Models of fracture orientation at oblique spreading centres

Tuckwell, George; Bull, Jonathan M.; Sanderson, David J.

doi:10.1144/gsjgs.153.2.0185

Cited by 27 publications

(43 citation statements)

References 27 publications

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“…Rivalta et al (2015) provide an overview from the perspective of dyke propagation. The geometric relationship between plate motion, plate boundary orientation and the resulting structures can be defined according to the model of Tuckwell et al (1996), who classified geometrical models of mid-ocean ridge spreading, three of which (orthogonal, oblique, transtension) are observed in nature. Robertson et al (2015) used a similar system to describe the geometry of rift extension, using the Kenyan Rift as an example.…”

Section: Factors That Could Affect Stress and Strain In The Earsmentioning

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: Factors That Could Affect Stress and Strain In The Earsmentioning

confidence: 99%

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

et al. 2016

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“…The angles between the plate motion vector, the plate margin orientation and the orientation of extensional faults can be used to classify the type of extension as oblique opening, short-segment opening (not observed in nature and therefore not discussed here), transtension and orthogonal opening (Tuckwell et al 1996;Fig. 2).…”

Section: Extensional Tectonic Settingsmentioning

confidence: 99%

“…Geometrically, transtension is where extensional faults form normal to the local minimum principal stress, but oblique to both the plate motion vector and the plate margin. This criteria fulfils f ¼ A/2 and w ¼ a/2 + 458, where f is the angle between the plate margin and the extensional faults, A is the angle between the plate motion vector and the normal to the plate margin, and w and a are the angles between the plate motion vector and the extensional faults and plate margin, respectively (Tuckwell et al 1996).…”

Section: Extensional Tectonic Settingsmentioning

confidence: 99%

“…These divergent plate margin models have largely been applied at MOR settings, primarily to explain the orientation of faults at MORs and to investigate morphological variations with the spreading rate (Tuckwell et al 1996;Wormald et al 2012). However, they have also been applied at continental rift settings such as the Main Ethiopian Rift (MER) (S.C. Wormald, pers.…”

Section: Extensional Tectonic Settingsmentioning

confidence: 99%

“…These studies showed that both transtension and orthogonal spreading are the dominant style of extension at both MORs and continental rifts globally. For MORs, the spreading rate exerts an important control on the type of extension: slow-spreading ridges (half-rate ,20 mm a 21 ) are more often in transtension and fast-spreading ridges more often show orthogonal opening (Tuckwell et al 1996).…”

Section: Extensional Tectonic Settingsmentioning

confidence: 99%

See 2 more Smart Citations

Influence of regional tectonics and pre-existing structures on the formation of elliptical calderas in the Kenyan Rift

Robertson

Biggs

Cashman

et al. 2015

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Calderas are formed by the collapse of large magma reservoirs and are commonly elliptical in map view. The orientation of elliptical calderas is often used as an indicator of the local stress regime; but, in some rift settings, pre-existing structural trends may also influence the orientation. We investigated whether either of these two mechanisms controls the orientation of calderas in the Kenyan Rift. Satellite-based mapping was used to identify the rift border faults, intra-rift faults and orientation of the calderas to measure the stress orientations and pre-existing structural trends and to determine the extensional regime at each volcano. We found that extension in northern Kenya is orthogonal, whereas that in southern Kenya is oblique. Elliptical calderas in northern Kenya are orientated NW-SE, aligned with pre-existing structures and perpendicular to recent rift faults. In southern Kenya, the calderas are aligned NE-SW and lie oblique to recent rift faults, but are aligned with pre-existing structures. We conclude that, in oblique continental rifts, pre-existing structures control the development of elongated magma reservoirs. Our results highlight the structural control of magmatism at different crustal levels, where pre-existing structures control the storage and orientation of deeper magma reservoirs and the local stress regime controls intra-rift faulting and shallow magmatism.

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Evolution of stress and fault patterns in oblique rift systems: 3‐D numerical lithospheric‐scale experiments from rift to breakup

Brune

2014

Geochem Geophys Geosyst

116

117

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Rifting involves complex normal faulting that is controlled by extension direction, reactivation of prerift structures, sedimentation, and dyke dynamics. The relative impact of these factors on the observed fault pattern, however, is difficult to deduce from field-based studies alone. This study provides insight in crustal stress patterns and fault orientations by employing a laterally homogeneous, 3-D rift setup with constant extension velocity. The presented numerical forward experiments cover the whole spectrum of oblique extension. They are conducted using an elastoviscoplastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Despite recent advances, 3-D numerical experiments still require relatively coarse resolution so that individual faults are poorly resolved. This issue is addressed by applying a post processing method that identifies the stress regime and preferred fault azimuth at each surface element. The simple model setup results in a surprising variety of fault orientations that are solely caused by the three-dimensionality of oblique rift systems. Depending on rift obliquity, these orientations can be grouped in terms of rift-parallel, extension-orthogonal, and intermediate normal fault directions as well as strike-slip faults. While results compare well with analog rift models of low to moderate obliquity, new insight is gained in advanced rift stages and highly oblique settings. Individual fault populations are activated in a characteristic multiphase evolution driven by lateral density variations of the evolving rift system. In natural rift systems, this pattern might be modified by additional heterogeneities, surface processes, and dyke dynamics.

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Models of fracture orientation at oblique spreading centres

Cited by 27 publications

References 27 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

Influence of regional tectonics and pre-existing structures on the formation of elliptical calderas in the Kenyan Rift

Evolution of stress and fault patterns in oblique rift systems: 3‐D numerical lithospheric‐scale experiments from rift to breakup

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