scholarly journals Early Neoproterozoic Deformation Kinematics in the Chottanagpur Gneiss Complex (Eastern India): Evidence from the Curvilinear Hundru Falls Shear ZoneAnalysis

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Nicole Sequeira ◽  
Abhijit Bhattacharya
Keyword(s):  
Shear Zone ◽  
Regional Scale ◽  
Shear Zones ◽  
Ratio Method ◽  
Strain Partitioning ◽  
Gneiss Complex ◽  
Deformation Kinematics ◽  
Detachment Zone ◽  
The Mean ◽  
Early Neoproterozoic

Abstract Curvilinear steep shear zones originate in different tectonic environments. In the Chottanagpur Gneiss Complex (CGC), the steeply dipping, left-lateral and transpressive Early Neoproterozoic Hundru Falls Shear Zone (HFSZ) with predominantly north-down kinematics comprises two domains, e.g., an arcuate NW-striking (in the west) to W-striking (in the east) domain with gently plunging stretching lineation that curves into a W-striking straight-walled domain with down-dip lineation. The basement-piercing HFSZ truncates a carapace of flat-lying amphibolite facies paraschist and granitoid mylonites, and recumbently folded anatectic gneisses. The carapace—inferred to be a midcrustal regional-scale low-angle detachment zone—structurally overlies an older basement of Early Mesoproterozoic anatectic gneisses intruded by Mid-Mesoproterozoic/Early Neoproterozoic granitoids unaffected by the Early Neoproterozoic extensional tectonics. The mean kinematic vorticity values in the steep HFSZ-hosted granitoids computed using the porphyroclast aspect ratio method are 0.74–0.83 and 0.51–0.65 in domains with shallow and steep lineations, respectively. The granitoid mylonites show a chessboard subgrain microstructure, but lack evidence for suprasolidus deformation. The timing relationship between the two domains is unclear. If the two HFSZ domains were contemporaneous, the domain of steep lineations with greater coaxial strain relative to the curvilinear domain formed due to strain partitioning induced by variations in mineralogy and/or temperature of the cooling granitoid plutons. Alternately, the domain of gently plunging lineations in the HFSZ was a distinct shear zone that curved into a subsequent straight-walled shear zone with steeply plunging lineation due to a northward shift in the convergence direction during deformation contemporaneous with the Early Neoproterozoic accretion of the CGC and the Singhbhum Craton.

scholarly journals Eburnean deformation pattern of Burkina Faso and the tectonic significance of shear zones in the West African craton

2020 ◽  
Vol 191 ◽  
pp. 2 ◽  
Author(s):  
Dominique Chardon ◽  
Ousmane Bamba ◽  
Kalidou Traoré
Keyword(s):  
Burkina Faso ◽  
Shear Zone ◽  
Regional Scale ◽  
Kinematic Model ◽  
Shear Zones ◽  
West African ◽  
Deformation Pattern ◽  
The West ◽  
West African Craton ◽  
Regional Flow

Shear zones of the Paleoproterozoic Eburnean accretionary Orogen (West African craton) are investigated by means of large-scale structural mapping. Regional scale (10-100 km) mapping was based on the aeromagnetic survey of Burkina Faso and craton-scale (1000 km) mapping on a compilation of fabric data. At both scales, shear zones are arranged as an anastomosed transpressional network that accommodated distributed shortening and lateral flow of the orogenic lithosphere between the converging Kénéma-Man and Congo Archean provinces. Structural interference patterns at both scales were due to three-dimensional partitioning of progressive transpressional deformation and interactions among shear zones that absorbed heterogeneities in the regional flow patterns while maintaining the connectivity of the shear zone network. Such orogen-scale kinematic patterns call for caution in using the deformation phase approach without considering the “bigger structural picture” and interpreting displacement history of individual shear zones in terms of plate kinematics. The West African shear zone pattern is linked to that of the Guiana shield through a new transatlantic correlation to produce an integrated kinematic model of the Eburnean-Transamazonian orogen.

Carbon ordering in an aseismic shear zone: implications for crustal weakening and Raman spectroscopy

2020 ◽  
Author(s):  
Lauren Kedar ◽  
Clare Bond ◽  
David Muirhead
Keyword(s):  
Raman Spectroscopy ◽  
Organic Carbon ◽  
Shear Zone ◽  
Experimental Studies ◽  
Carbonaceous Material ◽  
Shear Zones ◽  
Lower Limbs ◽  
Strain Partitioning ◽  
Increasing Temperature ◽  
Two Peaks

<p>Multi-layered stratigraphic sequences present ample opportunity for the study of strain localization and its complexities. By constraining mechanisms of crustal weakening, it is possible to gain a sounder understanding of the dynamic evolution of the Earth’s crust, especially when applied to realistic, field-based scenarios. One such mechanism is that of strain-related carbon ordering. This is the process whereby the amorphous nanostructure of fossilized organic matter contained within the rock is progressively organized towards a more sheet-like structure, similar to that of graphite. One common method of studying this process is through Raman spectroscopy. This is a non-destructive tool which makes use of the relative positions and intensities of two key spectral peaks, where one peak represents graphitic carbon and the other disordered (or amorphous) carbon. The intensity ratio between these two peaks suggests the degree to which the carbon has progressed from its original kerogen-like structure towards that of graphite. This progression can be due to increasing temperature or increasing strain, and until now, these two contributory factors have been difficult to separate, particularly in field examples.</p><p>Previous field-based studies have focused on carbon ordering on fault planes, while experimental studies have monitored the effects of strain-related ordering in organic carbon on both fault surfaces and more distributed shear zones. These studies confirmed the occurrence of strain-related ordering at seismic rates, particularly in the form of graphitization of carbon. However, these experiments showed the effects of strain-related ordering at aseismic rates to be limited when distributed shear zones were considered, in part due to the geological timescales required to emulate true conditions.</p><p>In this study, Raman spectroscopy is used to compare the relative nanostructural order of organic carbon within a recumbent isoclinal fold formed of interbedded limestones and marls. The central, overturned fold limb forms a 170m wide, 1km long aseismic shear zone, with evidence of increased strain recorded in calcite grains relative to the upper and lower limbs. Raman spectroscopy intensity ratios (I[d]/I[g]) are compared across the fold, showing a marked 23% decrease in the overturned limb. Such a decrease in I[d]/I[g] suggests increased carbon ordering within the overturned limb, which in combination with evidence for increased strain in calcite, suggests that the carbon ordering here is derived directly from strain-related ordering. This has important implications. We infer, from previous studies, that strain-related carbon ordering encourages further strain partitioning in carbonaceous material, and may enhance zones of weakness in the rock. This ordering in aseismic shear zones has so far been unreported in nature, and so our field-based results are significant in supporting previous experimental evidence for this phenomenon. Our results also have implications for understanding dynamic crustal evolution, and will play an important role in the development of Raman thermobarometry, especially since current methods do not distinguish between strain-related and temperature-related ordering.</p>

Proterozoic tectonic overprinting of Archaean gneisses in Nuussuaq, West Greenland

1999 ◽  
pp. 141-154
Author(s):  
Adam A. Garde ◽  
Agnete Steenfelt
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Indirect Evidence ◽  
Shear Zones ◽  
Boundary Structure ◽  
Crustal Extension ◽  
Northern Boundary ◽  
Crustal Shortening ◽  
West Greenland ◽  
Detachment Zone

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Garde, A. A., & Steenfelt, A. (1999). Proterozoic tectonic overprinting of Archaean gneisses in Nuussuaq, West Greenland. Geology of Greenland Survey Bulletin, 181, 141-154. https://doi.org/10.34194/ggub.v181.5122 _______________ Archaean orthogneisses and supracrustal rocks in eastern Nuussuaq in the southern part of the Rinkian orogen preserve much indirect evidence of Proterozoic reworking. In northern Nuussuaq, a marble occurrence which can be correlated with the Proterozoic Mârmorilik Formation of the Uummannaq district, is interleaved and intensely folded with Archaean orthogneisses. Dykes and sills of presumed Proterozoic age in southern Nuussuaq pre-date two major shear zones. Furthermore, published K-Ar and 40Ar-39Ar hornblende ages indicate that metamorphic temperatures of at least c. 550°C were reached in large parts of Nuussuaq during the Proterozoic. Although available data are not sufficient to firmly establish the tectonic evolution of Nuussuaq, it can be shown that development of a regional flat-lying structure was succeeded first by upright folding and development of a major NW–SE-trending shear zone during crustal shortening, and subsequently by formation of an ENE–WSW-trending shear zone during crustal extension. A Rinkian detachment zone across Nuussuaq, similar to those known in the Uummannaq district, may link Proterozoic marble occurrences south of the peninsula with the marbles known in northern Nuussuaq and in the Uummannaq district. Observations suggest that geological structures and lithologies can be traced from north to south across the fjord Torsukattak, into the Ataa area which is hardly affected by Proterozoic deformation. This is used to infer that a major crustal boundary structure along the fjord (previously assumed to form the northern boundary of the Burwell terrane in West Greenland) does not exist.

Complex kinematics in a major ductile shear zone, NW Shetland: Evidence of ductile extrusion during Caledonian transpression

2021 ◽  
Author(s):  
Timothy Armitage ◽  
Robert Holdsworth ◽  
Robin Strachan ◽  
Thomas Zach ◽  
Diana Alvarez-Ruiz ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Regional Scale ◽  
Shear Zones ◽  
White Mica ◽  
Strike Slip ◽  
Amphibolite Facies ◽  
Lateral Extrusion ◽  
Shear Sense ◽  
Ductile Shear

<p>Ductile shear zones are heterogeneous areas of strain localisation which often display variation in strain geometry and combinations of coaxial and non-coaxial deformation. One such heterogeneous shear zone is the c. 2 km thick Uyea Shear Zone (USZ) in northwest Mainland Shetland (UK), which separates variably deformed Neoarchaean orthogneisses in its footwall from Neoproterozoic metasediments in its hanging wall (Fig. a). The USZ is characterised by decimetre-scale layers of dip-slip thrusting and extension, strike-slip sinistral and dextral shear senses and interleaved ultramylonitic coaxially deformed horizons. Within the zones of transition between shear sense layers, mineral lineations swing from foliation down-dip to foliation-parallel in kinematically compatible, anticlockwise/clockwise-rotations on a local and regional scale (Fig. b). Rb-Sr dating of white mica grains via laser ablation indicates a c. 440-425 Ma Caledonian age for dip-slip and strike-slip layers and an 800 Ma Neoproterozoic age for coaxial layers. Quartz opening angles and microstructures suggest an upper-greenschist to lower-amphibolite facies temperature for deformation. We propose that a Neoproterozoic, coaxial event is overprinted by Caledonian sinistral transpression under upper greenschist/lower amphibolite facies conditions. Interleaved kinematics and mineral lineation swings are attributed to result from differential flow rates resulting in vertical and lateral extrusion and indicate regional-scale sinistral transpression during the Caledonian orogeny in NW Shetland. This study highlights the importance of linking geochronology to microstructures in a poly-deformed terrane and is a rare example of a highly heterogeneous shear zone in which both vertical and lateral extrusion occurred during transpression.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0cf6ef44e5ff57820599061/sdaolpUECMynit/12UGE&app=m&a=0&c=d96bb6db75eed0739f2a6ee90c9ad8fd&ct=x&pn=gepj.elif&d=1" alt=""></p>

The role of regional-scale shear zones in paleogeographic reconstructions: the case study of the Variscan belt in the Mediterranean area

2021 ◽  
Author(s):  
Matteo Simonetti ◽  
Rodolfo Carosi ◽  
Chiara Montomoli ◽  
Salvatore Iaccarino
Keyword(s):  
Earth Sciences ◽  
Shear Zone ◽  
Regional Scale ◽  
Shear Zones ◽  
Mediterranean Area ◽  
Variscan Belt ◽  
Metamorphic Evolution ◽  
The Mediterranean ◽  
Scale Shear

<p>Paleogeographic reconstruction and recognition of the tectono-metamorphic evolution of ancient orogenic belt is often complex. The combination of an adequate amount of paleomagnetic, metamorphic, structural and geochronological data is necessary. Fundamental data derive from the study of regional-scale shear zones, that can be directly observed, by combining detailed field work with structural analysis, microstructural analysis and petrochronology. The Southern European Variscan Belt in the Mediterranean area was partially overprinted by the Alpine cycle (Stampfli and Kozur, 2006) and correlations are mainly based on lithological similarities. Little attention has been paid to the compatibility of structures in the dispersed fragments. A main debate is the connection among the Corsica-Sardinia Block (CSB), the Maures-Tanneron Massif (MTM) and the future Alpine External Crystalline Massifs (ECM) (Stampfli et al., 2002; Advokaat et al., 2014) and if these sectors were connected by a network of shear zones of regional extent, known as the East Variscan Shear Zone (EVSZ).</p><p>We present a multidisciplinary study of shear zones cropping out in the CSB (the Posada-Asinara shear zone; Carosi et al., 2020), in the MTM (the Cavalaire Fault; Simonetti et al., 2020a) and in the ECM (the Ferriere-Mollières and the Emosson-Berard shear zones; Simonetti et al., 2018; 2020b).</p><p>Kinematic and finite strain analysis allowed to recognize a transpressional deformation, with a major component of pure shear and a variable component of simple shear, coupled with general flattening deformation. Syn-kinematic paragenesis, microstructures and quartz c-axis fabrics revealed that shear deformation, in all the studied sectors, occurred under decreasing temperature starting from amphibolite-facies up to greenschist-facies. A systematic petrochronological study (U-Th-Pb on monazite collected in the sheared rocks) was conducted in order to constrain the timing of deformation. We obtained ages ranging between ~340 Ma and ~320 Ma. Ages of ~340-330 Ma can be interpreted as the beginning of the activity of the EVSZ along its older branches while ages of ~320 Ma, obtained in all the shear zones, demonstrate that they were all active in the same time span.</p><p>The multidisciplinary approach revealed a similar kinematics and tectono-metamorphic evolution of the studied shear zones contributing to better constrain the extension and timing the EVSZ and to strength the paleogeographic reconstructions of the Southern Variscan belt during Late Carboniferous time, with important implications on the evolution of the Mediterranean area after the Late Paleozoic. This case study demonstrates how paleogeographic reconstructions could benefit from datasets obtained from large-scale structures (i.e., shear zones) that can be directly investigated.</p><p> </p><p>Advokaat et al. (2014). Earth and Planetary Science Letters 401, 183–195</p><p> </p><p>Carosi et al. (2012). Terra Nova 24, 42–51</p><p> </p><p>Carosi and Palmeri (2002). Geological Magazine 139.</p><p> </p><p>Carosi et al. (2020). Geosciences 10, 288.</p><p> </p><p>Simonetti et al (2020a). International Journal of Earth Sciences 109, 2261–2285</p><p> </p><p>Simonetti et al. (2020b). Tectonics 39</p><p> </p><p>Simonetti et al. (2018). International Journal of Earth Sciences. 107, 2163–2189</p><p> </p><p>Stampfli and Kozur (2006). Geological Society, London, Memoirs 32, 57–82</p><p> </p><p>Stampfli et al. (2002). Journal of the Virtual Explorer 8, 77</p>

Upper Carboniferous-Permian tectonics in Central Mediterranean: an updated revision

2020 ◽  
Author(s):  
Giancarlo Molli ◽  
Andrea Brogi ◽  
Alfredo Caggianelli ◽  
Enrico Capezzuoli ◽  
Domenico Liotta ◽  
...  
Keyword(s):  
Shear Zone ◽  
Regional Scale ◽  
Sedimentary Basins ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Low Grade ◽  
Central Mediterranean ◽  
Upper Carboniferous ◽  
Fold And Thrust Belt ◽  
Splay Faults

<p>An updated revision of the upper Carboniferous-Permian tectonics recorded in Corsica, Calabria and Tuscany is here proposed. We combine our and literature data to document how the sedimentary, tectono-metamorphic and magmatic upper Carboniferous-Permian record fits with a regional-scale tectonic scenario characterized by trascurrent fault systems associated with stretched crustal domains in which extensional regional structures, magmatism and transtensional basins developed. In Corsica, altogether with well-known effusive and intrusive Permian magmatism, the alpine S.Lucia nappe exposes a kilometer-scale portion of the Permian lower to mid-crust, with many similarities to the Ivrea-Verbano zone. The two distinct Mafic and Leucogranitic complexes, which characterize this crustal domain are juxtposed by an oblique-slip shear zone named as S.Lucia Shear Zone. Structural and petrological data document interaction between magmatism, metamorphism and shearing during Permian in the c. 800-400 °C temperature range. In Calabria (Sila, Serre and Aspromonte), a continuous pre-Mesozoic crustal section is exposed. The lower crust portion of such section is mainly made up of granulites and migmatitic paragneisses with subordinate marbles and metabasites. The mid-crustal section includes an up to 13 km thick sequence of granitoids of tonalitic to granitic composition, emplaced between 306 and 295 Ma and progressively deformed during retrograde extensional shearing to end with a final magmatic activity between 295 and 277 Ma, consisting in the injection of shallower dykes in a transtensional regime. The section is completed by an upper crustal portion mainly formed by a Paleozoic succession deformed as a low-grade fold and thrust belt, locally overlaying medium-grade paragneiss units, and therefore as a whole reminiscent of the external/nappe zone domains of Sardinia Hercynian orogen. In Tuscany we document, how late Carboniferous/Permian shallow marine to continental sedimentary basins characterized by unconformity and abrupt change in sedimentary facies (coal-measures, red fanglomerate deposits) and acid magmatism well fit a transtensional setting with a mid-crustal shear zone linked with a system of E-W trending (in present orientation) upper crust splay faults. We will frame the whole dataset in a regional framework of first-order transcurrent shear zones network which includes a westernmost S.Lucia Shear Zone and an easternmost East Tuscan Shear Zone, with intervening crustal domains in which extensional to transtensional shearing occured.</p>

Strain partitioning in the mid-crust of a transpressional shear zone system: Insights from the Homestake and Slide Lake shear zones, central Colorado

2012 ◽  
Vol 39 ◽  
pp. 237-252 ◽  
Author(s):  
P. Elizabeth Lee ◽  
Micah J. Jessup ◽  
Colin A. Shaw ◽  
Gordon L. Hicks ◽  
Joseph L. Allen
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strain Partitioning

scholarly journals The Hajjar Regional Transpressive Shear Zone (Guemassa Massif, Morocco): Consequences on the Deformation of the Base-Metal Massive Sulfide Ore

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 435 ◽  
Author(s):  
Safouane Admou ◽  
Yannick Branquet ◽  
Lakhlifi Badra ◽  
Luc Barbanson ◽  
Mohamed Outhounjite ◽  
...  
Keyword(s):  
Shear Zone ◽  
Base Metal ◽  
Regional Scale ◽  
Shear Zones ◽  
Massive Sulfide ◽  
Late Carboniferous ◽  
Tectonic Event ◽  
Sulfide Deposits ◽  
Massive Sulfide Deposits ◽  
Mining Work

The genesis of the base-metal massive sulfide deposits hosted within the Moroccan Hercynian Jebilet and Guemassa Massifs is still under debate. No consensus currently exists between the two models that have been proposed to explain the deposits, i.e., (1) syngenetic volcanogenic massive sulfide mineralization, and (2) synmetamorphic tectonic fluid-assisted epigenetic mineralization. Conversely, researchers agree that all Hercynian massive sulfide deposits in Morocco are deformed, even though 3D structural mapping at the deposit scale is still lacking. Therefore, while avoiding the use of a model-driven approach, the main aim of this contribution is to establish a first-order structural pattern and the controls of the Hajjar base metal deposit. We used a classical structural geology toolbox in surface and subsurface mining work to image finite strain at different levels. Our data demonstrate that: i) the Hajjar area is affected by a single foliation plane (not two) which developed during a single tectonic event encompassing a HT metamorphism. This syn-metamorphic deformation is not restricted to the Hajjar area, as it is widespread at the western Meseta scale, and it occurred during Late Carboniferous times; ii) the Hajjar ore deposit is hosted within a regional transpressive right-lateral NE-trending shear zone in which syn- to post-metamorphic ductile to brittle shear planes are responsible for significant inflexion (or virgation) of the foliation yielding an anastomosing pattern within the Hajjar shear zone. Again, this feature is not an exception, as various Late Carboniferous-Permian regional scale wrenching shear zones are recognized throughout the Hercynian Meseta orogenic segment. Finally, we present several lines of evidence emphasizing the role of deformation in terms of mechanical and fluid-assisted ore concentrations.

scholarly journals The problems of the post-Cenomanian tectonic evolution of the central parts of the Sredna Gora Zone. The wrench tectonics – how real is real?

2020 ◽  
Vol 49 (2) ◽  
pp. 39-58
Author(s):  
Alexandre Kounov ◽  
Ianko Gerdjikov
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Shear Zones ◽  
Strike Slip ◽  
Evidence Based ◽  
Strain Partitioning ◽  
Substantial Evidence ◽  
The North ◽  
Thrust Belts ◽  
The Moment

The Sredna Gora Zone holds a unique place in the tectonic subdivisions of the Balkanide orogen and its evolution is still a subject of debate. In the last twenty years, the idea of strike-slip-related evolution of the zone has been invoked. However, for the moment, the number of thorough studies where such a scenario is envisaged is limited, and substantial evidence based on detailed fieldwork is still missing. In this article, we discuss some of the major problems of the suggested wrench tectonic concept in the evolution of the central part of the Sredna Gora Zone. These are the character of some major shear zones in the area, to which strike-slip movements are attributed, and the transtension-transpression evolution scenario for the Chelopech and Panagyurishte basins. Despite refuting completely their wrench tectonic-related evolution, we confirm the presence of strike-slip and oblique slip structures cutting the sediments, whereas the time of their activity and role in the deformation of the basin fill are yet to be revealed. Finally, we present a model based on natural examples and analogue modeling, in which the long-lived dextral Maritsa shear zone represents a zone of localized strain partitioning, separating the opposite vergent thrust belts of the Rhodope to the south and the Sredna Gora and Balkan fold-thrust belt to the north, during oblique or possibly orthogonal convergence.

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