Buckle folding and deep-crustal shearing of high-grade gneisses at the junction of two major high-strain zones, Central Gneiss Belt, Grenville Province, Ontario

2005 ◽  
Vol 42 (10) ◽  
pp. 1907-1925 ◽  
Author(s):  
N Culshaw
Keyword(s):  
Shear Zone ◽  
High Strain ◽  
Pure Shear ◽  
Crustal Thickening ◽  
Shear Direction ◽  
High Angle ◽  
Grenville Province ◽  
Shear Component ◽  
Central Gneiss Belt ◽  
Upper Boundary

Low-plunging, transport-parallel F3 folds are common at all scales in the Central Gneiss Belt of the Grenville Province, but few of these folds are sheath folds. Where the D1–D2 Parry Sound shear zone intersects the D3 Shawanaga shear zone (SSZ) at a high angle, F3 folds formed at several scales (centimetre to greater than outcrop scale) in layered D1–D2 "straight" gneisses. At the start of their evolution, the F3 folds formed just beyond the SSZ with hinges near orthogonal to the D3 shear direction and with typical buckle features, e.g., wavelengths vary with layer thickness, and hinges are discontinuous and bifurcate. The buckle folds evolved within the SSZ by rotation of hinges towards the shear direction. Even though hinges initiated at a high angle to the shear direction, sheath folds were not produced. In addition to tightening the buckles, the ductile reorientation produced thin–thick (extended–shortened) limb pairs and very straight, ridge-like fold hinges and removed small folds from the extended limbs of larger folds. Such features may serve as criteria to distinguish transport-parallel folds that initiated in layering at high angles to the shear direction from those formed in layers containing the shear direction. A general shear parallel to the SSZ can reproduce several features inferred to mark stages in the progressive reorientation of the folds; the pure shear component of the general shear is inferred to have had a positive stretch direction down the dip of the shear zone, at a high angle to the transport (simple shear) direction. The interplay of buckling and shearing in the study area is, plausibly, the expression of deformation at the upper boundary of a channel-like flow that succeeded initial crustal thickening.

scholarly journals Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

2018 ◽  
Vol 55 (9) ◽  
pp. 1063-1078 ◽  
Author(s):  
Michelle J. Markley ◽  
Steven R. Dunn ◽  
Michael J. Jercinovic ◽  
William H. Peck ◽  
Michael L. Williams
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Boundary Zone ◽  
Grenville Province ◽  
Metamorphic History ◽  
Crustal Thinning ◽  
Tectonic Significance ◽  
History Of ◽  
Central Gneiss Belt ◽  
Scale Shear

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

scholarly journals Strain Pattern Analysis of Mylonites From Sitampundi-Kanjamalai Shear Zone, Thiruchengode, South India

2019 ◽  
Vol 1 (1) ◽  
pp. 25-34
Author(s):  
Thirukumaran V ◽  
Biswal T.K ◽  
Sundaralingam K ◽  
Sowmya V ◽  
Boopathi S ◽  
...  
Keyword(s):  
Shear Zone ◽  
Simple Shear ◽  
Pure Shear ◽  
Strain Analysis ◽  
Strain Pattern ◽  
Shear Sense ◽  
Shear Component ◽  
Deep Crustal Level ◽  
Dextral Shear ◽  
Shear Sense Indicators

This study aims to investigate the petrography and strain pattern of mylonites from parts of N-S trending Sitampundi-Kanjamalai Shear Zone (SKSZ) around Thiruchengode. The petrographic study indicates the presence of recrystallized quartz, K-feldspar, plagioclase, biotite and some hornblende. The kinematic analysis of Mylonites was done with the help of shear sense indicators such as recrystallized type quartz (quartz ribbon) around the cluster of feldspar, S-C fabric shows dextral shear sense and some sinisterly shear sense in some parts of SASZ which can be considered as a product of partitioning of both strain and vorticity between domains. These all indicates the simple shear extension along E-W direction and the mylonitic foliation shows the pure shear compression along N-S direction. Further the study of bulk strain analysis by Flinn plot method using L and T section of mylonite shows k<1 which lies in the field of flattening zone of finite strain. The kinematic vorticity number is calculated by Rxz/β method which gives the value of 0.36 indicating the general shear. The rigid grain graph shows that the pure shear component is more ­­­­dominant than the simple shear component. The analysis leads to the conclusion that the mylonite has experienced a high temperature shearing of above 700°cat deep crustal level.

scholarly journals Quantitative finite strain analysis of the quartz mylonites within the Three Pagodas shear zone, western Thailand

2018 ◽  
Vol 111 (2) ◽  
pp. 171-179
Author(s):  
Pitsanupong Kanjanapayont ◽  
Peekamon Ponmanee ◽  
Bernhard Grasemann ◽  
Urs Klötzli ◽  
Prayath Nantasin
Keyword(s):  
Shear Zone ◽  
Pure Shear ◽  
Strain Analysis ◽  
Strain Ratio ◽  
Kinematic Vorticity ◽  
The North ◽  
Shear Sense ◽  
Shear Component ◽  
The Mean ◽  
Vorticity Analysis

AbstractThe NW–trending Three Pagodas shear zone exposes a high–grade metamorphic complex named Thabsila gneiss in the Kanchanaburi region, western Thailand. The quartz mylonites within this strike–slip zone were selected for strain analysis. 2–dimensional strain analysis indicates that the averaged strain ratio (Rs) for the lower greenschist facies increment of XZ– plane is Rs = 1.60–1.97 by using the Fry’s method. Kinematic vorticity analysis of the quartz mylonites in the shear zone showed that the mean kinematic vorticity number of this increment is Wk = 0.75–0.99 with an average at 0.90 ±0.07. The results implied that the quartz mylonites within the Three Pagodas shear zone have a dominant simple shear component of about 72% with a small pure shear component. A sinistral shear sense is indicated by kinematic indicators from macro– to micro–scale. We conclude that the Three Pagodas shear zone deformed in the process of sinstral shear–dominated transpression, which is similar to the Mae Ping shear zone in the north.

Upper-crustal orogenic lid and mid-crustal core complexes: signature of a collapsed orogenic plateau in the hinterland of the Grenville Province 1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

2012 ◽  
Vol 49 (1) ◽  
pp. 1-42 ◽  
Author(s):  
Toby Rivers
Keyword(s):  
High Strain ◽  
Numerical Models ◽  
Pure Shear ◽  
Granulite Facies ◽  
Lower Grade ◽  
Conductive Heat ◽  
Upper Crust ◽  
Special Issue ◽  
Grenville Province ◽  
Orogenic Plateau

This paper provides a re-interpretation of the crustal architecture of the Ottawan hinterland of the Grenville Province in light of published empirical and numerical models of orogenic collapse. It is now seen as a series of high-grade, mid-crustal core complexes from tens to hundreds of kilometres across that are juxtaposed against segments of the lower grade upper and uppermost crust including the orogenic lid. Juxtaposition of such contrasting crustal levels, which exhibit decoupled tectonic styles corresponding to the orogenic infrastructure and suprastructure, respectively, is interpreted as a signature of the foundering of an orogenic plateau into a mid-crustal channel. Ottawan metamorphism progressed from granulite-facies in the mid crust at ∼1090–1050 Ma, through amphibolite-facies in the upper crust at ∼1050–1020 Ma, to heating to ≤500 °C in the uppermost crust at ∼1020–980 Ma. This temporal progression is interpreted to reflect conductive heat transfer during collapse, as hot mid-crustal core complexes were exhumed against successively higher crustal levels. Exhumation was facilitated by substantial thinning and lengthening of the mid crust by simple- and pure-shear mechanisms. This was accompanied by wholesale boudinage of the brittle uppermost crust. Moreover, it may have resulted in excision of part of the ductile upper crust, which appears under-represented. Collapse was accompanied by diverse magmatic and hydrothermal products, their range of structural states implying that high-strain Ottawan deformation in the mid crust took place beneath an orogenic lid that was not penetratively deformed. Preliminary analysis indicates the Grenvillian inliers exhibit a comparable range of crustal levels to the Grenville Province, suggesting the orogenic plateau may have extended ∼5000 km along strike from Labrador to Texas.

Non-steady strain in the terrane boundary shear zone of the Ambaji Granulite, NW India: Implications for understanding towards the dynamics of emplacement of the lower-middle crustal rocks.

2020 ◽  
Author(s):  
Ragini Saraswati ◽  
Tapas Kumar Biswal
Keyword(s):  
Shear Zone ◽  
Pure Shear ◽  
Strain Analysis ◽  
Shear Zones ◽  
Strike Slip ◽  
Ductile Deformation ◽  
Mobile Belt ◽  
High Grade ◽  
Crustal Rocks ◽  
Shear Component

&lt;p&gt;Shear zones in the high-grade terranes represent the tectonic- fossils of strain history. One such shear zones, namely Balaram-Jogdadi shear zones defining the terrane boundary of the Ambaji granulites of the South Delhi terrane Aravalli &amp;#8211;Delhi Mobile belt, NW India, provide evidence for strain variation during exhumation of lower-middle crustal rocks. Compilation of field and microscopic analysis of various samples of mylonite from shear zones suggest that the part of shear zone contains high-grade mineral assemblages such as cordierite, sillimanite, spinel, garnet in quartzo-feldspathic mylonite rock and exhibit signature of thrusting in which garnet behaved as brittle phase and quartz and feldspar grain show ductile deformation. 2D and 3D strain analysis estimate a plane to flattening type of strain pattern. Principal strain planes are used to calculate the strain ratios for estimation of variation of strain along the shear zone. This study indicates high-grade mylonite accommodates high strain. The flow of rigid porphyroclasts estimates mean kinematic vorticity number varies from 0.47 to 0.68, which indicates the dominance of pure shear during shearing. Vorticity by the Rs/&amp;#952; method in quartz grain estimates ranges from 0.7 to 0.95, suggesting a non-steady strain towards the end of deformation. High-grade mylonites were overprinted by low-temperature mylonitisation marked by minerals like quartz, feldspar, biotite in which feldspar porphyroclast shows brittle deformation and quartz, biotite show ductile deformation. Several shear kinematics indicate top-to-NW sinistral strike-slip shearing. Thus it has been interpreted that the shear zone had undergone non-steady strain. The initial thrusting phase was dominated by more pure shear component. The strike-slip shearing part was dominated by more simple shear component. Monazite geochronology sets the age of shearing at 834-778 Ma suggesting the exhumation was a transition event between Grenville to Pan-African orogeny.&lt;/p&gt;&lt;p&gt;Keywords: Shear zone, Deformation, Vorticity, 3D strain analysis, Monazite dating&lt;/p&gt;

Structural testing of tectonic hypotheses by field-based analysis of distributed tangential shear: examples from major high-strain zones in the Grenville Province and other parts of the southern Canadian Shield

2005 ◽  
Vol 42 (10) ◽  
pp. 1927-1947 ◽  
Author(s):  
W M Schwerdtner ◽  
U P Riller ◽  
A Borowik
Keyword(s):  
Shear Zone ◽  
High Strain ◽  
Shear Zones ◽  
Canadian Shield ◽  
Structural Testing ◽  
Grenville Province ◽  
Shallow Subsurface ◽  
Geometric Conditions ◽  
Actual Direction ◽  
Dip Angle

The Grenville Province and other parts of the Canadian Shield contain major (>100 km long) high-strain zones, also called shear belts or ductile shear zones, that are hosted by heterogeneously deformed gneisses and schists. In well-exposed segments of three nontabular zones whose dip angle is known locally, at the erosion level and (or) in the shallow subsurface, we investigate the tangential shear strain (better called the tangential unit shear or TUS) without assuming that mineral-shape lineations, common varieties of stretching lineations, are effectively parallel to the local TUS direction. Employing a graphic technique that copes with the geometric conditions of general triaxial strain, we approximate the actual direction and find the sense of local TUS in parts of (i) the Parry Sound shear zone, Grenville Province; (ii) the South Range shear zone, Southern Province; and (iii) the Uchi – English River subprovince boundary zone, Superior Province. Information thus obtained for individual high-strain zones in Ontario confirms the validity of published hypotheses: (i) 1020–970 Ma, normal-sense distributed shearing in the Grenvillian thrust stack; (ii) northwest- directed thrusting of Huronian rocks over Archean basement; and (iii) north-directed thrusting of English River metasediments and associated migmatites onto the Uchi granite–greenstone terrain, under peak metamorphic conditions.

scholarly journals Constrictional deformation of the Koster dyke swarm in a ductile sinistral shear zone, Koster islands, SW Sweden

1985 ◽  
Vol 34 ◽  
pp. 151-197
Author(s):  
Bjorn Hageskov
Keyword(s):  
Shear Deformation ◽  
Shear Zone ◽  
Simple Shear ◽  
Pure Shear ◽  
Dyke Swarm ◽  
Tectonic Event ◽  
Dyke Rock ◽  
Strain Ellipsoid ◽  
Shear Component ◽  
The Baltic

The Koster-Kattsund dyke swarm is an important element in the Sveconorwegian province of the Baltic shield. Dyke intrusion took place in the period 1225-1015 Ma. Throughout most of the swarm the dykes are strongly deformed and thoroughly recrystallised into lineated amphibolites as a result of a Sveconor- wegian tectonic event about 1000 Ma ago. However, in the Koster archipelago fresh dolerites can be fol­lowed northwards in to partially recrystallised metadolerites and finally into the totally recrystallised, line­ated amphibolites that characterise the swarm. In the Koster archipelago intense dyking resulted in the formation of a multilayered rock sandwich con­sisting of alternating layers of gneiss and dolerite. The sandwich trends NNE and dips 67°W. The dolerite dykes have a mean thickness of2.2 m and they occupy 15-20% of the total rock mass. To the northeast the sandwich becomes progressively deformed and ultimately shows very high strain of pure constrictional type. The deformation took place in a steep NW-SE-trending ductile shear zone. During the initial shear zone deformation (D4,) the sandwich underwent anticlockwise bending and the large Kyrkosund synform was formed. The fold plunges 303/66 and has a NW-SE-trending axial surface. The bending took place by means of flexural-slip folding in which the layer-parallel shearing was located in incompetent dyke layers. Increasing shearing and recrystallisation in a NW-SE-trending belt crossing the northern limb of the Kyr­kosund synform resulted in a softening of this belt. The succeeding event (D4b) was localised in this initial soft belt, and involved sinistral simple shear combined with pure shear resulting in horizontal widening and vertical shortening of the belt. This composite deformation formed the pure constrictional fabric now seen in the rocks. The strong D4b stretching was followed by the formation of trains of asymmetric folds (D 4c and d4a). It is demonstrated that volume changes in the dyke rock during deformation were negligible, and that no competence contrast between gneiss and dyke rock existed during the D 4b stretching. The finite con­strictional strain ellipsoid has the dimensions X = 7.07, Y = Z = 0.18. The composite simple/pure shear deformation that presumably caused the constriction has a simple shear component y = 10.9, correspond­ing to an angular shear of 84. 7°. The pure shear deformation resulted in a 3.4 times horizontal widening of the initial soft belt. The horizontal sinistral displacement within the shear zone was at least 35 km.

scholarly journals Insights into Machining of a β Titanium Biomedical Alloy from Chip Microstructures

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 710 ◽  
Author(s):  
Damon Kent ◽  
Rizwan Rahman Rashid ◽  
Michael Bermingham ◽  
Hooyar Attar ◽  
Shoujin Sun ◽  
...  
Keyword(s):  
Shear Band ◽  
Shear Zone ◽  
Biomechanical Properties ◽  
Temperature Fields ◽  
Large Strains ◽  
Shear Direction ◽  
Grain Sizes ◽  
Β Phase ◽  
Secondary Shear Zone ◽  
Cutting Speeds

New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study, machining chip microstructure has been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400–600 °C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20–50 nm, while further from the interface the β grains become highly elongated in the shear direction. An absence of the α phase in the region immediately adjacent to the cutting interface indicates recrystallization during cutting and temperatures in excess of the 720 °C β transus temperature.

scholarly journals Petrogenesis and tectonic of the Urucum granitic suite, Rio Doce Valley (Minas Gerais - Brazil): an example of syn to late collisional peraluminous magmatism associated with high-angle transcurrent shear zone

2015 ◽  
Vol 45 (1) ◽  
pp. 127-141 ◽  
Author(s):  
Hermínio Arias Nalini Júnior ◽  
Rômulo Machado ◽  
Essaid Bilal
Keyword(s):  
Trace Elements ◽  
Solid State ◽  
Shear Zone ◽  
Saturation Index ◽  
Minas Gerais ◽  
High Angle ◽  
Accessory Minerals ◽  
Major Oxides ◽  
Minas Gerais State ◽  
Alumina Saturation Index

The Urucum suite (582 ± 2 Ma, zircon U-Pb age), situated in the Mid-Rio Doce Valley, eastern part of Minas Gerais State, is characterized by elongated, NW-SE and N-S trending granitic massifs associated with the Conselho Peña-Resplendor high-angle shear zone. It corresponds to a syn to late collisional magmatism that presents dominant solid-state foliation. Four facies are distinguished within the Urucum suite: (i) a porphyritic (Urucum); (ii) a medium- to coarse nequigranular (Palmital); (iii) a tourmaline-bearing; and (iv) a pegmatitic facies. These facies are peraluminous, with alumina saturation index varying from 0.98 to 1.38. SiO2 contents vary from 70.7 to 73.7 wt%, with K2O values ranging from 3.5 to 5.7 wt%, Na2O from 1.9 to 4.4 wt%, MgO from 0.6 to 1.2 wt%, and CaO from 0.3 to 0.9%. Harker-type diagrams show rather continuous trends from the less-evolved Urucum facies to the more evolved tourmaline-bearing and pegmatitic facies. The behavior of several major oxides and trace elements (Fe2O3, MgO, MnO, CaO, TiO2, Al2O3, K2O, Rb and Ba) reflects the role played by fractionation of ferromagnesian minerals, feldspars and accessory minerals. Initial Sr87/Sr86 ratios vary from 0.711 to 0.716, with εNd (580 Ma) values between -7.4 to -8.2, and Sm-Nd TDM model ages ranging from 2290 to 1840 Ma.

scholarly journals Crustal thickness of the Grenville orogen: A Mesoproterozoic Tibet?

Geology ◽  
2021 ◽  
Author(s):  
Adam Brudner ◽  
Hehe Jiang ◽  
Xu Chu ◽  
Ming Tang
Keyword(s):  
Crustal Thickness ◽  
Detrital Zircons ◽  
Crustal Thickening ◽  
Geochemical Data ◽  
Geochronological Data ◽  
Grenville Province ◽  
Crustal Thinning ◽  
Paleoenvironmental Evolution ◽  
Orogenic Plateau ◽  
St Lawrence River

The Grenville Province on the eastern margin of Laurentia is a remnant of a Mesoproterozoic orogenic plateau that comprised the core of the ancient supercontinent Rodinia. As a protracted Himalayan-style orogen, its orogenic history is vital to understanding Mesoproterozoic tectonics and paleoenvironmental evolution. In this study, we compared two geochemical proxies for crustal thickness: whole-rock [La/Yb]N ratios of intermediate-to-felsic rocks and europium anomalies (Eu/Eu*) in detrital zircons. We compiled whole-rock geochemical data from 124 plutons in the Laurentian Grenville Province and collected trace-element and geochronological data from detrital zircons from the Ottawa and St. Lawrence River (Canada) watersheds. Both proxies showed several episodes of crustal thickening and thinning during Grenvillian orogenesis. The thickest crust developed in the Ottawan phase (~60 km at ca. 1080 Ma and ca. 1045 Ma), when the collision culminated, but it was still up to 20 km thinner than modern Tibet. We speculate that a hot crust and several episodes of crustal thinning prevented the Grenville hinterland from forming a high Tibet-like plateau, possibly due to enhanced asthenosphere-lithosphere interactions in response to a warm mantle beneath a long-lived supercontinent, Nuna-Rodinia.

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