Geodynamic evolution of the Pan-African belt in central Africa with special reference to Cameroon

2004 ◽  
Vol 41 (1) ◽  
pp. 73-85 ◽  
Author(s):  
Sadrack Félix Toteu ◽  
Joseph Penaye ◽  
Yvette Poudjom Djomani
Keyword(s):  
Central Africa ◽  
West African ◽  
Fault System ◽  
North Central ◽  
West African Craton ◽  
The North ◽  
Pan African ◽  
Northern Edge ◽  
The Many

The Pan-African belt in central Africa has benefited from the many petrographic, structural, and geochronological studies in the recent years that have improved our understanding of the belt. However, those studies have also produced various and often divergent evolutionary models for the belt, some of which do not even involve well-defined cratons. Following a review of the available data in Cameroon, we propose a model of continent–continent collision that involved the Congo craton and the north-central Cameroon active margin showing Archean to Paleoproterozoic inheritances. This model is based, among others, on (i) the prominent role of the Congo craton as demonstrated by the regional extension of external nappes on its northern edge and the concomitant exhumation of the 620 Ma granulitic rocks believed to have formed at the root of the collision zone, and (ii) the late development of a strike slip fault system in central Cameroon as the result of horizontal movement following the multistage collision. In the general framework of the Pan-Africano – Brasiliano belt, a comparison of the kinematic and age of deformation north of the Congo craton to that east of the West African craton, suggests that the overall tectonic evolution of the mobile domain between both cratons is controlled by their relative motion.

Within-field Pathogenic Diversity of Phytophthora sojae in Commercial Soybean Fields in Iowa

2009 ◽  
Vol 10 (1) ◽  
pp. 8 ◽  
Author(s):  
Alison E. Robertson ◽  
Silvia R. Cianzio ◽  
Sarah M. Cerra ◽  
Richard O. Pope
Keyword(s):  
The United States ◽  
Phytophthora Sojae ◽  
Soil Samples ◽  
Soybean Plant ◽  
North Central Region ◽  
North Central ◽  
The North ◽  
History Of ◽  
The Many ◽  
Pathogenic Diversity

Phytophthora root and stem rot (PRR), caused by the oomycete Phytophthora sojae, is an economically important soybean disease in the north central region of the United States, including Iowa. Previous surveys of the pathogenic diversity of P. sojae in Iowa did not investigate whether multiple pathotypes of the pathogen existed in individual fields. Considering the many pathotypes of P. sojae that have been reported in Iowa, we hypothesized multiple pathotypes could exist within single fields. In the research reported herein, several soil samples were collected systematically from each of two commercial fields with a history of PRR in Iowa, and each soil sample was baited separately for isolates of P. sojae. Numerous pathotypes of P. sojae were detected from both fields. As many as four pathotypes were detected in some soil samples (each consisting of six to eight soil cores), which suggests that a single soybean plant could be subjected to infection by more than one pathotype. This possibility presents important implications in breeding resistant cultivars and in the management of PRR. Accepted for publication 14 July 2009. Published 8 September 2009.

Where are the Eburnian–Transamazonian collisional belts?

1990 ◽  
Vol 27 (10) ◽  
pp. 1382-1393 ◽  
Author(s):  
Jean Michel Bertrand ◽  
Emmanuel Ferraz Jardim de Sá
Keyword(s):  
West African ◽  
High Grade ◽  
The West ◽  
West African Craton ◽  
Early Proterozoic ◽  
Late Proterozoic ◽  
Nappe Tectonics ◽  
Pan African ◽  
Orogenic Belts ◽  
Lower Crustal

The reconstruction of Early Proterozoic crustal evolution and geodynamic environments, in Africa and South America, is incomplete if cratonic areas alone are studied. If the presence of high-grade gneisses is considered as a first clue to past collisional behaviour, 2 Ga high-grade gneisses are more abundant within the Pan-African–Brasiliano mobile belts than in the intervening pre-Late Proterozoic cratons. The West African craton and the Guiana–Amazonia craton consist of relatively small Archaean nuclei and widespread low- to medium-grade volcanic and volcanoclastic formations intruded by Early Proterozoic granites. By contrast, 2 Ga granulitic assemblages and (or) nappes and syntectonic granites are known in several areas within the Pan-African–Brasiliano belts of Hoggar–Iforas–Air, Nigeria, Cameroon, and northeast Brazil. Nappe tectonics have been also described in the Congo–Chaillu craton, and Early Proterozoic reworking of older granulites may have occurred in the São Francisco craton. The location of the Pan-African–Brasiliano orogenic belts is probably controlled by preexisting major structures inherited from the Early Proterozoic. High-grade, lower crustal assemblages 2 Ga old have been uplifted or overthrust and now form polycyclic domains in these younger orogenic belts, though rarely in the cratons themselves. The Congo–Chaillu and perhaps the São Francisco craton are exceptional in showing controversial evidence of collisional Eburnian–Transamazonian assemblages undisturbed during Late Proterozoic time.

Évolution paléogéographique de la marge nord-ouest de l'Afrique du Cambrien à la fin du Carbonifère (du Maroc au Libéria)

1991 ◽  
Vol 28 (7) ◽  
pp. 1121-1130 ◽  
Author(s):  
Michel Villeneuve ◽  
Jean-Jacques Cornée
Keyword(s):  
West African ◽  
The West ◽  
Lower Paleozoic ◽  
West African Craton ◽  
Middle Cambrian ◽  
Early Devonian ◽  
Middle Ordovician ◽  
The North ◽  
Marine Platform ◽  
General Regression

Paleogeographic reconstructions of Paleozoic time are presented for the northwest margin of the West-African Craton. An extensional regime and a marine transgression were dominant during the Early Cambrian. During the Middle Cambrian, the Rokélides orogen was responsible for the sea regression to the south, while the proto-Atlantic opening was active to the north of the Reguibat shield. A large stable marine platform was present during Early and Middle Ordovician. A general regression and the formation of the West-African Inlandsis took place during the Late Ordovician. During Silurian time, this sea transgressed over most of the African platform. Incipient Hercynian deformations during the Early Devonian produced horsts and grabens in Morocco. At the end of the Devonian and the beginning of the Carboniferous, the sea was restricted to isolated basins and tectonic trenches. Collision between West Africa and North America during the Late Carboniferous transformed the Lower Paleozoic margin into an Hercynian orogenic belt, whose structure is controlled by the presence of crustal blocks, generated as early as the Cambrian, and probably reflecting, in turn, older Panafrican zones of weakness. [Translated by the Journal]

scholarly journals The Role of Surface Processes in Partitioning of Strain and Uplift, St. Elias Orogen, Southern Alaska

2016 ◽  
Vol 5 (1) ◽  
pp. 76 ◽  
Author(s):  
Benjamin Patrick Hooks
Keyword(s):  
Three Dimensional ◽  
Surface Processes ◽  
Fault System ◽  
Surface Model ◽  
Primary Control ◽  
Strain Partitioning ◽  
Font Size ◽  
The North ◽  
Oblique Convergence

<span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">Three-dimensional thermo-mechanical numerical simulations of the ongoing Yakutat–North America collision are used to identify the role of surface processes in triggering localized rapid uplift, exhumation, and strain observed within the St. Elias orogen of southern Alaska. Thermochronological data reveal localized rapid exhumation associated with the Seward-Malaspina and Hubbard Glaciers within a tectonic corner structure where transpressional motion to the south along the Fairweather Fault system transitions to shortening to the north and west within the active fold-and-thrust belt of the St. Elias orogen. The modeled deformation patterns are characteristic of oblique convergence within a tectonic corner, recording the transition from simple shear to contractional strain within a zone spatially consistent with the highest exhumation rates suggesting the corner geometry is the primary control of strain partitioning.</span><span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 12.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">The relative roles of surface-related processes versus tectonics-related processes in the development of this pattern of deformation were tested with the inclusion of an erosional surface model. The presence of surface processes enhanced the uplift and development of a localized rapid exhumation. When spatially and temporally erosion models are employed, the location of maxima is shifted in response. This indicates that efficient erosion, and resultant deposition and material advection can influence the localization of strain and uplift.</span>

scholarly journals A review of the Pan-African evolution of the Arabian Shield

GeoArabia ◽  
2002 ◽  
Vol 7 (1) ◽  
pp. 103-124 ◽  
Author(s):  
Pierre Nehlig ◽  
Antonin Genna ◽  
Fawzia Asfirane ◽  
C. Guerrot ◽  
J.M. Eberlé ◽  
...  
Keyword(s):  
Structural Evolution ◽  
Sedimentary Basins ◽  
Fault Zones ◽  
Fault System ◽  
Arabian Shield ◽  
Geologic History ◽  
Lower Paleozoic ◽  
The North ◽  
Pan African ◽  
History Of

ABSTRACT Recent fieldwork and the synthesis and reappraisal of aeromagnetic, geologic, structural, geochemical, and geochronologic data have provided a new perspective on the structural evolution and geologic history of the Arabian Shield. Although Paleoproterozoic rocks are present in the eastern part of the Shield, its geologic evolution was mainly concentrated in the period from 900 to 550 Ma during which the formation, amalgamation, and final Pan-African cratonization of several tectonostratigraphic terranes took place. The terranes are separated by major NW-trending faults and by N-, NW- and NE-oriented suture zones lined by serpentinized ultramafic rocks (ophiolites). Terrane analysis using the lithostratigraphy and geochronology of suture zones, fault zones, overlapping basins, and stitching plutons, has helped to constrain the geologic history of the Arabian Shield. Ophiolites and volcanic-arcs have been dated at between 900 and 680 Ma, with the southern terrane of Asir being older than the Midyan terrane in the north and the Ar Rayn terrane in the east. Final cratonization of the terranes between 680 and 610 Ma induced a network of anastomosing, strike-slip faults consisting of the N-trending Nabitah belt, the major NW-striking left-lateral transpressive faults (early Najd faults), lined by gneiss domes and associated with sedimentary basins, and N- to NE-trending right-lateral transpressive faults. Following the Pan-African cratonization, widespread alkaline granitization was contemporaneous with the deposition of the Jibalah volcanic and sedimentary rocks in transtensional pull-apart basins. Crustal thinning was governed by the Najd fault system of left-lateral transform faults that controlled the formation of the Jibalah basins and was synchronous with the emplacement of major E- to NW-trending dike swarms throughout the Arabian Shield. The extensional episode ended with a marine transgression in which carbonates were deposited in the Jibalah basins. Continuation of the thinning process may explain the subsequent deposition of the marine formations of the lower Paleozoic cover. Our interpretation of the distribution and chronology of orogenic zones does not correspond entirely to those proposed in earlier studies. In particular, the N-trending Nabitah and NW-trending Najd fault zones are shown to be part of the same history of oblique transpressional accretion rather than being two distinct events related to accretion and dispersion of the terranes.

scholarly journals Biology and Economics of Recommendations for Insecticide-Based Management of Soybean Aphid

2016 ◽  
Vol 17 (4) ◽  
pp. 265-269 ◽  
Author(s):  
Robert L. Koch ◽  
Bruce D. Potter ◽  
Phillip A. Glogoza ◽  
Erin W. Hodgson ◽  
Christian H. Krupke ◽  
...  
Keyword(s):  
Insect Pest ◽  
Soybean Aphid ◽  
North Central ◽  
The North ◽  
Central United States ◽  
Glycine Max L ◽  
Short And Long Term ◽  
Aphis Glycines Matsumura

Soybean aphid, Aphis glycines Matsumura, remains the key insect pest of soybean, Glycine max (L.) Merrill, in the north-central United States. Management of this pest has relied primarily on scouting and application of foliar insecticides based on an economic threshold (ET) of 250 aphids per plant. This review explains why this ET remains valid for soybean aphid management, despite changes in crop value and input costs. In particular, we review how soybean aphid impacts soybean yield, the role of biology and economics in recommendations for soybean aphid management, and the short- and long-term consequences of inappropriately timed insecticide applications. Accepted for publication 13 December 2016.

Rb-Sr age determinations of rocks from the Okenyenya igneous complex, northwestern Namibia

1993 ◽  
Vol 130 (3) ◽  
pp. 335-343 ◽  
Author(s):  
Simon C. Milner ◽  
Anton P. Le Roex ◽  
Ronald T. Watkins
Keyword(s):  
Nepheline Syenite ◽  
The South ◽  
Major Phase ◽  
Igneous Complex ◽  
Linear Feature ◽  
The North ◽  
Pan African ◽  
Structural Discontinuity ◽  
Younger Age ◽  
Northern Edge

AbstractThe Okenyenya igneous complex is one of a suite of intrusions which define a prominent northeast-trending linear feature in Damaraland, northwestern Namibia. Precise Rb–Sr internal isochron ages range from 128.6 ± 1 to 123.4 ± 1.4 Ma for the major phases of intrusion identified within the complex. The tholeiitic gabbros forming the outer rings of the complex, and the later alkali gabbros which form the central hills, cannot be distinguished in terms of Rb–Sr ages, although field relations clearly indicate the younger age of the latter. The intrusionsof nepheline-syenite and essexite comprising the mountain of Okenyenya Bergon the northern edge of the complex give ages of 123.4 ± 1.4 and 126.3 ± 1 Ma, respectively, and form the final major phase of intrusion. The ages obtained for early and late intrusive phases define a minimum magmatic ‘life-span’ of approximately 5 Ma for the complex. The determined age of the Okenyenya igneous complex (129–123 Ma), when taken together with the few reliable published ages for other Damaraland complexes (130–134 Ma), suggests that these sub-volcanic complexes were emplaced contemporaneously with the widespread Etendeka volcanics (˜ 130 Ma), and relate to magmatism associated with the breakup of southern Africa and South America with the opening of the South Atlantic Ocean. The linear distributionof intrusions in Damaraland is interpreted to be due to magmatism resultingfrom the upwelling Tristan plume being focused along a structural discontinuity between the Pan-African, Damaran terrain to the south, and Proterozoiccratonic basement to the north.

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