Tectonic History and Structural Evolution of the East Africa Margin

2017 ◽  
Author(s):  
S.T. Sutton ◽  
P.H. Figueredo ◽  
M.A Sullivan ◽  
C. Johnson ◽  
G. Karner
Keyword(s):  
East Africa ◽  
Structural Evolution ◽  
Tectonic History

Multiphase rotational extension and marginal flexure along a developing passive margin: the Western Afar Margin, East Africa

2020 ◽  
Author(s):  
Frank Zwaan ◽  
Giacomo Corti ◽  
Derek Keir ◽  
Federico Sani ◽  
Ameha Muluneh ◽  
...  
Keyword(s):  
East Africa ◽  
Large Scale ◽  
Structural Evolution ◽  
Good Evidence ◽  
Passive Margin ◽  
Fault System ◽  
Afar Depression ◽  
Multidisciplinary Study ◽  
Structural Architecture ◽  
Echelon Fault

<p>This multidisciplinary study focuses on the tectonics of the Western Afar Margin (WAM), which is situated between the Ethiopian Plateau and Afar Depression in East Africa. The WAM represents a developing passive margin in a highly volcanic setting, thus offering unique opportunities for the study of rifting and (magma-rich) continental break-up, and our results have both regional and global implications.</p><p>Earthquake analysis shows that the margin is still deforming under a ca. E-W extension regime (a result also obtained by analysis on fault measurements from recent field campaigns), whereas Afar itself undergoes a more SW-NE extension. Together with GPS data, we see Afar currently opening in a rotational fashion. This opening is however a relatively recent and local phenomenon, due to the rotation of the Danakil microcontinent modifying the regional stress field (since 11 Ma). Regional tectonics is otherwise dominated by the rotation of Arabia since 25 Ma and should cause SW-NE (oblique) extension along the WAM. This oblique motion is indeed recorded in the large-scale en echelon fault patterns along the margin, which were reactivated in the current E-W extension regime. We thus have good evidence of a multiphase rotational history of the WAM and Afar.</p><p>Furthermore, analysis of the margin’s structural architecture reveals large-scale flexure towards Afar, likely representing the developing seaward-dipping reflectors that are typical for magma-rich margins. Detailed fault mapping and earthquake analysis show that recent faulting is dominantly antithetic (dipping away from the rift), bounding remarkable marginal grabens, although a large but older synthetic escarpment fault system is present as well. By means of analogue modelling efforts we find that marginal flexure indeed initially develops a large escarpment, whereas the currently active structures only form after significant flexure. Moreover, these models show that marginal grabens do not develop under oblique extension conditions. Instead, the latter model boundary conditions create the large-scale en echelon fault arrangement typical of the WAM. We derive that the recent structures of the margin could have developed only after a shift to local orthogonal extension. These modeling results support the multiphase extension scenario as described above.</p><p>Altogether, our findings are highly relevant for our understanding of the structural evolution of (magma-rich) passive margins. Indeed, seismic sections of such margins show very similar structures to those of the WAM. However, the general lack of marginal grabens, which are so obvious along the WAM, can be explained by the fact that most rift systems undergo or have undergone oblique extension, often in multiple phases during which structures from older phases control subsequent deformation.</p>

scholarly journals Thermo-Structural Evolution of the Val Malenco (Italy) Peridotite: A Petrological, Geochemical and Microstructural Study

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 962
Author(s):  
Wenlong Liu ◽  
Yi Cao ◽  
Junfeng Zhang ◽  
Yanfei Zhang ◽  
Keqing Zong ◽  
...  
Keyword(s):  
Strain Localization ◽  
Structural Evolution ◽  
Coarse Grained ◽  
Prograde Metamorphism ◽  
Fine Grained ◽  
Tectonic History ◽  
Serpentinized Peridotite ◽  
Geochemical Study ◽  
Dissolution And Precipitation

The Val Malenco peridotite massif is one of the largest exposed ultramafic massifs in Alpine orogen. To better constrain its tectonic history, we have performed a comprehensive petro-structural and geochemical study. Our results show that the Val Malenco serpentinized peridotite recorded both pre-Alpine extension and Alpine convergence events. The pre-Alpine extension is recorded by microstructural and geochemical features preserved in clinopyroxene and olivine porphyroblasts, including partial melting and refertilisation, high-temperature (900–1000 °C) deformation and a cooling, and fluid-rock reaction. The following Alpine convergence in a supra-subduction zone setting is documented by subduction-related prograde metamorphism features preserved in the coarse-grained antigorite and olivine grains in the less-strained olivine-rich layers, and later low-temperature (<350 °C) serpentinization in the fine-grained antigorite in the more strained antigorite-rich layers. The strain shadow structure in the more strained antigorite-rich layer composed of dissolving clinopyroxene porphyroblast and the precipitated oriented diopside and olivine suggest dissolution and precipitation creep, while the consistency between the strain shadow structure and alternating less- and more-strained serpentinized domains highlights the increasing role of strain localization induced by the dissolution-precipitation creep with decreasing temperature during exhumation in Alpine convergence events.

Structural evolution and U/Pb zircon age of the Xambioá gneiss dome, contributions to the Araguaia fold belt tectonic history

2020 ◽  
Vol 104 ◽  
pp. 102753
Author(s):  
Rogério Alves Bordalo ◽  
Ticiano José Saraiva dos Santos ◽  
Elton L. Dantas
Keyword(s):  
Structural Evolution ◽  
Fold Belt ◽  
Gneiss Dome ◽  
Zircon Age ◽  
Tectonic History

Kinematic and sedimentological evolution of the Manyara Rift in northern Tanzania, East Africa

2005 ◽  
Vol 142 (4) ◽  
pp. 355-368 ◽  
Author(s):  
UWE RING ◽  
HILDE L. SCHWARTZ ◽  
TIMOTHY G. BROMAGE ◽  
CHARLES SANAANE
Keyword(s):  
East Africa ◽  
Structural Evolution ◽  
Magmatic Activity ◽  
Fault Geometry ◽  
East African ◽  
Lower Member ◽  
Northern Tanzania ◽  
Southward Shift ◽  
Fluvial Sedimentation ◽  
African Rift

We describe the stratigraphical/sedimentological and structural evolution of the Manyara Rift in the Tanzania Divergence Zone, East Africa. The rift-related Manyara Beds on the shoaling side of the Manyara Rift were deposited between <1.7 and 0.4 Ma and can be separated into a lacustrine lower member and a fluvial upper member. The transition from lacustrine to fluvial sedimentation at ∼ 0.7 Ma appears to be related to a southward shift of major rift faulting. Fault geometry and the kinematics of the faults are consistent with major faulting during NE/E-directed extension. There is also evidence for other extensional directions including radial extension, which might be caused by magmatic activity and/or might reflect oblate strain symmetry where the East African Rift propagated into the Archaean Tanzania Craton and associated termination of rifting caused an increase in the strained area.

Neoproterozoic structural evolution of SE Sinai, Egypt: II. Convergent tectonic history of the continental arc Kid Group

2010 ◽  
Vol 58 (3) ◽  
pp. 526-546 ◽  
Author(s):  
A. Fowler ◽  
I.S. Hassen ◽  
A.F. Osman
Keyword(s):  
Structural Evolution ◽  
Tectonic History ◽  
Continental Arc ◽  
History Of

scholarly journals Structural evolution of central Death Valley, California, using new thermochronometry of the Badwater turtleback

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 436-447
Author(s):  
Travis Sizemore ◽  
Matthew M. Wielicki ◽  
Ibrahim Çemen ◽  
Daniel Stockli ◽  
Matthew Heizler ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Structural Evolution ◽  
Detachment Fault ◽  
Death Valley ◽  
Normal Faults ◽  
Owens Valley ◽  
Tectonic History ◽  
Brittle Ductile Transition ◽  
History Of ◽  
Copper Canyon

Abstract The Badwater turtleback, Copper Canyon turtleback, and Mormon Point turtleback are three anomalously smooth, ∼2-km-high basement structures in the Black Mountains of Death Valley, California. Their structural evolution is linked to the Cenozoic tectonic history of the region. To explore their evolution, we apply (U-Th)/He, Ar/Ar, and U-Pb analyses, with multi-domain diffusion modeling to 10 samples from the Badwater turtleback. The cooling history of the Badwater turtleback is used as a proxy for its exhumation history as it uplifted from warmer depths. We find slow (<2 °C/m.y.) cooling from ca. 32 to 6 Ma, followed by rapid (120–140 °C/m.y.) cooling from ca. 6 to 4.5 Ma, and finally moderate (30–120 °C/m.y.) cooling occurred from ca. 4.5 Ma until the present. When these data are added to previously published cooling paths of the Copper Canyon turtleback and Mormon Point turtleback, a northwest cooling pattern is broadly evident, consistent with a top-to-NW removal of the hanging wall along a detachment fault. We propose a six-phase tectonic history. Post-orogenic collapse and erosion dominated from ca. 32 to 16 Ma. At 16–14 Ma, a detachment fault formed with a breakaway south and east of the Black Mountains, with normal faults in the hanging wall. Moderate extension continued from 14 to 8 Ma causing exhumation of the turtlebacks through the brittle-ductile transition. Dextral transtension at 7–6 Ma produced a pull-apart basin across the Black Mountains with rapid extension. The locus of deformation transferred to the Panamint and Owens Valley fault systems from 4.5 to 3.5 Ma, slowing extension in the Black Mountains until present.

Microstructure and reactivity of small metal particles: The role of Ce additives

1992 ◽  
Vol 50 (1) ◽  
pp. 318-319
Author(s):  
L.D. Schmidt ◽  
K. R. Krause ◽  
J. M. Schwartz ◽  
X. Chu
Keyword(s):  
Atmospheric Pressure ◽  
Noble Metals ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Chemical Shifts ◽  
Catalytic Converter ◽  
Structural Evolution ◽  
Single Particles ◽  
Small Metal Particles

The evolution of microstructures of 10- to 100-Å diameter particles of Rh and Pt on SiO2 and Al2O3 following treatment in reducing, oxidizing, and reacting conditions have been characterized by TEM. We are able to transfer particles repeatedly between microscope and a reactor furnace so that the structural evolution of single particles can be examined following treatments in gases at atmospheric pressure. We are especially interested in the role of Ce additives on noble metals such as Pt and Rh. These systems are crucial in the automotive catalytic converter, and rare earths can significantly modify catalytic properties in many reactions. In particular, we are concerned with the oxidation state of Ce and its role in formation of mixed oxides with metals or with the support. For this we employ EELS in TEM, a technique uniquely suited to detect chemical shifts with ∼30Å resolution.

The Structural Evolution of Morality

2007 ◽  
Author(s):  
J. McKenzie Alexander
Keyword(s):  
Structural Evolution ◽  
Evolution Of Morality

Canoes of East Africa

1918 ◽  
Vol 86 (2228supp) ◽  
pp. 170-170
Keyword(s):  
East Africa
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