Hydrological basin connectivity in a low-latitude rift: the impact of the Holocene African Humid Period (AHP) on fluvial activity and species dispersal in the Kenya Rift, East African Rift System (EARS)

2020 ◽  
Author(s):  
René Dommain ◽  
Simon Riedl ◽  
Lydia Olaka ◽  
Peter deMenocal ◽  
Alan Deino ◽  
...  
Keyword(s):  
Drainage System ◽  
Population Expansion ◽  
Aquatic Organisms ◽  
Rift System ◽  
East African Rift System ◽  
Species Dispersal ◽  
Dispersal Patterns ◽  
The North ◽  
Tectonic System ◽  
The Impact

<p>As a result of sustained tectonic and magmatic processes throughout the latter half of the Cenozoic, the eastern branch of the EARS exhibits an extensional tectonic system with pronounced relief contrasts, constituting both corridors and barriers for species dispersal. The tectono-magmatic history has generated a region of highly variable topography that results in widely varying amounts of rainfall and vegetation cover. Today, the generally dry eastern branch of the EARS hosts numerous sub-basins and adjacent local high-relief areas that are hydrologically isolated, with unique microclimates, vegetation types, faunas and superposed surface processes. However, during episodes of climate change with a trend toward more humid conditions, many of these basins hosted freshwater lakes that were hydrologically connected. These areas have repeatedly exhibited freshwater conditions and likely served as gateways and migration corridors mainly for aquatic organisms, in particular fish, facilitating population expansion, dispersal and gene flow.</p><p>Here, we analyze the manifold manifestations of the AHP in Kenya and adjacent sectors of the EARS to establish the timing and spatial extent of a paleo-drainage system documented by lake shorelines, deltas, overflow channels and sediments. These vestiges of fluvial connectivity in the rift have emerged as analogs for recurrent Pleistocene episodes with high lake levels and inter-basin linkage that repeatedly connected equatorial basins with regions to the north and south, respectively. For example, fossil evidence for the Pleistocene occurrence of the Nile crocodile (<em>Crocodylus niloticus</em>) as far south as equatorial Lake Bogoria (Kenya) and its present occurrence in the now closed Lake Baringo basin indicate fluvial connectivity over several degrees of latitude during more humid episodes in the past. Similarly, the occurrence of more than a dozen of the same fish species in the presently unconnected Lakes Albert and Turkana is likely due to a mutual connection during the AHP when Lake Turkana was overflowing into the White Nile.</p><p>Taken together, the divergent fossil and modern faunal evidence and geomorphic and sedimentological evidence of contrasting hydrological conditions between the wet AHP and the present, suggest that the conditions during the AHP provides a template of fluvial connectivity and potential dispersal patterns for earlier humid phases during the Plio-Pleistocene.</p>

scholarly journals The Impact of Complex Volcanic Plumbing on the Nature of Seismicity in the Developing Magmatic Natron Rift, Tanzania

2021 ◽  
Vol 8 ◽  
Author(s):  
Miriam Christina Reiss ◽  
James D. Muirhead ◽  
Amani S. Laizer ◽  
Frederik Link ◽  
Emmanuel O. Kazimoto ◽  
...  
Keyword(s):  
Volcanic Field ◽  
Tectonic Activity ◽  
Rift System ◽  
East African Rift System ◽  
Oldoinyo Lengai ◽  
Fault Plane Solutions ◽  
Magma Body ◽  
Volcanic Plumbing System ◽  
Stress Changes ◽  
The Impact

Constraining the architecture of complex 3D volcanic plumbing systems within active rifts, and their impact on rift processes, is critical for examining the interplay between faulting, magmatism and magmatic fluids in developing rift segments. The Natron basin of the East African Rift System provides an ideal location to study these processes, owing to its recent magmatic-tectonic activity and ongoing active carbonatite volcanism at Oldoinyo Lengai. Here, we report seismicity and fault plane solutions from a 10 month-long temporary seismic network spanning Oldoinyo Lengai, Naibor Soito volcanic field and Gelai volcano. We locate 6,827 earthquakes with ML −0.85 to 3.6, which are related to previous and ongoing magmatic and volcanic activity in the region, as well as regional tectonic extension. We observe seismicity down to ∼17 km depth north and south of Oldoinyo Lengai and shallow seismicity (3–10 km) beneath Gelai, including two swarms. The deepest seismicity (∼down to 20 km) occurs above a previously imaged magma body below Naibor Soito. These seismicity patterns reveal a detailed image of a complex volcanic plumbing system, supporting potential lateral and vertical connections between shallow- and deep-seated magmas, where fluid and melt transport to the surface is facilitated by intrusion of dikes and sills. Focal mechanisms vary spatially. T-axis trends reveal dominantly WNW-ESE extension near Gelai, while strike-slip mechanisms and a radial trend in P-axes are observed in the vicinity of Oldoinyo Lengai. These data support local variations in the state of stress, resulting from a combination of volcanic edifice loading and magma-driven stress changes imposed on a regional extensional stress field. Our results indicate that the southern Natron basin is a segmented rift system, in which fluids preferentially percolate vertically and laterally in a region where strain transfers from a border fault to a developing magmatic rift segment.

Thermal signature of the lithosphere below sedimentary basins in extensional, compressive and transform settings

2020 ◽  
Author(s):  
Magdalena Scheck-Wenderoth ◽  
Judith Bott ◽  
Mauro Cacace ◽  
Denis Anikiev ◽  
Maria Laura Gomez Dacal ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Internal Heat ◽  
Sedimentary Basins ◽  
Rift System ◽  
Upper Rhine Graben ◽  
East African Rift System ◽  
Forming Mechanism ◽  
Passive Margins ◽  
The North ◽  
Thermal Signature

<p>The configuration of the lithosphere below sedimentary basins varies in response to the basin-forming mechanism, the lifetime of the causative stress fields and the lithological heterogeneity inherited from pre-basin tectonic events. Accordingly, the deep thermal configuration is a function of the tectonic setting, the time since the thermal disturbance occurred and the internal heat sources within the lithosphere. We compare deep thermal configurations in different settings based on data-constrained 3D lithosphere-scale thermal models that consider both geological and geophysical observations and physical processes of heat transfer. The results presented come from a varied range of tectonic settings including: (1) the extensional settings of the Upper Rhine Graben and the East African Rift System, where we show that rifts can be hot for different reasons; (2) the North and South Atlantic passive margins, demonstrating that magma-rich passive margins can be comparatively hot or cold depending on the thermo-tectonic age; (3) the Alps, where we find that foreland basins are influenced by the conductive properties and heat-producing units of the adjacent orogen; and (4)the Sea of Marmara, along the westernmost sector of the North Anatolian Fault Zone, that suggest strike-slip basins may be thermally segmented.</p>

Imaging active magmatic systems at Oldoinyo Lengai volcano (Tanzania) via earthquake distribution and seismic scattering and absorption mapping

2020 ◽  
Author(s):  
Miriam Christina Reiss ◽  
Luca De Siena ◽  
Georg Rümpker ◽  
Emmanuel Owden Kazimoto
Keyword(s):  
Detection Threshold ◽  
Seismic Network ◽  
Rift System ◽  
Shield Volcano ◽  
East African Rift System ◽  
Oldoinyo Lengai ◽  
Seismic Scattering ◽  
The North ◽  
Cone Field ◽  
Plumbing Systems

<p>Oldoinyo Lengai volcano, located in the Natron Basin (Tanzania), is the only active natrocarbonatite volcano world-wide. As such, it presents an important endmember magmatic system, which occurs in a young rift segment (~3 Ma) of the East African Rift System. At this volcano, effusive episodes of long-duration are interrupted by short-duration explosive eruptions. At the end of February 2019, we installed a dense seismic network and four infrasound stations as part of the SEISVOL - Seismic and Infrasound Networks to Study the Volcano Oldoinyo Lengai - project. The seismic network spans an area of 30 x 30 km and encompasses Oldoinyo Lengai volcano, the extinct 1 Ma-old Gelai shield volcano, the active Naibor Soito monogenetic cone field and surrounding fault population. Here, we present temporal earthquake distributions combined with 2D absorption and scattering imaging.</p><p>On average, we report up to 34 earthquakes per day within and in the vicinity of our network. Given the dense station spacing, we are able to lower the detection threshold to -1.0 M<sub>L</sub> with a M<sub>C</sub> of -0.3. During the first months of data acquisition, the seismicity is clustered in distinct areas as background seismicity and in intermittent seismic swarms:</p><ol><li>Most of the events are located beneath the eastern and southern flank of Gelai shield volcano. These events are shallow and close to the dike intrusion that preceded the last explosive eruption of Oldoinyo Lengai in 2007-2008.</li> <li>In April 2019, a seismic swarm of ~262 earthquakes in three days forms a pipe-like structure beneath the north western flank of Gelai.</li> <li>Deeper events cluster beneath the monogenetic cone field located just NE of Oldoinyo Lengai. A distinct gap in seismicity can be traced down to 10 km depth between the monogenetic cone field and Gelai volcano.</li> <li>While there seems to be little seismicity directly beneath Oldoinyo Lengai in the upper 5 km of the crust, we observe a number of different, recurring seismic and infrasound signals at the crater, which are indicative of magmatic activity.</li> </ol><p>To image the magmatic plumbing system, we map scattering and absorption of the seismic dataset using the MuRAT (Multi-Resolution Attenuation Tomography) code. Our preliminary results show two well-resolved high-absorption and high-scattering anomalies below Oldoinyo Lengai and the Gelai intrusion in 2007 at all frequencies. With decreasing frequency (increasing depth) the anomalies converge, suggesting a link of the plumbing systems at depth.</p>

Rift-basin compartmentalization and changing environments: tectono-climatic forcing of environmental conditions and species dispersal in the East African Rift System (EARS)

2020 ◽  
Author(s):  
Manfred R Strecker ◽  
René Dommain ◽  
Yannick Garcin ◽  
Lydia A Olaka ◽  
Richard Potts ◽  
...  
Keyword(s):  
Climatic Conditions ◽  
Congo Basin ◽  
Disjunct Distribution ◽  
Rift System ◽  
East African Rift System ◽  
Species Dispersal ◽  
East African ◽  
African Rift ◽  
Spatially Varying ◽  
Wet Forests

<p>In the EARS orographic forcing of rainfall, pronounced relief contrasts between shoulder areas and the axial rift sectors results in steep environmental and surface-process gradients, severed fluvial networks, and diverse vegetation types. Due to sustained Quaternary tectono-volcanic activity and the effects of a superposed, highly variable climate these basins have been further differentiated into distinct environments that are either isolated or fluvially connected on time scales of several 10<sup>3</sup> to 10<sup>6</sup> years. The EARS thus comprises important physical corridors, but also barriers with spatially varying topographic conditions and resource distribution. Varying paleo-environmental settings and the present-day distribution of some mammal groups in the EARS' Kenya Rift highlight the importance of rift corridors for the migration of species and the interchange of now geographically isolated lineages.</p><p>For example, the presently disjunct distribution of the Bat-eared fox (<em>Otocyon megalotis</em>), the Black-backed jackal (<em>Canis mesomelas</em>) and the Oryx sister taxa (<em>Oryx beisa </em>and<em> O. gazella</em>) in northeastern vs. southern Africa, or of various rainforest antelopes such as Bongo (<em>Tragelaphus euryceros</em>) in the Congo basin and beyond the EARS in central Kenya, suggests that variability in connectivity along and across the rift has influenced species dispersal. Protracted rifting dictates the overall geomorphic character of the migration corridors, but fluvial connectivity varies significantly as a response to orbitally driven climatic conditions. These factors were responsible for lateral change in vegetation cover, such as the distribution of wet forests that enabled dispersal in the equatorial sectors of the rift. Such conditions ultimately determined whether the meridionally oriented rift segments acted as gateways or barriers.</p>

Seismic wave attenuation in the lithosphere of the North Tanzanian divergence zone (East African rift system)

2017 ◽  
Vol 58 (2) ◽  
pp. 253-265 ◽  
Author(s):  
A.A. Dobrynina ◽  
J. Albaric ◽  
A. Deschamps ◽  
J. Perrot ◽  
R.W. Ferdinand ◽  
...  
Keyword(s):  
Seismic Wave ◽  
Wave Attenuation ◽  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
Seismic Wave Attenuation ◽  
The North ◽  
African Rift

Revisiting Hotspots and Continental Breakup – Updating the Classical Three-arm Model

2021 ◽  
Author(s):  
Carol Stein ◽  
Seth Stein ◽  
Molly Gallahue ◽  
Reece Elling
Keyword(s):  
North Atlantic Ocean ◽  
Ocean Basin ◽  
Rift System ◽  
Plate Boundaries ◽  
East African Rift System ◽  
Continental Rifting ◽  
East African ◽  
Continental Breakup ◽  
The North ◽  
Junction Points

<p>In two classic papers, Burke and Dewey (1973) and Dewey and Burke (1974) proposed that continental rifting begins at hotspots - domal uplifts with associated magmatism - from which three rift arms extend. Rift arms from different hotspots link up to form new plate boundaries along which the continent breaks up, generating a new ocean basin and leaving failed arms termed aulacogens within the continent.  In subsequent studies, hotspots became increasingly viewed as manifestations of deeper upwellings or plumes, which were the primary cause of continental rifting. We revisit this conceptual model and find that it remains useful, though some aspects require updates based on subsequent results.  Many three-arm systems identified by Burke and Dewey (1973) are now recognized to be or have been boundaries of transient microplates accommodating motion between diverging major plates. Present-day examples include the East African Rift system and the Sinai microplate.  Older examples include rifts associated with the opening of the South Atlantic in the Mesozoic and the North Atlantic Ocean over the last 200 Ma,  rifts in the southern U.S associated with the breakup of Rodinia, and intracontinental rifts formed within India during the breakup of Gondwanaland. The microplates form as continents break up, and are kinematically distinct from the neighboring plates, in that they move separately. Ultimately, the microplates are incorporated into one of the major plates, leaving identifiable fossil features on land and/or offshore. In many cases the boundaries of microplates during continental breakup are located on preexisting zones of weakness and influenced by pre-existing fabric, including older collisional zones. Hotspots play at most a secondary role in continental breakup, in that most of the associated volcanism reflects plate divergence, so three-arm junction points may not reflect localized upwelling of a deep  mantle plume.</p>

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