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.

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