Cylindrical Folds Research Articles

A graphical method and workflow for the generation of structure contours for horizontal cylindrical folds

A graphical method developed for the construction of structure contours for inclined planar surfaces has been extended to curved or folded surfaces with cylindrical geometries and horizontal axes. These structure contours can be used to constrain the outcrop trace of a folded contact on a geological map. The extended method requires, as a minimum, a field of orientation data and the map position of a single elevation on the contact under investigation. The method utilises orientation data collected on and around a partially mapped trace of a folded contact to constrain the outcrop trace throughout a geological map. The method uses a vertical cross-section that is parallel to the profile plane of any folds present. Crest, trough and hinge points identified in the cross-section can be projected on to the geological map in their correct positions and elevations. Similarly, structure contours on fold axial surfaces can be projected on to the geological map and the contours used to locate the axial traces of cylindrical folds with horizontal axes.

Constructive development and design justification of the protective shell of a nuclear reactor made of reinforced concrete

Introduction. This paper provides materials justifying the introduction of a new constructive solution for the reinforced concrete protective shell of a nuclear reactor in a prefabricated and monolithic design.
 
 Aim. Among the tasks that were set during the development of the constructive solution, the main one was to ensure the work of reinforced concrete for compression under all types of loading and the perception of tensile forces by ropes that are in a free state, available for maintenance and operation.
 
 Materials and methods. The calculations were performed by the finite element method using a software package MicroFe-StaDiCon for calculation of the spatial structures for strength, stability and vibrations.
 
 Results. A fundamentally new constructive solution has been developed for the protective shell of the nuclear reactor of the NPP, consisting of reinforced concrete elements in the form of cylindrical folds with a bulge directed towards possible external and internal force emergency effects, including the explosion of the reactor. Variants of protective shells have been developed with the elaboration of fundamental technical solutions for unified folded elements made of reinforced concrete with the possibility of their monolithic and prefabricated manufacture. A scheme of open arrangement and tensioning of cable bundles with tension transfer to pre-fabricated structures of the inner and outer parts of the protective shell is proposed.
 
 Conclusions. This design solution provides compressive forces in reinforced concrete of the folds of the inner and outer parts of the protective shell from the load during loading, which prevents the formation of cracks in them. The tensile forces in the shell are perceived by the prestressed reinforcement located inside its structure, free for maintenance and control. In the process of work, fundamental solutions have been developed for the structural nodal joints of prefabricated folded reinforced concrete elements, technological holes in the shell structure and the implementation of prestressing in it. A comparative technical and economic analysis of the proposed and existing inner protective shell showed the possibility of reducing concrete consumption by 1.5–2 times, non-stressed reinforcement by 3–4 times, construction time by 4 times.

Forearc tectonics and volcanism during the Devonian–Carboniferous evolution of the North Patagonian segment, southern Chile (41,3°S)

Late Paleozoic to early Mesozoic subduction complexes formed during the evolution of southwestern Gondwana and extensively crop out along the Chilean continental margin. Recent findings in northern Patagonia (40°–43°S) revealed that accretionary processes were active since the Devonian when enhanced lithosphere stretching in the forearc led to the formation of Chaitenia island arc. The extension in the crust consecutively developed a backarc basin, which culminated during a compressive episode that re-amalgamated the Chaitenia island arc with the margin. This episode produced intermediate grade metamorphism in the sedimentary rocks that were formed throughout the extension. To constrain the tectonic evolution of these processes, we combined petrology, structural analysis, whole-rock geochemical, and whole-rock isotopic tracing (Sr-Nd-Pb) data along with thermodynamic modelling. Two petro-tectonic domains are here defined. The Western Coastal Range Domain is composed of Carboniferous to Permian metapsammopelitic rocks, which are mainly schists with a metasedimentary Carboniferous protolith exhibiting a penetrative northeast to southwest dipping main foliation associated with basal accretion. The Eastern Coastal Range Domain is comprised by garnet micaschists, metabasalts, metarhyolites, and metasandstones. This unit is folded by three ductile structures: The first is related to rootless isoclinal folds, the second is associated with kilometric scale west-verging tight folds, and the third is associated with west-verging cylindrical folds. The volcanic rocks of this domain are comprised by middle Devonian alkaline metarhyolites and metabasalts with enriched-MORB and normal-MORB affinities. Trace element composition suggests that the metabasalts formed through shallow melting in an extensional setting over a supra-subduction zone. Nd and Pb isotope data point to a mantle source change for the basaltic melts from an EM1-like to a DM-like and are interpreted to reflect the embryonic to mature evolution of the early Devonian to Carboniferous backarc system. The calculated P–T evolution of the garnet micaschists follows: 1) a clockwise IP–IT prograde Barrovian path, 2) an isobaric thermal increase at ∼7 kbar and 540°C, and 3) an adiabatic decompression. Finally, after the metamorphism, these rocks were uplifted by thrusting processes that probably occurred during the late Permian.

Dextral transpressional shearing and strike-slip partitioning developments in the Central Myanmar Basin during the collision between the India Plate and West Myanmar Block

Central Myanmar Basin (CMB) lies between the two major strike-slip faults: Sagaing Fault to the east and Kabaw Fault to the west. Central Volcanic Line of Myanmar emplaced en-echelon array of P-shears along the fault zone, which was active dextral as surrounding major faults at a low angle about 15° to the shear zone boundary. CMB was developed as strike-slip partitioned transpression model as proposed in this study. The transprsession tectonic is common with oblique convergence subduction as well as collision of India Plate to West Myanmar Block, especially effects on the CMB. Structural evidence are occurred as en-echelon folding and fracturing by satellite photos, field observation and 3D strain ellipsoid construction showing plane strain by pure shear upon ideal strike-slip with simple shear. In this study, two types of transpression distinguished as homogeneous and strike-slip partitioning which are developed within the frame of the strike-slip fault with progressive deformation. Under the condition of the strike-slip partitioned transpression, strain partitioning is distinctly occurred together with progressive deformation and reactivation of pre-existing structures such as cylindrical fold to double plunging fold, normal fault to oblique slip fault and positive flower structure. Deformation process related to the India Plate movement deduced the period of Late Miocene and Pliocene-Pleistocene based on the structural analysis in Rakhine Coastal region, western Myanmar. During the period between the Late Miocene to Pliocene-Pleistocene, pre-existing ophiolite zone in the Indo-Myanmar Ranges (IMR) was split up different zones by the Sagaing Fault displacement, accompanied to the West Myanmar Block movement with India Plate subduction. Accordance with the Sagaing Fault displacement and group of mud volcanoes shifting, the CMB moved northward about 450km with displacement rate 5–7cm per annum by the 45–50°convergent angle of India Plate collision to Eurasia Plate. Transpression deformation of northward compression was developed in the CMB, simultaneously on the other side transtension as pull-apart basin was formed by Andaman Sea opening at the south on the Sagaing Fault. During the Miocene time, collision of India Plate to Eurasia Plate was principal and caused the deformation at northern border the India, in which India Plate moved both in northwards and rotated anti-clockwise, whereas West Myanmar Block together with Sibumasu Block rotated clockwise becoming final closure of the northeasternmost Assam and Myanmar regions. During the Oligocene time, deposition of the shallow marine Barail formation in the Bengal Basin and shallow marine to continental shelf sequences in the CMB started as twin trough. This study provides the transpression deformation in the CMB and related regions during syn- and post-collision of India Plate to West Myanmar Block with position and kinematic structural interpretation.

Chapter 3 Thrusts, extensional faults and fold patterns of the major units

Abstract This chapter is concerned with the main faults and folds within the Southeastern Oman Mountains based on available literature. The main, best and most widely exposed thrusts are those related to the SW-directed late Cretaceous obduction of the allochthonous nappes onto the Arabian platform and margin. These thrusts are related to obduction of rocks, which had formed hundreds of kilometres offshore Oman. The thrusts were active from the Cenomanian to the Campanian. Obduction-related thrusts and folds are spectacularly exposed within the rocks of the Arabian platform in the eastern part of the Saih Hatat Dome, including large-scale recumbent cylindrical folds and sheath folds. At least six fold sets can be studied in the Southeastern Oman Mountains. At least two of them had formed prior to obduction and are exposed in the Pre-Permian formations of the Jabal Akhdar Dome. At least three fold sets formed in the course of obduction, while at least one fold set is postobductional in age. Besides the compressional structures, the Oman Mountains expose major post-obductional extensional faults, mostly at the margins of the Jabal Akhdar and Saih Hatat domes. The throw of these faults amounts to a few to several kilometres. Finally, this chapter provides an overview of the enigmatic Batinah Mélange which consists of slivers of Hawasina rocks, resting (unusually) structurally above the Semail Ophiolite.

GMDE: Extracting quantitative information from geologic maps

Abstract GMDE is a program, available on the desktop for Apple Macintosh, Microsoft Windows, and Linux platforms and in a mobile version for iOS, that enables geologists to extract quantitative structural information from geologic maps and satellite images. The program facilitates the digitizing of strikes and dips or calculating them from three-point problems, calculation of stratigraphic map thickness, determination of piercing points on faults, and the construction of down-plunge projections and vertical cross sections with projected apparent dips, contacts, and cylindrical folds. The program also enables the automatic plotting of planar contacts across topography based on orientation calculated from three clicked points, which can be carried out in the field for immediate hypothesis testing. Error propagation is built into many of the calculations. Maps and satellite images require no projection or datum information, just four points with known latitude and longitude information. Alternatively, the user can enter the map or image in MBTiles format. Users can easily extract X-Y-Z data for any clicked or calculated point or polygon, enabling them to make their own calculations.

Diagrama tangente: útil recurso do programa Ester 2.1 para projeção estereográfica em Geologia

Studies and applied works of structural analysis depend on specialized softwares and resources for 3D modeling. This article presents the results of a research that aimed to evaluate the effectiveness of version 2.1 of the Ester stereographic projection system for Structural Geology. The evaluation of the software involved tests with structural data of different geological contexts, submitted to graphic treatment in packages such as Stereonet, Stereonet9, QuickPlot, Dips, OpenStereo and other softwares accessible at low cost. The study privileged the truly free (open) softwares. One advance was the inclusion of the Tangent Polar Diagram into the Ester package. The tool helps to differentiate, in folded regions, conical folds from cylindrical folds. In the comparative evaluation, it was observed that diagrams produced by Ester 2.1 are similar to those generated by other programs. The advantage relates to resources that are not available in the other softwares analyzed. It is concluded that, in addition to resources heretofore unavailable, the tests showed good functionality. The experience signals new directions in the search for educational alternatives for teaching-learning in Structural Geology.

Fracture characterization in sigmoidal folds: Insights from the Siah Kuh anticline, Zagros, Iran

Fieldwork and remote-sensing data from the Siah Kuh anticline, simply folded belt, Zagros, Iran indicate that specific structures and fracture systems formed during the development of its sigmoidal shape, and that conceptual fracture models developed for cylindrical folds are inadequate for the correct evaluation and development of hydrocarbon accumulations in this type of anticline. The sigmoidal shape of the Siah Kuh anticline was achieved in the Pliocene due to vertical axis rotations of an already existing anticline. These rotations promoted the development of (1) two systems of normal faults in the outer arcs of the sigmoidal shape, (2) a low-angle thrust, and (3) the north–south Danan anticline in the inner arc of its easternmost bend. The passive margin to syn-folding structures, typically observed in nearby cylindrical and periclinal anticlines, predated the development of the sigmoidal shape and were passively rotated into the segments of the anticline. The sigmoid-related structures are spatially, geometrically, and kinematically related to the bends of the anticline trend, hence they can be predicted and modeled in the subsurface. The sigmoid-related normal faults have a great potential to preserve porosity and promote localized high flow rates or early water breakthrough. However, if they cut through thin reservoir and seal units, sigmoid-related thrusts and normal faults might compromise lateral reservoir continuity and seal integrity. The results of this study can help in reducing risks and uncertainty in the evaluation and development of business opportunities in secondary sigmoidal anticlines within the Zagros or any other fold-thrust belt.

Tangled up in folds: tectonic significance of superimposed folding at the core of the Central Iberian curve (West Iberia)

ABSTRACTThe amalgamation of Pangea during the Carboniferous produced a winding mountain belt: the Variscan orogen of West Europe. In the Iberian Peninsula, this tortuous geometry is dominated by two major structures: the Cantabrian Orocline, to the north, and the Central Iberian curve (CIC) to the south. Here, we perform a detailed structural analysis of an area within the core of the CIC. This core was intensively deformed resulting in a corrugated superimposed folding pattern. We have identified three different phases of deformation that can be linked to regional Variscan deformation phases. The main collisional event produced upright to moderately inclined cylindrical folds with an associated axial planar cleavage. These folds were subsequently folded during extensional collapse, in which a second fold system with subhorizontal axes and an intense subhorizontal cleavage formed. Finally, during the formation of the Cantabrian Orocline, a third folding event refolded the two previous fold systems. This later phase formed upright open folds with fold axis trending 100° to 130°, a crenulation cleavage and brittle–ductile transcurrent conjugated shearing. Our results show that the first and last deformation phases are close to coaxial, which does not allow the CIC to be formed as a product of vertical axis rotations, i.e. an orocline. The origin of the curvature in Central Iberia, if a single process, had to be coeval or previous to the first deformation phase.

Quantification of the geometrical parameters of non-cylindrical folds

The geometrical parameters of natural folds are used by structural geologists to estimate finite strain and rheological properties of deformed rocks. The relation between geometry and rheology is well understood in cases of cylindrical folds, but is still limited for non-cylindrical folds, although the latter are frequent in nature. The sparsity of quantitative geometrical data of non-cylindrical folds can be explained by the small number of 3D exposures and by the lack of robust methods to quantify their geometrical parameters in 3D space. We present a new workflow, which can be used to quantify geometrical parameters of non-cylindrical folds. 3D fold geometry is described using fold wavelength, λ, arc-length, L, and amplitude, A. As most natural folds do not show ideal shapes, but are affected by various types of discontinuities, the new procedure is not fully automatic, but requires the manual selection of measuring profiles along which the geometrical parameters are constrained. The new workflow is tested using natural and experimentally produced non-cylindrical folds.The geometric parameters obtained can be used to improve our understanding of fold kinematics and fold mechanics and should assist the quantitative analysis of non-cylindrical folds present in gneiss and salt domes and in rocks containing reservoirs of hydrocarbons and minerals deposits.

Spore morphology of the representatives of the subfamily Ceratopteridoideae (J. Sm.) R.M. Tryon from the family Pteridaceae E.D.M. Kirchn. (Pteridophyta)

<p>Scanning electron microscopy (SEM) was used to perform a comparative study for four representatives of the subfamily <em>Ceratopteridoideae</em> (J. Sm.) R.M. Tryon from East Asia: <em>Ceratopteris thalictroides</em> Brongn., <em>C. pteridoides</em> (Hook.) Hieron., <em>Acrostichum aureum</em> Linn., and <em>A.</em> <em>speciosum </em>Willd. The analysis of the external morphology of the representatives of <em>Ceratopteridoideae</em> revealed a strong difference between <em>Ceratopteris</em> and <em>Acrostichum</em>.</p><p>The external morphology of spores of <em>Ceratopteris</em> and <em>Acrostichum</em> exhibited the features characterizing the family Pteridaceae as a whole: tetrahedral spores with a three-ray laesure, from triangular-roundish to roundish, distinct exosporium with a pronounced surface ornamentation and absence of perisporium, the exosporium surface varying from smooth and rough to that covered with large tubercles and roller-like bulges.</p><p>The external morphology of spores of <em>Acrostichum</em> is quite simple, although among other representatives of the family Pteridaceae,<em> </em>the<em> </em>spores of <em>Ceratopteris</em> have distinctive features: very large equatorial diameter (106–124 µm); spores are almost roundish; distinct cylindrical folds running parallel to the corners of the spore across its extensive distal surface.</p><p> </p>

Formation of dome and basin structures: Results from scaled experiments using non-linear rock analogues

Dome and basin folds are structures with circular or slightly elongate outcrop patterns, which can form during single- and polyphase deformation in various tectonic settings. We used power-law viscous rock analogues to simulate single-phase dome-and-basin folding of rocks undergoing dislocation creep. The viscosity ratio between a single competent layer and incompetent matrix was 5, and the stress exponent of both materials was 7. The samples underwent layer-parallel shortening under bulk pure constriction.Increasing initial layer thickness resulted in a decrease in the number of domes and basins and an increase in amplitude, A, arc-length, L, wavelength, λ, and layer thickness, Hf. Samples deformed incrementally show progressive development of domes and basins until a strain of eY=Z = −30% is attained. During the dome-and-basin formation the layer thickened permanently, while A, L, and λ increased. A dominant wavelength was not attained. The normalized amplitude (A/λ) increased almost linearly reaching a maximum of 0.12 at eY=Z = −30%. During the last increment of shortening (eY=Z = −30 to −40%) the domes and basins did not further grow, but were overprinted by a second generation of non-cylindrical folds. Most of the geometrical parameters of the previously formed domes and basins behaved stable or decreased during this phase. The normalized arc-length (L/Hf) of domes and basins is significantly higher than that of 2D cylindrical folds. For this reason, the normalized arc length can probably be used to identify domes and basins in the field, even if these structures are not fully exposed in 3D.

Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet.

The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.

The Archean BIF-hosted Lamego gold deposit, Rio das Velhas greenstone belt, Quadrilátero Ferrífero: Evidence for Cambrian structural modification of an Archean orogenic gold deposit

ABSTRACT The Lamego orogenic gold deposit (1.3 Mt measured resources at 7.26 g/t Au) is located at the south-western end of the 5 km-long Cuiaba–Lamego trend, Quadrilatero Ferrifero region, Brazil. Both Archean orogenic gold deposits are situated in the Rio das Velhas greenstone belt with the lithological succession at Lamego consisting of metamorphosed (greenschist facies) mafic volcanic rock, chert and banded iron formation (BIF), and carbonaceous and micaceous pelites. The Lamego fold, which controls the Lamego deposit, is the most visible structure related to the D1–D2 event, with a perimeter of about 4.8 km and a maximum width of 450 m. The fold is defined by the layering of the mafic unit with minor BIF and large exposures of carbonaceous and micaceous pelites. It is a rootless, reclined, isoclinal, cylindrical fold with an axial trace striking northwest–southeast dipping 20° to 30°. The hinge zone is thickened and the limbs are thinned, with the limbs dipping 20° to 30° to the SE. Orebodies consist of the Lamego BIF, where gold-mineralized zones are related to iron-rich bands, and associated silicification zones. Replacement-style mineralization is associated with sulfide bands; mainly pyrite, As-rich pyrite, and arsenopyrite. Two structural generations, G1 and G2, are recognized and encompass a set of structural elements. The G1 structural generation developed in a progressive deformation event and resulted in structures oriented from NE to SW and dipping to the SE. Structures pertaining to the G2 structural generation are oriented N–S dipping to the W. The four major high-grade gold orebodies are Carruagem, Queimada, Arco da Velha, and Cabeca de Pedra. Their gold grade shows a spheroidal pattern and a distribution that varies along the S1–2 foliation. These lenses represent the hinge zone of F2 reclined folds with the plunge of the orebodies controlled by the F2 fold axes. The lower-grade gold lenses are controlled by pinch and swell, and locally expressed quartz boudins developed during D1–D2. They have two orthogonal directions, one to the NW–SE and the other to the NE–SW, thereby defining chocolate-tablet style boudinage. Hydrothermal monazite grains in a mineralized mafic volcanic rock indicate that mineralization formed at 2730 ± 42 Ma (U–Pb SHRIMP). Younger monazite dated at 2387 ± 46 Ma, and xenotime dated at 518.5 ± 9 Ma suggest Siderian and Cambrian imprint in the Lamego deposit area. The Cambrian age reflects the late stages of the Brasiliano orogenic cycle, which is expressed in the Lamego deposit by the S3 crenulation cleavage (trend NS and dip steeply to the E). Importantly, the Cambrian structural modification is responsible for the present geometry of the Lamego orebodies, but is not associated with hydrothermal alteration; it has not introduced any new gold and also has not caused remobilization of the orebodies or ore minerals.

Common problems encountered in 3D mapping of geological contacts using high-resolution terrain and image data

An experiment has been carried out to find a reliable method to map 3D geological contacts using high-resolution Digital Elevation Models (DEMs) and pictures. Various airborne and ground-based photos, and a classical geological map, have been draped by several users on DEMs of the Scex Rouge Mountain (Vaud, Swiss Alps) producing several 3D textured models of the relief. On each of these photorealistic models, geological contacts were then drawn as polylines by hand. The locations of resulting polylines have been then compared. The draping procedure, actually the choice of pairs of control points used for the texturing step, appears to be the main source of discrepancies between the results of the different models. The subjectivity of users in drawing polylines is of lesser importance. We observed also that the widely accepted geological map of the area does not provide an accurate representation of the local geology in steep areas, especially near-vertical rock faces where this effect is marked. Even if high quality and high-resolution data are becoming increasingly more available, a robust way to map geological structures directly in 3D is still lacking. In addition, there is a crucial lack of tools, with editing capabilities able to handle large point cloud datasets and gigapixel images. Finally, the methodology described in this Technical Note is intended to be useful for modelling simple geological structures, such as cylindrical folds, in a complex environment comprising near-vertical rock faces.

Fold interaction and wavelength selection in 3D models of multilayer detachment folding

Many fold-and-thrust belts are dominated by folding and exhibit a fairly regular fold-spacing. Yet, in map-view, the aspect ratio of doubly-plunging anticlines varies considerably from very elongated, and sometimes slightly curved, cylindrical folds to nearly circular, dome-like structures. In addition, the fold spacing often varies significantly around an average value. So far, it remains unclear whether these features are consistent with a folding instability.Therefore, we here study the dynamics of multilayer detachment folding, process by which shortening can be accommodated in thin-skinned fold-and-thrust belts. We start by analysing the physics of this process by using both a semi-analytical thick plate theory and numerical simulations. Results show that several different folding modes occur, about half of which are affected by gravity and have a wavelength that depends on the background deformation rate. Non-dimensional expressions are derived that predict the dominant wavelength and growth rate of each of these folding modes and mechanical phase diagrams are presented that illustrate the applicability of each of the modes.Next, we perform 3D simulations and compare the results with those of 2D models and analytical theory. Both 2D and 3D numerical simulations have wavelengths that are in good agreement with the analytical predictions. In the high-resolution 3D simulations the lateral growth of folds is studied, in particular with respect to fold segment interactions and evolution of fold width–length aspect ratio.The numerical simulations show a number of similarities with the Fars region of the Zagros fold-and-thrust belt including a large range of fold aspect ratio and a normally distributed fold wavelength around a dominant one.

Regional flow perturbation folding within an exhumation channel: A case study from the Cycladic Blueschists

Kilometre-scale cylindrical folds and associated parasitic folds that trend at small angles to the transport lineation are analysed along a 100-km-long transport-normal segment of the Cycladic Blueschists in an attempt to reconstruct the 3D structural architecture within an exhumation channel. Reversals in the polarity of both fold vergence and the hinge/lineation obliquity occur in a flow-normal direction, defining transport-parallel culmination and depression surfaces that root downwards onto an underlying detachment. Fold patterns generated around culmination and depression surfaces support models of flow-perturbation folding where folds initiate at small angles or sub-parallel to transport in response to wrench-dominated differential shearing. Successive culmination and depression surfaces are separated from one another by along strike distances of ∼20 km, although atypical fold geometries developed in the flanks of major culmination and depressions follow their own patterns, revealing that smaller perturbations occur within the larger scheme. Major culminations are interpreted to reflect regions of surging flow marked by increased velocity during exhumation, whilst the opposite is true for depressions. This behaviour implies that on a regional scale, differential shear varies laterally in an irregular-sinusoidal manner defining areas of relative high and relative low displacement within the exhumation channel.

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.

The Crystal Structure of the Polycystic Kidney Disease Domain (PKD) from Clostridium Histolyticum Collagenase: Insight into the Role of the PKD in Collagenase

Clostridium histolyticum secretes multidomain collagenases ColG and ColH to cause extensive tissue destruction in the presence of calcium. ColG collagenase consists of the catalytic domain (s1), a polycystic kidney disease domain (PKD, s2), and two collagen-binding domains (CBD, s3a and s3b). Meanwhile, ColH collagenase consists of s1, two PKDs (s2a and s2b), and one CBD (s3). The PKD domain was first identified in the Polycystic Kidney Disease protein, polycystin-1. Its role in collagenolysis is unknown. The high resolution crystal structures of the calcium bound (holo) s2b (1.4 A resolution, Rfactor = 17.4%, Rfree = 19.3%) and two crystal forms of the calcium free (apo) s2 (Form I 1.6 A resolution, Rfactor = 18.9%, Rfree = 21.3%. Form II 1.4 A resolution, Rfactor = 18.7%, Rfree = 23.0%) have been determined. PKD adopts an immunoglobulin-like cylindrical fold. Two beta-strands are shortened by a tight turn (FGDG) unique to PKD. The s2b chelates to a calcium ion in pentagonal bipyramidal coordination (one water, main-chain carbonyl, side-chains of asparagine and three aspartates). The structure based sequence alignment reveals that architecturally important hydrophobic residues found in the core, and calcium-chelating residues are conserved only in bacterial PKD. The calcium-chelating residues are not found in archaea and animal PKD. The molecular shape of s2a-s2b-s3 calculated from small angle X-ray scattering (SAXS) data resembles a crowbar. The tandem PKD domains occupy the 86.4 A handle of the “crowbar”. The tandem PKD segment is likely rigid only when bound to calcium and may collapse in the absence. The s2a-s2b-s3 segment possibly pries itself between collagen fibrils. It is also possible that collagen is sandwiched between s2b-s3.

Solution NMR structure of Dsy0195 homodimer from Desulfitobacterium hafniense: first structure representative of the YabP domain family of proteins involved in spore coat assembly

Protein domain family YabP (PF07873) is a family of small protein domains that are conserved in a wide range of bacteria and involved in spore coat assembly during the process of sporulation. The 62-residue fragment of Dsy0195 from Desulfitobacterium hafniense, which belongs to the YabP family, exists as a homodimer in solution under the conditions used for structure determination using NMR spectroscopy. The structure of the Dsy0195 homodimer contains two identical 62-residue monomeric subunits, each consisting of five anti-parallel beta strands (β1, 23-29; β2, 31-38; β3, 41-46; β4, 49-59; β5, 69-80). The tertiary structure of the Dsy0195 monomer adopts a cylindrical fold composed of two beta sheets. The two monomer subunits fold into a homodimer about a single C2 symmetry axis, with the interface composed of two anti-parallel beta strands, β1-β1' and β5b-β5b', where β5b refers to the C-terminal half of the bent β5 strand, without any domain swapping. Potential functional regions of the Dsy0195 structure were predicted based on conserved sequence analysis. The Dsy0195 structure reported here is the first representative structure from the YabP family.