D1 Structures Research Articles

Ultrasound as a feasible method for the assessment of malrotation.

SummaryBackgroundIn malrotation the position of third portion of duodenum (D3) is always intramesenteric. Demonstration of normal retromesenteric-retroperitoneal position of D3 on ultrasound (US) can rule out malrotation. The aim of this study was to evaluate the feasibility of US in demonstrating the retroperitoneal D3.Material/MethodsAbdominal US study was done for various indications in 60 newborns and infants (mean age: 33 days [range: 4–100 days]; 56.7% male) by an expert pediatric radiologist. The position of D3 and its adjacent structures was evaluated in axial and longitudinal planes by linear and curved transducers.ResultsA normal retromesenteric-retroperitoneal D3 located between the superior mesenteric artery and the aorta was seen on US in all patients, including those with extensive gas in the bowel. The mean time of D3 observation was 47.8 s (10–180 s). Ultrasound was also capable of demonstrating D3 structure, diameter, content, adjacent structures, relative position of the superior mesenteric artery and vein.ConclusionsUltrasound is a simple, fast and highly accurate tool to confirm the retroperitoneal position of D3. Ultrasound can be used as a screening method for malrotation eliminating the need for unnecessary barium studies.

Superposed deformation and inherited structures in an ancient dilational step-over zone: Post-mortem of the Rengali Province, India

In the eastern Indian shield, a dextral strike-slip system juxtaposed the Archaean Singhbhum Province against the Proterozoic Eastern Ghats Belt at ∼490–470 Ma. Two WNW–ESE trending strands of the strike-slip system enclose a multiply deformed (D1 to D3) intervening domain called the Rengali Province, with D3 representing dextral shearing. In a granulite lens within the province, an early fabric (Sgr) was deformed by an amphibolite facies D1–D2 deformation continuum in the late Archaean time, forming cylindrical folds. In the surrounding quartzofeldspathic gneisses, quartzites and mica schists of the province, superimposition of syn-D3 shortening on D1-D2 folds generated complex non-cylindrical geometries; the granulites escaped D3 strain. Microstructures in the province-bounding shear zones confirm that D3 deformation was associated with mylonitization, dynamic recrystallization and greenschist facies metamorphism. In the quartzites, syn-D3 folds can be correlated with rotation of D1–D2 structures through the shortening zone of bounding dextral shears. Since the province-bounding shears form a step-over zone, the structural complexity within the Rengali Province arises from superposition of syn-D3 shortening structures on initially asympathetically oriented inherited cylindrical D1-D2 folds. Hydrous fluid channeling causing greenschist facies metamorphism and quartz vein emplacement accompanied D3 as the step-over zone was dilational in nature.

Folded Variscan thrusts in the Herrera Unit of the Iberian Range (NE Spain)

Abstract The Variscan structure of the Herrera unit (Iberian Chain, NE Spain) is characterized by a system of NNW–SSE-striking, east-verging, foreland-dipping thrusts, generated in a thin-skinned context, whose formation was favoured by the presence of two main detachment levels (Precambrian and Silurian shales). During the formation of the thrust system (first phase of deformation, D 1 ), the thrust sheets were deformed internally, mainly by asymmetrical folds with axial surface cleavage and east-verging thrusts; the normal evolution of the thrust system and the emplacement of an underlying thrust sheet resulted in progressive tilting and stacking, thus generating a foreland-dipping thrust system. These structures were folded and tilted by the emplacement of the Datos thrust (second phase of deformation, D 2 ), generating an associated deformation characterized by subvertical folds with axial surface cleavage, with slight east vergence. These structures can obliterate the previous D 1 structures in the sector near the Datos thrust. D 1 and D 2 structures have not been observed in the same outcrops, but the relationship between bedding and cleavage as well as cleavage relationship with other structures allows discrimination between the two cleavage sets. Based on the features of Palaeozoic rocks of the Iberian Range and the Iberian Massif, we support the idea that the Herrera unit belongs to the Cantabrian Zone.

Tectonic evolution and provenance of the Santa Bárbara Group, Camaquã Mines region, Rio Grande do Sul, Brazil

Cu- and Pb–Zn-hosting sedimentary units of the upper part of the Camaquã Basin (Ediacaran-Lower Ordovician) in the Dom Feliciano Belt of southernmost Brazil were formed during the late stages of the West Gondwana amalgamation and were controlled by large left-handed strike-slip shear zones. Integration of structural geology, stratigraphy and thermochronology allow recognition of five structural events (D1, Ediacaran-Lower Cambrian, through D5, Cretaceous). D1 structures are related to a N30E-trending, sinistral strike-slip shear zone that controlled the deposition of the mineralized sedimentary unit and its overlying units, the Santa Barbara and Guaritas Groups, respectively, in a transtensional setting. Based on U–Pb in situ methods, it is possible (a) to establish a maximum depositional age of 566 ± 6.9 Ma for the basal section of the Santa Barbara Group and, therefore, a minimum age of ca. 566 Ma for D1, and (b) to recognize two main zircon populations, Neoproterozoic and Paleoproterozoic, with sources from the eastern and southern parts of the Dom Feliciano Belt and reworking of older units of the Camaquã Basin. The D2 structures are mainly N-trending shear zones that developed after the deposition of the Guaritas Group during the Cambrian. During the Phanerozoic (post-Cambrian), the recognized structures were connected to compressional and extensional events that affected West Gondwana and the South America Platform. Thermochronological fission track analyses on apatite revealed four main age populations. The first three are interpreted to have formed during tectonic processes at the Gondwana Margin, namely the Famatinian and Gondwanides orogenies, and can be related to the D3 and D4 tectonic events in the basin. The last age population formed from thermal heating by the Upper Cretaceous continental flood basalts, which are represented in the area by volcanic intrusions, that were related to the separation of Africa and South America.

Stability-Indicating RP-HPLC Method for Simultaneous Determination of Metformin Hydrochloride and Sitagliptin Phosphate in Dosage Forms

A new stability-indicating high-performance liquid chromatographic method has been developed for simultaneous analysis of metformin hydrochloride (MET) and sitagliptin phosphate (SIT) in pharmaceutical dosage forms. Chromatographic separation was achieved on a C8 column. The mobile phase was methanol–water 45:55 % (v/v) containing 0.2 % (w/v) n-heptanesulfonic acid and 0.2 % (v/v) triethylamine; the pH was adjusted to 3.0 with orthophosphoric acid. The flow rate was 1 mL min−1 and the photodiode-array detection wavelength was 267 nm. The linear regression coefficients for metformin and sitagliptin were 0.9998 and 0.9996 in the concentration ranges 50–450, and 10–150 μg mL−1, respectively. The relative standard deviations for intra and inter-day precision were below 1.5 %. The drugs were subjected to a variety of stress conditions—acidic and basic hydrolysis, and oxidative, photolytic, neutral, and thermal degradation. The products obtained from photolytic degradation were similar to those from neutral hydrolytic degradation and different from produced by acidic and basic hydrolysis. The method resulted in detection of 15 degradation products (D1–D15); among these, the structures of D1, D3, D9, and D13 were identified. The respective mass balance for MET and SIT was found to be close to 97.60 and 99.12 %. The specificity of the method is suitable for a stability-indicating assay.

Structural control and geological significance of the Zn–Pb ores formed in the Benasque Pass area (Central Pyrenees) during the post-late Ordovician extensional event of the Gondwana margin

The Benasque Pass area (Central Pyrenees) is located in the eastern part of the Variscan Lys-Caillaouas Massif, where Cambro-Ordovician rocks of the Hesperian massif crop out. In the area several Zn–Pb deposits are located in Variscan structures. Lead isotopes indicate a late Ordovician–early Devonian model age for the deposits. In the region, an unconformity between pre-late Ordovician and late Ordovician rocks has been defined by several authors and has been identified in the study area. The first structures observed in the Benasque Pass area consist of a pre-Variscan cleavage, which only affects the pre-late Ordovician rocks. In the study area, the main structures correspond to two Variscan generations: (i) E–W trending, north-verging folds, which are associated with the main foliation S1 (D1); (ii) E–W trending upright folds and associated small south-directed thrusts (D2). D2 structures are the ones hosting the zinc–lead ore. In the Benasque Pass area, D1 and D2 Variscan structures have developed under low grade metamorphic conditions. Some faults observed in the north and the south of the study area may have Alpine movement. In the Benasque Pass area, the strongly silicified and brecciated zinc–lead ore is mainly developed in the D1 short limb of the Mina Peak Syncline, within which S1 foliation is intensely folded and cross-thrust by D2 structures. Taking into account their model age, all these zinc–lead deposits seem to be stratiform, stratabound or filling open spaces in origin and related to the pre-Variscan extension described for the Central Pyrenees. However, the zinc–lead ore is hosted in strongly silicified and brecciated Variscan structures.The δ34S isotopic composition of sulfides indicates that the metamorphism and deformation did not completely obliterate the original isotopic composition, suggesting that sulfur in the Benasque Pass has mainly come from the reduction of marine sulfate extracted from the rocks of the metasedimentary sequence. In the Benasque Pass area, the lead isotope ratios are homogeneous and have a pre-Variscan model age, which is also the age of the host rocks. In the case of the Benasque Pass, the deposits occurred in Variscan structures, making it impossible to recognize their original pre-Variscan characteristics indicated by lead isotopes model age.The correlation between the Pb isotope data for deposits from the Benasque Pass and Aran Valley, also located in the Central Pyrenees, and those for other deposits from the Southern European Gondwana is evident and the isotopic data set closely fits the two-stage Pb evolution model for Sardinia terrane. The coherence of the Pb isotope trends in all the deposits suggests that Pb was extracted at various times from sources with similar time-averaged U/Pb, Th/Pb and Th/U values, through a process of leaching of the basement rocks by large volumes of hydrothermal fluids. In the case of the Pyrenees (Central and Eastern), the lead and other metals present in the deposit were extracted by hydrothermal fluids from the upper crust rocks during the post-late Ordovician extensional event of the Gondwana margin.

Phanerozoic polyorogenic deformation in southern Jiuling Massif, northern South China block: Constraints from structural analysis and geochronology

The structure of the Jiuling Massif has been investigated in order to delineate the polyorogenic deformation and discuss its geodynamic evolution and orogenic mechanisms. Detailed structural analysis indicates that the D1 event is characterized by top-to-the NNW ductile shearing with pervasive foliation, and mineral and stretching lineation developed in the entire region. Compared with the D1 deformation, D2 structures are localized in ductile shear zones with subvertical foliation and subhorizontal E–W trending lineation, indicating a dextral ductile shearing. The D3 event, marked by folds and thrusts mainly in a brittle domain, modified the D1 structures by asymmetrical folds. The dominant D4 structures are gravitational folds and normal faults, corresponding to a later extension. Our new geochronological data suggest that the D1 event occurred between 465 and 380Ma with D2 dextral shearing at the end of this Early Paleozoic orogen, and the D3 event has been constrained at 245–215Ma. The final uplift of the Jiuling Massif by the D4 event can be correlated with the Late Mesozoic extension across the eastern South China block. Along with previous studies in the South China block, the structural pattern of the Jiuling Massif elucidates the influence of the Early Paleozoic and Early Mesozoic intracontinental belts triggered by repeated reactivation of the Jiangshan–Shaoxing Fault. Combined with deformation to the south, the Early Paleozoic belt shows a positive flower pattern, with opposing kinematics, rooted in the Jiangshan–Shaoxing Fault. During the Early Mesozoic, a general intracontinental belt was developed with uniform kinematics in both the Jiuling Massif and the Xuefengshan Belt, possibly resulted from the far-field effect of the Triassic NW-directed Paleo-Pacific subduction.

AB0014 Implication of VEGFR2 in systemic lupus erythematosus: A combined genetic and structural biological approach

BackgroundThe vascular endothelial growth factor receptor 2 (VEGFR2) gene polymorphisms have already been correlated with vascular diseases such as Coronary Heart Disease (CHD). In view of the premature atherosclerosis observed...

Insights into the structure and phylogeny of the 28S rRNA expansion segments D2 and D3 of the plant-infecting nematodes from the genus Ditylenchus (Nematoda: Anguinidae).

Recently, it has been shown that the stem nematode, Ditylenchus dipsaci (Nematoda: Anguinidae), is genetically more related to the gall-forming nematodes from genera Anguina , Heteroanguina , and Mesoanguina than to other members of the genus Ditylenchus . This finding was provided by molecular data written in the evolutionary variable, non-coding internal transcribed spacers (ITS1 and ITS2) of the ribosomal DNA (rDNA). In the current paper, we analyze the nucleotide sequences and predict the secondary structures of two expansion segments (D2, D3) of the 28S ribosomal RNA (rRNA)-coding gene for the plant-parasitic nematodes from the genus Ditylenchus and their related anguinids. In general, the expansion segment D2 appeared to be more variable than the segment D3 illustrating their different evolutionary constraints. Comparative analysis of the aligned sequences and predicted secondary structures revealed similar trend showing the tight relationships between the stem nematodes ( D. dipsaci , D. gigas , D. weischeri ) and gall-forming nematodes from the subfamily Anguininae. Phylogeny reconstructions disjoined the family Anguinidae into two monophyletic clusters (Clade 1 and 2). Clade 1 constitutes the stem nematodes ( D. dipsaci , D. gigas , etc) and gall-forming nematodes from the genera Anguina , Heteroanguina , Subanguina and Mesoanguina , while clade 2 includes other Ditylenchus species like D. destructor and D. halictus . Collectively, deciphering the exact phylogenetic relationships within the family Anguinidae (Nematoda: Tylenchida) with respect to our results should provide a framework for a taxonomic revision in order to reflect biological history of these nematodes. In addition, we provide novel molecular data, which may be exploited in diagnostic tools for phytosanitary control of these economically important plant parasites.

Effects of the Protein Environment on the Spectral Properties of Tryptophan Radicals in Pseudomonas aeruginosa Azurin

Many biological electron-transfer reactions involve short-lived tryptophan radicals as key reactive intermediates. While these species are difficult to investigate, the recent photogeneration of a long-lived neutral tryptophan radical in two Pseudomonas aeruginosa azurin mutants (Az48W and ReAz108W) made it possible to characterize the electronic, vibrational, and magnetic properties of such species and their sensitivity to the molecular environment. Indeed, in Az48W the radical is embedded in the hydrophobic core while, in ReAz108W it is solvent-exposed. Here we use density functional theory and multiconfigurational perturbation theory to construct quantum-mechanics/molecular-mechanics models of Az48W(•) and ReAz108W(•) capable of reproducing specific features of their observed UV-vis, resonance Raman, and electron paramagnetic resonance spectra. The results show that the models can correctly replicate the spectral changes imposed by the two contrasting hydrophobic and hydrophilic environments. Most importantly, the same models can be employed to disentangle the molecular-level interactions responsible for such changes. It is found that the control of the hydrogen bonding between the tryptophan radical and a single specific surface water molecule in ReAz108W(•) represents an effective means of spectral modulation. Similarly, a specific electrostatic interaction between the radical moiety and a Val residue is found to control the Az48W(•) excitation energy. These modulations appear to be mediated by the increase in nitrogen negative charge (and consequent increase in hydrogen bonding) of the spectroscopic D2 state with respect to the D0 state of the chromophore. Finally, the same protein models are used to predict the relaxed Az48W(•) and ReAz108W(•) D2 structures, showing that the effect of the environment on the corresponding fluorescence maxima must parallel that of D0 absorption spectra.

Crystallization and preliminary X-ray diffraction analysis of three recombinant mutants of Vaccinia virus uracil DNA glycosylase.

Amino-acid residues located at a highly flexible area in the uracil DNA glycosylase of Vaccinia virus were mutated. In the crystal structure of wild-type D4 these residues lie at the dimer interface. Specifically, three mutants were generated: (i) residue Arg167 was replaced with an alanine (R167AD4), (ii) residues Glu171, Ser172 and Pro173 were substituted with three glycine residues (3GD4) and (iii) residues Glu171 and Ser172 were deleted (Δ171-172D4). Mutant proteins were expressed, purified and crystallized in order to investigate the effects of these mutations on the structure of the protein.

Geometry and kinematics of the late Proterozoic Angavo Shear Zone, Central Madagascar: Implications for Gondwana Assembly

This paper documents the 20 to 60km wide N–S trending Angavo Shear Zone (ASZ) in central Madagascar and its tectonic implications by examining its structural styles, kinematics and geometry. Our study indicates that the ASZ is characterized by at least two ductile Late Proterozoic deformation events (D1 and D2) followed by a brittle neotectonic deformation (D3). The early D1 event produced a regionally extensive S1 foliation, stretching/flattening mineral lineation L1 and symmetrical structural fabrics such as recumbent and isoclinal intra-folial folds (F1), implying a flattening deformation. D1 deformational fabrics are locally overprinted by D2 structures. D2 is characterized by a penetrative S2 foliation, shallow south plunging L2 lineation, asymmetric and sheath folds (F2) consistent with a right lateral sense of movement exhibited by delta- and sigma-type porphyroclast systems and asymmetric boudinage fabrics. D2 represents a non-coaxial flow regime formed in a dextral west over east shear zone during a partitioned transpression in response to east–west-directed compression during the assembly of Gondwana. A close resemblance with the Achankovil shear zone in India is noticed; however the continuation of the ASZ in Africa is uncertain.

Resolving Resolvins

In this issue of Chemistry & Biology, Dalli and colleagues report the chemical structures of resolvin D3 (RvD3) and aspirin-triggered RvD3, derived from the ω3-fatty acid docosahexaenoic acid. These compounds have a specific temporal appearance within inflammation resolution and display anti-inflammatory and proresolving properties. Together, the results will help design new resolvin mimetics, potential resolution agonists with anti-inflammatory properties.

Structural, petrological and U–Pb SHRIMP geochronological study of the western Beaverlodge domain: Implications for crustal architecture, multi-stage orogenesis and the extent of the Taltson orogen in the SW Rae craton, Canadian Shield

The Beaverlodge domain is a polydeformed Precambrian terrane in the southwestern Rae craton whose rocks variably record the effects of Archean tectonism and four major Paleoproterozoic tectonic events: the 2.5–2.3Ga Arrowsmith orogeny, the 1.99–1.93Ga Taltson orogeny, the ca. 1.90Ga Snowbird orogeny and the ca. 1.87–1.80Ga Hudsonian orogeny. Structural–metamorphic analysis and in situ U–Pb SHRIMP zircon and monazite geochronology reported herein demonstrate that this domain consists of two main structural levels variably exposed due to complex interference folding: a lower level comprising mainly high-grade Archean (ca. 3.0 and 2.7–2.6Ga) metaplutonic and metasedimentary gneisses and a higher level comprising mainly ca. 2.33 to <2.17Ga supracrustal rocks of the Murmac Bay Group at more variable metamorphic grade. Whereas the older package underwent thermal and/or metamorphic events in the Archean (ca. 2.57Ga) and early Paleoproterozoic (ca. 2.34Ga; Arrowsmith orogeny), rocks at higher structural levels bear no record of these events, recording only younger (1.94–1.90Ga) metamorphism interpreted to reflect two further stages of orogenesis. The first stage, correlated with Taltson orogeny, involved tight to isoclinal folding (D1/2) that led to development of the composite ESE-trending (S0/S1/S2) transposition foliation followed by more open folding (D3). The absence of Taltson-age plutonic rocks, except for low-volume crustal melts, suggests that this cycle was driven by crustal thickening, consistent with a clockwise P–T–t path derived for one sample. The high degree of strain along the contact between Archean rocks and the Murmac Bay Group, along with local structural discordance, indicates some degree of translation of cover rocks over basement during this stage. Pelitic rocks at higher structural levels (low- to medium-grade zone) underwent prograde metamorphism to middle amphibolite facies whereas rocks at deeper structural levels (high-grade zone) attained upper amphibolite facies conditions. Monazite data bracket prograde metamorphism (and related garnet growth) between 1939±6Ma and 1934±5Ma. The second stage, dated most precisely at 1906±7Ma, involved refolding of D1 to D3 structures about NE-trending axes (F4) and coeval dextral shearing and is correlated with Snowbird orogenesis. Rocks of the low- to medium-grade zone were held at roughly the same crustal level whereas rocks in the high-grade zone were uplifted via dextral–oblique displacement along domain-bounding shear zones, instigating decompression (garnet to cordierite) reactions. This study demonstrates that after <2.17Ga deposition of the upper Murmac Bay Group, rocks along the entire west-southwestern Rae margin, from the Northwest Territories/northern Alberta to the Snowbird tectonic zone, were affected by Taltson (1940–1930Ma) orogenesis. The Taltson tectono-metamorphic cycle then appears to have transitioned, as rocks underwent further shortening and uplift in a dextral transpressive regime, into Snowbird tectonism at ca. 1910–1900Ma. Snowbird orogenesis is therefore best viewed as part of a semi-continuous 1940–1900Ma cycle of tectonic burial and exhumation, with its inception at ca. 1910Ma triggered by a change in boundary conditions, as yet not fully understood, but consistent with arrival of the Hearne craton proposed by others. While the Beaverlodge domain has many features in common with the Tantato domain, future work needs to explore why rocks in the Tantato domain lack evidence for Arrowsmith orogeny and failed to record the cycle of 1.94–1.93Ga tectonic burial.

Specific Inhibition of Caspase-3 by a Competitive DARPin: Molecular Mimicry between Native and Designed Inhibitors

Dysregulation of apoptosis is associated with several human diseases. The main apoptotic mediators are caspases, which propagate death signals to downstream targets. Executioner caspase-3 is responsible for the majority of cleavage events and its therapeutic potential is of high interest with to date several available active site peptide inhibitors. These molecules inhibit caspase-3, but also homologous caspases. Here, we describe caspase-3 specific inhibitors D3.4 and D3.8, which have been selected from a library of designed ankyrin repeat proteins (DARPins). The crystal structures of D3.4 and mutants thereof show how high specificity and inhibition is achieved. They also show similarities in the binding mode with that of the natural caspase inhibitor XIAP (X-linked inhibitor of apoptosis). The kinetic data reveal a competitive inhibition mechanism. D3.4 is specific for caspase-3 and does not bind the highly homologous caspase-7. D3.4 therefore is an excellent tool to define the precise role of caspase-3 in the various apoptotic pathways.

Contrasting exhumation P–T paths followed by high-P rocks in the northern Caribbean subduction–accretionary complex: Insights from the structural geology, microtextures and equilibrium assemblage diagrams

The Río San Juan metamorphic complex exposes a segment of a high-pressure subduction–accretionary complex built during convergence between the Caribbean island arc and the North America continental margin. It is composed of accreted arc- and oceanic-derived metaigneous rocks, serpentinized peridotites and minor metasediments forming a structural pile. Combined structural geology, microtextural relations, multi-equilibrium calculations and thermodynamical modelling, together with published isotopic ages, allow reconstructing the metamorphic P–T–t paths of each nappe/unit and their links to the structural evolution. In all units of the complex, three major stages (M1 to M3) in the tectonothermal evolution have been distinguished. The M1 stage corresponds to the prograde evolution towards the pressure-peak of metamorphism under blueschist or eclogitic-facies conditions. The M2 stage is related to the main retrogressive event and is characterized by the S2–L2 fabric development in all lithologies and at all scales. The M3 stage represents continuous exhumation from ductile to ductile–brittle deformation regimes. However, the shape of the retrograde P–T path, the age of the exhumation-related D2 structures and the tectonic significance of D2 deformation are different in each structural unit.In the upper structural levels of the Jagua Clara serpentinitic-matrix mélange, the counter-clockwise P–T path of the eclogite blocks is typical of rocks exhumed in the early stages of intra-oceanic subduction zones. The clockwise P–T path obtained for the lower Cuaba unit is characterized by a strong isothermal decompression from the garnet-epidote amphibolite and eclogite-facies pressure-peak. This P–T evolution can be explained by rapid exhumation caused by extensional tectonics, in relation to a major modification of convergence conditions across the subduction zone. The P–T path also explains local syn-M2 partial melting processes, because it crosses the wet solidus for IAT mafic compositions. The P–T path obtained for the high-P Guineal Schists, with exhumation trajectory following the burial trajectory, can be related to exhumation during active subduction. This exhumation was most likely driven by a combination of underthrusting of tectonic units and erosion processes.Available geochronological data and T–t/P–t estimates reveal a Late Campanian to Maastrichtian retrograde M2 metamorphism in the lower structural units of the complex during a consistent D2 top-to-the-NE/ENE tectonic transport. A similar tectonic transport has also been recognized in the metasedimentary nappes of the Samaná complex during Eocene to earliest Miocene. These relations indicate a northeastward progradation of deformation during the successive tectonic incorporation of arc, oceanic and continental-derived terrains to the developing Caribbean subduction–accretionary complex.

Structural setting of gold deposits in the Oudalan-Gorouol volcano-sedimentary belt east of the Markoye Shear Zone, West African Craton

The Oudalan-Gorouol volcano-sedimentary belt (OGB) of Burkina Faso and Niger hosts meta-volcanic and metasedimentary sequences of the Birimian Supergroup that were folded and deformed during emplacement of the Dori Batholith (D1−x), the Tangaean Event (D1) and the Eburnean Orogeny (D2).The emplacement of the Dori Batholith accompanied aureole deformation (D1−x) and the development of proto-mylonite, migmatite, gneiss and schist on the northern margin of the batholith. Contact metamorphic grade reached granulite facies with partial melting of the supracrustal sequences. Emplacement of the Dori Batholith was succeeded by emplacement of monzonite dykes and sills through the OGB.The Tangaean Event (D1) accompanied formation of (a) the Saoga Branch of the Markoye Shear Zone (MSZ), (b) the Mukosi and Billiata mylonite zones that are hosted in the MSZ, (c) the Afu Branch of the Kargouna Shear Zone Complex (KSZC), and (d) northwest-trending thrust-folds (F1) that crosscut the OGB and coalesce with the MSZ. Metamorphic grade attained amphibolite facies in mylonite or proto-mylonite zones in the Saoga and Afu branches. D1 was succeeded by emplacement of alkali-granite plutons of the Dolbel Batholith.The Eburnean Orogeny, D2, accompanied formation of (a) the Korizéna Branch of the MSZ, (b) the Waho Branch of the KSZC, and (c) northeast–trending shear-faults that crosscut the OGB. D2 is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C. Metamorphic grade attained greenschist facies during D2 with development of the mineral assemblage quartz–chlorite–muscovite±actinolite. D2 was succeeded by emplacement of northwest-trending gabbro and dolerite dykes.The OGB hosts structurally-controlled gold deposits that are sited along five metallogenic corridors and include the Essakane, Tin–Fal, Bom Kodjelé, Kossa and Tassiri Trends. Gold mineralisation is preferentially located where northeast-trending faults and shears crosscut northwest-trending thrust-folds, or where northwest-trending thrust-folds coalesce with north–northeast trending shears. An intimate relationship thus exists between D1 and D2 structures and gold mineralisation in the OGB. Gold in sheeted-stockwork veins is hosted in competent rocks units including conglomerate beds, greywacke, quartzite, monzonite dykes, pyroxenite–gabbro sills and D1 buck quartz veins. Gold in fine veinlets may also be hosted in massive shale units.

High-grade iron ore at Windarling, Yilgarn Craton: a product of syn-orogenic deformation, hypogene hydrothermal alteration and supergene modification in an Archean BIF-basalt lithostratigraphy

Banded iron formation (BIF)-hosted iron ore deposits in the Windarling Range are located in the lower greenstone succession of the Marda–Diemals greenstone belt, Southern Cross domain, Yilgarn Craton and constitute a total hematite–martite–goethite ore resource of minimum 52 Mt at 60 wt.% Fe (0.07 P). Banded iron formation is interlayered with high-Mg basalts at Windarling and precipitated during episodes of volcanic quiescence. Trace element content and the rare earth element (REE) ratios Y/Ho (42 to 45), Sm/Yb (1.5), together with positive La and Gd anomalies in ‘least-altered’ hematite–magnetite–metachert–BIF indicate the precipitation from Archean seawater that was fertilised by hydrothermal vent fluids with a basaltic HREE-Y signature. Hypogene iron ore in sub-greenschist facies metamorphosed BIF formed during three distinct stages: ore stage 1 was a syn- to post-metamorphic, syn-D1, Fe–Ca–Mg–Ni–Co–P–REE metasomatism that produced local Ni–REE-rich Fe–dolomite–magnetite alteration in BIF. Hydrothermal alteration was induced by hot fluid flow controlled by brittle–ductile reactivation of BIF-basalt margins and crosscutting D1 faults. The Ni–Co-rich content of dolomite and a shift in REE ratios in carbonate-altered BIF towards Archean mafic rock signature (Y/Ho to 31 to 40, Sm/Yb to 1 to 2 and Gd/Gd* to 1.2 to 1.4) suggest that high-Mg basalts in the Windarling Range were the primary source of introduced metals. During ore stage 2, a syn-deformational and likely acidic and oxidised fluid flow along BIF-basalt margins and within D1 faults leached carbonate and precipitated lepidoblastic and anhedral/granoblastic hematite. High-grade magnetite–hematite ore is formed during this stage. Ore stage 3 hydrothermal specular hematite (spcH)–Fe–dolomite–quartz alteration was controlled by a late-orogenic, brittle, compressional/transpressional stage (D4; the regional-scale shear-zone-related D3 is not preserved in Windarling). This minor event remobilised iron oxides, carbonate and quartz to form veins and breccia but did not generate significant volumes of iron ore. Ore stage 4 involved Mesozoic(?) to recent supergene oxidation and hydration in a weathering environment reaching down to depths of ∼100 to maximum 200 m below surface. Supergene ore formation involved goethite replacement of dolomite and quartz as well as martitisation. Important ‘ground preparation’ for supergene modification and upgrade were mainly the formation of steep D1 to D4 structures, steep BIF/basalt margins and particularly the syn-D1 to syn-D2 carbonate alteration of BIF that is most susceptible to supergene dissolution. The Windarling deposits are structurally controlled, supergene-modified hydrothermal iron ore systems that share comparable physical, chemical and ore-forming characteristics to other iron ore deposits in the Yilgarn Craton (e.g. Koolyanobbing, Beebyn in the Weld Range, Mt. Gibson). However, the remarkable variety in pre-, syn- and post-deformational ore textures (relative to D1 and D2) has not been described elsewhere in the Yilgarn and are similar to the ore deposits in high-strain zones, such as of Brazil (Quadrilatero Ferrifero or Iron Quadrangle) and Nigeria. The overall similarity of alteration stages, i.e. the sequence of hydrothermal carbonate introduction and hypogene leaching, with other greenstone belt-hosted iron ore deposits supports the interpretation that syn-orogenic BIF alteration and upgrade was crucial in the formation of hypogene–supergene iron ore deposits in the Yilgarn Craton and possibly in other Archean/Paleoproterozoic greenstone belt settings worldwide.

The Dalradian rocks of the Highland Border region of Scotland

The Highland Border region is defined here by the outcrop of the Southern Highland Group that lies north-west of the Highland Boundary Fault and runs from Stonehaven south-west to the Isle of Bute, and thence to the Campbeltown peninsula. The late-Neoproterozoic to early-Ordovician rocks of the Dalradian Supergroup in this region form a stratigraphical and structural entity that encompasses the >300 km-long surface traces of both the Tay Nappe (D1–D2) and the Highland Border Downbend (D4). The least deformed and metamorphosed Southern Highland Group rocks occur along the south-east margin of the region and are in continuity with the younger, newly recognized Trossachs Group, which has therefore been assigned to the Dalradian Supergroup. The earliest (D1) structures in the Dalradian rocks are dominant close to the Highland Boundary Fault but are successively overprinted northwards by D2, D3 and D4 structures and fabrics, here represented by a series of zones near-parallel to the Highland Boundary. Regional metamorphism increases progressively away from the Highland Boundary Fault and ranges from greenschist to upper amphibolite facies (sillimanite zone). Three fundamental features of deformed and regionally metamorphosed rocks worldwide were first recognized in this area: the ‘stretching lineation’ by Clough in 1897; the concept of regional metamorphic ‘Barrovian zones’ by Barrow in 1901; and the ‘facing direction’ of folds by Shackleton in 1958. The Highland Border region has acquired international recognition for research undertaken into the origin and mode of emplacement of the Tay Nappe, one of the largest recumbent folds known worldwide. This structure provides a framework for linking together most of the GCR sites in this paper.

The Dalradian rocks of the north-east Grampian Highlands of Scotland

Abstract The north-east Grampian Highlands, as described here, are bounded to the north-west by the Grampian Group outcrop of the northern Grampian Highlands and to the south by the Southern Highland Group outcrop in the Highland Border region. The Dalradian succession therefore encompasses the whole of the Appin and Argyll groups, but also includes an extensive outlier of Southern Highland Group strata in the north of the region. The succession includes shallow-marine sequences, glacigenic deposits at two stratigraphical levels, the earliest evidence for volcanism in the Dalradian, a later major development of basaltic and picritic sub-marine lavas, and thick turbiditic sequences. In the south, the Grampian–Appin group boundary is a high-strain zone, with no obvious dislocation or stratigraphical excision, which was formerly termed the Boundary Slide. Shear-zones at higher structural levels are associated with pre-tectonic granites, such as the Ben Vuirich Granite, which have been dated at c. 600 Ma and hence place limits on the timing of sedimentation, deformation and metamorphism. The region is divided from north to south by a major zone of shearing and dislocation with associated igneous intrusions, termed the Portsoy Lineament. To the west of the lineament, the stratigraphy is more-or-less continuous along strike with that of the central Grampian Highlands. D1, D2 and D3 structures extend from the Tummel Steep Belt north-eastwards throughout this area. The stratigraphical succession is broadly continuous across the Portsoy Lineament but to the east, in the Buchan Block, correlations are more tenuous and do not extend below subgroup level. High-grade migmatitic paragneisses were once interpreted as pre-Dalradian basement but they are now assigned to the Crinan Subgroup, within the Dalradian succession. Within the Buchan Block the outcrop pattern is controlled by two broad, open, post-metamorphic folds, the Turriff Syncline and the Buchan Anticline. The Buchan Block is the international type area for the high-temperature/low-pressure Buchan-type regional metamorphism. To the south and west, this passes into higher pressure Barrovian-type metamorphism. South of Deeside, metamorphic conditions reached 820 °C and over 8 kbar, well into granulite facies and the highest recorded in the Grampian Terrane. The detailed relationship between the high heat-flow and the emplacement of large bodies of basic and silicic magma is a matter of ongoing research. Plutons of the north-east Grampian Basic Suite, emplaced at c. 474–470 Ma, during or shortly after the peak of metamorphism and the D3 deformation, provide key evidence for the timing of the Grampian orogenic event.