Intermittent folding and faulting in the Lake Moondarra area, Mount Isa, Queensland

Abstract

Abstract Faulting and folding are interspersed and locally interrelated in the Lake Moondarra area. Minor faulting occurred during deposition, after which the region was deformed by three folding events, developing weak slaty cleavages and regional folds. Geometrical constraints and overprinting relations between associated quartz veins have established the relative timing of cleavages. Following F1 folding, major E‐W trending faults formed with dip‐slip motion followed by an interval of strike‐slip movement. The second deformation produced N‐S folds in S0 and S1, and a slaty cleavage, S2. Some faults were dilated and infilled locally with quartz and country rock fragments during the second deformation or slightly earlier. The fault‐filling material contains a foliation, with about the same orientation as S2 throughout the region, and also a mineral‐elongation lineation of aligned quartz fibres and deformed elongate quartz grains. There was a further component of strike‐slip movement, the sense of which changes across and was apparently controlled by F2 folds. The third deformation caused NNW‐SSE folds and an associated cleavage. During D3 some faults underwent further extension and dilation, parallel and perpendicular to the maximum finite extension direction (i.e. L33), after which another group of faults formed at a low angle to S3 and subsequently underwent a component of sinistral strike‐slip displacement.