The evolution of slate microfabrics during progressive accretion of foreland basin sediments

Akker, Ismay Vénice; Berger, Alfons; Schrank, Christoph E.; Jones, Michael W. M.; Kewish, Cameron M.; Klaver, Jop; Herwegh, Marco (2021). The evolution of slate microfabrics during progressive accretion of foreland basin sediments. Journal of structural geology, 150, p. 104404. Elsevier 10.1016/j.jsg.2021.104404

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Here, we study slate microfabrics from the exhumed accretionary wedge of the central European Alps and focus on the development of foliation. High-resolution micrographs from novel BIB-SEM imaging and Synchrotron X-ray Fluorescence Microscopy are analysed with 2D auto-correlation functions to quantify the geometry and spacing of slate microfabrics along a metamorphic gradient covering the outer and inner wedge (200–330 °C). The sedimentary layering primarily controls the morphology of the slate microfabrics. However, from outer to inner wedge, a fabric evolution is observed where diagenetic foliations gradually transform to secondary continuous and spaced foliations. With increasing metamorphic grade, the amount of recrystallized phyllosilicate grains and their interconnectivity increase, as does clast/microlithon elongation (aspect ratios up to 11), while foliation spacing decreases to <20 μm. This foliation evolution under non-coaxial deformation involves a combination of mechanical rotation of phyllosilicates, fracturing, and fluid-assisted pressure-dissolution-precipitation creep. The latter is the dominant deformation mechanism at T > 230 °C and accommodates background strain in the inner wedge. The evolving microstructural anisotropy is interpreted to lead to strain weakening by structural softening and may provide preferential fluid pathways parallel to the foliation, enabling the dehydration of large rock volumes in accretionary sediment wedges undergoing prograde metamorphism.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Tectonics

UniBE Contributor:

Akker, Ismay Vénice; Berger, Alfons and Herwegh, Marco

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0191-8141

Publisher:

Elsevier

Funders:

[4] Swiss National Science Foundation

Language:

English

Submitter:

Ismay Vénice Akker

Date Deposited:

12 Aug 2021 12:10

Last Modified:

15 Aug 2021 03:10

Publisher DOI:

10.1016/j.jsg.2021.104404

BORIS DOI:

10.48350/158048

URI:

https://boris.unibe.ch/id/eprint/158048

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