The geology and structure of the mid-crustal Wawa gneiss domain: a key to understanding tectonic variation with depth and time in the late Archean Abitibi–Wawa orogen

1994 ◽  
Vol 31 (7) ◽  
pp. 1064-1080 ◽  
Author(s):  
D. E. Moser
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Fault Reactivation ◽  
Upper Crust ◽  
Middle Crust ◽  
Tectonic Events ◽  
Granulite Metamorphism ◽  
Stage 1 ◽  
Structural Levels ◽  
East West

The amphibolite-facies central Wawa gneiss domain (CWGD) preserves structures that developed at the mid-crustal level of the ca. 2.7 Ga Abitibi–Wawa orogen in the southern Superior Province. The relative ages of these domainal structures are documented and brackets on their absolute ages established using existing U–Pb age data. Correlation of tectonic events within the CWGD, and comparison of these events with the evolution of other structural levels of the orogen, has led to subdivision of orogenesis into five stages. During stage 1 (2700–2680 Ma), 2.9 and 2.7 Ga rocks were tightly folded and (or) thrusted at all crustal levels in at least one thick-skinned compression event. During stage 2 (2680–2670 Ma), folding and thrusting of Timiskaming-age sediments at high levels of the orogen was thin-skinned and had no effect on CWGD gneisses. During stage 3 (2670–2660 Ma), while the upper crust was relatively stable, a 1 km thick package of volcanics and sediments, the Borden Lake belt, was underthrust northwards to depths of 30 km and in-folded with orthogneiss of the CWGD. During stage 4 (2660–2637 Ma), coeval east–west extension and granulite metamorphism of the middle crust produced gently dipping shear zones that overprinted earlier fold structures in the CWGD and lower structural levels of the orogen. This took place with minimal effect on the upper crust. Stage 5 (2630–2580 Ma) marks a period of east–west shortening and (or) fault reactivation in the Kapuskasing uplift and upper-crustal greenstone belts that allowed penetration of deep-crustal metamorphic fluids into the latter. In general, analysis of the structural evolution of the CWGD indicates that deformation and metamorphism in the middle crust of the Abitibi–Wawa orogen outlasted that at upper-crustal levels, resulting in the generally shallower dips of planar fabrics in the deeper structural levels of the Kapuskasing uplift crustal cross section.

A discussion of the (re)activation of basement structures during multi-phase shortening in thin- and thick-skinned styles

2021 ◽  
Author(s):  
Nicolas Molnar ◽  
Susanne Buiter
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Fault Reactivation ◽  
Swiss Alps ◽  
Lateral Strain ◽  
Thrust Belts ◽  
Experimental Apparatus ◽  
Analogue Models ◽  
Fold And Thrust Belts ◽  
Multi Phase

<p>Shortening in fold-and-thrust belts can be accommodated with little or substantial basement involvement, with the former, thin-skinned, style arguably being the more common (Pfiffner, GSA Special Paper, 2006). Experimental studies on thin-skinned fold-and-thrust belts have confirmed critical taper theory and have highlighted the roles of bulk rheology, embedded weak layers, décollement strength, and surface processes in structural evolution. However, analogue models of thick-skinned fold-and-thrust belts are less common, which may be related to practical challenges involved in shortening thick layers of brittle materials. Here we focus on basement fault reactivation, which has been suggested for several fold-and-thrust belts, such as the Swiss Alps, the Laramide belt in North America and the Sierras Pampeanas in South America, which show evidence of deep-rooted thrust systems, pointing to a thick-skinned style of shortening.</p><p>Within an orogenic system, the shortening style may change between thin- and thick-skinned in space (foreland to hinterland) and time. This raises the question how inherited structures from one shortening phase may influence the next. We aim to use analogue experiments of multi-phase shortening to discuss the effects of deep-seated shortening-related inherited structures, such as thrusts and basement topography, on the structural evolution of fold-and-thrust belts.</p><p>We employ a push-type experimental apparatus that can impose shortening in both thick- and thin-skinned style. The device has two independently moving backstops, permitting to change between these shortening styles over time, allowing the simulation of multiple contractional scenarios. We start with an initial stage of thick-skinned shortening, followed by either thin- or thick-skinned reactivation. We use quartz sand to simulate crustal materials and microbeads for embedded weak (sedimentary) layers. Surface and lateral strain, as well as topography, is quantified using a high-resolution particle imaging velocimetry and digital photogrammetry monitoring system.</p><p>We will present preliminary results of this innovative experimental approach with the objective of discussing to what extent pre-existing conditions in the basement control the geometric, kinematic, and mechanical evolution of thick-skinned and basement-involved thin-skinned tectonics. In this presentation, we hope for a discussion of mechanisms of localisation of shortening in brittle analogue models, of sequences of thin- and thick-skinned deformation expected during multi-phase shortening, and comparisons to ongoing research and natural observations. Questions we aim to discuss are: Can weaknesses and anisotropies within the basement influence and control later structural evolution? Are pre-existing structures, such as thrusts or shear zones within the basement, responsible for subsequent fault nucleation, thin-skinned folding or basement uplift? What role does the rheology of the basement-cover interface play in the reactivation of basement thrusts? Can we model these reactivations with an analogue setup?</p>

Archean wrench fault tectonics and structural evolution of the Blake River Group, Abitibi Belt, Quebec

1984 ◽  
Vol 21 (9) ◽  
pp. 1024-1032 ◽  
Author(s):  
Claude Hubert ◽  
Pierre Trudel ◽  
Léopold Gélinas
Keyword(s):  
Volcanic Rocks ◽  
Structural Evolution ◽  
Shear Zones ◽  
Lateral Movement ◽  
Alpine Fault ◽  
San Andreas ◽  
Fault Tectonics ◽  
Tectonic System ◽  
Wrench Fault ◽  
East West

Structural analysis of the Blake River Group volcanic rocks in the Rouyn–Noranda region shows the formations to be distributed largely in Z shapes, resulting from the interference of two early fold systems oriented west-northwest–east-southeast and east–west, respectively. The first of these two fold systems is probably related to the shortening associated with left-lateral movement along the two major fractures in the region, namely the Porcupine–Destor and Larder Lake – Cadillac faults. The second system appears to be the result of north–south compression perpendicular to the two major fractures.The two major faults, the first system of early folding, the normal and reverse faults, and the minor dextral and sinistral strike-slip faults that have been observed in the Blake River Group rocks can all be integrated into one tectonic system, that of wrench fault tectonics. The orientations of the principal structures recognized in the Abitibi Belt (major shear zones, folding, and faulting) suggest that the deformation mechanism for the rocks in the belt could be a large lateral movement controlled by megashears similar to those observed at present on the California coast (San Andreas Fault), in New Zealand (Alpine Fault), and in Sumatra (Semangko Fault).

scholarly journals ΤΗE PELAGONIAN NAPPE PILE IN NORTHERN GREECE AND FYROM. STRUCTURAL EVOLUTION DURING THE ALPINE OROGENY: A NEW APROACH

2017 ◽  
Vol 43 (1) ◽  
pp. 276 ◽  
Author(s):  
Ad. Kilias ◽  
W. Frisch ◽  
A. Avgerinas ◽  
I. Dunkl ◽  
G. Falalakis ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Late Jurassic ◽  
Structural Evolution ◽  
Shear Zones ◽  
Low Grade ◽  
Northern Greece ◽  
Alpine Orogeny ◽  
Clastic Sediments ◽  
History Of ◽  
Structural Levels

The geometry of kinematics and the deformation history of the Pelagonian nappe pile during the Alpine orogeny have been studied in Northern Greece and FYROM. Deformation was started in Middle-Late Jurassic time and was initially associated with ocean-floor subduction followed by ophiolites obduction, nappe stacking and duplication of the Pelagonian continent. The footwall Pelagonian segment from top to bottom was metamorphosed under greenschist to amphibolit facies conditions and a relative high pressure (T = 450o to 620o C and P = 12,5 to 8 kb). Blueschist facies metamorphic assemblages of Late Jurassic age are immediately developed between both hangingwall and footwall Pelagonian segments. Transgressive Late Jurassic-Early Cretaceous neritic limestones and clastic sediments on the top of the obducted ophiolites are maybe related to extension and basins formation simultaneously with the nappe stacking and metamorphism at the lower structural levels of the Pelagonian nappes. Contractional tectonics and nappe stacking continued during the Albian-Aptian time. Simultaneously retrogression and pressure decreasing taken place at the tectonic lower Pelagonian footwall segment. Low grade mylonitic shear zones, possible related to extension, are developed during Late Cretaceous time simultaneously with basins formation and sedimentation of neritic Late Cretaceous to Paleocene limestones and flysch. Intense shortening and imbrication under semi-ductile to brittle conditions occurred during Paleocene to Eocene time resulting the onset of the dome like formation of the footwall Pelagonian segment. The next stages of deformation from Oligocene to Quaternary are related to brittle extension and the final uplift and configuration of the Pelagonian nappe pile.

Structural evolution of the eastern Amisk collage, Trans-Hudson Orogen, Manitoba

1999 ◽  
Vol 36 (2) ◽  
pp. 251-273 ◽  
Author(s):  
James J Ryan ◽  
Paul F Williams
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Detailed Structural Analysis ◽  
Vertical Extension ◽  
Deformational History ◽  
Flin Flon ◽  
Mountain Belts ◽  
Geochemical Studies ◽  
Early Late ◽  
East West

Deformation recorded in the Amisk collage in the central part of the Paleoproterozoic Flin Flon Belt (southeastern Trans-Hudson Orogen) is divided into pre-, early, late, and post-Hudsonian orogeny, distinguished by significant changes in metamorphic conditions and the orientation of structures. Detailed structural analysis, petrography, and high-precision geochronology, combined with previous mapping and geochemical studies, indicate a structural history spanning 180 Ma in the Amisk collage, and the database provides an excellent opportunity to study the structural evolution of Precambrian greenstone belts. Accretion of the 1.92-1.88 Ga tectono-stratigraphic assemblages in the Amisk collage began prior to 1.868 Ga. The deformational history records six generations of ductile structures (F1-F6), followed by development of brittle-ductile and brittle structures (F7), which may have continued as late as 1.690 Ga, during exhumation of the collage. The steep, generally north-northeast macroscopic structural grain is dominated by two regional foliations (S2 and S5), and contrasts strongly with the less steeply inclined, east-west grain in the adjacent Kisseynew Domain. Maximum displacements between tectono-stratigraphic assemblages occurred along early rather than late shear zones. Vertical extension was important in post-D1 deformations, even in the later stages. Postorogenic, low-angle extensional features that are common to many mountain belts appear to be absent, possibly indicating that erosion was the dominant unroofing mechanism.

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals Multi-Scale Digital Image Correlation Analysis of In Situ Deformation of Open-Cell UHMWPE Foam

2020 ◽  
Author(s):  
Eugene S. Statnik ◽  
Codrutza Dragu ◽  
Cyril Besnard ◽  
Alexander J.G. Lunt ◽  
Alexey I. Salimon ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Performance ◽  
Structural Evolution ◽  
Image Correlation ◽  
Deformation Bands ◽  
Open Cell ◽  
Polyether Ether Ketone ◽  
Structural Levels

Porous ultra-high molecular weight polyethylene (UHMWPE) is a high performance bioinert polymer used in cranio-facial reconstructive surgery in procedures where relatively low mechanical stresses arise. As an alternative to much stiffer and costly polyether-ether-ketone (PEEK) polymer, UHMWPE finds further wide application in hierarchically structured hybrids for advanced implants mimicking cartilage, cortical and trabecular bone tissues within a single component. The mechanical behaviour of open-cell UHMWPE sponges obtained through sacrificial desalination of hot compression-moulded UHMWPE-NaCl powder mixtures shows a complex dependence on the fabrication parameters and microstructural features. In particular, similarly to other porous media it displays significant inhomogeneity of strain that readily localises within deformation bands that govern the overall response. In this article, we report advances in the development of accurate experimental techniques for operando studies of the structure-performance relationship applied to the porous UHMWPE medium with pore sizes of about 250 µm that are most well-suited for live cell proliferation and fast vascularization of implants. Samples of UHMWPE sponges were subjected to in situ compression using a micromechanical testing device within Scanning Electron Microscope (SEM) chamber, allowing the acquisition of high-resolution image sequences for Digital Image Correlation (DIC) analysis. Special masking and image processing algorithms were developed and applied to reveal the evolution of pore size and aspect ratio. Key structural evolution and deformation localisation phenomena were identified at both macro- and micro-structural levels in the elastic and plastic regimes. The motion of pore walls was quantitatively described, and the presence and influence of strain localisation zones were revealed and analysed using DIC technique.

Rift inheritance controls the switch from thin- to thick-skinned thrusting and basal décollement re-localization at the subduction-to-collision transition

2021 ◽  
Author(s):  
Stefano Tavani ◽  
Pablo Granado ◽  
Amerigo Corradetti ◽  
Giovanni Camanni ◽  
Gianluca Vignaroli ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Complete Removal ◽  
Lower Plate ◽  
Accretionary Wedge ◽  
Convergent Margins ◽  
Middle Crust ◽  
Rifted Margins ◽  
Thrust System ◽  
Structural Levels ◽  
Rifted Margin

In accretionary convergent margins, the subduction interface is formed by a lower plate décollement above which sediments are scraped off and incorporated into the accretionary wedge. During subduction, the basal décollement is typically located within or at the base of the sedimentary pile. However, the transition to collision implies the accretion of the lower plate continental crust and deformation of its inherited rifted margin architecture. During this stage, the basal décollement may remain confined to shallow structural levels as during subduction or re-localize into the lower plate middle-lower crust. Modes and timing of such re-localization are still poorly understood. We present cases from the Zagros, Apennines, Oman, and Taiwan belts, all of which involve a former rifted margin and point to a marked influence of inherited rift-related structures on the décollement re-localization. A deep décollement level occurs in the outer sectors of all of these belts, i.e., in the zone involving the proximal domain of pre-orogenic rift systems. Older—and shallower—décollement levels are preserved in the upper and inner zones of the tectonic pile, which include the base of the sedimentary cover of the distal portions of the former rifted margins. We propose that thinning of the ductile middle crust in the necking domains during rifting, and its complete removal in the hyperextended domains, hampered the development of deep-seated décollements during the inception of shortening. Progressive orogenic involvement of the proximal rift domains, where the ductile middle crust was preserved upon rifting, favors its reactivation as a décollement in the frontal portion of the thrust system. Such décollement eventually links to the main subduction interface, favoring underplating and the upward motion of internal metamorphic units, leading to their final emplacement onto the previously developed tectonic stack.

Polygonal impact craters reveal a global fracture pattern on Mercury

2021 ◽  
Author(s):  
Isik Su Yazici ◽  
Christian Klimczak
Keyword(s):  
Fracture Pattern ◽  
Impact Craters ◽  
Fault Reactivation ◽  
Space Environment ◽  
Tectonic Activity ◽  
Plan View ◽  
Additional Information ◽  
Global Tectonics ◽  
The Impact ◽  
East West

<div> <div> <div> <p>Mercury’s surface displays a rich history in impact cratering and tectonic activity, which both provide insight into the geological evolution of the innermost planet. Global contraction, the volume decrease of the planet associated with a long, sustained period of cooling, and tidal despinning, the slowing of rotation to lock Mercury in its current 3:2 spin-orbit resonance with the sun, are both thought to have played an important role on the observed systematic variations of preferred orientations of thrust fault-related landforms across the planet. While these landforms show preferred north-south orientations in the equatorial and mid-latitudes, they show random or concentric (east-west) orientations at the poles. Other fractures, such as joints, are likely present on Mercury, too, but their expressions are too subtle to be identified unless they are utilized as crater rims during the emplacement of impact craters. Fracture sets that existed in the bedrock prior to impact are widely accepted to produce crater rims showing straight rim segments that overall result in polygonal plan-view shapes of the impact structures, with perhaps the most prominent example Meteor Crater, Arizona. To test if regional fracture sets actually governed the shape of polygonal impact craters on Mercury, we have rigorously mapped all impact craters with diameters between 20 to 400 km. A total of 7,146 impact craters were mapped using Mercury Surface Space ENvironment GEochemistry and Ranging (MESSENGER) global image and topography datasets. After analyzing the shape, lengths, and orientations of 124,671 rim segments, we assessed if these rim segments contain additional information about systematic tectonic patterns. Our results show a strong preferred east-west orientation of straight crater rims at the poles, while in the mid-latitude and equatorial regions, they only have weak north-south or random orientations. That straight crater rims to show preferred east-west orientation at the poles is consistent with observed fault orientations by previous studies. However, we observe a lack of correlation of straight crater rim orientations and mapped faults at the equatorial and mid-latitudinal regions. These results have implications for and will enable further quantitative investigations of the global tectonics and fault reactivation on Mercury.</p> </div> </div> </div>

scholarly journals A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

2019 ◽  
Author(s):  
Thomas M. Belgrano ◽  
Larryn W. Diamond ◽  
Yves Vogt ◽  
Andrea R. Biedermann ◽  
Samuel A. Gilgen ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Sedimentary Cover ◽  
Phase 1 ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Magma Ascent ◽  
Upper Crust ◽  
Vms Deposits ◽  
Geochemical Analyses ◽  
Semail Ophiolite

Abstract. Recent studies have revealed genetic similarities between Tethyan ophiolites and oceanic proto-arc sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction-initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in submarine fore-arcs. In contrast, the Semail ophiolite, in which the 3–5 km thick upper-crustal succession is exposed in an oblique cross-section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the protoarc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulphide (VMS) deposits that they host, we have re-mapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses and geophysical interpretations with pre-existing geological maps. By linking the major element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes) through to axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley) and finally boninites (Boninitic Alley). Geotimes (Phase 1) axial dykes and lavas make up ~55 vol% of the Semail upper crust, whereas post-axial (Phase 2) lavas constitute the remaining ~ 45 vol % and ubiquitously cover the underlying axial crust. The Semail boninites occur as discontinuous accumulations up to 2 km thick at the top of the sequence and constitute ~ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

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