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  • 1
    Series available for loan
    Series available for loan
    Volcanic rifted margins (2002)
    Boulder, Colo. : The Geological Society of America
    Associated volumes
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    Call number: S 90.0095(362)
    In: Special paper / The Geological Society of America, 362
    Type of Medium: Series available for loan
    Pages: VI, 230 Seiten , Illustrationen, graphische Darstellungen, Karten
    ISBN: 0-8137-2362-0
    Series Statement: Special paper / The Geological Society of America 362
    URL: http://digitale-objekte.hbz-nrw.de/storage2/2018/06/15/file_365/7918592.pdf
    Language: English
    Note: Preface 1. Characteristics of volcanic rifted margins Martin A. Menzies, Simon L. Klemperer, Cynthia J. Ebinger, and Joel Baker 2. Crust and upper mantle structure in East Africa: Implications for the origin of Cenozoic rifting and volcanism and the formation of magmatic rifted margins Andrew A. Nyblade 3. Development of the Lebombo rifted volcanic margin of southeast Africa M.K. Watkeys 4. Extension and uplift of the northern Rio Grande Rift: Evidence from ⁴⁰Ar/³⁹Ar geochronology from the Sangre de Cristo Mountains, south-central Colorado and northern New Mexico Daniel P. Miggins, Ren A. Thompson, Charles L. Pillmore, Lawrence W. Snee, and Charles R. Stern 5. Lithospheric mantle beneath Arabia: A Pan-African protolith modified by the Afar and older plumes, rather than a source for continental flood volcanism? Joel Baker, Gilles Chazot, Martin A. Menzies, and Matthew Thirlwall 6. Petrogenesis of the Late Cretaceous tholeiitic magmatism in the passive margins of northeastern Madagascar Leone Melluso, Vincenzo Morra, Pietro Brotzu, Massimo D'Antonio, and Lucia Bennio 7. Silicic volcanism: An undervalued component of large igneous provinces and volcanic rifted margins Scott E. Bryan, Teal R. Riley, Dougal A. Jerram, Christopher J. Stephens, and Philip T Leat 8. Volcanology and fades architecture of flood basalts Dougal A. Jerram 9. East Greenland coast-parallel dike swarm and its role in continental breakup Martin Bromann Klausen and Hans Christian Larsen 10. Crustal architecture of South Atlantic volcanic margins W.U. Mohriak, B.R. Rosendahl, J.P. Turner, and S.C. Valente 11. Volcanic passive margin of Namibia: A potential fields perspective B. Corner, J. Cartwright, and R. Swart 12. Petrophysical modeling of high seismic velocity crust at the Namibian volcanic margin R.B. Trumbull, S.V. Sobolev, and K. Bauer
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
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    The Afar Volcanic Province within the East African Rift System (2006)
    London : The Geological Society
    Details
    Description / Table of Contents: The seismically and volcanically active East African Rift System is an ideal laboratory for continental break-up processes: it encompasses all stages of rift development. Its northernmost sectors within the Afar volcanic province include failed rifts, nascent seafloor spreading, and youthful passive continental margins associated with one or more mantle plumes. A number of models have been proposed to explain the success and failure of continental rift zones, but there remains no consensus on how strain localizes to achieve rupture of 125–250 km thick plates, or on the interaction between the plates and asthenospheric processes. This collection of papers provides new structural, stratigraphic, geochemical and geophysical data and numerical models needed to resolve fundamental questions concerning continental break-up and mantle plume processes. It focuses on how mantle melt intrudes and is distributed through the plate, and how this magma intrusion process controls along-axis segmentation and facilitates break-up.
    Pages: Online-Ressource (VII, 327 Seiten)
    ISBN: 9781862391963
    URL: http://sp.lyellcollection.org/content/vol259/issue1/
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    Structural evolution of Lake Malaŵi, Africa (1984)
    [s.l.] : Nature Publishing Group
    Nature 308 (1984), S. 627-629 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Single-channel reflection surveys were conducted as part of a programme to evaluate sites for a proposed deep-drilling project (CEGAL) in the East African Rift Lakes2. Profiles were obtained using an airgun sound source (40 cubic inches) occasionally supplemented by an 800 J sparker, and radar ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/308627a0
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  • 4
    Electronic Resource
    Electronic Resource
    Cenozoic magmatism throughout east Africa resulting from impact of a single plume (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 395 (1998), S. 788-791 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The geology of northern and central Africa is characterized by broad plateaux, narrower swells and volcanism occurring from ∼45 Myr ago to the present. The greatest magma volumes occur on the 〉1,000-km-wide Ethiopian and east African plateaux, which are transected by the Red Sea, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/27417
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  • 5
    Electronic Resource
    Electronic Resource
    Magma-assisted rifting in Ethiopia (2005)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 433 (2005), S. 146-148 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03161
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  • 6
    Electronic Resource
    Electronic Resource
    Multiple episodes of rifting in Central and East Africa: A re-evaluation of gravity data (1994)
    Springer
    International journal of earth sciences 83 (1994), S. 689-702 
    Details
    ISSN: 1437-3262
    Keywords: Rifts ; Gravity anomalies ; Africa ; Gravity models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A compilation of new and existing gravity data, as well as geophysical and geological data, is used to assess the cumulative effects of multiple rifting episodes on crustal and upper mantle density structures beneath the Uganda-Kenya-Ethiopia-Sudan border region. This compilation includes new gravity and geological data collected in 1990 in south-western Ethiopia. Variations in the trends and amplitudes of Bouguer gravity anomalies reveal three overlapping rift systems: Mesozoic, Paleogene and Miocene-Recent. Each of these rift systems is a number of 40–100 km long sedimentary basins, and each system is approximately 1000 km long. The Bouguer anomaly patterns indicate that the Ethiopian and East African plateaux and corresponding gravity anomalies are discrete tectonic features. Models of structural and gravity profiles of two basins (Omo and Chew Bahir basins) suggest that pre-Oligocene (Cretaceous?) strata underlie 3 km or more of Neogene-Recent strata within the northern Kenya rift, and that more than 2 km of Neogene-Recent strata underlie parts of the southern Main Ethiopian rift. The superposition of perhaps three rifting episodes in the Lake Turkana (Omo) region has led to 90% crustal thinning (β ≈ 2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00251068
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  • 7
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    Palaeomagnetic constraints on continental break-up processes: observations from the Main Ethiopian Rift (2007)
    In:  Geological Society Special Publication 259: 165-183.
    Details
    Publication Date: 2007-10-08
    Description: We report the first palaeomagnetic results from the Main Ethiopian Rift (MER), the northernmost sector of the East African rift system. This part of the MER shows an along-axis tectono-magmatic segmentation pattern similar to that of slow-spreading mid-ocean ridges, which developed during the past 1.9 Ma. The aims of our palaeomagnetic, structural and geochronological studies are to test plate kinematic models for the right-stepping, en echelon 6080 km-long magmatic segments. Twenty palaeomagnetic sites were sampled on either basalt or ignimbrite outcropping in the region adjacent to, and within, the 〈1.9 Ma-old tectono-magmatic segments of Gademsa-Koka, Boset and Fentale-Dofan. Five K-Ar age determinations were made to bracket the age of units studied in the palaeomagnetic analyses. The natural remanent magnetization intensity possibly exhibited a unimodal distribution with a value of 6.6 A/m ({sigma} = 5.6 A/m) for the basalts and a bimodal distribution with magnetization intensity of 0.69 A/m ({sigma} = 0.55 A/m) and 0.03 A/m ({sigma} = 0.02 A/m), statistically similar to values from previous studies in the Afar triple junction zone (e.g. Kidane et al. 1999, 2002). Progressive heating, alternating field analysis, and susceptibility vs. temperature measurements indicated unblocking temperature ranging between 300 {degrees}C600 {degrees}C for basalts and between 500 {degrees}C660 {degrees}C for ignimbrites, suggesting the magnetic mineralogy to be titanomagnetite and magnetite for the former and magnetite and titanohematite for the latter. Palaeomagnetic measurements using both TH and AF technique revealed quasi-single component of magnetization with viscous remanent magnetization (VRM) on a few samples. Principal component analysis and statistical averaging resulted in an overall mean palaeomagnetic direction of (Ds = 2.3{degrees}, Is = 7.8{degrees}, {alpha}95 = 7, K = 26.9, N = 17) which is statistically identical to the expected direction (D = 1.9{degrees}, I = 13.5{degrees}, {alpha}95 = 2.5, K = 105.6, N = 32) from the Apparent Polar Wander Path reference curve for Africa at 1.5 Ma (Besse & Courtillot 2003). The angular difference between the observed and expected directions above with their uncertainty is calculated to be 0.4{degrees} {+/-} 7.5{degrees}. These results indicate that the Late Pliocene-Pleistocene rocks of the MER in the studied region do not suffer vertical axis rotation, arguing against transtensional and seafloor-spreading-transform kinematic models. We suggest that magma intrusion, rather than large offset faults, produce the right-stepping, en echelon magmatic segments of the MER, which is at the transition from continental to oceanic extension.
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  • 8
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    Strain accommodation in transitional rifts: extension by magma intrusion and faulting in Ethiopian rift magmatic segments (2007)
    In:  Geological Society Special Publication 259: 143-163.
    Details
    Publication Date: 2007-10-08
    Description: Active deformation within the northern part of the Main Ethiopian Rift (MER) occurs within approximately 60 km-long, 20 km-wide magmatic segments' that lie within the 80 km-wide rift valley. Geophysical data reveal that the crust beneath the 〈1.9 Ma magmatic segments has been heavily intruded; magmatic segments accommodate strain via both magma intrusion and faulting. We undertake field and remote sensing analyses of faults and eruptive centres in the magmatic segments to estimate the relative proportion of strain accommodated by faulting and magma intrusion and the kinematics of Quaternary faults. Up to half the [≤]10 km-long normal faults within the Boset-Kone and Fantale-Dofen magmatic segments have eruptive centres or extrusive lavas along their length. Comparison of the deformation field of the largest Quaternary fault and an elastic half-space dislocation model indicates a down-dip length of 10 km, coincident with the seismogenic layer thickness and the top of the seismically imaged mafic intrusions. These relations suggest that Quaternary faults are primarily driven by magma intrusion into the mid- to upper crust, which triggers faulting and dyke intrusion into the brittle upper crust. The active volcanoes of Boset, Fantale and Dofen all have elliptical shapes with their long axes in the direction N105, consistent with extension direction derived from earthquake focal mechanisms. Calderas show natural strains ranging from around 0.30 for Boset, 0.55 for Fantale, and 0.94 for Dofen. These values give extension strain rates of the order of 0.3 microstrain per year, comparable to geodetic models. Structural analyses reveal no evidence for transcurrent faults linking right-stepping magmatic segments. Instead, the tips of magmatic segments overlap, thereby accommodating strain transfer. The intimate relationship between faulting and magmatism in the northern MER is strikingly similar to that of slow-spreading mid-ocean ridges, but without the hard linkage zones of transform faults.
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  • 9
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    Temporal compositional variation of syn-rift rhyolites along the western margin of the southern Red Sea and northern Main Ethiopian Rift (2007)
    In:  Geological Society Special Publication 259: 121-130.
    Details
    Publication Date: 2007-10-08
    Description: Structural and geochronological relations indicate that the felsic rocks at the top of the Oligocene flood basalt sequences in the Afar volcanic province were erupted coevally with the initial rifting in the Red Sea and Gulf of Aden. In this study, we use the newly established volcanic-tectonic history to examine the geochemical evolution with time of felsic volcanics as rifting has progressed to seafloor spreading in the southern Red Sea and northern Main Ethiopian Rift. Geochemical analyses (major and trace elements; Sr, Nd and O isotopic compositions) of syn-rift rhyolites ranging in age from 28 to 2.5 Ma indicate that the rhyolites can be derived from mantle-sourced basaltic magma through fractional crystallization accompanied by variable amounts of crustal contamination (e.g. 87Sr/86Sr = 0.704890.70651; 143Nd/144Nd = 0.512540.51283; {delta}18O = +4.5 to +6.4{per thousand}). The input of crust tends to increase with time, which suggests the weakening and heating of the crust in response to lithospheric thinning and magma injection in the past c. 30 Ma. These results support earlier structural and thermomechanical models for rift formation in the southern Red Sea rift and the younger, less-evolved northern Main Ethiopian Rift system.
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  • 10
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    Kinematics of the East African Rift from GPS and earthquake slip vector data (2007)
    In:  Geological Society Special Publication 259: 9-22.
    Details
    Publication Date: 2007-10-08
    Description: Although the East African Rift (EAR) System is often cited as the archetype for models of continental rifting and break-up, its present-day kinematics remains poorly constrained. We show that the currently available GPS and earthquake slip vector data are consistent with (1) a present-day Nubia-Somalia Euler pole located between the southern tip of Africa and the Southwest Indian ridge and (2) the existence of a distinct microplate (Victoria) between the Eastern and Western rifts, rotating counter-clockwise with respect to Nubia. Geodetic and geological data also suggest the existence of a (Rovuma) microplate between the Malawi rift and the Davie ridge, possibly rotating clockwise with respect to Nubia. The data indicate that the EAR comprises at least two rigid lithospheric blocks bounded by narrow belts of seismicity (〈50 km wide) marking localized deformation rather than a wide zone of quasi-continuous, pervasive deformation. On the basis of this new kinematic model and mantle flow directions interpreted from seismic anisotropy measurements, we propose that regional asthenospheric upwelling and locally focused mantle flow may influence continental deformation in East Africa.
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