Fault kinematics and stress fields in the Rwenzori Mountains, Uganda

Sachau, Till; Koehn, Daniel; Stamps, D. S.; Lindenfeld, Michael

doi:10.1007/s00531-015-1162-6

Cited by 6 publications

(4 citation statements)

References 34 publications

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“…These include normal fault initiation from tension fractures and en echelon linking of faults Frontiers in Earth Science | www.frontiersin.org (Gudmundsson et al, 2010;Gudmundsson, 2011b, chapter 14). At mid-ocean ridges, the motion between segments is taken up on transform faults, but during rift development, there may be complex zones of mixed normal, strike-slip (e.g., Spacapan et al, 2016) and even compressional tectonics (e.g., Sachau et al, 2015). These can be several tens of kilometers in extent (Ebinger, 1989;Morley et al, 1990; Figure 2C) and are referred to as transfer or accommodation zones.…”

Section: Complexities In Rift Geometrymentioning

confidence: 99%

Historical Volcanism and the State of Stress in the East African Rift System

et al. 2016

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Crustal extension at the East African Rift System (EARS) should, as a tectonic ideal, involve a stress field in which the direction of minimum horizontal stress is perpendicular to the rift. A volcano in such a setting should produce dykes and fissures parallel to the rift. How closely do the volcanoes of the EARS follow this? We answer this question by studying the 21 volcanoes that have erupted historically (since about 1800) and find that 7 match the (approximate) geometrical ideal. At the other 14 volcanoes the orientation of the eruptive fissures/dykes and/or the axes of the host rift segments are oblique to the ideal values. To explain the eruptions at these volcanoes we invoke local (non-plate tectonic) variations of the stress field caused by: crustal heterogeneities and anisotropies (dominated by NW structures in the Protoerozoic basement), transfer zone tectonics at the ends of offset rift segments, gravitational loading by the volcanic edifice (typically those with 1-2 km relief) and magmatic pressure in central reservoirs. We find that the more oblique volcanoes tend to have large edifices, large eruptive volumes, and evolved and mixed magmas capable of explosive behavior. Nine of the volcanoes have calderas of varying ellipticity, 6 of which are large, reservoir-collapse types mainly elongated across rift (e.g., Kone) and 3 are smaller, elongated parallel to the rift and contain active lava lakes (e.g., Erta Ale), suggesting different mechanisms of formation and stress fields. Nyamuragira is the only EARS volcano with enough sufficiently well-documented eruptions to infer its long-term dynamic behavior. Eruptions within 7 km of the volcano are of relatively short duration (<100 days), but eruptions with more distal fissures tend to have lesser obliquity and longer durations, indicating a changing stress field away from the volcano. There were major changes in long-term magma extrusion rates in 1977 (and perhaps in 2002) due to major along-rift dyking events that effectively changed the Nyamuragira stress field and the intrusion/extrusion ratios of eruptions.

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Section: Complexities In Rift Geometrymentioning

confidence: 99%

Historical Volcanism and the State of Stress in the East African Rift System

et al. 2016

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“…On the basis of microtectonic measurements and focal mechanism analysis, the tectonic setting of the Rwenzori Mountains is assumed to be dominated by strike-slip movements (e.g. Koehn et al, 2010;McConnell, 1959;Ring, 2008;Sachau et al, 2016).…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

Deformation and sedimentary evolution of the Lake Albert Rift (Uganda, East African Rift System)

Simon

Guillocheau

Robin

et al. 2017

Marine and Petroleum Geology

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This study proposed a new reconstruction of the tectono-sedimentary evolution of the Lake Albert Rift based on a biostratigraphical, sedimentological and structural re-evaluation of the outcropping data and on an exceptional subsurface dataset.The infilling of the rift consists of lacustrine deposits wherein two major unconformities dated at 6.2 Ma and 2.7 Ma were characterized, coeval with major subsidence and climatic changes.Combined with the fault analysis, the evolution and distribution of the subsidence highlights a foursteps evolution of the rift after its initiation dated at 17.0 Ma.The first phase (17.0 -6.2 Ma) consists of low and diffuse extension associated with low accommodation rates ranging from 150 to 200 m/Ma. Restricted in the southern part of the basin, the depocenter location is poorly controlled by faults, meaning that the basin extension was potentially larger at this time.The second time interval (6.2 -2.7 Ma) shows an increase of accommodation rates with values reaching more than 800 m/Ma. These high rates combined with the location of the major depocenters down the bounding faults argue for a first true rifting phase.Between 2.7 Ma and 0.4 Ma, the accommodation rates decreases to reach less than 400 m/Ma and the individualization of major depocenters continue down the major fault in the southern, and northwestern parts of the basin.

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“…Such incremental, non-plane strains within evolving relay zones may be responsible for local instances of basin inversion, reverse and strike-slip faulting in otherwise extensional regimes, and complex compartmentalization characteristics (e.g. Lin and Okubo, 2016;Sachau et al, 2016). Importantly, for basin faults with displacements on the kilometre scale, significant amounts of horizontal bending and rotation are possible, driving associated strains that may go undetected.…”

Section: Rift-zone-parallel Extension Associated With Normal Fault Anmentioning

confidence: 99%

Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

et al. 2017

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Abstract. The mechanical interaction of propagating normal faults is known to influence the linkage geometry of firstorder faults, and the development of second-order faults and fractures, which transfer displacement within relay zones. Here we use natural examples of growth faults from two active volcanic rift zones (Koa'e, island of Hawai'i, and Krafla, northern Iceland) to illustrate the importance of horizontalplane extension (heave) gradients, and associated vertical axis rotations, in evolving continental rift systems. Secondorder extension and extensional-shear faults within the relay zones variably resolve components of regional extension, and components of extension and/or shortening parallel to the rift zone, to accommodate the inherently three-dimensional (3-D) strains associated with relay zone development and rotation. Such a configuration involves volume increase, which is accommodated at the surface by open fractures; in the subsurface this may be accommodated by veins or dikes oriented obliquely and normal to the rift axis. To consider the scalability of the effects of relay zone rotations, we compare the geometry and kinematics of fault and fracture sets in the Koa'e and Krafla rift zones with data from exhumed contemporaneous fault and dike systems developed within a > 5 × 10 4 km 2 relay system that developed during formation of the NE Atlantic margins. Based on the findings presented here we propose a new conceptual model for the evolution of segmented continental rift basins on the NE Atlantic margins.

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Fault kinematics and stress fields in the Rwenzori Mountains, Uganda

Cited by 6 publications

References 34 publications

Historical Volcanism and the State of Stress in the East African Rift System

Historical Volcanism and the State of Stress in the East African Rift System

Deformation and sedimentary evolution of the Lake Albert Rift (Uganda, East African Rift System)

Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

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