Turkana Rift Research Articles

Kinematics of rift linkage between the Eastern and Ethiopian rifts in the Turkana Depression, Africa

AbstractRift initiation within cold, thick, strong lithosphere and the evolving linkage to form a contiguous plate boundary remains debated in part owing to the lack of time–space constraints on kinematics of basement‐involved faults. Different rift sectors initiate diachronously and may eventually link to produce a jigsaw spatial pattern, as in the East African rift, and along the Atlantic Ocean margins. The space–time distribution of earthquakes illuminates the geometry and kinematics of fault zones within the crystalline crust, as well as areas with pressurized magma bodies. We use seismicity and Global Navigation System Satellites (GNSS) data from the Turkana Rift Array Investigating Lithospheric Structure (TRAILS) project in East Africa and a new digital compilation of faults and eruptive centres to evaluate models for the kinematic linkage of two initially separate rift sectors: the Main Ethiopian Rift (MER) and the Eastern rift (ER). The ca. 300 km wide zone of linkage includes failed basins and linkage zones; seismicity outlines active structures. Models of GNSS data indicate that the ca. 250 km‐wide zone of seismically active en echelon basins north of the Turkana Depression is a zone, or block, of distributed strain with small counterclockwise rotation that serves to connect the Main Ethiopian and Eastern rifts. Its western boundary is poorly defined owing to data gaps in South Sudan. Strain across the northern and southern boundaries of this block, and an ca. 50 km‐wide kink in the southern Turkana rift is accommodated by en echelon normal faults linked by short strike‐slip faults in crystalline basement, and relay ramps at the surface. Short segments of obliquely oriented basement structures facilitate across‐rift linkage of faults, but basement shear zones and Mesozoic rift faults are not actively straining. This configuration has existed for at least 2–5 My without the development of localized shear zones or transform faults, documenting the importance of distributed deformation in continental rift tectonics.

Structural differences and exploration potential of basins in the eastern and western branches of the East African Rift System

The East African Rift System (EARS) is the youngest rift with the eastern and western branches, consisting of multiple secondary rifts. It is generally characterized by low extent of exploration and great exploration potential. Identifying the differences in hydrocarbon accumulation conditions in various rifts is very important in providing guidance for hydrocarbon exploration and selecting favorable exploration targets in this area. Based on the interpretation of first-hand seismic-geological data, and combining other materials such as commercial databases and open access literature, the structural characteristics of the main rifts in the eastern and western branches of the EARS are comparatively analyzed; based on the anatomy of the discovered hydrocarbon reservoirs, the rifts of the EARS are classified into four types depending on their structural styles, including double-fault type, simple single-fault type, single-fault transfer type, and single-fault terrace type, and the control of structural style over hydrocarbon accumulation in the EARS is discussed. In the Western Branch of the EARS, large rifts such as the Albertine Rift and the Tanganyika Rift are mainly of double-fault type and single-fault transfer type, and only some small rifts are of the simple single-fault type. The rifts in the Eastern Branch of the EARS are generally small; the rifts in the northern section of the Western Branch are mainly of the simple single-fault type, and those in the southern section are mainly of the single-fault terrace type. The hydrocarbon potential of double-fault rifts is the greatest, followed by that of simple single-fault rifts and single-fault transfer rifts, and the hydrocarbon potential of single-fault terrace rifts is relatively limited. The results obtained from a comparative analysis of the structures, sediment fills, and reservoir elements of various rifts show that the west side of the Albertine Rift, the southeast of the Tanganyika Rift, the Kerio Rift, and the land in the northwest of the Turkana Rift have great exploration potential.

Spectral Analysis of Gravity Data Using Spectral Analysis with Piecewise Regression (SAPR): Application to the Lake Turkana Rift, Northern Kenya and Southern Ethiopia

Spectral Analysis of Gravity Data Using Spectral Analysis with Piecewise Regression (SAPR): Application to the Lake Turkana Rift, Northern Kenya and Southern Ethiopia

Transition to magma-driven rifting in the South Turkana Basin, Kenya: Part 1

Characterization of the role of magma in driving rift basin evolution is fundamental to our understanding of how extensional plate boundaries develop. Here, we examine patterns of normal faulting, volcanism and magmatism in the South Turkana Basin, Kenya, to test how magmatism has impacted the Quaternary evolution of this system. Utilizing high-resolution, single-channel reflection seismic data and radiocarbon-dated cores, we estimate that shallow Holocene normal faulting accounts for 3.5–5.8 mm a −1 of extension, consistent with estimates farther south in the Suguta Basin. Spatial fault patterns show that extension in the Holocene is concentrated along a c. 20 km wide intra-rift fault network, aligning with the axial volcano, South Island. We suggest that up to 85% of Late Quaternary regional extension is accommodated within an axial magmatic segment rather than on the border fault system responsible for the original basin architecture. Axial extension increases towards South Island, highlighting magmatism as crucial in driving recent shallow upper crustal faulting in the South Turkana Basin. Below this zone of extensional faulting, geochemical evidence supports a developed magma plumbing system that broadly parallels equivalent axial magmatic systems within the Main Ethiopian Rift. Overall, our data support a recent (Mid- to Late Pleistocene) transition to magma-driven axial extension in the Lake Turkana rift. Supplementary material: Supplementary text and the fault, volcanic cone and radiocarbon age data utilized in this study are available at https://doi.org/10.6084/m9.figshare.c.6026624

An age for the Korath Range, Ethiopia and the viability of 40Ar/39Ar dating of kaersutite in Late Pleistocene volcanics

The Korath Range is the northernmost of five Quaternary volcanic fields along the axis of the Turkana rift of northern Kenya and southern Ethiopia. It is located within the Omo River valley of Ethiopia, a culturally diverse region that contains abundant Plio-Pleistocene human remains, which have been essential to refining our understanding of hominid evolution. Yet, very little geochronologic information is available for the Korath Range. We have undertaken 40Ar/39Ar incremental heating experiments, using two techniques, on kaersutite phenocrysts from a pyroclastic flow and obtained a weighted mean age of 91 ± 15 ka (2σ). The results, although imprecise, suggest that 40Ar/39Ar geochronology of these Ti-rich amphiboles can yield useful age information.

Analysis of gravity field to reconstruct the structure of Omo basin in SW Ethiopia and implications for hydrocarbon potential

The Omo basin in south western Ethiopia at the Kenyan boundary is a northern extension of the trans- boundary Turkana rift. It is an Early Pliocene north-south trending depression bounded on either side by normal faulting. The Omo river flows in the middle of the basin and empties itself at its southern end into Lake Turkana. The structural pattern of the Omo basin is determined from 2D and 3D analyses of the gravity field. The basin is an asymmetric half-graben formed by and localized within the NS/NNE trending Early Pliocene normal faults. It is built up on the older NW trending structures that were reactivated and affected the recent NS faults. Automatic depth determination techniques and 3D inversion are used to estimate depth to the basement and determine the sedimentary thickness. The results indicate over 4 km thick sediments were deposited over the graben. The Omo basin lies within the East African Rift system and appears to connect the generally NW trending oil-rich Muglad-Melut basins of south Sudan and the highly prospective and similarly trending Anza graben of Kenya. The Omo basin contains thick sequence of sediments and appears to be a promising future site of intensive hydrocarbon exploration.

Dynamics of prolonged continental extension in magmatic rifts: the Turkana Rift case study (North Kenya)

Abstract The Turkana magmatic rift (Northern Kenya) initiated at 45 Ma as one of the nucleation zones of rifting in the East African Rift. It forms an anomalously broad-rifted zone ( c. 200 km) striking with a north-south trend and lying within a NW-SE topographic depression, floored on both sides of the Turkana area by Cretaceous rifts in the Sudan and Anza plains. From a compilation of available data, combined with newly acquired remote sensing and DEM dataset, we propose a five-stage tectono-magmatic model for the Turkana rift evolution (45–23 Ma; 23–15 Ma; 15–6 Ma; 6–2.6 Ma and 2.6 Ma-Present). The corresponding ‘restored’ maps clearly show the changing spatial distribution of magmatism and fault/basin network with time, hence supplying some clues about dynamics of continental extension. First-order basement-rooted transverse faults zones are identified and their influence on nucleation and propagation of strain is demonstrated, whereas the role of magmatic ‘soft-spots’ as concentrating strain is minimized. Blocking of deformation as well as rift jump and lateral transfer of strain are discussed in relation to various types of fault interaction (dip direction, strikes and acute/obtuse angle of the intersecting faults). The causal links between rift nucleation ‘cells’ and inherited transverse weakness zones in the Turkana rift might also exist elsewhere along the eastern branch of the East African Rift, hence suggesting a complex and discontinuous mode of rift propagation.

A comment on ‘Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses’

Basin ResearchVolume 17, Issue 2 p. 329-335 A comment on ‘Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses’ Francis H. Brown, Francis H. Brown Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USASearch for more papers by this authorPatrick N. Gathogo, Patrick N. Gathogo Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USASearch for more papers by this author Francis H. Brown, Francis H. Brown Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USASearch for more papers by this authorPatrick N. Gathogo, Patrick N. Gathogo Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USASearch for more papers by this author First published: 06 June 2005 https://doi.org/10.1111/j.1365-2117.2005.00267_1.x Francis H. Brown, Department of Geology and Geophysics, University of Utah, 135 S 1460 East, Salt Lake City, UT 84112,USA. E-mail: [email protected] Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume17, Issue2June 2005Pages 329-335 RelatedInformation

Reply to the comment of F. H. Brown & P. N. Gathogo on ‘Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses’

Reply to the comment of F. H. Brown & P. N. Gathogo on ‘Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses’

Inversion tectonics during continental rifting: The Turkana Cenozoic rifted zone, northern Kenya

Remote sensing data and revised seismic reflection profiles provide new insights about the origin of inverted deformation within Miocene‐Recent basins of the Turkana rift (northern Kenya) in the eastern branch of the East African rift system. Contractional structures are dominated by weakly inverted sets of fault blocks within <3.7 Myr old synrift series. Most of reverse extensional faults involve components of oblique‐slip, whereas associated hanging wall folds are characterized by large wavelength upright folding. The area of basin inversion is restricted to a 40 × 100 km elongated zone overlying a first‐order N140°E trending fault zone in the basement, referred to as the N'Doto transverse fault zone (NTFZ). In the proposed kinematic model, inversion tectonics is assigned to permutation of principal stress axes (σ1/σ2) in addition to the clockwise rotation of extension (from nearly N90°E to N130°E) during Pliocene. The transition from pure extension (Miocene) to a wrench faulting regime (Pliocene) first results in the development of T‐type fault networks within a dextrally reactivated shear zone (NTFZ). Inversion tectonics occurred later (<3.7 Ma) in response to a still rotated (∼20°) shortening axis (σ1) oriented N40°E that caused the oblique compression of earlier (NS to N20°E) extensional structures within the NTFZ. The origin of basin inversion and strain concentration in the Turkana rift is thus directly linked to a crustal weakness zone, transverse to the rift axis, and involving steep prerift anisotropies.

Geometry and growth of an inner rift fault pattern: the Kino Sogo Fault Belt, Turkana Rift (North Kenya)

A quantitative analysis is presented of the scaling properties of faults within the exceptionally well-exposed Kino Sogo Fault Belt (KSFB) from the eastern part of the 200-km-wide Turkana rift, Northern Kenya. The KSFB comprises a series of horsts and grabens within an arcuate 40-km-wide zone that dissects Miocene–Pliocene lavas overlying an earlier asymmetric fault block. The fault belt is ∼150 km long and is bounded to the north and south by transverse (N50°E and N140°E) fault zones. An unusual feature of the fault system is that it accommodates very low strains (<1%) and since it is no older than 3 Ma, it could be characterised by extension rates and strain rates that are as low as ∼0.1 mm/yr and 10 −16 s −1, respectively. Despite its immaturity, the fault system comprises segmented fault arrays with lengths of up to 40 km, with individual fault segments ranging up to ∼9 km in length. Fault length distributions subscribe to a negative exponential scaling law, as opposed to the power law scaling typical of other fault systems. The relatively long faults and segments are, however, characterised by maximum throws of no more than 100 m, providing displacement/length ratios that are significantly below those of other fault systems. The under-displaced nature of the fault system is attributed to early stage rapid fault propagation possibly arising from reactivation of earlier underlying basement fabrics/faults or magmatic-related fractures. Combined with the structural control exercised by pre-existing transverse structures, the KSFB demonstrates the strong influence of older structures on rift fault system growth and the relatively rapid development of under-displaced fault geometries at low strains.

Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analyses

AbstractThe Turkana rifted zone in northern Kenya is a long‐lived and polyphased rift system where the lack of well‐marked rift morphology makes it difficult to identify the zone of active deformation. A high‐density river network is exceptionally well developed over the study area and shows evidence of drainage anomalies that suggest recent fault‐induced movements at various scales. Correlation of surface drainage anomalies with Landsat remote sensing and deep seismic reflection data permits to characterize the deep geometry of the inferred fault structures. Seismic stratigraphy further allows distinction between the inherited (Oligocene–Pliocene) and the newly formed (&lt;3.7 Ma) origin of the recent deformation. Evidence for neotectonics are observed (1) along a large‐scale transverse (EW) fault rooted at depth along a steep basement discontinuity (Turkwell), (2) along a rift‐parallel (NS) fault zone probably emplaced during the Pliocene–Pleistocene and currently bounding the Napedet volcanic plateau to the west and (3) over a round‐shaped uplifted zone caused by positive inversion tectonics (Kalabata). The major contribution of this work is the recognition of a broad (80 km wide) zone of recent/active extensional deformation in the Turkana Rift in contrast with the narrow (20 km wide) N10°E‐trending axial trough forming the Suguta valley to the south, and the Chew Bahir faulted basin to the north. These along‐strike variations in structural style are partly controlled by the occurrence of rejuvenated Oligocene–Miocene rift faults and long‐lived transverse discontinuities in the Turkana Rift area. More generally, this study has implications for the use of river drainage network about recent/active extensional domains with subdued topography and slow deformation rate.

Quaternary volcanic centres of the Turkana Rift, Kenya

Three small islands (North, Central and South Island) rise above the surface of Lake Turkana in northern Kenya. They represent the tops of Quaternary volcanic centres aligned along the axis of the Turkana Rift. They are links in the continuous chain of axial volcanic centres that run the length of the Eastern Branch of the East African Rift and represent the most recent additions to the architecture of the Rift. Mapping and petrographic studies reveal that the three island volcanic centres have many similarities in their general stratigraphy, structure, and geologic history; however, there are significant differences in relative lithologic abundances and compositions among them. The island volcanic centres are situated near the centres of each of a series of half-graben that are linked together along the length of the Turkana Rift. Estimates of the volumes of basaltic and intermediate volcanic components coupled with likely fractionation histories suggest that significant mafic-ultramafic intrusive complexes underlie the island volcanic centres. These are probably just the most recent additions to magmatically thickened, but mechanically thinned crust in this section of the East African Rift.

Comparison of the Tanganyika, Malawi, Rukwa and Turkana Rift zones from analyses of seismic reflection data

Northwest-southeast extension has opened the East African Rift System along two main branches, the Western and Eastern Branches. Rift zones along the Western Branch are marked by narrow lakes floored by thick piles of fluvial clastic and ‘pelagic’ sediment. Magmatism is restricted to a few small areas in the ‘arches’ between the lakes. In contrast, rift zones along the Eastern Branch are largely filled with volcanic and volcaniclastic materials and magmatism is generally perceived to be an integral part of the rifting process. In an attempt to sort out the significance and meaning of these and other differences, we have compared multifold seismic data from three Western Branch rift zones (Tanganyika, Rukwa and Malawi) and one Eastern Branch zone (Turkana). The Tanganyika and Malawi Rift Zones are composed of half-graben basins linked in complex ways by accommodation zones which generally trend oblique to the rift axes, and sometimes oblique to the extension direction. Half-grabens alternate basinal polarities where the rift crosses Proterozoic dislocation zones. Complex fault geometries are associated with some accommodation zones; elsewhere faults are almost exclusively planar. Sedimentary fill reaches at least 4–5 km and the section is mostly Cenozoic in age. Patches of Permo-Triassic sedimentary rocks are believed to occur within both rift zones. The Rukwa Rift is a pull-apart zone that connects the northern (Livingstone) basin of Lake Malawi to the Kalemie Basin in central Lake Tanganyika. The entire pull-apart system may be a series of down-to-the-east half-grabens. An accommodation zone develops along a short stretch of the Rukwa Rift, but no full polarity reversal occurs. The break-away faults of the Livingstone, Rukwa and Kalemie basins are essentially coincident with the Proterozoic Rukwa dislocation zone, which sub-parallels the inferred extension direction. Fault geometries in the Rukwa Rift are markedly listric, especially in the pre-Cenozoic section. Sedimentary fill ranges in age from pre-Karroo through Cenozoic and locally exceeds 10 km in thickness. The Turkana Rift is composed of short, linear, NNE-trending normal fault segments that are offset in a left-lateral sense by numerous, NW-SE trending transfer faults, linking facing border fault segments together. The overall trend of the rift zone is oblique to the opening direction, like the Tanganyika and Malawi cases, but the border fault segments are sub-perpendicular. Fault geometries are highly variable, but flower structures associated with transfer faults predominate. Igneous activity is ubiquitous and appears to be localized along the transfer faults. Basin fill reaches 4–5 km in thickness and is dominated by fluvial clastic, volcaniclastic and volcanic materials. The structural differences within the Tanganyika-Rukwa-Malawi system stem mainly from the modifying effects of pre-rift anistropies on strain expressions. Fundamentally, this system is a NW-SE trending series of single-polarity pull-apart basins. At the two ends of the pull-apart zone, the rift is deflected into more N-S trending basins which have a high tendency to alternate polarities along strike. This explanation does not account for the differences in fault forms between the Tanganyika-Malawi (planar) and Rukwa (listric) Rifts. For the time being, we presume these differences arise from systematic differences between Tanganyika-Malawi and Rukwa in the age ranges of the fill and/or the maximum depths of seismic imaging. Rifting in Turkana is profoundly different than in the Tanganyika-Rukwa-Malawi sub-branch and seems to involve a softer, more ductile, more organized style of extension which may be closer to the ideal case. In a thermal sense, rifting has progressed further in Turkana than along the Western Branch zones. This does not preclude original, fundamental difference in the thermal states of two branches.

Geochemical variation of Quaternary basaltic volcanics in the Turkana Rift, northern Kenya

There are five Quaternary volcanic edifices along the axis of the Turkana Rift of northern Kenya. From north to south these are the Korath Range, North Island, Central Island, South Island and the Barrier. Each of these edifices occurs in a structurally distinct segment of the active Turkana Rift. Preliminary studies of these Quaternary volcanics show that crystalliquid differentiation is an important process in all centers, though there is evidence of magma mixing, multiple intrusive episodes and incorporation of earlier lava flows into younger eruptives. The least-fractionated lavas from each volcano have distinctive geochemical signatures, defined by Nb/Zr, Ba/Ti, Ba/Sr and similar ratios. The Korath Range is the most alkalic series, with high Nb/Zr and Ba/Ti. These differences are attributed in large part to melting of a veined mantle beneath the individual rift segments; assimilation of continental crust may be important in the North Island magmas. Elemental abundance patterns in the Korath Range and Central Range magmas are very similar to those for enriched or plume-type ocean ridge basalts. The source for these rift volcanics may not be fundamentally different than the veined mantle that has been postulated as the source for normal and enriched ocean-ridge basalts. Quaternary rift volcanism, much like volcanism along spreading ridges, is segmented both tectonically and chemically. Comparison of these five Quaternary centers to a few analyses of Tertiary lavas along the Turkana Rift indicate that magmas have been produced from similar sources and processes for most of the development of the rift, but that there is no persistence of a particular geochemical signature with time for each magmatic cell.

Structure and stratigraphy of the Turkana rift from seismic reflection data

A multichannel seismic survey was conducted on Lake Turkana, a rift lake occupying a portion of the Eastern Branch of the East African Rift System. This survey revealed the presence of a significant rift structure beneath the lake, the extent and structural details of which had been previously unknown. The lake is underlain by a series of half-graben basins which alternate in polarity along the axis of the lake, and are linked end to end by zones of structural high. These half-graben often have Quaternary volcanic centers located near their latitudinal midpoints. Half-graben basins beneath Turkana deepen progressively to the north, attaining thicknesses of up to 4 km. A deep seismic reflector has been identified, and is believed to correspond to the top of a thick series of Mio-Pliocene flood volcanics. Overlying reflectors are thought to correspond to fluvial, lacustrine and volcano-clastic sediments that are Plio-Pleistocene to Recent in age. The style of rifting beneath Lake Turkana is similar to that observed beneath Lake Tanganyika, which occupies a portion of the Western Branch of the East African Rift System. The most noticeable differences are the abundant volcanism and smaller half-graben size associated with Lake Turkana. These differences may be attributed to the warmer, thinner lithosphere underlying the Eastern Branch as compared to that underlying the Western Branch.

Structural style of the Turkana Rift, Kenya

Research Article| March 01, 1988 Structural style of the Turkana Rift, Kenya Thomas J. Dunkelman; Thomas J. Dunkelman 1Department of Geology, Duke University, Durham, North Carolina 27706 Search for other works by this author on: GSW Google Scholar Jeffrey A. Karson; Jeffrey A. Karson 1Department of Geology, Duke University, Durham, North Carolina 27706 Search for other works by this author on: GSW Google Scholar Bruce R. Rosendahl Bruce R. Rosendahl 1Department of Geology, Duke University, Durham, North Carolina 27706 Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas J. Dunkelman 1Department of Geology, Duke University, Durham, North Carolina 27706 Jeffrey A. Karson 1Department of Geology, Duke University, Durham, North Carolina 27706 Bruce R. Rosendahl 1Department of Geology, Duke University, Durham, North Carolina 27706 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (3): 258–261. https://doi.org/10.1130/0091-7613(1988)016<0258:SSOTTR>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas J. Dunkelman, Jeffrey A. Karson, Bruce R. Rosendahl; Structural style of the Turkana Rift, Kenya. Geology 1988;; 16 (3): 258–261. doi: https://doi.org/10.1130/0091-7613(1988)016<0258:SSOTTR>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Multifold seismic reflection and geologic mapping in part of the eastern branch of the East African Rift system of northern Kenya reveal a major rift structure containing at least 3 km of Neogene sediment fill beneath Lake Turkana. This includes a series of half-graben basins, with centrally located Quaternary volcanic centers, which are linked end-to-end by structural accommodation zones. Whereas the geometry of rifting is similar to that of the nonvolcanic western branch of the East African Rift system, the Turkana half-grabens are much smaller and may reflect extension of a thinner lithosphere or development of more closely spaced fracture patterns during rift evolution, or both. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.