Structural geometry, microstructural and strain analyses of L-tectonites from Paleoproterozoic orthogneiss: Insights into local transport-parallel constrictional strain in the Sikkim Himalayan fold thrust belt

Bhattacharyya, Kathakali; Dwivedi, Harsh Vardhan; Das, Jyoti Prasad; Damania, Sagar

doi:10.1016/j.jseaes.2015.04.038

Cited by 27 publications

(18 citation statements)

References 28 publications

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“…In our experience, most L‐tectonites appear to occur as isolated volumes in rock masses of other (S, S > L, or S ≈ L) tectonites, and they cannot always be attributed to nonsteady finite strain buildup associated with fold closures or curved segments of shear zones (Figures a and b). For instance, Bhattacharyya et al () described L‐tectonites from Paleoproterozoic orthogneiss in the Sikkim Himalayan fold thrust belt as “preferentially developed within the rheologically stronger Lingtse gneiss as compared to the weaker underlying Daling phyllites.” Krabbendam and Dewey () reported L‐tectonites in granitic gneiss sandwiched, in the map view, between LS‐ or SL‐tectonites in the SW of the Hgtsteinen Basin of Western Gneiss Region in West Norway (their Figure 6). Although the authors attributed the L‐tectonites to transtension, the presence of LS‐ or SL‐tectonites on both sides of the L‐tectonites is inconsistent with the transtension strain field.…”

Section: Introductionmentioning

confidence: 99%

“…(a) is modified after Sullivan (2013), (b) after Lin and Jiang (2001), (c) after Whitney et al (2004), and (d) after (S, S > L, or S ≈ L) tectonites, and they cannot always be attributed to nonsteady finite strain buildup associated with fold closures or curved segments of shear zones (Figures 1a and 1b). For instance, Bhattacharyya et al (2015) described L-tectonites from Paleoproterozoic orthogneiss in the Sikkim Himalayan fold thrust belt as "preferentially developed within the rheologically stronger Lingtse gneiss as compared to the weaker underlying Daling phyllites." Krabbendam and Dewey (1998) reported L-tectonites in granitic gneiss sandwiched, in the map view, between LS-or SL-tectonites in the SW of the Hgtsteinen Basin of Western Gneiss Region in West Norway (their Figure 6).…”

Section: Introductionmentioning

confidence: 99%

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Constrictional Strain and Linear Fabrics as a Result of Deformation Partitioning: A Multiscale Modeling Investigation and Tectonic Significance

Yang

Jiang

2019

Tectonics

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Rocks with a well‐developed lineation but weak or no foliation (L‐tectonites) commonly occur as isolated volumes dispersed in other tectonites. We consider L‐tectonites that reflect constrictional finite strains here and use a multiscale approach to investigate the conditions for constrictional strain fields. The approach combines the strength of kinematic and mechanical analyses in large strain three‐dimensional deformations. Our modeling shows that, in simple shearing and thinning zone progressive deformations, constrictional strains develop only in rheological heterogeneities that are moderately stronger than the bulk material as a whole. Stronger elements never accumulate enough internal strains for any fabric to develop. Inclusions weaker than the bulk material will develop flattening strains. L‐tectonites are most likely developed in macroscale simple shearing, simple‐shearing‐dominated plane‐strain general shearing, or simple‐shearing‐dominated Sanderson and Marchini transpression. The lineations of the L‐tectonites are always nearly parallel to the lineations in the bulk material. Where the lineations are nearly 90° from the vorticity axis, the macroscale flow is close to a plane‐strain general shearing. Where the lineations are oblique to the vorticity axis or more variable, a simple‐shearing‐dominated triclinic thinning zone with mainly uniaxial boundary stretching is likely. The concept of homogeneous transtension deformation, combining a homogeneous pure shearing and a transcurrent simple shearing, is unsupported by fabric evidence and is likely unrealistic. Under an oblique divergence boundary condition, the upper lithosphere deforms by folding and fracturing and the ductile lithosphere develops simple‐shearing‐dominated detachment shear zones. Constrictional strains (hence L‐tectonites) can develop in these detachment zones due to flow partitioning.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Constrictional Strain and Linear Fabrics as a Result of Deformation Partitioning: A Multiscale Modeling Investigation and Tectonic Significance

Yang

Jiang

2019

Tectonics

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“…In the eastern parts of the Himalayan orogen (Darjeeling-Sikkim Himalaya) detailed structural, metamorphic and geochronological investigations have provided insight into its crustal shortening, P-T conditions and timing of metamorphism. In the Darjeeling-Sikkim Himalayan fold thrust belt (FTB), a minimum shortening of ~450 km (~81%) is accommodated south of the STDS in a folded thrust system (Bhattacharyya et al, 2015a). From north to south these are the Main Central thrust (MCT), the Pelling thrust (PT), the Lesser Himalayan duplex, the Ramgarh thrust (RT), the Main Boundary thrust (MBT) and the Main Frontal thrust (MFT).…”

Section: (A) Tso Morari Crystallines (Tmc)mentioning

confidence: 99%

“…From north to south these are the Main Central thrust (MCT), the Pelling thrust (PT), the Lesser Himalayan duplex, the Ramgarh thrust (RT), the Main Boundary thrust (MBT) and the Main Frontal thrust (MFT). The average long-term shortening rate is estimated at ~20 mm/yr (Bhattacharyya et al, 2015a). The initial width of the Lesser Himalayan (LH) basin controlled the geometry and total number of LH imbricates and horses along the FTB, thereby controlling the minimum shortening estimates from the orogenic transects (Bhattacharyya and Ahmed, 2016).…”

Section: (A) Tso Morari Crystallines (Tmc)mentioning

confidence: 99%

Tectonics and Evolution of the Himalaya

Jain

Dasgupta²,

Bhargava³

et al. 2016

Proceedings of the Indian National Science Academy

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During the period 2011-2015, scientific investigations in the Himalaya incorporated various geological and geophysical aspects of evolution of this mountain, including sub-surface configuration, structure and metamorphism of the Lesser Himalaya and Himalayan Metamorphic Belt, geochemistry, magmatism, stratigraphy and paleontology of the Paleo-Mesozoic Tethyan sedimentary cover, the Himalayan foreland basins, exhumation, paleoseismology and GPS measurements of convergence rates. Certain remote areas of western Arunachal Pradesh in Kameng were covered for their metamorphism and exhumation. Sm-Nd isochron plot of garnet crystals from the Lesser Himalayan Jutogh Group metamorphics provided a mean regression age of 479.7±8.5 Ma as the timing of its crystallization during an Early Ordovician tectonometamorphic event. High-resolution work on metamorphism of the Lesser and Higher Himalayan belts of Sikkim incorporating P-T-t paths and geochronology of the imbricate zones of the Main Central Thrust provided better insight into their evolution.

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“…In particular, it is common to find L‐tectonites, surrounded by S‐ or SL‐tectonites (e.g. Bhattacharyya, Dwivedi, Das, & Damania, ; Collins, Van Kranendonk, & Teyssier, ; Fossen, ; Holst & Fossen, ; Hudleston, Schultz‐Ela, & Southwick, ; Kassem & Ring, ; Krabbendam & Dewey, ; Sullivan, ). The presence of localized L‐tectonites has been linked to specific geological settings, such as (a) closures of isoclinal folds, (b) shear zones, (c) and around diapirs and plutons (Yang, Jiang, & Lu, 2019; Sullivan, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Late Miocene constrictional strain in the northern Apennines: A case study from the Barabarca metaconglomerate (Elba Island, Italy)

Papeschi

2020

Geological Journal

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Finite strain analyses were performed on a deformed metaconglomerate from the Calamita Unit in the Island of Elba. The Calamita Unit is a synkinematic contact aureole that was shaped by Late Miocene contractional deformation coeval with high‐temperature metamorphism. The metaconglomerate occurs as an L‐tectonite in the footwall of a major thrust, entirely surrounded by S‐tectonites developed in schistose rocks. Object lineations, defined by the preferred orientation of clasts, trend subparallel to the stretching lineations in the associated rocks. Quartz microstructures registered ductile deformation of clasts by grain boundary migration to bulging recrystallization, suggesting temperature decrease during deformation. Rf/ϕ analyses were carried out on three metaconglomerate samples using quartzite clasts as markers. The finite strain data show that the metaconglomerates are strongly deformed in the constrictional field with K values between ~3 and ~7. The constrictional deformation registered by the metaconglomerate with respect to the surrounding metapelites, which likely deformed under plane strain, can be interpreted as the result of flow partitioning in rheologically heterogeneous sequences during deformation. These results suggest the presence of significant strain gradients in the Calamita Unit, strictly associated with heterogeneously distributed ductile shear zones.

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Structural geometry, microstructural and strain analyses of L-tectonites from Paleoproterozoic orthogneiss: Insights into local transport-parallel constrictional strain in the Sikkim Himalayan fold thrust belt

Cited by 27 publications

References 28 publications

Constrictional Strain and Linear Fabrics as a Result of Deformation Partitioning: A Multiscale Modeling Investigation and Tectonic Significance

Constrictional Strain and Linear Fabrics as a Result of Deformation Partitioning: A Multiscale Modeling Investigation and Tectonic Significance

Tectonics and Evolution of the Himalaya

Late Miocene constrictional strain in the northern Apennines: A case study from the Barabarca metaconglomerate (Elba Island, Italy)

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