Geology and Geophysics of the Anza Graben

Morley, Christopher; Bosworth, William; Day, R. A.; Lauck, R.; Bosher, R.; Stone, Denise M.; Wigger, S.T.; Wescott, William A.; Haun, D.; Bassett, N.

doi:10.1306/st44623c4

Cited by 23 publications

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“…On the eastern side of Lake Turkana are notable early-middle Miocene volcanic rocks around Moiti-Jarigole and the Jibsia ring complex, which include basic lavas and syenite intrusions (e.g., Wilkinson, 1988;Key, 1989;Furman et al, 2006). The early extension in Turkana overlaps with minor periods of late Paleogene extension in the Sudan and Anza rifts to the northwest and east respectively (e.g., Schull, 1988;Morley et al, 1999b;Mohamed et al, 2016;Yassin et al, 2017). The distribution of these basins over an area ~1800 km in a NW-SE direction and >400 km wide, and oblique to the more north-south trend of the Eocene-Oligocene volcanic rocks in southern Ethiopia and northern Turkana (Fig.…”

Section: Comparison Of Dike Development In Turkana Versus Southern Kementioning

confidence: 99%

Early syn-rift igneous dike patterns, northern Kenya Rift (Turkana, Kenya): Implications for local and regional stresses, tectonics, and magma-structure interactions

Morley

2020

Geosphere

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Four areas (Loriu, Lojamei, Muranachok-Muruangapoi, Kamutile Hills) of well-developed Miocene-age dikes in the northern Kenya Rift (Turkana, Kenya) have been identified from fieldwork and satellite images; in total, >3500 dikes were mapped. Three areas display NNW-SSE– to N-S–oriented dike swarms, with straight, radial, and concentric patterns in zones <15 km long, and indicate NNW-SSE to N-S regional maximum horizontal principal stress (SHmax) directions in the early to middle Miocene. Individual dikes are typically <2 m wide and tens to hundreds of meters long and have accommodated <2% extension. In places (Loriu, Lojamei, Lokhone high), dikes trend at a high angle to the rift trend, suggesting some local influence (e.g., overpressured magma chamber, cracked lid–style dike intrusions over a sill or laccolith, preexisting fabric in basement) on orientation, in addition to the influence from regional stresses. Only a minor influence by basement fabrics is seen on dike orientation. The early- to middle-Miocene dikes and extrusive activity ended a long phase (up to 25 m.y.) of amagmatic half-graben development in central Kenya and southern Turkana, which lay on the southern edge of the early (Eocene–Oligocene) plume activity. The Miocene dike sets and extension on major border faults in Turkana contrast with larger, more extensive arrays of dikes in evolved systems in the Main Ethiopian Rift that are critical for accommodating crustal extension. By the Pliocene–Holocene, magmatism and intrusion along dikes had become more important for accommodating extension, and the tectonic characteristics began to resemble those of rift basins elsewhere in the eastern branch of the East African Rift.

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Section: Comparison Of Dike Development In Turkana Versus Southern Kementioning

confidence: 99%

Early syn-rift igneous dike patterns, northern Kenya Rift (Turkana, Kenya): Implications for local and regional stresses, tectonics, and magma-structure interactions

Morley

2020

Geosphere

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Influence of Rift Superposition on Lithospheric Response to East African Rift System Extension: Lapur Range, Turkana, Kenya

et al. 2018

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The Turkana Depression of northern Kenya lies at the intersection of the NW‐SE trending late Mesozoic‐early Paleogene South Sudan and Anza rifts and the N‐S trending late Paleogene‐Recent East African Rift System (EARS). A low‐temperature thermochronology study in the Lapur Range reveals a complex tectonothermal evolution related to multiple periods of regional and local tectonism. Zircon (U‐Th)/He data from Precambrian basement record rapid Early Cretaceous denudational cooling. Coeval subsidence in the adjacent Anza and South Sudan rifts (Morley, Bosworth, et al., 1999; Schull, 1988) suggests that the northern Turkana region acted as a basement high separating the grabens, as well as an axial source of sediment. Between ~95 and 90 Ma, a period of reheating commenced with burial of Lapur basement beneath ~500 m of Late Cretaceous‐Eocene Lapur Sandstone and ~1.5–3.5 km of latest Eocene‐early Miocene Turkana volcanics. Apatite fission track (AFT) and apatite (U‐Th‐Sm)/He data record a transition to rapid denudational cooling in the mid‐Miocene (~14 Ma) in response to EARS‐related extension in the northern Turkana Basin. Thermal history models indicate that the Lapur Range experienced ~90–100°C of mid‐Miocene to Plio‐Pleistocene cooling, yielding the first Neogene AFT ages reported from Kenya related to EARS exhumation. We attribute the larger magnitude of cooling in the Lapur Range compared to other regions of the EARS to the attenuated crustal thickness and elevated heat flow of the Turkana Depression, crustal properties inherited from earlier Cretaceous‐Paleogene rifting. The resulting low effective elastic thickness of the Turkana lithosphere allowed for increased isostatic footwall uplift in response to EARS extension.

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A 300 Million Years History of Rift Lakes in Central and East Africa: An Updated Broad Review

Tiercelin

Lezzar

2002

Advances in Global Change Research

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Geology and Geophysics of the Anza Graben

Cited by 23 publications

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Early syn-rift igneous dike patterns, northern Kenya Rift (Turkana, Kenya): Implications for local and regional stresses, tectonics, and magma-structure interactions

Early syn-rift igneous dike patterns, northern Kenya Rift (Turkana, Kenya): Implications for local and regional stresses, tectonics, and magma-structure interactions

Influence of Rift Superposition on Lithospheric Response to East African Rift System Extension: Lapur Range, Turkana, Kenya

A 300 Million Years History of Rift Lakes in Central and East Africa: An Updated Broad Review

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