Pre-existing Basement Structures Research Articles

Structural Interactions Between Deep Mesozoic Strike‐Slip Faults and Shallow Cenozoic Contractional Folds in the Northern Tianshan Foreland Basin (NW China)

AbstractIn the rejuvenated mountain front, preexisting basement structures are often reactivated and interact with the subsequent thin‐skinned deformation. How the deep structures affect the shallower ones is key to establishing the processes and mechanisms for the foreland fold‐and‐thrust system. We presented an exceptional case study on the structural inheritance between the deep Mesozoic strike‐slip faults and the shallow Cenozoic contractional folds from the Northern Tianshan foreland basin, Northwest China, using high‐resolution 2‐D and 3‐D seismic data. Based on the interpretation of seismic data and progressive restoration, our study illustrated the NW‐trending Ai‐Ka strike‐slip faults controlled a dextral shear zone, which initiated the Gaoquan restraining bend in the basement during Jurassic. Later, these strike‐slip structures, close to the mountain front, were reactivated during the N‐S Mio‐Pliocene contraction, and folded the upper décollements that characterized the localization of thin‐skinned deformation. In contrast, in the further foreland, nonreactive strike‐slip faults controlled basal décollement pinch‐out, which localizes the thin‐skinned deformation, resulting in en échelon folds that trace the strike of the deep strike‐slip faults. The onset time of each anticline shows that the thin‐skinned deformation first extended laterally and then propagated further north, resulting in ca. 7 km shortening along the whole foreland. Moreover, the shortening rate decreased eastward from 0.90 to 1.46 mm/yr along the Gaoquan‐Kayindike structural line to 0.24–0.37 mm/yr along the Dunan structural line as the Sikeshu depression, constrained by the NW‐trending Ai‐Ka strike‐slip fault, narrowed eastward. This feature implies that the width of the depression may control the amount of displacement propagation.

New insights from conjugate transfer zones in the southern Cairo-Suez province: Implications for deformation history and mechanism

Detailed structural field mapping with the aid of high resolution satellite images were carried out to identify structural style and geometry of Middle Eocene conjugate divergent transfer zones along the southern part of Cairo-Suez Province, Egypt. Eight conjugate divergent transfer zones are recognized between the tips of oppositely-dipping main boundary faults of the mapped fault blocks. The internal geometry of the conjugate divergent transfer zones is represented by elongated fault belts of left-stepping, en echelon normal faults between the terminations of neutral or overlapped boundary faults. Also, dip polarities of the mapped en echelon faults are found to be related to the stepping of the main boundary faults. Accordingly, three main types of conjugate divergent transfer zones are identified in the present study, which are; right-stepping-, left-stepping- and hybrid-stepping-related conjugate divergent transfer zones. Structural analysis of the mapped transfer zones revealed a geometric relationship between the overstepping (Os) of the boundary faults and the total lengths (Tl) of the extended en echelon faults. In addition, the geometry of en echelon faults formed between conjugate divergent transfer zones is attributed to the reactivation of deep seated faults by dextral transtension during the Late Eocene and Oligocene-Miocene times. The interaction of the associated preexisting deep seated Riedel shears is found to have controls on sedimentation and present day architecture. The results of this work highlight the role of preexisting basement structures and boundary faults controlling the internal geometry of transfer zones. Because of the significance of transfer zones in petroleum exploration, the findings of this research provide new data that can be correlated with similar transfer zones in the subsurface and other outcrops in extensional systems.

Deciphering multi-phase inversion tectonics in the southern Dezful Embayment: insights from the Rag-e-Sefid Oilfield, SW Iran

ABSTRACT Identification of inversion tectonics and inverted structures is very important in petroleum exploration and production due to the positive or negative impacts they can exert on the hydrocarbon traps. In order to characterize the occurrence of multi-phase inversion tectonics and its effect in the Rag-e-Sefid Oilfield, located in the southern Dezful Embayment (SW Iran), this research describes the structural style and deformation history through structural and tectono-sedimentary analyses. The results obtained from the interpretation of seismic profiles and the investigation of the geometry of the sedimentary layers across the growth structures indicate that the Rag-e-Sefid anticline is created from multiple fault-propagation folds. The final shape and geometry of the Rag-e-Sefid anticline are affected by the Rag-e-Sefid and Nourooz-Hendijan-Izeh Faults activity. The deformation history in the north-western part of the Rag-e-Sefid anticline is older than the south-eastern part of it. The Rag-e-Sefid Fault set in the north-western and south-eastern parts of the Rag-e-Sefid Oilfield experienced activity at least during seven and four tectonic phases, respectively. Multiple fault-propagation folding and the fold axis rotation in the north-western part of the Rag-e-Sefid anticline controlled by the presence of several décollement surfaces and the occurrence of inversion tectonics along the pre-existing basement structures. Three-phase inversion tectonics along the Nourooz-Hendijan-Izeh Fault and the Rag-e-Sefid Fault set in the north-western part of the Rag-e-Sefid Oilfield occurred at the Late Devonian-Carboniferous (positive inversion), Permian-Early Triassic (negative inversion), and Late Cenomanian-Early Turonian (positive inversion) boundaries and modified the evolutionary history of the sedimentary basin. The inversion affected hydrocarbon trap development at the Late Cretaceous and controlled their current conditions in the southern Dezful Embayment. Based on the hydrocarbon migration in these regions from the Late Miocene to the present day, the N-S trending (Pan Africa trend) north-western part of the Rag-e-Sefid anticline has a larger share of oil and gas compared to the NW-SE trending (Zagros trend) south-eastern part. The results of this study could add data to worldwide examples of the positive impact of tectonic inversion on the hydrocarbon traps development in the foreland of a collisional orogen.

Three-dimensional anisotropic inversion and electrostratigraphic imaging of marine magnetotelluric data to understand the control of crustal deformations by pre-existing lithospheric structures in the Mexican Ridges Fold belt, Southwestern Gulf of Mexico

SUMMARY3-D imaging of the lithosphere in the Mexican Ridges fold belt is important for understanding how the crustal deformations in this basin relate to deep tectonic processes and structures inherited from extinct Jurassic seafloor spreading. Here, we use broad-band (0.0001–0.4642 Hz) marine magnetotelluric data from the basin to reconstruct the 3-D anisotropic resistivities of the lithosphere and their spatial gradients. The resistivity gradients maxima enabled independent definition of important geological boundaries (seen on collocated seismic reflection data) and estimation of crustal thickness. We found anomalous layered zones of low resistivity and high electrical anisotropy at 5–8 km depth (coinciding with the regional detachment zone in Eocene shales in 3-D seismic data) and in the upper mantle which we interpret as indicating intense deformation and/or recent magmatic influence. We also found a banded crystalline basement structure across the fossil spreading centre comprising WSW–ENE trending, 6–10 km wide, electrically resistive subvertical sheets with conductive and anisotropic borders, which merge into a basal resistive stock-like body at 15–20 km depth. These are cut or bounded by later NNW trending major faults. These WSW and NNW structural trends correlate with the previously interpreted transform and normal faults that formed during the Late Jurassic opening of the Gulf of Mexico only if rotated clockwise by 25–30°. Surprisingly, the rugged thrust-related seabed is offset at the projected positions of the steep resistive-conductive basement sheets (which also have spatially coincident high magnetic intensity and seismicity) enabling us to infer they represent magmatic intrusions facilitated by pre-existing faults. Their conductive borders spatially coincide with possibly fluid-filled vertical fracture-sets in the overlying sediments seen in seismic data which we interpret as hydrothermal fluid pathways. We infer that a magmatic body recently intruded our study area, its ascent controlled by pre-existing basement structures, and influenced the deformation of the Neogene sequences and the seafloor topography.

The Late Devonian contraction along the Precaspian Basin north margin: Transpressional range building in the intracratonic domain

The evolution of intraplate sedimentary basins located in the vicinity of an active convergent plate boundary is often controlled by the collisional dynamics of the adjacent orogen. The transfer of compression from the orogen to the platform's interior results in the formation of complex structural geometry and kinematics that often reactivate older crustal faults, focus far-field stresses and control the evolution of associated sedimentary basins. One place where this localisation can be optimally understood is the Precaspian Basin, situated at the SE periphery of the East European Craton and bordered to the east by the Uralian orogen. The Precaspian Basin and its northern margin experienced long-term extension and subsidence interrupted by several short-lived shortening episodes. To understand the impact and role of pre-existing basement structures on the geometry and kinematics of the subsequent deformation, we analysed subsurface data from the northern margin of the Precaspian Basin by the means of 3D seismic interpretation correlated with wells and structural modelling. The analysis results provide new insights into the kinematic effects of the Late Devonian contraction event. The superposition of stratigraphic units above and below the angular unconformity suggests an intra-Famennian age of the deformation event. Steeply dipping bi-verging reverse fault zones associated with variable amounts of sinistral strike-slip movement component display an arcuate geometry, trending from WSW-ENE to NW-SE. The distribution of deformation indicates that this complex kinematic pattern was driven by a NE-SW oriented contraction and transpression, where faults show the characteristics of a restraining bend area. This area is interpreted as part of a regional transcurrent fault system developed on the northern periphery of the Precaspian Basin. Furthermore, the study results suggest that intralithospheric stress localisation transmitted by the Paleouralian subduction zone resulted in the reactivation of pre-existing basement structures, propagation of faults, and localized short-term exhumation of the Precaspian Basin north margin. Generated by the collision of Magnitogorsk volcanic arc with East European Craton, far-field stress transfer produced a zone of oblique deformation. These data and interpretation demonstrate that the northern margin of the Precaspian Basin is an excellent natural setting to investigate and better understand mechanisms of far-field strain localisation and reactivation of deformational structures in stable platform areas resulting in the intracratonic mountain building process.

Mid-crustal reactivation processes linked to frictional melting and deep void development during seismogenic slip: examples from the Lewisian Complex, NW Scotland

Exhumed examples of ancient fault voids formed during seismic slip at depths >10 km are well preserved in the Assynt Terrane of the Lewisian Complex, NW Scotland. They are interpreted to have formed during regional Mesoproterozoic ( c. 1.55 Ga; ‘Assyntian’) strike-slip faulting. Deformation is characterized by sinistral reactivation of pre-existing NW–SE-trending features including intrusive contacts of ( c. 2.4 Ga) mafic dykes and Paleoproterozoic ductile shear zone fabrics ( c. 1.75 Ga). Reactivation occurred at palaeodepths of 10–15 km, where frictional–viscous deformation synchronous with co-seismic frictional melting led to cycles of millimetre- to decimetre-scale cavity dilation and collapse. Although individual melt-generating slip surfaces may have become rapidly welded, faulting was able to repeatedly localize along adjacent pre-existing planar anisotropies favourably oriented for slip, leading to the creation of a mesh of foliation-parallel melt generation surfaces linked by foliation-perpendicular dilational voids. The latter features are filled by chaotic clast-supported wall rock collapse breccias, localized injected frictional melts and hydrothermal mineralization. The fills act as natural props, holding cavities open and preserving them as long-term, pipe-like fluid flow conduits. These exhumed features are likely to be typical of multi-rupture seismogenic fault systems formed by direct reactivation of pre-existing basement structures.

Transtensional tectonics during the Gondwana breakup in northeastern Brazil: Early Cretaceous paleostress inversion in the Araripe Basin

Intraplate deformation during the Mesozoic breakup of West Gondwana predominantly occurred along major ancient lithospheric discontinuities. The Precambrian Patos Shear Zone (PASZ) is an inherited lithospheric discontinuity in the interior of northeastern Brazil which is closely linked to the evolution of the Araripe Basin. In this study, unlike previous interpretations of purely extensional tectonics, we conducted stratigraphic and structural field mapping as well as paleostress reconstruction to demonstrate the role of intraplate transtensional tectonics during the Araripe Basin evolution. Limited to the north by the PASZ and associated with sinistral reactivation, a set of normal to oblique NE–SW faults constituting a transtensional horsetail structure generated the initial basin geometry. Stratigraphic records of this rift phase comprise the Jurassic to Early Cretaceous Brejo Santo, Missão Velha, and Abaiara formations. Paleostress reconstruction showed a NE–SW/subhorizontal σ1 axis, a vertical σ2 axis, and a NW–SE/subhorizontal σ3 axis, resulting in a sinistral transtensional tectonic regime, which was mainly governed by intraplate processes that reflected the opening of the Brazilian East Margin. The subsequent Aptian post-rift early phase was characterized by NE–SW reverse faults and a succession of normal to oblique normal faults striking NW–SE to WNW–ESE. This fault arrangement generated a new NW–SE transtensional basin, which controlled the Barbalha Formation and modified and partially preserved the previous NE-SW transtensional basin. Paleostress reconstruction showed a NW–SE/subhorizontal σ1 axis and NE–SW/subhorizontal σ3 axis for strike-slip faults but NE–SW extension for normal faults. This is related to a second dextral reactivation of the PASZ following propagation of intraplate stress during the opening of the Brazilian Equatorial Margin. In summary, tectonic evolution of the Araripe Basin was strongly influenced by stress propagation from the Gondwana breakup into intraplate settings, with two distinct reactivations of the PASZ pre-existing basement structures which results in a paleostress inversion during basin evolution.

Interaction of inherited structures and contractional deformation in the South Dezful Embayment: Insights from the Gachsaran oilfield, SW Iran

Identifying the timing, geometry, mechanism and multiphase reactivation of the inherited structures on the structural style of the fold-and-thrust belt is important for hydrocarbon exploration and production.In this work, we present a multidisciplinary approach including field data, seismic profiles, well data analyses, isopach maps, 2D balanced cross-sections construction, and 2D sequential restoration. Such an approach is applied to decipher the multiphase deformation of the NNE-SSW trending deep-seated Kharg-Mish Fault (KMF) that controlled the tectono-sedimentary evolution and structural style of the Gachsaran Anticline (South Dezful Embayment - SDE). Kinematic analysis of the KMF reveals two different mechanisms from normal to reverse faulting (positive inversion) since the Cenomanian. From the Late Cretaceous-Late Miocene, the sedimentary cover thickness ∼2500 m decreases along-strike of the Gachsaran Anticline towards the east, over the KMF, due to regional erosion and pinch-out.The eastern sector of the Gachsaran Anticline shows an angular and smaller wavelength fold in the levels of Asmari and Sarvak formations due to the efficient local middle décollements of the Kazhdumi and Pabdeh formations. Different amounts of shortening, 19.4% for the western and 16.7% for the eastern sector, and fore-thrust propagation developed a tear fault that accommodated differential deformation. Long-term structural evolution and strain localization in the eastern sector of the Gachsaran Anticline over the KMF produced dense fracturing. Our study suggests that mechanism and timing of deformation along the pre-existing basement structures are important in structural evolution of the sedimentary cover, oil migration and accumulation in such a hydrocarbon province.

Post-rift geomorphological evolution of a passive continental margin (Paraíba region, northeastern Brazil): Insights from river profile and drainage divide analysis

The post-rift erosional history of elevated passive continental margins (EPCMs) has been considered of low-rate tectonics across many regions worldwide. However, research in the northeastern Brazilian passive continental margin suggests variations in the post-rift tectonic styles, timing and rates. This is especially the case of the Paraíba region, where there are reports of uplift affecting Quaternary strata. However, transient fluvial features potentially developed during this event remain to be investigated. In this study, we document transient responses of a fluvial landscape promoted by variations in Quaternary tectonic uplift in the Paraíba region, where outcrops are scarce. The aim was to trace the Quaternary post-rift geomorphological evolution and the mechanisms of development of the northeastern Brazilian margin. A digital elevation model (DEM) was utilised to provide long river profiles based on the χ approach, normalized channel steepness index (ksn), and drainage divide analysis. The results indicated non-linear χ-profiles, migration of knickpoints upstream along the river profiles, and incised channels in elevated areas close to the inner margin plateau. In addition, there were cross divide differences in topographic metrics, with divide movements following a high elevation, chevron-shaped plateau. These transient fluvial features were mostly recorded over lithologies of relatively similar strength, in or near pre-existing basement structures. Thus, they were attributed to a topographic rejuvenation due to variations in tectonic uplift during the Late Quaternary. This tectonic geomorphological interpretation supports previous studies that the late development of the eastern South American EPCM was marked by a period of locally increased tectonics, potentially driven by far-field compressive stresses concentrated along main shear zones.

Relations between inherited basement fabric and fault nucleation in a continental setting: The Rio do Peixe Basin, NE Brazil

The control of normal fault growth by preexisting basement structures is still a worldwide matter of debate. The objectives of the present study are (i) to investigate where rift faults nucleate in continental-scale ductile shear zones and how these zones influence fault architecture; (ii) how subvertical basement fabric controls listric fault geometry and evolution; (iii) how long reactivation of faults lasts; and (iv) which are the implications of fault reactivation for the oil industry. We contribute to these issues by defining the 3-D relationship between preexisting ductile strike-slip shear zones, the geometry and evolution of subsequent rift-related normal faults using airborne magnetic, 2-D and 3-D seismic reflection, and structural data from the Rio do Peixe Basin, a Cretaceous intracontinental basin in northeastern Brazil. Our results indicate that Precambrian mylonitic foliation and faults share a common strike at the surface, but not a common dip, mostly because the Precambrian shear zones are planar and the reactivated faults are listric (curved). The combined magnetic anomaly and seismic reflection help understand the 3-D geometrical relation between inherited structures and Cretaceous brittle reactivation, which is not obvious from the field data. As inferred from subsurface information, the mylonitic foliation (sub-vertical dip) and shear zone boundary (ca. 60° dip, parallel to brittle faulting) are not parallel. The basin-bounding faults reactivated along ductile shear zones that separate major terranes with mechanical contrast. We conclude that the map view spatial coincidence of Precambrian ductile shear zones and main brittle faults can be deceiving. Mylonitic foliation and faults are parallel along strike but not along dip, indicating that the geometry of rift faults is not controlled by the mylonitic foliation, but by the mechanical contrast between tectonometamorphic units separated by ductile shear zones.

Intra-basement structures and their implications for rifting of the northeastern South China Sea margin

• Intra-basement structures in the northeastern South China Sea margin are imaged by reflection seismic data . • A group of intra-basement reflectors are shear zones inherited from the former Andean-type orogeny . • Offshore shear zones are similar to onshore counterparts in the footwall of extensional detachments. • Late Mesozoic orogenic collapse reactivated basement structures and changed basement rheology. The present-day passive northern South China Sea (SCS) margin has evolved from an Andean-type margin since the Late Cretaceous and subsequently undergone multiple rifting events. However, few studies focused on the role of pre-existing basement structures and their influence on the Early Cenozoic SCS rifting. This paper addresses the nature and tectonic significance of intra-basement structures in outer northeastern SCS margin, based on 2D seismic reflection, well data and onshore geological studies. We identified three subunits (SF1, SF2 and SF3) of intra-basement reflections by their seismic amplitude and geometrical characteristics. By correlating to drilling and waveform modelling results, we interpret that these subunits represent magmatic and/or metamorphic rocks, residual Mesozoic strata, and layered deformation zone in the basement, respectively. The SF3 shows various spatial contacts with the rift-related faults and has influences on rifting fillings. For faults merging downwards with SF3 shear zones, obvious syn -rift depocenters are located in their hanging walls, while faults with higher dip angles above SF3 almost kept inactive during the rifting. The SF3 extend and rise upward to the shallow level, and form a preferential zone for fault activity. In analogy to the onshore extensional structures, structures in SF3 are most likely mylonitized shear zones in the footwall of detachment faults. The interaction of SF3 with the faults produces antiformal structures in the footwall of extensional detachments, recording ductile to brittle transition of the basement. The intra-basement structures inherited from the Early Mesozoic subduction were probably reactivated with significant rheological change following the Late Cretaceous orogenic collapse.

Post-Miocene topographic rejuvenation in an elevated passive continental margin not characterized by a sharp escarpment (northern end of the Mantiqueira Range, Brazil)

A sharp escarpment lying close to the coast or more in the continental interior defines the morphology of Elevated Passive Continental Margins (EPCMs). Most studies on the dynamics and evolution of EPCMs, including numerical modeling exercises, concentrate on the geometry and evolution of escarpments located at or near a continental drainage divide. However, topographic relief varies considerably along the length of an EPCM, as one can observe in southeastern Brazil and southeastern Australia, and in some cases, the steep, wall-like escarpment may not be present. Here we investigate the post-rift geomorphic evolution in an EPCM lacking a sharp escarpment (southeastern Brazil), focusing on exploring topographic rejuvenation and links with potential controls such as the arrangement of pre-existing structures and lithological variability. We present topographic data showing a regional zone of high channel steepness and local relief extending continuously through the middle part of all seaward-dipping catchments. In this regional “belt” of high topography lies many knickpoints, and all rivers crossing it are marked by non-linear shapes in elevation-χ space. The structural data show a large number of NE-SW and NW-SE oriented brittle structures with slickensides recorded on filling materials following the orientation of pre-existing basement structures, suggesting a multiphase brittle deformation with at least two main paleostress tectonic regimes between the Miocene and Pleistocene. Our results indicate post-Miocene topographic rejuvenation and brittle deformation, probably driven by the accumulation of far-field stresses in pre-existing weakness zones. Nevertheless, the origin of the regional drainage divide and adjacent areas, located considerably upstream of the regional knickzone, must predate the topographic resurgence we infer, implying that older and more recent topographic elements coexist in the landscape. Our study demonstrates that post-rift topographic rejuvenation (and brittle deformation) in an EPCM is not necessarily linked to the formation or persistence of a “Great Escarpment”.

Pre-existing Basement Faults Controlling Deformation in the Jura Mountains Fold-and-Thrust Belt: Insights from Analogue Models

Pre-existing faults in the mechanical basement are believed to play an important role in controlling deformation of the thin-skinned Jura Mountains fold-and-thrust belt, which constitutes the northernmost extension of the European Alps. We use brittle-viscous analogue models to investigate the influence of frontal and oblique basement steps on the subsequent evolution of structures during thin-skinned shortening. Vertical offset between two rigid baseplates (simulating the mechanical basement) causes the formation of reverse faults and grabens in the overlying brittle layers that are not reactivated during subsequent thin-skinned shortening. However, baseplate steps localise deformation, causing a temporary frontward propagation of deformation in an early stage and inhibiting propagation afterwards. Downward baseplate steps induce very strong deformation localisation and foster the formation of fault-bend folds. Models featuring upward steps develop step-controlled pop-up structures with imbricated fronts and viscous ramps that shorten dynamically with progressive contraction. We find that deformation localisation increases both with higher step-throws and lower obliquity (α) of the strike of the step (e.g. frontal step α = 0°). With increasing step-throws, α = 30° and α = 45° oblique upward-steps lead to a characteristic imbrication of the brittle cover with laterally confined thrust-slices and step-parallel oblique-thrusts, which rotate up to 15° about a vertical axis over time. Step-controlled backthrusts preceding the formation of thrust-slices do not show notable rotation and hence constitute excellent indicators for the orientation of oblique upward-steps. The topographic patterns of oblique-step models resemble individual thin-skinned structures of the Internal Jura (i.e. Pontarlier and Vuache fault zones, the nappe system SE of Oyonnax and the Chasseral anticline), strongly suggesting that pre-existing NNE-SSW and NW-SE striking oblique upward-steps in the basement controlled deformation in the overlying cover. Our model results may be applied to other thin-skinned fold-and-thrust belts worldwide that formed above pre-existing basement structures.

Tectonic history related to the southern section of the Kalinjala Shear Zone, Eyre Peninsula, South Australia: And correlations with Terre Adélie Craton, Antarctica

The southern edge of the Eyre Peninsula, experienced a separation from proto-Antarctica in the Cretaceous and has been projected to extend into Terre Adélie Craton, Antarctica. The Archaean and Palaeoproterozoic rocks of the southern Eyre Peninsula, have been modified by the Kimban Orogeny (~1730–1690 Ma) with the development of the regionally extensive Kalinjala Shear Zone, which has been correlated with the Mertz Shear Zone in Antarctica. In this contribution, new structural observations associated with the granulite facies Kalinjala Shear Zone, together with other shear zones, all showing similar kinematics of dextral top-to-the-north transport will be described. The Kimban Orogeny overprints and reworks a major lithospheric boundary between the Gawler Craton and a sequence of preceding events related to the ~ 1850 Ma Cornian Orogeny. Shear zones were initiated during the early stage of the Kimban Orogeny (KD1) in a dextral simple-shear regime, transitioning into a pure-shear (KD2) dominated regime. With shortenings of > 90% in the Kalinjala Shear Zone localized into regions containing pre-existing Tourneford Metdolerite Dykes emplaced at ~ 1810 Ma into the granites of the Donington Suite (1850–1843 Ma) and a basement of 2000–1859 Ma paragneisses. Geometrical relationships reveal the operation of oblique extrusion during the Kimban Orogeny, where a coaxial component acted sub-horizontal and orthogonal to the trend of the Kalinjala Shear Zone. Regions of low-strain and a ‘pinched-in’ and inverted sequence of Mesoproterozoic metasedimentary cover, the Hutchison Supergroup, are bounded by major km-scale shear zones with steep west-dipping tectonic contacts. Post-Kimban subvertical east–west-trending joints and faults record a rifting event which can be related to a Gondwana breakup. With post-rift Neogene fault activity recording additional tectonic episodes where pre-existing basement structures exert significant control on their orientation and distribution. Palaeogeographical reconstructions between the Eyre Peninsula and the Terre Adélie Craton, based on matching basement geology and structural style, are compared and reconciled with this new information.

Macroscopic structural styles in the southeastern Anadarko Basin, southern Oklahoma

The Anadarko Basin in south-central Oklahoma contains a number of oil and gas fields located on anticlinal structures formed during the Pennsylvanian Orogeny. We use new 2-D and 3D seismic and well data to interpret the structural geometry and kinematic evolution of the Carter-Knox, Cruce, Chickasha, and Cement structures. These structures consist of tight faulted-detachment folds within the Pennsylvanian units related to slip along a detachment at the base of the Springer Shale, cored by deeper low amplitude fault-related folds within the pre-Pennsylvanian thick carbonate units which are detached at the base of the Arbuckle Group. Slip on these detachments was derived from the Wichita Uplift, which was a Precambrian-Cambrian failed rift that became inverted during the Pennsylvanian Orogeny. The trend and location of these structures was probably controlled by discontinuities related to pre-existing rift-related basement normal faults.Variations in the structural styles among the major structures are related primarily to the shortening and the influence of late-stage normal/strike-slip faulting. Changes in shortening are manifested in the increasing tightness and relief of the anticlines from the Chickasha-Cement to the Carter-Knox and Cruce structures. Some of the E-W structures were cut by Virgilian age strike-slip and associated normal faults which formed as the maximum compressive stress rotated from NE-SW to ENE-WSW during the Late Pennsylvanian. In summary, the geometry, trend, and evolution of the structures were influenced by the mechanical stratigraphy, pre-existing basement structures, and a rotation in stresses during the final stage of their formation.

The role of structural inheritance in the development of high-displacement crustal faults in the necking domain of rifted margins: The Klakk Fault Complex, Frøya High, offshore mid-Norway

The role of inherited structures during the development of normal faults in continental rifts and proximal domains of passive margins have been extensively studied. Few studies, however, have a focus on deciphering the role of inheritance in the development of high-displacement (>10 km), low-angle (<30°) normal faults in necking domains of passive margins. We integrated and interpreted potential field, 2D and 3D reflection seismic, and well data to study the role of structural inheritance in controlling the location and development of the southern part of the Klakk Fault Complex, offshore mid-Norway. The down-to-the-west Klakk Fault Complex is an N-S non-collinear fault complex that separates the Frøya High in its footwall from the Rås Basin in its hanging wall. The fault segments vary from low-angle planar to listric fault geometries in cross-section, with displacements of 17 km–34 km. These displacements led to syn-rift basement thinning of 12–14 km toward the west, which consequently, also affected the crustal wedge geometry of the necking domains. We identify three intra-acoustic-basement structures based on seismic facies and define their 3D geometry: (i) a bowl-shaped basin, (ii) a hyperbolic surface, and (iii) a domal structure. We discuss their origin and elucidate their role during later rifting. We conclude that pre-existing basement structures controlled the rift-related structures during the second rift phase (thinning), and affected the location, geometries, orientation and segmentation of the high-displacement low-angle faults in the necking domains. The results of this work offer new insights into the development of necking domains in areas where a thick continental crust (>25 km) is present during rifting.

Physical modelling of superimposed tectonic events in the Volta Redonda Basin, Southeastern Brazil

Abstract This paper presents the results of a new approach based on sandbox models to the understanding of the tectonic evolution of the Volta Redonda Basin, southeastern Brazil. Those models were designed to replicate the overlapping process of two of the four superimposed tectonic events identified in the Volta Redonda Basin: the first one, a rifting event with NW-SE extension direction that created the basin, and the subsequent E-W sinistral transcurrent tectonics. The boundary conditions for the models were set from the geological premises described in previous works, which resulted in the current conceptual geological models of the study area. The sandbox models were composed of alternating layers of colored sand, deposited on two pieces of acetate or cardboard sheets, which acted as pre-existing basement structures. Once completed, the models were cut and photographed to allow observation and interpretation of the resulting internal structures. Moreover, the interpretations maintain similarities with adopted conceptual models and permit conclusions about structures previously identified in other works. Finally, the consequent structural framework exposes the effects of structural reactivation and Basin geometry changes due to the superposition of deformational events and matches with the general structural aspects identified in field studies.

Along-strike variations in thin-skinned thrusting style controlled by pre-existing basement structure in the easternmost Jura Mountains (Northern Switzerland)

Abstract A detailed analysis of the Late Miocene Mandach Thrust, a key tectonic structure of the easternmost Jura Mountains (northern Alpine foreland), is presented providing insights into the modes of along-strike structural cover–basement interactions in a classical foreland setting. Our study builds on the construction, restoration and forward modelling of eight closely spaced cross-sections constrained by depth-migrated 2D seismics and geological maps. The results indicate predominantly thin-skinned thrust tectonics without significant inversion of underlying basement structures. However, inherited pre-thrusting normal faults exerted a strong control on the observed thrusting style, changing along-strike from a comparatively simple geometry to a complex, partly overthrust, partly reactivated normal fault. The observed variations relate to changes in the relief of the mechanical basement and the characteristics of pre-thrusting normal faults. The thrust's complexity is further increased by the local activation of secondary detachment horizons and possibly along-strike sedimentary facies changes within the thrust-faulted sedimentary sequence. The variations in thrusting style go along with subtle changes in shortening that may point towards as yet undetected transfer structures. As such, our structural analysis of the Mandach Thrust provides an improved understanding of the fault's kinematics and serves to highlight existing exploration uncertainties.

Application of volumetric seismic attributes for complex fault network characterization on the North Slope, Alaska

The deeper formations on the North Slope, Alaska presents a structurally complex geologic system. The complex system contains a number of reservoirs with large volume of hydrocarbons, many of which are fault-controlled. An ensemble of volumetric seismic attributes are computed on a large 3D seismic reflection survey to interpret different sedimentary horizons and investigate the structural complexity in a few key intervals, such as the Kekiktuk, Shublik, and Kuparuk formations. Second-order (curvature) and third-order (aberrancy) derivatives at long and short wavelengths are extracted on each of the intervals to better understand the faulting styles, geometries, and infer the multi-phase deformation history. The results from the most-positive and most-negative curvature attributes show that there are at least two types of faults in the study area, which includes WNW-trending faults and N-S and E-W oriented extensional faults. It is inferred that the WNW-oriented faults are controlled by the pre-existing basement structures, the influence of which decreases in the upsection. The extensional faults display single-tip and double-tip abutting relations with the pre-existing WNW-trending faults. The deepest Kekiktuk horizon shows the presence of mostly WNW-oriented faults, whereas the shallower Shublik and Kuparuk formations are pervasively faulted, containing both WNW and N/NNE oriented faults.

Linkage of crustal deformation between the Archaean basement and the Proterozoic cover in the Peräpohja Area, northern Fennoscandia

Reconstructed variations in stratigraphic thicknesses combined with mapped variations in fold-and-thrust belt structural styles and patterns of the entire Palaeoproterozoic Peräpohja Belt in northern Finland show that both the deposition of the 2.4–1.9 Ga supracrustal rocks and the structural evolution during the subsequent Svecofennian Orogeny (1.9–1.8 Ga) have been tightly controlled by (i) the palaeo-topography of the Archaean (>2.5 Ga) basement, and (ii) the reactivation of Archaean basement faults during the multiple stages of rifting and deposition of the supracrustals, as well as during subsequent basin inversion and fold-and-thrust belt development. Folds and thrusts in the supracrustal sequence are found to be largely detached from the underlying basement along the Petäjäskoski Detachment Zone (PDZ) that formed within a mechanically weak stratigraphic unit in the basal part of the Peräpohja Belt stratigraphy. The pattern of contractional structures is complex, but developed during one phase of simple, progressive south-vergent thrusting. Two styles of basement-cover linkage are recognised: The hard-linked style is best illustrated by the reverse Sihtuuna Fault currently defining the northern margin of the E-W to ENE-WSW trending basement horsts and the overlying anticlines, and juxtaposing the stratigraphically lowermost Peräpohja Belt rocks with higher-up stratigraphy, indicating the fault is inherited after a pre-existing basement structure. Based on the distribution and thickness variation of the Palaeoproterozoic supracrustal units, the faults bounding the basement horst were active as extensional faults during deposition. The soft-linked style relationship is evident as abrupt terminations of thrust-related elongate domes and localisation of the compressional overprint into the NW-SE trending central graben. Understanding the basement architecture and basement-cover linkages is highly significant because the majority of the known mineralizations of the belt are located along or close to the basement faults.