Influence of fault reactivation during multiphase rifting: The Oseberg area,northern North Sea rift

Multiphase rifts tend to produce fault populations that evolve by the formation of new faults and reactivation of earlier faults. The resulting fault patterns tend to be complex and difficult to decipher. In this work we use seismic reflection data to examine the evolution of a normal fault network in the Oseberg Fault Block in the northern North Sea Rift System – a rift system that experienced Permian – Early Triassic and Middle Jurassic – Early Cretaceous rifting and exhibits N-S, NW-SE and NE-SW oriented faults.Both N-S- and NW-SE-striking faults were established during the Permian – Early Triassic rifting, as indicated by Triassic growth packages in their hanging walls. In contrast, the NE-SW-striking faults are younger, as they show no evidence of Permian – Early Triassic growth, and offset several N-S- and NW-SE-striking faults. Structural analysis show that a new population of NW-SE-striking faults formed in the Lower – Middle Jurassic (inter-rift period) together with reactivation of N-S-striking Permian – Early Triassic faults, indicating a NE-SW inter-rift extension direction.During the Middle Jurassic – Early Cretaceous rifting, faults of all orientations (N-S, NW-SE and NE-SW) were active. However, faults initiated during the Middle Jurassic – Early Cretaceous rifting show mainly N-S orientation, indicating E-W extension during this phase. These observations suggest a reorientation of the stress field from E-W during the Permian – Early Triassic rift phase to NE-SW during inter-rift fault growth and back to E-W during the Middle Jurassic – Early Cretaceous rift phase in the Oseberg area. Hence, the current study demonstrates that rift activity between established rift phases can locally develop faults with new orientations that add to the geometric and kinematic complexity of the final fault population.     

Deep-seated faults and hydrocarbon leakage in the Snøhvit Gas Field,Hammerfest Basin,Southwestern Barents Sea

High-quality 3D seismic data are used to analyze the history of fault growth and hydrocarbon leakage in the Snøhvit Field, Southwestern Barents Sea. The aim of this work is to evaluate tectonic fracturing as a mechanism driving hydrocarbon leakage in the study area. An integrated approach was used which include seismic interpretation, fault modeling, displacement analysis and multiple seismic attribute analysis.The six major faults in the study area are dip-slip normal faults which are characterized by complex lateral and vertical segmentation. These faults are affected by three main episodes of fault reactivation in the Late Jurassic, Early Cretaceous and Paleocene. Fault reactivation in the study area was mainly through dip-linkage. The throw-distance plots of these representative faults also revealed along-strike linkage and multi-skewed C-type profiles. The faults evolved through polycyclic activity involving both blind propagation and syn-sedimentary activity with their maximum displacements recorded at the reservoir zone. The expansion and growth indices provided evidence for the interaction of the faults with sedimentation throughout their growth history.Soft reflections or hydrocarbon-related high-amplitude anomalies in the study area have negative amplitude, reverse polarity and are generally unconformable with structural reflectors. The interpreted fluid accumulations are spatially located at the upper tips of the major faults and gas chimneys. Four episodes of fluid migration are inferred and are linked to the three phases of fault reactivation and Neogene glaciations. Hydrocarbon leakage in the Snøhvit Gas Field is driven by tectonic fracturing, uplift, and erosion. The interpreted deep-seated faults are the main conduits for shallow hydrocarbon accumulations observed on seismic profiles.     

A 3D structural analysis of the Goliat field,Barents Sea,Norway

The Goliat field consists of Middle to Late Triassic reservoirs which exploit an elongate anticline (the Goliat anticline) in the hanging wall of the Troms-Finnmark Fault Complex (TFFC), offshore Norway. The area is affected by a dense network of multiple trending fault populations which historically have inhibited seismic resolution owing to persistent fault shadow. Seismic investigations utilising a multi-azimuth three-dimensional survey (EN0901) allow much crisper delineation of seismic features previously unattainable by vintage single-azimuth surveys. Three dominant fault populations are identified in the area, two of which parallel TFFC segments, the Alke–Goliat (WSW–ENE) and the Goliat–Tornerose (NNE–SSW) segments. The Goliat field is located within a zone of intersection between both segments. A third E–W trending fault population, the Hammerfest Regional population, is likely influenced by the offshore extension of the Trollfjord-Komagelv Fault Complex (TKFZ). A local NW–SE trending fault population, the Goliat Central, affects the Goliat anticline and partitions Alke–Goliat and Goliat–Tornerose subsidiary faults resulting in curvilinear traces. Several cross-cutting relationships between fault populations are observed and may provide fluid compartmentalisation in the reservoirs. Compilation of regional transects and the EN0901 survey provides new insight into the evolution of the Goliat anticline which is underlain by a fault-bound basement terrace that became established in the Late Palaeozoic. The structure is interpreted to have formed due to vertical segmentation of the TFFC and cores the overlying broad anticline. The western limb of the Goliat anticline likely formed by differential compaction, whereas the eastern limb is primarily a result of hanging wall roll-over linked to variable listric to ramp-flat-ramp fault geometry. Rifting took place in the Palaeozoic (Carboniferous to Permian?), and in the Mesozoic, possibly as early as the Late Triassic, with a major event in the Late Jurassic to Early Cretaceous. Minor reactivations continued into the Late Cretaceous, and possibly the Early Cenozoic. Mesozoic syn-kinematic geometries in the hanging wall of the Goliat–Tornerose TFFC segment are consistent with deposition during up section propagation of a blind fault, over which, a monocline was established and later breached. Jogs (abrupt orientation changes) in fault traces, transverse folds (associated with displacement maxima/minima) and vertical fault jogs suggest the TFFC existed as a greater number of segments prior to amalgamation during the Late Triassic to Jurassic. A phase of Barremian inversion created local compression structures above blind extensional faults, and deeper seated buttressing against large faults. Polygonal faults affect the Late Cretaceous to Early Cenozoic successions.     

Holocene faulting on a tectonic margin: Georgia Basin,British Columbia,Canada

Multibeam bathymetric data collected in the Strait of Georgia, British Columbia, have revealed two areas of seabed disturbance, interpreted to be faults. The easterly fault zone (Fraser Delta Fault) is demarked by a pockmark chain extending along strike of a southwesterly-dipping fault offset 1 km to the northeast and having a throw of over 50 m. The pockmarks occur in a region of high sedimentation, located in the Fraser River prodelta. The eastern strait fault zone (Porlier Pass Fault) occurs within a fold of the Cretaceous Nanaimo Group. Here, a series of thrust faults displace sediments from Cretaceous to Holocene by up to 40 m with over 2 km of surface expression. Based on Holocene stratigraphic displacement in an area of significant sedimentation, these fault zones are considered to be active.     

Structure and evolution of the Northeastern German Basin and its transition onto the Baltic Shield

The post-Permian sequence stratigraphical and structural evolution of the Northeastern German Basin and its transition onto the Baltic Shield has been studied in the Bay of Mecklenburg (SW Baltic Sea) by means of seismic interpretation. Five major sequences have been identified: Middle Triassic, Upper Triassic, Jurassic, Cretaceous and Cenozoic. Time–isochore maps allowed the identification of several phases of salt pillow growth. The contemporaneity of active salt tectonics and the well studied tectonic evolution of the Northeastern German Basin suggest a causative correlation. The E–W directed extension during the Triassic-Early Jurassic marking the beginning break-up of Pangaea is seen as the trigger process for the first period of salt movement. A fault system outside the limit of the Zechstein evaporates is understood as the consequence of thin-skinned faulting and brittle thick-skinned deformation that accompanied this extension. The observed pronounced erosion of Upper Triassic and Lower Jurassic strata is considered to result from the uplift due to the Mid North Sea Doming event in Middle Jurassic times. The seismic data show an undisturbed Late Cretaceous succession which reflects a period of rising sea level, tectonic quiescence and no salt movement. In contrast to the salt pillows which emerged above Triassic fault systems in the westernmost Baltic and western North German Basin, the Cenozoic salt movement activity is the most pronounced. This period of reactivated salt pillow growth started coevally with the onset of the Alpine orogeny at the Cretaceous/Cenozoic transition when the Africa-Arabian plate collided with Eurasia. Generally, no significant faults were identified in the overburden of the salt floored southern Bay of Mecklenburg where ductile Zechstein salt decouples deep rooted faulting from supra-salt deformation.     

Extensional fault evolution within the Exmouth Sub-basin,North West Shelf,Australia

Structural analysis of the Indian Merge 3D seismic survey identified three populations of normal faults within the Exmouth Sub-basin of the North West Shelf volcanic margin of Australia. They comprise (1) latest-Triassic to Middle Jurassic N-NNE-trending normal faults (Fault Population I); (2) Late Jurassic to Early Cretaceous NE-trending normal faults (Fault Population II); and (3) latest-Triassic to Early Cretaceous N-NNE faults (Fault Population III). Quantitative evaluation of >100 faults demonstrates that fault displacement occurred during two time periods (210–163 and 145–138 Ma) separated by ∼20 Myr of tectonic quiescence. Latest Jurassic to Early Cretaceous (145–138 Ma) evolution comprises magmatic addition and contemporaneous domal uplift ∼70 km wide characterised by ≥ 900 m of denudation. The areally restricted subcircular uplift centred on the southern edge of the extended continental promontory of the southern Exmouth Sub-basin supports latest Jurassic mantle plume upwelling that initiated progradation of the Barrow Delta. This polyphase and bimodal structural evolution impacts current hydrocarbon exploration rationale by defining the nature of latest Jurassic to Early Cretaceous fault nucleation and reactivation within the southern Exmouth Sub-basin.     

西非宽扎盆地烃源岩分布及油气成藏

宽扎盆地为南大西洋被动大陆边缘盆地,构造演化可划分为裂谷期、过渡期和后裂谷期3个阶段,过渡期发育阿普特阶盐岩。宽扎盆地主要发育3套烃源岩:盐下下白垩统阿普特阶湖相烃源岩、盐间早白垩世阿普特期海相烃源岩和盐上古近纪始新世海相烃源岩。宽扎盆地油气田均围绕烃源灶分布,烃源岩是该盆地油气藏形成与分布的主控因素。宽扎盆地发育4套含油气系统(盐下下白垩统、盐间下白垩统、盐上上白垩统和盐上古近系)以及2种成藏模式(古生新储和自生自储)。宽扎盆地深水21区块Cameia-1井、Cameia-2井以及21区块Azul-1井盐下地层获得重大油气勘探突破,表明该盆地深水区存在盐下下白垩统含油气系统并发育优质湖相烃源岩,提高了宽扎盆地深水区油气勘探潜力。     

Regional constraints of the Sørkapp Basin: A Carboniferous relic or a Cretaceous depression?

The Sørkapp Basin (NW Barents Shelf) contains a comprehensive sedimentary succession that provides insight into regional tectonics and depositional development of the shelf from the Devonian to the Cretaceous. With its location east of the mid-Atlantic spreading ridge and south of Svalbard, the Basin serves as an important link between the offshore and onshore realms.This study subdivides this sparsely studied basin into six main seismic units (three Paleozoic and three Mesozoic). A metamorphic basement together with assumed Devonian sedimentary deposits form the foundation for a chiefly Carboniferous basin. The Basin forms a syncline with infill showing limited fault-influence. Overlying the early infill are Late Carboniferous deposits which show less lateral variation in thickness but also active growth on the few faults showing significant displacement. The overlying platform deposits of the latest Carboniferous and Permian show a change in depositional geometry, with onlapping deposits towards the east probably resulting from uplift of the Stappen High and regional flooding. Subsequent, particularly Late, Triassic sedimentation shows a more distinctly progradational pattern with a dominantly southeastern source for sediments. During this shallow shelf-filling stage, the Sørkapp Basin is sheltered by the Gardarbanken High, blocking the Early Triassic clinoform development. The High was transgressed in the Middle Triassic and the platform-edge progressively approached the present Svalbard coastline.The youngest Mesozoic unit forms a separate saucer-shaped depocenter west of the Sørkapp Basin, where deposits are truncated by the seafloor in a mid-basin position and across the Gardarbanken High. The depositional pattern for this succession correlates with the outcrop pattern of the Adventdalen Group implying a post Middle Jurassic to Cretaceous age. The Sørkapp Basin has been referred to as a Cretaceous feature based in this depocenter. However, the foundations are much older and the Cretaceous depression is located west of the deeper basin. Accordingly, we propose the informal term Sørkapp Depression for the Cretaceous basin.     

New insights into the tectono-stratigraphic evolution of the southern Stappen High and its transition to Bjørnøya Basin,SW Barents Sea

Within the context of the southwestern Barents Sea, the southern Stappen High and its transition to the Bjørnøya Basin are still underexplored. Improved quality seismic reflection data are utilised to describe new insights into the Paleozoic to early Cenozoic tectono-stratigraphic evolution of the area, as well as to discuss the structural inheritance and the rift development. Well-defined syn-rift wedges and better resolution images for both the deep Carboniferous and Permian successions are revealed. In particular, both the mid-Carboniferous and Late Permian-earliest Triassic extensional phases are characterized by widespread NE-SW oriented normal faults that are mostly westward dipping. Although Triassic is mostly considered as a tectonically stable period in the Barents Sea, in the southern Stappen High there is clear identification of a localised depocentre (named herein “Intra Stappen Basin”) where syn-tectonic geometries characterize the upper Paleozoic and Triassic deposits. Regional correlation to Middle and Upper Triassic outcrops in southwestern Svalbard reveals possible progradation from a west-northwest Northeast Greenland provenance as a western sediment source area during the Triassic, in addition to the well-known eastern sediment source area. Thin but distinct Jurassic sequences are expected to be present on Stappen High associated with prominent regional NW-SE extension throughout Late Jurassic that culminated during the earliest Cretaceous. Furthermore, structural and stratigraphic relations are observed within the study area that clearly indicate a distinct early Aptian rift phase with increasing evidence for its occurrence in the southwestern Barents Sea. Upper Cretaceous sequences bounded by major low-angle west-dipping detachment faults are observed in southwest Stappen High. During early Cenozoic, the study area was located at the proximity of the paleo-coastline and paleo-shelf edge for both Paleocene and Eocene gravity mass-waste deposits. These are most probably related to a progressively evolving steep bathymetric gradient between the developing margin, mainly towards the west and to the south, and the uplifted Stappen High.     

琼东南盆地陆架区晚中新世以来断层活动性研究

对琼东南盆地陆架区晚中新世以来的断层活动性进行研究, 有助于理解南海西北部晚中新世以来的构造演化, 也对该区钻井平台的安全性评估、海洋工程勘查以及区域稳定性评价等有重要意义。研究区断层走向主要为NWW向, 多数断层在晚中新世时期停止活动。通过对断层几何形态的统计分析以及使用高分辨率断层落差图法(T-Z图示法)对断层活动性进行量化分析, 结果显示: 断层活动性在晚中新世末期(5.5Ma)发生转变; 研究区南部的断层落差值大于北部; 南部断层停止活动的时间较北部断层稍晚。这些研究成果表明, 晚中新世末期研究区断层受构造应力变化的影响, 在生长发育过程中断层活动性质发生了改变, 由逆断层转为正断层。红河断裂带对琼东南盆地的构造演化起着重要的控制作用, 文章推测研究区断层活动性变化是由红河断裂带的构造反转所导致, 因为红河断裂带在5.5Ma时发生了走滑运动的反转, 与研究区的断层活动性变化在时间和性质上相耦合。     

南大西洋被动陆缘共轭盆地烃源岩分布与油气富集规律——以巴西桑托斯盆地和西非纳米贝盆地为例

巴西桑托斯盆地与西非纳米贝盆地属于南大西洋中部被动大陆边缘共轭盆地,其构造演化可划分为3个阶段:裂谷期、过渡期和后裂谷期,过渡期发育阿普特阶盐。南大西洋不对称裂开控制了桑托斯盆地和纳米贝盆地在盐下早白垩世裂谷地堑、盐发育和盐上晚白垩世地层厚度等方面的差异,这些差异控制了桑托斯盆地和纳米贝盆地盐下早白垩世湖相烃源岩发育及盐上晚白垩世海相烃源岩成熟度,进而控制了桑托斯盆地和纳米贝盆地油气富集规律。桑托斯盆地深水区盐下下白垩统构造或岩性圈闭是寻找巨型油气田的有利勘探方向;浅水区盐上上白垩统地堑深凹陷盐活动相关构造或岩性圈闭是寻找大中型油气田的有利勘探方向。     

High-resolution record of tectonic and sedimentary processes in growth strata

Growth strata are used to determine the kinematics of synsedimentary structures such as faults. Classical methods of analysis such as thickness versus throw plot consider that the available space created by fault slip in the hanging wall of faults is instantaneously filled up by sediments. This has lead many previous works to identify a cyclic activity for growth faults. Here we perform a careful analysis of the variation of strata thicknesses on each side of a very well documented normal growth fault in the Niger delta. We show that these thickness variations are induced by the alternation of sedimentary processes during continuous fault slip. Suspended-load processes induce either uniform or slightly variable thickness of a large majority of mudstone layers. Bedload processes result in a preferential thickening of sand layers in the hanging wall. These high quality data thus provide strong grounds for doubting the polycyclic growth diagnosed for some faults at the scale of sedimentary cycles and supports the notion that fault displacement rates can be very well behaved. Our study emphasizes the important conclusion that stable fault growth, and related displacement rates, can appear to be punctuated when viewed at the scale of sedimentary cycles. It follows that care should be taken when attempting to derive displacement rates on temporal scales equivalent to those of alternating sedimentological cycles.     

下刚果-刚果扇盆地东南部基底断裂复活及其与油气的关系

下刚果-刚果扇盆地位于西非被动大陆边缘,是典型的裂谷与被动陆缘叠合盆地。该区以往的研究多集中于盐上层系,对基底断裂研究较少。以构造分析为基础,探讨了基底断裂复活及其对盐上层系构造变形和油气分布的影响。结果表明,研究区盐下裂谷层系具有“两坳夹一隆”的构造格局,大西洋枢纽带夹持于内裂谷带和外裂谷带之间;基底断裂复活主要发生在紧邻大西洋枢纽带西侧、呈狭长带状分布的基底断裂复活带,断裂复活形式主要表现为继承性,其次为构造反转;基底断裂复活不仅对盐上层系的构造变形具控制作用,而且为油气从盐下层系向盐上层系运移提供了良好的垂向通道条件,是外裂谷带盐下油气向盐上层系运移的关键部位。     

Structural evolution of the Feda Graben area – A new model

The pre-Cretaceous basin evolution of the Feda Graben area in the vicinity of the Norwegian-Danish basin has been reconstructed utilizing geological and structural interpretation. The analysis reveals that the basin was faulted at its borders prior to the salt deposition in the Late Permian. Salt movement was initiated in Late Triassic and thick Triassic and Lower Jurassic pods were deposited in the graben area due to this movement. Salt pillows were developing along the Feda Graben bordering faults until Middle Jurassic when the pillows were collapsed. Salt diapirs within the study area preferentially occupy the crest of the Feda Graben and their occurrence is controlled by the underlying faulted topography. The diapirs were fed by salt from the central and southern parts of the basin and were developed by different processes i.e. upbuilding, downbuilding. Various raft structures were developed in the graben area hanging wall while some uplift occurred in the footwall during Mesozoic rifting. The Feda Graben area experienced rifting from Late Jurassic to Early Cretaceous. The most pronounced subsidence episode related with this rifting in the Feda Graben area took place along the eastern bounding Gert Fault. The Mesozoic rifting event is marked by a major unconformity on the seismic sections throughout the study area. Furthermore, the region experienced basin inversion in Late Cretaceous. The effects of inversion are more pronounced in the western part and along the Gert Fault. The inversion phenomenon can be properly understood only when considered together with the geometry of the Late Jurassic half-graben. Due to some inconsistencies in the previously proposed models for the development of the Feda Graben, a new conceptual model has been constructed.     

东海陆架盆地南部生长断层活动特征

生长断层是在伸展和走滑盆地中一种重要且广泛存在的构造样式。通过地震资料定性识别出东海陆架盆地南部地区18条生长断层; 根据断裂对研究区各级构造单元控制作用和纵向切穿地层情况, 将其划分为一级控盆断裂、二级控凹断裂、三级控带断裂和盖层断裂; 通过断裂平面分布特征研究认为研究区的断裂以NE、NNE延伸为主, 少数为NEE方向; 利用地震剖面在研究区识别出阶梯状组合断层带、“Y”字型组合断层、多米诺式断层带、地堑、地垒等多种断裂组合样式; 又结合生长指数和断层落差两种方法对研究区生长断层的运动学特征进行了定量统计分析, 发现研究区生长断层在古近纪时期活动强度具有自西向东逐渐递减趋势, 区内断层活动期次自西向东逐渐变新, 整个研究区内生长断层在古近纪盆地裂陷—断陷期活动强度最大, 中新世后断裂活动趋于稳定。认为晚中生代以来太平洋板块西缘俯冲后撤和印度板块向亚欧板块俯冲碰撞在东海陆架盆地形成的远程蠕散效应, 使东海陆架盆地形成了拉张伸展应力场环境, 是研究区发育大量生长断层的首要原因。同时, 加强对研究区生长断层伴生构造如滚动背斜和缓坡带阶梯状断裂组合封堵形成的岩性圈闭研究, 有利于推动东海陆架中新生代盆地资源勘探可持续发展。     

东海陆架盆地的前新生界

根据东海陆架盆地周边地质、地球物理和钻井资料,应用岩石学、古生物学、同位素年代学、层序地层学等分析方法,研究东海陆架盆地的前新生界.陆架盆地广泛发育中生界,其中盆地南部发育最全,以三叠—白垩系陆相碎屑岩为主,中部隆起带以发育侏罗—白垩系的陆相火山岩为主,以台湾海峡为中心的盆地南部有海相—海陆过渡相的中生界.在盆地南部钻遇的年龄为1680 Ma的黑云角闪斜长片麻岩和在北部钻遇的糜棱片麻岩分别为浙闽东部前震旦纪变质岩和浙北晚元古代变质岩在海中的延伸.陆架地区晚古生代可能属于亚洲大陆东缘优地槽带的冒地槽,在盆地内尤其在东部坳陷带可能有晚古生代浅变质岩.     

Different expressions of rifting on the South China Sea margins

Rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces, but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin. Being opened quite recently in the Tertiary in a scissor-shape manner, the South China Sea (SCS) offers an image of the rifting structures which varies along strike the basin margins. The SCS has a long history of extension, which dates back from the Late Cretaceous, and allows us to observe an early stretching on the northern margin onshore and offshore South China, with large low angle faults which detach the Mesozoic sediments either over Triassic to Early Cretaceous granites, or along the short limbs of broad folds affecting Palaeozoic to Early Cretaceous series. These early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone. Because these low-angle faults reactivate older trends, they vary in geometry according to the direction of the folds or the granite boundaries. A later set of faults, characterized by generally E–W low and high angle normal faults was dominant during the Eocene. Associated half-graben basement deepened as the basins were filling with continental or very shallow marine sediments. This subsequent direction is well expressed both in the north and the SW of the South China Sea and often reactivated earlier detachments. At places, the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the Phu Khanh Basin East of the Vietnam fault. A third direction of faults, which rarely reactivates the detachments is NE–SW and well developed near the oceanic crust in the southern and southwestern part of the basin. This direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part, and ended by the Late Miocene after the onset of the regional Mid Miocene unconformity known as MMU and dated around 15.5 Ma. Latest Miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast. The SE margin of the South China Sea does not show the extensional features as well as the Northern margin. Detachments are common in the Dangerous Grounds and Reed Bank area and may occasionally lead to mantle exhumation. The sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the Late Miocene, when it suddenly deepened. This period also corresponds to the cessation of the shortening of the NW Borneo wedge in Palawan, Sabah, and Sarawak. We correlate the variation of margin structure and composition of the margin; mainly the occurrence of granitic batholiths and Mesozoic broad folds, with the location of the detachments and major normal faults which condition the style of rifting, the crustal boudinage and therefore the crustal thickness.     

Salt tectonics and tear faulting in the central part of the Zagros Fold-Thrust Belt,Iran

The central part of the Zagros Fold-Thrust Belt is characterized by a series of right-lateral and left-lateral transverse tear fault systems, some of them being ornamented by salt diapirs of the Late Precambrian–Early Cambrian Hormuz evaporitic series. Many deep-seated extensional faults, mainly along N–S and few along NW–SE and NE–SW, were formed or reactivated during the Late Precambrian–Early Cambrian and generated horsts and grabens. The extensional faults controlled deposition, distribution and thickness of the Hormuz series. Salt walls and diapirs initiated by the Early Paleozoic especially along the extensional faults. Long-term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks. They created weak zones in the sedimentary cover, located approximately above the former and inactive deep-seated extensional faults. The N–S to NNE–SSW direction of tectonic shortening during the Neogene Zagros folding was sub-parallel with the strikes of the salt walls and rows of diapirs. Variations in thickness of the Hormuz series prepared differences in the basal friction on both sides of the Precambrian–Cambrian extensional faults, which facilitated the Zagros deformation front to advance faster wherever the salt layer was thicker. Consequently, a series of tear fault systems developed along the rows of salt diapirs approximately above the Precambrian–Cambrian extensional faults. Therefore, the present surface expressions of the tear fault systems developed within the sedimentary cover during the Zagros orogeny. Although the direction of the Zagros shortening could also potentially reactivate the basement faults as strike-slip structures, subsurface data and majority of the moderate-large earthquakes do not support basement involvement. This suggests that the tear fault systems are detached on top of the Hormuz series from the deep-seated Precambrian–Cambrian extensional faults in the basement.     

太阳盆地中新生代断裂特征及成因机制

太阳盆地位于北黄海盆地的东部,是一个发育在中-朝克拉通基底之上的中、新生代沉积盆地,勘探程度非常低。最新二维地震资料揭示,太阳盆地的断裂体系可以分控盆断裂、控凹(坳)断裂、控带断裂、控圈断裂和分割性断裂。盆地发育以NE向和NW向为主的的正断层和逆断层,而少量断层呈近EW或SN向。对不同类型的断裂构造特征及样式分析表明,断裂的活动期次可分为4期:晓侏罗世-早白垩世伸展断层、晓白垩世逆冲断层、始新世伸展正断层和新近纪正断层。中、新生代以来,中国东部构造演化主要受其东部太平洋板块活动控制,晓侏罗纪开始,洋壳俯冲在东部的欧亚大陆之下,伴随着太平洋-菲律宾板块的俯冲,太阳盆地发生NNE-SSW向的拉张;晓白垩世时期,由于太平洋板块俯冲方向的改变,区域性拉张变为区域性NNW-SSE向挤压,太阳盆地的一系列NW向逆断层形成;在始新世-渐新世,太平洋板块向东亚大陆作斜向减速俯冲,导致太阳盆地遭受Nww-SEE向拉张作用,再次断陷;渐新世末期,受喜山运动第Ⅱ幕的影响,太阳盆地发生再次的构造反转,形成一系列的小规模断层。     

Namibia volcanic margin

Two end members of passive margin types are present on the Namibia margin: volcanic and non-volcanic. The central and southern parts of the Namibia margin feature characteristic volcanic margin elements such as thickened initial oceanic crust, seaward dipping reflectors, and high-velocity/density lower crust that extends beneath the rift zone that was formed during initial seafloor spreading in Early Cretaceous. The margin north of the Walvis FZ is non-volcanic in character and probably formed as a result of a ridge jump that occurred after cessation of the initial magmatic activity. The Walvis Ridge forms the boundary between the two margin types and resulted from the persistent magmatism associated with the Tristan plume. MCS data in conjunction with gravity modeling reveal a Paleozoic rift zone beneath the Namibia margin south of the Walvis FZ. The Paleozoic rift zone partly overlaps the Jurassic/Early Cretaceous rift zone which produced the breakup between Africa and South America. We calculate an average stretching value of =1.4 for the Paleozoic rift, based on subsidence modeling. The rift is partly bounded by low-angle faults, related to the orogenic collapse of the Pan-African fold belt, which provided a major Paleozoic sediment source. The offshore continuity of onshore ophiolitic complexes is suggested by the coast parallel high-amplitude magnetic anomaly G, and low-angle detachment faults along the southern part of the margin. The average stretching value for the Jurassic/Early Cretaceous rift is =1.7, which implies a syn-rift displacement on this margin of 70 km. The minimum igneous volume of the South Atlantic LIP was found to be in excess of 3.62×106 km³.