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Continental breakup represents the successful process of rifting and thinning of the continental lithosphere, leading to plate rupture and initiation of oceanic crust formation. Magmatism during breakup seems to follow a path of either excessive, transient magmatism (magma-rich margins) or of igneous starvation (magma-poor margins). The latter type is characterized by extreme continental lithospheric extension and mantle exhumation prior to igneous oceanic crust formation. Discovery of magma-poor margins has raised fundamental questions about the onset of ocean-floor type magmatism, and has guided interpretation of seismic data across many rifted margins, including the highly extended northern South China Sea margin. Here we report International Ocean Discovery Program drilling data from the northern South China Sea margin, testing the magma-poor margin model outside the North Atlantic. Contrary to expectations, results show initiation of Mid-Ocean Ridge basalt type magmatism during breakup, with a narrow and rapid transition into igneous oceanic crust. Coring and seismic data suggest that fast lithospheric extension without mantle exhumation generated a margin structure between the two endmembers. Asthenospheric upwelling yielding Mid-Ocean Ridge basalt-type magmatism from normal-temperature mantle during final breakup is interpreted to reflect rapid rifting within thin pre-rift lithosphere.

Failed rifts are widely assumed to enter post‐rift tectonic quiescence after termination of intracontinental rifting, but a comprehensive understanding of their regional morphotectonics is lacking. Our quantitative, rift‐scale geomorphic analyses in the Suez Rift, an archetypal failed rift in Egypt, reveals widespread rifting after presumed rift “failure.” Stacked topographic swaths document normal fault offsets in Plio‐Quaternary rocks and fluvial metrics show steep gradients consistent with active faulting along the entire rift length. Quaternary shorelines uplifted along both margins constrain footwall uplift rates of up to 0.13 ± 0.04 mm/yr on normal faults with down‐dip heights of 10–15 km that were active by 3.12 ± 0.23 and 4.44 ± 0.2 Ma or earlier times. Pleistocene‐Recent extension rates of 0.26–0.55 mm/yr are lower than rates characterising preceding rift phases, albeit compatible with those of modestly active intracontinental rifts (e.g., Basin and Range). Our evidence of active extension after rift “abandonment” supports continued but decelerated rifting, not failure, in the Suez Rift.

The fate of continental lithosphere during rifting is central to the process of continental extension. The continental lithospheric mantle comprises both depleted and enriched domains that may contribute to magma generation during extension. The East African Rift System is the archetypal example of a magma‐rich continental rift, with the Turkana Depression containing the most extensive temporal record of mafic magmatism. There is debate as to the contribution of continental lithosphere to this mafic magmatism, with suggestions that HIMU‐like isotopic signatures, often attributed to the continental lithosphere, are derived instead from a heterogeneous mantle plume. We focus on Miocene lavas that are characterized by radiogenic 206Pb/204Pb > 19.3, requiring a contribution from an HIMU‐like endmember in their origin. We present a novel two‐stage chromatographic metasomatism model that demonstrates that a HIMU‐like endmember can be generated through time‐integrated evolution within the continental lithospheric mantle. The first model stage uses an initial composition for the metasomatizing agent equivalent to a subduction magma to generate metasomes within the continental lithosphere during the Pan‐African stabilization of the regional lithosphere (∼700 Ma). During Mesozoic rifting, the second model stage simulates destabilization and melting of these initial metasomes, re‐enriching the surrounding lithosphere to generate new Mesozoic metasomes. Melts of these metasomes, when combined with melts of the regional asthenosphere, are consistent with the observed trace element and isotopic signatures of Turkana Miocene lavas. These findings suggest an important role for the continental lithospheric mantle during rifting and obviate the need for a complex, heterogenous plume.

Rocks at various lithospheric depths commonly display a fabric, resulting in mechanical anisotropy. The mechanical response of such anisotropic rocks depends on both the intensity of the anisotropy and the orientation of the fabric relative to the applied stress. Despite its potential significance, the role of mechanical anisotropy in governing lithospheric strength and deformation style during extension remains poorly constrained. Here, we investigate how mechanical anisotropy influences the deformation of the lithosphere under tectonic extension. We use two‐dimensional numerical models of lithospheric deformation that incorporate a non‐linear, transversely isotropic model. Both viscous and plastic rheologies are direction‐dependent, and fabric orientations evolve using the director‐vector approach. We perform simulations of continental extension and show that mechanical anisotropy is a major factor in the development of continental rifts. It influences the architecture of rift basins and reduces the driving force required for rifting. We explore the role of extensional velocity and find that it has only a second‐order influence on the evolution of rift systems. Furthermore, we investigate the relative contributions of crustal and mantle anisotropy, and highlight that mantle anisotropy plays a more significant role. The driving forces required for continental rifting are quantified and systematically analyzed. Compared to isotropic models, the required driving force is reduced by up to a factor of three when mechanical anisotropy is included. As a result, forces below 10 TN/m can be achieved, which is consistent with estimates from the geological record.

Subduction zones are integral to Earth's deep water cycle, influencing magmatism, lithosphere dynamics and seismicity. They often exhibit development of extensional processes in the upper plate, which may lead to volcanic arc splitting and backarc basin opening. Here, we investigate numerically the factors controlling arc rifting and back‐arc opening and basin evolution, emphasizing the roles of slab dehydration, and melting processes linked to upper plate thermal structures and variable sediment fluxes. Using an extensive suite of 2D and 3D thermo‐mechanical models, we assess intra‐arc rift initiation timing in the upper plate, lithospheric thinning, and arc rifting patterns. Model results reveal that higher crustal temperatures and sedimentation rates enhance melting and crustal weakening along the arc, facilitating strain localization and faster roll‐back, but may simultaneously diminish stress transfer efficiency. Additionally, 3D modeling captures along‐strike variations, including slab tearing and toroidal mantle flows, offering insights into the complex interplay of subduction dynamics and their effect for arc rifting. These findings are compared with natural laboratories in the Mediterranean and in retreating subduction systems of SE Asia.

The Afro‐Arabian region is one of the few places on land, where rifting processes at divergent plate boundaries can be thoroughly investigated. One of the crucial factors in understanding rifting processes involves assessing the crustal thickness. In this study, gravity data from the Earth Gravitational Model 2008 is used to create a seamless map of the depth to the Moho interface. Unlike many previous investigations that focused on specific localized areas, within the region, results from the current study provide a comprehensive view. The depth obtained from the current investigation aligns well with findings from earlier studies, exhibiting a bias of 0.69 km and a standard deviation of 3.89 km. Within the region, maximum and minimum depths to the Moho interface are observed beneath the northwest Ethiopian Plateau and the Gulf of Aden Rift (GAR), respectively. Analyzing profiles across the Red Sea, Main Ethiopian, and GARs, the study concluded that the Southern Main Ethiopian Rift is in an earlier stage of the rifting process, while the GAR is at an advanced stage. Furthermore, the interpretation of the current findings led to the inference that there might exist two potential plume tails driving the rifting process in the East Africa Rift—one originating from the Afar region and the other from South Kenya. This inference primarily relies on the isostatic compensation stages observed in the various rift systems throughout the region. Key Points Moho depth from the Earth Gravitational Model 2008 model is derived with a bias of 0.69 km and a standard deviation of ±3.89 km when compared to prior studies The maximum depth to the Moho interface is 42.9 km beneath the NW Ethiopian Plateau and the shallowest depth is 5.3 km beneath the Gulf of Aden Rift The Southern Main Ethiopian Rift is at an early stage of rifting and two mantle plume tails are potentially driving the rifting process

Significant volumes of magma can be intruded into the crust during continental break‐up, influencing rift evolution by altering the thermo‐mechanical structure of the crust and its response to extensional stresses. Rift magmas additionally feed surface volcanic activity and can be globally significant sources of tectonic CO2 emissions. Understanding how magmatism may affect rift development requires knowledge on magma intrusion depths in the crust. Here, using data from olivine‐hosted melt inclusions, we investigate magma dynamics for basaltic intrusions in the Main Ethiopian Rift (MER). We find evidence for a spatially focused zone of magma intrusion at the MER upper‐lower crustal boundary (10–15 km depth), consistent with geophysical datasets. We propose that ascending melts in the MER are intruded over this depth range as discrete sills, likely creating a mechanically weak mid‐crustal layer. Our results have important implications for how magma addition can influence crustal rheology in a maturing continental rift. Plain Language Summary Continental rifting, the break‐up of continents to form new ocean basins, is a key component in the tectonic cycle that affects Earth's surface environment. The rifting process is aided by magmatic activity in its final stages, which weakens the crust by heating it. This is believed to facilitate present‐day rifting in Ethiopia, where we find rift‐related volcanoes. The depth of magma storage in the rifting crust will determine how heat is distributed, and therefore how the physical properties of the crust are altered. Here we study melt inclusions, small pockets of magmas trapped within growing crystals beneath rift volcanoes. Using the concentrations of CO2 and H2O in melt inclusions we infer the pressures (and therefore depths) that they formed. Our results demonstrate that magmas rising through the Ethiopian crust consistently stall at a depth range of 10–15 km beneath the surface. Furthermore, the diverse chemical composition of our melt inclusions show that magmas are stored in multiple small bodies versus a larger mixed magma reservoir. This study therefore provides new insights into how magmas are stored in the Ethiopian crust before volcanic eruptions and suggests that rising magmas may produce a weak layer in the middle of the rifting crust. Key Points We determine magma storage conditions in the Main Ethiopian Rift through geochemical analysis of olivine‐hosted melt inclusions Volatile saturation barometry reveals that basaltic melts are focused at 10–15 km depth in the Ethiopian crust Geochemical heterogeneity in melt inclusions suggests that magma storage is likely to occur in semi‐discrete sills

We present the Malawi Active Fault Database (MAFD), an open‐access (https://doi.org/10.5281/zenodo.5507190) geospatial database of 113 fault traces in Malawi and neighboring Tanzania and Mozambique. Malawi is located within the East African Rift's (EAR) Western Branch where active fault identification is challenging because chronostratigraphic data are rare, and/or faults are buried and so do not have a surface expression. The MAFD therefore includes any fault that has evidence for displacement during Cenozoic East African rifting or is buried beneath the rift valley and is favorably oriented to the regional stresses. To identify such faults, we consider a multidisciplinary data set: high‐resolution digital elevation models, previous geological mapping, field observations, seismic reflection surveys from offshore Lake Malawi, and aeromagnetic and gravity data. The MAFD includes faults throughout Malawi, where seismic risk is increasing because of population growth and its seismically vulnerable building stock. We also investigate the database as a sample of the normal fault population in an incipient continental rift. We cannot reject the null hypothesis that the distribution of fault lengths in the MAFD is described by a power law, which is consistent with Malawi's relatively thick seismogenic layer (30–40 km), low (<8%) regional extensional strain, and regional deformation localization (50%–75%) across relatively long hard‐linked border faults. Cumulatively, we highlight the importance of integrating onshore and offshore geological and geophysical data to develop active fault databases along the EAR and similar continental settings both to understand the regional seismic hazard and tectonic evolution. Plain Language Summary Earthquakes represent the occurrence of slip along cracks in the Earth's crust. Therefore, mapping these cracks, or “faults,” is important when assessing earthquake hazards. However, faults are challenging to identify as they may not be visible at the surface. Fault mapping also requires recognizing which faults have slipped in earthquakes in the recent geologic past, as these “active” faults are the most likely faults to have future earthquakes. Here, we describe how we identified active faults in Malawi, which is located along the tectonically active East African Rift. Faults under Lake Malawi were mapped using images of lake sediments that were generated from sound waves. Onshore, some faults were mapped from their expression in the landscape. Other faults, not visible at the surface, were identified from aeromagnetic data, which image the spatial distributions of magnetic minerals in the Earth's crust. Faults are considered active if that show evidence for slip during East African rifting in Malawi. We combined the active faults identified from these analyses into the Malawi Active Fault Database, a freely available geospatial database. We suggest that this database will be useful for seismic hazard planning in Malawi, where population growth and vulnerable buildings are increasing earthquake risk. Key Points Digital elevation models, offshore seismic reflection surveys, and aeromagnetic data are combined to identify active faults in Malawi Mapped faults are incorporated into the Malawi Active Fault Database, an open‐access geospatial database The mapped faults follow a power law length distribution, which is consistent with strain localization onto a few long (>50 km) faults

In many cases the initial stage of continental break‐up was and is associated with oblique rifting. That includes break‐up in the Southern and Equatorial Atlantic, separation from eastern and western Gondwana as well as many recent rift systems, like Gulf of California, Ethiopia Rift and Dead Sea fault. Using a simple analytic mechanical model and advanced numerical, thermomechanical modeling techniques we investigate the influence of oblique extension on the required tectonic force in a three‐dimensional setting. While magmatic processes have been already suggested to affect rift evolution, we show that additional mechanisms emerge due to the three‐dimensionality of an extensional system. Focusing on non‐magmatic rift settings, we find that oblique extension significantly facilitates the rift process. This is due to the fact that oblique deformation requires less force in order to reach the plastic yield limit than rift‐perpendicular extension. The model shows that in the case of two competing non‐magmatic rifts, with one perpendicular and one oblique to the direction of extension but otherwise having identical properties, the oblique rift zone is mechanically preferred and thus attracts more strain. Key Points Oblique extension facilitates the rift process in non‐magmatic settings Shearing a continent requires up to two times less force than rifting it An oblique rift zone attracts more strain than a competitive normal rift

Detrital zircon data have recently become available from many different portions of the Tibetan–Himalayan orogen. This study uses 13,441 new or existing U‐Pb ages of zircon crystals from strata in the Lesser Himalayan, Greater Himalayan, and Tethyan sequences in the Himalaya, the Lhasa, Qiangtang, and Nan Shan–Qilian Shan–Altun Shan terranes in Tibet, and platformal strata of the Tarim craton to constrain changes in provenance through time. These constraints provide information about the paleogeographic and tectonic evolution of the Tibet–Himalaya region during Neoproterozoic to Mesozoic time. First‐order conclusions are as follows: (1) Most ages from these crustal fragments are <1.4 Ga, which suggests formation in accretionary orogens involving little pre‐mid‐Proterozoic cratonal material; (2) all fragments south of the Jinsa suture evolved along the northern margin of India as part of a circum‐Gondwana convergent margin system; (3) these Gondwana‐margin assemblages were blanketed by glaciogenic sediment during Carboniferous–Permian time; (4) terranes north of the Jinsa suture formed along the southern margin of the Tarim–North China craton; (5) the northern (Tarim–North China) terranes and Gondwana‐margin assemblages may have been juxtaposed during mid‐Paleozoic time, followed by rifting that formed the Paleo‐Tethys and Meso‐Tethys ocean basins; (6) the abundance of Permian–Triassic arc‐derived detritus in the Lhasa and Qiangtang terranes is interpreted to record their northward migration across the Paleo‐ and Meso‐Tethys ocean basins; and (7) the arrival of India juxtaposed the Tethyan assemblage on its northern margin against the Lhasa terrane, and is the latest in a long history of collisional tectonism. Key Points Tibet is underlain mainly by juvenile terranes Tethyan realm consisted of three separate ocean basins Detrital zircons record changing provenance