A microstructural signature of the coesite-quartz transformation: New insights from high-pressure experiments and EBSD

ORCID

Abstract

Ultra-high pressure (UHP) metamorphism is difficult to identify in continental crust as few petrological barometers are suitable for dominantly felsic lithologies. In such cases, burial to extreme depths is commonly identified through the preservation of coesite, a high-pressure polymorph of SiO 2 that typically forms at depths exceeding ∼ 100 km (i.e., > 2 GPa pressure). Unfortunately, coesite readily transforms to quartz upon exhumation, meaning that UHP terranes may often be overlooked. While some studies have suggested that quartz may inherit an orientation signature indicative of former coesite, both the specific nature of this signature and the conditions favouring its development remain uncertain. To address this problem, we combine electron backscatter diffraction analysis of natural and experimental samples to explore microstructural evolution across the coesite-quartz phase transformation. We demonstrate that neighbouring domains of quartz commonly feature an 84 ± 4° rotation of [c] axes around the pole of a common {m} plane. This orientation relationship is a product of epitaxy, whereby the { 11 2 ¯ 2 } Japan twin plane in quartz nucleates on the (010) plane in coesite. In supercell simulations, the nucleation of Japan twins can be explained by the energetically favourable alignment of quartz tetrahedra on parental coesite tetrahedra. Through experiments, we demonstrate that this signature emerges over a broad range of conditions, regardless of the availability of nucleation sites (e.g., grain boundaries) or the density of crystal lattice defects (e.g., dislocations). Overall, our work provides a quantitative and unambiguous tool for identifying UHP terranes from quartz in isolation.

Publication Date

2025-10-25

Publication Title

Earth and Planetary Science Letters

Volume

672

Issue

119622

ISSN

0012-821X

Acceptance Date

2025-09-03

Deposit Date

2025-10-30

Embargo Period

2026-10-25

Funding

Natural samples were collected during three field seasons. Sample DW09-53 was collected on the 2009 field excursion, led by Philippe Agard, funding through a joint France-UK academic exchange programme grant entitled ‘The Hubert Curien Partnership (HCP) Alliance programme’ awarded to P.Agard and C.-J- De Hoog. Sample a05-10 was collected on the 2017 field excursion led by Anna Bidgood, funded by the Natural Environmental Research Council, grant number NE/L002612/1. Sample GSL-18-RG-11 was collected on the 2018 field excursion to the Northwest Territories led by Rellie M. Goddard, funded by the Natural Environmental Research Council, grant number NE/L002612/1 (to R.M.G), internal funds from University College, Oxford, The Mike Coward Fund from the Geological Society (to R.M.G), and support from a Natural Science and Engineering Research Council Discovery Grant, grant number RGPIN-2019-04248 (to B.D.). Experimental work was undertaken at the Advanced Photon Source (APS), an Office of Science User facility operated by the U.S. Department of Energy by Argonne National Laboratory. Use of the APS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Use of the 6-BM-B beamline was supported by COMPRES, the Consortium for Materials Properties Research in Earth Sciences, under NSF Cooperative Agreement EAR 16-06856. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-JRNL-2004734. Funding for materials and trips to APS was provided by NERC Environmental Research DTP grant NE/L002612/1 (to R.M.G.), the Royal Commission for the Exhibition of 1851 fellowship (to T.B.), National Science Foundation grants EAR-2003389 (to A.J.C.), EAR-2023128 (to A.J.C.), and EAR-1806791 (to K.M.K.), and UK Research and Innovation Future Leaders Fellowship grant MR/V021788/1 (supporting T.B.).

Keywords

Coesite, Crystallography, EBSD, Epitaxy, Quartz, UHP

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This item is under embargo until 25 October 2026

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