Quantitative kinematic flow analysis from the Main Central Thrust Zone (NW-Himalaya, India): implications for a decelerating strain path and the extrusion of orogenic wedges

Grasemann, Bernhard; Fritz, Harald; Vannay, Jean-Claude

doi:10.1016/s0191-8141(99)00077-2

Cited by 211 publications

(123 citation statements)

References 48 publications

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“…Both of these thrust faults are orogen-scale shear zones with penetrative deformation on the MT accommodating shortening at the foreland edge of the Caledonian orogeny (e.g., Peach et al, 1907;Elliot and Johnson, 1980;Law et al, 1986Law and Johnson, 2010;Dewey et al, 2015) and penetrative shear strains on the MCT accommodating southward-directed Oligocene-Miocene extrusion/exhumation of the overlying Greater Himalayan slab (e.g., Grujic et al, 1996;Grasemann et al, 1999;Godin et al, 2006;Law et al, 2013). Mylonitic grain shape foliations are well developed in rocks of both fault zones and mineral stretching lineations are parallel to the fault transport directions.…”

Section: Selected Quartz Mylonitesmentioning

confidence: 99%

“…Quartz-rich Greater Himalayan Series orthogneisses and paragneisses in the hanging wall to the MCT exposed in NW and Eastern Sutlej transects, respectively, include quartz mylonites, quartz-mica schists, and quartz-garnet schists ( Vannay and Grasemann, 1998;Grasemann et al, 1999;Law et al, 2013). Quartz grain shapes are not as highly elongate as observed in the MT mylonites, owing to their extensive recrystallization, with mean grain sizes on the NW transect that vary with structural level from 200 to 250 µm (grain boundary migration microstructures) at ∼ 1000 m above the MCT to 75-95 µm at 200-750 m above the thrust, and 35-60 µm (dominantly subgrain rotation microstructures) at ∼ 75 m above the thrust surface (Law et al, 2013).…”

Section: Selected Quartz Mylonitesmentioning

confidence: 99%

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Synchrotron FTIR imaging of OH in quartz mylonites

et al. 2017

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Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4-8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm 2 . This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm −1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm −1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm −1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

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Section: Selected Quartz Mylonitesmentioning

confidence: 99%

Section: Selected Quartz Mylonitesmentioning

confidence: 99%

Synchrotron FTIR imaging of OH in quartz mylonites

et al. 2017

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“…The bounding shear zones may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or thrust sense, depending on the relative velocity 2004), 7, schematic velocity profile during return channel flow; 8, 750 ~ C isotherm structurally below which partial melt starts; 9, theological tip of the channel: at lower temperatures (for a given channel width and pressure gradient) Couette flow will dominate and all the material will be underthrust; 10, extruding crustal block (palaeo-channel): if the theological tip is at steady state, material points may move through this tip and pass from the weak crustal channel into the extruding block; 11, lower shear zone of the extruding crustal block (dominantly thrust-sense kinematics); 12, upper shear zone of the extruding crustal block (dominantly normal-sense kinematics); 13, focused surface denudation (controlled by surface slope and, as in the Himalaya, by orographic precipitation at the topographic front). (B)-(D) Possible strain distribution in an extruding crustal block; possible end-members (inspired by Grujic et al 1996;Grasemann et al 1999). (B) Rigid block with high concentration of strain along the boundaries .…”

Section: E X T R U S I O Nmentioning

confidence: 99%

“…(C) Ductile block deforming by pervasive simple shear. (D) Ductile block deforming by general shear with a pure shear component increasing towards the bottom of the wedge, as well as with time following a 'decelerating strain path' (Grasemann et al 1999;Vannay & Grasemann 2001).…”

Section: E X T R U S I O Nmentioning

confidence: 99%

“…Godin et al 2006). Since the early recognition of the STD, the coeval activity on the two bounding (and innermost) shear zones (MCTu and STD0, and its implication for exhumation of the metamorphic core of the Himalaya, has been suggested (Burchfiel & Royden, 1985;Hubbard & Harrison 1989;Searle & Rex, 1989;Burchfiel et al 1992;Hodges et al 1992Hodges et al , 1996Grujic et al 1996;Grasemann et al 1999); however, the proposed driving forces and kinematic details vary between authors.…”

Section: Coeval Channel-bounding Structuresmentioning

confidence: 99%

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Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction

et al. 2006

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Abstract:The channel flow model aims to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya-Tibet system. Channel flow describes a protracted flow of a weak, viscous crustal layer between relatively rigid yet deformable bounding crustal slabs. Once a critical low viscosity is attained (due to partial melting), the weak layer flows laterally due to a horizontal gradient in lithostatic pressure. In the Himalaya-Tibet system, this lithostatic pressure gradient is created by the high crustal thicknesses beneath the Tibetan Plateau and 'normal' crustal thickness in the foreland. Focused denudation can result in exhumation of the channel material within a narrow, nearly symmetric zone. If channel flow is operating at the same time as focused denudation, this can result in extrusion of the mid-crust between an upper normal-sense boundary and a lower thrust-sense boundary. The bounding shear zones of the extruding channel may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or ttuqast sense, depending on the relative velocity between the upper crust and the underlying extruding material. This introductory chapter addresses the historical, theoretical, geological and modelling aspects of channel flow, emphasizing its applicability to the Himalaya-Tibet orogen. Critical tests for channel flow in the Himalaya, and possible applications to other orogenic belts, are also presented.

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Kinematic and thermal studies of the Leo Pargil Dome: Implications for synconvergent extension in the NW Indian Himalaya

et al. 2014

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Building of the Himalaya and Tibetan Plateau involved an interplay between crustal thickening and extension. The NW Indian Himalaya near the Leo Pargil dome contains approximately N trending brittle normal faults and NE trending normal-sense shear zones (i.e., bounding Leo Pargil dome) between the South Tibetan detachment system to the south and the Karakoram fault to the north. The Leo Pargil shear zone bounds the southwest flank of the Leo Pargil dome. Estimates of deformation temperatures and mean kinematic vorticity (W m ) from the shear zone were integrated with pressure-temperature estimates to evaluate its kinematic and thermal evolution. Oblique quartz fabrics yielded kinematic vorticity estimates indicating that the rocks within the shear zone were thinned by up to 62% during W directed shearing. Top-down-to-the-W ductile deformation is recorded at temperatures from >650°C at the deepest structural levels within the dome and from 400 to 500°C at shallower structural depths. Hanging wall rocks record much lower temperatures. Pressure-temperature data indicate that rocks in the dome were exhumed from depths of~36 to 22 km. In contrast to other mechanisms proposed for dome formation across the Himalaya, initiation of ductile movement on the Leo Pargil shear zone occurred at midcrustal levels in a region of localized synconvergent extension at >23 Ma. The timing and kinematic setting of deformation on the Leo Pargil shear zone suggest that exhumation could be related to a localized zone of transtension near the Karakoram fault zone.

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Quantitative kinematic flow analysis from the Main Central Thrust Zone (NW-Himalaya, India): implications for a decelerating strain path and the extrusion of orogenic wedges

Cited by 211 publications

References 48 publications

Synchrotron FTIR imaging of OH in quartz mylonites

Synchrotron FTIR imaging of OH in quartz mylonites

Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction

Kinematic and thermal studies of the Leo Pargil Dome: Implications for synconvergent extension in the NW Indian Himalaya

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