Kinematics, strain pattern, and temperature environment of the Yeba shear zone and multistage structural evolution of the Yeba Group

Many pre&#8208;Mesozoic basements of the Alpine belt contain kilometre&#8208;scaled folds with steeply inclined axial planes and fold axes. Those structures are referred to as Schlingen folds. They deform polymetamorphic gneisses, often Late&#8208;Ordovician metagranitoids and are cross&#8208;cut themselves by Permian intrusions. However, the structural evolution of such Schlingen is still not completely understood and their geodynamic significance for the Variscan evolution is not clear. To close this gap, this study investigates in detail a well-preserved Schlingen structure in the Gotthard nappe (Central Swiss Alps). This Schlingen fold evolved by a combination of shearing and folding under amphibolite facies conditions. Detailed digital field mapping coupled with petrological and structural investigations reveal local synkinematic migmatisation in the fold hinges parallel to axial planes. U&#8208;Pb dating of zircons separated from associated leucosomes reveal cores that record a detrital country rock age of 450 &#177; 3 Ma, and rims with a range of dates from 270 to 330 Ma. The main cluster defines an age of 316 &#177; 4 Ma. We ascribe this Late&#8208;Carboniferous age to peak metamorphic conditions of the late&#8208;Variscan Schlingen phase.The pre-Schlingen structures are subdivided into three older deformation events, which are connected to the Cenerian and post-Cenerian deformations. In addition, until now unknown, post Schlingen-, but pre-Alpine transpressional deformation have been detected and described. This superimposed deformation produced locally a low-grade foliation and minor undulation of the Schlingen structures.The detail data of the investigated fold structures are linked with already described Schlingen folds in the wider Alpine realm, which all are concentrated in the most southern parts of the Variscides. From a geodynamic point of view and based on the new tectono-metamorphic constraints, we propose Schlingen formation preceded and concurred the crustal-scale transpressional tectonics of the East Variscan Shear Zone. This scenario separates, at least in a structural sense, the Southern Variscides from more northern parts (also Gondwana derived) inside Pangea, where Schlingen folds are absent.

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Structural evolution of a crustal-scale shear zone through a decreasing temperature regime: The Yukon River shear zone, Yukon-Tanana terrane, Northern Cordillera

Lithosphere ◽

10.1130/l724.1 ◽

2018 ◽

Cited By ~ 2

Author(s):

A.J. Parsons ◽

M.J. Coleman ◽

J.J. Ryan ◽

A. Zagorevski ◽

N.L. Joyce ◽

...

Keyword(s):

Shear Zone ◽

Temperature Regime ◽

Structural Evolution ◽

Yukon River ◽

Scale Shear

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Structural geology of the Lardeau Group near Trout Lake, British Columbia: implications for the structural evolution of the Kootenay Arc

Canadian Journal of Earth Sciences ◽

10.1139/e92-104 ◽

1992 ◽

Vol 29 (6) ◽

pp. 1305-1319 ◽

Cited By ~ 6

Author(s):

Moira T. Smith ◽

George E. Gehrels

Keyword(s):

British Columbia ◽

Shear Zone ◽

Structural Evolution ◽

Strike Slip ◽

Ductile Deformation ◽

Lower Paleozoic ◽

Trout Lake ◽

Facies Metamorphism ◽

Dextral Strike Slip ◽

Greenschist Facies Metamorphism

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic eugeoclinal strata present in the Kootenay Arc in southeastern British Columbia. It is in fault contact with lower Paleozoic miogeoclinal strata for all or some of its length along a structure termed the Lardeau shear zone. The Lardeau Group was deformed prior to mid-Mississippian time, as manifested by layer-parallel faults, folds, and evidence for early greenschist-facies metamorphism. Regional constraints indicate probable Devono-Mississippian timing of orogeny, and possible juxtaposition of the Lardeau Group over miogeoclinal strata along the Lardeau shear zone at this time. Further ductile deformation during the Middle Jurassic Columbian orogeny produced large folds with subhorizontal axes, northwest-striking foliation and faults, and orogen-parallel stretching lineations. This deformation was apparently not everywhere synchronous, and may have continued through Late Jurassic time northeast of Trout Lake. This was followed by Cretaceous(?) dextral strike-slip and normal movement on the Lardeau shear zone and other parallel faults. While apparently the locus of several episodes of faulting, the Lardeau shear zone does not record the accretion of far-travelled tectonic fragments, as sedimentological evidence ties the Lardeau Group and other outboard units to the craton.

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Structural evolution of sulphide tectonites and their host rocks, Stratmat mine, New Brunswick

Canadian Journal of Earth Sciences ◽

10.1139/e96-037 ◽

1996 ◽

Vol 33 (3) ◽

pp. 472-492 ◽

Cited By ~ 3

Author(s):

Adrian F. Park

Keyword(s):

Grain Size ◽

New Brunswick ◽

Shear Zone ◽

Quartz Vein ◽

Structural Evolution ◽

Fluid Migration ◽

Soft Sediment ◽

Polyphase Deformation ◽

Fine Grain ◽

Host Rocks

The sulphide orebodies at the Stratmat mine in New Brunswick are treated as tectonites, because their primary characteristics have been so modified by deformation, recrystallization, and vein injection that most of their original features have been obscured. Pb–Zn–Cu sulphide orebodies at the Stratmat mine consist of sulphide and sulphide–silicate tectonites, gneisses, schists, phyllites, and slates produced by the mixing of two sulphide precursors and silicate host rocks by polyphase deformation, much of which relates to progressive non-coaxial deformation. Quartz-vein injection during and after this period of deformation, and the intermixing of nonsulphide lithotypes, led to dilution of the initial ore composition. Both the deformation of the orebodies and fluid migration, manifested by vein injection, reflect processes that were operative in a major shear zone. No indisputable primary characteristics of the orebodies are preserved, although a number of tectonic and (or) tectonically modified features mimic depositional features, e.g., quartz mylonites resemble "cherts," festoon veinlets resemble dismembered stockwork veins, sulphide mylonites resemble rock with an original fine-grain size and "extra" fold phases that could be mistaken for soft sediment folds.

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

International Journal of Civil, Environmental and Agricultural Engineering ◽

10.34256/ijceae1914 ◽

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.

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