scholarly journals Structural Geology of the Basement Complex Rocks in Iwaraja Area, Southwestern Nigeria

2016 ◽  
Vol 58 ◽  
pp. 16-28 ◽  
Author(s):  
Blessing Adeoti ◽  
Chukwuemeka Tony Okonkwo
Keyword(s):  
Shear Zone ◽  
Structural Evolution ◽  
Structural Features ◽  
Granitic Rocks ◽  
Basement Complex ◽  
Southwestern Nigeria ◽  
Basement Rocks ◽  
Deformation Phase ◽  
Two Phases ◽  
Orogenic Belts

The geological and structural evolution assessment of the Basement Complex rocks in Iwaraja area, southwestern Nigeria showed that the basement rocks comprise quartzites and quartz-schists of the Effon Psammite Formation, quartz-mica schists, biotite schists, migmatitic gneisses, granitic gneisses, late and post-tectonic granitic rocks including pegmatites, which have been subjected to two phases of deformation. The first phase is mainly a fabric forming deformation that also led to the development of moderately plunging mineral lineation. No minor fold of this phase was recognized. The second deformation phase gave rise to the development of Iwaraja (ductile) shear zone. Mylonitic foliation is sub-vertical and steeply dipping and while the mineral lineation is sub-horizontal and shallowly plunging. Within granitic gneiss mylonites, the shear zone is characterised by early and late open to tight folds of pegmatite dykes. Adjacent the shear zone, ptygmatic folds of quartzo-feldspathic veins in gneisses and crenulated cleavages that overprinted earlier schistosity surfaces in the quartz-mica schist also characterised this deformation phase. Extensional fractures in the various lithologies generally show bimodal orientations mainly in the WNW-ESE and NW-SE directions, which are nearly perpendicular to the regional metamorphic foliations. These deformation conditions depict structural features that are associated with internal zones of orogenic belts. Within the study area, the structures document late-Precambrian deformation during the closing stages of Pan-African orogenesis.

scholarly journals Polyphase evolution of a crustal-scale shear zone during progressive exhumation from ductile to brittle behaviour: a case study from Calabria, Italy

2015 ◽  
Vol 7 (1) ◽  
pp. 909-955
Author(s):  
E. Fazio ◽  
G. Ortolano ◽  
R. Cirrincione ◽  
A. Pezzino ◽  
R. Visalli
Keyword(s):  
Shear Zone ◽  
Regional Scale ◽  
Structural Evolution ◽  
Structural Features ◽  
Normal Faults ◽  
Field Variation ◽  
Axis Orientation ◽  
Progressive Development ◽  
Deformational History ◽  
Scale Shear

Abstract. Mylonitic rocks involved within a polyphase crustal-scale shear zone, cropping out in the Aspromonte Massif (Calabria, Italy), has been investigated to reveal the meso- and micro-structural evolution (from ductile- to brittle-type deformation) occurred during exhumation trajectory. A relatively small area (about 4 km2) has been selected in the central-eastern part of the massif to constrain the sequence of the structural features from the earliest ones (Hercynian in age), almost totally obliterated by a pervasive mylonitic foliation (plastic regime), up to recent ones, consisting of various sets of veins typical of semibrittle to brittle regime. The former ductile evolution was followed by a compressive thin-skinned thrusting stage developed during the Apennine phase of the Alpine Orogeny, interested by a second brittle stage, consistent with the switching from compressive to extensional tectonics. This last stage accompanied the final exhumation process causing the activation of regional scale normal faults, which partly disarticulated previous mylonitic microstructures. A suite of oriented specimens were collected and analyzed to complete the deformational history already recognized in the field. Quartz c axis orientation patterns confirm the greenschist facies conditions of the former ductile exhumation stage with a dominant top-to-NE sense of shear. Microstructural investigations highlighted the progressive development from plastic- to brittle-type structures, allowing to constrain each step of the multistage exhumation history, and to establish the relative timing of the stress field variation causing thrusting and subsequent normal faulting. Obtained results support a continue compressional exhumation of this sector since the opening of Tyrrhenian basin (10 Ma).

scholarly journals Geochemical trends in weathering profiles and their underlying Precambrian basement rocks in Akure, Southwestern Nigeria

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Oluwatoyin O. Akinola ◽  
Olusola A. OlaOlorun
Keyword(s):  
Residual Soils ◽  
Basement Complex ◽  
Southwestern Nigeria ◽  
Basement Rocks ◽  
Icp Ms ◽  
Analytical Result ◽  
The University ◽  
Plastic Clays ◽  
In Situ Weathering

Akure area in southwestern Nigeria falls within the basement complex underlain by migmatite, quartzite granite and charnockite. Geochemical features of these crystalline rocks and their overlying in-situ weathering profiles are investigated and reported. Analytical result from ICP-MS facility at the University of Malaya reveals average SiO2 content in quartzite (91.1%), granite (73.8%), migmatite (67.4%) and charnockite (58.6%) categorize the rocks as siliceous. SiO2 contents in the weathering profiles above these rocks are 61.9%, 60.2%, 52.2% and 54.6% respectively. Alumina contents in the weathering profiles overlying quartzite (23.8%), granite (19.9%), migmatite (26.3%) and charnockite (24.3%) are substantially higher than the precursor rocks. In the same order, average alkali (Na2O+K2O) contents in the profiles are 3.38%, 3.42%, 3.48% and 2.68%. Chemical features of the profiles reflect that there exists some correlation between the chemistry of crystalline basement and their in-situ weathering profiles. The residual soils contain low plastic clays with kaolinitic characteristics and compare well with other clays reported from other parts of Nigeria basement complex. 

Basement–cover relationships during polyphase deformation in the Svecokarelides of the Kaavi district, eastern Finland

1983 ◽  
Vol 74 (2) ◽  
pp. 95-118 ◽  
Author(s):  
Adrian F. Park ◽  
D. R. Bowes
Keyword(s):  
Structural Evolution ◽  
Structural Features ◽  
Prograde Metamorphism ◽  
Late Archaean ◽  
Polyphase Deformation ◽  
Basement Rocks ◽  
Granitoid Emplacement ◽  
Subsequent Deformation ◽  
Nappe Emplacement ◽  
Eastern Finland

ABSTRACTFor much of its length in eastern Finland, the contact between the late Archaean granitoid terrane and early Proterozoic supracrustal rocks is that of a depositional unconformity tectonically modified during the Svecokarelian orogeny. In the Kaavi district, this modification has been extensive, particularly because of thrusting which resulted in tectonic slices of basement being present as inliers within the cover rocks and cover rocks as outliers within the main basement outcrop. Both basement and cover have undergone repeated deformation and metamorphic recrystallisation reflected by the presence of multiple tectonic fabrics and sequential mineral growths. However, it is only locally in major zones of movement that the basement rocks of the Presvecokarelides show major modification as the result of the deformation which had such a profound effect on the cover rocks during the development of the Svecokarelides. Over large areas, the products of four phases of deformation (DI–IV) remain in the basement gneisses together with the products of basic and acidic intrusion whose positions in the deformational sequence can be established‥In the cover rocks, early nappe emplacement (Outokumpu nappe) was followed by the development of isoclinal folds associated with prograde metamorphism (D1). Regionally expressed asymmetrical folds, overturned to the E, with attenuation of overturned limbs and thrusting, involving basement, followed (D2). Subsequent deformation related to wrench faulting (D2c) was followed by the development of more open folds associated with declining geotherms (D3, D4); F3–F4 interference structures are expressed as domes, some of which were a locus of granitoid emplacement (Maarianvaara granitoid suite). D5 and D6 are expressed as cleavages and fractures.Correlation of the structural features in the Kaavi district with those in the Outokumpu and adjacent districts forms the basis both for establishing the regional disposition of basement and cover units and for determining the structural evolution of this part of the Svecokarelides.

Structural evolution of Iwaraja shear zone, southwestern Nigeria

2017 ◽  
Vol 131 ◽  
pp. 117-127 ◽  
Author(s):  
Blessing Adeoti ◽  
Chukwuemeka Tony Okonkwo
Keyword(s):  
Shear Zone ◽  
Structural Evolution ◽  
Southwestern Nigeria

Geologic Map of the Park Reservoir Quadrangle, Sheridan County, Wyoming

2020 ◽  
Vol 57 (4) ◽  
pp. 375-388
Author(s):  
Ryan Bessen ◽  
Jennifer Gifford ◽  
Zack Ledbetter ◽  
Sean McGuire ◽  
Kyle True ◽  
...  
Keyword(s):  
Structural Features ◽  
Geologic Mapping ◽  
Rock Types ◽  
Basement Rocks ◽  
Geologic Maps ◽  
Geologic Map ◽  
Tear Fault ◽  
Mapping Techniques ◽  
Wyoming Province ◽  
Bighorn Mountains

This project involved the construction of a detailed geologic map of the Park Reservoir, Wyoming 7.5-Minute Quadrangle (Scale 1:24,000). The Quadrangle occurs entirely in the Bighorn National Forest, which is a popular recreation site for thousands of people each year. This research advances the scientific understanding of the geology of the Bighorn Mountains and the Archean geology of the Wyoming Province. Traditional geologic mapping techniques were used in concert with isotopic age determinations. Our goal was to further subdivide the various phases of the 2.8–3.0 Ga Archean rocks based on their rock types, age, and structural features. This research supports the broader efforts of the Wyoming State Geological Survey to complete 1:24,000 scale geologic maps of the state. The northern part of the Bighorn Mountains is composed of the Bighorn batholith, a composite complex of intrusive bodies that were emplaced between 2.96–2.87 Ga. Our mapping of the Park Reservoir Quadrangle has revealed the presence of five different Archean quartzofeldspathic units, two sets of amphibolite and diabase dikes, a small occurrence of the Cambrian Flathead Sandstone, two Quaternary tills, and Quaternary alluvium. The Archean rock units range in age from ca. 2.96–2.75 Ga, the oldest of which are the most ancient rocks yet reported in the Bighorn batholith. All the Archean rocks have subtle but apparent planar fabric elements, which are variable in orientation and are interpreted to represent magmatic flow during emplacement. The Granite Ridge tear fault, which is the northern boundary of the Piney Creek thrust block, is mapped into the Archean core as a mylonite zone. This relationship indicates that the bounding faults of the Piney Creek thrust block were controlled by weak zones within the Precambrian basement rocks.

scholarly journals Mineralogical and Geochemical Trends in the Residual Soils above Basement Rocks in Ore Area, Southwestern Nigeria

2017 ◽  
Vol 9 (3) ◽  
pp. 42
Author(s):  
Adewole John Adeola ◽  
Emmanuel Tamunobelema Tubonemi
Keyword(s):  
Inductively Coupled Plasma ◽  
Soil Layer ◽  
Clay Mineralogy ◽  
Lateritic Soil ◽  
Residual Soils ◽  
Southwestern Nigeria ◽  
Thin Sections ◽  
Tropical Regions ◽  
Basement Rocks ◽  
Parent Rocks

Residual clays and laterite of economic values often occur within weathering profiles above basement rocks in tropical regions due to supergene enrichment and leaching of liable components. Previous studies in Ore area mainly on geochemistry of the basement rocks with scanty information on the weathered profiles. This study was carried out to determine the compositional characteristics of the basement rocks, the geochemical trends within the profiles above the parent rocks and the evaluation of their economic potentials.Petrographic study was carried out on thin sections of the rock samples. Elemental compositions of the rocks, clay, laterite, and top-soil were determined using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Clay mineralogy was determined using X-ray Diffraction (XRD) analysis. Chemical index of Alterations (CIA) was calculated from geochemical data.Weathering of granite and banded gneiss in Ore resulted in the formation of soil layer, which ranged 0-0.5m, laterite 1.2-3m and clayey zone 2.9-3.0m. Quartz, plagioclase feldspars, microcline, biotite and hornblende were the essential minerals in the parent rocks. Granite and banded gneiss is high SiO2 (>65%) but low in MgO (<2.0%) and CaO (<4.0%). Kaolinite (60-80%), goethite (3-12%) and microcline (4-10%) were the dominant minerals in the XRD of the weathering profiles. Traces of illite were present only in granite. The CIA was generally > 85 indicating advanced state of weathering producing lateritic soil. The lateritic profiles over granite and banded gneiss of Ore area varied with the composition of the parent rocks. The clay layer has economic potential for ceramics, fertilizer and structural wares.

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