Geochemistry and tectonic setting of early Pan-African metamorphosed volcano–sedimentary sequence in southern Solaf zone, SW Sinai, Egypt     

Doris Sadek Ghabrial  Michael Dawood Samuel  Hilmy Essa Moussa 《Arabian Journal of Geosciences》2013,6(10):3635-3649

The south Solaf zone in SW Sinai comprises a metasedimentary sequence of metagraywackes intercalated with minor metavolcanic sheets, metasiltstones, meta-arenites, and calc–silicates. The metavolcanics (basalt–andesite) show high- to medium-K calc–alkaline nature. They exhibit distinctive Nb-Ta negative anomalies relative to enriched LILE, being highly similar to active continental margin lavas, but they also have the characteristics of rift-related magmatism. Magmas of similar composition are interpreted to be formed in an extensional environment and their source regions are zones of enriched subcontinental lithosphere. The metasediments are poor to moderate sorting, intercalated to the north with minor impure calcareous layers. Geochemical investigation shows that they are immature to semi-mature sediments derived from a source of mafic to felsic composition. These metasediments are chemically similar to the active continental margins and are comparable to the Feiran gneisses and metagraywackes that were deposited before 800 Ma in an extensional environment. The investigated rocks suffered LP-HT amphibolite facies metamorphism. The P-T estimates using various thermobarometric calibrations gave temperatures of 554–610 °C and pressures of 2.2–4.0 kbar.  相似文献   

Eruptive history of the Barombi Mbo Maar, Cameroon Volcanic Line, Central Africa: Constraints from volcanic facies analysis     

Boris Chako Tchamabé  Dieudonné Youmen  Sébastien Owona  Issa  Takeshi Ohba  Károly Németh  Moussa Nsangou Ngapna  Asobo N. E. Asaah  Festus T. Aka  Gregory Tanyileke  Joseph V. Hell 《Central European Journal of Geosciences》2013,5(4):480-496

his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U₁, U₂ and U₃. Interpretation of these features indicates that U₁ consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U₂, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U₂ and U₃, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin.  相似文献   

Relationship between geo-structural evolution and development of karstic systems in the culminating area of Ouarsenis (West Algeria)     

Zaagane Mansour  Refas Soraya  Khaldi Abdelkader  Frédéric Donzé  Hamimed Abderahmane  Safa Aissa  Moussa Kacem  Sebbane Abbes  Azzaz Habib  Mouassa Souad 《Arabian Journal of Geosciences》2016,9(14):638

The Ouarsenis area is one of the most developed karstic systems of Algeria. It is a karst reservoir drinking water with a population of more than 50,000 people taking fully benefit from it. To understand the development of this karstic system, the local tectonic history of the four main mountain ranges of this culminating area (Ouarsenis) has been analyzed. Although previously identified primarily Cenozoic tectonic activities have been observed, a set of NW-SE joints intersecting the Jurassic limestone has been associated to a post-nappes tectonic events. Moreover, numerous joint sets oriented NNE/SSW have been identified almost over the entire culminating area. These joints are the direct consequence of the following stress history: (i) a NW/SE shortening responsible for a major overlap and the first fold (P1) phase, (ii) a second NNE/SSW shortening stage responsible for the second folding (P2) phase associated with 70° N sinistral strike-slip trend, (iii) a WNW/ESE extension phase resulting from the change of σ ₃ stress vertical axis, and (iv) a shearing stress creating a 120° N sinistral strike-slip fault. Only the late phases are responsible of the development of joints, which have been karstified later on. Indeed, significant families of karstified joints, i.e., 20° and 70° N have been found. These joints are related to the extensional and shearing modes, respectively, and linked to a particular in situ karstogenesis. Moreover, this study suggests an ancient establishment of the karstic systems in the Ouarsenis region in at least two stages: pre-figured and activated behaviors during the Cenozoic.  相似文献   

Impact of the spatial arrangement of land management practices on surface runoff for small catchments     

F. Colin  R. Moussa  X. Louchart 《水文研究》2012,26(2):255-271

Predicting the impact of land use changes on the hydrological response is crucial for water resource management. In the particular case of small catchments (1–10 km²), distributed models could provide useful answers regarding the effects of cultivation practices and man‐made works on water fluxes. However, the impacts of specific land use spatial arrangements are difficult to predict because of the prohibitive number of possible cases to consider. Focusing on surface runoff, this article describes a strategy based on a water particle tracking routine to be plugged‐in a distributed model that is designed to determine the spatial arrangements of land management practices that have the greatest impact on volume, peak discharge and lag time at the catchment outlet. A case study is described; the hydrological response of the Roujan catchment (Herault, France) is simulated with the MHYDAS model. The Roujan catchment contains a vineyard in a Mediterranean climate in a landscape in which weeding practices highly influence the partition between soil infiltration and runoff. Results showed that the proposed strategy is much more efficient than a random approach to design the spatial arrangements of the vineyard weeding practices with the greatest impact. Therefore, the proposed strategy may lead to innovative policies for the spatial planning of land management practices. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献