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.

Eruptive frequency of the Bora-Baricha-Tullu Moye (BBTM) volcanic system in the Central Main Ethiopian Rift

2021 ◽  
Author(s):  
Amdemichael Zafu Tadesse ◽  
Karen Fontijn ◽  
Abate Assen Melaku ◽  
Ermias Filfilu Gebru ◽  
Victoria Smith ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Volcanic Eruptions ◽  
Volcanic Field ◽  
Tectonic Activity ◽  
Explosive Eruptions ◽  
Ethiopian Rift ◽  
Rift System ◽  
Diagnostic Features ◽  
Volcanic System ◽  
Main Ethiopian Rift

<p>The Main Ethiopian Rift (MER) is the northern portion of the East African Rift System and separates the Eastern and Western plateaus of Ethiopia. The recent volcanic and tectonic activity is largely focused within the rift basin along a 20 km wide zone on the rift floor. Large silicic volcanic complexes are aligned along this central rift axis but their eruptive histories are not well constrained.</p><p>The Bora-Baricha-Tullu Moye (BBTM) volcanic field is situated in the central Main Ethiopian Rift and has a different appearance than the other MER volcanic systems. The BBTM constitutes several late Quaternary edifices, the major ones are: Tullu Moye, Bora and Baricha. In addition, there are multiple smaller eruptive vents (e.g. Oda and Dima), cones, and domes across the ca. 20 X 20 km wide area. Currently, there is very little information on the frequency and magnitude of past volcanic eruptions. We present a new dataset of field observations, componentry, petrography, geochronology (<sup>40</sup>Ar/<sup>39</sup>Ar), and glass major and trace element chemistry. The data are assessed as potential fingerprints to assign diagnostic features and correlate units across the area, and establish a tephrostratigraphic framework for the BBTM volcanic field.</p><p>Two large-volume and presumably caldera-forming eruptions are identified, the younger of which took place at 100 ka. The volcanic products exposed in the BBTM area show that the volcanic field has undergone at least 20 explosive eruptions since then. The post-caldera eruptions have comenditic (Tullu Moye) and pantelleretic (Bora and Baricha) magma compositions. Other smaller edifices such as Oda and Dima also erupted pantelleritic magmas, and only differ slightly in composition than tephra of Bora and Baricha. Tullu Moye had two distinct explosive eruptions that dispersed tephra up to 14 km away and on to the eastern plateau. Bora and Baricha together had at least 8 explosive eruptions. Their deposits can be distinguished by their light grey color and unique lithic components. Oda had 7 eruptions, the most recent of which generated a pyroclastic density current that travelled up to 10 km away from the vent. Dima experienced at least 3 eruptions, generating tephra with a bluish-grey colour.</p><p>This mapping and compositional analysis of the deposits from the BBTM in the MER indicates that the region has been more active in the last 100 ka than previously thought, which has implications for hazards assessments for the region.</p>

Chasing the Magma Chamber: MT meets Geodynamics and Seismology – A numerical case study of magmatic plumbing at Oldoinyo Lengai Volcano

2021 ◽  
Author(s):  
César Daniel Castro ◽  
Miriam Christina Reiss ◽  
Arne Spang ◽  
Philip Hering ◽  
Luca de Siena ◽  
...  
Keyword(s):  
Magma Chamber ◽  
Transfer Functions ◽  
Geophysical Methods ◽  
Gravity Anomalies ◽  
Active Volcano ◽  
Rift System ◽  
East African Rift System ◽  
Plumbing System ◽  
East African ◽  
Oldoinyo Lengai

<p>How well can geophysical methods image magmatic systems? Geophysical methods are commonly used to image magmatic systems; however, synthetic studies which give insights into the resolution of such methods and their interpretational scope are rare. Gravity anomalies, magnetotelluric, seismological and geodynamical modelling all have a different sensitivity to the rock parameters and are thus likely complementary methods. Our study aims to better understand their interplay by performing joint modelling of a synthetic magmatic system.  Our model setup of a magma chamber is inspired by seismological observations at the Natron plumbing system including active volcano Oldoinyo Lengai within the East African Rift system. The geodynamic modelling is guided by shear-wave velocity anomalies and it is constrained by a large Bouguer gravity anomaly which is modelled by a voxel-based gravity code. It yields the 3D distribution of several geological parameters (pressure, temperature, stress, density, rock type). The parameters are converted into a 3D resistivity distribution. By 3D forward modelling including the topography, synthetic MT transfer functions (phase tensor, induction vectors) are calculated for a rectangular grid of 441 sites covering the area. The variation of geodynamic parameters and/or petrological relations alters the related resistivity distribution and thus yields the sensitivity of MT responses to geodynamic parameters. In turn, MT observations may constrain geodynamic modelling by inverting MT transfer functions. The inversion is performed allowing for the recent seismicity distribution beneath the Natron plumbing system, assuming that active seismic areas are related to enhanced resistivity. The inversion is performed for a realistic distribution (in view of logistic accessibility) of about 40 MT sites.</p><p>By combining multiple forward models, this study yields insights into the sensitivity of different observables and thus provides a valuable base on how MT, gravity and seismological observations can help imaging a complex geological setting.</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>

scholarly journals The Impact of the Geologic History and Paleoclimate on the Diversification of East African Cichlids

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
Patrick D. Danley ◽  
Martin Husemann ◽  
Baoqing Ding ◽  
Lyndsay M. DiPietro ◽  
Emily J. Beverly ◽  
...  
Keyword(s):  
Great Lakes ◽  
Lake Victoria ◽  
Cichlid Fish ◽  
Rift System ◽  
East African Rift System ◽  
Geologic History ◽  
East African ◽  
African Great Lakes ◽  
History Of ◽  
The Impact

The cichlid fishes of the East African Great Lakes are the largest extant vertebrate radiation identified to date. These lakes and their surrounding waters support over 2,000 species of cichlid fish, many of which are descended from a single common ancestor within the past 10 Ma. The extraordinary East African cichlid diversity is intricately linked to the highly variable geologic and paleoclimatic history of this region. Greater than 10 Ma, the western arm of the East African rift system began to separate, thereby creating a series of rift basins that would come to contain several water bodies, including the extremely deep Lakes Tanganyika and Malawi. Uplifting associated with this rifting backponded many rivers and created the extremely large, but shallow Lake Victoria. Since their creation, the size, shape, and existence of these lakes have changed dramatically which has, in turn, significantly influenced the evolutionary history of the lakes' cichlids. This paper reviews the geologic history and paleoclimate of the East African Great Lakes and the impact of these forces on the region's endemic cichlid flocks.

Neogene rift tectonic activity in the West Somali Basin, offshore Tanzania: example of a segmented oblique rift structure.

2021 ◽  
Author(s):  
Salvatore Ruocco ◽  
David Iacopini ◽  
Stefano Tavani ◽  
Cynthia Ebinger ◽  
Marina Dottore Stagna ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Normal Fault ◽  
Passive Margin ◽  
Tectonic Activity ◽  
Rift System ◽  
East African Rift System ◽  
The West ◽  
Slip Vector ◽  
Seismic Reflection Data ◽  
Structural Style

<p>Little is still known about the structural fabric of a potential continuation of the East African Rift System (EARS) offshore Tanzania in the West Somali Basin. This continuation has been established mostly through sparse GPS measurements, earthquake slip vector data, spatial distribution of teleseismically detected earthquake focal mechanisms, and some recent seismic reflection data. West of the Davie Ridge (which part of a larger structure named the Davie Fracture Zone) and across its northern extension, regional seismic reflection profiles indicate the occurrence of continental - oceanic crust transition, which is characterized by early Cretaceous reverse faulting localized along deformation corridors. After the Aptian, the seafloor spreading ceased and the Tanzania margin evolved into a passive margin dominated by clastic deep-water deposition. In this contribution, we describe some results obtained from structural mapping of a 3D seismic dataset, calibrated by few explorations well, covering an area located between the Davie Ridge and the continent, south of Mafia Island.  The seismic data maps suggest a major structural style change across the Neogene that is still active today. The recent structures are represented by two main interacting fault trends: some NS boundary faults corridors and a NW-SE internal arcuate segmented fault, both depicting a widely and diffused distribution of normal fault (with an overall cumulative amount of horizontal brittle extension ranging between 5 to 10 km). Some of the largest faults appear to reactivate older extensional structures but the general absence of growth faults cutting across the Paleo-Neogene depositional units suggest very recent rift re-activation. The recent rift system appears to show a component of obliquity with respect to the orientation of the Davie Ridge, and to the onshore structure related to the EARS tectonics.</p>

Did the evolution of tropical river systems impact the Cenozoic climate system ? A preliminary study with the IPSL-CM5A2 earth system model.

2020 ◽  
Author(s):  
Pierre Sepulchre ◽  
Julia Bres
Keyword(s):  
Plate Tectonics ◽  
Earth System Model ◽  
Ocean Dynamics ◽  
System Model ◽  
Rift System ◽  
Earth System ◽  
East African Rift System ◽  
East African ◽  
African Rift ◽  
The Impact

<p>Driven by plate tectonics and geodynamics, Earth surface has been reshaped during the Cenozoic, with the uplift of numerous mountain ranges. Climate modellers have been tackling the direct impact of these changes on climate for decades, essentially thanks to sensitivity experiments to topography, aiming at quantifying the impact of mountains on atmospheric and ocean dynamics. An indirect consequence of mountain uplift is changes in the continental river routing system, that can be relocated and provide the ocean with freshwater fluxes very different from the present. Here we focus on the Amazon and the Congo river, which routing are known to have been altered by the uplifts of the Andes and the East African Rift System, respectively. We carried out numerical simulations with the IPSL-CM5A2 earth system model in which we alternatively relocated or cut the runoff of these two rivers, and compared the results to simulations where topography only has been changed. We analyze the consequences of the changes in routing in terms of ITCZ position, precipitation spatial patterns, and salinity budgets and associated AMOC strength over the oceans. We show that depending on the region considered, the direct (mechanical) and indirect (hydrology) consequences of uplift on climate can either add up or counteract each other.</p><p> </p>

Middle–late Miocene palaeoenvironments, palynological data and a fossil fish Lagerstätte from the Central Kenya Rift (East Africa)

2015 ◽  
Vol 154 (1) ◽  
pp. 24-56 ◽  
Author(s):  
CORNELIA RASMUSSEN ◽  
BETTINA REICHENBACHER ◽  
OLAF LENZ ◽  
MELANIE ALTNER ◽  
STEFANIE B. R. PENK ◽  
...  
Keyword(s):  
East Africa ◽  
Late Miocene ◽  
Explosive Volcanism ◽  
Tectonic Activity ◽  
Rift System ◽  
East African Rift System ◽  
Kenya Rift ◽  
Alkaline Lakes ◽  
Palynological Data ◽  
Central Kenya

AbstractThe Miocene epoch was a time of major change in the East African Rift System (EARS) as forest habitats were transformed into grasslands and hominids appeared in the landscape. Here we provide new sedimentological and palynological data on the middle–upper Miocene Ngorora Formation (Tugen Hills, Central Kenya Rift, EARS), together with clay mineral characterizations, mammal finds and a description of the Ngorora fish Lagerstätte. Furthermore, we introduce a revised age ofc. 13.3 Ma for the onset of the Ngorora Formation. The older part of the Ngorora Formation (c. 13.3–12 Ma) records low-energy settings of lakes, floodplains and palaeosols, and evidence of analcime indicates that lakes were alkaline. The palynomorph spectrum consists of tree pollen (Juniperus, Podocarpus), Euphorbiaceae pollen (Acalypha, Croton) and herbaceous pollen of Poaceae and Asteraceae, suggestive of wooded grasslands or grassy woodlands. Alkaline lakes, floodplains and palaeosols continue upsection (c. 12–9 Ma), but environmental fluctuations become more dynamic. Paucity of palynomorphs and the presence of an equid may point to progressively drier conditions. A total of about 500 articulated fish fossils were recovered from distinctive layers of almost all sections studied and represent different lineages of the Haplotilapiines (Pseudocrenilabrinae, Cichlidae). Some of the fish kills may be attributable to rapid water acidification and/or asphyxiation by episodic ash falls. Repeated instances of abrupt change in water depth in many sections are more likely to be due to synsedimentary tectonic activity of the Central Kenya Rift than to climatic variation. Overall, the preservation of the Ngorora fish Lagerstätte resulted from the interplay of tectonics, formation of alkaline lakes and explosive volcanism. As records of grasslands that pre-date late Miocene time are rare, our finding of middle Miocene (12–13 Ma) grassy savannah in the Central Kenya Rift is also relevant to models of human evolution in East Africa.

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>

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