Pub Date : 2024-10-15DOI: 10.1016/j.jafrearsci.2024.105451
On September 8, 2023, an Mw 6.8 earthquake struck Haouz province (Morocco), in the central Atlas Mountains, causing many casualties. In this study, we obtain the co-seismic deformation field with the D-InSAR and the Pixel Offset Tracking (POT), and three-dimensional displacement with the strain model-variance component estimation method (SM-VCE). The results indicate that this earthquake belongs to a typical thrust earthquake, and the displacement components in the west-east (W-E) and vertical are quite obvious. Besides, the rupture length from the POT method is about 40 km, and the strike is west-north-west (WNW), consistent with that of the Atlas Mountains. According to the slip inversion, the rupture depth of the fault is about 30 km, and the peak slip is approximately 1.6 m at depths of about 22.75 km. Similarly, the strike is 260°, the dip angle is 70° and the rake angle is 75°, respectively. Moreover, the released energy from this earthquake is approximately a Mw 6.8 earthquake. In addition to the earthquake destruction, the local economic foundation and building structure are crucial reasons for the serious casualties. Therefore, the method in this study could provide references for seismic research and the results could help explore the focal mechanism along the High Atlas in Morocco.
{"title":"The source kinematics and slip distribution of the 2023 Mw 6.8 Morocco earthquake","authors":"","doi":"10.1016/j.jafrearsci.2024.105451","DOIUrl":"10.1016/j.jafrearsci.2024.105451","url":null,"abstract":"<div><div>On September 8, 2023, an Mw 6.8 earthquake struck Haouz province (Morocco), in the central Atlas Mountains, causing many casualties. In this study, we obtain the co-seismic deformation field with the D-InSAR and the Pixel Offset Tracking (POT), and three-dimensional displacement with the strain model-variance component estimation method (SM-VCE). The results indicate that this earthquake belongs to a typical thrust earthquake, and the displacement components in the west-east (W-E) and vertical are quite obvious. Besides, the rupture length from the POT method is about 40 km, and the strike is west-north-west (WNW), consistent with that of the Atlas Mountains. According to the slip inversion, the rupture depth of the fault is about 30 km, and the peak slip is approximately 1.6 m at depths of about 22.75 km. Similarly, the strike is 260°, the dip angle is 70° and the rake angle is 75°, respectively. Moreover, the released energy from this earthquake is approximately a Mw 6.8 earthquake. In addition to the earthquake destruction, the local economic foundation and building structure are crucial reasons for the serious casualties. Therefore, the method in this study could provide references for seismic research and the results could help explore the focal mechanism along the High Atlas in Morocco.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-10DOI: 10.1016/j.jafrearsci.2024.105445
We examined the structural evolution of the poorly understood Sunub Structure, which is associated with the northern margin of the Saih Hatat Dome and the extensional Frontal Range Fault (northeastern Oman). The Sunub Structure is located at a dextral transtensional segment and on the hanging wall of the NNE-striking Frontal Range Fault. The fault was active during the Campanian(?)/Maastrichtian to early Eocene (Interval I) and mid-/late Eocene to early Miocene (Interval II). Gravitational inversion using 175 stations and mapping shows: (1) The Sunub Structure is possibly >1200–1350 m deep and filled mostly with the >900-m-thick Campanian(?)/Maastrichtian siliciclastic Al-Khod Formation, including shale, and some overlying Paleogene limestones. (2) The bottom of the basin cannot be depicted. (3) The lower part of the structure is a basin (Sunub Sedimentary Basin), bounded by sub-vertical to steep contacts. (4) The upper part of the Sunub Structure is a basin fold displaying a bowl-shape down to ∼300 m below the surface, referred to as the Sunub Bowl. (5) The bowl is cut by radial faults and five ∼E/W-striking transverse faults. The Sunub Structure formed during Interval I as a deep transtensional, syn-depositional basin. Gentle post-depositional tectonics during Interval II and visco-plastic shale movements produced the present-day bowl-shape that is visible at the surface. Gravitational inversion depict possible evidence for shale migration within the Al-Khod Formation. Although no hydrocarbons are present, the Sunub Structure can serve as an analogue for hydrocarbon migration and storage in similar structures.
{"title":"Architecture of the post-obductional Sunub Structure, northeastern Sultanate of Oman: Based on mapping, 3D gravity inversion and shale migration","authors":"","doi":"10.1016/j.jafrearsci.2024.105445","DOIUrl":"10.1016/j.jafrearsci.2024.105445","url":null,"abstract":"<div><div>We examined the structural evolution of the poorly understood Sunub Structure, which is associated with the northern margin of the Saih Hatat Dome and the extensional Frontal Range Fault (northeastern Oman). The Sunub Structure is located at a dextral transtensional segment and on the hanging wall of the NNE-striking Frontal Range Fault. The fault was active during the Campanian(?)/Maastrichtian to early Eocene (Interval I) and mid-/late Eocene to early Miocene (Interval II). Gravitational inversion using 175 stations and mapping shows: (1) The Sunub Structure is possibly >1200–1350 m deep and filled mostly with the >900-m-thick Campanian(?)/Maastrichtian siliciclastic Al-Khod Formation, including shale, and some overlying Paleogene limestones. (2) The bottom of the basin cannot be depicted. (3) The lower part of the structure is a basin (Sunub Sedimentary Basin), bounded by sub-vertical to steep contacts. (4) The upper part of the Sunub Structure is a basin fold displaying a bowl-shape down to ∼300 m below the surface, referred to as the Sunub Bowl. (5) The bowl is cut by radial faults and five ∼E/W-striking transverse faults. The Sunub Structure formed during Interval I as a deep transtensional, syn-depositional basin. Gentle post-depositional tectonics during Interval II and visco-plastic shale movements produced the present-day bowl-shape that is visible at the surface. Gravitational inversion depict possible evidence for shale migration within the Al-Khod Formation. Although no hydrocarbons are present, the Sunub Structure can serve as an analogue for hydrocarbon migration and storage in similar structures.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142532552","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}
Pub Date : 2024-10-10DOI: 10.1016/j.jafrearsci.2024.105447
Deposition of Neoarchaean carbonate platform sediments of the Campbellrand Subgroup (Transvaal Supergroup) are cyclic and exhibits a full range of facies, which extend from subtidal to supratidal deposition. The strata are host to Mississippi Valley-type lead-zinc deposits including the Pering mine and Bushy Park prospect, the latter of which is the focus of this study. Core spanning the top of the Klipfontein Heuwel Formation to the top of the Kogelbeen Formation where described in terms of the sedimentary environments that likely prevailed at the time. Key facies were identified that were used to identify parasequences and depositional sequences, which were based on stacking patterns of shoaling upward sequences and flooding surfaces. Progradational facies indicate sea level rise and retrogradational facies mark sea level fall of different magnitudes. Multiple breccia types were observed including early diagenetic, karst related breccias, slump breccias, as well as structurally controlled collapse breccias. Although an autocyclic origin for the 4th and 5th order parasequences cannot be ruled out, sedimentary parasequences in the Neoarchaean strata at Bushy Park are very similar to those recognised in Phanerozoic carbonate sections where deposition and accommodation space is believed to be controlled by orbitally forced eustatic sea level rise and fall (Milankovitch cycles). This work identifies a need to test the possible effects of Milankovitch cycles not only on other tectonic basins of similar Archean age but also other rocks through time to account for the possibility that Archean cycles are longer in duration than those of the Phanerozoic Eon.
{"title":"Sequence stratigraphy and metre-scale cyclicity of Neoarchean dolomite strata at Bushy Park, Griqualand West Basin, Transvaal, South Africa","authors":"","doi":"10.1016/j.jafrearsci.2024.105447","DOIUrl":"10.1016/j.jafrearsci.2024.105447","url":null,"abstract":"<div><div>Deposition of Neoarchaean carbonate platform sediments of the Campbellrand Subgroup (Transvaal Supergroup) are cyclic and exhibits a full range of facies, which extend from subtidal to supratidal deposition. The strata are host to Mississippi Valley-type lead-zinc deposits including the Pering mine and Bushy Park prospect, the latter of which is the focus of this study. Core spanning the top of the Klipfontein Heuwel Formation to the top of the Kogelbeen Formation where described in terms of the sedimentary environments that likely prevailed at the time. Key facies were identified that were used to identify parasequences and depositional sequences, which were based on stacking patterns of shoaling upward sequences and flooding surfaces. Progradational facies indicate sea level rise and retrogradational facies mark sea level fall of different magnitudes. Multiple breccia types were observed including early diagenetic, karst related breccias, slump breccias, as well as structurally controlled collapse breccias. Although an autocyclic origin for the 4th and 5th order parasequences cannot be ruled out, sedimentary parasequences in the Neoarchaean strata at Bushy Park are very similar to those recognised in Phanerozoic carbonate sections where deposition and accommodation space is believed to be controlled by orbitally forced eustatic sea level rise and fall (Milankovitch cycles). This work identifies a need to test the possible effects of Milankovitch cycles not only on other tectonic basins of similar Archean age but also other rocks through time to account for the possibility that Archean cycles are longer in duration than those of the Phanerozoic Eon.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142445696","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}
Pub Date : 2024-10-09DOI: 10.1016/j.jafrearsci.2024.105442
This article examines hydrothermally altered ophiolitic ultramafic rocks (HAOU), specifically Listvenite, which are thrust over the Meatiq dome in the context of gold mineralization. These rocks represent gneissic complexes located in Egypt's eastern desert. The analyses presented herein are essential for understanding the distribution of sheared serpentinite on and beneath the surface and the underlying domal structure. This study offers critical insights into the distribution of serpentinite at Meatiq. It combines remote sensing, aerial and ground magnetic data with petrological, geochemical, and geological analyses to create precise geological maps of potential subsurface igneous structures commonly linked to gold mineralization. Remote sensing is used to test for rock differentiation; intensive field geological investigations were conducted along several traverses. Petrographic and geochemical analysis of selected samples confirmed Au content in some localities. Additionally, tomographic inversion of the collected magnetic land profiles has unveiled previously unidentified subsurface distributions of magnetic susceptibilities, which are essential for explaining the observed surface magnetic anomalies and for understanding the subsurface arrangement of various rock units. Results show that the HAOU rocks have a lower magnetic susceptibility signature relative to the adjacent serpentinites, the serpentinite from South Meatiq shows relatively high gold content, and the gold content decreases with carbonation and alteration of the serpentinite into talc-carbonate, as detected geochemically. The procedure followed in the present study can be regionally applied to studying HAOU rocks of similar geologic conditions. The novelty of this study, beyond the introduction of a novel workflow, lies in the revelation that the rocks forming the Meatiq dome are in thrust contact with steeply dipping suprastructure units.
{"title":"Remote sensing and magnetic characterization of the Au mineralization and its structural implications: Meatiq dome, Eastern Desert, Egypt","authors":"","doi":"10.1016/j.jafrearsci.2024.105442","DOIUrl":"10.1016/j.jafrearsci.2024.105442","url":null,"abstract":"<div><div>This article examines hydrothermally altered ophiolitic ultramafic rocks (HAOU), specifically Listvenite, which are thrust over the Meatiq dome in the context of gold mineralization. These rocks represent gneissic complexes located in Egypt's eastern desert. The analyses presented herein are essential for understanding the distribution of sheared serpentinite on and beneath the surface and the underlying domal structure. This study offers critical insights into the distribution of serpentinite at Meatiq. It combines remote sensing, aerial and ground magnetic data with petrological, geochemical, and geological analyses to create precise geological maps of potential subsurface igneous structures commonly linked to gold mineralization. Remote sensing is used to test for rock differentiation; intensive field geological investigations were conducted along several traverses. Petrographic and geochemical analysis of selected samples confirmed Au content in some localities. Additionally, tomographic inversion of the collected magnetic land profiles has unveiled previously unidentified subsurface distributions of magnetic susceptibilities, which are essential for explaining the observed surface magnetic anomalies and for understanding the subsurface arrangement of various rock units. Results show that the HAOU rocks have a lower magnetic susceptibility signature relative to the adjacent serpentinites, the serpentinite from South Meatiq shows relatively high gold content, and the gold content decreases with carbonation and alteration of the serpentinite into talc-carbonate, as detected geochemically. The procedure followed in the present study can be regionally applied to studying HAOU rocks of similar geologic conditions. The novelty of this study, beyond the introduction of a novel workflow, lies in the revelation that the rocks forming the Meatiq dome are in thrust contact with steeply dipping suprastructure units.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433490","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}
Pub Date : 2024-10-09DOI: 10.1016/j.jafrearsci.2024.105443
This work concentrates on the recent ostracod community from the bottom sediments of Burullus lagoon (BuL), Egypt. It aims to identify the impacts of the environmental factors such salinity, substrate and pH on the ostracod community. Only four ostracod species are identified, Cyprideis torosa, Leptocythere castanea, Loxoconcha elliptica and Cypridopsis vidua. The results reflect the abundance of a sole tolerant species, C. torosa (79.59–100 %, with an average of 94.18 %), in all sites. Actually, this conclusion reflects the dominance of unfavorable conditions for increasing the biodiversity in the lagoon. Moreover, the associated benthic foraminiferal assemblage suffers from the rarity of species and the abundance of one tolerant species, Ammonia tepida. Therfore, there is an urgent need to understand the environmental conditions in the BuL. The measured low salinities are suitable for the survival of only brackish ostracod species. Moreover, the distribution and structure of the ostracod assemblage are mainly controlled by the type of bottom sediments. Actually, as the content of sand increases, particularly at sites near the connection to the sea, low numbers of individuals are recorded, whereas the number of living species increases in muddy substrate. Furthermore, the sites with sandy substrate display thick-walled carapaces, while the others with muddy substrate possess thin-walled carapaces. Also, the occurrence of Cypridopsis vidua is restricted only to the muddy substrate. In terms of the hydraulic conditions, the highest abundance of living species is recorded in the southern part, where the quiet conditions prevail. The lagoon water is alkaline, so pH has no observed effects on the ostracod community. Accordingly, salinity, sediment types and hydraulic conditions play the major role in controlling the abundabce, diversity and distribution of ostracods in the study area. Geographically, the identified ostracod species are broadly distributed in the brackish lagoons of the Mediterranean region.
{"title":"The community structure of recent ostracods in the Burullus lagoon, Egypt","authors":"","doi":"10.1016/j.jafrearsci.2024.105443","DOIUrl":"10.1016/j.jafrearsci.2024.105443","url":null,"abstract":"<div><div>This work concentrates on the recent ostracod community from the bottom sediments of Burullus lagoon (BuL), Egypt. It aims to identify the impacts of the environmental factors such salinity, substrate and pH on the ostracod community. Only four ostracod species are identified, <em>Cyprideis torosa</em>, <em>Leptocythere castanea</em>, <em>Loxoconcha elliptica</em> and <em>Cypridopsis vidua</em>. The results reflect the abundance of a sole tolerant species, <em>C. torosa</em> (79.59–100 %, with an average of 94.18 %), in all sites. Actually, this conclusion reflects the dominance of unfavorable conditions for increasing the biodiversity in the lagoon. Moreover, the associated benthic foraminiferal assemblage suffers from the rarity of species and the abundance of one tolerant species, <em>Ammonia tepida</em>. Therfore, there is an urgent need to understand the environmental conditions in the BuL. The measured low salinities are suitable for the survival of only brackish ostracod species. Moreover, the distribution and structure of the ostracod assemblage are mainly controlled by the type of bottom sediments. Actually, as the content of sand increases, particularly at sites near the connection to the sea, low numbers of individuals are recorded, whereas the number of living species increases in muddy substrate. Furthermore, the sites with sandy substrate display thick-walled carapaces, while the others with muddy substrate possess thin-walled carapaces. Also, the occurrence of <em>Cypridopsis vidua</em> is restricted only to the muddy substrate. In terms of the hydraulic conditions, the highest abundance of living species is recorded in the southern part, where the quiet conditions prevail. The lagoon water is alkaline, so pH has no observed effects on the ostracod community. Accordingly, salinity, sediment types and hydraulic conditions play the major role in controlling the abundabce, diversity and distribution of ostracods in the study area. Geographically, the identified ostracod species are broadly distributed in the brackish lagoons of the Mediterranean region.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433491","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}
Pub Date : 2024-10-09DOI: 10.1016/j.jafrearsci.2024.105441
The overlap of tectonic and magmatic events in the Bou Azzer-El Graara inlier causes a complexity for understanding the absolute and/or relative chronology between the deformation and the hydrothermal system. In the central northern part of the Bou Azzer-El Graara inlier, syn-orogenic ca. 650 Ma Aït Ahmane and Ousdrat plutons have been deformed under NE-SW shortening and with metamorphic conditions. These plutons are affected by fault systems with four mains directions: N015, N090, N140, and N040. The last two fault systems are the most mineralized and they are weakly constrained in the frame of deformation phases affecting the Bou Azzer inlier, and filling style. In addition, Pan-African, WACadomian or Hercynian origin of NE-SW faults is not yet reached. This contribution aims to clarify these issues based on structural, textural and morphological of these faults and veins. Our analyses highlight that most of these structures were formed through open-space filling and crack-seal-slip mechanisms. N140 contacts faults between serpentinite and quartz diorite experienced multiple reactivations during the WACadomian stages. The oldest activation was in ductile condition and later reactivated in a transpression to transtension regime leading to the development of N040 faults as sinistral antithetic faults due to NNE stress evolution. Field observations suggest that N040 structures affect late Ediacaran Ouarzazate Group, but not the Adoudounian Formation, highlight their WACadomian origine. The N040 structures preserve metric to microscopic cataclastic shear zones. This evolution suggests that the hydrothermal system in the Bou Azzer inlier shifted from ductile-brittle hydrothermal style along the N140 foliated contact to a brittle regime along the N040 sinistral-normal faults. Some intra-vein microtextures suggest that this hydrothermal fluid was emplaced in a predominantly extensional and tectonically active environment, as evidenced by extensional relay, syntaxial and antiaxial textures, and elongated grains. Consequently, a detailed analysis of the morphology, textures, filling types, and fault movements is an essential and important tool for establishing the relative chronology of deformation in front of the N140 and N040 veins.
{"title":"Constraints of the regional deformation on the hydrothermal veins in Ousdrat and Aït Ahmane ore deposits (Bou Azzer-El Graara inlier, central Anti-Atlas, Morocco): Implications for mineral exploration","authors":"","doi":"10.1016/j.jafrearsci.2024.105441","DOIUrl":"10.1016/j.jafrearsci.2024.105441","url":null,"abstract":"<div><div>The overlap of tectonic and magmatic events in the Bou Azzer-El Graara inlier causes a complexity for understanding the absolute and/or relative chronology between the deformation and the hydrothermal system. In the central northern part of the Bou Azzer-El Graara inlier, syn-orogenic ca. 650 Ma Aït Ahmane and Ousdrat plutons have been deformed under NE-SW shortening and with metamorphic conditions. These plutons are affected by fault systems with four mains directions: N015, N090, N140, and N040. The last two fault systems are the most mineralized and they are weakly constrained in the frame of deformation phases affecting the Bou Azzer inlier, and filling style. In addition, Pan-African, WACadomian or Hercynian origin of NE-SW faults is not yet reached. This contribution aims to clarify these issues based on structural, textural and morphological of these faults and veins. Our analyses highlight that most of these structures were formed through open-space filling and crack-seal-slip mechanisms. N140 contacts faults between serpentinite and quartz diorite experienced multiple reactivations during the WACadomian stages. The oldest activation was in ductile condition and later reactivated in a transpression to transtension regime leading to the development of N040 faults as sinistral antithetic faults due to NNE stress evolution. Field observations suggest that N040 structures affect late Ediacaran Ouarzazate Group, but not the Adoudounian Formation, highlight their WACadomian origine. The N040 structures preserve metric to microscopic cataclastic shear zones. This evolution suggests that the hydrothermal system in the Bou Azzer inlier shifted from ductile-brittle hydrothermal style along the N140 foliated contact to a brittle regime along the N040 sinistral-normal faults. Some intra-vein microtextures suggest that this hydrothermal fluid was emplaced in a predominantly extensional and tectonically active environment, as evidenced by extensional relay, syntaxial and antiaxial textures, and elongated grains. Consequently, a detailed analysis of the morphology, textures, filling types, and fault movements is an essential and important tool for establishing the relative chronology of deformation in front of the N140 and N040 veins.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142532553","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}
Pub Date : 2024-10-04DOI: 10.1016/j.jafrearsci.2024.105440
The rare-element pegmatites of Dibilo form intrusions in a tonalitic gneiss of the Paleoproterozoic Téra-Ayorou pluton about 4 km from the contact zone with the Diagorou-Darbani greenstone belt, in the Nigerien Liptako (NE portion of the Man Ridge of the West African Craton). The general objective of the present study is to determine the petrogenetic relationships between the granitoids and the Dibilo pegmatites through a multidisciplinary approach combining petrology, geochemistry, structural geology and metallogeny. Two generations of granitoids have been distinguished at Dibilo. A first generation of metaluminous to weakly peraluminous granitoids (tonalitic gneiss, metadiorite and two-mica granitic gneiss) constitute a calc-alkaline series. Trace element geochemical signatures suggest that these granitoids were emplaced in an island arc and subduction zone context. A second generation of granitoids (leucogranites), encompassing two-mica, muscovite and two-mica-garnet granites, are peraluminous and calc-alkaline. These leucogranites are fertile, i.e., rich in incompatible elements, with Li concentrations attaining 250 ppm in the richest. A model of partial melting shows that they could derive from the partial melting of Li-rich metadiorite, which is itself highly enriched in lithium (150 ppm). One sample of migmatite has Li contents of 300 ppm, which evidences the fertile nature of the tonalitic-dioritic-granitic gneiss complex.
Three types of pegmatite have been identified at Dibilo: sterile pegmatites (type I), peraluminous and poorly evolved; Nb-Ta pegmatites (type II-a) and Nb-Ta, Mo pegmatites (type II-b), moderately evolved, peraluminous, respectively mineralized with columbite-group minerals (type II-a) and columbite-group minerals and Mo-bearing sulfide (type II-b); and highly evolved, peraluminous Li and Nb-Ta pegmatites (type III) mineralized with spodumene and columbite-group minerals. The type I barren pegmatites share similarities with the leucogranites and could also originate from the partial melting of the dioritic gneiss. The highly evolved type II-a, type II-b and type III pegmatites correspond to the residual liquids resulting from the fractional crystallization of leucogranites. Therefore, we propose that the Dibilo rare-element pegmatites derive from both fractional crystallization and partial melting processes within the tonalitic-dioritic-granitic complex.
{"title":"Petrogenetic relationships between Paleoproterozoic granitoids and rare-element pegmatites from Dibilo (Liptako, West Niger, West African Craton)","authors":"","doi":"10.1016/j.jafrearsci.2024.105440","DOIUrl":"10.1016/j.jafrearsci.2024.105440","url":null,"abstract":"<div><div>The rare-element pegmatites of Dibilo form intrusions in a tonalitic gneiss of the Paleoproterozoic Téra-Ayorou pluton about 4 km from the contact zone with the Diagorou-Darbani greenstone belt, in the Nigerien Liptako (NE portion of the Man Ridge of the West African Craton). The general objective of the present study is to determine the petrogenetic relationships between the granitoids and the Dibilo pegmatites through a multidisciplinary approach combining petrology, geochemistry, structural geology and metallogeny. Two generations of granitoids have been distinguished at Dibilo. A first generation of metaluminous to weakly peraluminous granitoids (tonalitic gneiss, metadiorite and two-mica granitic gneiss) constitute a calc-alkaline series. Trace element geochemical signatures suggest that these granitoids were emplaced in an island arc and subduction zone context. A second generation of granitoids (leucogranites), encompassing two-mica, muscovite and two-mica-garnet granites, are peraluminous and calc-alkaline. These leucogranites are fertile, i.e., rich in incompatible elements, with Li concentrations attaining 250 ppm in the richest. A model of partial melting shows that they could derive from the partial melting of Li-rich metadiorite, which is itself highly enriched in lithium (150 ppm). One sample of migmatite has Li contents of 300 ppm, which evidences the fertile nature of the tonalitic-dioritic-granitic gneiss complex.</div><div>Three types of pegmatite have been identified at Dibilo: sterile pegmatites (type I), peraluminous and poorly evolved; Nb-Ta pegmatites (type II-a) and Nb-Ta, Mo pegmatites (type II-b), moderately evolved, peraluminous, respectively mineralized with columbite-group minerals (type II-a) and columbite-group minerals and Mo-bearing sulfide (type II-b); and highly evolved, peraluminous Li and Nb-Ta pegmatites (type III) mineralized with spodumene and columbite-group minerals. The type I barren pegmatites share similarities with the leucogranites and could also originate from the partial melting of the dioritic gneiss. The highly evolved type II-a, type II-b and type III pegmatites correspond to the residual liquids resulting from the fractional crystallization of leucogranites. Therefore, we propose that the Dibilo rare-element pegmatites derive from both fractional crystallization and partial melting processes within the tonalitic-dioritic-granitic complex.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420655","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}
Pub Date : 2024-10-04DOI: 10.1016/j.jafrearsci.2024.105439
Altered and gangue quartz in hydrothermal veins from the Kubi Gold deposit in Dunkwa on Offin in the central region of Ghana are investigated for possible Au-associated indicator minerals and to provide the understanding and increase the knowledge of the mineral hosting and alteration processes in quartz. X-ray diffraction, air annealing furnace, differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy have been applied on different quartz types outcropping from surface and bedrocks at the Kubi Gold Mining to reveal the material properties at different temperatures. From the diffraction results of the fresh and annealed quartz samples, we find that the samples contain indicator and the impurity minerals iron disulfide, biotite, titanium oxide, and magnetite. These minerals, under oxidation process between 574 and 1400 °C temperatures experienced hematite alterations and a transformation from α-quartz to β-quartz and further to cristobalite as observed from the calorimetry scans for hydrothermally exposed materials. The energy dispersive spectroscopy revealed elemental components of Fe, S, Mg, K, Al, Ti, Na, Si, O, and Ca contained in the samples, and these are attributed to the impurity phase minerals observed in the diffraction. The findings also suggest that during the hydrothermal flow regime, impurity minerals and metals can be trapped by voids and faults. Under favorable temperature conditions, the trapped minerals can be altered to change color at different depositional stages by oxidation and reduction processes leading to hematite alteration which is a useful indicator minerals in mineral exploration.
对加纳中部地区奥芬河畔敦夸的库比金矿床热液矿脉中的蚀变石英和矸石石英进行了研究，以寻找可能的金相关指示矿物，并了解和增加有关石英中矿物寄存和蚀变过程的知识。对库比金矿地表和基岩出露的不同类型石英采用了 X 射线衍射、空气退火炉、差示扫描量热仪、能量色散 X 射线光谱仪和透射电子显微镜，以揭示不同温度下的材料特性。从新鲜和退火石英样品的衍射结果来看，我们发现样品中含有指示剂和杂质矿物二硫化铁、生物铁、氧化钛和磁铁矿。这些矿物在 574 至 1400 °C 的氧化过程中发生了赤铁矿化，并从α-石英转变为β-石英，然后进一步转变为霞石。能量色散光谱显示了样品中含有的 Fe、S、Mg、K、Al、Ti、Na、Si、O 和 Ca 等元素成分，这些元素可归因于衍射中观察到的杂相矿物。研究结果还表明，在热液流动过程中，杂质矿物和金属会被空隙和断层困住。在有利的温度条件下，被截留的矿物会在不同的沉积阶段通过氧化和还原过程改变颜色，从而导致赤铁矿蚀变，这是矿产勘探中一种有用的指示矿物。
{"title":"Physico-thermal and geochemical behavior and alteration of the Au indicator gangue hydrothermal quartz at the Kubi Gold ore deposits","authors":"","doi":"10.1016/j.jafrearsci.2024.105439","DOIUrl":"10.1016/j.jafrearsci.2024.105439","url":null,"abstract":"<div><div>Altered and gangue quartz in hydrothermal veins from the Kubi Gold deposit in Dunkwa on Offin in the central region of Ghana are investigated for possible Au-associated indicator minerals and to provide the understanding and increase the knowledge of the mineral hosting and alteration processes in quartz. X-ray diffraction, air annealing furnace, differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy have been applied on different quartz types outcropping from surface and bedrocks at the Kubi Gold Mining to reveal the material properties at different temperatures. From the diffraction results of the fresh and annealed quartz samples, we find that the samples contain indicator and the impurity minerals iron disulfide, biotite, titanium oxide, and magnetite. These minerals, under oxidation process between 574 and 1400 °C temperatures experienced hematite alterations and a transformation from α-quartz to β-quartz and further to cristobalite as observed from the calorimetry scans for hydrothermally exposed materials. The energy dispersive spectroscopy revealed elemental components of Fe, S, Mg, K, Al, Ti, Na, Si, O, and Ca contained in the samples, and these are attributed to the impurity phase minerals observed in the diffraction. The findings also suggest that during the hydrothermal flow regime, impurity minerals and metals can be trapped by voids and faults. Under favorable temperature conditions, the trapped minerals can be altered to change color at different depositional stages by oxidation and reduction processes leading to hematite alteration which is a useful indicator minerals in mineral exploration.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420656","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}
Pub Date : 2024-09-29DOI: 10.1016/j.jafrearsci.2024.105437
The paleoenvironmental conditions during the Coniacian-Santonian interval within the Kometan Formation in northeastern Iraq have been analyzed through the distribution of depth-related planktonic foraminifera in the carbonate rocks (limestone and marly limestone) of the Kometan Formation using standard washing method for soft samples and thin section method for hard samples supported by mineralogical investigations, geochemical analysis and stable isotopic δ13C and δ18O data. The findings indicate that saline marine waters and a hot, dry to semi-arid climate with low to medium oxygen conditions were conducive to deposition, which was characterized by high organic productivity due to marine transgression. The study revealed that the distribution of shallow water forms (SWF) of globular-shaped foraminifera, compared to deep water forms (DWF) of keeled-shaped genera, along with δ13C data from the late Turonian-early Campanian succession, indicated a relatively low sea level throughout the Late Turonian period. The water level began to rise in the early Coniacian, continuing gradually until the late Coniacian, when a noticeable increase in sea level was observed. This elevated sea level persisted through the early and late Santonian periods, before starting to drop. A slight marine transgression was noted at the beginning of the early Campanian period, followed by a significant drop in sea level. During the late Turonian, a subtropical climate prevailed. Temperature increased during the early to middle Coniacian, decreased slightly at the beginning of the late Coniacian, and then rose again at the end of the late Coniacian, indicating a shift from tropical to subtropical climatic conditions. Similar hot climatic conditions persisted in a tropical-subtropical climate during the early to late Santonian and early Campanian, with a relative temperature drop near the end of the early Campanian. No evidence of an oceanic anoxic event (OAE3) was found in the Kometan Formation during the late Coniacian–early Santonian period. The hypothesized event, based on biostratigraphy, facies analysis, stable isotopes, geochemical evidence, and field study, was limited to demonstrating an increase in the ratio of keeled chamber planktonic foraminifera compared to globular chamber ones. This ratio increase of the keeled chamber types is believed to result from a deepening sedimentary environment due to rising sea levels, creating organic matter-rich beds with high productivity and relatively low oxygen conditions during the Coniacian-Santonian boundary.
{"title":"Paleoenvironmental conditions across the Coniacian-Santonian in the Kometan Formation, northeastern Iraq: Insights from planktonic foraminifera distribution, mineralogy and geochemistry","authors":"","doi":"10.1016/j.jafrearsci.2024.105437","DOIUrl":"10.1016/j.jafrearsci.2024.105437","url":null,"abstract":"<div><div>The paleoenvironmental conditions during the Coniacian-Santonian interval within the Kometan Formation in northeastern Iraq have been analyzed through the distribution of depth-related planktonic foraminifera in the carbonate rocks (limestone and marly limestone) of the Kometan Formation using standard washing method for soft samples and thin section method for hard samples supported by mineralogical investigations, geochemical analysis and stable isotopic δ<sup>13</sup>C and δ<sup>18</sup>O data. The findings indicate that saline marine waters and a hot, dry to semi-arid climate with low to medium oxygen conditions were conducive to deposition, which was characterized by high organic productivity due to marine transgression. The study revealed that the distribution of shallow water forms (SWF) of globular-shaped foraminifera, compared to deep water forms (DWF) of keeled-shaped genera, along with δ<sup>13</sup>C data from the late Turonian-early Campanian succession, indicated a relatively low sea level throughout the Late Turonian period. The water level began to rise in the early Coniacian, continuing gradually until the late Coniacian, when a noticeable increase in sea level was observed. This elevated sea level persisted through the early and late Santonian periods, before starting to drop. A slight marine transgression was noted at the beginning of the early Campanian period, followed by a significant drop in sea level. During the late Turonian, a subtropical climate prevailed. Temperature increased during the early to middle Coniacian, decreased slightly at the beginning of the late Coniacian, and then rose again at the end of the late Coniacian, indicating a shift from tropical to subtropical climatic conditions. Similar hot climatic conditions persisted in a tropical-subtropical climate during the early to late Santonian and early Campanian, with a relative temperature drop near the end of the early Campanian. No evidence of an oceanic anoxic event (OAE3) was found in the Kometan Formation during the late Coniacian–early Santonian period. The hypothesized event, based on biostratigraphy, facies analysis, stable isotopes, geochemical evidence, and field study, was limited to demonstrating an increase in the ratio of keeled chamber planktonic foraminifera compared to globular chamber ones. This ratio increase of the keeled chamber types is believed to result from a deepening sedimentary environment due to rising sea levels, creating organic matter-rich beds with high productivity and relatively low oxygen conditions during the Coniacian-Santonian boundary.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420461","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}
Pub Date : 2024-09-26DOI: 10.1016/j.jafrearsci.2024.105438
The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.
该研究评估了构造和侵蚀作用对早始新世-中新世早期 Al Jabal Al Akhdar 碳酸盐沉积层序结构演变的影响。通过对位于利比亚东北部 Al Jabal Al Akhdar 隆起带的五个测量断面的微地貌、沉积解释和层序地层框架进行详细分析，完成了这项评估工作。根据岩性变化、颗粒大小和成分、沉积质地和结构、化石含量、颜色和垂直堆积模式，研究区间被细分为不同的微地层。划分了六种主要沉积环境：限制性泻湖、开放性海洋泻湖、平台边缘和浅滩、平台边缘礁石、前坡和中下部斜坡。根据垂直和横向面层分布、化石含量的变化以及成岩特征，确定了四个三阶无断裂沉积序列。除较年轻的序列只包含一个迭压单元外，每个序列都由一个迭压-迭压区间组成。四个演化阶段分别为：起始阶段、生长阶段、高隆起平台阶段和次隆起阶段。构造运动和沉积物负载造成的沉降，加上海平面上升，为所研究的碳酸盐岩的沉积创造了容纳空间。反复的震旦纪海平面波动控制着内部地层的异质性和层序的发展。构造隆升导致海平面大幅后退，从而形成了碳酸盐岩序列。在晚白垩世-早始新世期间经历大隆起的中生代和古新世序列形成了碳酸盐沉积物形成的浅水正前缘地形。这项研究建立了不同循环沉积次序的碳酸盐序列地层层次，增进了我们对倒置盆地环境中碳酸盐平台的沉积和地层结构演化及沉积机制的了解。这些知识有助于预测具有重要经济意义的岩相和沉积系统的分布。
{"title":"Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy","authors":"","doi":"10.1016/j.jafrearsci.2024.105438","DOIUrl":"10.1016/j.jafrearsci.2024.105438","url":null,"abstract":"<div><div>The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357128","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}
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