Transfer Zones in the East African Rift System and Their Relevance to Hydrocarbon Exploration in Rifts (1)

Morley, Christopher; Nelson, Robert A.; Patton, Thomas L.; Münn, Sebastian

doi:10.1306/0c9b2475-1710-11d7-8645000102c1865d

Cited by 114 publications

(52 citation statements)

References 53 publications

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“…Unlike the North Basin-Central Basin accommodation zone, where there is ~25 km of along-strike overlap, there is instead a gap of ~30 km between the Central and South Basin border-fault systems, which may further allow for a broadly extended region and a wide rift to develop in this area. Accordingly, this broadly rifted zone is a consequence of a segmentation linkage geometry of opposite-facing half-graben basins (e.g., divergent transfer zone of Morley et al, 1990) but with no overlap, and aspects of this geometry are consistent with some analogue models of orthogonal rifting (e.g., Paul and Mitra, 2013).…”

Section: Mcs Results-accommodation Zone Central and South Basinssupporting

confidence: 70%

“…There is no observation of progressive onlap of basal sediment packages onto basement either in strike or dip view that has been proposed to explain rift basin expansion and enlargement in some systems (e.g., Schlische, 1991). Rather the basal sediment package in each segment extends along almost the full width and length of the half-graben basin, implying that the border faults each established nearly their full length early in the history of the rift, similar to what has been observed in Lake Tanganyika (Morley et al, 1990) and the Okavango region (Kinabo et al, 2008).…”

Section: Research Papersupporting

confidence: 58%

“…These segments vary in length, width, and internal structural fabric depending on several factors, including strength of the continental lithosphere (Ebinger et al, 1991), antecedent heterogeneities, and preexisting crustal structures (Dunbar and Sawyer, 1989;Versfelt and Rosendahl, 1989;Corti et al, 2007;Brune et al, 2017) and the degree of magmatic involvement in rifting processes (e.g., Baker, 1986;Morley, 1994;Hayward and Ebinger, 1996;Ebinger and Casey, 2001;Corti et al, 2007;Muirhead et al, 2016). The linkage behavior of discrete rift segments, in the form of accommodation zones or transfer zones, may also be influenced by these same factors, and different linkage geometries may produce structures of markedly varying morphologies (e.g., Rosendahl, 1987;Morley et al, 1990). The sequential evolution of both the rift bounding and intrarift faults dictates the surface expression of rift zones, adjacent uplifted footwall mountain ranges, and zones of intrarift subsidence, which may be filled with thick sequences of synrift deposits and at times be occupied by large tectonic lake basins, sometimes for the life history of the rift zone (e.g., Tiercelin et al, 1988).…”

Section: ■ Introductionmentioning

confidence: 99%

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Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

et al. 2020

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The Lake Malawi (Nyasa) Rift, in the East African Rift System (EARS), is an ideal modern analogue for the study of extensional tectonic systems in low strain rate settings. The seismically active rift contains the 700-m-deep Lake Malawi, one of the world’s oldest and largest freshwater lakes with one of the most diverse endemic faunal assemblages on Earth. Modern and reprocessed legacy multichannel seismic-reflection data are constrained by velocity information from a wide-angle seismic experiment to evaluate variability in extension, segmentation, and timing of fault development along the 550-km-long rift zone. Fault geometries and patterns of synrift sediment fills show that the Lake Malawi Rift is composed of three asymmetric rift segments, with intervening accommodation zone morphologies controlled by the degree of overlap between segment border faults. Most extension occurs on the basin border faults, and broadly distributed extension is only observed at one accommodation zone, where no border fault overlap is observed. Structural restorations indicate a weakly extended rift system (~7 km), with diminishing values of extension and thinner rift fill from north to south, suggesting a progressively younger rift to the south. There is no evidence of diking, sill injection, or extrusives within the synrift fill of the Lake Malawi Rift, although the volcanic load of the Rungwe magmatic system north of the lake and related subsidence may explain the presence of anomalously thick synrift fill in the northernmost part of the lake. The thickest synrift depocenters (~5.5 km) are confined to narrow 10- to 20-km-wide zones adjacent to each rift segment border fault, indicating concentration of strain on border faults rather than intrarift faults. Intrarift structures control axial sediment delivery in the North and Central rift segments, focusing sediment into confined areas resulting in localized overpressure and shale diapirs. The asymmetric, basement-controlled relief was established early in rift development. When overprinted with frequent high-amplitude hydroclimate fluctuations, which are well documented for this basin, the resulting highly variable landscape and lake morphometry through time likely impacted the diverse endemic faunas that evolved within the basin. New seismic-reflection data, augmented by wide-angle seismic data and age constraints from drill core, offer the most highly resolved 3D view to date of latest Cenozoic extensional deformation in East Africa and provide a foundation for hazards analysis, resource assessments, and constraining deformation in a low strain rate, magma-poor active rift.

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Section: Mcs Results-accommodation Zone Central and South Basinssupporting

confidence: 70%

Section: Research Papersupporting

confidence: 58%

Section: ■ Introductionmentioning

confidence: 99%

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Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

et al. 2020

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“…This along-axis segmentation effectively partitions stratigraphic sequences and strongly infl uences erosion and drainage patterns in rifts (e.g., Gawthorpe and Leeder, 1997;Mats et al, 2000;Densmore et al, 2004;Dorsey and Umhoefer, 2012). Initially discrete border-fault segments interact and are mechanically connected through transfer faults and relay ramps oriented obliquely to the strikes of border faults (e.g., Larsen, 1988;Morley and Nelson, 1990;Walsh and Watterson, 1991;Peacock and Sanderson, 1994). Rift segments may grow or link through along-axis propagation and interaction of faults and magmatic plumbing systems (e.g., Ebinger et al, 1989;Densmore et al, 2004;San'kov et al, 2000San'kov et al, , 2009Beutel et al, 2010;Allken et al, 2012).…”

Section: Along-axis Segmentationmentioning

confidence: 99%

“…Rift segments may grow or link through along-axis propagation and interaction of faults and magmatic plumbing systems (e.g., Ebinger et al, 1989;Densmore et al, 2004;San'kov et al, 2000San'kov et al, , 2009Beutel et al, 2010;Allken et al, 2012). Transfer fault zone geometries may change, or be abandoned, during linkage (e.g., Morley and Nelson, 1990;Schlische, 1993;Cartwright et al, 1995;Densmore et al, 2007). The role of magmatism in segment linkage during the spe 500-11 1st pgs page 5 early rifting stages remains poorly understood owing to the general lack of detailed subsurface data (e.g., Ebinger et al, 1989;Rowland and Sibson, 2001), but clear patterns are seen in mature rift zones, as outlined below.…”

Section: Along-axis Segmentationmentioning

confidence: 99%

The time scales of continental rifting: Implications for global processes

Ebinger

Wijk

Keir

2013

The Web of Geological Sciences: Advances, Impacts, and Interactions

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The rifting cycle initiates with stress buildup, release as earthquakes and/or magma intrusions/eruptions, and visco-elastic rebound, multiple episodes of which combine to produce the observed, time-averaged rift zone architecture. The aim of our synthesis of current research initiatives into continental rifting-to-rupture processes is to quantify the time and length scales of faulting and magmatism that produce the time-averaged rift structures imaged in failed rifts and passive margins worldwide. We compare and contrast seismic and geodetic strain patterns during discrete, intense rifting episodes in magmatic and amagmatic sectors of the East African rift zone that span early-to late-stage rifting. We also examine the longer term rifting cycle and its relation to changing far-fi eld extension directions with examples from the Rio Grande rift zone and other cratonic rifts. Over time periods of millions of years, periods of rotating regional stress fi elds are marked by a lull in magmatic activity and a temporary halt to tectonic rift opening. Admittedly, rifting cycle comparisons are biased by the short time scale of global seismic and geodetic measurements, which span a small fraction of the 10 2 -10 5 year rifting cycle. Within rift sectors with upper crustal magma chambers beneath the central rift valley (e.g., Main Ethiopian, Afar, and Eastern or Gregory rifts) seismic energy release accounts for a small fraction of the deformation; most of the strain is accommodated by magma intrusion and slowslip. Magma intrusion processes appear to decrease the time period between rifting episodes, effectively accelerating the rift to rupture process. Thus, the inter-seismic period in rift zones with crustal magma reservoirs is strongly dependent upon the

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An abandoned rift in the southwestern part of the South Scotia Ridge (Antarctica): Implications for the genesis of the Bransfield Strait

Lodolo

Pérez

2015

Tectonics

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The western segment of the South Scotia Ridge is a narrow submarine ridge composed of continental crustal blocks, which hosts the left-lateral boundary between the Scotia and Antarctic plates. This plate boundary segment gradually merges westward with the Bransfield Strait, a young (<4 Ma) basin located between the South Shetland Islands and the northern segment of the Antarctic Peninsula. Here we present a series of multichannel seismic profiles that reveal the presence of a linear chain of submarine volcanic edifices running parallel to the present-day Scotia-Antarctic plate boundary. These edifices consist of alkali basalts (~4 Ma), as shown by published data from a dredge haul. The occurrence, distribution, and shape of these magmatic manifestations suggest that they were emplaced in a rift-related environment, associated with the activity of the former western segment of the Scotia-Antarctic plate boundary. When spreading centers of the Phoenix-Antarctic ridge NW of the South Shetland Islands became inactive at about 3.3 Ma, the former western Scotia-Antarctic plate boundary was abandoned, and it moved to the present-day location of the Bransfield Strait, where the motion was accommodated, and where active extension is ongoing. The proposed mechanism for the development of the Bransfield Strait, consistent with the temporal sequence of tectonic events, reconciles discrepancies in tectonic evolutionary models presented till now and does not require the presence of slab-pull and/or slab retreat forces. The Bransfield Strait is not a classic back-arc basin, but rather an actively extending marginal basin at the transition from mature rifting to incipient, punctiform spreading.

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Transfer Zones in the East African Rift System and Their Relevance to Hydrocarbon Exploration in Rifts (1)

Cited by 114 publications

References 53 publications

Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

Intrarift fault fabric, segmentation, and basin evolution of the Lake Malawi (Nyasa) Rift, East Africa

The time scales of continental rifting: Implications for global processes

An abandoned rift in the southwestern part of the South Scotia Ridge (Antarctica): Implications for the genesis of the Bransfield Strait

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