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The East Kunlun Orogenic Belt (E-KOB) in the northern Tibet Plateau has undergone a long multi-stage history of drifting, accretion, and collision of the Proto- and Palaeo-Tethyan oceans. It has been addressed a trench-arc-back-arc basin system of the Proto-Tethys in the E-KOB, and the tectonic history of this major ocean has been well constrained by previous studies. However, the evolution of the back-arc basin still remains unclear. In this study, the Yugusayi monzodiorite, quartz-bearing syenite, and gradually contacted skarn rocks characterized by garnet megacrysts, in the North Qimantagh Belt were investigated. To reveal the tectonic setting and skarnization mechanism, geochemical and geochronological studies were conducted on the intrusions and garnet skarn, and the elemental compositions of the garnet megacrysts were also analysed. These monzodioritic rocks have high MgO (6.87–8.31 wt.%), Sr and La contents, low Y and Yb contents, and relatively high La/Yb (31–55) and Sr/Y (41–51) ratios, resembling to high-Mg adakites. They display right-sloping chondrite-normalized REE patterns, enriched in LILEs, and depleted in Ti with significant Nb-Ta troughs, which are similar to those of continental arc rocks. Zircons from monzodiorite and skarn samples have contemporaneous U-Pb ages of 459 ± 3 Ma and 454 ± 4 Ma with εHf(t) values of − 8.53 to − 4.64 and − 7.7 to + 12.8, respectively. In addition, the chemical zoning garnet megacrysts are composed mainly of grossular and andraditic grossular, and are characterized by spoon-shaped REE patterns. Based on our new data and the regional geology, it can be concluded that the Yugusayi intrusive rocks formed in a subduction-related tectonic setting and resulted in the skarnization. These data not only provide key constraints on the initial subduction of the Qimantagh back-arc basin's oceanic crust, but also offer a unique opportunity to explore the Caledonian skarnization in the Qimantagh Belt. [ABSTRACT FROM AUTHOR]

Abstract Anisotropic structures within the crust are frequently perceived to originate from stress-induced cracks, which have been mainly estimated on land through different wave speeds of orthogonally polarized S waves propagating in the anisotropic media. However, such estimations of crustal anisotropic structures in ocean areas, particularly for subduction zones around trenches, have not been investigated in detail due to the lack of long-term ocean bottom observations. In this study, we used ocean bottom seismometers of a permanent network deployed across the Japan Trench and the southern part of the Kuril Trench and applied the shear-wave splitting analysis to P-to-s converted waves extracted by receiver function analyses using teleseismic events. We estimated the anisotropic structures in marine sediments and oceanic crust for the incoming Pacific Plate and marine sediments for the overriding North American Plate. The obtained fast polarization directions for the incoming plate are mainly oriented to be parallel to the trench axis for the marine sediment and oceanic crust, which are formed by normal faults and cracks due to the upward plate bending in the outer-rise region, whereas results for marine sediments at the northern part of the Japan Trench are obliquely aligned to the trench axis. The oblique direction is consistent with the magnetic lineations of the incoming plate, indicating that ancient faults within the plate, which were formed in the shallow part of the crust during the creation of the oceanic plate at the ridge, are reactivated by the plate flexure. For the overriding plate, the fast polarization directions in the northern and southern parts of the study area are nearly normal to the trench axis. The central part shows two distinct features: the fast polarization directions parallel to the trench axis and small degrees of anisotropy. These patterns may reflect crack alignments associated with the lateral variation in postseismic crustal deformation after the 2011 Tohoku-Oki earthquake. Our results suggest substantial lateral variations in the stress field at the tip of the overriding plate along the strike direction. Graphical Abstract

Rhombic structures have been observed in the Qom-Zefreh-Nayin-Dehsheir-Baft region, specifically along the direction of the dextral faults, which have caused significant changes in strike length. This study investigates the geological features and fault interactions in the region through the examination of aerial images, fault-lithology correlations, petrology, crustal thickness, and seismic studies. The analysis of aerial photos and geological correlations revealed the presence of ophiolites and pluto-volcanics associated with faults and rhombic structures. By conducting field geology and combining various geological studies, a pull-apart basin was identified in the area, contributing to the formation of three rhombic structures. This basin played a crucial role in the genesis of the region's ophiolites and pluto-volcanics. The research suggests that the initial tensional stress leading to the pull-apart basin was caused by the right step of a dextral fault within the Urumieh-Dokhtar magmatic arc. This fault formation occurred due to the oblique Arabian subduction towards the Iranian plateau. During the Zagros orogeny, the stretched area persisted, leading to the formation of oceanic crust in this location. The subduction angle changes from subduction to super-subduction, resulting in the classification of the region into two types: C and E genes. Different types of magma, including alkaline, subalkaline, shoshonite, calcalkaline, and adakitic, were identified in this region. The study highlights the significance of tholeiitic arcs, abyssal features, crust thickness, and seismicity in understanding oblique diagonal subduction models and tensional pull-apart basins, which are crucial in the transition from subduction to super-subduction. This research offers valuable insights into the geological complexities of the region and opens up opportunities for further exploration of similar models. [ABSTRACT FROM AUTHOR]

Enriched mid‐ocean ridge basalts (E‐MORB) commonly erupt at mid‐ocean ridges (MOR) and seamounts, but their relationship to "depleted" MORB (D‐MORB) and the processes controlling their magmatic evolution at MORs are not fully understood, hence raising more general questions about magma generation in the mantle. We here explore this conundrum through an investigation of the Masirah ophiolite (southeast Oman), a near‐unique "true" MOR ophiolite. Unlike most (e.g., Tethyan) ophiolites, it was not affected by subduction and is therefore potentially able to provide valuable geological insights into the magmatic evolution of a full section of oceanic crust. Previous work has shown that the igneous crust at Masirah was thin (1.5–2.0 km) and constructed from both D‐ and E‐MORB magmas, concluding that it formed at a slow‐spreading ridge at ∼150 Ma followed by an episode of "Nb‐enriched" magmatism with trace‐element enrichments exceeding E‐MORB during intraplate rifting ∼20 Ma later. We reinvestigate the geology of Masirah and present new field observations, geochemical data and high‐precision U‐Pb ages to constrain the magmatic history of seafloor spreading and off‐axis magmatism. We found that D‐MORB and E‐MORB magmatism at Masirah was synchronous and overlapped in both composition and time with the Nb‐enriched magmatism (no older than 135 Ma). Both types of magmatism were therefore integral in the formation of the Masirah ocean crust. The relationship between D‐MORB and E‐MORB magmatism described here may be applicable to modern MORs more broadly, but is especially prominent at Masirah due to reduced magmatism and hence a weaker crustal filter. Plain Language Summary: The oceanic crust forms approximately two‐thirds of the Earth's surface and is continuously being formed at mid‐ocean ridges. Due to the difficulties involved in accessing oceanic crust directly, especially the deeper stratigraphic levels, the magmatic processes involved in forming the oceanic crust remain poorly understood. Ophiolites, fragments of oceanic lithosphere that were emplaced onto the continent, can offer valuable insights to geologists, but since most ophiolites are thought to have originated in marginal oceanic basins or at the initiation of subduction, a direct comparison remains problematic. In this study, we circumvent this problem by investigating the Masirah Ophiolite, a rare example of a "true" mid‐ocean ridge ophiolite. By combining field observations, geochemistry and geochronology at a level of detail not possible for present‐day oceanic crust, we reconstruct the magmatic evolution of the Masirah paleoridge. We present a more accurate formation age for Masirah and find that magmatism was compositionally variable throughout crustal accretion, with later off‐axis melts becoming more enriched in incompatible trace elements. We propose that the large geochemical variations observed at Masirah may be commonplace at modern mid‐ocean ridges, but that these are often masked due to the typically higher volumes of magmatism that enhance mixing and homogenization. Key Points: Two ophiolite nappes exposed on Masirah were formed by ocean crustal accretion at 135 and 131 Ma respectivelyOn‐axis magmatism shows varying degrees of trace element enrichment and depletion, and is followed by Nb‐enriched "near‐axis" magmatismSimilar processes may be common along modern mid‐ocean ridges but masked by the homogenizing effect of an enhanced "crustal filter" [ABSTRACT FROM AUTHOR]

Plate tectonics theory, established in the 1960s, has been successful in explaining many geological phenomena, processes and events that occurred in the Phanerozoic. However, the theory has often struggled to provide a coherent framework in interpreting geological records in continental interior and Precambrian period. In dealing with the relationship between plate tectonics and continental geology, continental interior tectonics was often separated from continental margin tectonics in the inheritance and development of their structure and composition. This separation led to the illusion that the plate tectonics theory is not applicable to Precambrian geology, particularly in explaining the fundamental geological characteristics of Archean cratons. Although this illusion does not mean that the Archean continental crust did not originate from a regime of plate tectonics, it led to the development of alternative tectonic models, often involving vertical movements under a regime of stagnant lid tectonics, including not only endogenous processes such as gravitational sagduction, mantle plumes and heat pipes but also exogenous processes such as bolide impacts. These vertical processes were not unique to the Archean but persisted into the Phanerozoic. They result from mantle poloidal convection at different depths, not specific to any particular period. Upgrading the plate tectonics theory from the traditional kinematic model in the 20th century to a holistic kinematic-dynamic model in the 21st century and systematically examining the vertical transport of matter and energy at plate margins, it is evident that plate tectonics can explain the common geological characteristics of Archean cratons, such as lithological associations, structural patterns and metamorphic evolution. By deciphering the structure and composition of convergent plate margins as well as their dynamics, the formation and evolution of continental crust since the Archean can be divided into ancient plate tectonics in the Precambrian and modern plate tectonics in the Phanerozoic. In addition, there are the following three characteristic features in the Archean: (1) convective mantle temperatures were 200–300°C higher than in the Phanerozoic, (2) newly formed basaltic oceanic crust was as thick as 30–40 km, and (3) the asthenosphere had a composition similar to the primitive mantle rather than the depleted mantle at present. On this basis, the upgraded plate tectonics theory can successfully explain the major geological phenomena of Archean cratons. This approach provides a new perspective on and deep insights into the evolution of early Earth and the origin of continental crust. In detail, Archean tonalite-trondhjemite-granodiorite (TTG) rocks would result from partial melting of the over-thick basaltic oceanic crust at convergent plate margins. The structural patterns of gneissic domes and greenstone keels would result from the buoyancy-driven emplacement of TTG magmas and its interaction with the basaltic crust at convergent margins, and komatiites in greenstone belts would be the product of mantle plume activity in the regime of ancient plate tectonics. The widespread distribution of high-grade metamorphic rocks in a planar fashion, rather than in zones, is ascrible to separation of the gneissic domes from the greenstone belts. The shortage of calc-alkaline andesites in bimodal volcanic associations suggests the shortage of sediment accretionary wedges derived from weathering of granitic continental crust above oceanic subduction zones. The absence of Penrose-type ophiolites suggests that during the subduction initiation of microplates, only the upper volcanic rocks of the thick oceanic crust were offscrapped to form basalt accretionary wedges. The absence of blueschist and eclogite as well as classic paired metamorphic belts suggests that convergent plate margins were over-thickened through either warm subduction or hard collision of the thick oceanic crust at moderate geothermal gradients. Therefore, only by correctly recognizing and understanding the nature of Archean cartons can plate tectonics reasonably explain their fundamental geological characteristics. [ABSTRACT FROM AUTHOR]

At mid-ocean ridges (MORs), seawater carrying dissolved sulfate (SO4) infiltrates the oceanic crust. Hydrothermal fluid emissions from such systems have much lower δ34S and sulfur is mostly present as reduced sulfide, albeit in lower total sulfur concentrations than in seawater. This has been explained by anhydrite formation and sulfate reduction based on petrographic evidence and mass balance considerations. Here, we utilize the chemical and stable isotope (δ34S, δ18O) systematics in natural anhydrite and pyrite from various locations along the submarine and on-land section of the Mid-Atlantic ridge near Iceland to quantify the key variables that control anhydrite formation and sulfate recycling in the oceanic crust. Hydrothermal anhydrite exhibited δ34S values of +20.6 ± 1.0‰ and δ18O values between +2.4 to +25.3‰. Volcanogenic anhydrite in encrustations showed δ34S values of −1.7 to +21.4‰ and δ18O values between +1.4 and +38.0‰. Hydrothermal pyrite exhibited δ34S values ranging from +3.4 and +19.7‰. Comparison of the natural dataset with results from geochemical isotope modelling revealed that δ34S and δ18O values of anhydrite and pyrite were dependent on the isotope composition of the source fluid, extent of water–rock interaction, temperature, and redox conditions. Departures of δ34S and δ18O values in anhydrite from the source fluid were caused by progressive fluid-basalt interaction where lower δ34S and δ18O values reflected a change in sources of S and O from solely fluid to basaltic origin. The δ18O values of anhydrite were additionally affected by temperature. Quantitative formation of anhydrite mainly occurred at temperatures < 150 °C, whereas at elevated temperatures (>200 °C) reduction of seawater-sulfate to H2S and subsequent pyrite precipitation were found to limit anhydrite formation. Extending our calculations to the oceanic crust revealed that the majority of seawater-sulfate is sequestered into anhydrite (3–38 Tg S yr−1) in vicinity of MORs at < 200 °C at shallow depth (

Abstract Devastating megathrust earthquakes and slow earthquakes both occur along subducting plate interfaces. These interplate seismic activities are strongly dependent on the nature of the plate interface, such as the shape of the plate interface and the materials and physical conditions along the plate interface. The oceanic plate, which is the input to the subduction zone, is the first order control on the nature of the plate interface. To reveal the nature of the subduction inputs to the northeastern Japan arc, we have conducted large-scale controlled-source seismic surveys of the northwestern part of the oceanic Pacific plate. The obtained seismic data have revealed (1) oceanic plate structural evolution caused by plate bending prior to subduction, suggesting the promotion of the oceanic plate hydration; (2) spatial variation of the oceanic plate structure, such as variations in the thickness of sediment and crust; (3) that the spatial variations are caused by both ancient plate formation processes and more recent volcanic activities; and (4) that spatial variations of the nature of the subduction inputs show good correlation with the along-strike variations in the seismic structure and seismic activities after subduction, including the coseismic slip distribution of the 2011 Tohoku earthquakes and the structural differences between the northern and the southern Japan Trench. These observations indicate that the incoming oceanic plate structure is much more spatially variable than previously thought and also imply that the spatial variation of the subduction inputs is a key controlling factor of the spatial variation of various processes in subduction zones, including interplate seismic activities and evolution of the forearc structure.

The heat budget of sedimentary basins is determined by heat transfer across the lithosphere-asthenosphere boundary and lithospheric heat sources, such that the tectonic evolution of their host continental and oceanic lithosphere ultimately impact the present-day heat flow and average geothermal gradients. Recent increase in availability of publicly-accessible geothermal gradient measurements across the world provides an opportunity to globally assess the dominant controls on the thermal regime of sedimentary basins. Thus, we compile a global dataset of ∼ 152,000 unique data points with constrained bottomhole temperature measurements and assess the relationships between geothermal gradient and selected independent tectonic variables, including crustal and lithospheric thicknesses, crustal age, sediment thickness, and basin type. The results show that in both oceanic and continental settings, geothermal gradients exhibit a non-linear, systematic variation with the tectonic variables. We find that oceanic geothermal gradients decrease with increasing crustal age and lithospheric thickness. Geothermal gradients in the continents show no clear relationships with thermotectonic crustal age, but decrease with increasing crustal and lithospheric thicknesses. Gradients drop significantly at 1.5 km sediment-cover thickness, likely reflecting the effect of high sedimentation rates, but show a striking rise at > 12 km thicknesses, potentially influenced by thinned lithosphere and thermal blanketing effects. The commonly-assumed ‘normal’ gradient of 25 °C/km for continents is only valid for a narrow range (1.5–12.5 km) of sedimentary cover-thickness, and oceanic ‘normal’ gradient may be as high as 50–75 °C/km for > 20 Ma crustal age and > 50 km-thick lithosphere. We show that, conditionally, crustal age may best predict average geothermal gradients in oceanic settings, and lithosphere thickness in continents. Further, we observe that tectonic basin types exhibit distinct ranges of gradients that reflect their prevalent tectonic and geodynamic origins. Despite the complexities of determining shallow-crustal thermal conductivities, the results provide insights that fingerprint distinct tectonic settings based on the broad distribution of their geothermal gradients.

The Porgera Transfer Zone (PTZ) is a major crustal and probably lithospheric structure across Papua New Guinea recording >50 km offset of ophiolites and very different patterns of geology and topography on either side. In the Late Jurassic, the PTZ probably separated oceanic crust and thick Jurassic Om shales to the west from a continental promontory to the east. During the Late Miocene to Recent orogenesis, the differential compression of these features is interpreted to have created a dextral strike slip fault across the fold belt with pull-apart basins at sites of fault relays. This facilitated the ascent of intrusions and mineralization at Porgera. The acquisition of high-resolution LIDAR data semi-regionally around the Porgera Gold Mine greatly improved interpretation of the regional geology and particularly the recognition of normal faults. By correlating with sparse dip data and paly-dated samples, it was possible to create stratigraphic sections and interpret structural cross-sections using the LIDAR data. As the area involved strike–slip offsets, it was important to construct sections in multiple orientations in order to interpret the 3D geology. Both dips and fault orientation could be directly inferred from the LIDAR data such that sections could be constructed orthogonally to them. A balanced, restored and forward-modelled cross-section illustrates the interaction between thrust faults and normal faults during compression and that it was synchronous with the development of a pull-apart basin. A semi-regional 3D geological model, which was developed mainly from the LIDAR data, supports the hypothesis of inversion of the thick Om beds to the west before or during compression of the continental promontory to the east resulting in dextral strike–slip offsets across the PTZ. A jog or relay in the faults occurred and caused a pull-apart collapse basin to develop in the area of the Porgera mine. Similar pull-apart graben, or negative flower structures, were detected nearby and may be areas for future exploration. [ABSTRACT FROM AUTHOR]

Abstract Studies of oceanic crust, which covers a large proportion of the Earth's surface, have provided significant insight into the dynamics of crustal accretion processes at mid‐ocean ridges. It is now recognized that the nature of oceanic crust varies fundamentally as a function of spreading rate. Ocean Drilling Program (ODP) Hole 1256D (eastern Pacific Ocean) was drilled into the crust formed at a superfast spreading rate, and hence represents a crustal end member. Drilling recovered a section through lava and sheeted dykes and into the plutonic sequence, the study of which has yielded abundant insight into magmatic and hydrothermal processes operating at high spreading rates. Here, we present zircon U‐Pb dates for Hole 1256D, which constrain the age of the section, as well as the duration of crustal accretion. We find that the main pulse of zircon crystallization within plutonic rocks occurred at 15.19 Ma, consistent with magnetic anomalies, and lasted tens of thousands of years. During this episode, the main plutonic body intruded, and partial melts of the base of the sheeted dykes crystallized. One sample appears to postdate this episode by up to 0.25 Myr, and may be an off‐axis intrusion. Overall, the duration of crustal accretion was tens to several hundreds of thousands of years, similar to that found at the fast‐spreading East Pacific Rise and the slow‐spreading Mid‐Atlantic Ridge. This indicates that crustal accretion along slow‐ to superfast‐spreading ridges occurs over similar time scales, with substantially longer periods of accretion occurring at ultraslow‐spreading ridges characterized by thick lithosphere.

The Mohorovičić discontinuity, often known as the Moho, marks the boundary separating the Earth's crust from the mantle. Techniques such as isostatic-gravity and seismic methods can be used to determine this division. The Moho marks the boundary between the continental and oceanic crust and the upper mantle. Simply put, the Moho acts as a physical/chemical boundary between the mantle and the crust and causes significant changes in geophysical properties such as seismic wave velocity, density, pressure, and temperature (Mooney and Masters, 1998; Martinck, 1994; Bagherbandi, 2011 and Dashtbazi et al., 2023). An accurate and high resolution Moho depth model in fields such as geodesy, geology, geophysics, geodynamic modeling, seismic risk assessment, stress field modeling caused by mantle convection (Li et al., 2018; Behr et al., 2022; Singh and Yadav, 2023; Heilman and Becker, 2022; Hashima et al., 2016; Eshagh et al., 2020; Eshagh, 2015 and Gido et al., 2019), and understanding seismic source mechanisms is important, among other applications (Gido et al., 2019 and Dashtbazi et al., 2023). Furthermore, a reliable Moho model can reveal details of crustal structure that provide valuable insights into the complexities of deeper mantle layers; related to the calculations and detailed examination of gravity, geothermal, geomagnetic models (Stalk et al., 2013). Although there are several Moho models, their accuracy and resolution are insufficient in the complex tectonic geometry of the Makran subduction zone (Brizi et al., 2021 and Heilman and Becker, 2022), because these zones show a complex Moho configuration (Shad Manaman et al., 1390; Taghizadeh Farhamand et al., 2015 and Dashtbazi et al., 2023). As a result, the existing models lack the necessary accuracy for the Makran subduction zone, a region approximately 1000 km long located in southeast Iran and southwest Pakistan (Byrne et al., 1992; Shad Manaman et al., 1390, Penney et al., 2017; Dashtbazi et al., 1398; Dashtbazi. et al., 2023). In geophysical and geodetic studies, hybrid methods are mainly used to determine the Moho depth when seismic data with appropriate distribution and abundance are not available. These techniques include the Parker-Oldenberg method and the Wenning-Mines-Moritz method. In an effort to strengthen the existing Moho depth models in the Makran subduction zone, two distinct models named BC and SC through the integration of gravity (VMM) and seismic (CRUST1.0) data, which are processed through the Butterworth filter, spectral combination approaches and the least squares technique, was developed (Bagherbandi, 2011 and Dashtbazi et al., 2023). The resulting models provide a resolution of 5' x 5' degrees of arc, corresponding to a grid size of 9 x 9 km (Dashtbazi et al., 2023). The accuracy of these models was evaluated against four separate regional and local models. The resulting RMS values were 5.28, 1.55, 4.18, and 1.27 km for the BC model and 5.59, 1.17, 3.74, and 3.04 km for the SC model. Also, the Moho depth model obtained for the west Makran region in Iran significantly improved the accuracy and resolution of the Moho depth models in the studied area. The SC Moho model exhibits improved RMS metrics compared to the combined BC model, so we recommend it as the first priority. While the Moho depth models in our research really bring significant improvements to the existing models of the Makran subduction Moho zone, the integration of more detailed seismic data with SC and BC Moho models can improve the developed model for the Makran subduction zone. In the end, we suggest that a similar approach be adopted for the analysis of the Moho model in the eastern Makran region in Pakistan, which allows a comparative evaluation of the Moho depth and structure between the western and eastern parts in order to obtain a better picture of the Moho depth model of the Makran subduction zone. [ABSTRACT FROM AUTHOR]

Abstract The 110,000 km2 Yucatan Basin in the northern Caribbean Sea is critical for understanding the Late Cretaceous to Recent tectonic evolution of the Caribbean‐North American plate boundary. This study integrates gravity, magnetic, and a 5,500 km grid of 2D seismic data to carry out a tectonostratigraphic analysis of the Yucatan Basin. These data provide the first recognition of 38–102 km‐long spreading ridges that constrain a SW‐NE opening direction in the western Yucatan Basin. The age of this oceanic crust is constrained to be late Paleocene‐middle Eocene (57–42 Ma) based on heat flow measurements, depth‐to‐seafloor, and three sedimentary sequences inferred to be Eocene—Recent in age based on stratigraphic correlations to distant wells. We interpret the Yucatan Basin as a back‐arc basin formed during the northeastward movement of the Caribbean volcanic arc that is now exposed in Cuba, evolved during the early Cretaceous to middle Eocene, and was terminated by collision with the Bahama carbonate platform during the late Paleocene to middle Eocene. We identify regional, left‐lateral strike‐slip faults that extend into the Cuban volcanic arc, as observed in other active back‐arc basins. We propose that the Yucatan back‐arc basin once formed the northwestern extension of age‐equivalent back‐arc basins in Hispaniola, where the basin is inverted, topographically elevated, and strongly shortened, and in the Lesser Antilles where the Paleogene back‐arc basin has remained undeformed and submarine. This once‐continuous back‐arc basin was disrupted and left‐laterally offset by ∼500 km during the Late Eocene‐Recent formation of the Cayman trough strike‐slip system.

The features of the structure formation of the Earth's crust at the early stage of formation of the Southeast Indian Ridge were studied. The process of formation was associated with the separation of Australia from Antarctica and the advance of the rift zone westward towards the ancient oceanic lithosphere and, then, towards the large igneous province of Kerguelen, formed by the activity of the plume of the same name. The separation of Australia and Antarctica spanned a long period of continental rifting (~160‒80 Ma), which was followed by ultraslow spreading (~80‒45 Ma), slow spreading (~45‒40 Ma), and, finally, by recent stationary spreading at average rates (after 40 Ma). The advance of the rift zone towards the ancient oceanic lithosphere gave way to the accretion of young oceanic crust on the emerging Southeast Indian Mid-Oceanic Ridge. The early stages of development of the young spreading ridge are reflected in the modern structural plan of the study region. The advance of the rift zone from the continent into the boundaries of the ancient oceanic lithosphere led to the formation of the Naturalist Plateau and the Bruce Bank near the Antarctic margin. The break-up of the ancient oceanic lithosphere and the formation of the young crust on the Southeast Indian Ridge led to the formation of conjugated Diamantina and Labuan suture zones, fixing the position of the initial rifting. The transition from ultraslow spreading at the initial stage of oceanic crust formation to stationary spreading at average rates is clearly recorded in the change in the ruggedness of the accretionary relief. The Southeast Indian Mid-Oceanic Ridge collided as a result of its propagation westward with a large igneous province during the formation of the Kerguelen Plateau and separated the Broken Range from the plateau. The authors carried out physical modeling of the development conditions of rifting and spreading processes, as well as structure formation within the Southeast Indian Ridge. [ABSTRACT FROM AUTHOR]

A tectonic window into the upper 2,000 m of oceanic crust generated at the superfast spreading (∼142 mm/yr) southern East Pacific Rise exposes a continuous layered structure of basaltic lavas and sheeted dikes over gabbroic rocks. This relatively simple structure is in accord with expectations for crustal accretion at a very fast spreading rate and high magma budget where magmatic construction keeps pace with plate separation. Detailed observations show that basaltic lava flows dip progressively more steeply inward (toward the spreading axis where they were erupted). Underlying sheeted dikes are faulted and tectonically rotated to dip steeply outward. These structures are interpreted in terms of subsidence beneath the axis of the southern East Pacific Rise during crustal construction that allowed the lava unit to thicken to >400 m without creating comparable relief at the spreading center. Transitional units above and below the sheeted dike complex show that the thickness of upper crustal rock units is modified by tectonic and intrusive processes during accretion. The crustal structure shows that even approaching the superfast spreading end‐member of seafloor spreading, crustal accretion involves dramatic tectonic processes that are not obvious from the surface geology of spreading centers. Plain Language Summary: Studies of mid‐ocean ridge spreading centers document the surface expression of spreading axes where new oceanic crust is constructed. Where major fault scarps cut into the oceanic crust, the structure and composition of that crust can be viewed in the third dimension. The Pito Deep Rift (PDR) in the SE Pacific exposes the upper 2,000 m of the oceanic crust that was created by seafloor spreading at the southern East Pacific Rise at a rate of >140 mm/yr, one of the fastest spreading parts of the global Mid‐Ocean Ridge system. The geologic structure of lava flows, dikes that feed them, and magma‐chamber rocks shows how these units were assembled beneath the spreading center. At high spreading rates, new oceanic crust is thought to be constructed mainly by the eruption of lava flows and the intrusion of dikes above a magma chamber, with little faulting. The pattern of tilting and fracturing of lava flows and dikes at the PDR shows that even at a very high spreading rate, building the upper crust is more complicated than suggested by surface studies alone. Key Points: Upper oceanic crust of the superfast‐spreading southern East Pacific Rise is exposed along escarpments at the Pito Deep Rift (SE Pacific)The upper crustal units include continuous layers of lavas, sheeted dikes, gabbroic rocks, and transitional unitsTilted and fractured lava flows and dikes show that subaxial subsidence and brittle deformation occurred during superfast crustal accretion [ABSTRACT FROM AUTHOR]

Abstract To assess the paleo‐permeability structure of oceanic crust, we used 3‐D X‐ray Computed Tomography (XCT) images to quantify the distribution and geometry of mineral veins in core samples from Oman Drilling Project Holes GT1A, GT2A, and GT3A, which correspond to the upper to lower crustal sections of the Samail ophiolite. We developed a new method that automatically detects veins in the XCT core images based on iterative adaption of the two‐step Hough transform combined with multiscale Hessian filtering for identifying an elongate structure. Application of the developed method allowed us to identify the geometry and Computed Tomography number of more than 1500 veins with millimeter‐scale apertures in core sections with a total length of ∼1,200 m. High‐CT (HCT) veins in the drilled cores can be related to relatively high‐temperature fluid circulation near the mid‐ocean ridge, whereas Low‐CT (LCT) veins can be related to subsequent low‐temperature fluid circulation. Applying fracture fluid‐flow models to the geometric information for the detected veins, we found that the HCT and LCT vein systems both yielded bulk permeability of 10−13–10−9 m2 for each hole. This indicates that millimeter‐wide fractures can control crustal‐scale permeability, even in the lower oceanic crust. However, these vein systems show different depth dependencies and anisotropies of permeability, possibly reflecting the different spatial variations of high‐ and low‐temperature fluid circulation in oceanic crust.

Abstract Heat flow across oceanic transform faults (TFs) and fracture zones (FZs) has rarely been studied in detail, despite these features representing distinct thermal boundaries within the oceanic lithosphere. Here, we present heat flow measurements across the St Paul fracture zone (SPFZ) in the equatorial Atlantic Ocean, from 48 Ma crust in the south to 71 Ma in the north. To the north of the FZ we find a basal heat flow of 63 mWm−2, and to the south a basal heat flow of 79 mWm−2, both in agreement with plate cooling models. However, within the SPFZ we find a heat flow of 83 mWm−2, greater than the values of the adjacent crust and 10–15 mWm−2 higher than predicted from conductive cooling models, suggesting that the thermal structure of the FZ has been modified. Evidence from seismic and sub‐bottom profiler data indicate recent active deformation within the SPFZ, potentially driven by lithospheric flexure across the FZ or temporal changes in TF configuration. We propose that this deformation may enable fluid circulation and heat advection within the basement, creating the seafloor heat flow anomaly within the FZ. These findings suggest that FZs may remain important zones predisposed to host deformation and fluid flow in the oceanic lithosphere, despite not being active plate boundaries.

Abstract A tectonic window into the upper 2,000 m of oceanic crust generated at the superfast spreading (∼142 mm/yr) southern East Pacific Rise exposes a continuous layered structure of basaltic lavas and sheeted dikes over gabbroic rocks. This relatively simple structure is in accord with expectations for crustal accretion at a very fast spreading rate and high magma budget where magmatic construction keeps pace with plate separation. Detailed observations show that basaltic lava flows dip progressively more steeply inward (toward the spreading axis where they were erupted). Underlying sheeted dikes are faulted and tectonically rotated to dip steeply outward. These structures are interpreted in terms of subsidence beneath the axis of the southern East Pacific Rise during crustal construction that allowed the lava unit to thicken to >400 m without creating comparable relief at the spreading center. Transitional units above and below the sheeted dike complex show that the thickness of upper crustal rock units is modified by tectonic and intrusive processes during accretion. The crustal structure shows that even approaching the superfast spreading end‐member of seafloor spreading, crustal accretion involves dramatic tectonic processes that are not obvious from the surface geology of spreading centers.

Abstract Oceanic Transform Faults are one of manifestations of the three major plate boundaries and a key tectonic feature of oceanic crust. They are broadly considered to accommodate strike‐slip displacement along simple vertical faults and to be largely without magmatic addition. We present the first observations from broadband 3D seismic of buried, Cretaceous‐aged transform faults in the Gulf of Guinea with complex internal architectures including crustal scale detachments and rotated packages of volcanics within oceanic crust. In the study area, several Oceanic Fracture Zones (OFZ) are described from Top Crust to Moho. OFZ scarps are observed to connect at depth with zones of low angle reflectivity which dip into the OFZ and perpendicular to the spreading orientation. At depth they detach onto the Moho, necking the adjacent crust in the manner of extensional shear zones. Thickly stacked and tilted reflectors, interpreted as extrusive lava flows, are common above the shear zones and infill up to 75% of the crustal thickness. The entire OFZ stratigraphy is overlain and sealed by late‐stage lavas that are continuous from the abyssal hills of the trailing spreading ridge. These insights demonstrate complexity previously only predicted in numerical simulations. We propose a model with extension at a high angle to the spreading orientation along a low angle shear zone that acts as a conduit for decompression related melt and volcanism. We conclude that oceanic transforms are non‐conservative and not simple strike slip fault zones, contradicting the conventional view.

On the basis of the available geochronological data, the main stages of formation of Archean rocks belonging to the tonalite-trondhjemite-granodiorite (TTG) association, with ages of about 3240, 3150, 2900, 2850, 2800, and 2750 Ma, are identified and characterized within the Karelian Province of the Fennoscandian Shield. The distinctive features of geological positions and chemical compositions of TTG rocks of different stages are shown. For example, early TTG melts could have been melted not from basalts of the greenstone belts of the Karelian Province, but from lower crustal basites or from early amphibolites of the Vodlozero domain. Features of the geological position, chemical composition, and εNd(t) isotopic evolution do not support the assumption that most of the TTGs formed from tholeiites of the greenstone belts, thus excluding their genetic connection with subduction of the ancient oceanic crust. The most acceptable model seems to be the formation of TTGs in the Karelian Province as a result of plume-affected melting of lower crustal mafites. Archean TTGs differ markedly from Phanerozoic plagiogranitoids not only in the shape and size of the massifs but also in a number of geochemical features, in particular, lower HREE, Sc, Y, and Ti contents. [ABSTRACT FROM AUTHOR]

New data on the crust structure of the Black Sea‒Caspian region, including the Scythian and Anatolian plate margins, the Caucasus, Black Sea and Southern Caspian structures are reported. Generalization and analysis of the data of deep seismic studies with an estimate of their reliability were performed and the velocity sections of the crust were constructed. Based on the data of deep drilling data and studies of the crust composition in xenoliths in these sections, three major layers were identified in the crust: granite-gneiss (6.0‒6.4 km/s), granulite-gneiss (6.5‒6.7 km/s), and basic (6.8‒7.2 km/s). According to the thickness of these layers, the major types of the crust were distinguished. Three continental types with all three layers, but different in the total thickness of the crust types were distinguished in the area of the Scythian and Anatolian plates. The oceanic type with thin basic crust and two transitional types, subcontinental and suboceanic, with the different total thickness of the crust and the thickness of the basic layer were distinguished within the deep sea basins. There are anomalous types of the crust in the Caucasus region: the thick crust of the Lesser Caucasus with anomalously low velocities and the thick high-velocity crust of the Reon‒Kura Trough. According to the seismological data, the crust of the Black Sea–Caspian region is separated from the platform plates bounding it by the deep faults and crossed by two transform faults; the upper mantle of the Caucasus differs from neighboring regions by reduced velocities. Based on the analysis of the material obtained and CDP data on the basement structure, the new structural and geodynamic schemes of the crust of the entire region were compiled, and it was shown that the formation of depressions with oceanic and suboceanic crust types corresponds to the platform regime characteristic of the depressions of Eastern Europe. A new collisional model with the overthrust of the Anatolian Plate crust onto the crust of the Lesser Caucasus without change of the structure of the upper mantle was proposed to explain the structure of the Caucasus region. [ABSTRACT FROM AUTHOR]

The lowest unit of the Cide-Kurucaşile region is the Carboniferous coal-bearing terrestrial sediments. Permian aged terrestrial Çakraz Formation and the Triassic lacustrine Çakrazboz Formation unconformably overlie the Palaeozoic sequence. Dogger-aged Himmetpaşa Formation represents a short-period marine invasion. The transgression started in the Kimmerician has led to the development of a carbonate platform, which has risen and demised after the Berriasian. A second carbonate platform, much more limited than the previous one, developed in the Late Barremian, and then the whole region deepened. The Cenomanian is a period of regional uplift and erosion. The first effective volcanic activity in the region started in the Middle Turonian. During this period, extensional faults coeval with the deposition, and the region gained an irregular topography. In the Middle-Late Santonian, the volcanism became silent for a while, the region rapidly subsided and became a completely deep marine environment. These events indicate that the continental crust of the region was broken up and the oceanic crust began to develop in the Western Black Sea back-arc basin. In the Campanian, the volcanism reactivated, but ceased after a short time, leaving its place to pelagic sediments forming the southern passive continental margin deposits of the Black Sea. In the Maastrichtian, the region was tectonically compressed and uplifted and provided turbiditic material to the Black Sea in the north and the Devrek Basin in the south. Siliciclastic turbidites have been deposited in the region until the Middle Eocene. At the end of the Middle Eocene, following the uplifting of the entire region and the destruction of marine environments, the north-vergent thrusts were developed due to intense compression and the region became a fold-thrust belt. [ABSTRACT FROM AUTHOR]

Abstract To explore a local relationship between geological structures and the occurrence of very-low-frequency earthquakes (VLFEs), a particular class of slow earthquakes with characteristic periods of 10–100 s, we investigated three-dimensional (3D) structural features using reprocessed 3D seismic data from the Nankai Trough off Kumano, southwestern Japan. In this region, VLFEs have been observed along the subducting Philippine Sea Plate. Although the detailed source distribution of VLFEs was estimated by means of recent land-based and offshore seismic networks, the relation with geological features is not well understood. First, we reprocessed the 3D seismic data with advanced techniques and reinterpreted the fault distribution in the sediment layer of the accretionary prism and tracked two key horizons: a décollement and the oceanic crust surface. In the accretionary prism sediments, multiple continuous reflectors of basal detachments in the underthrust sequence and conjugate faults cutting the shallow imbricated thrust sequence were identified. In contrast to the gentle variation in the décollement surface, the topographic relief of the oceanic crust was prominent, with ridges and surface displacement due to faults in the oceanic crust. Then, we compared the structural features with the VLFE source locations. Most VLFEs were located deep in the underthrust sediments where the sediments may consist of underconsolidated muds. Furthermore, a high spatial correlation was observed between the VLFE distribution and the oceanic crust topographic relief. The maximum stress direction, which was inferred from the conjugate faults in the imbricated thrust zone, was consistent with the spatial relation between the VLFE localization and the oceanic crust central ridge. Oceanic crust ridges may cause strain accumulation in the underthrust sediments on the landward sides of the ridges, and low-angle slow thrust movements might be caused using weak slip planes in the underthrust muddy sediments. That is, the topographic relief of the oceanic crust may control the occurrence of shallow VLFEs in the Nankai Trough.

It is shown that the continent of Antarctica, where the South Geographical Pole of the Earth is located, is the geodynamic center of formation of the primary crust of the planet. It is in the southern region of the planet, in accordance with the rules of the driller with respect to inertial forces, that the heavy mantle substance emission was directed, which formed the blocks prisms of increased rigidity. Now they are located within the limits of oceanic depressions, marginal and inland seas and middle massifs of continents.

In this study 3D inversion of satellite gravimetric data with 3DINVER.M program is applied to model the depth of the crust in the Gulf of California rift. This rift dextrally separates Baja California Peninsula from the North American continent since Miocene, period in which the change occurred from a fundamentally extensional tectonic regime to the present transtensional. Incipient oceanization occurs in various southern sectors along the rift axis, while to the north the presence of oceanic crust is controversial. As a consequence, the crust of the Gulf marine basin and that of adjacent terrestrial regions exhibit important differences in density and thickness, both fundamental parameters of the method, and therefore, we opted to model independently each domain. The crustal thickness models were compared with previous punctual estimates based on seismic methods, obtaining that 98% of the confronted points of the marine model and 87% of the terrestrial model are adjusted to a range of ± 6 km difference, with mean differences of 1.5 km and 3.5 km, respectively. In our models, along the Gulf basin axis and from the south to the north evolves from a hyper-thinned crust (~8-12 km), characteristic of oceanic to transitional crust, to a moderately thinned continental crust (~12-18 km). In the surrounding extended area, known as the Gulf Extensional Province, the continental crust usually varies between ~15 and ~28 km, while on this province flanks the crust reaches ~35-40 km in the thickened domains (Sierra Madre Occidental and Colorado Plateau). Based on our estimates of crustal thickness and the regional geology, a new demarcation for the Gulf Extensional Province is proposed. [ABSTRACT FROM AUTHOR]

Abstract Seismic attenuation properties were tested as indicators of lateral variation in geological structures and detection of faults within poorly reflective oceanic crust, on a seismic survey line along the Nankai Trough. We can specify both sedimentary structures by configuration of reflections and faults by offsetting of reflections on seismic reflection profiles. This procedure is often applied to analyze geological structures and existence of faults within sedimentary layers; however, it is almost impossible to analyze them within igneous oceanic crust because seismic reflections are inherently invisible there. Therefore, we applied seismic attenuation profiling to visualize geological structures and faults within poorly reflective oceanic crust. As a result, oceanic crust altered by late-coming volcanisms as well as damaged by intraplate earthquakes was imaged as extremely high-attenuation property, which was clearly distinguished from normal oceanic crust. Many faults were observed in the sedimentary unit on the seismic reflection profile, whereas possible lower segments of the faults were imaged as high-attenuation stripes in the oceanic crust on the seismic attenuation profile. Thus, the effectiveness of seismic attenuation profiling to structural and fault imaging within poorly reflective oceanic crust was successfully demonstrated.

The lower plate is the dominant agent in modern convergent margins characterized by active subduction, as negatively buoyant oceanic lithosphere sinks into the asthenosphere under its own weight. This is a strong plate-driving force because the slab-pull force is transmitted through the stiff sub-oceanic lithospheric mantle. As geological and geochemical data seem inconsistent with the existence of modern-style ridges and arcs in the Archaean, a periodically-destabilized stagnant-lid crust system is proposed instead. Stagnant-lid intervals may correspond to periods of layered mantle convection where efficient cooling was restricted to the upper mantle, perturbing Earth's heat generation/loss balance, eventually triggering mantle overturns. Archaean basalts were derived from fertile mantle in overturn upwelling zones (OUZOs), which were larger and longer-lived than post-Archaean plumes. Early cratons/continents probably formed above OUZOs as large volumes of basalt and komatiite were delivered for protracted periods, allowing basal crustal cannibalism, garnetiferous crustal restite delamination, and coupled development of continental crust and sub-continental lithospheric mantle. Periodic mixing and rehomogenization during overturns retarded development of isotopically depleted MORB (mid-ocean ridge basalt) mantle. Only after the start of true subduction did sequestration of subducted slabs at the core-mantle boundary lead to the development of the depleted MORB mantle source. During Archaean mantle overturns, pre-existing continents located above OUZOs would be strongly reworked; whereas OUZO-distal continents would drift in response to mantle currents. The leading edge of drifting Archaean continents would be convergent margins characterized by terrane accretion, imbrication, subcretion and anatexis of unsubductable oceanic lithosphere. As Earth cooled and the background oceanic lithosphere became denser and stiffer, there would be an increasing probability that oceanic crustal segments could founder in an organized way, producing a gradual evolution of pre-subduction convergent margins into modern-style active subduction systems around 2.5 Ga. Plate tectonics today is constituted of: (1) a continental drift system that started in the Early Archaean, driven by deep mantle currents pressing against the Archaean-age sub-continental lithospheric mantle keels that underlie Archaean cratons; (2) a subduction-driven system that started near the end of the Archaean.

The study examines the Egyptian Red Sea shelf and throws more light on the structural set‐up and tectonics controlling the general framework of the area and nature of the crust. Herein, an integrated study using gravity and magnetic data with the available seismic reflection lines and wells information was carried out along the offshore area. The Bouguer and reduced‐to‐pole aeromagnetic maps were processed and reinterpreted in terms of rifting and plate tectonics. The qualitative interpretation shows that the offshore area is characterized by positive gravity everywhere that extremely increases towards the centre of the graben, supporting the presence of an intrusive zone below the axial/main trough. The gravity data were confirmed by the presence of high magnetic amplitudes, magnetic linearity and several dipoles concentrated along the rift axis for at least 250 km. The lineament analysis indicates widespread of the Erythrean (Red Sea) trend that was offset/cut by transform faults in the NE direction (Aqaba). The tectonic model suggests the presence of one tensional (N65°E) and two compressional (N15°W, N30°W) phases of tectonism, resulted in six cycles of deformations, classified into three left lateral (N35°E, N15°E and N–S) and three right lateral (N85°W, N45°W and N60°W). The basement relief map reveals a rough basement surface that varies in depth between 1 and 5.6 km. It outlines several offshore basins, separated from each other by ridges. The models show that the basement consists of tilted fault blocks, which vary greatly in depth and composition and slopes generally to the west. They indicate that the coastal plain is underlain by acidic basement blocks (continental crust) with no igneous activity while suggesting elevated basic materials (oceanic crust) below the rift axis. The study suggests that northern Red Sea forms an early stage of seafloor spreading or at least moved past the late stage of continental rifting. [ABSTRACT FROM AUTHOR]

Abstract The alteration and dehydration of predominantly basaltic subducting oceanic crustal material are thought to be important controls on the mechanical and hydrological properties of the seismogenic plate interface below accretionary prisms. This study focuses on pillow basalts exposed in an ancient accretionary complex within the Shimanto Belt of southwest Japan and provides new quantitative data that provide insight into clay mineral reactions and the associated dehydration of underthrust basalts. Whole-rock and clay-fraction X-ray diffraction analyses indicate that the progressive conversion of saponite to chlorite proceeds under an almost constant bulk-rock mineral assemblage. These clay mineral reactions may persist to deep crustal levels (~320 °C), possibly contributing to the bulk dehydration of the basalt and supplying fluid to plate-boundary fault systems. This dehydration can also cause fluid pressurization at certain horizons within hydrous basalt sequences, eventually leading to fracturing and subsequent underplating of upper basement rock into the overriding accretionary prism. This dehydration-induced breakage of the basalt can explain variations in the thickness of accreted basalt fragments within accretionary prisms as well as the reported geochemical compositions of mineralized veins associated with exposed basalts in onland locations. This fracturing of intact basalt can also nucleate seismic rupturing that would subsequently propagate along seismogenic plate interfaces. Graphical abstract Schematic model showing the setting for décollement step-down into the ocean-plate basalts at the subdution plate interface. The diagram also shows textures of intact basalt and its expected frictional properties and behaviors associated with seismogenesis.

• Mineralization of the Gongpengzi deposit occurred at ca. 173 Ma. • Granitoids were derived by partial melting of a mixed depleted mantle and crustal source. • Crustal and mantle mixing was important for mineralization at Gongpengzi. The Gongpengzi Cu-Zn-W polymetallic deposit is a typical skarn deposit located in the Lesser Xing'an-Zhangguangcai Range, NE China. Although the deposit was first discovered in the 1950s, the timing of mineralization, source of the ore-forming materials, and geodynamic setting of the deposit, remain unclear. We present whole-rock geochemical and zircon U-Pb geochronological data for granitoids, molybdenite Re-Os geochronological data, and S-Pb isotopic analyses of sulfide minerals and feldspars from granitoids within the deposit. The results of molybdenite Re-Os and zircon U-Pb dating of biotite granites and granodiorite from the Gongpengzi polymetallic deposit suggest that ore formation occurred at 176.7 ± 5.9 Ma, and that the granodiorite hosting the mineralized zone were emplaced at 173.6 ± 1.0 and 173.9 ± 1.0 Ma, respectively. The granites and granodiorites have high SiO 2 and Na 2 O + K 2 O contents, are enriched in Rb, Th, U, Ta, and Pb, and depleted in U, P and Ti, and therefore classify as I-type granitoids. One granodiorite sample yielded a (87Sr/86Sr) i value of 0.70444, ε Nd (t) value of 2.30, and two-stage model age (T DM2) of 785 Ma. The biotite granite samples yielded (87Sr/86Sr) i values of 0.70433–0.70445, ε Nd (t) values of 2.34–2.54, and T DM2 of 785–765 Ma. These observations suggest that the granites were probably derived by partial melting of both mantle and juvenile crustal material, and that these partial melts underwent fractional crystallization. The ore-forming elements were magmatic source, and may have been derived by mixing between crustal and mantle sources. We interpret granitoid relating to skarn mineralization in the Lesser Xing'an-Zhangguangcai Range to have resulted from subduction of Paleo-Pacific oceanic crust toward the Eurasian continent. [ABSTRACT FROM AUTHOR]

Abstract Structural inheritance control of oceanic fracture zone formation by a large basement shear zone during continental breakup is still a matter of debate. In this research, we investigated the reactivation of Precambrian shear zones and their role in the formation of the Ascension and Fernando Poo fracture zones during the evolution of the South Atlantic Ocean. We used aeromagnetic and multichannel 2D seismic reflection data associated with previous geological and geophysical data to analyze how the Precambrian shear zones may have influenced the formation of oceanic fracture zones. Our results suggest that the fracture zones are extensions of the shear zones in the transition between continental and oceanic crust. The São Miguel do Aleixo and Pernambuco shear zones were reactivated during the Pangea breakup and acted as zones of weakness controlling the location of the Ascension and Fernando Poo fracture zones during the process of oceanic crust spreading. Our model suggests that the formation of these fracture zones influenced by the shear zones occurred in the early stages of ocean opening. It indicates that the fracture zones that formed in the late opening stages were related to the thermal subsidence stage, as suggested in previous studies. Highlights • Precambrian shear zones reactivated during Pangea breakup. • Precambrian shear zones acted as zones of weakness during breakup. • Shear zones reactivation controlled the location of oceanic fracture zones. • The fracture zones occur along strike from the continental basement shear zones. [ABSTRACT FROM AUTHOR]

Sampling the upper mantle via scientific ocean drilling remains elusive. Although the technologies required for drilling to the Moho still don't exist, we have made significant progress over the last five decades in piecing together the complex geology of the oceanic crust. Here, we highlight key findings that reveal the architecture of oceanic crust and the thermal, physical, and chemical processes that are responsible for the growth and structure of the oceanic lithosphere. These advances result from enduring efforts to drill and collect downhole geophysical logs of oceanic crust near both slow and fast spreading ridges. [ABSTRACT FROM AUTHOR]

Abstract The motion of diverging tectonic plates is typically constrained by geophysical data from preserved ocean crust. However, constraining plate motions during continental rifting and the breakup process relies on balancing evidence from a diverse range of geological and geophysical observations, often subject to differing interpretations. Reconstructing the evolution of rifting and breakup between Australia and Antarctica epitomizes the challenges involved in creating detailed models of Pangea breakup. In this example, differing degrees of emphasis on and alternative interpretations of offshore geophysical data, in particular magnetic anomalies and seismic reflection profiles, and onshore geological data, lead to starkly contrasting views of how the continents were configured at the onset of Mesozoic rifting. Here, we critically review reconstructions of rifting and breakup in the light of all available geological and geophysical data, including magnetic anomalies, fracture zones, conjugate crustal domains, amounts of continental extension, continental geology, plate boundary locations, break-up ages and stratigraphy. We identify the most viable plate tectonic reconstructions both with and without the input of the oldest, more controversial magnetic anomaly interpretations, and discuss implications for reconstructions of other margin pairs. Our analysis highlights key discrepancies between reconstructions based solely on geological piercing points, and those based on a range of constraints. These insights provide a powerful framework for reducing the range of viable models for Australian-Antarctic rifting, and provide key lessons for future efforts aimed at constraining pre- and syn-rift plate tectonic reconstructions. [ABSTRACT FROM AUTHOR]