Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures: A review

Law, Richard D.

doi:10.1016/j.jsg.2014.05.023

Cited by 335 publications

(278 citation statements)

References 172 publications

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“…The quartz mylonites selected to test synchrotron FTIR and imaging of OH come from the footwall of the Moine Thrust (MT) at the Stack of Glencoul, NW Scotland (Christie, 1963;Law et al, 1986, and the hanging wall of the Main Central Thrust (MCT) exposed in the Sutlej Valley, NW India (Law et al, 2013;Stahr, 2013;Law, 2014). 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).…”

Section: Selected Quartz Mylonitesmentioning

confidence: 99%

“…Deformation temperatures for the MT footwall mylonites at the Stack of Glencoul are estimated at between 300 and 350 • C based on illite crystallinity (Johnson et al, 1985). Opening angles of c-axis fabrics measured separately on old and recrystallized grains indicate far higher apparent deformation temperatures using the Kruhl (1998) fabric opening angle thermometer (390-440 and 475-530 • C, respectively) than are compatible with their prehnite-pumpellyite to lower greenschist (chlorite) facies phyllosilicates (Law, 2014). Deformation temperatures for MCT hanging wall mylonites range between ∼ 535 and 610 • C on the NW Sutlej transect, using the Kruhl (1998) opening angle thermometer, and ∼ 610-> 735 • C based on fabric opening angles and petrologic constraints on the Eastern Sutlej transect (Table 1; Law et al, 2013;Stahr, 2013).…”

Section: Selected Quartz Mylonitesmentioning

confidence: 99%

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Synchrotron FTIR imaging of OH in quartz mylonites

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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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“…For example, the western leading edge of Ganderia was still undergoing the late stages of the Salinic orogeny at the time of the onset of Acadian-related arc magmatism and deformation at its eastern trailing edge (van Staal et al, 2009;2014).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…The opening angle of crossed-girdle quartz c-axis fabric may be related to the temperature at which the fabric was established (Kruhl, 1998;Morgan and Law, 2004;Law, 2014). Employing the opening-angle thermometer, however, requires a number of assumptions including temperature being the primary control, stable critical resolved shear stress, lack of hydrolytic weakening, and consistent strain rate (see Law (2014) for a detailed review).…”

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Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

Kellett

Warren

Larson

et al. 2016

Lithos

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Midcrustal discontinuities and the assembly of the Himalayan midcrust

Larson

Cottle

2014

Tectonics

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Detailed quartz lattice preferred orientation (LPO) data define two structural discontinuities in the exhumed high-grade metamorphic core of the Himalaya exposed in the upper Tama Kosi region of east central Nepal. The structures are marked by abrupt breaks in a general trend of up structural section increasing quartz LPO-defined deformation temperatures. Deformation associated with the upper structural discontinuity, which occurs within sillimanite grade rocks, is postpeak metamorphism in both the hanging wall and the footwall. New geochronologic data constrain the timing of metamorphism in the hanging wall of the upper discontinuity to between 24 and 16 Ma, indistinguishable from previously published ages for the footwall. Movement across this structure represents Early Miocene strain localization and thickening in the Himalayan midcrust. Movement across the lower discontinuity, which occurs between staurolite and kyanite grade rocks, appears to be synmetamorphic with material in its footwall at approximately 10 Ma, but postpeak metamorphism for material in its hanging wall. This movement is interpreted to reflect the underplating and incorporation of material into the metamorphic core. The recognition of two thrust-sense discontinuities in the exhumed Himalayan core in the Tama Kosi region is consistent with other similar structures recognized along the Himalaya. The widespread nature of these structures reinforces that they are important to our understanding of the evolution of the kinematics of large, hot orogens.

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Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures: A review

Cited by 335 publications

References 172 publications

Synchrotron FTIR imaging of OH in quartz mylonites

Synchrotron FTIR imaging of OH in quartz mylonites

Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

Midcrustal discontinuities and the assembly of the Himalayan midcrust

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