Microstructures and strain variation: Evidence of multiple splays in the North Almora Thrust Zone, Kumaun Lesser Himalaya, Uttarakhand, India

Joshi, Gaurav; Agarwal, Amar; Agarwal, K. K.; Srivastava, Seema; Alva‐Valdivia, Luis M.

doi:10.1016/j.tecto.2016.11.008

Cited by 28 publications

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“…However, rocks in the target subsurface of A37 and A38 experienced peak shock pressures <2 GPa, which is below the Hugoniot elastic limit of magnetite (~5.0 GPa; Ahrens and Johnson), although tensile fractures formed during decompression of the wave may have also affected the magnetite grains (Figure 3e). AMS investigations on phyllosilicate-bearing rocks deformed in tectonic regimes attribute reorientation of K3 to shearing and folding of paramagnetic minerals, such as biotite and chlorite, in response to the tectonic stresses, which is partly similar to the present situation (e.g., Borradaile & Henry, 1997;Borradaile & Jackson, 2010;Hrouda, 1982;Joshi et al, 2017;Martín-Hernández & Hirt, 2004;Tarling & Hrouda, 1993).…”

Section: Intensity Of Magnetic Fabric Reorientation In Crater Subsurfacementioning

confidence: 77%

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

et al. 2019

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Magnetic fabrics provide important clues for understanding impact cratering processes. However, only a few magnetic fabric studies for experimentally shocked material have been reported so far. In the framework of MEMIN (Multidisciplinary Experimental and Modeling Impact Research Network), we conducted two impact experiments on blocks of Maggia gneiss with the foliation oriented perpendicular (A38) and parallel (A37) to the target surface. Maggia gneiss has plenty of biotite bands forming a strong rock foliation. The bulk magnetic susceptibility varies from 0.376 × 10−3 to 1.298 × 10−3 SI in unshocked and from 0.443 × 10−3 to 3.940 × 10−3 SI in shocked gneiss. The thermomagnetic curves reveal a Verwey transition at −147 °C and a Curie temperature between 576 and 579 °C in unshocked and shocked samples, indicating nearly pure magnetite, which carries the magnetic fabrics. In A37 and A38 kinking is prominent from the point source down to a depth of 2 and 4.2 dp (projectile diameter) or 1 and 2.1 cm, respectively. Kinking, folding, and fracturing changed the position of magnetite grains with respect to each other to reorient the magnetic fabrics. Reorientation of magnetic fabrics is conspicuous down to 20 dp (10 cm) in A38, where no other impact‐related deformation is visible. The reorientation of magnetic fabrics may, therefore, aid in identifying impact processes at very low pressures, starting at 0.1 GPa, when other common indicators are absent.

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Section: Intensity Of Magnetic Fabric Reorientation In Crater Subsurfacementioning

confidence: 77%

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

et al. 2019

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“…c and d in Joshi et al. ). The individual lamellae, typically ≥2 μm, are curved or irregular (Christie and Raleigh ).…”

Section: Discussionmentioning

confidence: 93%

“…; Joshi et al. ). In the context of the present discussion, the most important characteristic of MDL is that they are not parallel with the rational crystallographic planes (Christie and Raleigh ; figs.…”

Section: Discussionmentioning

confidence: 99%

“…In the context of the present discussion, the most important characteristic of MDL is that they are not parallel with the rational crystallographic planes (Christie and Raleigh 1959; figs. 5c and 5d in Joshi et al 2016). The individual lamellae, typically ≥2 lm, are curved or irregular (Christie and Raleigh 1959).…”

Section: Impact Origin Of the Wedgesmentioning

confidence: 97%

“…MDL generally form sets of narrow planar to subplanar lamellae (French and Koeberl [2010] and references therein), which are always accompanied by recognizable penetrative petrographic foliation (e.g., Agarwal et al 2011;Joshi et al 2016). In the context of the present discussion, the most important characteristic of MDL is that they are not parallel with the rational crystallographic planes (Christie and Raleigh 1959; figs.…”

Section: Impact Origin Of the Wedgesmentioning

confidence: 99%

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Alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden: A new shock wave‐induced deformation feature

Agarwal

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Alva‐Valdivia

et al. 2016

Meteorit & Planetary Scien

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This paper reports peculiar alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden. The combined microscopic and spectroscopic studies of the micro/nanoscale wedges reveal that these are deformation‐induced features. First, samples showing wedges, 12 out of 18 studied, are distributed in the impact structure within a radius of up to 10 km from the crater center. Second, the margins between the augite and labradorite wedges are sharp and the {110} prismatic cleavage of augite develops into fractures and thereafter into wedges. The fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain. Third, compared to the bulk labradorite, the dislocation density and the residual strain in the labradorite wedges are significantly higher. A possible mechanism of genesis of the wedges is proposed. The mechanism explains that passing of the shock waves in the basement dolerite induced (i) formation of microfractures in augite and labradorite; (ii) development of the augite prismatic cleavages into the wedges, which overprint the microfracture in the labradorite wedges; and (iii) thereafter, infilling of microfractures in the augite wedges by labradorite.

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Evaluation of neotectonic variability along major Himalayan thrusts within the Kali River basin using geomorphic markers, Central Kumaun Himalaya, India

2019

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We have analysed the geomorphic signatures in aggregation with the geomorphic indices with respect to hinterland and foreland neotectonic variability across the major Himalayan thrust system along the Kali River valley of eastern Kumaun Himalaya. The valley floor morphology in the vicinity of the major thrust gave rise to the accommodation space for the aggradation of the recent fluvial sediments. For a longitudinal distance of 212 km between the South Tibet Detachment (STD)and Himalayan Frontal Thrust (HFT), the valley has preserved significant aggradational landforms. These landforms have been physically examined to explain the spatial and temporal variability in phases of aggradation/incision in response to the tectonic activity during the late Quaternary. Fossil valleys and associated epigenetic gorges, cut-and-fill terraces with thick alluvial cover, debris-flow terraces, bedrock strath terraces, and alluvial fan terraces are the significant aggradational landforms observed within the valley. They provide signatures of tectonic activity and past climatic records. We have analysed various geomorphic indices, namely, stream-gradient index (SL), steepness index (Ks), hypsometric curve and index (HI), and asymmetric factor (AF) to map the spatial variability in tectonic processes across the major thrusts. The channel morphology (depth and width) of a river becomes adjusted in geological time because of long-term tectonic and erosional processes. However, the channel geometry and deviations can be highly adjustable in a tectonically disturbed mountainous region. The deviations along the river course can be attributed to active tectonic movement along thrusts/faults or because of erosion/sedimentation processes. We applied a novel method called the river Gradient Length Anomaly (GLA) for 37 subbasins of the Kali River to deduce active deformation (uplift/subsidence) corresponding to the increased sedimentation and erosional rates, both from the upstream and downstream parts of the thrusted blocks, from where river flows through. The results of basin-wise morphometric indices were corroborated with GLA anomaly and field observations, which suggests that the area has undergone active deformation between the Main Central Thrust (MCT) and Himalayan Frontal Thrust (HFT), which is attributed to the regional compression. The results of geomorphic and morphometric data are validated with the focal mechanisms of moderate earthquakes. The geomorphic analysis suggests that the hinterland part of eastern Kumaun is more active than the foreland region.

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Microstructures and strain variation: Evidence of multiple splays in the North Almora Thrust Zone, Kumaun Lesser Himalaya, Uttarakhand, India

Cited by 28 publications

References 50 publications

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

Variation in Magnetic Fabrics at Low Shock Pressure Due to Experimental Impact Cratering

Alternating augite‐plagioclase wedges in basement dolerites of Lockne impact structure, Sweden: A new shock wave‐induced deformation feature

Evaluation of neotectonic variability along major Himalayan thrusts within the Kali River basin using geomorphic markers, Central Kumaun Himalaya, India

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