Pre-existing Basement Research Articles

Zircon and cassiterite geochronology of Sn-polymetallic pegmatite from the Xianghualing ore field, South China: Implications for multi-stage magmatic-hydrothermal events

The Nanling metallogenic belt (South China) is one of the largest W-Sn polymetallic provinces in the world. The ore bodies are mainly hosted in Triassic-Jurassic granitoids which formed during a complex history of magmatic evolution. Among them, the Laiziling pluton, which forms the northern part of the Xianghualing district, is an example of Sn-polymetallic deposits that underwent multiple Mesozoic episodes. In this study, the first in-situ U-Pb age dating of zircon and cassiterite minerals, trace element, and Lu-Hf isotopic data are reported for Laiziling NYF-type pegmatites. Four types of pegmatites are identified: stock-like pegmatite, vein-type pegmatite, peripheral vein-type pegmatite, and cap/sill-like pegmatite. Zircon LA-ICP-MS U-Pb geochronology of pegmatites yields an age of ~150 Ma, which is consistent with the age of the associated mineralized granitic pluton. Results of cassiterite age dating indicate that the W-Sn mineralization took place at ca. 150 Ma coeval with pegmatite emplacement. Combined with structure and trace element composition, two young ages (i.e., ~130 and 90 Ma) can be identified from pegmatite veins, suggesting that the studied zircon crystals experienced two distinct periods of magmatic-hydrothermal evolution during the Cretaceous (related to Late Yanshanian magmatism). In addition, some zircon grains are obviously enriched in LREE, which is associated with hydrothermal metasomatism. Compared to the narrow range of magmatic zircons, a wide range of inherited zircons (Proterozoic to Paleozoic) are observed in the studied Late Jurassic pegmatite (Pg1 and Pg2b), suggesting that they were incorporated from pre-existing basement rocks during magma ascent and/or emplacement. Furthermore, U-Pb data for 14 disseminated cassiterite grains yield a 206Pb/238U age of 221.5 ± 4.2 Ma, documenting evidence of cassiterite inheritance during melt ascension from country rocks or representing the initial stage of Sn enrichment. The εHf values of magmatic zircons show negative εHf values from −4.4 to −16.6 and their crustal model ages (TDM2) vary between 1328 Ma to 2200 Ma, suggesting the parent magma of the Laiziling pegmatites were derived from partial melting of older crustal components (Proterozoic basement in the Cathaysian Block of South China) and the mixing of mantle materials. This study proposes that multi-stage magmatic-hydrothermal events may have occurred not only in the Xianghualing area but also in the whole Nanling Range, and provides fresh insights into the formation processes of rare metal-bearing pegmatites in South China.

Interaction between basement inherited strike-slip structures and thrust wedge propagation in the Northern Tianshan foreland basin: insight from analogue modelling experiments

Basement inherited structures represent a significant factor affecting thrust propagation dynamics during the growth of fold-and-thrust belts. In this study inspirited from seismic data analysis of Gaoquan anticline in the Northern Tianshan foreland basin, we devised an experimental approach to investigate the structural and kinematical evolution of deformation from preexisting basement restraining bend to subsequent contractional deformation. Tested parameters included reactivation of the basement restraining bend and erosion. Results indicated that when preexisting basement restraining bend was reactivated and folded an overlying décollement, subsequent thrust nucleated preferentially at the top of the folded décollement. Erosion helped localize deformation, thereby reducing the width of the deformation zone and promoting “out-of-sequence” thrusting during compression. Finally, as we employed silicone polymer to simulate overpressured mudstone layer in the major décollement, our experiments also provide insights into a better understanding of the relationship between shallow salt-detached thrusting and deep inherited basement structures, such as in the Jura Mountains structures.

Variable controlling factors lead to contrasting patterns of volcanism in the Changbaishan volcanic area (Tianchi-Longgang), China-North Korea: Insights from morphometry and spatial-temporal analyses

The coexistence of monogenetic and polygenetic volcanoes is a common phenomenon in volcanic areas. However, the genetic relationship between monogenetic and polygenetic systems and the factors controlling their distinct eruptive styles are not well understood. In active volcanic areas, analysing the clustering and vent alignment of monogenetic volcanoes, as well as examining the geomorphology and relative ages of scoria cones, offers quantitative insights into magma supply rates, volcano type distribution, and volcanic development trends. Our study presents geomorphological and spatio-temporal analyses of the co-existing monogenetic volcanoes in the Longgang Volcanic Field (LVF) and those associated with a polygenetic volcano (Tianchi) in the Changbaishan Volcanic Area, China. The distance between the two volcanic areas is around 150 km. Monogenetic vents in the LVF exhibit greater density compared to the dispersed system associated with Tianchi. The LVF vents also show better alignment, particularly in the direction of pre-existing basement faults (NE-SW, NW-SE and EW). By using scoria cone morphometric parameters and features, we estimated the relative ages and erupted volumes of monogenetic volcanoes in the LVF and the Tianchi area. We classified the cones of the two volcanic systems into five eruptive periods and found that, despite similar magma sources and output rates over approximately 870 kyr, differing numbers of scoria cones across age classes suggest that Tianchi's magma system influences its associated monogenetic volcanic plumbing. Furthermore, the continuous rise in output rates of monogenetic volcanoes in the Tianchi area highlights the increasing magma supply sustaining Tianchi volcano. Together, these interpretations are consistent with the two systems being controlled by different factors: the Tianchi monogenetic volcanic system is more controlled by magmatism, whereas the LVF is more strongly controlled by local tectonic structures, alongside an increasing magma supply causing the formation of progressively larger individual volcanoes. In volcanic areas, analysing monogenetic volcanoes' spatial-temporal distribution, volumes and recurrence rate provides a framework to evaluate magma supply rates and tectonic associations, which are key to the development of different volcano types.

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.

Inherited extensional faults and bed-parallel slip in Mae Moh Basin, Thailand with implication for basement fabrics

The 3D seismic analysis with structural reconstruction and outcrop study in Mae Moh mine, located in the Central Sub-basin of the Mae Moh Basin, unveil multiple extensional phases and the controls of pre-existing basement fabrics on extensional faults, bed-parallel slip (BPS) and post-rift folding. The coexistence of orthogonal and oblique extensional fault systems characterizes the mine area as a result of regional E-W extension in the Middle Miocene. The dominant NNE-striking normal faults comprise easterly dipping domino-style faults with minor western dipping antithetic faults. Left-stepping en-echelon arrays of NNE-to NNW-striking normal faults at coal levels in the 3D survey follow the deeper early-rift fault that bends along strike from NNE to NW direction. Locations of intra-basin fault bends and offset of basin-bounding faults reflect E-W to ENE-WSW striking basement fabrics that potentially activate during rifting as a transfer zone across the Mae Moh Basin. The focus of rifting migrates eastward with up to 56% extension in the mine. The initial depocenter of early rift phase and the deepest economical coal seams at the center of the post-rift syncline align above the transfer zone. The presence of BPS is observed at outcrop scale, characterized by the offsetting of normal faults or fault zones with antithetic movement. BPS develops during the late rift phase under a NW-SE extension preceding the Late Miocene-Pliocene inversion.

Influence of basement high and detachment on the kinematics of a fold-and-thrust belt in the central South Yellow Sea Basin, China: Insights from analog modeling

A fold-and-thrust belt (FTB) characterized by a basement high and detachment layer was developed beneath the South Yellow Sea Basin, an important petroleum exploration target. In the central basin, magnetic anomalies have revealed the basement high developed under the Laoshan Uplift. Seismic reflection together with drilling data have revealed the Lower Silurian Gaojiabian Formation exceeding ∼500 m acting as a low-cohesion detachment layer. However, the influence of these features on regional structures and the consequent hydrocarbon preservation conditions remains unclear. This study examined the kinematic characteristics and deformation localization associated with the basement high and intermediate detachment, respectively and collectively, using four sandbox models and particle velocity analysis under the FTB framework. Model 1, the reference, used pure quartz sand without either feature. Model 2 examined the role of the intermediate detachment using glass microbeads, finding very limited effect in producing typical thin-skinned FTB. Model 3 considered the basement high, finding that it strongly constrained the deformation regime of the wedge. Model 4 examined both features and suggested combined influence on FTB deformation processes. In Model 2, with the absence of a pre-existing basement high, the intermediate detachment did not play a role in FTB deformation. In Model 3, with the absence of an intermediate detachment, deformation propagated along the surface of the basement high after reaching its edge. In Model 4, shortening propagated upward along the edge of the basement high and then into the intermediate detachment; moreover, comparable structural geometry to the prototype was produced, including both thick- and thin-skinned FTBs in nature. The results indicate that in the central South Yellow Sea Basin, structural layers between the basement high and detachment should similarly experience weak deformation; thus, good hydrocarbon preservation conditions can be expected there. This study is of significant importance to guide future petroleum exploration in the central South Yellow Sea Basin.

Formation mechanism of salt piercement structures in a compressive environment: An example from the Kuqa depression, western China

The formation mechanism of piercement structures is more complex than that of concealed piercement structures, and little research has been conducted on this topic. In this work, based on surveys of field geological outcrops and detailed interpretation of seismic data, combined with the evolution of the tectonic-sedimentary environment and stratum growth characteristics, the geometry and evolutionary history of salt piercement structures in the Kuqa Depression are investigated. Through discrete element numerical simulation experiments, the influences of various factors on the formation and evolution of the piercement structure are discussed. The results show that the piercement structures in the Kuqa Depression are mainly developed in the northern margin of the Wensu paleohigh, the Quele passive salt diapir, and at the top of the Kelasu basement fault. The salt can directly pierce the overlying strata or contact the surrounding rock through faulting. The characteristics of the growth strata reveal that the Kelasu piercement structure formed first, followed by the Wenshu piercement structure, and the Quele piercement structure formed later. The evolution of the piercement structure can be divided into three stages: quiet, weak compression and strong compression. Relying solely on tectonic compressive stress, it is difficult for salt layer to form piercement structures. The most advantageous location for the development of the piercement structure in a compressive environment is in the margin of the paleohighs and low bulges and at the top of early passive salt diapirs and preexisting basement faults. The front of the sedimentary wedges is also a preferential location for the development of piercement structures. The barrier of the paleo-high, reactivation of the preexisting basement fault, priority activation of the early passive salt dome, and progradation of the sedimentary wedge from the orogenic belt to the basin interior are favorable factors inducing piercement structure formation. An important mechanism for controlling salt piercement is to promote strong thrusting in suprasalt strata, which provides a channel for salt upwelling.

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.

Characteristics and genetic mechanism of the Mesoproterozoic rift system, Ordos Basin, China

The Mesoproterozoic rifts are developed in the Ordos Basin located in the western margin of the North China Plate. Based on the latest 3D seismic data and previous research results, this study intends to discuss the zonal differential deformation characteristics and genetic mechanism of the Mesoproterozoic rifts in the Ordos Basin. NE-trending rifts are developed in the Mesoproterozoic in the south-central Ordos Basin, the main part of which are located near the western margin of the North China Plate. NNW-trending rifts are developed in the north of the basin, while NW-NNW rifts in the Mesoproterozoic in Hangjinqi area. The genetic mechanism of the Mesoproterozoic rifts is related to regional extensional stress field, plate boundary conditions and internal preexisting structures. The main extensional stress direction strikes NWW-SSE (120°) in the western margin of the North China Plate, based on the forward rift trend of the northern Mesoproterozoic. In Hangjinqi area, the reactivation of the existing NW-trending Wulansu fault and NW-NW-trending Daolao fault, results in dextral shear stress field. The boundary between the western margin of the North China Plate and its adjacent plates forms a nearly NS-trending preexisting basement tectonic belt, which intersects with the NWW-SSE (120°) extensional stress at an acute angle of 60°. Therefore, the western margin of the North China Plate is formed by oblique normal faults under oblique extension. Due to the long time span of Columbia Supercontinent breakup (1.8–1.6 Ga), the oblique rift in the south-central Ordos Basin is formed under the continuous oblique extension at the western margin of the North China Plate.

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.

Multiphase faults activation in the southwest Huizhou Sag, Pearl River Mouth basin: Insights from 3D seismic data

The southwest Huizhou Sag is located in the Zhu I depression in the northern part of Pearl River Mouth Basin, which is influenced by the pre-existing basement fabrics and multiphase rifting, and has complex fault patterns in the Cenozoic. Using 3D seismic data of the southwest Huizhou Sag, we used seismic interpretation, fault pattern analysis from isochron maps, detailed fault throw analysis and structural evolution section analysis to constrain the initial formation timing, active periods and genesis of different striking normal faults, and the influence of basement faults on Cenozoic faults and the evolution progress of the sag was discussed, which significantly improve our understanding on the tectonic evolution of the northern Pearl River Mouth Basin. There are four groups of faults developed in the southwest Huizhou Sag, consisting of NE-SW, ENE-WSW, E-W and WNW-ESE striking, and the boundary faults of the subsag are mostly curved. Selective reactivation of ENE-WSW and WNW-ESW striking basement faults controlled the evolution of fault system during the Cenozoic. The southwest Huizhou Sag experienced multiple phases of extension, and the extension direction rotated clockwise from NW-SE to NNE-SSW. During the Early Eocene (Rift Ia), a large number of NE-SW striking faults were formed, accompanied by reactivation of ENE-WSW and WNW-ESW striking basement faults. These group of faults continued to be active during the Middle Eocene (Rift Ib) and some ENE-WSW striking faults were newly formed. The Late Eocene to Early Oligocene (Rift II) was dominated by E-W striking faults, and the depocenter shifted to the northwestern part of the study area. The Middle-Late Oligocene to Quaternary (Post-rift) was dominated by WNW-ESE striking faults, and the depocenter was not obvious.

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.

Antecedent geological control on transgressive delta and shoreline preservation: Examples from the SE African shelf

Using a suite of ultra-high resolution geophysical tools, remote operated vehicle dives, legacy cores, and isolated grab samples, we demonstrate at a regional shelf scale, the influence of antecedent geology (basement topography, shelf gradient and submerged shoreline features) on the evolving transgressive shelf stratigraphy of a subaqueous delta. The unconsolidated uppermost delta occurs as isolated remnants scattered across the low-gradient shelf. Seismic data reveal across-shelf heterogeneity in bedrock elevation, with prominent bedrock highs and depressions and several well-preserved aeolianite palaeo-shoreline complexes at water depths of −100, −60 and − 40 m. Analysis of bathymetric and seismic data demonstrates that these pre-existing shoreline complexes exert an overarching control on the distribution patterns of i) deltaic sediments, where they abut the landward flank of the shoreline form, acting as a barrier to seaward dispersal, and ii) shoreface sediments which remain sequestered on the mid-shelf on the seaward flank of the shoreline complex, hampering the landward translation of the shoreface in step with rising sea levels. Moreover, sediment distribution/accumulation is further constrained where elevated portions of the basement topography provide little to no accommodation, and act as zones of sediment bypass, and adjacent basement depressions accommodate sediment to seaward. The gentle antecedent slope, coupled with the gentle shoreline trajectory mediated transgressive erosion directly to landward. This is reinforced where local inflections in the wave ravinement profile form due to the presence of palaeo-shoreline complexes, aiding in the ultimate preservation of these submerged delta facets in the palaeo-shoreline lee. This study shows that low antecedent gradients, and palaeo-shoreline features, lead to development of transgressive coastal profiles that are predisposed to delta overstepping. The pre-existing basement topography and palaeo-shorelines constrain the positioning and morphology of the delta. We suggest that antecedent conditioning has partitioned accommodation for delta accumulation and moderated wave ravinement associated with transgression since the Last Glacial Maximum (LGM). The geological framework has acted as a recurring primary control on the geomorphic evolution of the submarine delta and shelf.

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.

Fault reactivation in No.4 structural zone and its control on oil and gas accumulation in Nanpu sag, Bohai Bay Basin, China

Based on seismic and drilling data, the reactivation mechanism of the pre-existing basement F4 strike-slip fault in Nanpu sag and its controlling effect on hydrocarbon accumulation difference are systematically studied. By defining fault activation stages, back-stripping fault throw and physical modeling, it is found that the Nanpu No.4 structural zone formed by the Cenozoic reactivity of the F4 fault grew from south to north, with strike-slip deformation dominated in the south and extensional deformation dominated in the north. Faults in the No.4 structural zone and those in the adjacent No.2 and No.3 structural zones were different fault systems, which grew separately, contacted and connected, and finally interwove under the action of unified stress field. By constructing the identification chart of deformation mechanisms of reactivation of pre-existing faults, it is concluded that during the sedimentary period of the Paleogene Shahejie Formation, F4 fault was reactivated by strike-slip faulting, and during the sedimentary period of Paleogene Dongying Formation and Neogene Guantao–Minghuazhen formations, it was reactivated by oblique extension. The controlling effects of Cenozoic reactivation of F4 fault on hydrocarbon accumulation include: (1) As the oil-source fault, it controlled the vertical cross-layer migration of oil and gas. (2) It gave rise to strike-slip transfer zone to control the distribution of sand bodies. (3) It grew upward and interacted with faults in the neighboring area, controlling the formation of two types of traps, and was favorable for oil and gas accumulation.

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.

Stratigraphy and depositional evolution of the terminal Ediacaran platform in the central to northern Sichuan Basin, Southwest China

The upper Ediacaran Dengying Formation in the Sichuan Basin provides well-preserved sedimentary records for investigating Precambrian microbialites and platform evolution. However, as previous studies have mainly focused on the broad platform-basin architecture, the depositional evolution of the platform has not been fully illuminated in the central to northern Sichuan Basin, where an intraplatform rift trough developed. Therefore, based on drilling wells and outcrops in the area, 20 lithofacies were identified and grouped into eight lithofacies associations indicating peritidal flat, shallow subtidal flat, lagoon, mixed tidal flat, slope, basin, coast and shallow sea environments. Moreover, two transgressive-regressive depositional cycles (Cycle 1 and Cycle 2) were recognized based on the five shallowing-upward (types A–E) and three deepening-upward (types F–H) cycle types. A ramp-like epeiric platform with a gentle slope developed in Cycle 1. The platform is dominated by shallow subtidal grainstones and peritidal microbialites, and the trough is in a slope environment without deep-water basin facies. In the transgression of Cycle 2, a siliciclastic-dominated environment comprising the coast and shallow sea developed on the shelf. Then a rimmed carbonate platform developed in the regression of Cycle 2, with the accumulation of shoal grainstone and peritidal microbialite in the platform margin, lagoonal dolomudstone in the platform interior, and steep slope rhythmite and basinal chert in the distal rift trough. Eustatic sea-level fluctuation and climatic change controlled the lithological transitions between carbonate and siliciclastic deposits. The platform configuration change is closely related to the evolution of the rift trough, which is the result of intense differential subsidence and sedimentation rates between the trough and platform under the effect of pre-existing basement rifts and coeval growth fault activities. A detailed depositional history of the Ediacaran Dengying Formation around the intraplatform rift trough was finally obtained, providing a good template for the study of the Precambrian microbialite-dominated platform with a similar tectonic setting.