Journal Of African Earth Sciences 

About: Journal Of African Earth Sciences is an academic journal published by Elsevier BV. The journal publishes majorly in the area(s): Geology & Paleontology. It has an ISSN identifier of 0899-5362. Over the lifetime, 367 publications have been published receiving 481 citations.

Gold-bearing listwaenites in ophiolitic ultramafics from the Eastern Desert of Egypt: Subduction zone-related alteration of Neoproterozoic mantle?

Abstract: Dike-like variable listwaenites with significant Au (up to 25 ppm) are exposed along fault zones in serpentinites at Um Khasila-Um Huweitat (Kh-H) and Malo Grim (MG) in central and southern Eastern Desert of Egypt, respectively. The protoliths of serpentinites were mainly Neoproterozoic fore-arc mantle olivine-rich peridotites. The Kh-H serpentinites are similar to those formed in the mantle wedge, but the MG serpentinites are similar to those formed in the subducted oceanic slab. Serpentinization fluids sourced from dehydrated subducted sediments and oceanic crust. However, the Kh-H serpentinites received more lighter fluids mobile trace elements relative to MG serpentinites (av. Ba/Th = 312 vs. 0.79; av. U/Th = 466 vs. 0.018; av. As/Sm = 0.057 vs. 0.76; av. Cs × depleted mantle = 5075 vs. 7272). The Kh-H listwaenites are allometamorphic, formed by the intrusion of gabbro-diorite and the release of the subducted slab-derived CO2 into the mantle wedge serpentinites giving talc-carbonate (Type I) with high K2O (av. 3.27 wt%), Sr (av. 1131 ppm), Rb (av.165 ppm), Ba (av.407 ppm), and Zr (av. 23 ppm). The MG listwaenites, which have substantially lower K2O, Na2O, TiO2, and Al2O3 concentrations, are autometamorphic and were generated by the loss of SiO2 and addition of CO2 into the subducted serpentinites. With temperature decrease, in Kh-H listwaenites magnesite was overgrown by ankerite, while in MG listwaenites carbonate changed from magnesite to dolomite to calcite. SiO2-bearing fluids could have mixed from continental crust during Kh-H ophiolite emplacement, forming silica-rich listwaenite (Type III) with enriched K2O, TiO2, As, Ba, W and Th. This could be linked to carbonation of serpentinites in MG, forming silica-carbonate listwaenite (Type II) with enriched MnO, Sc, Cr, As, Sr, Cs, Ba, Pb, and U. Mixing of silicification fluids with the Kh-H altered serpentinites most likely increased gold concentration in the enclosed listwaenites. In the MG listwaenites, however, there is no correlation between Au content and SiO2/(CaO + MgO) ratios, indicating that gold was frequently concentrated by the carbonation process.

Assessment of heavy metal contamination and health risk in the coastal sediments of Suez Bay, Gulf of Suez, Egypt

Abstract: Urban and industrial wastewaters, and the weathering of rocks are the main anthropogenic and natural sources of heavy metals (HMs) in coastal worldwide environments. The present work examined the content, distribution, potential sources, and ecological risks of HM contamination in the coastal sediments of Suez Bay, Egypt. Six pollution and health risk indices and multivariate statistical tools were applied. The ranges of HMs (μg/g) were in order: Fe (239–983), Mn (4.70–189), Cr (1.75–19.49), Co (0.04–12.87), Zn (0.78–15.57), Ni (0.78–10.90), Cu (0.23–7.53), Pb (0.74–6.92), Cd (0.10–0.97), and Hg (0.11–0.89). The results of pollution load index (PLI) and modified contamination degree (mCdeg) indicated that the Suez Bay area seems to be free from pollution. However, some individual sites recorded high concentrations of Cd and Hg, which might be attributed to the presence of some ports, industrial activities, sewage, shipbuilding workshops and heavy traffic of commercial ships. Moreover, the assessment of the carcinogenicity risks by dermal absorption was in order Cr > Pb > Cd for adults and children. However, the study area does not suffer from any potential carcinogenic risk because the total cancer risk (LCR) was less than 1 × 10−6.

Assessment of rainfall-induced landslide susceptibility in Artvin, Turkey using machine learning techniques

Abstract: In this study, the performances of machine learning models, such as artificial neural networks (ANN), gradient-boosting machines (GBM), random forest (RF) and support vector machines (SVM) in rainfall-induced landslide susceptibility mapping were evaluated. For this purpose, the Arhavi, Hopa and Kemalpaşa districts of Artvin, which is one of the highest rainfall areas in Turkey, were identified as the study area. A landslide inventory comprising 533 landslide polygons (3959 pixels at 10-m resolution) was used; 70% of the pixels showing the landslides were used for training the models and the remaining 30% were used to validate the models. For landslide susceptibility modelling, 13 factors associated with landslides were considered. The area under the receiver operating characteristic curve was found to reveal the predictive capabilities of the models. As a result, the prediction rates of the ANN, SVM, RF and GBM models were found to be 93.8%, 94.8%, 96.1%, and 97%, respectively. According to the results, the GBM outperformed other models.

Mantle source characteristics of the late Neoproterozoic post-collisional gabbroic intrusion of Wadi Abu Hadieda, north Arabian-Nubian Shield, Egypt

Abstract: This article presents geochemical and mineralogical data for the Neoproterozoic Abu Hadieda mafic intrusion (AHMI), which exposed at the boundary between the northern and central domains of the Eastern Desert of Egypt, to study its magma source and petrogenesis. Field relations indicate that the AHMI is younger than the syn-tectonic tonalite-granodiorite, but older than post-collisional monzogranite and alkali feldspar granite. The AHMI is neither deformed nor metamorphosed and keep the primary texture and mineralogy indicating a post-collisional setting. It consists mainly of medium to high-K calk-alkaline pyroxene-hornblende gabbro with minor diorite. The low Mg# (32–41) values of the gabbro are typical of young post-collisional mafic intrusion in the Arabian-Nubian Shield (ANS). Geothermobarometric calculations suggest that the pyroxene-hornblende gabbro was crystallized at relatively high pressure (0.6 GPa) and temperature (800–915 °C). The samples show a general enrichment in LREEs and LILEs (e.g., Sr, Ba, K) relative to HREEs and HFSEs (e.g., Nb, Ta, Hf, Ti, Zr). The chemical and mineralogical signatures are consistent with evolution of the AHMI from emplacement of a primitive partial melt derived from a lithospheric mantle source that had previously been metasomatized, in an early stage of ANS evolution, by subduction-related melts. Remobilization and melting of this lithospheric source occurred in a post orogenic setting, likely driven by crustal thinning and extension.

Comparison of analytic network process and artificial neural network models for flash flood susceptibility assessment

Abstract: Floods are natural risks with devastating consequences for the environment, people and the economy. Gabes Catchment is regularly devastated by floods owing to urban sprawl, population growth, unregulated municipal systems and indiscriminate land use. However, mitigation of flood impacts can be achieved via flood implementation forecasting systems. In this study, Analytical Network Process (ANP) and Artificial Neural Network (ANN) models were integrated into a Geographic Information System (GIS) to identify and classify flood-prone areas. A geographic information database was derived from the existing geological map, digital elevation model (DEM), precipitation and land-use data. The evaluation of different factors can affect the flood analysis. The ranked and normalized indicators were then weighted and classified with an ANP model to establish the training database. The normalized layers, combined with the training site maps, were then fed to a multilayer perceptron neural network (MLP) to yield a flood risk map. Using a field survey, historical flood data, and satellite imagery, 226 flood locations were identified and classified into 70% training data sets and 30% validation data. Results obtained from ANP and ANN showed that 10% and 14% of all areas were classified as high and very high flood susceptibility, respectively. The performance of both models was assessed using the operational characteristic of the ROC model. The Area Under the Curve ‘AUC’ of ANP and ANN models were 0.861 and 0.876, respectively. The obtained results show the similarity and comparability of the used methods. These results corroborate the perception of susceptibility in the population of the city of Gabes. The study outcomes are of great value to policy makers and state authorities in order to achieve greater awareness and adopt strategies for the preparation and management of the environment in the future for the city of Gabes.