Ductile extrusion of the Higher Himalayan Crystalline in Bhutan: evidence from quartz microfabrics

Grujić, Djordje; Casey, Martin; Davidson, Cameron; Hollister, L. S.; Kündig, Rainer; Pavlis, Terry L.; Schmid, Stefan M.

doi:10.1016/0040-1951(96)00074-1

Cited by 423 publications

(425 citation statements)

References 55 publications

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“…Unit divisions, structure and stratigraphic contact locations, and rock unit descriptions on our map benefit greatly from recent studies that describe the structural geometry, metamorphic grade, and deformation history of GH rocks in Bhutan (Chakungal et al, 2010;Daniel et al, 2003;Davidson et al, 1997;Gansser, 1983;Grujic et al, 1996;Hollister and Grujic, 2006;Kellett et al, 2009;Long and McQuarrie, 2010;Long et al, 2011a;Swapp and Hollister, 1991;Warren et al, 2011). Recent studies that present new detrital geochronology data Richards et al, 2006) provide valuable constraints on the age range of deposition of sedimentary protoliths of GH rocks and the age of intrusive rocks within the GH section.…”

Section: Previous Workmentioning

confidence: 99%

Geologic Map of Bhutan

et al. 2011

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We present a new, 1:500,000-scale geologic map of the kingdom of Bhutan, and surrounding areas of India and southern Tibet. The map is a compilation of the most complete and most recent mapping datasets available, and presents an unprecedented amount of structural data when compared to previous published geologic maps of Bhutan. The map is a combination of: 1) new data presented in this study; 2) compilation of small-scale, published geologic maps of specific areas of Bhutan, Tibet, and parts of India; and 3) compilation of specific areas of published, country-scale geologic maps of Bhutan. Mapping detail is focused primarily on Subhimalayan, Lesser Himalayan, and Greater Himalayan rocks, with a lower level of detail on Tethyan Himalayan rocks. We present new 3-part stratigraphic divisions for the Siwalik Group and the structurally-lower Greater Himalayan section, and compile detailed stratigraphic divisions and structural geometries for the Lesser Himalayan section and Paro Formation. We also compile detailed mapping of the Yadong cross-structure and other structurally-complex areas of southern Tibet, and present new locations for the South Tibetan detachment. Our map compilation also highlights specific areas in Bhutan that would benefit from future geologic mapping. It is our hope that this map will be a valuable tool to be utilized by Bhutanese geologists, future researchers visiting Bhutan, and travelers and trekkers as well. We also hope that this map will serve as a new starting point for future mapping in Bhutan and throughout the Himalayan orogen.

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Section: Previous Workmentioning

confidence: 99%

Geologic Map of Bhutan

et al. 2011

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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%

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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“…The STDS separating these two tectonostratigraphic units is exposed on top of the steep south facing cliffs of the Table Mountains at Gansser [1983], Cogan et al [1998], Grujic et al [1996], Burg and Chen [1984], Burchfiel et al [1992], and Edwards et al [1999]. Seismotectonic Goalpara lineament after De and Kayal [2003].…”

Section: Geological Setting In Eastern Lunanamentioning

confidence: 99%

Active tectonics in Eastern Lunana (NW Bhutan): Implications for the seismic and glacial hazard potential of the Bhutan Himalaya

Meyer

Wiesmayr

Brauner³

et al. 2006

Tectonics

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Paleoseismological investigations, brittle fault analysis, and paleostrain calculations combined with the interpretation of satellite imagery and flood wave modeling were used to investigate the seismic and associated glacial hazard potential in Eastern Lunana, a remote area in NW Bhutan. Seismically induced liquefaction features, cracked pebbles, and a surface rupture of about 6.8 km length constrain the occurrence of M ≥ 6 earthquakes within this high‐altitude periglacial environment, which are the strongest earthquakes ever been reported for the Kingdom of Bhutan. Seismicity occurs along conjugate sets of faults trending NE‐SW to NNW‐SSE by strike‐slip and normal faulting mechanism indicating E‐W extension and N‐S shortening. The strain field for these conjugate sets of active faults is consistent with widespread observations of young E‐W expansion throughout southern Tibet and the north Himalaya. We expect, however, that N‐S trending active strike‐slip faults may even reach much farther to the south, at least into southern Bhutan. Numerous glacial lakes exist in the investigation area, and today more than 100 × 106 m3 of water are stored in moraine‐dammed and supraglacial lakes which are crosscut by active faults. Strong earthquakes may trigger glacial lake outburst floods, and the impact of such flash floods may be worst 80 km downstream where the valley is broad and densely populated. Consequently, tectonic models of active deformation have to be closely linked with glacial hazard evaluation and require rethinking and modification.

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Ductile extrusion of the Higher Himalayan Crystalline in Bhutan: evidence from quartz microfabrics

Cited by 423 publications

References 55 publications

Geologic Map of Bhutan

Geologic Map of Bhutan

Synchrotron FTIR imaging of OH in quartz mylonites

Active tectonics in Eastern Lunana (NW Bhutan): Implications for the seismic and glacial hazard potential of the Bhutan Himalaya

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