Precambrian Basement Rocks Research Articles

Machine learning models for predicting unconfined compressive strength: A case study for Precambrian basement complex rocks from Ado-Ekiti, Southwestern Nigeria

This study investigates the applicability of four distinct machine learning (ML) models – Random Forest (RF), Relevance Vector Machine (RVM), Support Vector Machine (SVM), and Artificial Neural Network (ANN) - for predicting the unconfined compressive strength (UCS) values of Precambrian basement rocks. The models employ input parameters such as rock aggregate index (Aggregate Crushing Value (ACV), Aggregate Impact Value (AIV), and Los Angeles Aggregate Value (LAAV)) and mechanical test index values (Schmidt Hammer Rebound Number (SHR) and Point Load Strength Index (IS(50)) for prediction purposes. Additionally, a multilinear regression (MLR) model was implemented to compare the predictive performance of the ML models against the traditional linear regression model. The developed models were validated using performance metrics such as Mean Absolute Error (MAE), Root Mean Squared Error (RMSE), and Adjusted R-Squared (Adj.R2). The Friedman statistical test was also employed to investigate the significance of the differences in the performance of the models. The results indicate that all the models performed well and showed better predictive performance compared to the MLR model during both the training and testing phases, except for the ANN model, which exhibited slightly poorer performance than the MLR model in the testing phase. However, the SVM model demonstrated the best predictive accuracy among all the models with MAE, RMSE, and Adj.R2 scores of 0.76 and 1.45; 1.16 and 1.8; 0.98 and 0.90, respectively, for the training and testing phases. The difference in the performance of the predictive models was statistically significant, as revealed by the Friedman statistical test. A feature importance analysis was conducted to verify the significance of each input parameter, revealing that all input features had a positive effect on the output of all the models. However, IS(50) had the most significant impact on the models.

The Campinas-Jaguariúna Sill, NE Paraná Magmatic Province, Brazil: Insights on the mechanisms of emplacement and differentiation from geochemical and magnetic data

The Paraná Magmatic Province (PMP), one of the largest magmatic provinces on Earth, is composed of lava flows, dike swarms and sills that occupy thousands of kilometers across central-eastern South America. The Campinas-Jaguariúna Sill (CJS) is a large (>50 m thick and ±150 km2) diabase intrusion showing frequent medium- to coarse-grained gabbroic segregations and was emplaced at the interface between the Precambrian basement and sedimentary rocks in the northeastern Paraná Basin. This paper applies airborne magnetic and geochemical modeling to help understand the emplacement mechanisms and petrological evolution of the CJS. Magnetic field filtering techniques demonstrate that the CJS continues for tens of kilometers in the subsurface; analogous features are shown to be associated with other neighbor diabase occurrences, creating lobe-shaped structures that seem to freeze their original geometry and are not fully exposed by the current erosion levels. Petrological modeling indicates that the parental magma of the CJS was emplaced at ∼1 kbar, 1000 ppm H2O, and oxygen fugacity near FMQ-1. The gabbroic segregations, exposed as cm- to dm-sized sheets and eye-shaped lenses, are more evolved than the host diabase and can be shown by geochemical modeling to correspond to residual melts formed by crystal fractionation in a closed system. The parent magma of the CJS is akin to the more primitive Paranapanema magma type of the PMP, and we tested the possibility that sills intruding upper sedimentary layers may be part of a single episode of intrusions. For this purpose, we used geochemical data from the well-studied Limeira Sill, which is akin to the more evolved Pitanga magma type. Our modeling shows that, under crystal fractionation in the representative system condition, the CJS starting compositions cannot generate the Limeira rocks.

Large-scale basement mobilization endows the giant Carlin-type gold mineralization in the Youjiang Basin, South China: Insights from mercury isotopes

The metal source and genesis of hydrothermal mercury-rich gold metallogenic systems occurring far away from active continental margins remain puzzling. The Youjiang Basin of South China, where exists numerous Carlin-type gold deposits and some synmineralization hidden intrusions, is a natural laboratory to address this issue due to it was up to 1000 km inward from the active continental margins of South China when mineralization. Here, we use mass-independent fractionation of mercury isotope ratios (reported as ∆199Hg), which is predominantly generated during Hg photochemical reactions on Earth’s surface and has superiority of isotopic inheritance during hydrothermal processes, to address the metal source of the Youjiang Carlin-type gold deposits. Ore-associated sulfides from seven representative deposits display negative to near-zero ∆199Hg values (−0.29‰ to 0.04‰), which fall in between that of the regional Precambrian basement rocks (−0.21‰ to 0.06‰) and deep magmatic-hydrothermal systems (∼0‰), suggesting a binary mixing of Hg from these two sources. An isotope mixing model and mass balance calculations demonstrate that ∼1000 km3 of the basement rocks, which contributed to 86% of Hg budget, were leached and remobilized by magmatic-hydrothermal fluids and deep-circulating crustal fluids to endow the gold reserves of these deposits. Given that traditional S, Pb, C, and O isotopic data yielded indirect and ambiguous constraints on metal source due to their complex evolution processes and isotope fractionation during the fluids ascended. Our results, therefore, highlight the great advantage of using Hg isotope as a new tracer to understand metal sources of hydrothermal deposits.

Geochemical evolution of magmatic rocks in the Vioolsdrif Domain, Namibia

AbstractGeological, lithological, petrographical, geochemical, and geochronological data in the Palaeoproterozoic Richtersveld Subprovince/Magmatic Arc (RMA) of Precambrian basement rocks of the Vioolsdrif Domain in southern Namibia, strongly support linkages in the history of formation between the volcanic rock types of the Orange River Group (ORG) and the plutonic rocks of the Vioolsdrif Suite (VS). Previous age dating indicates volcanics of the ORG are more-or-less synchronous with granitic phases of the VS. Geochemical, mineralogical, and comprehensive field and petrological characteristics of the volcanic and granitic rocks suggest genetically linked, parallel igneous-effusive rock suites through processes of fractional crystallisation. Intermittent tapping of evolving residual magmas produced an extrusive carapace of volcanic rocks covering the granitic rocks in a classic magmatic differentiation context of parallel geochemical and lithological evolution. As the magma chamber fractionated plutonic phases of the VS at depth, it extruded residual liquids as volcanic flows and ejecta at surface to form the ORG. A first principal model, based on Ba, Rb and Sr trace element and SiO2, MgO, Al2O3, TiO2 major element behaviour, is supported by multivariate modelling of 28 major and trace elements in 129 rock analyses using Principal Component Analysis (PCA). PCA indicates the first four components account for more than 80% of the total compositional variance in all rock types lending comprehensive support for a linked geochemical differentiation model for both the igneous and the volcanic suites. Strong evidence for the magmatic co-evolution of the plutonic and effusive series includes the Cu-mineralisation event, which manifests itself as a resolvable, orthogonal fifth principal component, geochemically overprinting the intermediate ‘porphyry monzogranite’ differentiation stages, but not related to the terminal leuco-granites. The full spectrum of geochemical relationships is consistent with current models of a direct genetic relationship between evolving high Sr/Y magmas and hydrothermal porphyry Cu deposits, in overall agreement with the full context of field, rock, mineralogical, geochemical, and economic geology interpretations presented here.

Widespread Cadomian–Pan-African Ediacaran magmatism across the Moroccan Meseta: Implication for the geodynamic evolution of the NW Gondwana margin

The Moroccan Meseta constitutes a key peri-Gondwanan and Variscan terranes linking the branches between the SW European Cadomian and the north West African Craton (WAC), anti-Atlas metacratonic Pan-African terranes. While the Paleozoic sedimentary and tectono-magmatic record of the different blocks of the Moroccan Meseta is well documented, there is still a lack of systematic absolute ages and geochemical isotopic data of putative Precambrian basement rocks from different Meseta blocks. Here we present new U–Pb zircon ages, petrological, and whole-rock major, trace, and Sr–Nd–Pb isotope geochemical data of (meta)igneous rocks from the Bou-Acila, Jbel-Hadid, Goaïda, Midelt and El Jadida, constituting the basement of two main Moroccan Meseta blocks. Basaltic rocks, unconformably overlain by Cambrian platform sediments, in the Western Meseta Bou-Acila basement yield U–Pb zircon age of c. 581 ± 9 Ma that unveils the existence of Ediacaran magmatism in the Moroccan basement of this area. Alleged early Paleozoic mafic sills in the metasedimentary series of the Midelt Sidi-Saïd yield U–Pb zircon ages of c. 554 ± 12 Ma reveals, for the first time, the presence of Ediacaran magmatism in the basement of the Moroccan Eastern Meseta. U–Pb zircon ages in the Jbel-Hadid and El Jadida rhyolitic basement rocks (c. 604–543 Ma and c. 575–559 Ma, respectively), as well as granitic pebbles (c. 573 Ma) in the Goaïda Cambrian limestone series, further attest for coeval Ediacaran magmatism in the basement of Western Meseta. The geochemical affinity of the investigated Moroccan Meseta Ediacaran magmatic rocks is mainly metaluminous, low-K tholeiites for mafic rocks, and peraluminous, high-K calc-alkaline for the felsic rocks, consistent with a back-arc tectonic setting. Geochemical and Sr–Nd–Pb isotopic data indicate that the source of the Moroccan Meseta Ediacaran magmatism involved sources from the depleted mantle and old WAC crustal basement. Altogether, these data show widespread Ediacaran magmatism in the Moroccan Meseta mostly likely formed in a back-arc south of the Cadomian active margin along the NW Gondwana during the waning stages of the Cadomian–Pan-African orogeny, recording a transitional stage between the Ediacaran subduction and early Paleozoic rifting.

Timing the Mikir Hill uplift in Assam Basin: Record of stress propagation along the eastern margin of the Indian Plate

The Shillong Plateau-Mikir Hill complex is a comparatively small but significant geological feature located in the NE part of India. It mostly constitutes of Precambrian basement rocks and is covered by Cretaceous, Tertiary and Quaternary sediments. There are several studies that estimate the exhumation timing of these basement complexes, either by directly dating the basement rocks or indirectly by dating the sediments. The present study tried to use the available seismic and well data to establish a relative chronology of exhumation and uplift of the Mikir Hill with respect to other tectonic and geological events. The study finds that the Mikir Hill upliftment started at the end of deposition of Nazira sandstone at ∼3.6 Ma (Early Pliocene) and stopped by the end of Pleistocene (∼0.012 Ma) which is marked by a prominent unconformity at the top of Namsang Formation. These observations are broadly in agreement with the timing of the surface uplift of the Mikir Hill and Shillong Plateau from previous authors. The study also shows that the structures formed in the Assam foreland along the Naga Thrust front, the frontal thrust of the Schuppen belt, shows a progressive younging in deformation from the NE to the SW. This shows a broad correlation in their formation with the eastern subduction history of the Indian plate.

A Stratigraphic Discussion of the Tano Basin: From Shallow Waters to Deep Waters

Over the years, several attempts have been made to reveal the stratigraphy of the prolific hydrocarbon bearing Tano Basin in Ghana. However, with over two hundred well locations drilled in the shallow to deep water seismic coverage, there is a need to build on previous stratigraphic knowledge using recent, relevant data and available reports. Thus, this paper reviews the stratigraphy of the Tano Basin from available well data and reports. This review produced a summarized chronostratigraphic framework showing the various lithofacies distributions with the sedimentation periods through geologic time. The lithic fill in the Basin is controlled by notable structural configuration, a result of the rifting events which typically gave rise to two major depocenters suites amongst other. The stratigraphy of the Tano Basin is underlain by Precambrian Basement rocks, followed by sedimentation from the Pre-Aptian to Recent, associated with notable undifferentiated stratigraphic gaps, as either hiatuses or unconformities. The authors recommend further studies to ascertain the provenance and depositional processes that geologically characterize some of the interesting revelations such as the localized Cenomanian calcarenite sediments, undifferentiated Aptian to Albian volcanic/ igneous intrusion amongst others to collapse or validate the diverse proposed hypothesis.

Using geophysics to follow and model the Precambrian basement terranes beneath the Caledonian nappes in Finnmark, northern Norway: A case study

The bedrock geology of Finnmark, northern Norway, consists primarily of rock complexes dating back to the Precambrian and early Mid Palaeozoic eras and comprises (1) a mid-crustal lithospheric basement which is characterised by granitoid and greenstone complexes dating from Neoarchean to late Paleoproterozoic in age; (2) the Caledonide Orogen, characterised by a series of nappes and thrust sheets. Finnmark forms part of the northern margin of the Fennoscandian Shield, which extends across northern Finland into northwestern Russia. Precambrian rock complexes are also found as thrust slices in Caledonian nappes at several places in Finnmark and Troms, as well as in tectonic windows.Recently acquired high-resolution aeromagnetic data have provided spectacular and confirmatory evidence for the continuation of the diverse Precambrian greenstone belts and granulite terranes beneath the magnetically transparent Caledonian nappes.This study aims at analysing this subsurface continuation of the terranes using potential field data and estimating the depths of the main magnetic sources beneath the nappes. In this study, several geophysical methods are used, including 3D Euler deconvolution and 2D Werner deconvolution. We have focused specifically on the depth-to-basement beneath nappes and purposefully excluded anomalies associated with shallow structures, such as dykes and faults. Different methods have produced similar results and indicate an appreciable increase in the depth of the Precambrian basement rocks from south to north. In the south, Precambrian basement rocks are either exposed on the surface southeast of the Caledonian front or reappear within tectonic windows. A prominent positive magnetic anomaly on the Porsanger Peninsula is thought to represent an extension of the anomaly ascribed to the greenstone belt of the Repparfjord Tectonic Window. A 3D model of this has also been provided. According to estimates, the depths-to-basement below nappes close to the Caledonian front range from less than 500 to 2000 m, whilst in the northern part of the study area the depths generally reach 3000 to 4000 m, and are locally estimated to range between 5000 m and 6000 m.

Structure and thermochronology of basement/cover relations along the Defiance uplift (AZ and NM), and implications regarding Laramide tectonic evolution of the Colorado Plateau

Interpretation of the late Cretaceous to Eocene Laramide tectonic evolution of the Colorado Plateau is hampered by the difficulty of placing precise temporal constraints on fault-induced basement uplift, for there is a paucity of exposed basement from which thermochronologic ages might be obtained. The Defiance and Zuni uplifts, located on the southeasternmost Colorado Plateau, offer rare basement exposure that provide additional temporal insights. The Zuni uplift exposes abundant Precambrian basement rock, which has been the subject of previous apatite thermochronologic study to interpret low-temperature tectonic/exhumation history. In the Defiance uplift region, which is the main focus of this study, there are two outcrop areas of Precambrian-basement rock along the trace of the East Defiance monocline. Both sites are quarries. Uplift/erosion consequences of Pennsylvanian-Permian Ancestral Rocky Mountains (ARM) deformation are explicit in the geology of these quarries, for the contact between the Supai Group (Permian) and underlying basement (1,703 ± 1.3 Ma, zircon U-Pb) is a nonconformity. Here, we apply a combination of structural analysis of Laramide fold/fault relations and multi-method thermochronology to the exposed granitic basement of both the Defiance and Zuni uplifts. Zircon U-Pb, zircon (U-Th)/He, apatite fission-track, apatite (U-Th-Sm)/He, and hematite (U-Th)/He reveal a poly-phase thermo-tectonic history. Initially, the Paleo-Proterozoic 1.7 Ga basement cooled to ∼400 °C by at least 1.4 Ga, followed by 1.4–1.0 Ga unroofing to depths of ∼8 km. Following cooling, the Defiance-Zuni granitic basement experienced protracted residence at temperatures ≤200 °C (∼8 km) between <i>ca.</i> 900 and 600 Ma. Sedimentary evidence and hematite (U-Th)/He dates bracket the ARM event (400–200 Ma), which may suggest fluid-rock interaction or near-surface exposure associated with the ARM. Following the ARM, the Defiance uplift experienced heating (&gt;120 °C) associated with burial consistent with the stratigraphic overburden, until approximately 80 Ma. Finally, the Defiance-Zuni region experienced initial cooling at &lt;70 Ma, with the main phase of exhumation to the upper crust (&lt;2 km) at <i>ca.</i> 60–40 Ma. Detailed structural modeling along 15 normal-profile cross-sections across the east margin of the Defiance uplift reveals that Laramide trishear monoclinal folding was generated by an oblique-slip master fault that partitioned ∼8 km of strike-slip and ∼1.5 km of reverse-slip displacement. Inferred strike-slip compartmental faulting in the Zuni uplift appears to fit coherently within this overall kinematic model in relation to Laramide loading direction. In the context of geodynamic models for flat-slab subduction during the Laramide tectonic event, consideration of new data from the Defiance uplift (along with other recently reported thermochronology data) provides support for models that bring the flat slab beneath North America along an east-northeastward trajectory, rather than along a more northward trajectory.

Airborne geophysics and remote sensing of an Nimas-Khadra area, southern Arabian shield: New insights into structural framework and mineral occurrences

The Shwas-Tayyah and Khadra belts belonging to the Asir terrane include potential mineralization zones, hosted in intensely deformed Precambrian basement rocks. Analysis of geophysical aeromagnetic data and satellite images, constrained by field data, highlights the deep hierarchy and structuring of the An Nimas-Khadra area in its regional litho-structural setting and geodynamic evolution. The N-S and NNE-SSW major trends, with other E-W, NE-SW and NW-SE minor directions, were identified. The Tarj, Ibran, and Junaynah close to N-S oriented master shear zones, delimit and cross the Al Lith-Bidah, Shwas-Tayyah and Khadra belts; they characterize the Asir composite terrane. Structural and kinematic models were highlighted, showing the control of intense deformations on the basement structures. The deep-seated faults are linked to wide tectonic movements induced by regional E-W to ENE-WSW contractional orogenic episodes. The tectonics induced genesis of the accreted terrane rocks with differentiated belts and shear zones. The resulted structures seem to be in accordance with the Riedel model that includes conjugate movements of right-lateral strike slip faults and right-oblique reverse faults.Correlation of geophysical and geochemical analyses is a crucial technique used for better assessment and valorization of mineral resources. The spatial association between the interpreted lineament patterns and mineralization rates testifies the tectonic deformations-mineral deposits relationship. The AHP-based MCDM statistical support model highlights the mining interest areas. The MCDM allows further spatial statistical evaluation and reveals new prospective metal occurrences in the Shwas-Tayyah and Khadra belts. N-S and NNE-SSW lineament networks show the highest mineralization rates, suggesting their priority for more detailed prospections. The metallic mineral deposits have to be related to prominent steeply dipping and brittle-ductile shear zones.

Diagenesis and pervasive dolomitization of pre- and post evaporite shallow marine carbonates, Ras Banas Peninsula, Red Sea Coast, Egypt

The present study deals with diagenesis and dolomitization modeling of Middle Miocene – Quaternary sedimentary sequence outcropped at Ras Banas Peninsula, Egyptian Red Sea Coast. This sequence is comprising successively overlapped clastics, carbonates, and evaporites attaining 254 m total thickness resting on the Pre-Cambrian basement rocks in the Peninsula. Diagenetic history and dolomitization were carefully investigated using several techniques including petrographic microscope, XRD, SEM, cathodoluminescence, atomic absorption, and isotopes of oxygen and carbon. The conspicuous phenomena is the pervasive dolomitization of directly pre- and post evaporite limestone components. These dolomites are mostly nonstochiometric, poorly to moderately ordered crystals. Based on all the results obtained from this study, the dolomitization processes of Ras Banas Peninsula are the result of complex geologic setting, paleo-climate changes, tectonic activity, and sea-level fluctuations. The proposed graphic model describes dolomitization mechanism which refers to mixed meteoric-hypersaline water environments.

Late Jurassic Wenjiaping high Sr/Y granite: A product of partial melting of the Precambrian basement rocks trigged by lithospheric extension in the Songpan–Garzê fold belt, SW China

The Wenjiaping granite, as one of the few Late Jurassic granites in the Songpan–Garzê fold belt (SGFB), can provide an important clue for comprehensively recognizing the tectonic evolution and mineralization of this belt. In this contribution, we present new age and geochemical data for this pluton to better constrain its petrogenesis and discuss the tectonic and metallogenic implications. LA‐ICP‐MS zircon U–Pb dating shows that the Wenjiaping pluton was emplaced at ~159 Ma. The granite contains minor amphibole, and exhibits slightly peraluminous characteristics (A/CNK = 1.03–1.10) and lower initial Sr–Pb isotope ratios than those of the Liwu Group, which excludes the possibility that the Wenjiaping granite was derived from partial melting of the metasedimentary rock‐dominated Liwu Group as previously suggested. Significantly, high Sr/Y (40.93–54.30), LaN/YbN (39.64–56.64), and K2O/NaO (0.77–1.11) ratios, low MgO (0.47%–0.86%) and Cr (25.1–41.3 ppm) contents, and relatively enriched Sr–Nd–Pb–Hf isotope compositions of the Wenjiaping granite are comparable to those of the Late Triassic adakitic rocks in the SGFB, indicating that they probably share a similar source. Combined with previous researches, we propose that large‐scale detachment of the Jianglang dome caused by post‐collisional lithospheric extension in the SGFB‐induced decompressional partial melting of the Precambrian basement rocks can account for the generation of the Late Jurassic Wenjiaping pluton. In addition, our results also suggest that the Wenjiaping pluton probably cannot supply abundant metal elements for the Liwu‐type Cu‐polymetallic deposits in the Jianglang dome, SGFB.

Tectonic evolution of the Beishan orogen in central Asia: Subduction, accretion, and continent-continent collision during the closure of the Paleo-Asian Ocean

AbstractThe Beishan orogen is part of the Neo-proterozoic to early Mesozoic Central Asian Orogenic System in central Asia that exposes ophiolitic complexes, passive-margin strata, arc assemblages, and Precambrian basement rocks. To better constrain the tectonic evolution of the Beishan orogen, we conducted field mapping, U-Pb zircon dating, whole-rock geochemical analysis, and Sr-Nd isotopic analysis. The new results, when interpreted in the context of the known geological setting, show that the Beishan region had experienced five phases of arc magmatism at ca. 1450–1395 Ma, ca. 1071–867 Ma, ca. 542–395 Ma, ca. 468–212 Ma, and ca. 307–212 Ma. In order to explain the geological, geochemical, and geochronological data from the Beishan region, we present a tectonic model that involves the following five phases of deformation: (1) Proterozoic rifting that separated the North Beishan block from the Greater North China craton that led to the opening of the Beishan Ocean, (2) early Paleozoic north-dipping subduction (ca. 530–430 Ma) of the Beishan oceanic plate associated with back-arc extension followed by collision between the North and South Beishan microcontinental blocks, (3) northward slab rollback of the south-dipping subducting Paleo-Asian oceanic plate at ca. 450–440 Ma along the northern margin of the North Beishan block that led to the formation of a northward-younging extensional continental arc (ca. 470–280 Ma) associated with bimodal igneous activity, which indicates that the westward extension of the Solonker suture is located north of the Hongshishan-Pengboshan tectonic zone, (4) Late Carboniferous opening and Permian north-dipping subduction of the Liuyuan Ocean in the southern Beishan orogen, and (5) Mesozoic-Cenozoic intracontinental deformation induced by the final closure of the Paleo-Asian Ocean system in the north and the Tethyan Ocean system in the south.

86Kr excess and other noble gases identify a billion-year-old radiogenically-enriched groundwater system

Deep within the Precambrian basement rocks of the Earth, groundwaters can sustain subsurface microbial communities, and are targets of investigation both for geologic storage of carbon and/or nuclear waste, and for new reservoirs of rapidly depleting resources of helium. Noble gas-derived residence times have revealed deep hydrological settings where groundwaters are preserved on millions to billion-year timescales. Here we report groundwaters enriched in the highest concentrations of radiogenic products yet discovered in fluids, with an associated 86Kr excess in the free fluid, and residence times >1 billion years. This brine, from a South African gold mine 3 km below surface, demonstrates that ancient groundwaters preserved in the deep continental crust on billion-year geologic timescales may be more widespread than previously understood. The findings have implications beyond Earth, where on rocky planets such as Mars, subsurface water may persist on long timescales despite surface conditions that no longer provide a habitable zone.

The nature of Paleoproterozoic basement in the northern Yangtze and its geological implication

Archean-Paleoproterozoic crystalline basements are sporadically distributed in the Yangtze Craton, but the fundamental problems about the formation and evolution of these Precambrian basements have not been completely solved. In this study, Precambrian basement rocks in the Feidong Complex provide an excellent opportunity for inspecting the evolution of the Yangtze Craton. It is composed mainly of Paleoproterozoic granitic gneiss (2470–2434 Ma), amphibolite (2482–2461 Ma) and potassic granite (2002–1963 Ma). Granitic gneisses show typical I-type affinity, their relatively enriched Nd-Hf isotopic components (εNd(t) = –1.3 to –1.2; εHf(t) = –5.2 to 1.1) indicate the Archean crustal growth (3.3–3.1 Ga) and subsequent reworking during Early Paleoproterozoic. Meanwhile, the arc-like geochemical signature as well as εNd(t) (3.1–3.8) and εHf(t) (–1.9–3.0) values in amphibolite reveal the interaction between lithospheric mantle wedge peridotite and slab-derived fluids. Early Paleoproterozoic magmatic activities in the Feidong Complex most likely occurred at convergent continental margin related to a subduction event. Furthermore, a comparison of crustal evolution in various Precambrian continental blocks scattered in the Yangtze Craton proves their independence prior to Paleoproterozoic. The potassic granites show typical S-type granites affinity with high Sr/Y, Rb/Sr ratios, their negative εNd(t) (–15.5 to –11.5) and εHf(t) (–12.8 to –7.7) values indicate the reconstruction of Archean continental crust related to continental collision. In conjunction with broadly coeval magmatism and metamorphism events distributed in Yangtze Craton, it is speculated that the orogeny is linked to the internal assembly and convergence event of Yangtze and Columbia supercontinent, respectively.

Investigation of a Relation between Radiogenic Heat Production Rate (RHPR) and Land Surface Heat Temperature (LST) from Thermal Bands of ASTER and Landsat-8 (TIR-Data): Case Study of West Ras Gharib area North Eastern Desert, Egypt

In this paper, an attempt was tried to study the relation between the land surface heat temperature (LST), extracted, from the thermal emission infrared data (ASTER-TIR) and (Landsat-8-TIR) imagery and radiogenic heat production rate (RHPR) that calculated from airborne gamma-ray spectrometric data applied on west Ras Gharib area at Northeastern Desert of Egypt. The area is geologically covered mainly by Precambrian basement rocks, which are unconformably overlain by Phanerozoic sedimentary succession. The method used for extraction land surface heat temperature for both ASTER-TIR and Landsat-8-TIR images is the reference channel emissivity technique and founded as the best method comparing to others. The study results showed a relative higher RHPR threshold value reached 4.8 μW/m3. On the other hand, ASTER-TIR Land Surface Temperature (AST-LST) ranges between 27.64oC to 47.2oC and, the Landsat 8-TIR Land Surface Temperature (LS8-LST) ranges between 30.64oC to 50.68oC. Comparing all results, there were a weak relationship or to some extent parallel relation between RHPR and satellite LST; as when the value of the Y-axis is constant, there are multiple values on X-axis, so it is not possible to deduce the value of one variable in terms of the other. The poor relation is regarded to the very weak RHPR which is not enough to affect the surface heat temperature, emission that could be detected by both thermal sensors of ASTER and Landsat-8 satellite TIR data. Other factors such as: topography, wind, shading and scattering, rock moisture and density, can strongly affect the surface temperature. In conclusion, the output results could be improved in areas of very high radioelement concentrations especially 235U, and through the use of the enhanced spatial resolution of future satellite TIR imaging instruments.

Petrology and Detail Geological Mapping of the Precambrian Basement Rocks of the Sn-Ta-Nb Numbi Deposit, Democratic Republic of the Congo

The Numbi district of eastern Democratic Republic of the Congo (DRC) has high mineral interest; it has been exploited for decades by small scale artisanal miners for rare metals such as Sn, W, Ta and Nb. This area was investigated to elucidate the petrology of the basement rocks and to make their detailed geological map. From the petrographical and geochemical analyses, six lithological units were characterized. Granite and schist were the two main lithologies with some associated smaller rock units such as amphibolite, diorite, quartzite and pegmatite. Biotite is the common mineral found in all lithologies. The granite displays the mineralogical assemblages with the abundance of muscovite, biotite, feldspar, plagioclase and quartz. Diorite and amphibolite display less amount of quartz. Hornblende is very abundant in the amphibolite; less is the schist and a very small amount in the granite. Feldspar is mostly found in the granite, quite found in the quartzite and less in the schist rocks. In adding to these mineral assemblages, accessory and opaque minerals (iron oxide) are in a very small amount. Pegmatite is mostly found as altered veins. Schist, quartzite and granite samples share the fields of granodiorite while diorite and amphibolite samples share the fields of diorite and gabbroic diorite on the total alkali-silicate classification diagram and ranged under intermediate and acidic rocks. The area is abundantly rich in rare metals (pegmatite with Nb-Ta-Sn mineralization) and is fairly suitable for quarry activities.

Geology and Structural Studies of Precambrian Basement Rocks Around Mahuta, Zuru Schist Belt, Northwestern Nigeria

The study of geology and structures in part of Zuru schist belt northwestern Nigeria was aimed at understanding the rock units, mineralogy, structural configuration, distribution and deformation. This was achieved through lineament analysis, petrographic study and structural analysis (geometric, kinematic and dynamic). Lineament analysis revealed the distribution, relative abundance and orientations of linear-curvilinear features. Three (3) main lithologic units were revealed; medium-grained granite, quartz-mica schist, and quartzite while minor ones are quartz vein, quartzofeldspathic pegmatite and aplitic dyke; this was arrived at because of minerals assemblages like quartz, feldspars, biotite, and muscovite. Structural analysis revealed the presence of normal fault, strike-slip fault and systematic joint (orthogonal). The joints trend is dominantly NE-SW, N-S, E-W. The normal faults reveal maximum principal stress (σ1) orientation in 087, the intermediate stress (σ2) was oriented in 222 while the minimum stress (σ3) was oriented in 312 directions. The kinematic axes revealed from the fault data are P-axis (Compressional) is 87/087; B-axis (Tensional) is 02/222 while T-axis (Transpressional) is 02/312. The component of deformation of the normal fault is elongated by 10-30 cm, while the vertical deformation effect is neutral. The area experienced multiple phases of deformation. The study will aid in mineral exploration.

Hydrogeological Investigations in Basement Terrains Using Geological, Geomor-Phological and Geophysical Methods, Western Hamissana Area, NE Sudan

This study aims at identifying target zones for groundwater exploration in basement terrains using geological, geomorphological, and geoelectrical methods. The study area is located on the northwestern side of the Red Sea Hills in the western Hamissana area. It is part of the Arabian Nubian Shield (ANS), which dates to the Pan-African Era. The study area is covered by Precambrian basement rocks which are overlain by alluvial deposits. The climate in the region is arid. As a result, severe water shortage is experienced. The geological and geomorphological investigations were carried out to locate potential sites for groundwater prospecting. On this basis, three categories of groundwater potential zones were delineated as good, moderate, or poor. The electrical resistivity method using vertical electrical sounding (VES) technique was used to determine the vertical geological profile of the study area. The sequence was revealed to consist of four zones: a high-resistance unsaturated zone, an intermediate-resistance water-bearing formation, a low-resistance wet weathered basement, and high-resistance fresh basement rock. Catchment boundaries were delineated using digital elevation models, and potential locations for surface and subsurface dams were proposed to improve the groundwater recharge.

Petrography and structural features of the Precambrian basement rocks in the Benin-Nigerian Shield, NW Nigeria: Implications for their correlation with South Atlantic Precambrian terranes

&lt;abstract&gt; &lt;p&gt;This study investigated the petrographic and structural features of the Precambrian (Neoproterozoic) basement rocks of the Benin-Nigerian Shield that crop out in northwestern Nigeria within Kanoma and its environs to give an insight into the evolution and deformational episodes that pervaded them. The major rock types in the area are schists and quartzites, which have been intruded by granitic rocks that appear to be metamorphosed. The origin of these rocks is attributed to the Eburnean Precambrian orogenic episode and the Pan-African orogeny, which started and ended with the intrusion of the granite suites. The dominant mineralogy associated with the rock types includes quartz, orthoclase, plagioclase, microcline, biotite, chlorite, and very few accessory minerals. The schist shows the dominance of quartz, feldspars (alkali and plagioclase), biotite, muscovite, chlorite, and opaque minerals. The quartzite is typically dominated by quartz that appears recrystallized in places, whereas the meta-granite contains quartz, feldspars (alkali and plagioclase), biotite, and opaque minerals. Structural features such as joints, quartz veins with minor folds, and faults observed in the lithological units have a predominant N-S trend and are the imprints of the last tectonic event (Pan-African orogeny). The level of deformation in Kanoma led to the development of N to NNE trending moderately (S&lt;sub&gt;1&lt;/sub&gt;) to steeply (S&lt;sub&gt;2&lt;/sub&gt;) dipping foliations in the schist. The evolution of these deformational mechanisms from moderately dipping foliations to steeply dipping foliations along the N to NNE- trend is associated with late orogenic uplift and exhumation following oblique convergence during the Pan-African orogeny. Structural overprinting relations recognized within Kanoma and its environs allow us to decipher the geologic structures into three successive Pan-African deformational events (D1–D3). D1 fabrics are manifested by simple anticline micro folds in the schist. The D2 structures are the predominant ones in the area comprising the N-S directional joints and faults. The D3 phase of deformation is a progressive one, which started as N-S high angle thrusts and thrust-related folds that resulted from the NE–SW contraction during the orogenic episodes. The studied rocks can be correlated with the Pan-African and Brasiliano belts based on their overlapping features.&lt;/p&gt; &lt;/abstract&gt;