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Summary geological map of the Eyasi–Natron–Manyara Basins at the southern end of the Eastern Rift, illustrating the predominance of long normal faults and wide basins. A–A , B–B and C–C are lines of cross-sections shown in figure 3. Elevations are from 1:50 000 topography maps and gravity station heights. ODO is Ol Donyo Ogol Fault.
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Although the morphology and dimensions of continental rift basins vary considerably worldwide, one aspect is similar; tectonicall active rifts are bordered on one or both sides by relatively long (tens of kilometres) normal fault systems (termed borde faults) that largely control basin morphology. We compile data constraining the geometry of border...
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Context 1
... northern part of this segment cuts the less than 1 Ma flood basalt sequence, whereas its southern part cuts Pan-African base- ment, making it difficult to assess its age and continuity there. South and west of the Manyara Basin, seismically active, greater than 40 km long, normal faults are morphologically the youngest faults in the region (see, for example, Balangida Fault, figure 4 and ). They may mark the initial stage of development of long border faults. ...
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West Africa continues to host a growing number of low and intermediate-magnitude earthquakes (M2-5) along its passive margins, and its continental interior. Earthquake activity in these regions raises the need to comprehend the causes and the tectonic controls of the seismicity. Unfortunately, such studies are rare. Here, we apply single-station in...
Citations
... Whereas faults elsewhere in the EARS are generally steep and planar, older basins in Turkana (e.g., the Lokichar Basin) display evidence of listric and potentially detachment faulting in places (Morley et al., 1999). The length scales of proposed rift segments are also generally shorter than other areas in the EARS (Ebinger et al., 1999), possibly reflecting the comparatively thinner, warmer crust in the region (Rosendahl et al., 1992). Finally, models for mature continental rifts in the eastern branch (e.g., Ethiopia) suggest that rifting initiates on border faults, but later migrates to intra-rift structures with time (Corti, 2009;Ebinger and Casey, 2001;Keranen et al., 2004;Nutz et al., 2020). ...
Scientific drill cores provide unique windows into the processes of the past and present. In the dynamic tectonic, environmental, climatic, and ecological setting that is eastern Africa, records recovered through scientific drilling enable us to look at change through time in unprecedented ways. Cores from the East African Rift System can provide valuable information about the context in which hominins have evolved in one of the key regions of hominin evolution over the past 4 Myr. The Deep Drilling in the Turkana Basin (DDTB) project seeks to explore the impact of several types of evolution (tectonic, climatic, biological) on ecosystems and environments. This includes addressing questions regarding the region's complex and interrelated rifting and magmatic history, as well as understanding processes of sedimentation and associated hydrothermal systems within the East African Rift System. We seek to determine the relative impacts of tectonic and climatic evolution on eastern African ecosystems. We ask the follow questions: what role (if any) did climate change play in the evolution of hominins? How can our understanding of past environmental change guide our planning for a future shaped by anthropogenic climate change? To organize the scientific community's goals for deep coring in the Turkana Basin, we hosted a 4 d ICDP supported workshop in Nairobi, Kenya, in July 2022. The team focused on how a 4 Myr sedimentary core from the Turkana Basin will uniquely address key scientific research objectives related to basin evolution, paleoclimate, paleoenvironment, and modern resources. Participants also discussed how DDTB could collaborate with community partners in the Turkana Basin, particularly around the themes of access to water and education. The team concluded that collecting the proposed Pliocene to modern record is best accomplished through a two-phase drilling project with a land-based transect of four cores spanning the interval from 4 Ma to the Middle–Late Pleistocene (< 0.7 Ma) and a lake-based core targeting the interval from ∼ 1 Ma to present. The second phase, while logistically more challenging due to the lack of drilling infrastructure currently on Lake Turkana, would revolutionize our understanding of a significant interval in the evolution and migration of Homo sapiens for a time period not currently accessible from the Kenyan part of the Turkana Basin. Collectively, the DDTB project will provide exceptional tectonic and climatic data directly associated with one of the world's richest hominin fossil localities.
... Typically, large continental rift zones evolve from isolated tectonic basins during the early stages of extension into larger, throughgoing, and topographically linked depressions (e.g., Ebinger & Scholz, 2012;Ebinger et al., 1999;and references therein). Before this connectivity between individual basins is achieved, kinematic linking between these basins is accommodated within structurally complex transfer zones by the generation of closely spaced normal faults, the formation of local transfer faults, and pronounced magmatic activity accompanied by diking (Bosworth & Morley, 1994;Morley et al., 1992;Riedl et al., 2022). ...
The Gofa Province and Chew Bahir Basin in the Broadly Rifted Zone (BRZ) between the southern Main Ethiopian Rift (sMER) and the northern Kenya Rift (nKR) record early volcanism and associated faulting in East Africa; however, the spatiotemporal relationships between volcanism and faulting remain poorly constrained. We applied apatite (U‐Th)/He (AHe) and zircon (U‐Th)/He (ZHe) thermochronometry to Neoproterozoic basement rocks from exhumed footwall blocks of the extensional Gofa Province and Chew Bahir Basin, and analyzed our result in the context of well‐dated regional volcanic units in the BRZ to unravel the interplay between tectonic exhumation, faulting and volcanism. Single‐grain AHe ages ranging from 1.0 to 136.8 Ma were recorded in 32 samples, and single‐grain ZHe ages from three samples range between 142.2 and 335.6 Ma. The youngest AHe ages were obtained from the Chew Bahir Basin and the narrow deformation zone in the Gofa Province. Our thermal modeling results reflect little or no significant regional crustal cooling prior to extensive volcanism, which started at about 45 Ma. Conversely, new and previously published thermal history models suggest that widespread crustal cooling related to regional extension occurred between ∼27 and 20 Ma. Thermal modeling results from subsets of samples indicate that following this initial diffuse extensional deformation, renewed exhumation occurred along a narrow zone within the Gofa Province and the Chew Bahir Basin during the middle to late Miocene (15‐6 Ma) and Pliocene (<5 Ma), respectively. The crustal cooling phases follow a regional trend in volcanic episodes. For example, initial cooling between 27 and 20 Ma corresponds with the end of widespread flood‐basalt volcanism (45–28 Ma), suggesting that spatially diffuse normal faulting may have initiated shortly after the emplacement of voluminous and areally extensive flood basalts. The Miocene and Pliocene shifts in deformation along the Mali‐Dancha and Bala‐Kela basins in the Gofa Province and the Chew Bahir Basin, respectively, may indicate strain localization during the late stage of rifting and ongoing tectonic interaction between the sMER and the nKR. Our results support the notion of crustal weakening by massive volcanism as a precursor to widespread extensional faulting, and thus offer further insights into magma‐assisted deformation processes in the East African Rift System.
... Normal fault systems bounding the Western and Eastern rifts and MER strike sub-N-S, and formed in Proterozoic orogenic belts surrounding the unusually thick, strong, Archaean cratons ( Fig. 1), suggesting that the pre-existing lithospheric thickness variations guided initial rift and magma localization (e.g., Sleep et al., 2002;Muirhead et al., 2020). Although segments of border and intrabasinal faults may parallel pre-existing shear zones (e.g., Daly et al., 2020), many steep border faults cut shallow basement fabric and show a regular along-axis segmentation that scales with plate strength (e.g., Ebinger et al., 1999). Obliquely-trending faults linking initially disconnected border faults are in many cases transtensional and may reactivate basement shear zones, but these are local features (e.g., Muirhead and Kattenhorn 2018;Musila et al., 2023). ...
... The overall structure of the Malawi Rift, with its long (∼150 km), large-offset (up to ∼7.3 km) border faults is similar in morphology to other magma-poor WB rift basins (e.g., Lake Tanganyika and Albert), and this overall structure is consistent with end-member rifting in strong, cold lithosphere (Buck, 1991;C. J. Ebinger et al., 1999). The importance of crustal thickness, lithospheric rheology, and pre-existing structures in strain localization in rifts are well recognized, but challenging to quantify (e.g., Accardo et al., 2018;Buck, 1991Buck, , 2004Corti et al., 2007;Hodge et al., 2018;Hopper et al., 2020;Wright et al., 2020). ...
Half‐graben basins bounded by border faults typify early‐stage continental rifts. Deciphering the role that intra‐rift faults play in rift basin development is challenging as patterns of early‐stage faulting are commonly overprinted by subsequent deformation; yet the characterization of these faults is crucial to understand the fundamental controls on their evolution, their contribution to rift opening, and to assess their seismic hazard. By integrating multiple offshore seismic reflection data sets with age‐dated drill core, late‐Quaternary and cumulative faulting patterns are characterized in the Central and South Basins of the Malawi (Nyasa) Rift, an active, early‐stage rift system. Almost all intra‐rift faults offset a late‐Quaternary lake lowstand surface, suggesting they are active and should be considered in hazard assessments. Fault throw profiles reveal sawtooth patterns indicating segmented slip histories. Observed extension on intra‐rift faults is approximately twice that predicted from hanging wall flexure of the border fault, suggesting that intra‐rift faults accommodate a proportion of the regional extension. Cumulative and late‐Quaternary throws on intra‐rift faults are correlated with throw measured on the border fault in the Central Basin, whereas an anticorrelation is observed in the South Basin. Viewed in a regional context, these differences do not relate solely to the proposed southward younging of the rift. Instead, it is inferred that the distribution of extension is also influenced by variations in lithospheric structure and crustal heterogeneities that are documented along the rift axis.
... Several factors may cause these variations in faulting along axis. A primary control on fault scaling is elastic thickness (e.g.,Ebinger et al., 1999;Jackson & White, ...
Magmatic intrusion and faulting both accommodate crustal extension in magma‐rich rifts. However, quantitative constraints on the contribution of faulting to total extension and along‐rift variations of faulting during the final stages of break‐up are lacking. We targeted the Danakil Depression (Afar, Ethiopia) to conduct a quantitative, high‐resolution study of fault activity and interaction in a magma‐rich rift near break‐up. Quantitative analysis of >500 rift axis faults, identified using remote sensing data (satellite imagery, DEMs), shows an increase in fault density, length and connectivity away from magmatic segments. Kinematic and earthquake focal mechanism data demonstrate a transition from transtensional opening in the northern and central sub‐regions of the rift to oblique opening in the southern Giulietti Plain and Tat‐Ali sub‐regions. Oblique opening is attributed to the along‐axis step between the Erta‐Ale and Harak sub‐regions. Integration of seismic reflection and borehole data with the mapped faults shows that extension is primarily accommodated by magmatism within the rift center, with faulting more significant toward the ends of the rift. ∼30% of crustal extension is accommodated by axial faulting in areas of low magmatism, highlighting the importance of faulting even in the final stages of magma‐rich rifting. Comparing our findings with spreading ridge morphology and structure, relevant due to the rift maturity and extensive magmatism, we conclude that the Danakil Depression is in a transitional stage between continental rifting and seafloor spreading. Spatial changes in the importance of faulting and magmatism in accommodating extension, alongside rift morphology, resemble the relationships observed along spreading ridges.
... Normal fault systems bounding the Western and Eastern rifts and MER strike sub-N-S, and formed in Proterozoic orogenic belts surrounding the unusually thick, strong, Archaean cratons ( Fig. 1), suggesting that the pre-existing lithospheric thickness variations guided initial rift and magma localization (e.g., Sleep et al., 2002;Muirhead et al., 2020). Although segments of border and intrabasinal faults may parallel pre-existing shear zones (e.g., Daly et al., 2020), many steep border faults cut shallow basement fabric and show a regular along-axis segmentation that scales with plate strength (e.g., Ebinger et al., 1999). Obliquely-trending faults linking initially disconnected border faults are in many cases transtensional and may reactivate basement shear zones, but these are local features (e.g., Muirhead and Kattenhorn 2018;Musila et al., 2023). ...
... Moreover, extension in an area may cause the formation of segmented blocks with subparallel arrays of normal faults, which might host dyke swarms in the presence of magma (e.g., Dabbahu Rift in Afar, Rowland et al. 2007). In general, segmentation scales with the thickness of the mechanical layer that is breaking (Ebinger et al. 1999). The displacement between resulting segments must be accommodated, i.e., it should be coupled or linked with another movement. ...
Although heat source, in terms of enthalpy and/or temperature, is usually considered the prime factor driving geothermal systems and has traditionally been the basis of their classification, this approach undermines the importance of the tectonic settings they exist in. The tectonic setting defines the regional stress regime that controls the permeability structure and determines the nature of heat source—magmatic or non-magmatic—and thermal regime—convective or conductive or a combination of the two, and also prevailing geothermal gradient and heat flow. Moreover, despite the tectonic setting being favorable, the local stress regime may make a geothermal system either highly productive or uneconomic, depending upon whether it aids the fluid circulation or not. Understanding the tectonic setting and local structural conditions may help enhance a low-performing exiting geothermal system's performance or even create a new one by developing artificial fractures to facilitate fluid circulation if a heat source—magmatic or non-magmatic (viz. radioactive)—is available.
... Our velocity profile of the southern Malawi Rift is the first to cross an amagmatic section of the western branch of the EARS, with unusually thick lithosphere (130-180 km; Priestley et al., 2018) and elevated topography (500-1,000 m asl; Figure 3b). For each of the six velocity profiles across the EARS (see Table S1), we compile the range of the lithospheric thickness along each profile from surface-wave tomography (Priestley et al., 2018; Figure S2), the range of crustal thickness along each profile from receiver function studies (Dugda et al., 2005;Ebinger et al., 2017;Stuart et al., 2006;Sun et al., 2021;Tugume et al., 2012;Wölbern et al., 2010; see Figure S3), the seismogenic thickness, defined as the maximum depth of upper crustal seismicity beneath each profile (Craig & Jackson, 2021;Ibs-von Seht et al., 2001;Keir et al., 2006), and the effective elastic thickness, measured using the coherence method (Ebinger & Hayward, 1996;Ebinger et al., 1999). ...
... Despite evidence for lateral heterogeneities localizing permanent strain near the surface (Hodge et al., 2018;, the southern Malawi Rift has a strong, dry crust (Hellebrekers et al., 2019), and seismicity down to the Moho (Craig et al., 2011;Sun et al., 2021). The maximum crustal thickness in southern Malawi is comparable to the other EARS profiles considered here (Figure 3c), but estimates of the depth of seismicity ( Figure 3e) and effective elastic thickness ( Figure 3f) are much higher (Craig et al., 2011;Ebinger et al., 1999). Larger elastic thicknesses smooth lower-crustal strain, causing a broader pattern of strain at the surface (Turcotte & Schubert, 2002). ...
Plain Language Summary
The breakup of continental plates is a fundamental part of plate tectonics, but little is known about how the plates start to stretch. In southern Africa, which is slowly extending, we use Global Positioning System (GPS) instruments to precisely measure the motion of the plates. Statistical tests show that southern Africa, which had previously been modeled as a single rigid plate called Nubia, can be better modeled as two separate plates, by the addition of the San microplate in southern Africa. We find that the plate‐boundary in southern Malawi is extending at ∼2 mm per year. However, the region that is actively extending is 890 km wide, which is wider than the 150 km wide region where we observe earthquakes and faults. Our new geodetic constraints suggest that in southern Africa, the continental plates are stretching apart at weaknesses around multiple microplates of old, thick crust, rather than along one single plate boundary.
... One alternative is the mechanical segmentation of a region upon which a unique regional stress is acting. In this case segmentation can be due to variations of thickness or strength of the country rock, to nucleation of two faults that are not coplanar but propagate towards each other, or to the influence of local inhomogeneities in the country rock (Ebinger et al., 1999;Gudmundsson and Philipp, 2006;LeGall et al., 2000). Another possibility for the occurrence of more than one preferred orientation of aligned vents is the swap of the minimum and intermediate stresses in a biaxial extensional regime, although in this case only two preferred orientations of dykes would be produced, each parallel to the two principal extensional stresses (Caputo, 1995). ...
Characterization of spatially distributed volcanism includes analysis of vent alignments, zones of high probability density and cluster membership assignment. Attempts to identify patterns from the spatial distribution of vents have resorted to various methods with the underlying assumption that results from any of those methods should provide quantitative evidence concerning the structure of the array. In contrast, the physical conditions leading to the creation of specific patterns of distribution have received less attention. In this work, the basis for some of the common expectations of studies of vent distribution, and how those expectations match the individual method-inherent assumptions, are reviewed. Throughout this work it is shown that the spatial distribution of volcanic vents allows us to extract much information concerning the physical structure of the sub-volcanic system. Nevertheless, attention must be given to the fact that not all systems are equal, and therefore, that it is a myth that any quantitative method can provide reliable information. Furthermore, it is shown that some methods even might yield false clues leading to the statistical validation of structures that have no physical support. Thus, in this paper it is highlighted that the selection of methods that fulfill the physical constraints likely to exist on the case of interest is extremely important to promote identification of the most plausible configurations in a robust form. Failure to acknowledge the importance of method selection can be detrimental for the correct understanding of the physical mechanisms underlying volcanic activity, and therefore such practices need to be avoided.
... It is commonly observed that tectonic stresses are a significant factor controlling the volcano's morphology. This is the case, both on large scales, for example, the alignments of central volcanoes in continental rift systems (Ebinger et al., 1999) or on a smaller scale within a single volcanic edifice, for example, oriented dike swarms at the Krafla volcanic system on Iceland associated with the extension along the MAR (Gudmundsson, 1987(Gudmundsson, , 1998. The injection of dikes commonly occurs perpendicular to the maximum extensional stress σ 3 (Walker, 1999), that is, along a NW-SE strike direction in the Hirondelle Basin area of the Terceira Rift. ...
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.
