SEM-EBSD Analysis of Broad Ion Beam Polished Rock Thin Sections — The MFAL Protocol

Mamtani, Manish A.; Chakraborty, Ritwik; Biswas, Santu; Suryawanshi, Abhijeet; Goswami, Sumit; Bhatt, Sandeep

doi:10.1007/s12594-020-1441-0

Cited by 6 publications

(4 citation statements)

References 20 publications

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“…The mounted samples were cleaned for approximately 20 min by low‐angle Ar sputtering using a Leica RES102 ion mill (operated at 4° tilt, 8 kV, 4 mA). This step served to remove residues from solvents and surface layers containing crystallographic defects from polishing (e.g., Mamtani et al., 2020). These defects might accumulate hydroxyl groups during processing.…”

Section: Samples and Methodsmentioning

confidence: 99%

Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites

Harries

Zhao

Franchi

2023

Meteorit & Planetary Scien

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Hydroxyl defects in nominally anhydrous minerals (NAMs) were potential carriers of water in the early Solar System and might have contributed to the accretion of terrestrial water. To better understand this, we have conducted a nanoscale secondary ion mass spectrometry survey of water contents in olivine and orthopyroxene from a set of equilibrated ordinary chondrites of the L and LL groups (Baszkówka, Bensour, Kheneg Ljouâd, and Tuxtuac) and several ultramafic achondrites (Zakøodzie, Dhofar 125, Northwest Africa [NWA] 4969, NWA 6693, and NWA 7317). For calibration, we used terrestrial olivine and orthopyroxene with H 2 O contents determined by Fourier transform infrared. Our 99.7% (~3SD) detection limits are 3.6-5.4 ppmw H 2 O for olivine and 7.7-10.9 ppmw H 2 O for orthopyroxene. None of the meteoritic samples studied consistently shows water contents above the detection limits. A few exceptions slightly above the detection limits are suspected of terrestrial contamination by ferric oxyhydroxides. If the meteorite samples investigated accreted in the presence of small amounts of water ice, the upper limits of water contents provided by our survey suggest that the retention of hydrogen during thermal metamorphism and differentiation was ineffective. We suggest that loss occurred through combinations of low internal pressures, high permeability along grain boundaries, and speciation of hydrogen into reduced compounds such as H 2 and methane, which are less soluble in NAMs than in water.

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Section: Samples and Methodsmentioning

confidence: 99%

Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites

Harries

Zhao

Franchi

2023

Meteorit & Planetary Scien

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“…For this, SEM-EBSD analysis was done on Broad Ion Beam (BIB) polished rock thin sections. BIB polishing was done following the MFAL protocol of Mamtani et al (2020). Slides were initially polished with colloidal silica, followed by BIB polishing, consisting of two steps: 5 minutes of surface cleaning followed by 30 minutes of polishing.…”

Section: Analytical Techniquesmentioning

confidence: 99%

Lattice preferred orientation of quartz in granitic gneisses from Tso Morari Crystalline Complex, Eastern Ladakh, trans-Himalaya: evaluating effect of Dauphiné twin in dynamic recrystallization during exhumation

Dey,

Sen,

Mamtani

2023

Geol. Mag.

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The Tso Morari Crystalline complex (TMCC) of eastern Ladakh, India, is part of the north Indian continental margin and is characterized by eclogitic enclaves embedded within ortho- and paragneisses known as the Puga Gneiss. Two fault zones bound the TMCC: the Karzok fault to the southwest and the Zildat fault to the northeast. In the present study, we carried out Electron Backscatter Diffraction study of quartz of 10 samples collected from the Puga Gneiss. The relict and recrystallized quartz grains were treated separately to understand the deformation conditions of the Puga Gneiss during early and late deformation stages related to UHP metamorphism and final stage of exhumation during retrogression, respectively. Microstructural observations suggest dynamic recrystallization in quartz and plagioclase at different temperature ranges. Misorientation analysis of both relict and recrystallized quartz grains reveals presence of Dauphiné Twins. Lattice preferred Orientation (LPO) of <c> axis of relict quartz grains generally shows more than one point maxima indicating that the relict grains preserve LPO developed during different stages of metamorphism/deformation. On the other hand, LPO of <c> axis of recrystallized grains from Karzok and Zildat fault zones shows asymmetric single girdle either normal or at an angle to the foliation plane, which suggests simple shear. We conclude that grain size reduction and recrystallization of the Puga Gneiss was greatly influenced by Dauphiné Twin and the final exhumation of the TMCC took place in a simple shear environment aided by activity along its two binding fault zones.

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“…Finally, a section perpendicular to the inferred foliation plane (parallel to preferred orientation of omphacite observed in petrography on the foliation plane) was prepared for EBSD analyses. For preparing samples for EBSD analyses, Mamtani's Fabric Analysis Lab (MFAL) protocol was adopted [59]. Accordingly, conventional polishing of slides by colloidal silica gel is followed by broad ion beam polishing (BIBP).…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…Abbreviations: AM: amphibolite; Amp-EC: amphibolite-eclogite; BS: blueschist; EA: epidote amphibolite; EC: eclogite; Ep-EC: epidote eclogite; GR: granulite; GS: green schist; HGR: high-pressure granulite; Law-EC: lawsonite eclogite. Lithosphere Department of Geology and Geophysics, Indian Institute of Technology (IIT) Kharagpur, India (see [59] for detailed parameters of the MFAL protocol). After sample preparation, EBSD patterns were acquired at 30 kV accelerating voltage, 1:49 × 10 −6 mbar system vacuum, and ~15 mm working distance using the Carl Zeiss Auriga Compact FEG-SEM fitted with the NordlysMax2 EBSD detector (Oxford instruments, UK) housed in Central Research Facility (IIT Kharagpur, India).…”

Section: Analytical Techniquesmentioning

confidence: 99%

Electron Backscatter Diffraction Study of Ultrahigh-Pressure Tso Morari Eclogites (Trans-Himalayan Collisional Zone): Implications for Strain Regime Transition from Constrictional to Plane Strain during Exhumation

2022

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The Tso Morari Crystalline Complex (TMCC) of trans-Himalaya (eastern Ladakh, India) contains enclaves of ultrahigh-pressure eclogites that underwent deep burial (≥80 km) and subsequent rapid exhumation during continental subduction, collision, and final accretion of the Indian plate with the Eurasian plate. We present an electron backscatter diffraction (EBSD) study of eight eclogite samples to investigate the deformation mechanism and strain regimes active during peak (HP) metamorphism and subsequent postpeak rapid exhumation of the TMCC. Our study shows that the least retrogressed eclogite exhibits strong linear fabric (L tectonite) characterized by omphacite, having [001] axes parallel to and (110) poles perpendicular to lineation. These features concur with constrictional strain during peak (HP) metamorphism. A transitional planolinear fabric (LS tectonite) is shown by other eclogites that show petrographic evidence of omphacite alteration to amphibole and the presence of lower metamorphic grade minerals like actinolite and chlorite. Characteristics of lattice preferred orientation (LPO) of omphacite and quartz, indicated, respectively, by the LS and B indices, also suggest variation in strain regime from pristine eclogites to their altered counterparts. Based on these results, it is suggested that a constrictional strain regime prevailed during peak (HP) metamorphism in the TMCC due to the buoyant rise of TMCC in response to slab break-off and reverse slab pull during and after the deepest continental subduction. This buoyant rise was also facilitated by compression related to the ongoing India-Eurasia collision. This regime evolved later to plane strain that was superimposed on the UHP rocks at a shallower depth. It is plausibly associated with foliation-parallel extension during exhumation at midcrustal depths. A high-temperature prism c-slip in quartz shown by few samples is interpreted to have formed due to a subsequent granulite facies metamorphic overprint on the eclogite during collisional thickening.

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SEM-EBSD Analysis of Broad Ion Beam Polished Rock Thin Sections — The MFAL Protocol

Cited by 6 publications

References 20 publications

Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites

Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites

Lattice preferred orientation of quartz in granitic gneisses from Tso Morari Crystalline Complex, Eastern Ladakh, trans-Himalaya: evaluating effect of Dauphiné twin in dynamic recrystallization during exhumation

Electron Backscatter Diffraction Study of Ultrahigh-Pressure Tso Morari Eclogites (Trans-Himalayan Collisional Zone): Implications for Strain Regime Transition from Constrictional to Plane Strain during Exhumation

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