Implications of gravity data from East Kalimantan and the Makassar Straits: a solution to the origin of the Makassar Straits?

Recent free-air gravity data covering the Makassar Straits is integrated with Bouguer gravity data from onshore East Kalimantan to provide new insights into the basement structure of the region. Onshore Kalimantan, gravity highs on the northern margin of the Kutai Basin trend NNE–SSW and N–S and correspond with the axes of inverted Eocene half-grabens. NW–SE trending lows correspond to deep seated basement weaknesses reactivated as normal faults during the Tertiary. An intra-basin gravity high trending NNE–SSW, the Kutai Lakes Gravity High, is modelled as folded high density Paleogene sediments flanked by syn-inversion synclines infilled with low density sediments. Offshore Kalimantan, the Makassar Straits include two basins offset by an en-echelon fault zone, suggestive of an extensional origin. The regional signature of the free-air anomaly data mirrors the bathymetry, but this effect can be reduced by the use of filters in order to examine the basin architecture. The free-air gravity minimum in the Makassar Strait is only −20 mGal, much smaller than that appropriate for a foreland basin, and more indicative of an extensional basin. The steepness of the gradients on the flanks of the basins indicates fault control of their margins. A regional 2D profile across the North Makassar Basin suggests the presence of attenuated crust (<14 km) in the basin axis at the present day, whereas flexural backstripping implies the presence of oceanic crust of middle Eocene age. The presence of oceanic crust in the North Makassar Straits Basin has implications for regional plate tectonic models.     

Brittle tectonism in relation to the Palaeogene evolution of the Thulean/NE Atlantic domain: a study in Ulster

The tectonic effects of the Thulean mantle plume on the opening of the North Atlantic Ocean is still poorly understood. An analysis of the brittle deformation affecting the Late Cretaceous Chalk and Lower Tertiary igneous formations cropping out in Ulster (Northern Ireland), part of the Thulean Province, leads to the recognition of two tectonic phases. Each of these phases is characterized by different stress regimes with similar trends of the horizontal maximum principal stress σ_H. The first phase, syn-magmatic and dominated by NE–SW to ENE–WSW extension, occurred during the Palaeocene. It is followed by a second post-magmatic phase, characterized initially by a probably Eocene strike-slip to compressional palaeo-stress regime with σ₁ (=σ_H) trending NE–SW to NNE–SSW associated with the partial reactivation (as reverse faults) of normal faults formed during the first phase NE–SW extension. This episode is postdated by an Oligocene extension, with σ_H (=σ₂) still striking NNE–SSW/NE–SW, which reactivated Eocene strike-slip faults as nearly vertical dip-slip normal faults. This Palaeogene tectonic evolution is consistent with the tectonic evolution of similar age in western Scotland and in the Faeroe Islands. In particular, the post-magmatic NE–SW compression is here related to the ‘Faeroe compressive event’, which is related to the earliest stages of drift of the Greenland plate.     

Tertiary facies architecture in the Kutai Basin,Kalimantan, Indonesia

The Kutai Basin occupies an area of extensive accommodation generated by Tertiary extension of an economic basement of mixed continental/oceanic affinity. The underlying crust to the basin is proposed here to be Jurassic and Cretaceous in age and is composed of ophiolitic units overlain by a younger Cretaceous turbidite fan, sourced from Indochina. A near complete Tertiary sedimentary section from Eocene to Recent is present within the Kutai Basin; much of it is exposed at the surface as a result of the Miocene and younger tectonic processes. Integration of geological and geophysical surface and subsurface data-sets has resulted in re-interpretation of the original facies distributions, relationships and arrangement of Tertiary sediments in the Kutai Basin. Although much lithostratigraphic terminology exists for the area, existing formation names can be reconciled with a simple model explaining the progressive tectonic evolution of the basin and illustrating the resulting depositional environments and their arrangements within the basin. The basin was initiated in the Middle Eocene in conjunction with rifting and likely sea floor spreading in the Makassar Straits. This produced a series of discrete fault-bounded depocentres in some parts of the basin, followed by sag phase sedimentation in response to thermal relaxation. Discrete Eocene depocentres have highly variable sedimentary fills depending upon position with respect to sediment source and palaeo water depths and geometries of the half-graben. This contrasts strongly with the more regionally uniform sedimentary styles that followed in the latter part of the Eocene and the Oligocene. Tectonic uplift documented along the southern and northern basin margins and related subsidence of the Lower Kutai Basin occurred during the Late Oligocene. This subsidence is associated with significant volumes of high-level andesitic–dacitic intrusive and associated volcanic rocks. Volcanism and uplift of the basin margins resulted in the supply of considerable volumes of material eastwards. During the Miocene, basin fill continued, with an overall regressive style of sedimentation, interrupted by periods of tectonic inversion throughout the Miocene to Pliocene.     

Stratigraphic and structural evolution of the Blue Nile Basin,Northwestern Ethiopian Plateau

The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ∼1400 m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early–Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre‐sedimentation phase, include pre‐rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic–Early Jurassic fluvial sedimentation (Lower Sandstone, ∼300 m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ∼30 m thick); (c) Early–Middle Jurassic deepening of the basin (Lower Limestone, ∼450 m thick); (d) desiccation of the basin and deposition of Early–Middle Jurassic gypsum; (e) Middle–Late Jurassic marine transgression (Upper Limestone, ∼400 m thick); (f) Late Jurassic–Early Cretaceous basin‐uplift and marine regression (alluvial/fluvial Upper Sandstone, ∼280 m thick); (3) the post‐sedimentation phase, including Early–Late Oligocene eruption of 500–2000 m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ∼300 m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic–Cretaceous NE–SW‐directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW‐trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW–SE‐directed extension related to the Main Ethiopian Rift that formed NE‐trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E–W and NNE–SSW‐directed extensions related to oblique opening of the Main Ethiopian Rift and development of E‐trending transverse faults, as well as NE–SW‐directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E–W‐directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N‐, ESE‐ and NW‐trending extensional structures within the Blue Nile Basin. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

The Variscan tectonic inheritance of the Upper Rhine Graben: evidence of reactivations in the Lias,Late Eocene–Oligocene up to the recent

Processing of gravity and magnetic maps shows that the basement of the Upper Rhine Graben area is characterized by a series of NE–SW trending discontinuities and elongated structures, identified in outcrops in the Vosges, Black Forest, and the Odenwald Mountains. They form a 40 km wide, N30–40° striking, sinistral wrench-zone that, in the Visean, shifted the Variscan and pre-Variscan structures by at least 43 km to the NE. Wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340–325 Ma. The sub-vertical, NE–SW trending discontinuities in the basement acted as zones of weakness, susceptible to reactivation by subsequent tectonism. The first reactivation, marked by mineralizations and palaeomagnetic overprinting along NE–SW faults of the Vosges Mountains, results from the Liassic NW–SE extension contemporaneous with the break-up of Pangea. The major reactivation occurred during the Late Eocene N–S compression and the Early-Middle Oligocene E–W extension. The NE–SW striking basement discontinuities were successively reactivated as sinistral strike-slip faults, and as oblique normal faults. Elongated depocenters appear to form in association with reactivated Variscan wrench faults. Some of the recent earthquakes are located on NE–SW striking Variscan fault zones, and show sinistral strike-slip focal mechanisms with the same direction, suggesting also present reactivation.     

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.     

Synorogenic basins of central Cuba and collision between the Caribbean and North American plates

The synorogenic basins of central Cuba formed in a collision-related system. A tectono-stratigraphic analysis of these basins allows us to distinguish different structural styles along the Central Cuban Orogenic Belt. We recognize three distinct structural domains: (1) the Escambray Metamorphic Complex, (2) the Axial Zone, and (3) the Northern Deformation Belt. The structural evolution of the Escambray Metamorphic Complex includes a latest Cretaceous compressional phase followed by a Palaeogene extensional phase. Contraction created an antiformal stack in a subduction environment, and extension produced exhumation in an intra-arc setting. The Axial Zone was strongly deformed and shortened from the latest Cretaceous to Eocene. Compression occurred in an initial phase and subsequent transpressive deformation took place in the middle Eocene. The Northern Deformation Belt consists of a thin-skinned thrust fault system formed during the Palaeocene to middle Eocene; folding and faulting occurred in a piggyback sequence with tectonic transport towards the NNE. In the Central Cuban Orogenic Belt, some major SW–NE structures are coeval with the Cuban NW–SE striking folds and thrusts, and form tectonic corridors and/or transfer faults that facilitated strain-partitioning regime attending the collision. The shortening direction rotated clockwise during deformation from SSW–NNE to WSW–ENE. The synchronicity of compression in the north with extension in the south is consistent with the opening of the Yucatan Basin; the evolution from compression–extension to transpression is in keeping with the increase in obliquity in the collision between the Caribbean and North American plates.     

Caractérisation géométrique et cinématique des structures liées aux phases compressives de l'Éocène au Quaternaire inférieur en Tunisie : exemple de la Tunisie nord-orientale

During Eocene to Early Quaternary period, three compressive tectonic phases are recognized in Northeast Tunisia: a NW–SE to north–south phase during the Late Eocene, a N120-to-N140 phase in the Late Miocene, and a NW–SE to north–south phase in the Plio-Early Quaternary. The first Eocene phase has built NE–SW folds and remobilised east–west-to-N120 and NE–SW faults with a reverse component. The second Miocene phase is characterized by east–west-to-N120 faults with a normal component and NE–SW folds. The third phase occurred during the Plio-Early Quaternary has edified NE–SW folds associated with east–west-to-N120 dextral reverse strike-slip faults and NE–SW faults with a reverse component. To cite this article: H. Mzali, H. Zouari, C. R. Geoscience 338 (2006).     

Paleostress reconstructions of Jabal Hafit structures,Southeast of Al Ain City,United Arab Emirates (UAE)

This paper presents the first paleostress results obtained from displacement and fracture systems within the Lower Eocene sediments at Jabal Hafit, Abu Dhabi Emirate, UAE. Detailed investigation of Paleogene structures at Jabal Hafit reveal the existence of both extensional structures (normal faults) and compressional structures (strike-slip and reverse faults). Structural analysis and paleostress reconstructions show that the Paleogene kinematic history is characterized by the succession of four paleostress stages. Orientation of principal stresses was found from fault-slip data using an improved right-dihedra method, followed by rotational optimisation (TENSOR program).The paleostress results confirm four transtensional tectonic stages (T1–T4) which affected the study area. The first tectonic stage (T1) is characterized by S_Hmax NW–SE σ₂-orientation. This stage produced NW–SE striking joints (tension veins) and E–W to ENE–WSW striking dextral strike-slip faults. The proposed age of this stage is Early Eocene. The second stage (T2) had S_Hmax N–S σ₂-orientation. N–S striking joints and NNE–SSW striking sinistral strike-slip faults, E–W striking reverse faults and N–S striking normal faults were created during this stage. The T2 stage is interpreted to be post-Early Eocene in age. The third stage (T3) is characterized by S_Hmax E–W σ₂-orientation. This stage reactivated the E–W reverse faults as sinistral strike-slip faults and created E–W striking joints and NE–SW reverse faults. The proposed age for T3 is post-Middle Eocene. During the T3 (S_Hmax E–W σ₂-orientation) stage the NNW-plunging Hafit anticline was formed. The last tectonic stage that affected the study area (T4) is characterized by S_Hmax NE–SW σ₂-orientation. During this stage, the ENE–WSW faults were reactivated as sinistral strike-slip and reverse faults. NE–SW oriented joints were also created during the T4 (S_Hmax NE–SW σ₂-orientation) stage. The interpreted age of this stage is post-Middle Miocene time but younger than T3 (S_Hmax E–W σ₂-orientation) stage.     

Active tectonism in the central Alps: contrasting stress regimes north and south of the Rhone Valley

An integrated interpretation of seismicity, fault plane solutions and deep seismic reflection data suggests that the NE–SW to NW–SE trending Rhone–Simplon fault zone and the gently S-dipping basal Penninic thrust separate fundamentally different stress regimes in the western Swiss Alps. North of the Rhone-Simplon fault zone, strike-slip earthquakes on steep-dipping faults within the Helvetic nappes are a consequence of regional NW–SE compression and NE–SW extension. To the south, vertical maximum stress and N–S extension are responsible for normal mechanism earthquakes that occur entirely within the Penninic nappes above the basal Penninic thrust. Such normal faulting likely results from extension associated with southward movements (collapse) of the Penninic nappes and/or continued uplift and relative northward displacements of the underlying Alpine massifs. Geological mapping and fission-track dating suggest that the two distinct stress regimes have controlled tectonism in the western Swiss Alps since at least the Neogene.     

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。     

Structural Mapping of the Bentong‐Raub Suture Zone Using PALSAR Remote Sensing Data,Peninsular Malaysia: Implications for Sediment‐hosted/Orogenic Gold Mineral Systems Exploration

The Bentong‐Raub Suture Zone (BRSZ) of Peninsular Malaysia is one of the major structural zones in Sundaland, Southeast Asia. It forms the boundary between the Gondwana‐derived Sibumasu terrane in the west and Sukhothai Arc in the east. The BRSZ is genetically related to the sediment‐hosted/orogenic gold deposits associated with the major lineaments in the Central Gold Belt of Peninsular Malaysia. In this investigation, the Phased Array type L‐band Synthetic Aperture Radar (PALSAR) satellite remote sensing data were used to map major geological structures in Peninsular Malaysia and provide detailed characterization of lineaments and curvilinear structures in the BRSZ, as well as their implication for sediment‐hosted/orogenic gold exploration in tropical environments. Major structural lineaments such as the Bentong‐Raub Suture Zone (BRSZ) and Lebir Fault Zone, ductile deformation related to crustal shortening, brittle disjunctive structures (faults and fractures) and collisional mountain range (Main Range granites) were detected and mapped at regional scale using PALSAR ScanSAR data. The major geological structure directions of the BRSZ were N–S, NNE–SSW, NE–SW and NW–SE, which derived from directional filtering analysis to PALSAR fine and polarimetric data. The pervasive array of N–S faults in the Central Gold Belt and surrounding terrain is mainly linked to the N–S trending of the Suture Zone. N–S striking lineaments are often cut by younger NE–SW and NW–SE‐trending lineaments. Gold mineralized trend lineaments are associated with the intersection of N–S, NE–SW, NNW–SSE and ESE–WNW faults and curvilinear features in shearing and alteration zones. Compressional tectonic structures such as the NW–SE trending thrust, ENE–WSW oriented faults in mylonite and phyllite, recumbent folds and asymmetric anticlines in argillite are high potential zones for gold prospecting in the Central Gold Belt. Three generations of folding events in Peninsular Malaysia have been recognized from remote sensing structural interpretation. Consequently, PALSAR satellite remote sensing data is a useful tool for mapping major geological structural features and detailed structural analysis of fault systems and deformation areas with high potential for sediment‐hosted/orogenic gold deposits and polymetallic vein‐type mineralization along margins of Precambrian blocks, especially for inaccessible regions in tropical environments.     

Tectonic controls on the hydrocarbon habitats of the Barito,Kutei, and Tarakan Basins,Eastern Kalimantan,Indonesia: major dissimilarities in adjoining basins

The Barito, Kutei, and Tarakan Basins are located in the eastern half of Kalimantan (Borneo) Island, Indonesia. The basins are distinguished by their different tectonic styles during Tertiary and Pleistocene times. In the Barito Basin, the deformation is a consequence of two distinct, separate, regimes. Firstly, an initial transtensional regime during which sinistral shear resulted in the formation of a series of wrench-related rifts, and secondly, a subsequent transpressional regime involving convergent uplift, reactivating old structures and resulting in wrenching, reverse faulting and folding within the basin. Presently, NNE–SSW and E–W trending structures are concentrated in the northeastern and northern parts of the basin, respectively. In the northeastern part, the structures become increasingly imbricated towards the Meratus Mountains and involve the basement. The western and southern parts of the Barito Basin are only weakly deformed. In the Kutei Basin, the present day dominant structural trend is a series of tightly folded, NNE–SSW trending anticlines and synclines forming the Samarinda Anticlinorium which is dominant in the eastern part of the basin. Deformation is less intense offshore. Middle Miocene to Recent structural growth is suggested by depositional thinning over the structures. The western basin area is uplifted, large structures are evident in several places. The origin of the Kutei structures is still in question and proposed mechanisms include vertical diapirism, gravitational gliding, inversion through regional wrenching, detachment folds over inverted structures, and inverted delta growth-fault system. In the Tarakan Basin, the present structural grain is typified by NNE–SSW normal faults which are mostly developed in the marginal and offshore areas. These structures formed on older NW–SE trending folds and are normal to the direction of the basin sedimentary thickening suggesting that they developed contemporaneously with deposition, as growth-faults, and may be the direct result of sedimentary loading by successive deltaic deposits. Older structures were formed in the onshore basin, characterized by the N–S trending folds resulting from the collision of the Central Range terranes to the west of the basin. Hydrocarbon accumulations in the three basins are strongly controlled by their tectonic styles. In the Barito Basin, all fields are located in west-verging faulted anticlines. The history of tectonic inversion and convergent uplift of the Meratus Mountains, isostatically, have caused the generation, migration, and trapping of hydrocarbons. In the Kutei Basin, the onshore Samarinda Anticlinorium and the offshore Mahakam Foldbelt are prolific petroleum provinces, within which most Indonesian giant fields are located. In the offshore, very gentle folds also play a role as hydrocarbon traps, in association with stratigraphic entrapment. These structures have recently become primary targets for exploratory drilling. In the Tarakan Basin, the prominent NW–SE anticlines, fragmented by NE–SW growth-faults, have proved to be petroleum traps. The main producing pools are located in the downthrown blocks of the faults. Diverse tectonic styles within the producing basins of Kalimantan compel separate exploration approaches to each basin. To discover new opportunities in exploration, it is important to understand the structural evolution of neighbouring basins.     

Tectonically‐controlled Evolution of the Late Cenozoic Nihewan Basin,North China Craton: Constraints from Stratigraphy,Mineralogy, and Geochemistry

The Late Cenozoic basins in the Weihe–Shanxi Graben, North China Craton are delineated by northeast-striking faults. The faults have, since a long time, been related to the progressive uplift and northeastward expansion of the Tibetan Plateau. To show the relation between the basins and faults, two Pliocene–Pleistocene stratigraphic sections(Chengqiang and Hongyanangou) in the southern part of the Nihewan Basin at the northernmost parts of the graben are studied herein. Based on the sedimentary sequences and facies, the sections are divided into three evolutionary stages, such as alluvial fan-eolian red clay, fan delta, and fluvial, with boundaries at ~2.8 and ~1.8 Ma. Paleocurrent indicators, the composition of coarse clastics, heavy minerals, and the geochemistry of moderate–fine clastics are used to establish the temporal and spatial variations in the source areas. Based on features from the middlenorthern basin, we infer that the Nihewan Basin comprises an old NE–SW elongate geotectogene and a young NW–SE elongate subgeotectogene. The main geotectogene in the mid-north is a half-graben bounded by northeast-striking and northwest-dipping normal faults(e.g., Liulengshan Fault). This group of faults was mainly affected by the Pliocene(before ~2.8–2.6 Ma) NW–SE extension and controlled the deposition of sediments. In contrast, the subgeotectogene in the south was affected by northwest-striking normal faults(e.g., Huliuhe Fault) that were controlled by the subsequent weak NE–SW extension in the Pleistocene. The remarkable change in the sedimentary facies and provenance since ~1.8 Ma is possibly a signal of either weak or strong NE–SW extension. This result implies that the main tectonic transition ages of ~2.8–2.6 Ma and ~1.8 Ma in the Weihe–Shanxi Graben are affected by the Tibetan Plateau in Pliocene–Pleistocene.     

Sedimentation in an actively tilting half-graben: sedimentology and stratigraphy of Late Tournaisian–Viséan (Mississippian, Lower Carboniferous) carbonate rocks in south County Wexford, Ireland

The Wexford Basin (south-eastern Ireland) is a NE–SW-trending sedimentary basin containing carbonates and evaporites deposited during the Late Tournaisian and Viséan. Two separate depositional areas are defined on the basis of facies and facies associations. Sediments were deposited in inner ramp, lagoonal and peritidal environments near Rosslare, and in a more open-marine, shallow- to moderately deep-water, mid to outer ramp environment in the western area around Duncormick. Thick breccia deposits that occur in the Wexford Basin formed as a result of (i) fault movement that produced syn-sedimentary debris flows in the Late? Chadian (Breccia type I); (ii) dissolution of anhydrite/gypsum and subsequent collapse of sedimentary strata (Breccia type II); and (iii) fracturing and brecciation of porous rock caused by the movement of high temperature, late diagenetic fluids along fault planes (Breccia type III). The NE–SW facies polarity displayed by both sedimentary successions was the result of NW–SE extension and the reactivation of the NE–SW-trending Wexford Boundary Fault during the Chadian. Extension at the SE margin of the basin with downthrow to the NNW gave the basin a half-graben character. Thickening of the debris flow deposits to the SW suggests that while the half-graben was being tilted it also underwent a NE–SW block rotation due to an axial component of that normal fault.     

京津唐地区深部挤压带特征及其与地震的关系

京津唐地区的深部挤压带轴线沿宁河、香河、昌平一线呈南东—北西走向，在通过该带的北东向Ｍ和Ｃ面上均有一向北西弯曲的弧形。地壳下部和上地幔顶部层位呈透镜状增厚，浅部的北东向断裂也向北西弯曲。应力测量表明现今该带的应力场为向北西挤压。深部挤压作用是由渤海底部的扩张所产生的。该挤压带控制着地震的发生，特别其北东侧是一个强地震区     

渤海湾盆地黄骅坳陷新生代伸展量的时空分布特征*

以渤海湾盆地黄骅坳陷22条区域地震剖面的构造解释为基础,利用平衡剖面技术计算了不同位置剖面的伸展量、伸展率和伸展系数,并分析了伸展量的时空分布规律。研究表明,黄骅坳陷新生代具有幕式伸展的特点,而且伸展量的时空分布极不均匀。空间上,伸展量主要是由盆地主边界断层伸展位移造成的,主边界断层位移较大处的伸展量也相应较大;时间上,水平伸展运动可以分为始新世、渐新世和新近纪3个时期,其中,始新世伸展主要发生在盆地南部,渐新世发生在中北部,新近纪伸展量较小,主要发生在中部。伸展量时空分布是受盆地构造变形、构造演化控制的。始新世,NNE向沧东断层的伸展位移是控制盆地伸展变形的主要因素,且沧东断层在盆地南区的伸展位移量较大。渐新世,NNE向沧东断层在盆地中北区的伸展位移量相对较大,同时盆地内部NNE向基底断层的右旋走滑诱导的NE向基底正断层对盆地伸展变形做出贡献。新近纪,盆地在后裂陷的热沉降过程中NNE向基底断层仍然有右旋走滑位移,致使盆地中部发育NE向盖层正断层。     

Is the current stress state in the Central Amazonia caused by surface water loading?

We present new fault data for the region of the Manaus, Central Amazonia, Brazil. Field measurements concentrate on the Miocene–Holocene sedimentary deposits exposed on the Amazonas River Basin, in order to investigate the development of this region in this time-interval. Two faulting events are distinguished since the Miocene. The oldest one is related to NW–SE extension during Miocene times and associated with paleoseismicity, while the younger is associated with NE–SW extension direction and seems to persist today. These two deformational events may be thereby considered Neotectonic. Moreover, the second extensional pulse with NE–SW orientation can be explained by the surface hydrological loading, which induces the Central Amazonia flexural subsidence and may promote extensional stresses in the upper crust.     

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.