Quartz deformation across interlayered monomineralic and polymineralic rocks

A comparative analysis

Nicholas J.R. Hunter, Roberto Ferrez Weinberg, C. J.L. Wilson, V. Luzin, S. Misra

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Given the increased availability of EBSD and fabric analyzer facilities, quartz microstructural and CPO analysis have become ‘tools of-the-trade’ for studies investigating crustal tectonics. Therefore, improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes. We contribute to this understanding by comparing quartz deformation between monomineralic rocks, which have simple compositions; and polymineralic rocks, which are more complex and representative of the crust. Mylonite quartzites and gneisses of the Main Central Thrust (NW Himalaya) are used for comparison. Under similar deformation conditions, quartz inside monomineralic rocks forms well-developed CPOs and dynamically recrystallized microstructures, typical of grain size insensitive (GSI) creep mechanisms. Quartz inside polymineralic rocks, by contrast, exhibits weak CPOs and fine-grained microstructures commonly interpreted as grain size sensitive creep; but also exhibits lattice distortions (e.g. undulose extinction, sub-grain boundaries), associated with GSI creep. We postulate that intrinsic factors, such as interphase boundaries, cause these ambiguous results. The lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and CPOs for rapid diagnoses of their rheology and broader tectonic significance.

Original languageEnglish
Pages (from-to)118-134
Number of pages17
JournalJournal of Structural Geology
Volume119
DOIs
Publication statusPublished - 1 Feb 2019

Cite this

@article{f2a0e713576d4235b6dc53e674266446,
title = "Quartz deformation across interlayered monomineralic and polymineralic rocks: A comparative analysis",
abstract = "Given the increased availability of EBSD and fabric analyzer facilities, quartz microstructural and CPO analysis have become ‘tools of-the-trade’ for studies investigating crustal tectonics. Therefore, improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes. We contribute to this understanding by comparing quartz deformation between monomineralic rocks, which have simple compositions; and polymineralic rocks, which are more complex and representative of the crust. Mylonite quartzites and gneisses of the Main Central Thrust (NW Himalaya) are used for comparison. Under similar deformation conditions, quartz inside monomineralic rocks forms well-developed CPOs and dynamically recrystallized microstructures, typical of grain size insensitive (GSI) creep mechanisms. Quartz inside polymineralic rocks, by contrast, exhibits weak CPOs and fine-grained microstructures commonly interpreted as grain size sensitive creep; but also exhibits lattice distortions (e.g. undulose extinction, sub-grain boundaries), associated with GSI creep. We postulate that intrinsic factors, such as interphase boundaries, cause these ambiguous results. The lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and CPOs for rapid diagnoses of their rheology and broader tectonic significance.",
author = "Hunter, {Nicholas J.R.} and Weinberg, {Roberto Ferrez} and Wilson, {C. J.L.} and V. Luzin and S. Misra",
year = "2019",
month = "2",
day = "1",
doi = "10.1016/j.jsg.2018.12.005",
language = "English",
volume = "119",
pages = "118--134",
journal = "Journal of Structural Geology",
issn = "0191-8141",
publisher = "Pergamon",

}

Quartz deformation across interlayered monomineralic and polymineralic rocks : A comparative analysis. / Hunter, Nicholas J.R.; Weinberg, Roberto Ferrez; Wilson, C. J.L.; Luzin, V.; Misra, S.

In: Journal of Structural Geology, Vol. 119, 01.02.2019, p. 118-134.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Quartz deformation across interlayered monomineralic and polymineralic rocks

T2 - A comparative analysis

AU - Hunter, Nicholas J.R.

AU - Weinberg, Roberto Ferrez

AU - Wilson, C. J.L.

AU - Luzin, V.

AU - Misra, S.

PY - 2019/2/1

Y1 - 2019/2/1

N2 - Given the increased availability of EBSD and fabric analyzer facilities, quartz microstructural and CPO analysis have become ‘tools of-the-trade’ for studies investigating crustal tectonics. Therefore, improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes. We contribute to this understanding by comparing quartz deformation between monomineralic rocks, which have simple compositions; and polymineralic rocks, which are more complex and representative of the crust. Mylonite quartzites and gneisses of the Main Central Thrust (NW Himalaya) are used for comparison. Under similar deformation conditions, quartz inside monomineralic rocks forms well-developed CPOs and dynamically recrystallized microstructures, typical of grain size insensitive (GSI) creep mechanisms. Quartz inside polymineralic rocks, by contrast, exhibits weak CPOs and fine-grained microstructures commonly interpreted as grain size sensitive creep; but also exhibits lattice distortions (e.g. undulose extinction, sub-grain boundaries), associated with GSI creep. We postulate that intrinsic factors, such as interphase boundaries, cause these ambiguous results. The lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and CPOs for rapid diagnoses of their rheology and broader tectonic significance.

AB - Given the increased availability of EBSD and fabric analyzer facilities, quartz microstructural and CPO analysis have become ‘tools of-the-trade’ for studies investigating crustal tectonics. Therefore, improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes. We contribute to this understanding by comparing quartz deformation between monomineralic rocks, which have simple compositions; and polymineralic rocks, which are more complex and representative of the crust. Mylonite quartzites and gneisses of the Main Central Thrust (NW Himalaya) are used for comparison. Under similar deformation conditions, quartz inside monomineralic rocks forms well-developed CPOs and dynamically recrystallized microstructures, typical of grain size insensitive (GSI) creep mechanisms. Quartz inside polymineralic rocks, by contrast, exhibits weak CPOs and fine-grained microstructures commonly interpreted as grain size sensitive creep; but also exhibits lattice distortions (e.g. undulose extinction, sub-grain boundaries), associated with GSI creep. We postulate that intrinsic factors, such as interphase boundaries, cause these ambiguous results. The lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and CPOs for rapid diagnoses of their rheology and broader tectonic significance.

UR - http://www.scopus.com/inward/record.url?scp=85059777719&partnerID=8YFLogxK

U2 - 10.1016/j.jsg.2018.12.005

DO - 10.1016/j.jsg.2018.12.005

M3 - Article

VL - 119

SP - 118

EP - 134

JO - Journal of Structural Geology

JF - Journal of Structural Geology

SN - 0191-8141

ER -