Liegeois J.-P.,Royal Museum for Central Africa |
Stern R.J.,University of Texas at Dallas
Journal of African Earth Sciences | Year: 2010
Neoproterozoic gneisses at Meatiq and Hafafit in the Eastern Desert of Egypt give Rb-Sr and U-Pb zircon ages of 600-750Ma. These gneisses are interpreted by different workers to represent deeper levels of juvenile Neoproterozoic crust or Archaean/Palaeoproterozoic crust that was remobilized during Neoproterozoic time. Geochemical and Sr-Nd isotope compositions for these gneisses reported here are remarkably homogeneous: Initial 87Sr/86Sr (0.70252±0.00056) and Nd (+6.4±1.0). These values are best explained as reflecting derivation from depleted asthenospheric mantle sources during Neoproterozoic time, consistent with mean Nd model ages of 0.70±0.06Ga. The increasing recognition of old, xenocrystic zircons in juvenile ANS igneous rocks can be explained in several different ways. The participation of ancient crust is allowed as one of the explanations, but it is the isotopic composition of radiogenic elements such as Sr and Nd for whole-rock specimens that are the most reliable indicators of whether or not a given crustal tract is juvenile or reworked older crust. These isotopic data indicate that the protolith for the Meatiq and Hafafit gneisses were juvenile Neoproterozoic igneous rocks and sediments derived from them. There is no support in the isotopic data for any significant contribution of pre-Neoproterozoic crust in these two sections of Eastern Desert crustal infrastructure. © 2009 Elsevier Ltd.
Liegeois J.-P.,Royal Museum for Central Africa |
Abdelsalam M.G.,Missouri University of Science and Technology |
Ennih N.,Chouaïb Doukkali University |
Ouabadi A.,University of Science and Technology Houari Boumediene
Gondwana Research | Year: 2013
In this paper, we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events, leading to the transformation of their margins. In some cases, craton interiors can also be shaped by intense collisional processes, leading to the generation of intracratonic orogenic belts. We propose to call these events "metacratonization" and the resulting lithospheric tract "metacraton". Metacratons can appear similar to typical orogenic belts (i.e. active margin transformed by collisional processes) but are actually sharply different. Their main distinctive characteristics (not all are present in each metacraton) are: (1) absence of pre-collisional events; (2) absence of lithospheric thickening, high-pressure metamorphism being generated by subduction, leading to high gradient in strain and metamorphic intensity; (3) preservation of allochthonous pre-collisional oceanic terranes; (4) abundant post-collisional magmatism associated with shear zones but not with lithospheric thickening; (5) presence of high-temperature-low-pressure metamorphism associated with post-collisional magmatism; (6) intracontinental orogenic belts unrelated to subduction and oceanic basin closures. Reactivation of the rigid but fractured metacratonic lithosphere will cause doming, asthenospheric volcanism emplacement, and mineralizations due to repetitive mineral enrichments. This paper provides several geological cases exemplifying these different metacratonic features in Scandinavia, Sahara, Central Africa and elsewhere. A special focus is given to the Saharan Metacraton because it is where the term "metacraton" originated and it is a vastly expanded tract of continental crust (5,000,000km 2). Metacratonization is a common process in the Earth's history. Considering the metacraton concept in geological studies is crucial for understanding the behavior of cratons and their partial destruction. © 2012 International Association for Gondwana Research.
News Article | November 30, 2015
These are the majority of the participants in the study in Brisbane, Australia, 2012. Credit: CRP cryptic fruit fly pest species. Considered among the agricultural pests with the greatest economic impact, the tephritid fruit flies (Diptera: Tephritidae) are a serious worldwide problem. Destroying fruit and vegetable production and markets across all major continents, some key species have raised international attention, leading to six years of coordinated multidisciplinary research that will contribute to overcome phytosanitary trade barriers and apply more sustainable pest management strategies such as the Sterile Insect Technique (SIT). The collaboration between over fifty researchers from more than twenty countries resulted in twenty-five articles, compiled by editors Drs. Marc De Meyer, Royal Museum for Central Africa, Belgium, Anthony R. Clarke, Queensland University of Technology, Australia, M. Teresa Vera, Facultad de Agronomia y Zootecnia, Universidad Nacional de Tucuman, Argentina, and Jorge Hendrichs, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Austria. They have now been published in a special volume of the open-access journal ZooKeys. Females from numerous native as well as invasive fruit flies species cause tremendous economic losses by laying their eggs directly into ripening fruit and vegetables, where their larvae feed, destroying the crop. Their presence also results in the loss of export markets and expensive quarantine and regulatory controls that further increase the associated costs. The impact of these pests and the requests from the Member States led the Joint Food and Agriculture Organisation / International Atomic Energy Agency (FAO/IAEA) Programme on Nuclear Techniques in Food and Agriculture to assist the governments in developing and applying more environment-friendly pest suppression systems. One example is the SIT package developed and applied against the Mediterranean fruit fly, which resulted in the successful management of this pest species in a number of countries. To further develop such techniques to deal with other major fruit fly species threatening the agriculture in many countries around the world, the scientists needed to resolve first controversies related to species identities, so that they can differentiate taxonomic groups and better understand their biology. Therefore, researchers used multiple, independent lines of evidence to delimit the species boundaries. These included traditional morphology, but also morphometrics, developmental physiology, pre- and postzygotic mating incompatibility, karyology, chemoecology, and a wide range of molecular techniques such as multi-locus markers and microsatellites among others. The present Special Issue presents some of the major findings that are of utmost significance for international horticultural trade and the application of biologically-based pest control methods. The volume is dedicated to two prominent and leading figures in the scientific and research community, Serge Quilici and Peter Teal. Both were part of the initiative from the beginning, but regrettably, passed away recently and were not able to see its conclusion. Explore further: What's in a name? Everything—if you're a fruit fly
Delvaux D.,Royal Museum for Central Africa |
Barth A.,University of Heidelberg
Tectonophysics | Year: 2010
The kinematic models and the associated orientation of extensional stress of the East African Rift System have been subjected to much debate since a long time. In the past decades, the proposed models relied on the interpretation of the overall rift geometry, geological fault-slip data and the few focal mechanisms available. These models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space. In the recent years, there has been a significant increase in the number of focal mechanisms available for the entire rift system, and it is now possible to estimate the present-day stress field in relative detail based on seismotectonic data alone. We compile 347 focal mechanism data from the Global/Harvard CMT catalogue and various other sources and grouped 332 of them in 24 distinct regions (boxes) on the basis of their geographical proximity, kinematic homogeneity and tectonic setting. For each box and for the same data set, reduced stress tensors have been obtained by formal stress inversion using both the TENSOR program (Delvaux & Sperner, 2003) and the SLICK method (Michael, 1984/1987). Both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes, which stem for the robustness of the approach. The obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces, including plate boundary forces, and 2nd and 3rd order effects as gravitational potential of topography, intra-lithospheric processes, and the influence of structural heterogeneities of the rift structures. The evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field. Additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns. © 2009 Elsevier B.V. All rights reserved.
Martin-Benito D.,Lamont Doherty Earth Observatory |
Beeckman H.,Royal Museum for Central Africa |
Canellas I.,Japan Forestry and Forest Products Research Institute
European Journal of Forest Research | Year: 2013
We investigated the influence of climate on the ring width and xylem anatomy of two co-occurring pines (Pinus nigra Arn. and P. sylvestris L.) in the mountains of east-central Spain in order to test their utility for dendroclimatic reconstructions. We developed chronologies of ring width, mean lumen diameter and mean cell-wall thickness (in the earlywood, latewood, and the total annual ring) and the number of cells between 1960 and 2006. Drought, expressed as the standardized precipitation-evapotranspiration index (SPEI), was the main climatic driver of tree radial growth, although trees were also sensitive to temperature (negative effect in previous autumn and current summer) and precipitation (with a general positive effect). P. sylvestris response was stronger to climate of the current year, whereas the effect of previous-year climate was more important for P. nigra. Warm and dry summers reduced ring width, tracheid lumen, and wall thickness in both species, whereas warm winter-spring temperatures had the opposite effect, primarily for P. sylvestris. Previous-year or early-season conditions mainly affected earlywood features, whereas latewood was more responsive to summer climate. Overall, climate appeared to be a stronger limiting factor for P. sylvestris. During periods of drought, cell-wall thickness was reduced while lumen width increased in the latewood of P. sylvestris. This could compromise its hydraulic safety against drought-induced cavitation as our site was close to the southern and dry edge of the species distribution area. Our results suggest that anatomical variables record different and stronger climate information than ring width variables, especially in P. sylvestris. Reconstruction models for SPEI at the 3-month scale were developed for July-August and September-October using principal components regression. The best models included anatomical and width variables of both pine species suggesting that tracheid chronologies can be useful for drought reconstructions especially at mesic sites or with species that encode a mixed drought and temperature-precipitation signal. © 2012 Springer-Verlag.
Tentler T.,Royal Museum for Central Africa |
Acocella V.,Third University of Rome
Journal of Geophysical Research: Solid Earth | Year: 2010
Oceanic ridge segments interact forming different types of structures, of which transform faults and overlapping spreading centers represent the most common end-members. This study uses analogue models for testing the role of the initial configuration of the ridges on the geometry and kinematics of the resulting interaction zones. The models, run in a centrifuge, consist of a lighter silicone (LDS), rising within a denser silicone (HDS) below a brittle layer simulating the oceanic lithosphere. Precut fractures in the brittle layer simulate the initial configuration of oceanic ridges. The rise and lateral spreading of the LDS induce the propagation, widening, interaction, and linkage of the fractures. We varied the offset and overlap between the fractures, obtaining 10 distinctive types of interaction. Variations in fracture overlap and offset define several interaction types. Increase of fracture overlap leads to interaction zones of lower aspect ratio, with fractures propagating at lower angles to the mean extension direction. Increase of offset leads to the elongation of the interaction zones with the new fractures propagating subparallel to the extension direction. The comparison with several examples of natural ridges shows close geometric similarities, confirming the existence of predominant types of ridge interaction. Among these, ridges with smaller offsets develop interactions similar to overlapping spreading centers, whereas ridges with larger offsets have geometries reminiscent of transform zones. The comparison between experimental and natural examples suggests that the observed wide spectrum of ridge interaction types in nature results from the initial configuration of the divergent plate boundary. Copyright 2010 by the American Geophysical Union.
Fannes W.,Royal Museum for Central Africa
Zootaxa | Year: 2013
Two new species of the goblin spider genus Antoonops are described, bringing the total number of species to six. Antoon-ops kamieli sp. nov. is described from two males and one female collected in Bouaké, Ivory Coast. The species can be easily distinguished from congeners by its large eyes. In addition, the males are characterized by a distinct depression on the ventral abdomen. Antoonops sarae sp. nov. is described from four females collected in Tchabal Mbabo, Cameroon. The species is unusual in having a long postepigastric scutum and a genital duct with finger-like protrusions. A key to the species of Antoonops is provided. Copyright © 2013 Magnolia Press.
Fannes W.,Royal Museum for Central Africa
Bulletin of the American Museum of Natural History | Year: 2013
The goblin spider genus Zyngoonops Benoit, 1977 is revised. The type and hitherto only species, Z. clandestinus Benoit from the Democratic Republic of Congo (D.R.C.), is redescribed on the basis of topotypical material. Nine new species are described from the D.R.C. (Z. moffetti, Z. redii, Z. goedaerti, Z. rockoxi, Z. beatriceae, Z. chambersi, Z. swammerdami, Z. marki) and the Central African Republic (Z. walcotti). Members of Zyngoonops show remarkable modifications of the sternum and pedicel tube: the sternum has two heavily sclerotized posterior extensions, and the pedicel tube has a protruding ventral lip. The female genitalia are complex, consisting of an epigastric scape, two uterine sclerites, and a long genital duct. In most species, the distal part of the duct is highly coiled. Males resemble those of Antoonops Fannes and Jocqué and Coxapopha Platnick in having elaborately modified endites, a pair of pleural flaps, and a carapace with extended anterolateral corners. The type species of Coxapopha is redescribed, and new images of the female genitalia of Antoonops and Coxapopha are provided. A cladistic analysis of morphological characters provides support for the monophyly of Zyngoonops and identifies Z. redii as the most basal species of the genus. © 2013 American Museum of Natural History.
Beeckman H.,Royal Museum for Central Africa
IAWA Journal | Year: 2016
The largest part of forest biomass consists of wood. A global estimate of carbon stored in lignified tissues rises up to 400 Pg. Given these quantities, there is a growing interest of implementing wood research in diagnoses and evaluations of the carrying capacity of the global ecosystem and its forests. The question arises how disciplines like wood anatomy could respond to the increasing demands of a trait-based ecology, understood as a paradigmatic shift in addressing global changes. Dendrochronology and ecological wood anatomy, traditionally operating within the paradigm of species-based ecology, developed robust methods to address ecological questions. However, sampling strategies and database design will likely be different when wood traits are to be used to study individual tree performance, including responses to stress. Aiming at optimally involving wood research in trait-based ecology, some trait concepts are analysed. The value of the IAWA standard lists of wood anatomical features as starting points for trait databases is recognized. A summary of the functionality of wood is given to inform the trait-research community of basic aspects of tree performance. The time dimension is highlighted, as well as the foundations for understanding bio-hydraulics, bio-mechanics and metabolism of wood and relevant traits. Guidelines are given for sampling strategies and database concepts. Prospects of time axis construction and system integration are discussed, as well as the importance of standardizing for size. © 2016 International Association of Wood Anatomists.
Virgilio M.,Royal Museum for Central Africa
Bulletin of entomological research | Year: 2011
Most of the current knowledge about African tephritids originates from studies performed in agricultural areas, while information about their distribution in pristine or moderately disturbed environments is extremely scarce. This study aims at (i) describing levels of spatial variability of frugivorous tephritids in tropical forests and small rural villages of the Congo River basin and (ii) verifying if human-mediated activities, such as small-scale agriculture and trade, can affect their distribution patterns. Four locations were sampled along a 250 km stretch of the Congo River. At each location, pristine and disturbed habitats (i.e. tropical forests and small rural villages, respectively) were sampled, with three replicate sites in each combination of habitat and location. Sampling with modified McPhail traps baited with four different attractants yielded 819 tephritid specimens of 29 species from seven genera (Bactrocera, Carpophthoromyia, Ceratitis, Dacus, Celidodacus, Perilampsis, Trirhithrum). The three most abundant species sampled (Dacus bivittatus, D. punctatifrons, Bactrocera invadens) showed significant variations in abundance across locations and sites and accounted for 98.29% of the overall dissimilarity between habitats. Assemblages differed among locations and sites while they showed significant differences between pristine and disturbed habitats in two out of the four locations. This study shows that frugivorous tephritids in central Congo have remarkably patchy distributions with differences among locations and sites representing the main source of variability. Our data show that, in rural villages of central Democratic Republic of Congo, human activities, such as small-scale agriculture and local commerce, are not always sufficient to promote differences between the tephritid assemblages of villages and those of the surrounding tropical forests.