Structural Style Of Deformation Research Articles

The role of tectonic inheritance in the development of an Andean retroarc foreland basin system: The Acre Basin (NW Brazil)

The Andes, located on the western edge of the South American platform, corresponds to a classic example of subduction, which results in one of the most extensive mountain ranges on Earth. However, little is still understood about the area of influence of the fold-thrust belt in the deformation of the distal retroarc region to the east, close to the craton. In this context, Acre Basin is one of the least understood provinces, located in the Peruvian flat slab, a region that involves one of the greatest deformations in the Andes. Therefore, this research aims to understand the tectono-stratigraphic evolution of the Acre Basin and its relationships with the sub-Andean basins through 2D seismic lines and exploration wells. The definition and mapping of six seismic units aged between the Devonian and the Neogene, confirmed by restoration, indicated a tectonic history compatible with the main events recorded in the sub-Andean basins, marked by an intercalation between extensional rift and compressional regimes, with an important role of basement and structural inheritance in deposition and in the structural style of deformation. Seismic units representative of the Famatinian, Gondwanide, Juruá and Andean orogenies, and the Pangea breakup were identified. The current positioning of the forebulge was conditioned by a locally non-elastic mechanism of forebulge uplift related to the upper Jurassic basement high (Envira High Arch), Cenozoic reactivation of Triassic rift faults and by the uplift of intraforeland basement blocks in thick-skinned tectonics during the Miocene. Thus, in addition to placing the Acre Basin in the context of sub-Andean basins, these deposits help to understand the geodynamic mechanisms and the complexity of Andean deformation even in regions distal to the fold-thrust belt.

Pre- and post-Messinian deformational styles along the northern Nile Delta Basin in the framework of the Eastern Mediterranean tectonic evolution

The present work is focused on the structural deformation styles of the pre- and post-Messinian sequences of the Nile Delta Basin. The structural interpretations presented in this study shed critical insight about the evolution of the Nile Delta Basin through pre- and post-Messinian times, provides high reliability about its origin and development in the context of the Eastern Mediterranean tectonic history. The explanation for the seismic data covering three different gas fields (Baltim Field, Temsah Field and North Sinai Field) extend along the northern offshore portion of the Nile Delta Basin revealed significant variations in the deformational styles between the pre- and the post-Messinian sequences. The pre-Messinian rocks were mainly compressed in northwest-southeast direction creating folding-related compressional deformations which gradually decline eastward. The post-Messinian sequence exhibits differences in the deformational models between the examined fields. In Baltim field, it shows extensional features caused by the bulk northeast-southwest extensional deformation. However, in Temsah and North Sinai fields, this post-Messinian succession exposes north–south compressional deformation. These interpreted deformational directions are extremely well-matched with the regional structure configuration of the Nile Delta Basin and the eastern Mediterranean regions.

Timing of exhumation and deformation across the Taimyr fold–thrust belt: insights from apatite fission track dating and balanced cross-sections

Abstract The exhumation and shortening history associated with the Taimyr fold–thrust belt is determined using apatite fission track and balanced cross-section analysis. Eighteen samples from across northern, central and southern Taimyr are used for apatite fission track analysis. These include granite, meta-arenite and sandstone samples with stratigraphic ages ranging from the late Proterozoic to Early Cretaceous. Fission track lengths and central ages are used to model the thermal history of the region and indicate three episodes of cooling in the Early Permian, earliest Triassic and Late Triassic. The thermochronological data are integrated with two balanced regional cross-sections. The regional structural style of deformation reflects a thick-skinned thrust system with 15% shortening (minimum estimate). This is consistent with thickening during early Permian Uralian orogenesis, followed by later heating, uplift and cooling associated with Siberian Trap magmatism and/or Mesozoic transpression.

Structural geometrical analysis and simulation of decollement growth folds in piedmont Fauqi Anticline of Zagros Mountains, Iraq

Abstract This study carried out detailed structural analyses of the plane structural deformation pattern and sectional structural deformation styles of the Fauqi Anticline by the 3D seismic section with full cover collection, and carried out the kinematical simulation of the Fauqi anticlinal deep decollement coupling shallow growth folds and faults based on the fault decollement fold model and the forward balanced geological section technique. The study subsequently evaluated the differentiated petroleum enrichment mechanism of the Fauqi Anticline by utilizing the results of the structural analysis and combining the spatial-temporal relationship analysis of the source, the reservoir, and the caprock. The results showed that the differentiated plane structural deformation pattern and hierarchical sectional structural deformation style were developed by the superposed coupling of deep decollement, syntectonic sedimentation of shallow growth strata, and the compression of the south-west horizontal tectonic stress from the Zagros Mountains. It was found that the differentiated structural deformation caused the differentiated enrichment of petroleum in the Fauqi Anticline. It was also found that the horizontal slip distance of the Fauqi Anticlinal Folds reached around 3.5 km by the simulation of deep decollement coupling the movement of the shallow growth folds and the faults.

Differential Hydrocarbon Accumulation Controlled by Structural Styles along the Southern and Northern Tianshan Thrust Belt

Abstract:The Kuqa and the Southern Junggar foreland thrust belts, which lie to the southern and northern Tianshan, respectively, were formed under a strong compressional tectonic setting. Due to the differential propagation and deformation under the control of the décollement horizon, the structural deformation styles differ in the Kuqa and Southern Junggar thrust belts. Imbricated stacking is developed in the Kuqa thrust belt, forming a piggyback imbricated pattern of faulted anticline and fault‐block structural assemblage dominated by salt structures. In contrast, wedge‐shaped thrusts are developed in Southern Junggar, mainly forming vertical laminated patterns of multi‐wedge‐structure stacks strongly influenced by the décollement horizons. The different deformation patterns and structural styles of the north and south of Tian Shan control the contrasting characteristics of hydrocarbon accumulation in the foreland thrust belts of the Kuqa and the Southern Junggar thrust belts, including the variance in the hydrocarbon trap types, pathway systems and hydrocarbon‐bearing horizons. Proven by the hydrocarbon accumulation research and exploration achievements, recent exploration targets should focus on sub‐salt piggyback imbricated structural patterns in the Kuqa and the deep laminated patterns in the Southern Junggar thrust belt.

Space–time variations of stresses in the Miocene–Quaternary along the Calama–Olacapato–El Toro Fault Zone, Central Andes

We describe the temporal and spatial changes in the tectonic state of stress occurred during the Miocene–Quaternary in the trans-orogen area of the Calama–Olacapato–El Toro (COT) fault zone in the Central Andes, at about 24°S within the northern portion of the Puna Plateau. This work sheds new light on the complexity of stress pattern distribution in general, and contributes to the analysis of the relationships between tectonics and volcanism, and of the seismic hazard of the area. Field geological surveys, along with kinematic analysis and numerical inversion of ~140 new fault-slip measurements, have revealed that this portion of the COT zone, previously considered a continuous, long-lived lineament, in reality has been subjected to three different kinematic regimes: 1) a Miocene transpressional phase with the maximum principal stress (σ1) chiefly trending NNE–SSW; 2) an extensional phase that started by 9Ma, with a horizontal NW–SE-trending minimum principal stress (σ3), and 3) a left-lateral strike-slip phase with a horizontal ~E–W σ1 and ~N–S σ3 dating to the late Pliocene–Quaternary, which decreases toward the westernmost part of the studied zone, where it transitions to extension producing a N–S-trending graben structure. Hence, even if transcurrence is still active in the eastern portion of the COT, as focal mechanisms of crustal earthquakes indicate, our study demonstrates that extension is becoming the predominant structural style of deformation, at least in the western region. The major changes in the tectonic regimes are attributed to changes in the magnitude of the boundary forces due to subduction processes, whereas gravitational effect of a thickened crust might be responsible for the overall orogen-perpendicular extension.

Structural collapse of a transpressive hanging‐wall fault wedge, Charwell region of the Hope Fault, South Island, New Zealand

The northeast‐trending dextral‐reverse oblique slip Hope Fault is one of the major structures of the Marlborough Fault System and the Australia‐Pacific plate boundary zone in the South Island of New Zealand. This study presents an analysis of the structural and tectonic geomorphic development of the Hope Fault Zone in the vicinity of the Charwell River to understand the near‐surface temporal and spatial structural style of deformation and fault zone kinematics along a 10 km section of the fault. Significant fault‐related landscape units include: (1) flights of aggradation‐degradation terraces in the footwall forming an extensive piedmont; (2) fault‐dissected, sloping topography in the hanging wall containing 95% of all the faults; and (3) eroded subhorizontal piedmont terrace remnants that indicate the range front has repeatedly propagated to the southeast into the footwall block. We recognise four distinct types of fault scarps: (1) the main range‐front trace of the Hope Fault defines a releasing bend geometry, with a projected step‐over width of c. 1000 m; (2) at the foot of the range front, two thrust faults ramp over the aggradational surfaces in the footwall block; (3) in the toe of the hanging‐wall block, c. 20 normal fault scarps are mapped near‐parallel to the main Hope Fault; and (4) more than 100 late normal faults are oblique to the main Hope Fault and cut obliquely across all other faults. The overall fault pattern outlines an initial fault wedge between the thrust and early normal faults that is 5 km in length and 1 km at its widest point. A secondary wedge defined by the late normal faults is 7 km in length, 2 km at its widest, and it overprints the initial wedge. The structural/geomorphic interactions between the initial and secondary fault wedges developed in a series of at least four successive stages. These spatial and temporal changes in the structural geometry and style of deformation of the Hope Fault Zone at Charwell are interpreted to reflect the role of topographic loading in adjusting the fault zone break‐out along the range front, and is recorded by the tectonic geomorphic landforms there.

Combined thin-skinned and thick-skinned deformation in the central Andean foreland of northwestern Argentina

The Choromoro Basin, an intramontane structural depression in the foreland fold-and-thrust belt of the central Andes of northwestern Argentina, is underlain by Proterozoic–Recent sedimentary deposits, with Cretaceous–Paleogene and older rocks exposed along the margins and Neogene and Quaternary deposits exposed within it. The Cretaceous–Paleogene deposits represent part of an extensive rift system. Late Cenozoic Andean compression followed rifting and initiated the foreland basin stage of sedimentation. The Choromoro Basin developed in response to the fragmentation of the Andean foreland during the latest Cenozoic Andean orogeny. Regionally, the Choromoro Basin is located in an area dominated by a thick-skinned structural style of deformation, which is marked by high-angle, eastward-verging reverse faults rooted in a mid-crustal detachment that uplifted the basement blocks that bound the basin along its western and eastern margins. Faulting is associated with eastward-verging folds that involve the basement rocks and overlying Cretaceous–Neogene sedimentary strata. In contrast, Neogene beds in the Choromoro Basin show a thin-skinned structural style of deformation with an eastward-verging, imbricated thrust system and associated folds related to a shallow detachment located at approximately 2.5–3 km depth in the Cenozoic succession. The superposition in space and time of thick- and thin-skinned structural styles in the Choromoro Basin gives rise to a combined style of deformation. Several orogens, including the Andes, show the coeval development of thick- and thin-skinned structural styles, but they are spatially distributed in the orogen and foreland realms, respectively. In the Choromoro Basin, the thin-skinned deformation developed in an area dominated by thick-skinned deformation.

Structural evolution of the southernmost segment of the West European Variscides: the South Portuguese Zone (SW Iberia)

The South Portuguese Zone (SPZ) represents the southernmost unit of the Iberian Massif. It is mainly composed of three structural domains, from north to south, the Beja–Acebuches Ophiolitic Complex (BAOC), The Pulo do Lobo Antiform (PLA) and the Iberian Pyrite Belt (IPB).This study proposes a structural analysis of the Spanish part of the SPZ that allows us to point out two main kinds of deformation; one accommodated by early top-to-the-south and following sinistral strike-slip tectonics in the northern part of the SPZ and the other by top-to-the-south thrusting in a wide southern branch. This transition, underlining the strain partitioning, is analysed by lattice preferred orientation of quartz using the texture goniometry method. It shows that the deformation is accommodated in the PLA at low to middle temperature by basal and prismatic 〈a〉 slip. Quartz textures suggest increasing thermal conditions of deformation from thrust to strike-slip tectonics.Our work within the IPB allows us to present a sequence of deformation showing a primary south-verging ductile thrusting and coeval crustal thickening in response to the thin-skinned tectonics. The progressive deformation generated backthrusts while it turns shallower southward. These features are summarised in an interpretative cross-section of the SPZ that underlines the main structural style of deformation, the fore-mentioned southward propagating thin-skinned thrusts.

Tectonic activity in the Croatian part of the Pannonian basin

Three main stages in structural development of the SW Pannonian basin are differentiated: the onset of extensional tectonics between the Oligocene and the Early Miocene, main extensional processes in the Early and Middle Miocene and prevailing transpression in the Pliocene and Quaternary. The neotectonic phase is given special attention in this paper. Structural fabrics allow to subdivide the area into three large structural zones: corresponding to the Western, Southern and Central marginal part of the Pannonian basin in Croatia. These zones are bounded by important faults: the Periadriatic–Drava fault, the Medvednica fault zone and the southern marginal fault of the Pannonian basin. The recent displacements within the Dinarides and the Eastern Alps form the boundary conditions for active transpressional deformation in the Western marginal part of the Pannonian basin. Dextral transcurrent displacement is evident in the zone of the Periadriatic–Drava wrench fault. The formation of the new types of structures is observed, especially in zones of compression along the faults. Narrowing of the area between the Sava and Drava rivers causes structural changes in the marginal parts of the corresponding basins, i.e. in the areas close to the Slavonian Mts. Recent tectonic activity is marked by the occurrence of earthquakes which are most common in the northwestern part of Croatia. The spatial distribution of hypocentres and of seismotectonically active zones is used to reconstruct probable displacements and the structural style of deformation in depth. The earthquake sources in the vicinity of the Medvednica fault and the Periadriatic–Drava fault are given special attention.

Variable deep structure of a midcontinent fault and fold zone from seismic reflection: La Salle deformation belt, Illinois basin

Deformation within the United States midcontinent is frequently expressed as quasilinear zones of faulting and folding, such as the La Salle deformation belt, a northwest-trending series of folds cutting through the center of the Illinois basin. Seismic reflection profiles over the southern La Salle deformation belt reveal the three-dimensional structural style of deformation in the lower Paleozoic section and uppermost Precambrian(?) basement. Individual profiles and structural contour maps show for the first time that the folds of the La Salle deformation belt are underlain at depth by reverse faults that disrupt and offset intrabasement structure, offset the top of interpreted Precambrian basement, and accommodate folding of overlying Paleozoic strata. The folds do not represent development of initial dips by strata deposited over a preexisting basement high. Rather, the structures resemble subdued “Laramide-style” forced folds, in that Paleozoic stratal reflectors appear to be flexed over a fault-bounded basement uplift with the basement-cover contact folded concordantly with overlying strata. For about 40 km along strike, the dominant faults reverse their dip direction, alternating between east and west. Less well expressed antithetic or back thrusts appear to be associated with the dominant faults and could together describe a positive flower structure. The overall trend of this part of the La Salle deformation belt is disrupted by along-strike discontinuities that separate distinct fold culminations. Observations of dual vergence and along-strike discontinuities suggest an original deformation regime possibly involving limited transpression associated with distant late Paleozoic Appalachian-Ouachita mountain building. Moderate-magnitude earthquakes located west of the western flank of the La Salle deformation belt have reverse and strike-slip mechanisms at upper crustal depths, which might be reactivating deep basement faults such as observed in this study. The La Salle deformation belt is not necessarily typical of other well-known major midcontinent fault and fold zones, such as the Nemaha ridge, over which Paleozoic and younger sediments appear to simply be draped.

Tectono-stratigraphy of the North Celtic Sea Basin

Abstract The Celtic Sea, offshore southern Ireland, is underlain by several discrete rift basins, which are part of a larger set of such basins that developed marginal to the North Atlantic within the tectonic framework of Pangaean break-up and episodic opening of the North Atlantic Ocean. This paper documents the development of depositional systems within a rift basin setting by analysis of the sequence stratigraphic evolution of the North Celtic Sea Basin, the largest basin in the area, with particular emphasis on the influence of pre-existing structural fabric on that evolution. The Caledonian and Variscan orogenies each imprinted distinct structural grains on this area, and the intersection pattern of their respective tectonic trends provided the structural framework which influenced subsequent Triassic, Late Jurassic and Early Cretaceous phases of rifting. Detailed analysis of an extensive well and seismic database indicates that the mode of reactivation of pre-existing lines of structural weakness depended on the orientation of the principal extensional stress direction relative to these lineaments. Triassic and Late Jurassic northwest-southeast orientated extensional stress reactivated Caledonian lineaments as half-graben boundary faults and Variscan lineaments as accommodation zones and lateral transfer faults which offset the basin margin faults. In contrast, during the Early Cretaceous, extensional stress was orientated approximately north-south, oblique to the Caledonian trend. This resulted in transtensional pull-apart basin geometries dominated by reactivation of Variscan structures. The intrinsic relationship between plate tectonic setting, pre-existing structural fabric and the resulting structural style provides insight into the influence of tectonism on depositional system development in an evolving rift basin. During Late Jurassic and Early Cretaceous rifting, depositional system development was predominantly controlled by tectonism and partly conforms to empirically derived tectono-stratigraphic models of sequence development in non-marine rifts. Depositional environments changed from fluvial-dominant to lacustrine-dominant as each rifting episode evolved through its early to active rift stages. During post-rift subsidence, marine transgressions dominated depositional system development, overriding the influence of local tectonism. Spatially, pre-existing structural fabric and the style of structural deformation are the dominant influences on sediment input and drainage systems within the evolving rift basin. Recognition of the intrinsic structural fabric of a rift basin is one of the key factors in understanding and predicting stratigraphic distributions within this type of basin.

Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics

AbstractSeveral rock stratigraphic successions, metamorphosed and non-metamorphosed, are found to be similar and/or identical with each other across the so-called ‘Main Zagros Thrust’. Stratigraphic successions form thin allochthonous sheets carried from northeast to southwest by numerous low-angle thrust faults of either ductile to brittle-ductile type or brittle type. Similarities in lithic and faunal characteristics of the stratigraphic units and in the style of structural deformation across the ‘Main Zagros Thrust’ imply that either the suture between the Afro-Arabian and Iranian lithospheric plates is not located in the Nahavand region or, if it is, it must be buried under several thrust sheets.

Metamorphogenic Au‐W veins and regional tectonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand

Abstract Gold‐scheelite (Au‐W) vein mineralisation in the Mesozoic Haast Schist (Otago, Alpine, and Marlborough Schist belts) resulted from metamorphic dewatering and fluid channelling periodically throughout the >100 Ma tectonic history of the schist belt. The earliest metal mobilisation occurred during synmetamorphic vein formation and was both accompanied and succeeded by ductile deformation. Structural style of deformation within vein zones became progressively more brittle as mineralisation accompanied Mesozoic‐Tertiary isostatic and extension‐related uplift of the Otago Schist. Rapid tectonic uplift in the Late Cenozoic resulted in mineralisation in the narrow belt of Alpine Schist along the Alpine Fault. The wide range of structural styles of vein systems seen in the Haast Schist represents different erosion levels exposed in tectonic zones. Geothermal gradients during Otago Schist mineralisation appear to have been close to normal, whereas mineralisation in the Southern Alps took place under anoma...

Contrasts in Thermal Maturity within Terranes and across Terrane Boundaries of the Franciscan Complex, Northern California

The Franciscan subduction complex of northern California includes several tectonostratigraphic units. We have used the technique of vitrinite reflectance to document levels of thermal maturity for the Central Belt and the Yager, Coastal, and King Range terranes. Spatial variations in thermal maturity help define the thermal structure of each Franciscan terrane, and each terrane displays a different geometry of thermal structure. These differences are controlled by the style of structural deformation, the overprinting effects of deformation following metamorphism, and thermal overprinting caused by hydrothermal circulation. Anomalies along and contrasts across terrane boundaries help establish the relative timing and the structural mechanisms of terrane amalgamation. For example, localized anomalies are evident along the Eel River fault (Central-Yager boundary), and these increases in thermal maturity may be due to shear heating, hydrothermal discharge, or conductive heat transfer across the fault. Cross-c...

Shelf-Margin Deltaic Sediment Deposited on Diapir-Controlled Slope: Pleistocene of Garden Banks Area, Northwestern Gulf of Mexico: ABSTRACT

Pleistocene sediment in the Texas-Louisiana outer shelf and upper slope salt basin (including the outer West Cameron and Garden Banks offshore lease areas) can be related to glacial and interglacial events. Integration of well logs, biostratigraphic data, cores, and conventional two-and three-dimensional seismic data demonstrates that depositional patterns are inseparably linked to the timing and style of structural deformation associated with delta progradation onto a diapir-controlled slope. Sediments of the Garden Banks field (Blocks 192, 193, 236, and 237) were deposited in an upper slope salt-withdrawal basin located 15 mi (24 km) downdip of a late Pleistocene (glacial stage) shelf-margin delta complex. Reservoir sands are deltaic sediments redistributed to the slope by slumping and sediment gravity flows. Two genetically related sand-body types are recognized: (1) channelized gravity flow sequences characterized by elongate sand bodies oriented parallel with paleoslope, and (2) progradational lobes deposited adjacent to channels that offlap in a basinward direction. Sand bodies stack vertically and onlap the flanks of the salt ridge that encloses the field to the east, west, and south. The overall retrogressive vertical sequence indicates salt-ridge growth coeval with deposition of the sequence. The rapid lateral variations in reservoir sand thickness and sequence character are related to deltaic deposition in an unstable basin, where mass transport deposits are diverted or blocked by salt-controlled bathymetric highs. The complex geometry and the restricted size of salt-withdrawal basins and submarine troughs in the Garden Banks slope area contrast sharply with deep-sea fans that spread sediment across broad, unrestricted basin plains (e.g., Mississippi Canyon and Fan). In any one portion of the study area, the vertical succession of facies and structural styles indicates an evolution from (1) relatively stable slope to (2) unstable shelf margin to (3) increasingly stable (shelf) environments as fault-bounded basins filled and the shelf-margin prograded through time. This evolution controlled the distribution and geometry of Pleistocene sediments, as well as the position and character of potential reservoir intervals. Regional shifts in depocenter position created dramatic differences in sequence character and depositional history along the shelf margin. This study indicates that sand development in Pleistocene slope environments is best in structural lows along the flanks of penecontemporaneous salt features and residual shale masses. However, detai s of sedimentation history and basin evolution vary with geographic location and stratigraphic position in the basin. End_of_Article - Last_Page 1432------------