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>

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>

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>

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

The North Tanganyika hydrothermal fields, East African Rift system: Their tectonic control and relationship to volcanism and rift segmentation

1994 ◽  
Vol 237 (3-4) ◽  
pp. 155-173 ◽  
Author(s):  
C. Coussement ◽  
P. Gente ◽  
J. Rolet ◽  
J.-J. Tiercelin ◽  
M. Wafula ◽  
...  
Keyword(s):  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
Tectonic Control ◽  
The North ◽  
African Rift ◽  
Hydrothermal Fields

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>

Tectono-thermal evolution of a long-lived segment of the East African Rift System: Thermochronological insights from the North Lokichar Basin, Turkana, Kenya

2018 ◽  
Vol 744 ◽  
pp. 23-46 ◽  
Author(s):  
Samuel C. Boone ◽  
Barry P. Kohn ◽  
Andrew J.W. Gleadow ◽  
Christopher K. Morley ◽  
Christian Seiler ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
The North ◽  
African Rift

scholarly journals Linking surface and subsurface volcanic stratigraphy in the Turkana Depression of the East African Rift system

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-110 ◽  
Author(s):  
Nick Schofield ◽  
Richard Newton ◽  
Scott Thackrey ◽  
Douglas Watson ◽  
David Jolley ◽  
...  
Keyword(s):  
Petroleum Exploration ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
Volcanic Stratigraphy ◽  
Seismic Reflection Data ◽  
The North ◽  
Reflection Data ◽  
African Rift ◽  
Magmatic History

The Northern Kenya Rift is an important natural laboratory for understanding continental rifting processes. However, much of the current understanding of its geological evolution is based on surface outcrops within footwall highs due to a lack of subsurface geological constraints. In this paper, we present an investigation of the Cenozoic stratigraphy and volcano-tectonic relationship of the volcanic sequences within the Turkana Depression (namely the North Lokichar, North Kerio and Turkana Basins). We integrate regional seismic reflection data collected as part of ongoing petroleum exploration in the area with lithological and biostratigraphic data from new wells that were drilled in 2014 and 2015 (Epir-1 and Emesek-1). This has allowed linking and extrapolation of the detailed stratigraphy of the paleontologically important Lothagam site to the volcanic sequences within the Napedet Hills, North Lokichar, North Kerio and Turkana Basins. The site of the Plio-Pleistocene-age Turkana Fault, which separates the North Lokichar Basin from the Turkana and North Kerio Basins, appears previously to have acted as a focus of Middle Miocene volcanism c. 5 Ma prior to the main period of movement on the fault. Our study highlights how subsurface and outcrop information can be combined to give a more in-depth knowledge of the magmatic history within rift basins.

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