case study because it is well exposed and resurgence is ongoing. On the western and eastern flanks of the Ischia resurgent horst, uplift occurred along NNW-striking normal faults with inclination from sub-vertical to vertical (>85°). The geometry of these faults suggests negligible extension within the horst. Along the northern flank, uplift was accomplished by ENE-striking normal faults that dip 60–85° outward; a few bear striae which indicate almost pure dip-slip. The southern flank of the horst is a monocline trending ENE associated with vertical faults. In a NNW–SSE section, the resulting resurgent horst has a wedge shape with an upward apex. The uplift of this wedge can be accommodated by contemporaneous regional extension along NE- to east–west striking normal faults whose motions create space for resurgence without deformation of the caldera floor. Similar interaction with regional tectonics could exist in other calderas, such as Yellowstone (USA) in an extensional setting, Los Azufres (Mexico) in a transtensional regime and Chalupas (Ecuador) in a transpressional one. At other calderas, resurgence was accommodated by caldera-floor arching as at Valles (USA) or by shortening deformations between the caldera rim and the uplifting block as at Latera (Italy).     

东濮凹陷伸展连锁断层系统及其演化作用

东濮凹陷NNE向的主干基底断层向深部延伸与深层的拆离滑脱断层衔接在一起,与诱导出的调节断层以不同的方式连接,构成东濮凹陷的伸展连锁断层系统。东濮凹陷不同区段的连锁断层形态表现出不同的几何学和运动学特征。北区兰聊主断层面表现为相对较缓的平面式形态,伸展连锁断层系统总体上为多米诺式半地堑系。中区伸展连锁断层系统总体上表现为大型铲式正断层上盘的一个不对称的地堑。南区兰聊主断层面表现为坡坪式形态,断陷结构相对复杂。东濮凹陷伸展连锁断层系统的演化大体分为4期,不同区带伸展连锁断层系统演化模式不同,对古近系沉积和石油地质条件有较大的影响。     

金湖凹陷隐性断裂带形成机制及分布

金湖凹陷基底存在北东、北西向两组断裂。北西向基底断裂活动较弱,对盖层变形影响较小,在盖层中多以隐性断裂带显现;北东向基底断裂活动强烈,对凹陷盖层变形影响较大,不仅形成了凹陷东部边界杨村断裂在内的多条显性断裂,而且形成了多条隐性断裂带。凹陷中部的北东向石港显性断裂带将凹陷分割成西部斜坡带和东部凹陷带。东部凹陷带受基底北西向断裂隐性活动的影响呈现南北分段特征。凹陷盖层中还发育了大量近东西走向的三、四级正断层,它们大致平行成带分布,形成了宝应平行雁列式断裂构造带、唐港雁列式断裂构造带、卞闵杨平行雁列式断裂构造带、西斜坡平行入字型断裂构造带、汊涧泥沛平行雁列式断裂构造带等一系列油气富集区带。上述构造带中的油气藏分布明显受到北东和北西向基底断裂活动影响,呈现北东、北西或近南北向成带、成串分布特征。应用区域地质、重磁等资料开展隐性断裂带预测,识别出10条北东向、5条北西向、6条南北向隐性断裂带。沉积盖层中形成的这些隐性断裂带控制了储集砂体分布、改善了储层物性、使隐性圈闭成带成串分布,是油气聚集成藏的有利区带。     

呼和湖凹陷断裂特征及其对油气成藏的影响

断裂的形成演化过程对油气的运聚成藏具有重要的影响。本文系统分析了呼和湖凹陷断裂特征、断裂演化及其与油气成藏的关系。研究表明,呼和湖凹陷以T_(22)和T_(04)反射层为界,划分为3套构造层,分别为下部伸展断陷构造层、中部断坳构造层,上部坳陷构造层,其中上部构造层中断裂不发育。纵向上主要发育了两套断裂系统,下部断裂系统展布方向主要是北东东向、北东向和北北东向。上部断裂系统展布方向主要为北北东向和北北西向。发育4种类型的断裂,分别为早期伸展断裂,中期走滑断裂,早期伸展中期走滑断裂和早期伸展中期走滑晚期反转断裂。断裂的主要形成时期为南屯组末期、伊敏组末期和青元岗组末期。断裂的形成和演化影响烃源岩的分布和热演化程度,形成多种类型的圈闭,为油气垂向运移提供良好的运移通道。其中在主力生油洼槽及其周边的几个控陷断层附近有利于油气富集。     

Joints,faults and palaeostress evolution in the Campo de Dalias (Betic Cordilleras,southeastern Spain)

The Campo de Dal??as, located between the central and eastern Betic Cordilleras, shows an evolution determined by the overprinting of two main stress fields since Pliocene times. The first of these develops hybrid and tensional joint sets up to Pleistocene (100 000 yr) and is characterized by NNW–SSE horizontal trend of compression and an ENE–WSW horizontal extension. The second stress field has prolate to triaxial extensional ellipsoids, also with ENE–WSW horizontal extension, and continues to be active today. The most recent stresses produce the reactivation of previous joints as faults whose trends are comprised mainly from N120°E to N170°E and have a normal and transtensional regime, with dextral or sinistral components. The palaeostress evolution of this region is similar to that undergone by other basins of the Eastern Betic Cordilleras, although the Pliocene–Pleistocene transcurrent deformations in the Campo de Dal??as only develop joints and not strike-slip faults.     

Seismogenic basin and range and intra‐arc normal faulting in the central Mexican Volcanic Belt,Querétaro,México

North‐northwest normal faults intersect ENE normal faults in the vicinity of Querétaro City, in central México, affecting the Miocene–Pliocene northern‐central sector of the Mexican Volcanic Belt province. This intersection produced an orthogonal arrangement of grabens, half‐grabens and horsts that include the Querétaro graben. The NNW faults are part of the Taxco–San Miguel de Allende fault system, which is proposed here as part of the southernmost Basin and Range province in México. The ENE to E–W faults are part of the E–W oriented Chapala–Tula fault zone, which has been interpreted as an active intra‐arc fault system of the Mexican Volcanic Belt. Seventy‐four normal faults were mapped, of which the NNW faults are the largest and have the best morphological expression in the region. More numerous, although shorter, are the ENE faults. Total length of the ENE faults is greater than the total length of the NNW faults. Both sets are dominantly normal faults, indicating ENE extension for the NNW set and NNW extension for the ENE set. Field data indicate that displacement on the two fault sets has overlapped in time, as some NNW faults are younger than some ENE faults, which are supposed to be the younger ones. Seismicity in 1998 on a NNW fault indicates ENE active extension on the NNW faults. These observations support our interpretation that the northern Mexican Volcanic Belt lies on the boundary between the Basin and Range province, which is undergoing ENE extension, and the central Mexican Volcanic Belt province, which is undergoing northerly extension. The apparent overlap in space and time of displacements on the two fault sets reflects the difference in stress regime between the two provinces. Copyright © 2005 John Wiley & Sons, Ltd.     

东濮凹陷构造变形的物理模拟研究

东濮凹陷是一个研究程度较高的含油气区,前人在构造变形研究方面多注重于伸展变形的几何学分析而忽略了形成机制中走滑分量的作用。本文在对区域地质背景和东濮凹陷构造特征分析基础上,设计平、剖面砂箱实验对该凹陷的构造变形进行伸展-走滑模拟研究。结果表明:(1)具走滑性质的断裂组合形成的构造样式更加复杂多样,走滑断层弯曲会产生挤压或伸展分量,在相邻的区域内形成局部的凹陷和隆起,主动盘的不同会形成不同的断裂组合;(2)在区域NNW—SSE向伸展变形下,形成了东濮凹陷两洼一凸的近对称格局,基底深断裂的张扭性开裂加速了凹陷的形成,主断层上、下盘均有明显的活动;(3)受基底断裂活动影响,大约Es~2-Ed沉积期凹陷存在一个明显的右旋走滑变形期,在凹陷的中部隆起带上出现了负花状、火焰状等典型走滑构造样式,走滑变形具有阵发性特点。     

Tectonic indentation in the central Alboran Sea (westernmost Mediterranean)

The Alboran Sea constitutes a Neogene–Quaternary basin of the Betic–Rif Cordillera, which has been deformed since the Late Miocene during the collision between the Eurasian and African plates in the westernmost Mediterranean. NNE–SSW sinistral and WNW–ESE dextral conjugate fault sets forming a 75° angle surround a rigid basement spur of the African plate, and are the origin of most of the shallow seismicity of the central Alboran Sea. Northward, the faults decrease their transcurrent slip, becoming normal close to the tip point, while NNW–SSE normal and sparse ENE–WSW reverse to transcurrent faults are developed. The uplifting of the Alboran Ridge ENE–WSW antiform above a detachment level was favoured by the crustal layering. Despite the recent anticlockwise rotation of the Eurasian–African convergence trend in the westernmost Mediterranean, these recent deformations—consistent with indenter tectonics characterised by a N164°E trend of maximum compression—entail the highest seismic hazard of the Alboran Sea.     

Paleostress analysis of the brittle deformations on the northwestern margin of the Red Sea and the southern Gulf of Suez,Egypt

Shear fractures, dip-slip, strike-slip faults and their striations are preserved in the pre- and syn-rift rocks at Gulf of Suez and northwestern margin of the Red Sea. Fault-kinematic analysis and paleostress reconstruction show that the fault systems that control the Red Sea–Gulf of Suez rift structures develop in at least four tectonic stages. The first one is compressional stage and oriented NE–SW. The average stress regime index R' is 1.55 and S_Hmax oriented NE–SW. This stage is responsible for reactivation of the N–S to NNE, ENE and WNW Precambrian fractures. The second stage is characterized by WNW dextral and NNW to N–S sinistral faults, and is related to NW–SE compressional stress regime. The third stage is belonging to NE–SW extensional regime. The S_Hmax is oriented NW–SE parallel to the normal faults, and the average stress regime R' is equal 0.26. The NNE–SSW fourth tectonic stage is considered a counterclockwise rotation of the third stage in Pliocene-Pleistocene age. The first and second stages consider the initial stages of rifting, while the third and fourth represent the main stage of rifting.     

Structural style and fault kinematics of the Lower Eocene Rus Formation at Jabal Hafit area,Al Ain,United Arab Emirates (UAE)

The current contribution presents aspects of the structural style and fault kinematics of the Rus Formation that expose at Jabal Hafit, Al Ain, United Arab Emirates. Although the major structure of Jabal Hafit is an anticlinal fold, fractures (joints and faults) are the prominent structure of the study area. The fractures can be interpreted as the distributed effect of deep-seated basement fault reactivation or to be as reactivation of deep-seated basement faults. These fractures were created during two main tectonic stress regimes. The first is a WNW–ESE S _Hmax strike-slip stress regime, responsible for producing E–W to ESE–WNW joints and E–W dextral strike-slip and NNE–SSW reverse faults. This stress is interpreted to be post-Early Eocene in age and related to the second phase of thrusting in the Oman Mountains in the Miocene. The second stress regime is a NNE–SSW S _Hmax transtensional (strike-slip extensive) stress regime that was responsible for N–S to NNE–SSW striking joints and NE–SW sinistral strike-slip and N–S normal faults. This regime is interpreted to be post-Middle Eocene in age. This stress was the response to the collision of the Arabian–Eurasian Plates which began during the Late Eocene and continues to the present day.     

歧口凹陷及周缘新生代构造的成因和演化

歧口凹陷及周缘构造带发育不同方向的新生代断层,主要包括NE、NNE、NEE、近EW和NW向等,从运动学平衡角度推测这些断层均应不同程度地表现为具走滑分量的正断层或上盘斜落的走滑断层。本文提出一个双动力过程模式来解释歧口凹陷及周缘构造带的形成和演化。始新世时主要发生NWW—SEE向区域裂陷伸展,形成NE—NNE向正断层和NEE—近EW向传递断层;渐新世时,受纵贯研究区的NNE向深断裂右旋走滑的影响,叠加了SN向的局部伸展,形成大量NEE—近EW向盖层正断层。晚第三纪时NNE向区域性伸展作用基本停止,深断裂仍继续右旋走滑活动,引起盆地区断层进一步活动。     

A ‘core-complex-like structure’ formed by superimposed extension,folding and high-angle normal faulting. The Santi Petri dome (western Betics,Spain)

The Santi Petri dome (western Betics, southern Spain) shows a core-complex-like structure, where migmatitic gneisses and schists outcrop below low-grade slates and phyllites, all of which form the basement of the Neogene Málaga basin. The migmatites and schists suffered a coaxial-flattening event during isothermal decompression and were later exhumed by ductile ESE non-coaxial stretching. Further exhumation was achieved by W- to SW-transport brittle low-angle normal faulting. Subsequently these extensional structures were gently folded in the core of a NE/SW-oriented antiform during the Tortonian. Finally the Santi Petri domal geometry was accentuated by the interference of orthogonal high-angle faults with ENE–WSW and NNW–SSE orientation. This core-complex-like structure, formed by superposition of extensional and compressive tectonic events, does not represent a classical, purely extensional core complex, which shows that metamorphic structure and geometry are not decisive criteria to define a core-complex.     

Tectonics of the Northern Bresse region (France) during the Alpine cycle

Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE–SW, E–W and NW–SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N–S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE–SW in the graben. After a transitional minor E–W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE–SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE–SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.     

西江凹陷早新生代断裂演化及其对南海北缘应力场顺时针旋转的响应

南海北部发育了一系列的新生代盆地,该类盆地记录了新生代早期南海北缘应力场顺时针旋转过程,西江凹陷位于珠江口盆地内,记录了这一过程.利用丰富的二维、三维地震资料,针对西江凹陷断裂体系的演化过程进行了研究.凹陷基底在新生代之前作为华南陆缘的一部分,经历了多期次复杂的构造演化,形成了NE和NW两个方向的基底断层; 早-中始新世,NE向先存断裂优先复活,由太平洋板块俯冲后撤在研究区产生的NW-SE向伸展应力所致; 晚始新世-早渐新世,近EW向断裂大量发育,NW向断裂以走滑方式复活,该时期断层演化主要受太平洋俯冲方向的变化、印度板块碰撞及古南海的拖拽导致该地区应力场顺时针转变为近NS向的影响; 进一步通过物理模拟实验验证了断裂的演化机制,NE向先存断裂施加NS向拉张应力,先存NE向断裂局部复活,大量近EW向断层沿着NE向先存断裂展布位置形成,剖面上表现为正断层; NW向断裂在NS向拉张应力条件下,可见NW向走滑大量复活,局部发育少量的近EW向断裂.该研究对南海北缘新生代应力转变过程研究具有重要的借鉴意义.      

Active tectonics,fault patterns,and stress field of Deception Island: A response to oblique convergence between the Pacific and Antarctic plates

Palaeostress results derived from brittle mesoscopic structures on Deception Island (Bransfield Trough, Western Antarctica) show a recent stress field characterized by an extensional regime, with local compressional stress states. The maximum horizontal stress (σ_y) shows NW–SE and NNE–SSW to NE–SW orientations and horizontal extension (σ₃) in NE–SW and WNW–ESE to NW–SE directions. Alignments of mesofractures show a maximum of NNE–SSW orientation and several relative maxima striking N030-050E, N060-080E, N110-120E, and N160-170E. Subaerial and submarine macrofaults of Deception Island show six main systems controlling the morphology of the island: N–S, NNE–SSW, NE–SW, ENE–WSW to E–W, WNW–ESE, and NNW–SSE. Geochemical patterns related to submarine hydrothermally influenced fault and fissure pathways also share the same trends. The orientation of these fault systems is compared to Riedel shear fractures. Following this model, we propose two evolutionary stages from geometrical relationships between the location and orientation of joints and faults. These stages imply a counter-clockwise rotation of Deception Island, which may be linked to a regional left-lateral strike-slip. In addition, the simple shear zone could be a response to oblique convergence between the Antarctic and Pacific plates. This stress direction is consistent with the present-day movements between the Antarctic, Scotia, and Pacific plates. Nevertheless, present basalt-andesitic volcanism and deep earthquake focal mechanisms may indicate rollback of the former Phoenix subducted slab, which is presently amalgamated with the Pacific plate. We postulate that both mechanisms could occur simultaneously.     

Palaeogene structural evolution of Dongying Depression,Bohai Bay Basin,NE China

Based on the new all-covering 3D seismic data and the drilling-logging data, we established the sequence stratigraphic framework for Dongying Depression and identified two kinds of structural systems in Palaeogene, i.e. the extensional structural system and the transtensional structural system. The extensional structural system consists of different normal faults that predominantly trend NE, EW, and NW. The attitudes of the normal faults vary in different tectonic settings. However, the transtensional structural system consists of some strike–slip faults and some normal faults. According to the analysis of the relationships between the faults and the sedimentary sequences of Dongying Depression, we considered that the extensional structural system was developed mainly from the Palaeocene to the middle Eocene, whereas the transtensional structural system was mostly developed from the middle Eocene to the Oligocene. In addition, we found that the structural systems had transformed since 43.5 Ma, when the subduction direction and activity rates of the Pacific Plate changed and the dextral strike–slip movement of the large-scale Tanlu fault zone started from eastern China. The extensional structural deformation was probably derived from the back-arc extension triggered by subduction rollback of the Pacific Plate under the Eurasian Plate, whereas the transtensional structural deformation was probably related to the regional dextral strike–slip movement induced by the subduction of the Pacific Plate and the continents’ collision between the Indian Plate and the Eurasian Plate.     

惠民凹陷临南地区新生代构造演化特征研究

运用去压实校正原理编制了惠民凹陷临南地区东西部新生代连井投影构造演化剖面图，较系统地总结了临南地区新生代构造特征以及该地区的新生代构造演化序列，指出该区东西部的构造演化存在明显的时间差异，西南缓坡带从新生代以来一直表现为稳定斜坡，而曲堤地垒在沙河街组第一段沉积期一东营组沉积末期发生了强烈的旋转。最后综合分析认为，夏口断层控制了临南地区的构造演化．另外，盖层滑脱断层在研究区不发育，从而为该区的油气保存提供了良好的条件。     

Successive Extensional Tectonic Regimes during the Mesozoic as Evidenced by Neptunian Dikes in the Pontide Magmatic Arc,Northeast Turkey

The eastern Pontide magmatic arc extends ～600 km in an E-W direction along the Black Sea coast and was disrupted by a series of fault systems trending NE-SW, NW-SE, E-W, and N-S. These fault systems are responsible for the formation of diachronous extensional basins, rift or pull-apart, in the northern, southern, and axial zones of the eastern Pontides during the Mesozoic. Successive extensional or transtensional tectonic regimes caused the abortive Liassic rift basins and the Albian and Campanian pull-apart basins with deep-spreading troughs in the southern and axial zones. Liassic, Albian, and Campanian neptunian dikes, which indicate extensional tectonic regimes, crop out within the Paleozoic granites near Kale, Gumushane, and the Malm–Lower Cretaceous platform carbonates in Amasya and Gumushane. These neptunian dikes correspond to extensional cracks that are filled and overlain by the fossiliferous red pelagic limestones. Multidirectional Liassic neptunian dikes are consistent with the general trend of the paleofaults (NE-SW, NW-SE, and E-W), and active dextral North Anatolian fault (NAF) and sinistral Northeast Anatolian fault (NEAF) systems. The Albian neptunian dikes in Amasya formed in the synthetic oblique left-lateral normal faults of the main fault zone that runs parallel to the active North Anatolian fault zone (NAFZ).

Kinematic interpretation of the Liassic and Albian neptunian dikes suggests N-S extensional stress or northward movement of the Pontides along the conjugate fracture zones parallel to the NAFZ and NEAFZ. This northward movement of the Pontides in Liassic and Albian times requires left-lateral and right-lateral slips along the conjugate NAFZ and Northeast Anatolian fault zones (NEAFZ), respectively, in contrast to the recent active tectonics that have been accommodated by N-S compressional stress. On the other hand, mutual relationships between the neptunian dikes and the associated main fault zone of Campanian age extending in an E-W direction in the Kale area, Gumushane suggest the existence of a main left-lateral transtensional wrench zone. This system might be accommodated by the counterclockwise convergence of the Turkish plate with the Afro-Arabian plate relative to the Eurasian plate, and the southward oblique subduction of Paleotethys beneath the eastern Pontide magmatic arc during the Mesozoic.