Macrostructures vs microstructures in evaporite detachments: An example from the Salt Range, Pakistan

•Structural measurements mirror the larger scale deformation in the region.•Rheological heterogeneity in the detachment indicates a varied response to stress.•Limited meso-/micro-structure correlation due to telogenetic alteration.•Current salt deformation understanding does not reflect true complexity.

The Salt Range, Pakistan is the surface expression of an evaporite detachment over which the Potwar Plateau fold-thrust belt has moved. Whilst previous publications regarding this region have focused on the petroleum prospectivity, deformation, and large-scale processes, this paper characterises the Salt Range detachment at the meso-(10 cm to 10s of metres) and micro-scale (cm to μm) and examines correlations to the macro-scale (10s of metres to kms). Two detailed scaled cross sections are analysed alongside structural measurements to characterise the detachment at the meso-scale with optical analysis of microstructures that formed during deformation characterising the micro-scale. Both ductile and brittle features observed in cross section indicate composite deformation processes acting simultaneously; this contrasts with models of salt detachments behaving homogeneously. Microstructural analysis indicates processes of grain boundary migration and crystal lattice distortions. The microstructurally revealed competition between intra-crystalline deformation and recrystallization at shallow depths and low temperatures links passes up-scale to mesoscale evaporite mylonites and progressively in the weaker units, whereas more brittle processes operate in the stronger lithologies in this near-unique outcrop of a the emergent toe of a major salt-bearing detachment fault.