Reversals in the polarity of structural facing across an early ductile thrust; the Central Donegal Slide, northwest Ireland

Abstract

AbstractThe Dalradian succession of central Donegal represents a tectono‐stratigraphic sequence everywhere separated into two distinct successions by the Central Donegal Slide. Each stratigraphic package consistently youngs away from this major D1structure which originated during lower greenschist facies metamorphism and corresponds with the development of locally preserved penetrative S1fabrics. The tectonic slide and associated reversal in the direction of structural facing are commonly marked by mylonites and tectonic schists, which have been subsequently folded and reactivated by kilometric‐scale sheath folds and the Ballybofey Nappe.Structural correlations with northwest Donegal suggest that the Central Donegal Slide relates to the Knockateen Slide, and represents an early thrust with top to the northwest sense of shear. The Central Donegal Slide cuts up‐section through the Middle Dalradian sub‐basin centred on southern Donegal, emplacing younger, anoxic basinal sediments and turbidites over an older, inverted, shelf succession. The location of the Central Donegal Slide adjacent to the margin of this sub‐basin suggests that the siting and form of ductile thrusts may be strongly influenced by the geometry of the pre‐existing sedimentary basin.