Abstract
Folding and shear zone movement occurred synchronously in rocks of the Mid-Proterozoic Mount Isa Group in the Hilton area, Northwest Queensland. Syndeformational veins developed in shear zones and in sets spatially associated with shear zone intersections. Veins can be divided into the following two types: 1. (1)Fibrous and non-fibrous quartz-dolomite veins which formed in orientations consistent with the regional E-W subhorizontal shortening direction. 2. (2)Fibrous and non-fibrous quartz-dolomite veins which formed parallel to shear planes, S 3 cleavage, and bedding, indicating local syndeformational extension parallel to the regional shortening direction. The complex geometry of the shear zones suggests that shear parallel veins formed as a result of movement over asperities during shear zone movement. S 2- parallel veins, on the other hand, appear to have formed during restricted episodes of fluid overpressuring during post-failure stress drops. Shear zones are divisible into highly graphitic and weakly graphitic end member types. Highly graphitic shear zones show abundant dissolution and little veining, while weakly graphitic shear zones show abundant veining and little dissolution. This indicates that highly graphitic shear zones were syndeformational fluid pathways, while weakly graphitic shear zones were syndeformational fluid sinks.
Published Version
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