African Orogeny Research Articles

Geochronological assessment of the Arabian-Nubian Shield plutonic intrusions in the arc assemblages along the Qift-Quseir transect, Central Eastern Desert of Egypt

The ophiolitic mélange and granitic intrusions along the Qift‒Quseir transect in the Central Eastern Desert (CED) of Egypt are parts of the Egyptian Nubian Shield (ENS), which is the northern segment of the East African Orogeny (EAO). The Arabian-Nubian Shield (ANS) is the longest Neoproterozoic belt on Earth, and it was formed during the East and West Gondwanaland collisions within the framework of the EAO. The ANS basement rocks were developed during three distinct phases of magmatic activity: the island arc and syn-collisional phases, identifying a compressional tectonic regime, and a post-collisional phase that identifies changing the tectonic regime into an extensional type. The geochronological assessment of these magmatic activities is essential for understanding the regional geology and tectonic development of the ANS. In our study, we dated different rock units along the Qift‒Quseir transect and revealed ages ranging from the Late Tonian (820 ± 8 Ma) to the Late Ediacaran (563 ± 4 Ma). These ages were associated with three different magmatic pulses: (1) a seafloor spreading and island arc phase (ophiolite and related rocks), represented by sample QQ05, which was dated from 820 ± 8 Ma; (2) a syn-collisional phase, represented by samples QQ08 and QQ10, dated from 733 ± 10 Ma and 729 ± 10 Ma, respectively; and (3) a post-collisional phase, represented by all the other samples, dated from the Ediacaran at 603 ± 9 Ma to 563 ± 5 Ma. These results showed that the post-collisional phase was dominant, especially in terms of the alkali-feldspar granites, relative to ophiolitic rocks, and the syn-collisional granites in the CED. Initiation of the Dokhan Volcanic eruptions at 639 ± 2 Ma gave us the date of the compressional-to-extensional tectonic transition setting, and the post-collisional tensional regime was activated at 603 ± 9 Ma. Additionally, we identified evidence of local magmatic sources by dating 11 grains of Paleo-to Meso-Proterozoic xenocrysts with ages ranging from 1876 ± 18 to 1070 ± 13 Ma (i.e., components of the pre-Arabian-Nubian Shield).

New geological insights on the Palaeoproterozoic Sembé-Ouesso Basin in northern Congo-Brazzaville – Implications for the Kibaran orogeny, Neoproterozoic rifting and Pan-African overprint

The Palaeoproterozoic Sembé-Ouesso Basin (SOB) is the northeasternmost of six foreland subbasins of the Eburnean orogen; it covers an area of about 64,000 km2 in the northern Republic of Congo, southeast Cameroun and the Central African Republic. The structural architecture and tectono-metamorphic history of the SOB have been studied in the Republic of Congo by airborne geophysical interpretation, geological mapping, and petrography, analysis of illite crystallinity and K-Ar geochronology.The oldest tectono-metamorphic event (D1/M1), which caused the main structuring of the SOB, coincides in age with the last (1.0–1.07 Ga) stage of Kibaran orogeny. Metamorphic conditions decrease from greenschist facies in the east to upper diagenesis in the west. D1 deformation started with west-vergent folding followed by N-S sinistral transpression in discrete shear zones. The tectonic style characterises the SOB as foreland in the external zone of an eastern concealed orogen that either represents the continuation of the Kibaran Belt or forms a separate, as yet unidentified unit.Subsequent Neoproterozoic extension is marked by two conjugate N-S/NNE-SSW and E-W/NW-SE fault systems and a local pull-apart structure (D2). Coeval mafic magmas were emplaced in the faults of both systems. At regional scale, the extension can be linked to Tonian rifting in the central part of the Congo Basin and within the West Congo Belt.The influence of the Neoproterozoic (600 Ma) Central African orogeny is mainly restricted to the north-western part of the SOB where the Dja nappe was thrust from the north over the Palaeoproterozoic rocks (D3/M2). Elsewhere, the Pan-African event had no thermal and only minor structural effects on the SOB.

Geology and Geochemistry of Aberma and Its Environ Sheet 54se Gusau, Zamfara State, Nigeria

The study area falls within the northwestern part of Nigeria and is underlain by crystalline rocks of the Basement Complex. Field mapping in Aberma and its environs were carried out using topographical map sheet of 54 SE Gusau on a scale 1: 25,000 with an area extends of about 30.8052km2. This field work was carried out using traverse method in conjunction with field equipment such as compass/clinometers, geologic hammer, sample bag and global positioning system. This study however, aims at producing a detail geological map, including the various rock geochemistry and petrography of the study area. The area is underlain by two major lithological rock type which is mica schist and granite gneiss. The granite gneiss is strongly foliated, caused by high temperature and pressure and the minerals observed in plane polarized light include quartz, orthoclase, plagioclase, muscovite, opaque mineral and biotite. The mica schists in the study area are mostly weathered in ditches below the ground surface, the rock is moderately weathered and show schistocyte. The minerals observed in plane polarized light include quartz and muscovite. The dominant structures observed include; joints, Quartz veins, foliation and pegmatite dyke. Structural analysis shows that the rocks have been affected by the Pan African orogeny with the joint’s orientation trending dominantly NNE-SSW and Quartz vein trending in somewhat E-W direction. The microscopic studies revealed that the mineralogical composition of the rocks types of the study area contain varying percentages of quartz, muscovite, plagioclase, orthoclase, opaque mineral and biotite as the major minerals. The geochemical analysis revealed the major and minor elemental distribution of the rock types of the study area. The chemical assay revealed that the granite gneiss and mica schist rock type of the study area are super-saturated with respect to silica, silica (SiO<sub>2</sub>) is the most abundant oxide with an average value of 78.12% in the rock sample. This implies that the rock analyzed is acidic in nature and must have formed from crystallization of an acidic magma because the silica content being greater than 65%.

Deformational History Reconstruction of Basement Complex Rocks in Okomita, Ojirami and Environs, South Western Nigeria

Deformation histories aid in remodeling the forces related to rock formation. Hence, the objectiveof this paper as to examine the deformational history of the Basement Complex rocks in Okomita, Ojirami and Environs, South Western Nigeria using appropriate standard methods. Results of the field work embarked upon revealed that the major rocks encountered include older granite and metasediments like mica schist, quartzite and gneiss. The analysis of the structures contained in the rocks was achieved by plotting the orientation of the structures on rose diagrams and stereonet. The results show that the rocks were subjected to polyphase deformation, comprising of pre-Pan African and the Pan-African orogeny. While the Pan African orogeny left imprint of NE-SW trend as observed in all the rocks, the pre-Pan African orogeny generally has a NW-SE trend which was observed to be associated more commonly with only the metasediments.

Crustal evolution of the northern Nyika Subdomain of the Palaeoproterozoic Ubendian belt in Malawi

The Ubendian belt extends from eastern Congo through SW Tanzania and NW Zambia across northern Malawi and into Mozambique. It results from the Palaeoproterozoic accretion of a number of crustal blocks followed by the collision of the Tanzanian and Congo cratons. The Ubendian belt has been classically divided into eight “terranes”, (termed “subdomains” in this work), based on rock assemblage, magmatic and metamorphic history. This paper is concerned with the geological evolution of the southernmost of these, the Nyika Subdomain.We present an extensive dataset to decipher the geological history of the northern part of the Nyika Subdomain, including field observation, LA-ICP-MS U/Pb geochronology on zircon and monazite and a metamorphic petrological study of the extensive characteristic migmatitic cordierite-bearing gneisses. The U/Pb zircon data records four magmatic pulses. The first is represented by xenocrysts dated between 2200 and 2150 Ma. The second, major pulse is dated at ca. 2030 Ma, followed by minor magmatic activity at ca. 1980 Ma. This event is coeval with regional granulite facies metamorphism (ca. 780 °C and 0.6 Gpa), constrained in age U/Pb monazite and xenotime dated at 1977 ± 14 Ma and 1984 ± 13 Ma, respectively and also probably dates the collision between the Congo and Tanzania cratons. A fourth event represented by the intrusion of the Nyika Suite granites at 1944 ± 7 Ma terminates the Palaeoproterozoic history. There follows a long time interval with no recorded orogenic history before the tectonic activity during the Neoproterozoic Pan African orogeny. The regional significance of the evolution of the Nyika Subdomain with respect to the adjacent Ufipa Subdomain and the “Bangweulu Block” to the west are discussed within the framework of the Ubendian orogeny and the wider Palaeoproterozoic history of the region.

The layered gabbroic intrusion in the Southern Eastern Desert of Egypt: Implications for Fe-Ti-rich magmatism at the end of the East African Orogeny

The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxene hornblende-, and hornblende gabbros. It hosts thick FeTi oxide ore layers that are composed of titanomagnetite with subordinate ilmenite and magnetite. To understand the petrogenesis of the FeTi rich gabbroic rocks, the nature of their parent high-Fe primitive mantle melts and condition of FeTi oxide layer formation, we obtained new mineral chemistry and whole-rock major and trace element compositions. The geochemical characteristics of the gabbroic rocks resemble those of picro-basalts, suggesting generation from picritic basaltic-like melts of tholeiitic affinity. Their high-Fe-Ti-Mg nature (TiO2, ∼1.91 wt%; MgO, ∼11.0 wt%; Fe2O3, ∼14 wt%) probably indicates elevated mantle potential temperatures due to upwelling of hot asthenospheric mantle. Rare earth elements (REEs) of clinopyroxene show flat patterns with depletion in LREEs, similar to those of the host gabbros and picritic basaltic lava, suggesting a mantle origin for their parental melts. Moreover, clinopyroxene compositions show differentiation trends similar to low-pressure igneous intrusions, and reveal a rift-related origin. Chemistry of plagioclase (An45–62), clinopyroxene (Wo38.4–45.3, En39.9–43, Fs14–19.3; Mg#: 0.71–0.92) and olivine (Fo56–80) shows wide compositional ranges due to variable degrees of crystal fractionation. The calculated equilibrium temperature for the Rahaba Fe-Ti-rich gabbros is mainly 820–1000 °C, at pressure below 5 kbar, reflecting depth of rock solidification of <15 Km. These rocks show both subduction-like and rift-related geochemical signatures comparable to other post-collisional layered intrusions in the Arabian-Nubian Shield. The low average Ce/Pb (8.3) and high Ba/Nb (391) ratios together with the enriched large-ion lithophile elements (Cs, Ba, K and Sr) and depleted high-field strength elements (Th, Nb, Ta and Zr) reflect the contribution from a preceding subduction event. The lineament map, structural lineament and lineament density map reveal main WNW-ESE and NW-SE structural trends of the Najd System in the Rahaba area. The Rahaba FeTi rich gabbroic intrusion was likely formed by initial impact of a mantle plume head with Fe-rich streaks at the base of metasomatized lithospheric mantle during an extensional phase associated with activity of the Najd-related strike-slip faults, at the end of the East African Orogeny. The resultant mantle-derived melt compositions and Najd-related structures possibly controlled the distribution of FeTi ore deposits during this Orogeny. The Rahaba gabbroic intrusion was emplaced during post-collisional extension after slab break-off and lithospheric delamination following collision of accreted island-arcs with the Saharan Metacraton.

Metamorphic evolution of granulites from Grovnes Peninsula of Larsemann Hills, East Antarctica: Constraints from phase equilibrium modelling and geochronology

Petrology, geothermobarometry, and phase equilibrium modelling of garnetiferous felsic gneiss from Grovnes peninsula in the Larsemann Hills of Prydz Bay, East Antarctica provide pristine evidence for the preservation of high-grade metamorphic imprint in the area. The metamorphic evolution of the sample is demonstrated by the development of the assemblage Grt+Bt+Melt+Pl+Sill+Kfs+Qtz+Ilm at peak metamorphic conditions of ∼790 °C and ∼7.5 kbar, which subsequently underwent retrogression and cooling to lower P-T conditions along a clockwise path. Texturally constrained chemical dating of monazites constrain the timing of peak metamorphism and garnet formation at ∼575 Ma, whereas the apatite U–Pb ages constrain cooling ages at ∼518 Ma. The clockwise P˗T˗t trajectory of the studied samples, together with the Ediacaran-Cambrian metamorphic/cooling ages demonstrate the long-lived nature of metamorphism in Prydz Bay, which is ascribed to collisional tectonism prevalent during the final stages of the assembly of East Gondwana supercontinent. Similar results from adjacent continental fragments including Sri Lanka, Eastern Ghats Belt, Madagascar, and South India suggest their coeval metamorphic evolution during the East African orogeny.

Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al-Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.

Fluid inclusions, H-O-S-Pb isotopes, and Rb-Sr geochronology of the Augaro gold deposit, West Eritrea, NE Africa: Implications for ore genesis

Northeast Africa is an emerging world-class gold province due to the numerous lode gold deposits with Au resources of over 43 Moz discovered in the Nubian Shield. The Augaro gold deposit, located in the Adobha-Augaro Cu-Au belt of west Eritrea, is composed of several auriferous quartz veins. The orientations of the auriferous quartz veins in this deposit are strictly controlled by NE-trending shear zones and nearly E-trending fractures. The most common metallic mineral is pyrite, and gold has been identified as native gold, electrum, and calaverite. Fluid inclusion study, H-O-S-Pb isotope analysis, and Rb-Sr dating were carried out in the Augaro gold deposit. A petrographic investigation revealed that fluid inclusions of type W (Liquid-rich aqueous), type C (CO2-rich), and type S (halite-bearing) are prevalent in auriferous quartz veins. The H2O, NaCl, and CO2 are the main components of the metallogenic fluids, which are medium-low temperatures (150–360 °C) and medium to low salinities (<34 wt% NaCl eqv.). The physicochemical features of fluid inclusions indicate that magmatic fluids experienced phase separation earlier in their evolution and mixed with meteoric water subsequently. Rb-Sr dating of fluid inclusions in auriferous quartz suggests that the Augaro gold deposit formed during the post-orogenic stage (543 ± 14 Ma) of East African orogeny in the Late Neoproterozoic, which is a new metallogenic epoch for the lode gold deposits in Nubian Shield. Geological and Geochemical features refer to the Augaro gold deposit being an intrusion-related gold deposit (IRGD).

Qualitative interpretation of high resolution aeromagnetic data of abeokuta metropolis for geological characterisation

Qualitative interpretation of aeromagnetic maps involves the visual inspection and pattern analyses of produced maps to identify potential geological structures in the magnetic field by processing the dataset to characterize the Earth's magnetic variations and map subsurface geological structure which is important to tackle the challenges of resource management, environmental assessment and infrastructure design in the study area. This technique has been employed to a part of Abeokuta metropolis of Ogun state, Southwestern Nigeria, using high resolution aeromagnetic dataset acquired from the Nigerian Geological Survey Agency (NGSA). Pre-processing analyses such as data transformation, map re-projection and power spectrum plot were performed on the dataset to minimize noises and remove unwanted variations. The application of Reduction to Magnetic Equator (RTE) filter was to remove asymmetries in the data and position the peaks of magnetic anomalies over their sources while the Gaussian (low pass) filter was aimed at improving the signal-to-noise ratio. Low magnetic zones indicated by blue colours from the total magnetic fields possibly reveal the sedimentary intrusions into the area, intermediate magnetic regions having green, yellow and red colourations suggest transition zones and the Northeastern portion of the maps indicated with pink colours correlate to the core basement regions. Derivative filters are applied as enhancement techniques to accentuate the inferred linear subsurface structures interpreted as cracks, fractures, lineaments, etc. These structures are predicted mineral entrapments or fault lines whose NE-SW orientation conforms to the Pan African Orogeny and they can aid environmental assessments generally.

Proterozoic fold and thrust belt imaged on reflection seismic in Arabian plate basement

Major structures are imaged on 2D reflection seismic data within the Precambrian basement of the western Rub’ Al-Khali of Saudi Arabia for the first time. In this area the base-Cambrian Angudan Unconformity that defines top basement is at a depth of 1–2 km with a gentle easterly dip. Large antiformal structures are clear on 2D reflection seismic within the basement. The antiforms are separated by zones that are interpreted as low-angle faults. No basal detachment is seen and the faults pass below the base of reflection seismic at a depth of approximately 12 km. Individual folds have dimensions in the order of 20 km wavelength and 2 km amplitude and occur between 3 and 10 km depth. The structural style is interpreted as compressional by comparison with thrust systems and accretionary prisms elsewhere. Regional studies indicate that basement is comprised of a series of north-south trending oceanic Proterozoic terranes that were brought together in the Ediacaran East African Orogeny. Based on current regional tectonic maps the newly-imaged fold belt is on the east margin of the Khida-Abas terrane. Depth conversion shows the thrusts dip at approximately 10° north in the line of section. A novel combination of cross-section to structural trend obliquity estimates combined with matched filtering of potential field data indicate the fold and thrust belt trends 015°-195° with ESE vergence. This compressional belt may be some internal structure of the Khida-Abas terrane, or may be a non-outcropping accretionary prism on the margin of that terrane, or may even represent a set of amalgamated microterranes that do not outcrop along trend. Either way, these observations represent a major, previously undescribed element of this sector of the East African Orogen.

Multiple timings of garnet-forming high-grade metamorphism in the Neoproterozoic continental collision zone revealed by petrochronology in the Sør Rondane Mountains, East Antarctica

The Sør Rondane Mountains (SRM), East Antarctica is located in a key area of Gondwana formation where the East African-Antarctic Orogen and the Kuunga Orogen cross. Timing of peak metamorphism has been considered at ca. 650–600 Ma in the SRM, on which previous tectonic models were built. In this study, timing of garnet-forming metamorphisms is determined using in situ U-Pb dating of zircon and petrochronological approach utilizing distribution coefficient of rare earth elements (DREE) between zircon and garnet and REE patterns of zircon. As a result, we obtained several different periods of garnet-forming metamorphism at ≥600 Ma and ≤580 Ma both from the NE- and SW-terranes. This is the first report of multiple timings of garnet formation detected within single samples from the SRM. The latest garnet formation in each sample is probably caused by regional metamorphism, because the garnets accompany pressure shadows and are wrapped by the penetrative foliation defined mainly by the arrangement of biotite. Therefore, multiple timings of garnet formation during a single metamorphism or polymetamorphism are both likely. In the former case, the SRM may be affected by a single long-lived regional metamorphism. This implies that the regional metamorphism belongs only to the East African-Antarctic Orogeny or that the East African Orogeny continuously transformed into the Kuunga Orogeny in the deep crust. In the latter case, the former regional metamorphism corresponds to the East African(-Antarctic) Orogeny, whereas the latest metamorphism may correspond to the final stage of East African-Antarctic Orogeny or the Kuunga Orogeny. Any temperature drops during these two garnet-forming timings support the polymetamorphism, which needs to be cleared in the future works.

Geochemistry and Petrogenesis of the Ediacaran Post-Collisional Granitoid Rocks in the Midyan Terrain, Northern Arabian Shield, Saudi Arabia

Midyan granites are located in the northern Arabian shield, northwest Saudi Arabia, in the Midyan terrain. They represent the most northerly segment of the Arabian–Nubian shield, which comprises the northern part of the East African orogeny. Consequently, understanding the origin of post-collisional and anorogenic magmatism in the Midyan terrain has significant geodynamic implications. Midyan granites are mainly composed of alkali feldspar granite, syenogranite, and rarely of granodiorite and diorite. Most of the studied granites are alkali-calcic, calc-alkaline, and metaluminous to peraluminous magma types. They are characterized by enrichment with light rare earth elements (LREEs), large-ion lithophile elements (especially Rb and Th), and some high-field strength elements (HFSE, e.g., Nb, Ta, Zr, and U), and the slight depletion of heavy rare earth elements (HREEs). Therefore, the Midyan granites and Hael granites studied in this paper represent good sources of geothermal heat, uranium–thorium, and REE mineralization. The studied granites have moderately strong negative Eu anomalies and a distribution pattern that is very consistent with that of the upper crust, indicating the presence of plagioclase or potassium feldspar cumulates. They have a Th/Ta ratio similar to that of the source of the crust, which may be derived from the upper crust following the collision between East and West Gondwana in the final stage of the Arabian Shield evolution. The data presented in this study are therefore consistent with the post-collisional intraplate magmatism that occurred at the beginning of the transition from convergent to extensional tectonics. The studied granites are derived from melt generated at a crystallization temperature of around 750°C at a pressure of around 0.2–0.5 GPa, emplaced at relatively shallow to moderate depths of between 20 and 30 km.

Neoproterozoic Mafic Magmatism in Nagercoil Block, Southern India and Its Implications on the Gondwana Collisional Orogeny

The Nagercoil block situated at the southernmost tip of India occupies a key position in the East Gondwana collisional tectonic models. The Nagercoil block is dominated by Orosirian I-type charnockite massifs that host numerous gabbroic emplacements. Our present understanding about the crustal architecture of the Nagercoil block is derived mostly from these charnockites, while detailed studies on gabbros are lacking. We present new petrology, geochemistry, and zircon U-Pb/Hf isotopic data of gabbros from the Nagercoil block to understand their petrogenesis and tectonic significance. The results reveal that these are formed by the partial melting of a subduction-modified lithospheric mantle source in a continental arc setting. Zircon U-Pb geochronology results reveal that the gabbros were emplaced between 561 and 531 Ma. Hafnium isotopic studies on zircons argue for a mid-Mesoproterozoic melting source with near-juvenile magmatic signatures. The Hf-TDM ages together with the available data from the terrane point to the involvement of the adjacent Achankovil unit as a possible melting source contributor. The genetic link between the Achankovil unit and Sri Lanka together with the remarkable similarity in ages and isotopic characteristics of mafic rocks from both these terranes point to their coeval formation during the East African Orogeny associated with the final stages of the Gondwana supercontinent assembly.

Relics of ophiolite-bearing accretionary wedges in NE Brazil and NW Africa: Connecting threads of western Gondwana´s ocean during Neoproterozoic times

Neoproterozoic breakup of Rodinia resulted in the formation of several oceanic realms between dispersing cratons, which were later consumed during the assembly of Gondwana. In its western portion, the interior orogenic belts of Gondwana formed during the Brasiliano-Pan African Orogeny in the late Neoproterozoic-early Cambrian. Available geophysical, structural and petrological data suggest that the complex network of shear zones that once connected the Borborema province (NE Brazil), Tuareg shield (Hoggar) and Central African domain (NW Africa) likely represent ancient sutures that mark collisional episodes between Archean-Paleoproterozoic paleocontinents such as Amazonian-West African and São Francisco-Congo. Mafic, ultramafic and sedimentary sequences associated with this set of structures respresent dismembered ophiolite slices interpreted as oceanic remnants (sensu lato) that were emplaced during the late stages of the Gondwana assembly. For instance, the composite Transbrasiliano-Khandi-In-Tedeini-Silet shear system crosscuts rock assemblages preserving a complex history of oceanic-crust-transition development (Novo Oriente complex) in association with primitive to evolved magmatic arcs and UHP rocks both in the Borborema province and NW Africa. In the central Borborema province, preserved ophiolitic slices are strongly overprinted by ductile and brittle deformation events, but partially preserved MORB-like amphibolites are akin to subduction-related-types that crystallized in early- and late Neoproterozoic times docked via terrane accretion and dispersed by strike-slip shear zones. In the southern Borborema province, an example of a Neoproterozoic ophiolitic assemblage is the Monte Orebe complex, that encompasses T-MORB mafic rocks, ultramafic lenses, and exhalative sedimentary rocks akin to early to late stages of oceanic basin spreading, emplaced during convergent plate motions between the Pernambuco-Alagoas superterrane and the São Francisco craton. Correlative units are found in Cameroon, including the strongly hydrotermalized ultramafic rocks of the Lomié and Boumnyebel complexes, that are structurally controlled by top-to-the-south verging nappes found in the N-NW margin of the Congo craton. In all scenarios, the ophiolitic complexes are related to intra-oceanic and continental magmatic arcs as well as to geophysical signatures comparable to Phanerozoic suture zones. Although strongly dismembered, scrapped off Neoproterozoic oceanic crust partially preserved within the major belts of western Gondwana demonstrate the role of accretion-collisional orogenesis during its assembly.

GEOLOGICAL FEATURES IDENTIFIED FROM FIELD OBSERVATIONS AND REMOTE SENSING DATA ON THE UM TAGHIR AREA, EASTERN DESERT, EGYPT

The current study presents the integration between field observations and remotely sensed data for detection and extraction of geological structural features using Sentinel-2A and Aster DEM images. The area under investigation is represented by the Neoproterozoic East African Orogeny encompassing a part of the Arabian Nubian Shield. All the rock units studied belong to the Late Cryogenian-Ediacaran periods that are divided into two large terrains (continental arc terrain and oceanic arc terrain). The metagabbro and metavolcaniclastic rocks make up the oceanic terrain, while the gabbro, tonalite, granodiorite, dokhan volcanic, monzogranite and alkali feldspar granite comprise continental arc terrain. The Sentinel-2A remote sensing and ASTER DEM data have meaningful application in respect of geological interpretation. Lineament analysis is one of the most useful tools in geological mapping and mineral exploration. Several methods of processing and extracting lithological information and lineaments were applied to the Sentinel-2A and ASTER DEM data covering the present study. The methods include various image enhancements (FCC, MNF and PCA) and the application of directional filters (Sobel). The study results show that the area was subjected to stresses of various directions (WNW – ESE, NW-SE, NE-SW, N-S, NNE – SSW, and E-W). There occurred some important structure-related and mineralization events like migmatization (in granodiorites) and bearing mineralization (in gabbro), which are associated with major elements of evidence-based structural control of the area and with the proximity of the Quena Safaga shear zone-related mineralization.

Sequence stratigraphy and paleoenvironmental significance of the Neoproterozoic Bambui Group, Central Brazil

The Bambui Group is a ca. 2,000 m-thick mixed biochemical-siliciclastic sedimentary succession that accumulated in the Sao Francisco Basin, central Brazil. Its age is contentious, but deposition during the Cryogenian-Ediacaran (ca. 635–550 Ma) is consistent with a new sequence stratigraphic model presented herein and previously published geochemical and structural data. Six stratigraphic sequences are recognized that record depositional evolution from an epeiric sea to foreland basin during the Marinoan snowball glaciation (ca. 635 Ma) to shortly after the Gaskiers (ca. 580 Ma) glaciation. Although this stratigraphic architecture differs from the classic lithostratigraphic and more recent chemostratigraphic and sequence stratigraphic interpretations of the Bambui Group, it is supported by correlation to other Cryogenian-Ediacaran successions globally. Collectively, these six sequences preserve a robust record of seawater redox structure leading up to the oxygenation threshold that triggered the evolution of multicellular animals in the Ediacaran.Sequence 1 is composed of Marinoan glacial deposits and an overlying cap carbonate with aragonite fan pseudomorphs and barite. Sequence 2 is composed of lime-mudstone that changes laterally into loess-rich peritidal phosphorites, suggesting oxygen stratification in shallow paleoenvironments. Sequence 3 is a carbonate succession with abundant stromatolites implying widespread oxygen production. The top of Sequence 3 is marked by a regional subaerial unconformity developed during uplift associated with the onset of the Brasiliano-Pan African Orogeny. Sequence 4 signals a return to loess derived sedimentation. Distal deposits contain abundant organic matter with framboidal pyrite reflecting bacterial sulfate reduction in low sulfate Ediacaran seawater. Sequence 5 is composed of well-developed aggradational parasequences composed of alternating deep subtidal organic-rich siltstones and shallow-water carbonate grainstones. Their well-defined cyclicity is interpreted to record extreme sea level fluctuations during the onset of the Gaskiers glaciation. Stromatolites suggest an oxygen-stratified water column. Sequence 6 marks the change from an epeiric sea to a foreland basin. Interbedded basinal glauconitic siltstone and shale loess-rich are correlative with shoreface sandstones. Authigenic glauconite requires suboxic bottom waters to precipitate and thus reflects oxygenation of distal settings. Most of the deposition ended by ca. 560–550 Ma when the entire Bambui Group was deformed during the assembly of West Gondwana.In sequences 1, 2, 3, 4, 5, and the lower portion of 6, the lateral continuity of lithofacies, predictable layer-cake stratigraphy, and lack of fluvial coarse siliciclastic deposits are characteristics of epeiric sea successions. The appearance of immature sandstone, poorly sorted conglomerate, braided fluvial deposits, and synsedimentary deformation in the upper part of Sequence 6 are interpreted as the onset of foreland basin development. Stacking relationships of redox sensitive, authigenic lithofacies in both the epeiric sea and foreland phases support recent research suggesting seawater redox conditions were in a state of flux during the apex of the purported Neoproterozoic Oxygenation Event. Organic matter and authigenic pyrite in Sequences 4 and 5 reflect increased primary productivity in surface waters fertilized by nutrients such as P and Fe adsorbed on loess particles. This mechanism could be expanded to a global scale and have contributed to the increase in atmospheric and oceanic oxygen levels. These findings redefine and highlight the significance of the Bambui Group for Neoproterozoic Earth history.

Geophysical investigation of crustal structural framework of Ilesha, southwestern Nigeria

The interpretation of the aeromagnetic dataset of Ilesha southwestern Nigeria has been carried out to reveal possible future earthquake hazard as well as establish the groundwater potential of the area. The edge detection methods involving the analytical signal amplitude, the total horizontal derivative, the first vertical derivative and the 3D Euler deconvolution were performed on the residual magnetic intensity anomalies to identify the linear structural discontinuities associated with lithological boundaries/ faults in the area. The upward continuation filter and depth estimation procedures of source parameter imaging and radially averaged power spectrum were applied to the residual magnetic intensity data to map geological structures such as faults as well as determine the depth to crystalline basement rocks in the area. The obtained lineaments observed to trend predominantly towards the NE-SW direction indicative of Pan African Orogeny, suggest possible high yield groundwater aquifer zones. The upward continuation filtered maps showed evidence of deep-lying faults to depth beyond 2 km. The 3D Euler deconvolution plots and spectral analysis revealed depth to magnetic sources ranging from 55 m to 345 m and 13 m to 250 m, respectively. The delineated structural discontinuities in the study area revealed stress history similar to Ifewara-Zungeru fault network, suggestive of possible future earthquake occurrence in the area. It is however recommended that further geophysical studies should involve electrical method to establish the groundwater potential as well as the stability of the basement underlying the area.

Petrogenesis and geotectonic setting of Berguda granitoids of Neoproterozoic Burji-Finchawa granite-gneiss complex, southern Ethiopia: implication for the cessation of subduction control magmatism in East African Orogeny

Petrogenesis and geotectonic setting of Berguda granitoids of Neoproterozoic Burji-Finchawa granite-gneiss complex, southern Ethiopia: implication for the cessation of subduction control magmatism in East African Orogeny

Combined Zircon/Apatite U-Pb and Fission-Track Dating by LA-ICP-MS and Its Geological Applications: An Example from the Egyptian Younger Granites

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is classically used in U-Pb dating to measure U and Pb isotopic concentrations. Recently, it has become frequently used in fission-track (FT) chronometry too. As an advantage, the U-Pb and FT double dating will enable efficiently determining the crystallization ages and the thermo-tectonic history concurrently as samples volume, analytical time, efforts, and cost will be greatly reduced. To demonstrate the validity of this approach, a Younger granite (Ediacaran age) sample from North Eastern Desert (NED), Egypt was analyzed for U-Pb and FT double dating. The integration of multiple geochronologic data yielded a zircon U-Pb crystallization age of 599 ± 30 Ma, after emplacement, the rock cooled /uplifted rapidly to depths of 9–14 km as response to the post-Pan African Orogeny erosional event as indicated by apatite U-Pb age of 474 ± 9 Ma. Afterwards, the area experienced a slow cooling/exhumation for a short period, most-likely as response to denudation effect. During the Devonian, the area was rapidly exhumed to reach depths of 1.5–3 km as response to the Hercynian tectonic event, as indicated by a zircon FT age of 347 ± 16 Ma. Then the studied sample has experienced a relatively long period of thermal stability between the Carboniferous and the Eocene. During the Oligocene-Miocene, the Gulf of Suez opening event affected the area by crustal uplift to its current elevation. This integration of Orogenic and thermo-tectonic information reveals the validity, efficiency, and importance of double dating of U-Pb and FT techniques using LA-ICP-MS methodology.