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This contribution explores the formation and evolution of hyper‐extended basins, associated with the early stage of core complex formation, controlled by low‐angle normal faults active at <30°. Based on a high‐resolution industrial 3D seismic reflection survey along the southern margin of the South China Sea (SCS) (Dangerous Grounds), we mapped and analyzed the 3D geometry of low‐angle normal fault systems and the related stratigraphy. Two main hyper‐extended basins were documented, filled by up to 6 km of sediments including pre‐ to post‐rift sequences. The observed normal faults on depth migrated seismic sections show an average dip angle of <30° and appear planar, characterized by continuous reflections with no clear steepening at depth and sole‐out on distinct decollement levels. Detailed fault surface mapping reveals the occurrence of km‐scale corrugations together with large wavelength undulation. The formation of these hyper‐extended basins is associated with polyphased syn‐rift infill during the development of the low‐angle normal faults. The first syn‐rift sequence appears as chaotic and discontinuous packages that has been dismembered and fragmented during the activity of low‐angle normal faults. The second syn‐rift package shows unexpected sedimentary wedges developing successively toward the footwall and the hangingwall. This geometry results from the interplay between the main low‐angle normal fault and antithetic faults defining a so‐called extensional fishtail. The deep structure of these basins shows nascent domes with limited evidence of magmatism. Eventually, these basins likely capture the earliest stage of core complex development in the proximal margin of the southern SCS. Key Points: Hyper‐extended basins in Dangerous Grounds (South China Sea) are controlled by normal faults formed and active at low‐angle (<30°)High‐resolution 3D mapping shows the formation of nascent continental core complexesAlternating syn‐rift wedges form from the interaction between low‐angle normal faults and antithetic faults, defining an extensional fishtail [ABSTRACT FROM AUTHOR]

We present the first sequential structural restoration with flexural backstripping of the Gulf of Mexico US‐Mexico conjugate margin salt basin. We construct four large‐scale (100s of km) balanced, sequential structural restorations to investigate spatio‐temporal patterns of subsidence, geometry of the original salt basin, feedbacks between post‐salt structural and stratigraphic evolution, paleo‐bathymetry, and crustal configurations. The restorations are based on interpretations of 2D and 3D seismic data, and include sequential sedimentary decompaction, flexural isostatic backstripping, and thermal isostatic corrections. The spatially variable crustal thinning factor is directly measured from seismic data, and lithologic parameters are determined by well penetrations. We present a model for the original salt basin and discuss evidence for and implications of a deep water salt basin setting for the GoM. Our analysis suggests a salt basin that contained ∼1–2 km thick salt in a basin 175–390 km across with ∼1 km of bathymetry after salt deposition. The base of salt is mostly smooth with <1 km of local relief in the form of normal faults that disrupt a pre‐salt sedimentary section. We find that supra‐salt extension and shortening are not balanced, with measurable extension exceeding shortening by 18–30 km on each cross‐section. Our subsidence analysis reveals anomalous subsidence totaling 1–2 km during Late Jurassic and Early Cretaceous times that may reflect dynamic topography or depth‐dependent thinning. We offer an interpretation of crustal breakup invoking pre‐salt clastic sedimentation, salt deposition in a deep water syn‐thinning basin, and post‐salt lower‐crustal exhumation. Plain Language Summary: The Gulf of Mexico is a large basin that formed over 200 million years ago due to tectonically driven extension of a supercontinent. Early in its formation it accumulated thick salt deposits. Due to that salt and the later deposition of several kilometers of sedimentary rock that conceal the deep geology, it is difficult to know exactly how extension started and progressed. This study uses new 2D and 3D seismic data that images the deep geology corresponding to that early extension. We sequentially remove each rock layer to reconstruct what the margin looked like in the Mesozoic. By systematically moving back in time we are able to reconstruct the changing geometry, deformation, and bathymetry of the Gulf of Mexico. Our results reveal periods of time when the bathymetry was influenced by unknown factors, which we posit reflects mantle forces. Key Points: We present sequential structural restorations with flexural backstripping of the post‐rift eastern GoM conjugate US‐MX margin from Mesozoic to presentWe interpret the geometry and bathymetry of the restored Mesozoic salt basinOur analysis indicates significant and widespread Mesozoic anomalous subsidence [ABSTRACT FROM AUTHOR]

Continental extension is primarily accommodated by the evolution of normal fault networks. Rifts are shaped by complex tectonic processes and it has historically been difficult to determine the key rift controls using only observations from natural rifts. Here, we use 3D thermo‐mechanical, high‐resolution (<650 m) forward models of continental extension to investigate how fault network patterns vary as a function of key rift parameters, including extension rate, the magnitude of strain weakening, and the distribution and magnitude of initial crustal damage. We quantitatively compare modeled fault networks with observations of fault patterns in natural rifts, finding key similarities in their along‐strike variability and scaling distributions. We show that fault‐accommodated strain summed across the entire 180 × 180 km study area increases linearly with time. We find that large faults do not abide by power‐law scaling as they are limited by an upper finite characteristic, ω0. Fault weakening, and the spatial distribution of initial plastic strain blocks, exert a key control on fault characteristics. We show that off‐fault (i.e., non‐fault extracted) deformation accounts for 25%–45% of the total extensional strain, depending on the rift parameters. As fault population statistics produce distinct characteristics for our investigated rift parameters, further numerical and observational data may enable the future reconstruction of key rifting parameters through observational data alone. Key Points: Numerical models are qualitatively and quantitatively comparable to observational fault networksThe scaling distribution of fault strain is not entirely power‐law as there is a characteristic upper‐bound limitOff‐fault (i.e., non‐extracted) deformation is significant in all models, accommodating from 25% to 45% of extension depending on rift parameters [ABSTRACT FROM AUTHOR]

The factors that control the spatial variation of the topological characteristics of normal fault networks at the rift‐scale are poorly understood. Here, we use 3D seismic reflection data from the northern North Sea to investigate the spatial variation of the geometry, topology, and strain heterogeneity of the Late Jurassic normal fault network along the rift margin. Our results show that fault orientation varies spatially along the rift margin. Normal faults within fault blocks that are adjacent to the North Viking Graben exhibits dominant N‐S and NE‐SW strikes that are sub‐parallel to the graben axis and associated step‐over, whereas in fault blocks farther from the graben, there is a dominant NW‐SE strike. Furthermore, we identify two broad topological domains within the fault network: (a) dominated by isolated nodes, partially connected branches, and low fault connectivity, and (b) dominated by abutting nodes, fully connected branches, and moderate to high fault connectivity. These topological domains correlate with previous sub‐division of the rift margin in the northern North Sea into platform and sub‐platform structural domains, respectively. There is also a positive correlation between the spatial variability of the fault orientations and intensity, with the fault network connectivity, highlighting the relationship between normal fault geometry and topology. We conclude that the across and along‐strike variation in strain, presence of pre‐existing structures, and accommodation zone‐related deformation are key factors influencing the spatial variation of fault network properties at the rift scale. Key Points: The relative amount of strain, pre‐existing structures and rift accommodation zones influence the spatial variation of fault network topology at the rift‐scaleThe connectivity of normal fault network is largely dependent on the fault network geometry, that is, the combination of the orientation and intensity of the faultsTopological analysis of rift fault network provides a new, but complimentary way to characterize and distinguish large‐scale structural domains in rift systems [ABSTRACT FROM AUTHOR]

Previous models of strike‐slip basins do not consider the rotation of the basin itself; however, we show that the Tanakura transtensional basin in Japan was rotated and propose that this basin rotation was related to rifting caused by back‐arc spreading. The Tanakura Basin was formed by displacement along the Tanakura Fault Zone, one of the major active transform faults during the opening of the Sea of Japan. We carried out paleomagnetic analyses and U–Pb dating of the Neogene Tanakura Basin fill rocks. We present a revised, high‐precision stratigraphic record for the Neogene Tanakura Basin fill sequence shows that vertical‐axis counter‐clockwise rotation occurred between ∼17.2 and ∼16.6 Ma. Comparison with paleomagnetic data from adjacent areas shows that rotation was restricted to the basin. In addition, the timing of basin rotation corresponds to the rifting phase of the Tanakura Basin, suggesting that rapid basin subsidence owing to rifting and rapid basin rotation owing to strike‐slip faulting occurred simultaneously. The Tanakura Basin has the characteristics of both rift and transtensional basins that have experienced rotation. This study reveals the detailed relationships between the development and rotation of the Tanakura Basin: rifting‐related subsidence accompanied by basin rotation. Rifting owing to back‐arc spreading may have been accompanied by tectonic basin rotation in Northeast Japan, leading to variations in the magnitude and age of rotation, as the rifting occurred at different times in different locations. Key Points: We demonstrate the vertical‐axis rotation of blocks in the strike‐slip Tanakura transtensional basin, JapanBasin rotation coincided with basin riftingRifting owing to back‐arc spreading may have been accompanied by tectonic basin rotation in Northeast Japan [ABSTRACT FROM AUTHOR]

Tectonic quiescence is a period of nearly null relative plate motion. During the Atlantic Ocean opening, rifting cut across continental segments of supercontinent Pangea that had been through different periods of quiescence, which varied from tens to hundreds of Myr. Using numerical models, we explored the effects of quiescence between orogeny and rifting on the pre‐rift lithosphere and subsequent conjugate rifted margin configuration. Our model results showed that quiescence of ∼30–60 Myr caused wide orogenic wedges (>300 km) to be heated beneath their centers, which led to the breakup of the lithospheric mantle before the breakup of the continental crust during rifting, resulting in hyperextended conjugate rifted margins. In these scenarios, continental lithosphere breakup away from the suture contributed to the preservation of previously subducted lower crust along the subduction zone. Long periods of tectonic quiescence (∼100 Myr) experienced by a wide orogen permitted efficient orogenic collapse and lateral spreading, with pronounced lithospheric thermal weakening. Consequently, post‐quiescence rifting reactivated the suture and effectively drove plate eduction, exhuming most of the subducted continental lower crust and mantle lithosphere. Ultimately, ultra‐wide domains developed into asymmetric conjugate margins. Contrastingly, in narrow orogenic wedges (<200 km), different quiescence durations had minor effects on the margin architecture. In these cases, a longer quiescence time contributed to a larger preservation of subducted crust in the fossil subduction zone after rifting. Our models agree with conjugate rifted margins in the North and South Atlantic, which probably developed after the collapse of wide orogens and subsequent periods of tectonic quiescence. Key Points: Tectonic quiescence duration controls the pre‐rift lithospheric thermal structureTectonic quiescence duration and orogen size control rifted margins architecturePreservation of crust in the fossil subduction zone after rifting is controlled by quiescence time [ABSTRACT FROM AUTHOR]

Located on the Hellenic Arc, the Christiana‐Santorini‐Kolumbo (CSK) rift zone represents one of the most active and hazardous volcano‐tectonic systems in the Mediterranean. Although this rift zone has been intensively studied, its tectonic evolution and the interplay of volcanism and tectonism are still poorly understood. In this study, we use high‐resolution reflection seismic imagery to reconstruct the opening of the rift basins. For the first time, we relate the activity of individual faults with the activity of specific volcanic centers in space and time. Our analysis shows a pre‐volcanic NNE‐SSW‐oriented paleo basin underneath the CSK volcanoes, representing a transfer zone between Pliocene ESE‐WNW‐oriented basins, which was overprinted by a NE‐SW‐oriented tectonic regime hosting Late Pliocene volcanism that initiated at the Christiana Volcano. All subsequent volcanoes evolved parallel to this trend. Two major Pleistocene tectonic pulses preceded fundamental changes in the volcanism of the CSK rift including the occurrence of widespread small‐scale volcanic centers followed by focusing of activity at Santorini with increasing explosivity. The observed correlation between changes in the tectonic system and the magmatism of the CSK volcanoes suggests a deep‐seated tectonic control of the volcanic plumbing system. In turn, our analysis reveals the absence of large‐scale faults in basin segments affected by volcanism indicating a secondary feedback mechanism on the tectonic system. A comparison with the evolution of the neighboring Kos‐Nisyros‐Yali volcanic field zone and Rhodos highlights concurrent regional volcano‐tectonic changes, suggesting a potential arc‐wide scale of the observed volcano‐tectonic interplay. Plain Language Summary: How do regional tectonic movements and large volcanoes interact? Seismological studies indicate complex volcano‐tectonic feedback links, but, so far, information on the long‐term interactions between tectonics and volcanism is rarely available. The Christiana‐Santorini‐Kolumbo (CSK) rift zone lies in the Aegean Sea and is notorious for its devastating volcanic eruptions, earthquakes, and tsunamis. This region offers the opportunity to study volcano‐tectonic interactions over several million years. In this study, we use high‐resolution seismic imagery to reconstruct the evolution of the rift basins and the CSK volcanoes. We find that all volcanoes lie in a Pliocene transfer zone connecting extensional basins. Volcanism initiated as this older tectonic regime was intersected by a NE‐SW‐directed fault system. Subsequently, all volcanoes evolved parallel to this trend. Several distinct tectonic reorganizations occurred in the Pleistocene, which had a pronounced influence on the CSK volcanoes. In turn, our analysis indicates that the emergence of volcanism also impacted the tectonic evolution of the rift system hindering the evolution of large‐scale normal faults in the volcanic basins. The observed tectonic reorganizations seem to reflect major changes in the stress regime of the Hellenic Arc, potentially also affecting adjacent volcanic centers whose volcano‐tectonic evolution is only poorly constrained so far. Key Points: We reconstruct the volcano‐tectonic evolution of the Christiana‐Santorini‐Kolumbo rift zone using multichannel seismic dataThe overprint of a Pleistocene NE‐SW striking fault system on a Pliocene E‐W oriented system initiated the emergence of volcanismRegional tectonics had a primary control on the volcanic plumbing system, while magmatism had a secondary influence on the tectonic system [ABSTRACT FROM AUTHOR]

Rift‐Rift‐Rift triple junctions are key features of emergent plate boundary networks during fragmentation of a continent. A key example of such a setting is the Afar triple junction where the African, Arabian and Somalian plates interact. We performed analog and numerical models simulating continental break‐up in a Rift‐Rift‐Rift setting to investigate the resulting structural pattern and evolution. We modified the ratio between plate velocities, and we performed single‐stage (with all plates moving at the same time) and two‐stage (where one plate first moves alone and then all the plates move simultaneously) models. Additionally, the direction of extension was changed to induce orthogonal extension in one of the three rift branches. Our models suggest that differential extension velocities in the rift branches determine the localization of the structural triple junction, which is located closer to the rift branch experiencing slower extension velocities. Furthermore, imposed velocities affect the deformation resulting in end‐member fault patterns. The effect of applying similar velocities in all rift arms is to induce a symmetric fault pattern (generating a Y‐shaped geometry). In contrast, a faster plate generates structures trending orthogonal to dominant velocity vectors, while faults associated with the movement of the slower plates remain subordinate (generating a T‐shaped pattern). Two‐stage models reveal high‐angle faults interacting at the triple junction, confirming that differential extension velocities strongly affect fault patterns. These latter models show large‐scale similarities with fault patterns observed in the Afar triple junction, providing insights into the factors controlling the structural evolution of this area. Plain Language Summary: When continents break‐up a rift valley can form and eventually grow to form an ocean. For particular conditions, more than two tectonic plates can be involved in this process. In this case, a "triple junction" is formed that consists of three rift branches. This process shaped the Afar region, where the movement of the Arabian, African, and Somalian plates, which separate at different rates of motion, created the Gulf of Aden, Red Sea, and Ethiopian rifts. The way in which triple junctions work can be difficult to study due to their large extent and several million year‐long activity. Therefore, we performed physical laboratory experiments and numerical experiments on the computer to investigate how triple junction form. We performed models with different rates of motion for the three plates, simulating one or two tectonic stages. The models show that the difference in the rate of motion between the three plates is the main control on the distribution and type of faults forming at triple junctions. Our results suggest that the fault pattern at the Afar triple junction observed nowadays may be explained by two tectonic stages and a lower extension rate occurring between the African and Somalian plates. Key Points: We perform single and two‐stage analog and numerical models of Rift‐Rift‐Rift triple junctionsModels show that differential velocity of extension between the plates is key for the geometry of fault patterns at triple junctionsTwo‐stage models shed light on the geometry and evolution of the Afar triple junction [ABSTRACT FROM AUTHOR]

Rifted margins are often associated with widespread and thick evaporite (salt) deposits and pronounced salt tectonics. The largest salt basins formed during the latest stages of rifting, immediately prior to continental breakup. Salt tectonics along these rifted margins commonly exhibit structural domains characterized by gravity‐driven updip extension, translation, downdip shortening, and salt nappe advance. The precise spatial and temporal links between these structural processes, their relative contributions and dynamics are still a topic of debate on many margins. We use 2D thermo‐mechanically coupled finite‐element modeling of lithospheric extension to investigate the evolution of salt tectonics along wide rifted margins and the interplay between rifting and post‐rift deformation. The models integrate lithospheric extension with post‐rift salt tectonics using a geodynamically self‐consistent approach where the geometries of the lithosphere and salt basins are not prescribed. They confirm that wide salt‐bearing rifted margins are characterized by gravity‐driven updip extension and downdip shortening, but also that syn‐depositional salt flow and salt stretching occurs in their distal portions prior to and during continental breakup. This produces widening of the basin and emplacement of a salt nappe over newly formed oceanic crust. Post‐rift updip extension is mostly balanced by downdip diapir shortening, all related to Couette flow. The salt nappe initiated by late syn‐rift stretching advances further by post‐rift pressure‐driven Poiseuille salt flow so that its final width is a product of both processes. The results can be directly compared to examples from various salt‐bearing rifted margins and improve our understanding of their enigmatic genesis and evolution. Plain Language Summary: Rifting of the continental lithosphere may lead to continental breakup and formation of passive margins. These margins often exhibit thick rock‐salt deposits which are deposited in hypersaline basins, and which deform in a ductile, flow‐like manner, developing highly complex tectonic structures. Salt deformation in these settings is commonly characterized by linked domains of updip extension, translation, downdip shortening and distal salt advance. However, the precise spatial and temporal links between these processes and their contribution to the overall salt flow are still a topic of debate. In this paper, we use 2D thermo‐mechanical numerical models to explore how these salt basins develop and their interplay with continental rifting. The models show that typical, wide margin salt basins are characterized by broadly balanced post‐rift updip extension and downdip shortening, but that the salt starts to deform during its deposition due to ongoing continental rifting in the distal margin. This stretches the distal salt and emplaces an allochthonous salt sheet over newly‐formed oceanic crust, which is later amplified sediment‐load‐driven salt flow. These results can be directly compared to examples from various salt‐bearing margins and improve our understanding of their enigmatic genesis and evolution. Key Points: Geodynamic numerical models of lithosphere extension and post‐rift salt tectonics quantify different types of salt flow on rifted marginsThe models show that updip extension balances largely with downdip diapir shortening, but salt nappe advance is mostly unrelated to theseSalt nappes form by late syn‐rift salt stretching and post‐rift pressure‐driven salt flow and are largely disconnected from updip extension [ABSTRACT FROM AUTHOR]

The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip, or as the locus of extension shifts toward the embryonic ocean spreading center. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre‐existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift‐related depocentre located in the southern, most proximal part of the Santos Basin, Brazil, along‐strike of a failed spreading center, the Abimael Ridge. The graben is defined by up to 3.5 km of base‐salt relief along its basinward‐bounding fault and internal base‐salt horsts that are up to 1 km high. This compartmentalizes deformation, producing intra‐graben extensional and contraction salt structures, ramp‐syncline basins, and expulsion rollovers, resulting in a remarkably different salt‐tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyze the spatial and temporal evolution of salt‐tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono‐stratigraphic development of other salt‐bearing rifted margins. Key Points: The Merluza Graben is a large rift depocentre located in the proximal part of the Santos Basin, connected to a failed spreading centerThe graben compartmentalizes salt deformation producing extensional and contraction structures, ramp‐syncline basins and rolloversRestorations and discrepancies in salt area indicate that the Merluza Graben and related sub‐salt faults were active after salt deposition [ABSTRACT FROM AUTHOR]

The Tyrrhenian back‐arc basin developed at the rear of the E‐ward migrating Apennine fold‐and‐thrust belt, with northward decreasing rollback of the subducting Adria slab leading to northward fading of back‐arc extension. The northern portion of the Tyrrhenian basin is made of thinned continental crust, whereas in the central/southern portion extension eventually evolved to oceanic crust production. In this framework, a long‐lasting debate concerns the existence of a >200 km long transform zone along the 41st parallel, which should separate the two portions of the Tyrrhenian basin. At its eastern termination, a branch of the presumed transform zone enters the Tyrrhenian margin of the Apennine belt and occurs as an accommodation zone made of a ribbon of extensional faults and related basins. This accommodation zone, which separates areas of mutually perpendicular extension directions, is here introduced, described, and named the Ponza‐Alife accommodation zone. Interpretation of seismic lines and new structural and stratigraphic data from this accommodation zone have been used to constrain the pre‐orogenic and syn‐orogenic architecture of the subducting plate and the Plio‐Quaternary back‐arc extensional stage. Our data indicate that the studied zone retraces a deep‐seated transform fault system located in the subducting plate and inherited from an Early Jurassic rifting episode, which caused the lateral juxtaposition of different rift domains in the subducting plate. We propose that during collision and trench retreat, this lateral juxtaposition has controlled differential retreat of the subducting plate across the studied zone, forcing the development of the Ponza‐Alife accommodation zone in the overlying back‐arc basin's margin. Key Points: The Ponza‐Alife accommodation zone segmenting the Apenninic margin of the Tyrrhenian back‐arc basin is introducedStructural and stratigraphic data, and seismic interpretation allowed us to unravel the evolution of this accommodation zoneThe accommodation zone originated from tearing in the downgoing plate reworking Jurassic faults that segmented the associated rift system [ABSTRACT FROM AUTHOR]

The Dom João de Castro seamount in the Hirondelle Basin (Azores) is a central volcano on the ultraslow diverging Terceira Rift axis. The combination of structural and geochemical data provides insights into the evolution of central volcanoes in oceanic rift systems above the Azores melting anomaly. The orientation of fault scarps and volcanic structures at D. João de Castro and the adjacent Castro fissure zone indicate that the regional SW‐NE extending stress field dominates the morphology of the NW Hirondelle Basin. The regional tectonic stress field controls the crustal melt pathways and leads to dike emplacement along fissure zones and the prevalent eruption of mafic lavas. The occurrence of mafic to felsic lavas at D. João de Castro gives evidence for both a deep and a shallow crustal melt reservoir generating a subordinate local stress field at the seamount. New Sr‐Nd‐Pb isotope data along with incompatible trace element ratios indicate that D. João de Castro and the Castro Ridges originated from similarly heterogeneous mantle source but did not form simultaneously. Our new model implies that central volcanoes along the Terceira Rift form by the growth of volcanic ridges and transitioned into circular edifices after magmatic systems generate local changes in the regional lithospheric stress field. The geometry of D. João de Castro and other magmatic systems along the Terceira Rift combined with the alkaline nature of the erupted lavas, and the large lithosphere thickness indicates that young oceanic rifts are more similar to continental rifts rather than mid‐ocean ridges. Plain Language Summary: Dom João de Castro seamount is a large submarine volcano located in the submarine Hirondelle Basin in the Azores archipelago. The Hirondelle Basin is formed as a result of extensional forces in the oceanic crust along the Azorean Terceira Rift that causes rifting of the Eurasian and Nubian plates. The presence of the D. João de Castro volcano and several elongated volcanic ridges inside the basin shows that the extensive magmatic activity in the Azores contributes to the opening of the basin. By quantifying the orientations of the tectonic and volcanic structures in the basin, it can be shown that the formation is controlled by a dominant SW‐NE directed extensional stress combined with extensive magmatic activity. Based on combined structural and geochemical observations, we conclude that the D. João de Castro seamount formed from the growth of elongated volcanic ridges and transitioned into a circular edifice after a magma system generates a local change in the crustal stress field. The geometry and geochemical composition of volcanic rocks from the D. João de Castro magmatic system, as well as other magmatic systems along the Terceira Rift are more similar to continental rift systems rather than oceanic spreading centers. Key Points: D. João de Castro seamount in the Terceira Rift, Azores is influenced by a SW‐NE regional transtensional and a local radiating stress fieldStructural, seismic, and geochemical data imply formation by the growth of volcanic ridges along with local stress field changesThe geometry, chemistry, and rifting rates of the Terceira Rift are more comparable to continental rifts rather than mid‐ocean ridges [ABSTRACT FROM AUTHOR]

The plate kinematics of the Iberian plate and their implications on the plate tectonic evolution of the Bay of Biscay during rifting and subsequent opening of the southern North Atlantic continue to be topics of scientific discussion and debate. Constrained by previous plate reconstruction, geophysical, and geological studies, deformable plate tectonic reconstructions of the Bay of Biscay‐Parentis rift system are created in this study using the GPlates software. These deformable plate models are used to investigate the kinematics of the Landes High, Le Danois High, and Ebro Block previously recognized as independent continental blocks within deformable regions. A comparison between results calculated via deformable plate models with previously published and newly presented gravity inversion crustal thickness estimates provided a good metric for delineating the most probable plate kinematic scenario for the Bay of Biscay‐Parentis system and investigating the effect of the plate kinematic scenarios on the present‐day structure. The preferred plate kinematic model implies a transtensional Bay of Biscay‐Parentis rift system from the Jurassic to Early Cretaceous, with the onset of significant crustal thinning initiating during the Late Jurassic (∼150 Ma) induced by the motion of the Landes High and its interplay with the Ebro Block. Aside from demonstrating the role of the Landes High and its suggested interplay with structural inheritance on the deformation experienced within the Bay of Biscay, the timing and orientation of regional stress directions, and the velocities induced by the preferred deformable model provide good comparisons with previously calculated subsidence rates. Key Points: The independent plate kinematics of the Landes High played an important role during the formation of the Bay of BiscayResults of deformable plate models suggest the Ebro Block had minimal impact on the deformation experienced within the Bay of BiscayMajor lithospheric boundaries played a significant role in shaping the present‐day crustal structure of the Bay of Biscay [ABSTRACT FROM AUTHOR]

During rifting, pre‐existing penetrative basement fabrics can affect new faults in cover rocks by a mechanism that does not appear to involve reactivation. This subtle form of inheritance can significantly impact fault network architecture in rift basins above laterally variable basement domains with geomechanical anisotropies. Here we use multi‐layer, brittle‐ductile, crustal‐scale analogue experiments to study the influence of penetrative basement anisotropies on fault patterns in the overlying cover during a single phase of orthogonal rifting. The experiments were designed to test whether basement anisotropies, oriented 45° to the extension direction, can lead to the formation of rift faults that are oblique to both the imposed extension direction and basement anisotropies. Our experiments show that a penetrative, vertically layered, mm‐wide basement anisotropy creates extension‐oblique faults in the overlying cover. We interpret this to arise when local strike‐slip kinematics along the interfaces of mechanically contrasting materials in the basement combine with the regional imposed orthogonal extension, creating a transtensional regime. The width and spacing of alternating "strong" and "weak" basement zones interact with rift kinematics, impacting the orientation, kinematics and spacing of new faults in the cover. New insights on the influence of penetrative, pre‐existing basement fabrics on localized re‐orientation of 3D strain in the cover have implications for understanding complex fault systems in rift basins and transfer zones. Key Points: Analogue models of rifting demonstrate how extension‐oblique faults in cover rocks are inherited from penetrative basement anisotropiesThe width and spacing of basement anisotropies impact the distribution, orientation, and kinematics of faults in the coverWe invoke strain re‐orientation as the mechanism for inheritance as opposed to direct reactivation of basement weaknesses [ABSTRACT FROM AUTHOR]

Tectonics inheritance controls the evolution of many orogens. To unravel the role of the Gondwanan heritage (late Paleozoic to Triassic) over the building of the Central Andes in northern Chile (Domeyko Range), we performed detrital U‐Pb zircon and 40Ar/39Ar muscovite geochronology along with structural analyses (kinematics and structural balancing). 40Ar/39Ar dating of detrital muscovite reveals contrasting cooling histories for the Paleozoic basement of Triassic rift sub‐basins, indicating that NW‐striking crustal structures segmented the Andean forearc since at least the middle Permian, likely related to an accretional fabric developed along SW Gondwana. These structures can be inferred based on scattered faults, gravimetric data, and basement age disruptions. During the Late Triassic, NS‐striking master faults and secondary NW‐ to NNW‐striking faults configured an oblique rift, primarily driven by subduction dynamics. We suggest that along SW Gondwana, the slab‐pull would have controlled the development of subduction‐related rift basins close to the trench whereas Triassic inland rifts were mainly driven by Pangea‐breakup stresses. Compressional tectonics began in the Late Cretaceous, yet the inversion of the Triassic rift would have started during the Eocene with the inception of the metallogenic‐fertile transpressional Domeyko fault system. Thus, the structural style of this range was determined by the architecture of the Triassic rift, where the inversion of deep‐seated faults accounted for west‐vergent thick‐ and thin‐skinned structures. Pre‐Andean NW‐striking structures also accommodated tectonic rotations during the Incaic orogeny (Eocene‐Oligocene) and may delimit the rupture zone of large earthquakes, suggesting an underestimated role of such ancient discontinuities in Andean neotectonics. Key Points: The synrift Domeyko Basin (Triassic) developed as an oblique rift driven by subduction and secondary far‐field Pangea‐breakup stressesDuring rift inversion, the metallogenic‐fertile Domeyko fault system nucleated over the former Domeyko Basin master rift faultsGondwanan NW‐striking structures controlled Paleozoic exhumation, synrift basin segmentation, and the main Domeyko Range structural style [ABSTRACT FROM AUTHOR]

Structures related to orogenic "collapse" may provide an important template for reactivation during later rifting. In the proximal rifted margin offshore Norway, the tectono‐sedimentary template related to collapse of the Caledonian mountain belt became widely eroded but inherited metamorphic core complexes and detachment faults evolved further in Late Paleozoic and Earliest Mesozoic time and became associated with very significant crustal thinning. The earliest rifting mode was dominated by structures that mimic the Devonian post‐Caledonian template and comprised a suite of Late Paleozoic to Early Triassic metamorphic core complexes, detachment faults, and supradetachment basins. The deep structure indicates necking of brittle over remnant ductile crust, and we document how the main decoupling level utilized by the earliest rifting structures were cut by a suite of steeper, more deeply incising set of seaward‐ and landward‐dipping Triassic faults. The latter exploited deep shear zones related to the previous intracrustal necking, enabling changes in polarity over short distances. The change from a core complex mode of extension to one involving more deeply incising faults took place prior to deposition of the Late Triassic‐Early Jurassic interrift succession and pre‐dated the main phase of lithospheric‐scale necking associated with Jurassic‐Cretaceous extension. The latter phase of large‐magnitude faulting commenced with reactivation of seaward‐dipping, deeply incised faults inherited from early rifting as well as structures related to the phase of Devonian post‐orogenic transtension. The current study demonstrates that great structural complexity and significant magnitudes of extension may be present in proximal margins, in particular those developed along collapsed orogens. Plain Language Summary: The extensional "collapse" of orogens leaves behind a structural template which becomes reused and developed further in subsequent stages of rifting. Offshore Mid‐Norway, it was the earliest phase of rifting that became most profoundly affected by this inherited structural template. A system of detachment zones and faults, similar in style but younger in age than the orogenic collapse structures, became responsible for very significant crustal thinning in what was to become the margin's proximal domain. A suite of Late Paleozoic into Early Triassic basins became associated with this stage of deformation. This early configuration became cut by more deeply rooted normal faults in the Early Triassic, prior to thermal relaxation and deposition of a Late Triassic and Early Jurassic "interrift sequence." In Late Jurassic times, a suite of seaward‐dipping large magnitude faults reactivated the more steeply dipping Triassic faults, heralding what was to become a necking of the entire crust. The significance of these observations lies in the documentation of the complex structural evolution and very significant crustal thinning that may accompany formation of the proximal parts of margins that develop on collapsed orogens. Key Points: At rifted margins that evolve on collapsed orogens, inherited structures may be profoundly reactivated during early riftingThe proximal domains of some rifted margins may be characterized by very significant amounts of crustal thinningThe evolution of proximal margins may be complex involving detachment faults, core complexes, and incising steeper faults [ABSTRACT FROM AUTHOR]

Synrift stratigraphy and the distribution of breakup‐related erosional unconformities vary vastly between passive margins and cannot be explained by classical rifting models. Here we use numerical modeling to predict their spatiotemporal distribution. We show that synrift stratigraphy mimics rift architecture, which is controlled by lithospheric strength. Basinward rift migration during extension produces (1) oceanward younging, syntectonic and posttectonic sequences, (2) rift migration unconformities, RMUs, predating breakup, and (3) a breakup unconformity, BU, that only extends over the outermost margins, since breakup is not linked with a sudden stress drop. With small synrift sedimentation, the RMUs and BU laterally merge to form a margin‐wide unconformity. In symmetric, wide conjugate margins, which arise for weak lithospheres such as the South China Sea, a long phase of distributed deformation with little subsidence results in early synrift sediment over most of the margins. RMUs merge into a single event that marks the subsequent focusing of deformation into a narrow breakup area, which experiences short‐lived intense thinning and subsidence. In asymmetric conjugate margins, lateral rift migration transports shallowly deposited, early synrift sediments from the narrow to the wide, hyperextended margin, leading to a condensed syntectonic sequence and a single BU in the narrow margin and a series of RMUs in the wide one. For very weak lower crusts, lateral rift migration generates large synrift sag basins in the wide margin, as in Angola and Congo margins. Our models resemble the observed margins tectonic diversity and may be used as templates for interpreting their distal, unexplored areas. Key Points: Synrift stratigraphy closely mimics rift architecture, which depends on lithospheric strength and hence inheritanceBasinward rift migration produces unconformities predating breakup and a breakup unconformity, BU, over the most outer marginsAsymmetric margins present condensed synrift and a single BU in the narrow margin and before breakup migrating unconformities in the wide one [ABSTRACT FROM AUTHOR]

Conflicting models of Rodinian rifting have been proposed to explain the recognized variation in the Neoproterozoic and early Cambrian tectonostratigraphic architecture of the western Laurentian margin. However, discrimination among rift models is hampered by limited exposure and metamorphism of the rocks. Southeastern Idaho preserves more than 6 km of Neoproterozoic and Cambrian strata. In contrast, along the inferred continuation of the margin in east central Idaho, correlative rocks are missing across the Lemhi arch. Our field mapping and U‐Pb dating studies, located approximately 50 km west of the Lemhi arch unconformity, focused on a succession of regionally extensive rocks that were previously assigned an Ordovician age. We show that ~1.5 km of strata here overlies a ~667 Ma reworked felsic tuff and was intruded by a 601 ± 27 Ma gabbro sill; we thus redesignate these rocks as Cryogenian and Ediacaran in age. These rocks are overlain by a ~1 km thick Ediacaran to middle Cambrian quartzite. Middle Ordovician quartzites overlie these middle Cambrian strata, indicating that though Neoproterozoic and lower Cambrian rocks are present west of the Lemhi arch, upper Cambrian and Lower Ordovician rocks are thin or absent. Comparison of this redesignated section to the closest correlative sections suggests an initial stage of symmetric rifting followed by later asymmetric rifting. We suggest that prerifting ~1,370 Ma magmatism within the Belt basin produced lithospheric rigidity that influenced the final stage of rifting and produced heterogeneity in the geometries of structural domains similar to those documented in other well‐defined, modern rift margins. Plain Language Summary: Over hundreds of millions of years, Earth's continents come together and rift apart in a process known as the supercontinent cycle. Approximately 750 Ma, a supercontinent called Rodinia began a prolonged rifting process and eventually formed a new margin to ancient North America. This ancient continental margin is inferred to run through Idaho, connecting ca. 600 Myr old rocks in southeastern and north central Idaho. However, rocks of this age were generally thought to be missing in central Idaho and thus led to disagreements on rifting processes. Our geologic mapping and isotopic dating of rocks near Bayhorse, in central Idaho, has revealed that a ~2.5 km thick package of regionally extensive rocks is actually over 150 Myr older than previously thought and was deposited during Rodinia breakup. Comparison of these newly redefined ca. 600 Myr old rocks to those in southeastern and north central Idaho supports that Rodinian rifting occurred in two stages. The first stage appears similar throughout Idaho. However, the final stage shows more erosion and magmatism in central Idaho. We propose that variations in prerifting crustal rigidity are responsible for the differences in rift geometry. This suggests that ancient rifting processes through Idaho were similar to modern rifting processes. Key Points: A revised Neoproterozoic and Cambrian age of sedimentary rocks in central Idaho is anchored by a 667 Ma tuff and a 601 Ma gabbroThese rocks record two‐stage Rodinian rifting and development of structural domains similar to those in well‐defined modern rift marginsPre‐rifting heterogeneities in lithospheric rigidity (the Belt basin) influenced the final rift geometry [ABSTRACT FROM AUTHOR]

The Afar region in East Africa represents a key location to study continental breakup. We present an integrated structural analysis of the Western Afar Margin (WAM) aiming to better understand rifted margin development and the role of plate rotation during rifting. New structural information from remote sensing, fieldwork, and earthquake data sets reveals that the N‐S striking WAM is still actively deforming and is characterized by NNW‐SSE normal faulting as well as a series of marginal grabens. Seismicity distribution analysis and the first‐ever borehole‐calibrated sections of this developing passive margin show recent slip concentrated along antithetic faults. Tectonic stress parameters derived from earthquake focal mechanisms reveal different extension directions along the WAM (82°N), in Afar (66°N) and in the Main Ethiopian Rift (108°N). Fault slip analysis along the WAM yields the same extension direction. Combined with GPS data, this shows that current tectonics in Afar is dominated by the local rotation of the Danakil Block, considered to have occurred since 11 Ma. Earlier stages of Afar development (since 31–25 Ma) were most likely related to the large‐scale rotation of the Arabian plate. Various authors have proposed scenarios for the evolution of the WAM. Any complete model should consider, among other factors, the multiphase tectonic history and antithetic fault activity of the margin. The findings of this study are not only relevant for a better understanding of the WAM but also provide insights into the role of multiphase rotational extension during rifting and passive margin formation in general. Plain Language Summary: The Earth's continents are in gradual but perpetual motion, driven by large plate tectonic forces in the Earth's deep interior. A crucial process is the stretching and breaking up of continents, initially forming localized rift or graben depressions, followed by the opening of a new ocean flanked by the margins of the newly divided continents (passive margins). Rifts and passive margins are important because of their vast resource potential (e.g., oil, gas, geothermal energy), but pose also severe risks (volcanism, earthquakes, and landslides) since they are often home to large populations. We focus on the Western Afar Margin in Ethiopia, where the African continent is currently splitting apart, providing a unique research opportunity. In the framework of an international collaborative effort, we combined satellite imagery, topography data, field observations, GPS, and earthquake measurements in order to map out the present‐day geology and tectonic activity along the margin. Our results show the complexity of tectonic plate movements: We find evidence for two phases of continental stretching in Ethiopia that both involve the rotation of tectonic plates. We also observe active faulting, which may help to assess seismic risks in the area. Our study helps to better understand passive margins worldwide. Key Points: Structural, borehole, and seismicity data from the Western Afar Margin serve to study continental breakup processes and rotational riftingAntithetic faults bounding marginal grabens are currently accommodating significant deformation along the marginCurrent extension is due to rotation of the Danakil Block; a previous oblique extension phase was likely related to Arabian plate motion [ABSTRACT FROM AUTHOR]

Preexisting crustal heterogeneities are shown to influence rift process at a variety of scales. However, our understanding of how crustal inheritance influences rift‐scale spatiotemporal kinematics of faulting in magma‐poor rift environments is still very limited. Studies of active continental rifts can provide high‐fidelity assessments of extensional processes and structures that are not possible through examination of ancient rifts that have undergone subsequent deformation events or are buried deeply beneath passive margins. We examine the influence of crustal inheritance on active rifting through balancing and restoring a series of regional cross sections across the Lake Tanganyika Rift in the Western Branch of the East African Rift System. The cross sections are produced using legacy seismic reflection data, reprocessed through prestack depth migration. This type example of a young, magma‐poor continental rift transects several different basement terranes, including an Archean/Paleoproterozoic craton, and Proterozoic mobile belts. The Lake Tanganyika Rift exhibits two classic bell‐shaped profiles of extension along strike, reaching a maximum of 7.15 km. A spatiotemporal integration of the extension data, and comparison with the various basement terranes the rift transects, reveals that extension in cratonic blocks is more widely distributed compared to mobile belt terranes, where strain rapidly localizes onto border faults by later rift stages. These results reveal how crustal inheritance exerts a fundamental control on the evolution of extension localization, ultimately impacting the geometry and structural architecture of rift basins. Key Points: The first detailed study using balanced cross sections to identify how crustal inheritance influences extension in the Lake Tanganyika RiftExtension is observed to be segmented along‐strike reaching a maximum of 7.15 kmExtension shows greater distribution across the intrarift faults in cratonic areas but is focused on border faults in mobile belts [ABSTRACT FROM AUTHOR]

We present a new model of the stress state and present‐day tectonics of the Red Sea Rift (RSR) based on an instantaneous geodynamic mantle flow model. The initial density and viscosity variations in the mantle are derived from a joint inversion of gravity, residual topography, and tomography, which provides higher resolution than existing models. The calculated mantle flow shows clear distinctions along the rift axis. The tectonics of the southern part of the Red Sea is mainly controlled by the Afar plume and characterized by divergent mantle flow. The passive rifting along the central part of the RSR can be explained either by asthenospheric upwelling due to the Red Sea floor spreading or by the plume, rising from the transition zone and not directly related to the Afar plume. We also observed ridge‐axis‐aligned flow in the uppermost mantle in the northern part of the RSR. Plain Language Summary: The Red Sea region is a highly populated area that is characterized by very active tectonics, which is responsible for earthquakes and geothermal activity. Mantle convection is one of the main driving forces that control plate tectonics at all levels. Therefore, modeling of the mantle convection can aid in understanding the origin and development of the tectonic processes in the region. The main difficulty in such modeling in the Middle East is that there exists a strong interplay of regional and global factors. To date, dynamic models for this region were based on low‐resolution global models. We present a novel dynamic model, which includes high‐resolution density and viscosity distributions as well as weak plate boundaries, which are embedded in the global convection model. Mantle flow velocities and principal stress directions were thus estimated for the lithosphere and upper mantle in the region. The resulting mantle flow patterns show a clear distinction in tectonics of three different parts of the Red Sea Valley. Furthermore, the stress orientations explain the fault structures in the Red Sea Basin. Key Points: The Afar plume acts only in the southern part of the Red Sea Rift forming two flow branches in the northern and nearly eastern directionsThe central part of the Red Sea Rift is a passive rift not directly related to the Afar plumeThe modeled stress field shows an off‐axis extension with a strike‐slip component along all segments of the Red Sea Rift [ABSTRACT FROM AUTHOR]

Prominent preexisting structural heterogeneities within the lithosphere may localize or partition deformation during tectonic events. The NE‐trending Great South Basin, offshore New Zealand, formed perpendicular to a series of underlying crustal terranes, including the dominantly granitic Median Batholith Zone, which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics. We find that the crustal‐to‐lithospheric scale southern terrane boundary of the Median Batholith Zone is associated with a crustal‐scale shear zone that was reactivated during Late Cretaceous extension between Zealandia and Australia. This reactivated terrane boundary is oriented at a high angle to the faults defining the Great South Basin. We identify a large granitic laccolith along the southern margin of the Median Batholith, expressed as subhorizontal packages of reflectivity and acoustically transparent areas on seismic reflection data. The presence of this strong granitic body inhibits the lateral southwestward propagation of NE‐trending faults, which segment into a series of splays that rotate to align along the margin as they approach. Further, we also identify two E‐W‐ and NE‐SW‐oriented basement fabrics, likely corresponding to prominent foliations, which are exploited by small‐scale faults across the basin. We show that different mechanisms of structural inheritance are able to operate simultaneously, and somewhat independently, within rift systems at different scales of observation. The presence of structural heterogeneities across all scales needs to be incorporated into our understanding of the structural evolution of complex rift systems. Key Points: We document multiple styles of structural inheritance that influence various aspects of rift physiography in the Great South Basin, New ZealandThe southern boundary of the Median Batholith Zone is reactivated as a large extensional shear zone and detachmentFaults splay, segment, and eventually terminate as they approach an area of stronger crustal material associated with a granitic body [ABSTRACT FROM AUTHOR]

New marine geophysical data acquired across the partly ice‐covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup‐related lava flows are imaged in reflection seismic data as seaward dipping reflectors, which are found to decrease in size both northward and southward from a central point at 75°N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the seaward dipping reflectors have been emplaced over a period of 2–4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post‐middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post‐40‐Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The breakup of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present‐day segmentation of the margin. The original rift basins were subsequently connected by steady‐state seafloor spreading that propagated southward, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone. Key Points: Polyphase Cenozoic volcanic rifting and consecutive emplacement of breakup‐related lava flows along the northern East Greenland marginBreakup along restricted margin segments is followed by north to south directed progressive opening of the Greenland SeaWidespread post‐middle Eocene (<40 Ma) offshore magmatism, associated with the breakup of the Jan Mayen microcontinent from East Greenland [ABSTRACT FROM AUTHOR]

Information on structure, stress, and their interrelationship is essential for understanding structurally controlled geothermal permeability. Active fault mapping, borehole image analysis, and well testing in the Te Mihi geothermal area, New Zealand, allows us to refine structural and fluid flow architecture of this resource. The Te Mihi area is structurally complex, comprising a set of NW dipping master faults containing pervasive SE dipping antithetic and splay structures in their hanging walls. These faults are also intersected by E‐W striking faults. A localized, N‐S striking structural trend is also observed at Te Mihi. In consideration with Global Navigation Satellite System velocity vectors, both active NE‐SW and E‐W striking faults create biaxial extension at Te Mihi, though the observed NE‐SW SHmax direction suggests that contemporary extension is NW‐SE dominated. Stress field perturbations coincide with structural complexities like fault splays and intersections and/or proximity to recently active E‐W and NE‐SW striking structures. Borehole fluid flow at Te Mihi is concentrated at NW dipping master fault intersections, travel time fractures on acoustic image logs, halo fractures on resistivity image logs, NE‐SW and E‐W striking fractures, intervals of high fracture density, and spatial concentrations of wide aperture fractures and recently active NE‐SW and E‐W striking fractures. This study suggests Te Mihi geothermal expression results from biaxial extension evident from active structural trend intersections and the predominance of NE‐SW and E‐W striking structures within permeable well zones. Biaxial extension is therefore an important control on crustal fluid flow within the Taupo Volcanic Zone and thus geothermal resource delineation. Key Points: Fault mapping and borehole imaging provide detail on the structure, stress, and fluid flow architecture of the Te Mihi geothermal areaData analyses reveal intersecting, active, E‐W, NE‐SW striking, normal fault trends which create a zone of biaxial extension at Te MihiRegions of biaxial extension contribute to the control of geothermal expression in the Taupo Volcanic Zone [ABSTRACT FROM AUTHOR]

Mesozoic‐Cenozoic rifting between Greenland and North America created the Labrador Sea and Baffin Bay, while leaving preserved continental lithosphere in the Davis Strait, which lies between them. Inherited crustal structures from a Palaeoproterozoic collision have been hypothesized to account for the tectonic features of this rift system. However, the role of mantle lithosphere heterogeneities in continental suturing has not been fully explored. Our study uses 3‐D numerical models to analyze the role of crustal and subcrustal heterogeneities in controlling deformation. We implement continental extension in the presence of mantle lithosphere suture zones and deformed crustal structures and present a suite of models analyzing the role of local inheritance related to the region. In particular, we investigate the respective roles of crust and mantle lithospheric scarring during an evolving stress regime in keeping with plate tectonic reconstructions of the Davis Strait. Numerical simulations, for the first time, can reproduce first‐order features that resemble the Labrador Sea, Davis Strait, Baffin Bay continental margins, and ocean basins. The positioning of a mantle lithosphere suture, hypothesized to exist from ancient orogenic activity, produces a more appropriate tectonic evolution of the region than the previously proposed crustal inheritance. Indeed, the obliquity of the continental mantle suture with respect to extension direction is shown here to be important in the preservation of the Davis Strait. Mantle lithosphere heterogeneities are often overlooked as a control of crustal‐scale deformation. Here, we highlight the subcrust as an avenue of exploration in the understanding of rift system evolution. Key Points: The role of mantle sutures during Mesozoic rifting and Cenozoic ocean basin development in Laurentia has not been studiedWe present 3‐D models that reproduce first‐order tectonics of Labrador Sea, Davis Strait, and Baffin Bay through mantle suture reactivationThe obliquity of the mantle suture to the extension preserves continental lithosphere, interpreted as the creation of the Davis Strait [ABSTRACT FROM AUTHOR]

The parallelism between older collisional belts and younger rift systems is widely known and particularly well portrayed along the Atlantic Ocean. How tectonic inherited and new‐formed shear zones control rift nucleation and the final architecture of rifted conjugate passive margins is still poorly understood. Here we present lithospheric‐scale thermo‐mechanical numerical models that self‐consistently create extensional and contractional tectonic inheritance, where prior extension and contraction are systematically varied. Our results show that (1) initial reactivation occurs along the former lithospheric suture zones; (2) upper crustal thick‐skinned basement thrusts are partially or fully reactivated depending on the amount of prior contraction and size of the orogen; (3) with a small amount of contraction, thick‐skinned thrusts are efficiently reactivated in extension and provide the template for rifted margin formation; (4) with larger amounts of contraction, thick‐skinned thrusts distal to the lithospheric suture zone do not reactivate in extension; and (5) reactivation of prior contractional shear zones dominates during the early stages of rifting, while during the final stage of margin formation new‐formed extensional shear zones dominate. Force balance analysis predicts an inverse relation between midcrustal viscosity and the maximum offset for reactivation of weak upper crustal structures. Force balance also predicts that the degree of weakening or healing of the weak suture and the thermal thinning of the necking area control at which stage suture reactivation is deactivated and extension proceeds by mantle lithosphere thermal necking. Two rifted conjugate margins with orogenic inheritance in the North and South Atlantic are used for comparison. Key Points: Offset between lithospheric and crustal scale inherited shear zones controls their reactivation upon extensionCrustal scale shear zones far from lithospheric scale shear zones (suture) are left unreactivated and preserve orogenic structureWide margin development reactivates inherited contractional structures, while narrow margin reactivates inherited extensional structures [ABSTRACT FROM AUTHOR]

The Triassic geodynamic evolution of the Pontides Belt, which geographically corresponds to northern Anatolia, is still a matter of debate. We present and interpret geological, petrographical, geochemical, and geochronological data from small, discordant, metagabbroic rocks exposed in the Tokat Massif. Field and petrographic characteristics distinguish four subgroups: (i) medium‐grained, slightly lineated, clinopyroxene‐rich metagabbros; (ii) fine‐grained, nonlineated, clinopyroxene‐rich metagabbros; (iii) medium‐grained, nonlineated, brown amphibole‐rich metagabbros; and (iv) medium‐grained, slightly lineated, brown and blue amphibole‐rich metagabbros. Magmatic kaersutites give 39Ar/40Ar plateau ages of 244.6 ± 0.5 and 243.16 ± 0.92 Ma and overlap the U‐Pb age of titanite from a clinopyroxene‐rich sample. Inherited zircons (~460, ~880, and ~2600 Ma) in fine‐grained clinopyroxene‐rich metagabbros indicate interaction with a range of crustal rocks during the intrusion. The blue amphiboles are magnesioriebeckites that formed during metamorphism or late‐stage crystallization. Geochemical data, including whole rock major and trace element concentrations, and Sr‐Nd‐Pb isotope compositions reveal that both clinopyroxene‐ and amphibole‐rich metagabbros are alkaline in composition but derived from distinct mantle sources. They are compositionally distinct from mafic igneous rocks in the contemporaneous Permo‐Triassic Karakaya Complex that is well exposed in the western part of the Pontides Belt. Considering all data, we suggest that the Pontides Belt was shaped above a south dipping subduction zone during Permo‐Triassic and the alkaline gabbros that were emplaced into crustal rocks during Early Triassic back‐arc rifting of the northern margin of Gondwana. Key Points: Geochemical data reveal that both clinopyroxene‐ and amphibole‐rich metagabbros are alkaline in compositionThere is no evidence in the gabbros of a high‐pressure metamorphic event as previously suggestedThey were emplaced into crustal rocks during Early Triassic rifting of the northern margin of Gondwana [ABSTRACT FROM AUTHOR]

During continental breakup, the locus of strain shifts from a broad region of border faulting and ductile plate stretching to a narrow zone of magma intrusion in a young ocean basin. Recent studies of volcanic rifts and margins worldwide suggest this shift occurs subaerially, before the onset of seafloor spreading. We test this hypothesis using recently acquired seismic reflection and borehole data from the Danakil Depression, Ethiopia, a unique region of transition between continental rifting and seafloor spreading. Our data, located near Dallol, ~30 km northwest of the Erta'Ale Volcanic Segment, reveal a remarkably thick (>1‐km) sequence of young (~100‐ka) evaporites in a basin bound by a major (≤400‐m‐throw), east‐dipping normal fault. To generate such a large amount of subsidence in such a relatively short time, we propose that upper‐crustal extension in Danakil is currently dominated by faulting, not magmatic intrusion. Given the region's markedly thinned crust (~15‐km‐thick), relative to elsewhere in Afar where magma‐assisted rifting dominates and maintains crustal thickness at ~25 km, mechanical extension in Danakil is likely coupled with ductile extension of the lower‐crust and mantle lithosphere. Despite proximity to the voluminous lavas of the active Erta'Ale Volcanic Segment, evidence for igneous material in the upper ~2 km of the 6‐ to 10‐km‐wide basin is limited. Late‐stage stretching was likely aided by thermal/strain‐induced lithospheric weakening following protracted magma‐assisted rifting. Basin formation immediately prior to the onset of seafloor spreading may also explain the accumulation of thick marine‐seepage‐fed evaporite sequences akin to those observed, for example, along the South Atlantic rifted margins. Key Points: New seismic reflection, and borehole data from the Danakil Depression, Ethiopia, constrains late‐stage continental breakupA thick sequence of evaporites has been deposited over tens to hundreds of thousands of years in a basin bounded by a major, E‐dipping normal faultThe onset of magmatic extension during continental rift development does not necessarily herald the onset of seafloor spreading [ABSTRACT FROM AUTHOR]

Abstract: Eastern Iberia preserves a complex succession of Mesozoic rifts partly or completely inverted during the Late Cretaceous and Cenozoic in relation with Africa‐Eurasia convergence. Notably, the Valencia Trough, classically viewed as part of the Cenozoic West Mediterranean basins, preserves in its southwestern part a thick Mesozoic succession (locally ≈10 km thick) over a highly thinned continental basement (locally only ≈3.5 km thick). This subbasin, referred to as the Columbrets Basin, represents a Late Jurassic‐Early Cretaceous hyperextended rift basin weakly overprinted by subsequent events. Its initial configuration is well preserved allowing us to unravel its 3‐D architecture and tectonostratigraphic evolution in the frame of the Mesozoic evolution of eastern Iberia. The Columbrets Basin benefits from an extensive data set combining high‐resolution seismic reflection profiles, drill holes, seismic refraction data, and expanding spread profiles. The interactions between halokinesis, involving the Upper Triassic salt, and extensional deformation controlled the architecture of the Mesozoic basin. The thick uppermost Triassic to Cretaceous succession displays a large‐scale “syncline” shape, progressively stretched and dismembered toward the basin borders. We propose that the SE border of the basin is characterized by a large extensional detachment fault acting at crustal scale and interacting locally with the Upper Triassic décollement. This extensional structure accommodates the exhumation of the continental basement and part of the crustal thinning. Eventually, our results highlight the complex interaction between extreme crustal thinning and occurrence of a prerift salt level for the deformation style and tectonostratigraphic evolution of hyperextended rift basins. [ABSTRACT FROM AUTHOR]

Abstract: Rift inheritance can play a key role in foreland basin geometry and behavior. If the foreland basin initiates soon after rifting, thermal cooling can also contribute significantly to subsidence. We investigate the effects of crustal inheritance (Aptian‐Cenomanian rifting) on the evolution of the Campanian to middle Miocene flexural Aquitaine foreland basin, northern Pyrenees, France. Surface and subsurface data define rifted crustal geometry and postrift thermal subsidence. Analysis of Bouguer gravity anomalies coupled with flexural modeling constrains the lateral variations of elastic thickness, plate flexure, and controlling loads. The Aquitaine foreland is divided along‐strike into three sectors. The relative role of surface and subsurface (i.e., buried) loading varies along‐strike, and the elastic thickness values decrease from the northeast (25 km) to the southwest (7 km) where the plate is the most stretched. The eastern foreland crust was not rifted and underwent a simple flexural subsidence in response to orogenesis. The central sector was affected by crustal stretching. Here the basin is modeled by combining topographic and buried loads, with postrift thermal subsidence. In the western sector, the foreland basin was created mainly by postrift thermal subsidence. The eastern and central sectors are separated by the Eastern Crustal Lineament, which is one of a series of inherited transverse faults that segment the orogen. [ABSTRACT FROM AUTHOR]

The Tumblagooda Sandstone in Western Australia documents Early Paleozoic rifting in East Gondwana and provides the earliest evidence for terrestrial activity of multicellular animals on Earth. We constrain the provenance of this sequence using 737 concordant U-Pb ages of detrital zircons from two stratigraphic wells in the northern Perth Basin and Southern Carnarvon Basin and outcrops of the type sections near Kalbarri. Detrital zircon age signatures are linked to infrared spectral data and stratigraphic logs. These ages span 3,312-466 Ma, including major Precambrian age peaks at 1,079-1,544 Ma, 1,695-2,403 Ma, and 2,640-2,879 Ma, consistent with igneous sources in the West Australian Craton. Significant Early Paleozoic age peaks at 499-541 Ma suggest a North Indian Orogen source. The maximum depositional age is constrained by the youngest detrital zircon, which yields an age of 466 ± 8 Ma. Our age constraints imply that terrestrial activity of multicellular animals on Earth may not be older than Middle Ordovician (Darriwilian). Rifting resulted in the exposure of the Yilgarn Craton and the segmentation of the Pinjarra Orogen. The Northampton Complex segment of the Pinjarra Orogen constituted a basement high that separated subbasins during the onset of rifting. Discordant Archean zircons provide a consistent record of radiogenic Pb loss at ~470 Ma, which we interpret as being related to the denudation of the Yilgarn Craton. The Pb loss event suggests that intracratonic rifting in the Pinjarra Orogen was initiated in the Middle Ordovician, after the Kuunga Orogeny completed the final amalgamation of Gondwana. [ABSTRACT FROM AUTHOR]

Onshore and offshore geological and geophysical observations and numerical modeling have greatly improved the conceptual understanding of magma-poor rifted margins. However, critical questions remain concerning the thermal evolution of the prerift to synrift phases of thinning ending with the formation of hyperextended crust and mantle exhumation. In the western Pyrenees, the Mauléon Basin preserves the structural and stratigraphic record of Cretaceous extension, exhumation, and sedimentation of the proximal-to-distal margin development. Pyrenean shortening uplifted basement and overlying sedimentary basins without pervasive shortening or reheating, making the Mauléon Basin an ideal locality to study the temporal and thermal evolution of magma-poor hyperextended rift systems through coupling bedrock and detrital zircon (U-Th)/He thermochronometric data from transects characterizing different structural rifting domains. These new data indicate that the basin was heated during early rifting to >180°C with geothermal gradients of ~80-100°C/km. The proximal margin recorded rift-related exhumation/cooling at circa 98 Ma, whereas the distal margin remained >180°C until the onset of Paleocene Pyrenean shortening. Lithospheric-scale numerical modeling shows that high geothermal gradients, >80°C/km, and synrift sediments >180°C, can be reached early in rift evolution via heat advection by lithospheric depth-dependent thinning and blanketing caused by the lower thermal conductivity of synrift sediments. Mauléon Basin thermochronometric data and numerical modeling illustrate that reheating of basement and synrift strata might play an important role and should be considered in the future development of conceptual and numerical models for hyperextended magma-poor continental rifted margins. [ABSTRACT FROM AUTHOR]

The lateral propagation of rifts is a consequence of the relative divergence of lithospheric plates about a pole of rotation. Modern and ancient examples of rifts are known to overprint preexisting linear anisotropies in the crust and lithosphere, such as lithospheric boundaries, crustal sutures, and thermal anomalies. Here we investigate how propagating rifts interact with preexisting structures by using three-dimensional analogue experiments with rotational extensional boundary conditions and variably oriented linear weak zones in the lithospheric mantle. When linear weaknesses are oriented at low angles to the rift axis, early strain localization occurs in narrow domains, which merge at later stages, resulting in continental breakup by unzipping. Strong strain partitioning is observed when the linear heterogeneity is oriented at high angles with respect to the rift axis. In these experiments, early subparallel V-shaped basins propagate toward the pole of rotation until they are abandoned and strain is transferred entirely to structures developed in the vicinity of the strongly oblique weak lithosphere zone boundary. The experimental results are characterized in terms of their evolution, patterns of strain localization, and surface topography as a function of the lithospheric heterogeneity obliquity angle. Comparison of the experiments to ancient and modern examples in nature may help to elucidate the common but still poorly understood process of propagating rift-lithospheric heterogeneity interaction. [ABSTRACT FROM AUTHOR]

The seminunatak Kilen in eastern North Greenland, with its complexly deformed Carboniferous-Cretaceous strata, is a key area to understand the tectonic history of the transform plate boundary between eastern North Greenland and Svalbard. Detailed 3-D geological mapping from oblique photogrammetry along with limited ground fieldwork and interpretation of previously published data forms the basis for a new structural model of Kilen. Previous structural models interpreted rhombic-shaped fault patterns as the evidence for strike-slip tectonics. These structures are here interpreted to be the result of a post-Coniacian NE-SW extension with NW-SE trending normal faults followed by later, N-S compression of presumable Paleocene-Eocene age, folding the faults passively and suggesting the presence of a basal detachment. Furthermore, two thrust sheets have been distinguished on Kilen: a lower Kilen Thrust Sheet and an upper Hondal Elv Thrust Sheet separated by a subhorizontal fault: the Central Detachment. The style of deformation and the structures described are interpreted as the result of Paleocene-Eocene N-S directed compression resulting in basin inversion with strike-slip faults only having minor status. This indicates that the Greenland margin as exposed on Kilen and the conjugate Svalbard margin in the West Spitsbergen fold-and-thrust belt are more similar than previously anticipated. [ABSTRACT FROM AUTHOR]

We constructed a thermomechanical model to examine the changes in rheology caused by the periodic intrusion of basaltic dykes in a two-layered continental crust. Dyke intrusion can locally change the mineralogical composition of the crust in space and time as a result of temperature-induced metamorphism. In our models we paid particular attention to determine how different mineral assemblages and reaction kinetics during metamorphism impact on the thermomechanical behavior of the crust, in terms of differential stress values. We investigated several lithologies characteristic for intracontinental crust: (1) a quartz-feldspathic crust (QF), (2) a crust with a mineralogical assemblage resembling the average chemical composition occurring in literature (CC), and (3) a micaschist crust (MS). Our model shows that temperature profiles are weakly influenced by metamorphism, with negligible variations in the T-t paths. The results indicate that intrusion-induced changes in the crustal rheology are strongly dependent on mineralogical assemblage variation. The strength of a dyke aureole in the upper crust increases during dyke emplacement, which may cause migration of later dykes and influence the dyke spacing. In contrast, in the lower crust the strength of a dyke aureole decreases during dyke emplacement. Fast kinetics results in a ductile lower crust in proximity of the dykes, whereas slower kinetics leads to the formation of partial melts and subsequent switch from ductile to brittle behavior. Lithology exerts a dominant role on the quantity of melt produced, with higher volume percentages occurring in the MS case study. Produced melts may migrate and support acidic volcanic activity. [ABSTRACT FROM AUTHOR]

Recent research in Afar (northern Ethiopia) has largely focused on the formation of the present-day ocean-continent transition at active segments (e.g., Manda Hararo). However, the Oligo-Miocene history of extension, from the onset of rifting at ~25 Ma to the eruption of the massive Stratoïd flood basalts at ~4 Ma, remains poorly constrained. Here we present new structural data and radiometric dating from Central Afar, obtained along a zone stretching from the undeformed Oligocene Ethiopian plateau to the Manda Hararo and Tat'Ale active volcanic segments. Basaltic and rhyolitic formations were mapped in two key areas corresponding to the proximal and distal parts of a half-rift. We present a balanced composite cross section of Central Afar, reconstructed using our new data and previously published geophysical data on the crustal structure. Our main findings are as follows: (1) Extension during the Mio-Pliocene corresponds to a 'wide rift' style of rifting. (2) The lower crust has been underplated/intruded and rethickened during rifting by magmatic injection. (3) Our restoration points to the existence of midcrustal shear zones that have helped to distribute extension in the upper crust and to localize extension at depth in a necking zone. Moreover, we suggest that there is a close relationship between the location of a shear zone and the underplated/intruded material. In magma-rich environments such as Central Afar, breakup should be achieved once the initial continental crust has been completely replaced by the newly, magmatically accreted crust. Consequently, and particularly in Afar, crustal thickness is not necessarily indicative of breakup but instead reflects differences in tectono-magmatic regimes. [ABSTRACT FROM AUTHOR]

Deep seismic profiles and subsidence history of the Gulf of Lion margin reveal an intense stretching of the distal margin and strong postrift subsidence, despite weak extension of the onshore and shallow offshore portions of the margin. We revisit this evolution from the geological interpretation of an unpublished multichannel seismic profile and other published geophysical data. We show that an 80 km wide domain of thin lower continental crust, the 'Gulf of Lion metamorphic core complex,' is present in the ocean-continent transition zone and exhumed mantle makes the transition with oceanic crust. The exhumed lower continental crust is bounded upward and downward by shallow north dipping detachments. The presence of exhumed lower crust in the deep margin explains the discrepancy between the amount of extension deduced from normal faults in the upper crust and total extension. We discuss the mechanism responsible for exhumation and present two scenarios: the first one involving a simple coupling between mantle extension due to slab retreat and crustal extension and the second one involving extraction of the lower crust and mantle from below the margin by the southeastward flow of hot asthenosphere in the back-arc region during slab rollback. In both scenarios, the combination of Eocene crustal thickening related to the Pyrenees, the nearby volcanic arc, and a shallow lithosphere-asthenosphere boundary weakened the upper mantle and lower crust enough to make them flow southeastward. The overall hot geodynamic environment also explains the subaerial conditions during most of the rifting stage and the delayed subsidence after breakup. [ABSTRACT FROM AUTHOR]

This study focuses on an east-west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern Dur Kan Complex, a continental slice outcropping to the north of the exposed Makran accretionary wedge in southeastern Iran. Field observations, petrographic descriptions, trace element, and isotope analyses combined with U-Pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks. Results document three magmatic episodes with different melt sources for (1) granites, (2) a diorite-trondhjemite-plagiogranite sequence, and (3) diabases and lavas. Granites, dated at 170-175 Ma, represent crystallized melt with a strong continental isotopic contribution. The diorite-trondhjemite-plagiogranite sequence is 165-153 Ma old and derives from a mantle magma source with minor continental contribution. East-west trending diabase dikes and bodies intruded the granitoids, which were eroded and then covered by Valanginian (140-133 Ma) alkaline lavas and sediments. Alkaline dikes and lavas have a mantle isotopic composition. Temporal correlation with plutonites of the Sanandaj-Sirjan Zone to the northwest defines a narrow, NW-SE striking and nearly 2000 km long belt of Jurassic intrusions. The increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling/decompression melting. Accordingly, the formation of the studied igneous rocks is related to the extension of the Iranian continental margin, which ultimately led to the formation of the Tethys-related North Makran Ophiolites. [ABSTRACT FROM AUTHOR]

The prerift Mesozoic sequences of the Cretaceous passive margins fossilized in the North Pyrenean Zone (NPZ) are characterized by high-temperature deformation in relation with thinning of the continental basement. Our compilation of chronological and geological data confirms a clear correlation between the distribution of the highest paleotemperatures in the prerift sedimentary cover and the loci of extreme crustal stretching. Geological evidences such as the occurrence of peridotite bodies directly underlying metamorphic prerift sediments indicate an early attenuation of the rifted continental crust. This leads us to propose a mechanism of rifting involving boudinage of the continental crust. The lateral extraction of the Paleozoic basement occurred under the prerift cover that is decoupled on the Triassic clays and evaporites. The thermal conditions allowing coeval ductile deformation of the crust and of the prerift sediments leaded to the widening of basins devoid of large faulted blocks. We discuss the implications on the origin and significance of the granulites and the relations between flysch deposition and high-temperature metamorphism of the prerift sediments. In the NPZ, Albian-Cenomanian flysch sequences were deposited synchronously with the synmetamorphic ductile deformation of the prerift sequences. Since the base of the flysch deposits also recorded locally the high-temperature tectonic event, we propose an original mechanism for the evolution of the basins involving continuous deformation of the prerift metamorphic sediments. At the scale of the Pyrenean domain, our results suggest a strong lateral variability in the tectonic style of passive margins, in direct link with their thermic pattern. [ABSTRACT FROM AUTHOR]

The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The presence of linear magmatic-tectonic belts in the relatively immature central MER may indicate that the transition from mechanical to magmatic rifting is more spatially distributed and temporally protracted than has previously been assumed. Here we examine lava geochemistry and vent distribution of a Pliocene-Quaternary linear magmatic chain along the western margin of the central MER-the Akaki Magmatic Zone. Our results show limited variability in parental magma that evolve in a complex polybaric fractionation system that has not changed significantly over the past 3 Ma. Our results suggest the following: (1) channeling of plume material and the localization of shear- or topography-induced porosity modulates melt intrusion into the continental lithosphere. (2) Pre-existing lithospheric structures may act as catalysts for intrusion of magmas into the lithospheric mantle. (3) The midcrustal to upper crustal strain regime dictates the surface orientation of volcanic vents. Therefore, although linear magmatic belts like those in the central MER may young progressively toward the rift axis and superficially resemble oceanic style magmatism, they actually represent prebreakup magmatism on continental crust. The oldest linear magmatic belts observed seismically and magnetically at the edge of the ocean basins thus may not, as is often assumed, actually mark the onset of seafloor spreading. [ABSTRACT FROM AUTHOR]

Ongoing extension in Tibet may have begun in the middle to late Miocene, but there are few robust estimates of the rates, timing, or magnitude of Neogene deformation within the Tibetan plateau. We present a comprehensive study of the seismically active South Lunggar rift in southwestern Tibet incorporating mapping, U-Pb geochronology and zircon (U-Th)/He thermochronology. The South Lunggar rift is the southern continuation of the North Lunggar rift and comprises a ~50 km N-S central horst bound by two major normal faults, the west-dipping South Lunggar detachment and the east-dipping Palung Co fault. The SLD dips at the rangefront ~20°W and exhumes a well-developed mylonite zone in its footwall displaying fabrics indicative of normal-sense shear. The range is composed of felsic orthogneiss, mafic amphibolite, and leucogranite intrusions dated at ~16 and 63 Ma. Zircon (U-Th)/He cooling ages are Oligocene through late Pliocene, with the youngest ages observed in the footwall of the SLD. We tested ~25,000 unique thermokinematic forward models in Pecube against the structural and (U-Th)/He data to fully bracket the allowable ranges in fault initiations, accelerations, and slip rates. We find that normal faulting in the SLR began in the middle Miocene with horizontal extension rates of ~1 mm a−1, and in the north accelerated at 8 Ma to 2.5-3.0 mm a−1 as faulting commenced on the SLD. Cumulative horizontal extension across the SLR ranges from <10 km in the south to 19-21 km in the north. [ABSTRACT FROM AUTHOR]

Studies conducted in present-day magma-poor rifted margins reveal that the transition from weakly thinned continental crust (∼30 km) in proximal margins to hyper-extended crust (≤10 km) in distal margins occurs within a narrow zone, referred to as the necking zone. We have identified relics of a necking zone and of the adjacent distal margin in the Campo, Grosina and Bernina units of the fossil Alpine Tethys margins and investigated the deformation and sedimentary processes associated with extreme crustal thinning during rifting. Within the basement rocks of the necking zone, we show that: (1) Grosina basement represents pre-rift upper/middle crust, while the underlying Campo unit consists of pre-rift middle/lower crust that was exhumed and cooled below ∼300°C by ca. 180 Ma, when rifting started to localize within the future distal margin; (2) the juxtaposition of the Campo and Grosina units was accommodated by the Eita shear zone, which is interpreted as a decollement/decoupling horizon active at mid-crustal depth at 180-205 Ma; (3) the Grosina unit hosts a large-scale brittle detachment fault. Our observations suggest that crustal thinning, accommodated through the necking zone, is the result of the interplay between detachment faulting in the brittle layers and decoupling and thinning in ductile quartzo-feldspatic middle crustal levels along localized ductile decollements. The excision of ductile mid-crustal layers and the progressive embrittlement of the crust enables major detachment faults to cut into the underlying mantle, exhuming it to the seafloor. This structural evolution can explain the first-order crustal architecture of many present-day rifted margins. [ABSTRACT FROM AUTHOR]

Preexisting zones of weakness significantly influenced the structural development of the Fundy basin during rifting and subsequent basin inversion. The preexisting fabric, consisting of NE striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments, formed during Paleozoic and older orogenic activity. During Mesozoic rifting, the preexisting fabric was reactivated, creating a border-fault system composed of linked NE and east striking extensional fault zones with anomalous dips (gentle and steep) compared to those of newly formed normal faults. During inversion, the preexisting fabric was again reactivated as the hanging wall of the composite border-fault system moved NNE relative to the footwall. Inversion was highly oblique on the NE striking fault zones, producing gentle fault-parallel buttress folds and fault-perpendicular detachment folds above the low-angle fault zones. Inversion was moderately oblique on the east striking fault zone, producing relatively tight fault-parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left-lateral strike-slip faults. Thus, inversion-related deformation on the east striking fault zone was partitioned at shallow levels (i.e., partitioned updip). Our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion. Namely, the type of inversion-related faults, the type and shape of inversion-related folds, and the distribution of deformation (e.g., updip partitioning) depend, in part, on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike. [ABSTRACT FROM AUTHOR]

Regional (2-D) seismic reflection profiles, outcrop, and borehole data are used to characterize the evolution of deep offshore sedimentary basins in southwest Iberia (Alentejo Basin). The interpreted data indicate the bulk of Late Jurassic-earliest Cretaceous subsidence occurred in the present-day continental slope area, as shown by (1) significant thickening of synrift strata basinward from a slope-bounding fault system (SFS), west of which the total thickness of sediment can reach more than 9.0 km, and (2) relatively thin Mesozoic strata east of the SFS, where thickening of synrift units against principal faults is limited. Five principal regressive events and their basal unconformities reflect tectonic uplift and relative emersion in proximal basins, which were located on the rift shoulder to subsiding tilt blocks west of the SFS. These regressive events are correlated with major rift-related events occurring on the deeper margin. Direct comparisons with the Peniche Basin of northwest Iberia reveal that significant portions of the Iberian lower plate margin were uplifted and eroded during the last stages of continental rifting. This process was repeated at different times (and in different areas) as the locus of rifting and continental breakup migrated northward. As a result, two distinct rift axes are recognized in west Iberia, a first axis extending from the Porto Basin to the Alentejo Basin and a second axis located on the outer proximal margin north of 38°30N. In addition, the SFS delimited (1) prograding deposits of Cretaceous-Paleogene age and (2) late Cenozoic deposits draping the modern continental slope. These latter facts demonstrate that on lower plate passive margins, the relative position of the continental slope is established during the final rifting episode(s) preceding continental breakup. [ABSTRACT FROM AUTHOR]

Tectonic analysis reveals a previously unidentified link between alkaline rocks and carbonatites (ARCs) forming the Kola Alkaline and Carbonatite Province (KACP) in Arctic Russia, and ARCs of the Seiland Igneous Province (SIP), in the northern Caledonides of Finnmark, Norway. We here conclude that the rocks of the two provinces have been derived by decompression melting of deformed alkaline rocks and carbonatites (DARCs) under rifts and within the underlying lithospheric mantle preserved within the Paleoproterozoic Lapland-Kola Suture Zone (LKSZ) and its extension beneath the allochthons of the Norwegian Caledonides. The LKSZ projects under the Caledonide allochthons to the postulated site of eruption of the ARCs of the SIP in an intra-continental rift at a place where an ocean was soon to open. We suggest that the SIP ARCs formed in this intra-continental rift by decompression melting involving DARCs that had lain in the underlying lithospheric mantle within the along-strike extension of the LKSZ for more than one billion years. Thrusting and metamorphism during the Scandian collision between Laurentia and Baltica transformed the SIP ARCs into DARCs that occupy the immediate footwall to the suture zone between Laurentia and Baltica. At the collision, the SIP rocks were carried south-southeastwards from their then location on the outermost continental margin of Baltica to their current location in the highest level of a sandstone-dominated nappe complex. The ARCs and DARCs of Kola and Finnmark provide independent evidence of the operation of two complete Wilson cycles of the opening and the closing of oceans in the region. [ABSTRACT FROM AUTHOR]

Most of the conceptual ideas concerning sedimentary architecture and tectonic evolution of deep rifted margins are based on either intracontinental rift basins or proximal margins, both of which underwent only small amounts of crustal thinning. In this paper, we investigate the tectonosedimentary and morphotectonic evolution related to continental breakup of the highly extended, deep Iberia-Newfoundland margins. Our results show that continental breakup is a complex process distributed in time and space. On the basis of mapping of dated seismic units and borehole data we are able to identify two major phases of extension. During a first phase, dated as Tithonian to Barremian (145-128 Ma), deformation is related to exhumation of mantle rocks; basins become younger oceanward, and fault geometry changes from upward to downward concave resulting in complex sedimentary structures and basin geometries. A second phase, dated as latest Aptian (112 Ma), overprints previously exhumed mantle and accreted juvenile oceanic crust over more than 200 km leading to the formation of basement highs. The observed complex breakup history challenges classical concepts of rifting and leads to new interpretations for the tectonosedimentary evolution of deep rifted margins. [ABSTRACT FROM AUTHOR]

The older geological units of the volcanic island of Fuerteventura (Canary Islands), i.e., the so-called basal complex and the lower part of the subaerial volcanic rocks, show abundant structures indicative of a long-lived period of Miocene tectonic activity. These structures include faults, dike swarms, kilometer-scale folds, tilted sequences, and fissural and central volcanic edifices. A detailed structural study, based on geological mapping and the use of fault slip inversion techniques and statistical analysis of dike orientation, has allowed the identification of three separated Miocene deformation phases: M-D1, M-D2, and M-D3. The average extension directions determined for these phases are NW-SE, NNE-SSW, and ENE-WSW, respectively. A model of oceanic lithosphere rifting is proposed to account for this deformation history. A buoyant, anomalous sublithosphere mantle triggered the extension in the lithosphere beneath Fuerteventura, isolating it during the early and middle Miocene from the plate-scale collision regime predominant in the NW corner of the African plate. [ABSTRACT FROM AUTHOR]

The Tertiary reactivation of the Paleozoic basement in NE Sardinia is shown to reflect transtensional back-arc tectonics, related to the western Mediterranean subduction rollback. During the Algéro-Provençal basin opening, the left-lateral Nuoro Fault, which is the prevailing structure in central Sardinia, operated as radial transfer between the west Sardinian rift and northern Tyrrhenian basin. Subsequently, it contributed to a tension gash-like opening of the southern Tyrrhenian basin as conjugate fault to a right-lateral fault set in SE Sardinia. Resulting antithetic rotations with respect to the arc are revealed by reoriented dikes in the basement. The tension gash-like opening of the southern Tyrrhenian basin determined the gulf shape of the east Sardinian margin and the arc shape of its Calabrian counterpart. This structural control on the southern Tyrrhenian rollback scenario suggests that tension gash-like opening of back-arc basins represents an intrinsic aspect of subduction rollback. [ABSTRACT FROM AUTHOR]

Orogenic building leaves a complex heritage consisting of a stack of nappes that may have contrasting lithologic structures resulting in heterogeneous mechanical behavior of the system during the postorogenic stages. While the thermal state of the region is reequilibrating, strong lateral variations of the depth to the brittle-ductile transition develop as a consequence of these preexisting heterogeneities. We use a thermomechanical model to quantify how an inherited weak nappe influences the development of fault patterns resulting from postorogenic extension. The competence contrast between the nappe and the rest of the upper crust as well as the strength of the crust itself are the principal variable parameters of our experiments. The results suggest that a dipping weak nappe introduces a lateral velocity discontinuity and serves as a localization factor for deformation. The presence of a preexisting nappe with a low competence contrast is sufficient to localize strain along the nappe leading to the formation of a flexural rolling hinge. In this case, the migration of the basin is slow, continuous, and limited by gravity driven processes that lead to the rise of hot (weak) material under the subsiding basin. In case of a high competence contrast, overall crustal strength is reduced by a 'dipping pie' effect. Assuming overall high crustal strength, the presence of a contrasting nappe leads to a bimodal fault pattern governed by two types of faults: crustal-scale planar faults rooting on the brittle ductile transition of the crust and thin-skinned listric faults rooting on the nappe itself. This bimodality results in a jump-like migration of the basin downward along the dipping weak nappe. Applying this model to the case of the Gulf of Corinth (Greece) allows us to explain, in the case of assumed high competence contrast, the observed microseismicity patterns, the asymmetry of the Gulf, and the kinematics of fault migration within the basin. [ABSTRACT FROM AUTHOR]