Flat-lying Structures Research Articles

Coadsorption of ZnTPP and 2HMCTPP on Rutile TiO2(110).

Pure zinc tetraphenylporphyrin (ZnTPP) adsorbs on rutile TiO2(110) as flat-lying molecules, mostly interacting with the surface through weak van-der-Waals interactions. Pure monocarboxyphenyl triphenylporphyrin (2HMCTPP) forms a covalent bond to the rutile TiO2(110) surface through the carboxylic acid group, yielding densely-packed layers of upright-standing molecules. If given the chance, 2HMCTPP could therefore be expected to displace the weaker-bonding ZnTPP molecules. However, if 2HMCTPP is deposited on top of a ZnTPP layer, a coadsorption structure instead forms, with the carboxylic-acid groups of the 2HCMTPP molecules bonding to titanium atoms of the surface exposed by gaps between the molecules in the flat-lying ZnTPP adsorption structure.

Restoring a syntectonic transtensional pluton by integrating structural geology, anisotropy of magnetic susceptibility, and gravimetric modelling

The kinematic analysis of magmatic structures is key evidence for the tectonic settings and deformation mechanisms related to the emplacement of intrusive bodies. The Dom Feliciano Belt (DFB), southernmost Brazil, registers voluminous post-collisional magmatism during the Neoproterozoic and the Arroio do Silva Pluton (ASP) is a diorite-monzonite-syenite body emplaced in this tectonic setting. The ASP structural investigation and magnetic fabric analysis showed the coexistence of flat-lying and steeply-dipping planar structures in most rock types. Heterogeneous shearing along the steeply-dipping planes led to heterogeneities in the fabric, providing individual analyses of zones affected and unaffected by shearing. The magnetic fabric analysis corroborated the interpretation of dextral kinematics based on field structural data. Complementary gravimetric modelling of the ASP demonstrates its continuity in the subsurface along an NNE-SSW axis. The integration of structural and magnetic fabric analyses combined with gravimetric modelling indicates that the older ASP rock types register a syntectonic emplacement within a transtensional setting, whereas younger magmatic activity in the pluton occurred under extensional conditions. The integrative approach allowed a comprehensive characterisation of the magmatic structures developed under different tectonic stresses and their association with emplacement conditions for the pluton.

Elevated concentrations cause upright alpha-synuclein conformation at lipid interfaces

The amyloid aggregation of α-synuclein (αS), related to Parkinson’s disease, can be catalyzed by lipid membranes. Despite the importance of lipid surfaces, the 3D-structure and orientation of lipid-bound αS is still not known in detail. Here, we report interface-specific vibrational sum-frequency generation (VSFG) experiments that reveal how monomeric αS binds to an anionic lipid interface over a large range of αS-lipid ratios. To interpret the experimental data, we present a frame-selection method ("ViscaSelect”) in which out-of-equilibrium molecular dynamics simulations are used to generate structural hypotheses that are compared to experimental amide-I spectra via excitonic spectral calculations. At low and physiological αS concentrations, we derive flat-lying helical structures as previously reported. However, at elevated and potentially disease-related concentrations, a transition to interface-protruding αS structures occurs. Such an upright conformation promotes lateral interactions between αS monomers and may explain how lipid membranes catalyze the formation of αS amyloids at elevated protein concentrations.

Structure and reaction pathways of octanoic acid on copper

The surface chemistry of octanoic acid was studied on a copper foil or a Cu(100) single crystal in ultrahigh vacuum using reflection-absorption infrared spectroscopy, temperature-programmed desorption, and supplemented by first-principles density functional theory (DFT) calculations. Octanoic acid adsorbs molecularly at 90 K, converting from a flat-lying species at low coverages to a more upright species at saturation. Adsorption at 300 K results in the formation of an η2-octanoate species, which binds with the alkyl group parallel to the surface with a tilted carboxylate group, as evidence by both infrared data and calculations. The flat-lying structure facilitates octanoate decomposition, which reacts by desorbing carbon dioxide at ~550 K. Increasing the octanoate coverage induces the alkyl chains to be more perpendicular to the surface to form a self-assembled monolayer with significant intermolecular van der Waals’ interactions. This stabilizes the adsorbate, which now decomposes by desorbing carbon dioxide at ~640 K, where infrared spectroscopy confirms that this also occurs by the carboxylate tilting towards the surface. The resulting heptyl species can either decompose by desorbing hydrogen or can also polymerize on the surface.

Advanced Use of Borehole Acoustic Televiewer (ATV) for Structural Interpretation of Unconformity-Related Uranium Deposits

Abstract The structural controls on unconformity-related uranium deposits of the Athabasca basin, Saskatchewan, Canada, are a matter of debate regarding the role of inherited fault systems and their reactivation. This can be related to the lack of outcrops allowing for direct observations, the strong clay alteration halos wrapping deposits that often obliterate structures, and the poor core recovery related to drilling strongly altered and mineralized intervals, which limits observation of structures and reliable oriented measurements. Borehole imaging technology is an invaluable alternative for obtaining oriented data through challenging drilling intervals. The use of borehole Acoustic Televiewer (ATV) has been integrated in recent exploratory campaigns in the Athabasca basin by Orano Canada. Here, we present the inputs and benefits of the use of the ATV in the exploration of unconformity-related uranium deposits and the structural analysis of oriented data from seven inclined diamond drill holes completed in 2016 during the McClean project (Sue deposits). The main objectives were to precisely identify the structural controls of the basement-hosted mineralization, and to test the tool in a well-known site. This work shows the applicability and added value of using televiewer probes to provide reliable oriented data in zones where there is much less information available. The ATV data structural interpretation supports the concept of mineralization of dilational jogs opening during preexisting shear-related foliation under right-lateral reverse fault reactivation. The ATV provides robust oriented data, allowing for a better understanding of the meaning of flat-lying mineralized structures along the Sue trend.

Joint inversion of gravity with cosmic ray muon data at a well-characterized site for shallow subsurface density prediction

SUMMARYEstimating subsurface density is important for imaging various geologic structures such as volcanic edifices, reservoirs and aquifers. Muon tomography has recently been used to complement traditional gravity measurements as a powerful method for probing shallow subsurface density structure beneath volcanoes. Gravity and muon data have markedly different spatial sensitivities and, as a result, the combination is useful for imaging structures on spatial scales that are larger than the area encompassed by crossing muon trajectories. Here we explore and test a joint inversion of gravity and muon data in a study area where there is an independently characterized target anomaly: a regionally extensive, high-density layer beneath Los Alamos, New Mexico, USA. We resolve the nearly flat-lying structure using a unique experimental set-up wherein surface and subsurface gravity and muon measurements are obtained above and below the target volume. Our results show that with minimal geologic (prior) constraints, the joint inversion correctly recovers salient features of the expected density structure. The results of our study illustrate the potential of combining surface and subsurface (e.g. borehole) gravity and muon measurements to invert for shallow geologic structures.

Understanding corrosion inhibition with van der Waals DFT methods: the case of benzotriazole.

The corrosion of materials is an undesirable and costly process affecting many areas of technology and everyday life. As such, considerable effort has gone into understanding and preventing it. Organic molecule based coatings can in certain circumstances act as effective corrosion inhibitors. Although they have been used to great effect for more than sixty years, how they function at the atomic-level is still a matter of debate. In this work, computer simulation approaches based on density functional theory are used to investigate benzotriazole (BTAH), one of the most widely used and studied corrosion inhibitors for copper. In particular, the structures formed by protonated and deprotonated BTAH molecules on Cu(111) have been determined and linked to their inhibiting properties. It is found that hydrogen bonding, van der Waals interactions and steric repulsions all contribute in shaping how BTAH molecules adsorb, with flat-lying structures preferred at low coverage and upright configurations preferred at high coverage. The interaction of the dehydrogenated benzotriazole molecule (BTA) with the copper surface is instead dominated by strong chemisorption via the azole moiety with the aid of copper adatoms. Structures of dimers or chains are found to be the most stable structures at all coverages, in good agreement with scanning tunnelling microscopy results. Benzotriazole thus shows a complex phase behaviour in which van der Waals forces play an important role and which depends on coverage and on its protonation state and all of these factors feasibly contribute to its effectiveness as a corrosion inhibitor.

Quantitative 3D microstructural analysis of naturally deformed amphibolite from the Southern Alps (Italy): microstructures, CPO and seismic anisotropy from a fossil extensional margin

Abstract The anisotropy of a rock is intimately related to the development of shape-preferred orientations (SPOs) and crystallographic-preferred orientations (CPOs). Quantifying the three-dimensional (3D) CPOs and SPOs in natural rocks is therefore critical for understanding the processes underlying the development of anisotropy. In this work, we present a CPO study of six amphibolite samples from the western Southern Alps (Italy) that have been characterized previously. Quantitative texture analyses using neutron diffraction data provided 3D CPOs for amphibole and plagioclase and were used to calculate seismic properties. We describe the relations between mesoscopic foliation and lineation, crystallographic fabrics and seismic anisotropies for lower–middle crust amphibolites. Based on these relations and in the context of lower–middle crust within fossil extensional margin, we suggest that seismic profiles should display large-scale geological features commonly present in extensional tectonics, such as folds and shear zones, rather than flat-lying structures. Moreover, from the integration of CPOs with geological data, we observe that samples from the Strona Ceneri boundary are characterized by a granulite to amphibolite facies transition while those from the Scisti dei Laghi only record the amphibolite facies evolution, supporting the idea of two independent tectono-metamorphic units pre-dating the amphibolite re-equilibration.

Orientation-Dependent Electronic Structures and Optical Properties of the P3HT:PCBM Interface: A First-Principles GW-BSE Study

In this work, the effect of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) orientation on the electronic and optical properties of the regioregular poly(3-hexylthiophene) (P3HT):PCBM blend interface was studied by means of first-principles density functional theory calculations with G0W0 approximation plus the Bethe–Salpeter equation (BSE). The band structures and photoresponse are shown to depend on the PCBM orientation. The origin of the two main optical absorption peaks is determined, and the effect of PCBM rotation on optical properties is revealed. The calculated lowest charge transfer complex state energy, exciton binding energy, and the absorption spectrum for the flat-lying model are in good agreement with the experimental values, which indicates the flat-lying structure is the predominant interface structure in the experiments. The lowest-energy configuration is also determined as the flat-lying orientation in our calculations. Our results further suggest that the dissociation of excitons and charge transfer at the interface is more efficient for the PCBM flat-lying orientation than that for the upright-standing one, which provides a possible explanation for the increased performance of the P3HT:PCBM devices after a thermal annealing treatment.

Arisite-(La), a new REE-fluorcarbonate mineral from the Aris phonolite (Namibia), with descriptions of the crystal structures of arisite-(La) and arisite-(Ce)

AbstractArisite-(La), ideally NaLa2(CO3)2[F2x(CO3)1–x]F, is a new layered REE-fluorcarbonate mineral from miarolitic cavities within the Aris phonolite, Namibia (IMA no. 2009-019). It occurs as distinct chemical zones mixed with its Ce-analogue, arisite-(Ce). Crystals are vitreous, transparent beige, beige-yellow, light lemon-yellow to pinkish, and occur as tabular prisms up to 1.5 mm. Arisite-(La) is brittle, has conchoidal fracture, poor cleavage perpendicular to (001), a Mohs hardness of ~3–3½, is not fluorescent in either long- or shortwave UV radiation, dissolves slowly in dilute HCl at room temperature and sinks in methylene iodide, Dcalc. = 4.072 g cm–3. Arisite-(La) is uniaxial negative, has sharp extinction, with both ω and ε exhibiting a range of values within each grain: ω = 1.696–1.717(4) and ε = 1.594–1.611(3), a result of chemical zoning attributed to both Ce ⇌ La and Na ⇌ Ca substitutions. The crystal structure of both arisite-(Ce) and arisite-(La) were solved by direct methods and refined to R = 1.66%, wR2 = 4.31% (Ce) and R = 2.09%, wR2 = 5.26% (La), respectively. Arisite is hexagonal, Pm2, Z = 1, with unit-cell parameters of a = 5.1109(2) Å, c = 8.6713(4) Å, V = 196.16(6) Å3 for arisite-(Ce), and a = 5.1131(7) Å, c = 8.6759(17) Å, V = 196.43(5) Å3 for arisite-(La). Arisite-(Ce) and arisite-(La) are members of the layered, flat-lying REE-fluorcarbonate group which have crystal structures characterized by separate layers of triangular planar groups that parallel the overall layering of the structure, F, REE and alkali or alkaline-earthelements. Overall, the arisite structure can be defined by three distinct layers which parallel (001): (1) ∞[REE(CO3)2F] slabs, (2) sheets of Naϕ9 polyhedra, and (3) ∞[2F/CO3]2–. Based on its (M+F)/C ratio, arisite can further be described as having a dense, flat-lying fluorcarbonate structure, a classification which includes the structurally related mineral species cordylite, kukharenkoite, cebaite, lukechangite, huanghoite, and one incompletely characterized synthetic phase, NaY2(CO3)3F.

付加体の構造侵食による前弧の構造発達

This paper proposes a new model for the evolution of geologic structures in forearcs concerning subduction erosion after tectonic accretion. The model was generated from a high-pressure (HP) metamorphic unit, in which the early history of frontal offscraping accretion is recorded, in the Kamuikotan Zone of central Hokkaido. It was transported from the trench to the interior of the subduction zone during a non-accretionary stage, and the process is regarded to be subduction erosion and subsequent underplating re-accretion at greater depths. This mode of material transport persuasively explains the common and abundant occurrences of terrigenous meta-clastic rocks in HP subduction complexes, in spite of common evidence that sediments had been scraped off at much shallower depths as seen in coeval non-metamorphic accretionary units. It is thus suggested that significant amounts of HP metasediments originated from tectonically eroded materials of the frontal accretionary complex, instead of rocks directly underplated from the subducted slab. Subduction erosion in Hokkaido occurred contemporaneously with the exhumation of a higher-grade HP unit with similar rates of vertical movement of opposite senses. It suggests that exhumation was a counter flow of subduction erosion: the higher-grade rocks were lifted up by the insertion and accumulation of tectonically eroded rocks at depths, and were unroofed by lateral extension of the oversteepened non-accretionary wedge. This model can also explain common flat-lying structures of accretionary and subduction complexes exposed on land. They originally had rather high-angle structures formed by lateral shortening during early accretionary stages, and then were tilted trench-ward by the removal of materials near the trench by subduction erosion and their underplating at rear-side portions during the subsequent non-accretionary stages.

Adsorption and Vibrations of α,β-Unsaturated Aldehydes on Pure Pt and Pt−Sn Alloy (111) Surfaces I. Prenal

The adsorption and thermal decomposition of the α,β-unsaturated aldehyde prenal (3-methyl-2-butenal) have been studied on Pt(111), the Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys, and the corresponding terminations of the Pt3Sn(111) bulk alloy by means of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). By comparing the experimental results with extensive theoretical calculations of the multitude of possible adsorption configurations of prenal using density functional theory (DFT), the adsorption configurations actually present on all model catalysts have been identified. This approach, thus, reveals a new way to identify complex, multifunctional molecules adsorbed on model catalyst surfaces. On Pt(111), prenal is strongly adsorbed and decomposes at approximately 300 K. By the aid of density functional theory (DFT), five flat-lying adsorption structures of η2, η3, and η4 hapticity, which exhibit similar adso...

Superposition of shear zones during orogenic development: an example from the NW Variscan Belt (Viana do Castelo, NW Portugal)

The Viana do Castelo region of NW Portugal is the only domain in the West Variscan where the transition from the D 1 strike-slip structures to the D 1 east vergent flat-lying structures, formed during Devonian–Carboniferous continental collision, has been recognized. Although intrusion of voluminous granite bodies has resulted in extensive recrystallization of host rocks, kinematic analysis of these rocks, using mesoscopic criteria and quartz CPOs (crystallographic preferred orientation) reveals shear senses coherent with the field evidence and suggests that D 1 deformation was partitioned into transpressional and compressional components. We also interpret the strain patterns to the effects of non-cylindrical superposed shear zones. The above aspects can be useful to understand the complex tectonic evolution of the most internal zone of the Variscan Belt and of other internal zones of collisional orogenic belts with similar characteristics.

Origin of the Nchanga copper–cobalt deposits of the Zambian Copperbelt

The Cu-Co deposits of the Nchanga Mine in the Zambian Copperbelt are consistently hosted by a arenites or arkoses with mineralization progressing for short distances into overlying shales. The ore horizons show a consistent association with flat-lying structures and in the Upper Orebody, are developed with thrust controlled antiformal structures. Hydrothermal alteration includes phlogopite ± sericite followed by dolomite precipitation and available stable δ34S of sulfides and δ13C data for carbonates are consistent with “in situ” thermochemical reduction of a sulphate rich fluid. The new data reported here suggest a strong link between Cu and Co ore formation in the Zambian Copperbelt and the development of structures during basin inversion and the onset of the Luffilian orogeny.

Structures of sub-monolayered silicon carbide films

The electronic and geometrical structures of silicon carbide thin films are presented. The films were deposited on graphite by ion-beam deposition using tetramethylsilane (TMS) as an ion source. In the Si K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra for sub-monolayered film, sharp peaks due to the resonance from Si 1s to π*-like orbitals were observed, suggesting the existence of Si=C double bonds. On the basis of the polarization dependencies of the Si 1s → π* peak intensities, it is elucidated that the direction of the π*-like orbitals is just perpendicular to the surface. We conclude that the sub-monolayered SiCx film has a flat-lying hexagonal structure of which configuration is analogous to the single sheet of graphite.

Electronic structures of ultra-thin silicon carbides deposited on graphite

Electronic structures of ultra-thin silicon carbide films have been investigated by X-ray photoelectron spectroscopy (XPS) and Si K-edge X-ray absorption near edge structure (XANES) using linearly polarized synchrotron soft X-rays. Silicon carbide films were deposited on the surface of highly oriented pyrolytic graphite (HOPG) by ion beam deposition method. Tetramethylsilane (Si(CH 3) 4) was used as a discharge gas. The XPS and XANES features for the thick layers were similar to those for the bulk SiC. For sub-monolayered films, the Si 1s binding energy in XPS was higher by 2.5 eV than that for bulk SiC. This suggests the existence of low-dimensional SiC x where the silicon atoms are more positively charged than those in bulk SiC. After annealing the sub-monolayered film at 850 °C, a new peak appeared around 1840 eV in the XANES spectrum. The energy of this new peak was lower than those for any other silicon compounds. The low-energy feature of the XANES peak suggests the existence of π *-like orbitals around the silicon atom. On the basis of the polarization dependencies of the XANES spectra, it was revealed that the direction of the π *-like orbitals are nearly perpendicular to the surface. We conclude that sub-monolayered SiC x film exhibits flat-lying structure of which configuration is similar to a single sheet of graphite.

A pop-up structure exposed in the outer foothills, Crowsnest Pass area, Alberta

ABSTRACT Recent mapping in the Blairmore East-Half map area indicates a pop-up structure transected by the Crowsnest River, near the leading edge of Eastern Cordilleran deformation. At scenic Falls, the sub-horizontal attitude of the Santonian Virgelle Formation (Milk River Group) is anomalous in comparison to fault-bounded slices to both the east and west, where strata display steep to moderate dips more typical of Foothills structures. The relatively broad (750 m across strike), flat-lying structure exposed at Falls is bounded downstream to the east by a foreland-directed thrust placing Virgelle Formation on Campanian Formation (Belly River Group). To the west, this sub-horizontal structure is overridden by a steeply west-dipping, foreland-directed thrust carrying Milk River and Belly River strata in its hanging wall. Stratigraphic offset across this thrust fault is apparently small to negligible at the Crowsnest River, but increases at higher elevations to the north and south. On either side of this thrust fault, north of the Crowsnest River, two anticlines involving the Virgelle Formation face each other. These atypical relationships suggest that, at the river and adjacent low elevations, the sub-horizontal structure may be bounded to the west by a cryptic, west-directed backthrust that is overridden up-slope by the foreland-directed fault just described. These features are inferred to comprise a pop-up structure, similar to those interpreted elsewhere within the triangle zone in the subsurface, but never before described in outcrop in the Foothills of Alberta. Although they appear to be very rare in the Foothills, the inferred backthrust is not alone in this immediate area. Two kilometres downstream, the hinge of an upright anticline, involving a well-exposed section of Milk River Group strata at the classic Lundbreck transition outcrop, is removed to the north by another west-directed backthrust. This backthrust could also be associated with a pop-up structure, as suggested by its configuration in restored cross-sections. An association between the pop-up structures and the triangle zone is implied by their proximity, but relative timing relationships are unclear. The recognition of these structures, using a refined stratigraphy in an area mapped previously, suggests that pop-up structures associated with the triangle zone may be more common than published studies indicate, and therefore may be more important features of the Outer Foothills belt than is widely appreciated. End_Page 139------------------------

Insights from the Ocean Drilling Program on shear and fluid-flow at the mega-faults between actively converging plates

Abstract The mega-faults between actively converging plates have recently been penetrated by the Ocean Drilling Program at three plate margins: Barbados, Costa Rica and Nankai. Cores, downhole instrumentation and detailed seismic imagery provide data which may be helpful in interpreting ancient examples of shear zones. The mega-faults, developed in poorly lithified sediments, separate major lithospheric plates yet are merely tens of metres in thickness. They respond to ongoing strain by intensifying inwards rather than propagating outward splays and can grow thinner because of continuing compaction. Surprisingly, lithological influence on the localization of fault propagation seems slight, but lithology determines the deformation style within the faults. The resulting structures show asymmetric distributions within the zones but, in these flat-lying structures, tend to show a downward increase in strain. Upper margins are typically gradational whereas lower boundaries can be strikingly abrupt. The fluid-transport behaviours are complex. In some situations the horizontal flux is very diffuse but centred around the fault. Some faults can efficiently channelize fluids — for distances of tens of kilometres — while at the same curbing flow across them. The fluid transport is clearly episodic and heterogeneous. Fingers of pressured fluid migrate within the fault zone, in patterns that constantly change through time.

Prolonged Paleoproterozoic magmatic participation in the Neoproterozoic Dom Feliciano belt, Santa Catarina, Brazil, based on zircon U–Pb SHRIMP geochronology

The dating of 47 spots in 42 zircon crystals from three rock samples using sensitive high-resolution ion microprobe (SHRIMP II) leads to a much better understanding of Paleoproterozoic magmatic participation in the construction of the Dom Feliciano Belt from the Precambrian shield of Santa Catarina, Brazil. One Archean age from the presumed basement of the Camboriú region is preserved as an inherited core in a zircon crystal, but 3.2–2.6 Ga model Nd T DM ages are present in several granitic rocks. The gneisses and migmatites of the Camboriú Complex were generated in a tectonic scenario, possibly comparable to an active continental margin setting at approximately 2.25–2.00 Ga during the Trans-Amazonian cycle. The precursor volcano-sedimentary basin of the Brusque Complex formed in a rift basin younger than 2.02 Ga. The Itapema Granite crystallized at approximately 2.02 Ga, controlled by flat-lying structures during a major event of the Trans-Amazonian cycle, and was again deformed at 598±6 Ma. A long period of stability occurred in the region between 2.00 and 0.63 Ga, followed by thrusting of the Trans-Amazonian units during an early event of the Brasiliano cycle. Widespread deformation and magmatism took place along transcurrent shear zones that compose the southern Brazilian shear belt, peaking at approximately 0.63–0.59 Ga, which eventually led to the construction of the Florianópolis Batholith. These previously unknown ages place significant constraints on the evolution of the southern Brazilian shield, with implications for the history of amalgamation and dispersal of the Precambrian supercontinents.

Pan-African nappe system in southwest Nigeria: the Ife-Ilesha schist belt

This paper presents new petrostructural data and a detailed geological map of the Ife-Ilesha area, a classical schist belt in southwest Nigeria. The overall syn-metamorphic flat-lying structures, recumbent folding and associated strong boudinage of the mafic and ultramafic rocks are the result of Pan-African syn-metamorphic stacking of thrust units above the Archæan basement. Supracrustal units are considered to be part of a former late Palæoproterozoic pericratonic cover, whereas mafic/ultramafic rocks may derive from a dismembered Proterozoic sill complex. It is proposed that this area is part of a Pan-African nappe system observed at mid-crustal levels. The northeastward tectonic vergence of units reconstructed from kinematic criteria is at variance with the southwestward motion of the nappes near the Pan-African suture 400 km to the west. Such stacking of units resulting from the same northeast-southwest compression at the scale of that part of Gondwana may correspond to the closure of a former basin floored by thinned Archæan crust with abundant magmatism of late Neoproterozoic age. Post-nappe upward doming of the slightly anatectic Archæan basement and upright folding of the already formed recumbent structures were linked to the initiation of the dextral strike-slip motion along the steep north-northeast-trending Ifewara mylonitic zone that compares well with similar shear zones of the Trans-Saharan Belt in the Tuareg Shield.