Microstructures in quartz and feldspars of the Bomdila Gneiss from western Arunachal Himalaya, Northeast India: Implications for the geotectonic evolution of the Bomdila mylonitic zone

Singh, Rakesh Kumar; Gururajan, N. S.

doi:10.1016/j.jseaes.2011.06.014

Cited by 27 publications

(10 citation statements)

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“…The LHC occur either as synformal klippe over the LHSS or as a roughly continuous belt below the Higher Himalayan Crystallines (HHC) (Valdiya, ). The LHC are composed of quartzite, phyllite, schist, and granitoids, whereas the HHC is made up of high‐grade metamorphic rocks of kyanite–sillimanite‐bearing gneiss/schist, migmatite, leucogranite, and amphibolites (Bikramaditya & Gururajan, ). At the core of the Siang window of the EHS, meta‐sedimentary rocks of Miri‐Buxa Group are interbedded and cofolded with the AVR of Abor Formation and sedimentary rocks of Yinkiong Formation (Figure b).…”

Section: Geological Backgroundmentioning

confidence: 99%

Zircon U–Pb geochronology, Hf isotopic compositions, and petrogenetic study of Abor volcanic rocks of Eastern Himalayan Syntaxis, Northeast India: Implications for eruption during breakup of Eastern Gondwana

et al. 2019

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This paper reports new zircon U–Pb ages and Hf isotopic compositions of felsic units of the Abor volcanic rocks (AVR) of Eastern Himalayan Syntaxis (EHS), Northeast India, and discusses their relationship to the Kerguelen plume activity. The AVR are bimodal and predominantly constituted by mafic rocks with minor felsic units. Mafic volcanics are identified as basalt and basaltic andesite with light rare earth elements (LREE) enriched and slightly depleted heavy rare earth elements (HREE) pattern without Eu anomalies. Low concentrations of LILE, high contents of Fe2O3, and other incompatible trace elements ratios reflect enriched nature of these mafic volcanics. Felsic volcanic rocks are dacitic to rhyolitic in composition, which have high REE content, high LREE/HREE, and pronounced negative Eu anomalies. Enriched LREE, high Th/Nb, Ce/Nb ratios, and variations in Rb/Zr, K/Rb, La/Sm ratios with negative anomalies of Ba, Nb, Sr, P, Ti in felsic rocks suggest substantial contribution of crustal contamination at the time of eruption. Zircons from felsic units yield an average U–Pb age of ~132 Ma and unradiogenic (ƐHf(t) < 0) Hf isotope values of −7.0 to −13.3 with model ages between 1.5 and 2.1 Ga, suggesting old crustal assimilation in their genesis. The AVR were emplaced in the continental rift tectonic setting, and depth of the magma source is confirmed as near spinel stability zone. The AVR are positively comparable with other flood basalts that were formed due to the Kerguelen plume activity. Therefore, our combined new geochemical and geochronological data show that the AVR were emplaced at early stage (~132 Ma) of eastern Gondwana breakup due to outbreak of the Kerguelen plume. This study thus supports the idea of the Kerguelen plume affecting a large area of Eastern India, Western Australia, and Antarctica during early stage of Gondwana breakup.

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Section: Geological Backgroundmentioning

confidence: 99%

Zircon U–Pb geochronology, Hf isotopic compositions, and petrogenetic study of Abor volcanic rocks of Eastern Himalayan Syntaxis, Northeast India: Implications for eruption during breakup of Eastern Gondwana

et al. 2019

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“…Based on the microstructural features of the BG, Bikramaditya Singh & Gururajan (2011) proposed that the early ductile deformation in the BG was superimposed by brittle deformation during the exhumation of the LHC towards shallow structural levels from a deeper level. The presence of high-temperature deformation microstructures like recrystallized quartz with partially or completely recrystallized feldspars in the BG from the upper zone suggests that the BG was buried or underthrust at a deeper level below the Higher Himalayan Crystallines at an early stage.…”

Section: Discussionmentioning

confidence: 99%

“…The temperature of deformation increases from the lower to the upper zone as the lower zone deforms dominantly in the brittle regime and the upper regime deforms dominantly in ductile regime. This increase in deformation temperature from the lower to the upper zone produced an inverted thermal gradient from the lower to the upper zone (Bikramaditya Singh & Gururajan, 2011). The microstructural variation and decreasing temperature of deformation from the upper to the lower zone indicate that the LHC was initially buried below the Higher Himalayan Crystallines along the MCT and exhumed along the Bomdila Thrust at a later stage, as thrusting was transferred from the MCT to the Lesser Himalaya, towards shallow structural levels.…”

Section: Discussionmentioning

confidence: 99%

“…The LHC of the western Arunachal Himalaya is extensively covered by the granitoids locally known as the Bomdila Gneiss. It shows mylonization and bears a ductile deformation zone in the Lesser Himalaya, which is termed the Bomdila mylonitic zone (Gururajan & Choudhuri, 2003; Bikramaditya Singh & Gururajan, 2011). Development of penetrative foliation in association with down-dipping stretching lineation during the second phase of deformation (D 2 ) is the prominent structure of the BG.…”

Section: Introductionmentioning

confidence: 99%

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Detection of a weak late-stage deformation event in granitic gneiss through anisotropy of magnetic susceptibility: implications for tectonic evolution of the Bomdila Gneiss in the Arunachal Lesser Himalaya, Northeast India

Singh

Sen

et al. 2016

Geol. Mag.

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Outcrop-scale structures and magnetic fabric anisotropy of the Bomdila Gneiss (BG) that intruded the Lesser Himalayan Crystallines (LHC) of the Arunachal Lesser Himalaya are studied to understand the BG deformation history and tectonic evolution. Detailed analysis of structures reveals that the LHC have undergone three phases of deformation, D1, D2 and D3. The S2 foliation developed during the second phase of deformation (D2) is the most penetrative planar fabric in the studied rock, which shows a general ENE–WSW strike with moderate NW dip. Mesoscopic evidence of a later phase of deformation (D3) in the BG is lacking. Evidence of D3 deformation in the form of F3 folds is only observed in the adjacent metasedimentary rocks of the LHC. The magnetic foliations recorded from anisotropy of magnetic susceptibility (AMS) analysis of the BG are mostly striking NW–SE with a moderate dip towards the NE or SW, and magnetic lineation is mostly sub-horizontal and dominantly plunging towards the SE. Our study shows that the magnetic fabric of the BG does not correspond to any visible outcrop-scale mesoscale foliation. However, the magnetic foliation of the BG is parallel to the axial plane of the F3 folds of the adjacent metasedimentary rocks of the LHC. Integration of AMS and outcrop-scale structural analysis helps us envisage the superposed deformation history of the BG. Our study emphasizes the importance of AMS to detect late-stage or feeble deformation events that leave no visible outcrop-scale imprint and are difficult to discern through conventional geological means.

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“…The western Arunachal Himalaya comprises three major tectonic units from south to north: the Sub Himalaya, the Lesser Himalaya and the Higher Himalaya (Fig. , Table ; Das et al ., ; Verma and Tandon, ; Bhushan et al ., ; Yin et al ., ; Bikramaditya Singh and Gururajan, ). The Sub Himalaya comprises sandstone, siltstone and conglomerate of the Siwalik Group, which has a faulted contact (Himalayan Frontal Thrust—HFT) with Brahmaputra alluvium in the south.…”

Section: Geological Settingmentioning

confidence: 99%

Microstructural and geochemical studies of Higher Himalayan Leucogranite: implications for geodynamic evolution of Tertiary Leucogranite in the Eastern Himalaya

Singh¹,

Singh²

2013

Geol. J.

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The Higher Himalayan Leucogranites (HHLG) intruded into the high grade rocks of the Higher Himalayan Crystallines (HHC) in Arunachal Himalaya of the Eastern Himalaya, yield distinctive field data, petrography, microstructures, geochemical and mineral chemistry data. The Arunachal HHLG are characterized by the presence of two micas; normative corundum; high contents of SiO2 (67–78 wt.%), Al2O3 (13–18 wt.%), A/CNK (0.98–1.44) and Rb (154–412 ppm); low contents of CaO (0.33–1.91 wt.%) and Sr (19–171 ppm), and a high ratio of FeO(tot)/MgO in biotite (2.54–4.82). These distinctive features, along with their strong depletion in high field strength elements (HFSE), suggest their affinity to peraluminous S‐type granite generated by the partial melting of crustal material. Geothermobarometric estimations and mineral assemblages of the HHC metapelites confirm that the HHLG were probably generated in the middle crust (~20 km) and the produced melts intruded the HHC in the form of sills/dykes. Microstructurally, the HHLG shows high temperature deformation features including chessboard extinction in quartz and cuspate/lobate grain boundaries between quartz and feldspars (plagioclase and K‐feldspar). The deformation microstructures suggest that the HHLG was deformed under early high temperature ductile deformation conditions. These fabrics were subsequently superimposed by later brittle deformation features associated with decreasing temperatures during the exhumation of the HHLG towards shallow structural levels at the time of Himalayan orogeny. Copyright © 2013 John Wiley & Sons, Ltd.

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Microstructures in quartz and feldspars of the Bomdila Gneiss from western Arunachal Himalaya, Northeast India: Implications for the geotectonic evolution of the Bomdila mylonitic zone

Cited by 27 publications

References 75 publications

Zircon U–Pb geochronology, Hf isotopic compositions, and petrogenetic study of Abor volcanic rocks of Eastern Himalayan Syntaxis, Northeast India: Implications for eruption during breakup of Eastern Gondwana

Zircon U–Pb geochronology, Hf isotopic compositions, and petrogenetic study of Abor volcanic rocks of Eastern Himalayan Syntaxis, Northeast India: Implications for eruption during breakup of Eastern Gondwana

Detection of a weak late-stage deformation event in granitic gneiss through anisotropy of magnetic susceptibility: implications for tectonic evolution of the Bomdila Gneiss in the Arunachal Lesser Himalaya, Northeast India

Microstructural and geochemical studies of Higher Himalayan Leucogranite: implications for geodynamic evolution of Tertiary Leucogranite in the Eastern Himalaya

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