Journal of African Earth Sciences最新文献

{"title":"Exploring the Gebel Kamil impactoclastic fallback deposits in Egypt: Their origin and post-impact alteration using SEM/AM and Cathodoluminescence techniques","authors":"Nahla A. Shallaly ,&nbsp;Mona Kabesh ,&nbsp;Sabine Gilbricht ,&nbsp;Ahmed N. El Barkooky ,&nbsp;Mohamed El Sharkawi ,&nbsp;Jens Götze ,&nbsp;Bernhard Schulz","doi":"10.1016/j.jafrearsci.2025.105618","DOIUrl":"10.1016/j.jafrearsci.2025.105618","url":null,"abstract":"<div><div>A Scanning Electron Microscope (SEM)-based Automated Mineralogy (SEM-AM) analysis and Cathodoluminescence (CL) were used to study the mineralogy and texture of a vertical 60 cm profile within the Gebel Kamil impactoclastic fallback deposits. The SEM/AM technique was employed to quantify mineralogical and textural criteria such as distribution, grain size, sorting, mineral association, and shape of clastic deposits in two units of the profile. Microscopically, these deposits are composed mainly of unshocked and shocked quartz, along with impactogenic particles such as lithic ejecta, glassy and impact melt fragments, and projectile shrapnel. SEM/AM effectively identified taenite as the main projectile debris, distinguished various primary mineral phases and related alterations, and microscopically unresolvable inclusions such as tantalite. The impact melt composition was characterized as a Si-rich lechatelierite white melt surrounded by a dark melt. The SEM/AM analysis delineated the composition variance between (Fe-rich) hematite and (Fe-Al-Si-rich) almandine melts. Quantitative textural aspects of the SEM/AM indicate a higher concentration of shocked and other impactogenic particles in the lower unit of the deposits created by the impact plume, whereas the more sorted, finer, more altered upper unit inferred a higher degree of mixing with non-impact related Holocene sediments. The CL results identified shock-induced features, alteration products, and zoning in specific minerals. They also provided insight into the origin of the target rocks, indicating their derivation from a Precambrian complex. The vertical variation of authigenic minerals suggests the presence of a phyllic, post-impact hydrothermal alteration affecting these porous deposits.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105618"},"PeriodicalIF":2.2,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phase relations in Co-Ni-Fe-(±Au ±Ag) mineralizations of Bou Azzer-El Graara inlier, central Anti-Atlas, Morocco: Insights from mineral chemistry and fluid inclusions analysis","authors":"Muhammad Souiri ,&nbsp;Mohamed Aissa ,&nbsp;Abdelaziz El Basbas ,&nbsp;Ahmed H. Ahmed ,&nbsp;Ilyasse Loudaoued ,&nbsp;Hafid Mezougane ,&nbsp;Mohammed El Azmi ,&nbsp;Azizi Moussaid ,&nbsp;Hassane Ouguir ,&nbsp;Mohamed Ait Addi","doi":"10.1016/j.jafrearsci.2025.105606","DOIUrl":"10.1016/j.jafrearsci.2025.105606","url":null,"abstract":"<div><div>The Bou Azzer East deposit is located in the western part of the Bou Azzer inlier, where many orebodies of Co-Ni-Fe ± Au ± Ag are actively mining. These orebodies are mainly controlled by late Pan-African and/or Hercynian structures. The Co–Ni arsenide-sulfarsenide mineralization at Bou Azzer East is associated with serpentinite rocks, and possesses two modes of occurrence: (i) at the contact between serpentinite and quartz diorite or Ediacaran volcanic rocks, with veins sometimes extending into serpentinite; (ii) as orebodies crosscutting quartz diorite (vein-type). The Bou Azzer Co-Ni mineralization proposed to be formed by three stages: (1) pre-mineralization stage, characterised by the presence of chromite and talc; (2) arsenide mineralization stage (mono-, di-, tri-arsenides and sulfarsenides) associated with quartz gangue; and (3) sulphide mineralization stage accompanied by carbonate gangue. These stages of mineralization are temporally arranged and separated by brittle deformation episodes. Except for the first stage, inclusions of native-Au and electrum (Au-Ag) are found in the subsequent stages of arsenides, sulfarsenides, and sulphides. Native-Au is also emphasized in the supergene stage. Micrometric analysis of fluid inclusions (FI) was carried out on quartz and calcite gangues. FI trapped in quartz show that arsenides and Au-Ag mineralization precipitated from hydrothermal fluids at temperatures ranging from 200 to 350 °C and salinities ranging from 15 to 45wt% NaCl equiv. The sulphide and Au-Ag assemblage, hosted in calcite gangue, is most probably formed from fluids with temperature ranging from 200 to 250 °C and salinities between 25 and 45 wt% NaCl equiv. The precipitation of the ore minerals is related to fluid mixing, boiling, and cooling at different temperatures and salinities. Weathering of hypogene arsenides and sulphides minerals led to the formation of heterogeneous secondary minerals, including erythrite, roselite, chalcocite, bornite, and native gold. This phenomenon, driven by leaching and fluid-rock interactions, contributed to the formation of these secondary minerals.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105606"},"PeriodicalIF":2.2,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143642949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison of ground and aero magnetic data in the Eastern Pontides (Türkiye) and inferences regarding the crustal structure with the support of gravity data","authors":"Murat Özkaptan ,&nbsp;Tuğçe Özkaptan ,&nbsp;Ali Erden Babacan","doi":"10.1016/j.jafrearsci.2025.105620","DOIUrl":"10.1016/j.jafrearsci.2025.105620","url":null,"abstract":"<div><div>Magnetic and gravity surveys are widely utilized in geological research due to their efficiency and rapid data acquisition capabilities. Various global data platforms integrate measurements obtained from ground, sea, and airborne surveys. However, combining these datasets can sometimes lead to a reduction in resolution.</div><div>This study aims to analyze both airborne and ground magnetic data in the Eastern Pontides to assess this issue. A comparison of the two data sources, following normalization, reveals significant similarities. Magnetic anomaly values obtained from both different data sources overlap by almost 90 %. Additionally, the findings suggest that conducting ground magnetic surveys at intervals of no more than 10 km is sufficient for modeling large-scale deep structures.</div><div>The second objective of this study is to integrate magnetic data with Bouguer gravity data to develop a conceptual crustal model for the Eastern Pontides. Contrary to the commonly suggested monotonous increase in crustal thickness from north to south, this study identifies a gravity anomaly of approximately 50 mGal in the southern part of the region, indicating a localized thinning of the crust. Furthermore, the results demonstrate that combining ground and aeromagnetic data provides a more detailed and reliable assessment of crustal thickness variations.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105620"},"PeriodicalIF":2.2,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143619266","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry and provenance of Birimian metasedimentary rocks of Téra area, Leo-Man Shield, West Niger","authors":"Hamidou Garba Saley ,&nbsp;Moussa Konate ,&nbsp;Olugbenga Akindeji Okunlola","doi":"10.1016/j.jafrearsci.2025.105609","DOIUrl":"10.1016/j.jafrearsci.2025.105609","url":null,"abstract":"<div><div>This study presents the provenance of metasedimentary rocks (including amphibolites, mica schists, quartzites, and gondites) of the Téra area, using petrographic and geochemical (whole rock) analyses.</div><div>The methodology employed in this study involves a field investigation (sampling and mapping) followed by a petrographic analysis using a transmitted light polarized microscope and finally, a geochemical analysis through ICP-MS method. The major oxides (SiO₂/Al₂O₃ vs K₂O/Na₂O diagram) and trace elements (La-Th diagram) show that all the samples come from Archean sediments, except for three amphibolite samples which are highly enriched in La and Th due to contamination. The geochemical classification plot [log (Na₂O/K₂O) vs log (SiO₂/Al₂O₃)] shows a shale-sand-ferruginous composition of sediments. Calculation of the Index of Compositional Variability (ICV) indicates that the amphibolites and gondites sediments characterized by high ICV values are derived from immature sediments, reflecting a proximal source rock and rapid deposition. on the other hand, the mica schist samples, with low ICV values, be mature sediments derived from a distal source rock. The quartzite samples are a mixture. The Al₂O₃/TiO₂ ratios, the TiO₂ vs. Zr plot and the La/Th vs. Hf diagram suggest a mafic, intermediate to felsic igneous parent source origin with an intermediate source predominant from active tectonic setting (magmatic arc). The LILE group (Sr, Ba, Rb, K) and incompatible elements (Ce, La, Nb, Th) concentrations of mica schists, amphibolites, and quartzites samples are close to those of crust continental, except for gondites and two quartzite samples (A1 and A3) which are close to Morb, and show LILE depletion. The evaluation of the alteration degree shows that all amphibolites and quartzites (except one) samples have the lowest degrees of alteration. While the mica schists and the fresh gondite samples (at the bottom of hills) have a moderate degree of alteration. The gondite samples located towards the top of hills have extreme degrees of alteration. These high alterations suggest a chemical weathering in warm and humid climatic conditions.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105609"},"PeriodicalIF":2.2,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143637476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Two interconnected stages in the formation of the Tamazeght magmatic complex (Moroccan central High Atlas) determined by apatite, zircon and titanite U-Pb geochronology","authors":"Jamal Achmani ,&nbsp;Thomas Blaise ,&nbsp;Ilham Chraibi ,&nbsp;Jocelyn Barbarand ,&nbsp;Nathan Cogné","doi":"10.1016/j.jafrearsci.2025.105623","DOIUrl":"10.1016/j.jafrearsci.2025.105623","url":null,"abstract":"<div><div>The intraplate magmatic complex of Tamazeght (or Tamazert), located in the central High Atlas of Morocco, formed during the Eocene in response to N-S oriented compressive shear movements associated with the convergence between Africa and Europe. The ages of emplacement of certain rocks forming this complex have been determined so far using K-Ar radiometric dating on biotite (from carbonatites and monzonites) and K-feldspar (from nephelinite dykes), as well as Rb-Sr geochronology on whole rock (nepheline monzodiorite). Furthermore, U-Pb geochronology has so far only been applied to eudialytes in the syenites and zircon in the monzonite and late-stage vein. However, uncertainties remain regarding the timing of emplacement of basic cumulates, syenites and lamprophyre dykes. In addition, the ages reported in the literature do not allow discussion of the continuous or multistage formation of the Tamazeght complex. In this paper, we use U-Pb geochronology on zircon, apatite and titanite crystals to clarify the sequence of events that formed the Tamazeght complex. Considering previously published and our new data, two interconnected magmatic stages have been identified. The first stage (ca. 47-44 Ma) corresponds to the plutonic rocks of the jacupirangite-ijolite ultrabasic cumulate sequence, whose age was previously undocumented. The second stage (ca. 44-35 Ma) includes more differentiated plutonic units (ca. 44-41 Ma), as defined by two U-Pb ages obtained from syenite zircons that agree with previous ages. A lamprophyre dyke located south of the complex gave a U-Pb age of 42.2 ± 1.9 Ma on titanite and can be attributed to the vein phase (ca. 43-35 Ma) of this second magmatic stage. This phase involves the intrusion and/or extrusion of several carbonatite, lamprophyre, and phonolite dykes. The Tamazeght magmatic activity is characterized by its short duration, from the early Lutetian to the early Priabonian (ca. 10 My), in relation to the regional geodynamic processes of the first Atlasic phase during the Alpine orogeny.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105623"},"PeriodicalIF":2.2,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soil erosion and sediment yield in Africa: Processes and factors","authors":"Abdelali Gourfi ,&nbsp;Matthias Vanmaercke ,&nbsp;Jean Poesen ,&nbsp;Joris de Vente ,&nbsp;Mourad Aqnouy ,&nbsp;Aude Nuscia Taibi ,&nbsp;Roberto Valentino ,&nbsp;Lahcen Daoudi ,&nbsp;Sofie De Geeter ,&nbsp;Hamza Briak","doi":"10.1016/j.jafrearsci.2025.105622","DOIUrl":"10.1016/j.jafrearsci.2025.105622","url":null,"abstract":"<div><div>Africa experiences diverse and often intense soil erosion processes, yet the interplay between these processes and observed sediment yield (SY) at catchment scales is insufficiently understood. Building on previous continental-scale assessments, this study integrates a newly verified database of measured SY at 425 river outlets with, model-based estimates of Rill and Sheet Erosion (RSE), Landslide Mobilization Rates (LMR), and Gully Head Susceptibility (GHS). Our approach addresses a key gap in earlier work, which primarily relied on environmental predictors without explicitly quantifying the contribution of multiple geomorphic processes.</div><div>Our results indicate that the mean observed SY is 6.07 t⋅ha⁻¹⋅yr⁻¹, whereas modelled RSE and LMR average 9.42 t⋅ha⁻¹⋅yr⁻¹ and 1.51 t⋅ha⁻¹⋅yr⁻¹, respectively. Although direct estimates of gully erosion were not available, the moderate to strong correlations between SY and both LMR (r = 0.47) and GHS (r = 0.57) underscore the importance of gullies and landslides in delivering sediment to catchment outlets. In contrast, RSE shows a weaker relationship with measured SY, suggesting that traditional RUSLE-type models may substantially over- or underestimate total sediment yield if they neglect gully erosion, landslides, and in-channel deposition processes.</div><div>This study contributes novel insights into continental-scale sediment dynamics by explicitly linking observed SY to distinct geomorphic processes. Our findings highlight the need for integrated modeling frameworks that account for rill and sheet erosion, landslides, and gully erosion in order to enhance the accuracy of sediment yield predictions. Such approaches are vital for guiding land management and soil conservation strategies across Africa's diverse biophysical and climatic regions.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105622"},"PeriodicalIF":2.2,"publicationDate":"2025-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143629227","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Facies analysis of Late Pleistocene mixed carbonate-siliciclastic transgressive-regressive sequence along the coast near Mogadishu (Somalia)","authors":"Federico Carbone ,&nbsp;Ruggero Matteucci ,&nbsp;Giovanni Accordi ,&nbsp;Mario Voltaggio","doi":"10.1016/j.jafrearsci.2025.105607","DOIUrl":"10.1016/j.jafrearsci.2025.105607","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The raised sedimentary complex outcropping along the coastal belt just south of the Mogadishu airport is a roughly 10-m-thick carbonate–siliciclastic, coral-bearing depositional sequence. This complex is defined by eight primary depositional facies that form a transgressive–regressive sedimentary cycle, capped by a regressive surface that gently dips seaward.&lt;/div&gt;&lt;div&gt;Facies analysis reveals a transgressive system tract consisting of a stratal set of siliciclastic sand deposited above a wave-ravinement surface, as indicated by an eroded quartz sand substratum. The transgressive succession continues with loose siliciclastic sand that contains a rich mollusk fauna intermixed with coarse skeletal debris of stony corals and both encrusted and articulated coralline algae. The macrofossil assemblage indicates diverse shoreface environments, where water depth, bottom morphology, and distance from the shoreline are critical in characterizing each facies.&lt;/div&gt;&lt;div&gt;Comparisons with the modern biological zonation of the shallow shelf along the southern Somali coast have helped clarify the depositional characteristics of the Pleistocene facies succession. The distribution of fossil coral communities—often with colonies still in growth position—suggests a series of shallow-water facies related to back reef–shore environments that migrated landward over time. In contrast, the highstand system tract differs from the underlying facies by exhibiting a drastic decrease in the siliciclastic granular fraction and corals in growth position, which is offset by an increase in articulated and encrusted coralline algae that comprise most of the sediment source. Locally, skeletal rubble rich in large coralline algal nodules is typical of the regressive phase. The deposition of these facies results in a smoothing of seafloor roughness due to the burial of coral buildups by skeletal sand that shows less facies diversification.&lt;/div&gt;&lt;div&gt;The marine succession—affected in its upper part by the calichification process—culminates in a marine terrace capped by aeolian sands deposited during various depositional–erosional events. Some of these deposits correlate with raised beachrock that outcrops discontinuously just above present sea level and corresponds to a minor Holocene sea level highstand.&lt;/div&gt;&lt;div&gt;To assess the time interval required for the deposition of this transgressive–regressive cycle, which is related to a Late Pleistocene sea level positive peak, sedimentation rates and U–Th dating of two samples of massive &lt;em&gt;Porites lutea&lt;/em&gt; from the transgressive system tract have been considered. The ages of approximately 114 kyr indicate a flooding event on the southern Somali coast during the transition between stages 5e and 5d of the Last Interglacial, while the overall duration of the sedimentary cycle is likely much less than 10 kyr. Furthermore, by matching the investigated cycle with positive peaks on significant global and local sea level curves, addit","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105607"},"PeriodicalIF":2.2,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143619375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrological change from space geodetic data and correlation with climate indices in Sudan","authors":"Walyeldeen Godah ,&nbsp;Samuel Milki Yadeta ,&nbsp;Alexander Braun","doi":"10.1016/j.jafrearsci.2025.105608","DOIUrl":"10.1016/j.jafrearsci.2025.105608","url":null,"abstract":"<div><div>Terrestrial hydrological data in Sudan are heterogeneous with a limited quantity and quality that hinders reliable monitoring of natural or anthropogenic hydrological change. Thus, alternative data sources such as satellite observations are essential for monitoring hydrological change in Sudan. Moreover, like many other regions around the world, hydrological change in Sudan is strongly related to climate change presenting an opportunity to analyse the correlation of these processes. The aim of this research is to investigate the usefulness of space geodetic data to monitor hydrological change in Sudan and its relation with climate indices.</div><div>Temporal variations of equivalent water thickness were determined over the area of Sudan using GLDAS dataset and data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow–On (GRACE–FO) satellite missions. Temporal surface water variations at nine river crossings were obtained from satellite altimetry (Sentinel, Jason-2/3). The correlations between temporal variations of equivalent water thickness and sea surface temperature from both the El Niño–Southern Oscillation and the Indian Ocean Dipole climate indices were investigated. The results indicate good agreement between temporal variations of equivalent water thickness from GRACE/GRACE–FO data and GLDAS dataset. These temporal variations of equivalent water thickness were further correlated with the temporal surface water variations from altimetry data. In addition, there exist clear correlations between hydrology change in Sudan and sea surface temperature from El Niño 1 + 2 and El Niño 3 climate indices. In general, the results revealed the usefulness of space geodetic data for determining hydrological change in Sudan.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105608"},"PeriodicalIF":2.2,"publicationDate":"2025-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143610151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Northwest africa 16273: 4Vesta's mantle sampled during the giant impact","authors":"Ratiba Kared ,&nbsp;Bertrand N. Moine ,&nbsp;Jean-Luc Devidal ,&nbsp;Abdelmadjid Seddiki","doi":"10.1016/j.jafrearsci.2025.105604","DOIUrl":"10.1016/j.jafrearsci.2025.105604","url":null,"abstract":"<div><div>We report here the results of a comprehensive petrological and geochemical study of Northwest Africa (NWA) 16273. NWA 16273 is classified as a mesosiderite-B2/3 and contains a significant amount of metal and silicates phases. It is composed of pyroxene, olivine, plagioclase, iron-metal + sulfide phases, and minor amounts of phosphate, chromite, phosphide, rutile, ilmenite and quartz. Olivines appear as xenocrysts surrounded by reaction rims composed of pyroxene and chromite. Some pyroxenes occur as xenocrysts and as small grains in the matrix. Pyroxene shows significant variation in composition: Low-Ca pyroxene (Fs_18-36 Wo_3-4; n = 22) and pigeonite Fs_22-26 Wo_12-20 (n = 2). The Fe/Mn ratios of all pyroxenes show a large variation and have molar Fe/Mn rations of 27.6 ± 3.1 (n = 24). Whereas, olivines have molar Fe/Mn ratios of 45.5 ± 4.2 (n = 20). These ratios are compatible with 4Vesta compositions. Plagioclase are bytownites and anorthite (An_87-92 Or_0.2-0.6). Additionally, Olivine displays a bimodal distribution with two populations: olivine-Mg-rich (Fo_72-81 Fa_19-28) and olivine less magnesian (Fo_60-67 Fa_33-40). The combination of an harzburgitic composition and a high metal content in the NWA 16273 suggests a complex origin involving several parent bodies, which may have undergone a collision, melting and ejection to form the mesosiderite. Textural, mineral and geochemical characteristics indicate that a metallic impactor melted an eucritic crust of 4Vesta. The eucritic magma and molten metal were injected into the harzburite mantle prior to ejection. Nickel phosphides oxidized on contact with silicate magma to form secondary phosphates. Olivine underwent a more or less intense peritectic reaction to produce secondary orthoproxenes and chromites. The orthopyroxene xenocrysts are zoned and partially chemically re-equilibrated. These features show that a fraction of 4Vesta mantle was sampled during the giant impact.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105604"},"PeriodicalIF":2.2,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Miocene–Quaternary stratigraphy and sedimentation along EL Daba'a Plateau, Northwestern coast of Egypt","authors":"Hesham M. El-Asmar,&nbsp;Mahmoud Sh. Felfla,&nbsp;Zaki A. Abdel-Fattah,&nbsp;Ehab M. Assal","doi":"10.1016/j.jafrearsci.2025.105603","DOIUrl":"10.1016/j.jafrearsci.2025.105603","url":null,"abstract":"<div><div>The current research investigates the stratigraphy, sedimentation, and neotectonics of the Miocene–Quaternary succession along El Daba'a Plateau, northwestern coast of Egypt. In order to unveil the environments of deposition in connection with paleoclimate and sea-level variations, the stratal architecture, including bed geometries, orientation, and field relationships, is highlighted. The field observations of five sections at El Daba'a Plateau reveal two formations: the lower one is the Marmarica Formation of Middle Miocene age, and the upper one is the Alexandria Formation of Quaternary carbonate aeolianites and inter-aeolianite deposits. The Marmarica Limestone Formation is subdivided into two members: the lower is the Oasis Member, and the upper is the Siwa Escarpment Member. A distinct disconformity separates the two formations, with the recognition of twelve lithofacies units (L1–L12) and thirteen microfacies associations (<em>Mf1</em>–<em>Mf13</em>). The Oasis Member belongs to the inner carbonate ramp siliciclastic-carbonate facies association (<em>Mf1</em>–<em>Mf3</em>), while the Siwa Escarpment Member belongs to the mid-ramp carbonate-dominated facies association (<em>Mf4</em>–<em>Mf6</em>). Seven microfacies (<em>Mf7</em>–<em>Mf13</em>) are tied to the Quaternary carbonate aeolianites and inter-aeolianite deposits. Evidence of Late Pleistocene normal faults, trending WNW-ESE, ENE-WSW, and NNW-SSE, has moulded the coastal geomorphology, with a general vertical uplift of up to 15 m. Results of the current work contribute to understanding the geology of the Mediterranean margin at the NW part of Egypt, which needs further studies.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105603"},"PeriodicalIF":2.2,"publicationDate":"2025-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143601586","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}