Evaluation of a regional strain gradient in mylonitic quartzites from the footwall of the Main Central Thrust Zone (Garhwal Himalaya, India): Inferences from finite strain and AMS analyses

Tripathy, Nihar R.; Srivastava, H. K.; Mamtani, Manish A.

doi:10.1016/j.jseaes.2008.03.008

Cited by 24 publications

(5 citation statements)

References 51 publications

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“…A fundamental correlation between finite strain and magnetic anisotropy has often been proposed (Fig. 2; e.g., Benn, 1994;Cogne and Perroud, 1988;Henry and Daly, 1983;Hirt et al, 1993;Housen et al, 1995;Hrouda, 1987Hrouda, , 1993Kligfield et al, 1977Kligfield et al, , 1981Kontny et al, 2012;Lüneburg et al, 1999;Plissart et al, 2012;Rathore, 1979;Tikoff et al, 2005;Tripathy et al, 2009). This correlation would apply to both the magnitude of strain and magnetic anisotropy, and to the principal directions of the strain and magnetic anisotropy tensors.…”

Section: Introductionmentioning

confidence: 96%

Deformation and magnetic fabrics in ductile shear zones: A review

et al. 2014

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The Anisotropy of Magnetic Susceptibility (AMS) is a well-established petrofabric tool for indicating relative strain and microstructural character and has been validated on various rock types and different structural settings. The magnetic susceptibility of a rock (K) depends primarily on the nature and abundance of magnetic minerals. The physical arrangement and lattice-preferred orientation of these magnetic minerals give rise to magnetic anisotropy. The AMS scalar parameters most commonly used to constrain strain include the corrected degree of anisotropy (P′ N 1), a proxy for fabric intensity, and the shape factor (−1 ≤ T ≤ +1), an indicator of the magnetic fabric symmetry (prolate vs. oblate). A number of studies have shown that a positive correlation generally exists between P′ and strain. Thus, the AMS shows a great potential as a tool for examining deformation in geologic structures characterized by large strain gradients such as shear zones. However, a number of caveats exist: (i) The increase of P′ with strain cannot be solely attributed to deformation because P′ also increases with K regardless of deformation; (ii) Strain across shear zones is typically heterogeneous and is often localized in units of different lithology, thus making the separation of the lithological and strain controls on AMS difficult; also, deformation is commonly accompanied by mineral segregation or fluid-rock interaction that induces changes in magnetic mineralogy; (iii) Even if the undeformed lithology was uniform across a shear zone, variations in strain rate or temperature may result in different deformation mechanisms; hence, the relationship between P′ and strain depends strongly on both the mineral carriers of AMS and on deformation mechanisms; and (iv) The AMS is unable to resolve composite fabrics, such as those resulting from S-C structures, where minerals on the C and S planes, respectively, contribute to AMS.

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Section: Introductionmentioning

confidence: 96%

Deformation and magnetic fabrics in ductile shear zones: A review

et al. 2014

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“…During ductile deformation of any shear zones, the rocks of the footwall side may remain rigid or may suffer deformation along with the shear zone with similar geometry of structures (Ramsay and Huber 1983;Daniel et al 1996;Gutikrrez-Alonso 1996;Singh and Thakur 2001;Tripathy et al 2009;Fossen 2010). The wall rocks generally remain undeformed where the deformation in the shear zone is by simple shear only.…”

Section: Discussionmentioning

confidence: 99%

Deformation of footwall rock of Phulad Shear Zone, Rajasthan: Evidence of transpressional shear zone

et al. 2016

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Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e., the hanging wall contains a variety of rocks namely calc-silicates, pelites and amphibolites and the southwestern unit, i.e., the footwall unit contains only granitic rocks. Systematic investigation of the granites of the southwestern unit indicate a gradual change in the intensity of deformation from a distance of about 1 km west of the shear zone to the shear zone proper. The granite changes from weakly deformed granite to a mylonite/ultramylonite as we proceed towards the PSZ. The weakly deformed granite shows a crude foliation with the same attitude of mylonitic foliation of the PSZ. Microscopic study reveals the incipient development of C and S fabric with angle between C and S varying from 15 • to 24 •. The small angle between the C and S fabric in the least deformed granite variety indicates that the deformation has strong pure shear component. At a distance of about 1 m away from the PSZ, there is abrupt change in the intensity of deformation. The granite becomes intensely foliated with a strong downdip lineation and the rock becomes a true mylonite. In mesoscopic scale, the granite shows stretched porphyroclasts in both XZ and YZ sections indicating a flattening type of deformation. The angle between the C and S fabric is further reduced and finally becomes nearly parallel. In most places, S fabric is gradually replaced by C fabric. Calculation of sectional kinematic vorticity number (W n) from the protomylonitic and mylonite/ultramylonite granites varies from 0.3 ± 0.03 to 0.55 ± 0.04 indicating a strong component of pure shear. The similarity of the geometry of structures in the PSZ and the granites demonstrates that the deformation of the two units is broadly synchronous and the deformation in both the units is transpressional.

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“…(a) Simultaneous deformation of layer-parallel shortening and heterogeneous simple shear; (b) simultaneous deformation of layer-normal shortening and heterogenous simple shear. documented strain to address the internal deformation of different tectonostratigraphic units (GHS and LHS) in western Himalaya (N. Bose et al, 2018;Joshi et al, 2017Joshi et al, , 2019Puniya et al, 2019;Singh & Thakur, 2001;Tripathy et al, 2009), Nepal Himalaya (Goscombe et al, 2006;Law et al, 2004), and Arunachal Himalaya (Joshi et al, 2021). However, to the best of our knowledge, this is the first study that addresses how shortening gets partitioned across scales (thrust-sheet scale vs. grain-scale), strain geometry variation among all the exposed thrusts, and their contribution to the total shortening budget across an orogen.…”

Section: Penetrative Strain Variation In Orogenic Beltsmentioning

confidence: 99%