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Mid-crustal reactivation processes linked to frictional melting and deep void development during seismogenic slip: examples from the Lewisian Complex, NW Scotland

Hardman, K.; Holdsworth, R. E.; Scott, L.; Dempsey, E.; McCaffrey, K. J. W.

Authors

K. Hardman

R. E. Holdsworth

L. Scott

Profile image of Eddie Dempsey

Dr Eddie Dempsey E.Dempsey@hull.ac.uk
Senior Lecturer in Structural Geology and Geohazards

K. J. W. McCaffrey



Abstract

Exhumed examples of ancient fault voids formed during seismic slip at depths > 10 km are well preserved in the Assynt Terrane of the Lewisian Complex, NW Scotland. They are interpreted to have formed during regional Mesoproterozoic (ca 1.55 Ga; ‘Assyntian’) strike-slip faulting. Deformation is characterised by sinistral reactivation of pre-existing NW-SE trending features including intrusive contacts of (ca 2.4 Ga) mafic dykes and Paleoproterozoic ductile shear zone fabrics (ca 1.75 Ga). Reactivation occurred at palaeodepths of 10-15km, where frictional-viscous deformation synchronous with co-seismic frictional melting led to cycles of mm to dm-scale cavity dilation and collapse. Although individual melt-generating slip surfaces may have become rapidly welded, faulting was able to repeatedly localise along adjacent pre-existing planar anisotropies favourably oriented for slip leading to the creation of a mesh of foliation-parallel melt generation surfaces linked by foliation-perpendicular dilational voids. The latter features are filled by chaotic clast-supported wall rock collapse breccias, localised injected frictional melts and hydrothermal mineralization. The fills act as natural props, holding cavities open and preserving them as long-term, pipe-like fluid flow conduits. These exhumed features are likely to be typical of multi-rupture seismogenic fault systems formed by direct reactivation of pre-existing basement structures.

Citation

Hardman, K., Holdsworth, R. E., Scott, L., Dempsey, E., & McCaffrey, K. J. W. (in press). Mid-crustal reactivation processes linked to frictional melting and deep void development during seismogenic slip: examples from the Lewisian Complex, NW Scotland. Journal of the Geological Society, https://doi.org/10.1144/jgs2022-037

Journal Article Type Article
Acceptance Date Nov 19, 2022
Online Publication Date Nov 29, 2022
Deposit Date Dec 13, 2022
Publicly Available Date Dec 15, 2022
Journal Journal of the Geological Society
Print ISSN 0016-7649
Electronic ISSN 2041-479X
Publisher Geological Society
Peer Reviewed Peer Reviewed
DOI https://doi.org/10.1144/jgs2022-037
Keywords Geology
Public URL https://hull-repository.worktribe.com/output/4152050

Files

Accepted manuscript (5.7 Mb)
PDF

Publisher Licence URL
http://creativecommons.org/licenses/by/4.0

Copyright Statement
© 2022 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0/). Published by The
Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics





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