Geology of hill end trough Molong high: multiple deformation associated with the wiagdon fault zone along the turon river, near sofala

Abstract

In an area (3 ? 4 km) immediately west of the Wiagdon Fault Zone near Sofala, four crenulation cleavages with associated folds postdate the regional slaty cleavage (Hordern, 1973). Cross-cutting and refolding relationships indicate the relative ages of the cleavages. The structural surfaces are: S0 bedding, defined by sandy and slaty interbeds, the sandy beds ranging up to 3 m thick. Graded bedding and bottom structures indicate meso- and macroscopic first-generation folds overturned towards the east. These regional folds are close to very tight, and plunge gently northward, and have: S1, axial-surface slaty cleavage that dips west at variable angles from nearly vertical to horizontal as the axial surfaces of associated folds vary from overturned to recumbent, as, for example, at Wallaby rocks. S1 has been overprinted by at least four crenulation cleavages (Fig. 1), viz., S2, a dark hair-like foliation in hand specimen, that dips steeply east in slate (modal plane, 71/103) and west in psammite (68/288). In thin-section, S2 appears as whisker-like bands of reoriented phyllosilicates. Bands vary in width and have ragged boundaries. S3, a weak southerly dipping crenulation cleavage (66/184), that is more restricted in occurrence than S2 and appears as crenulations of Slf or as crenula-tions within S2. S4, an extremely penetrative, shallowly westward-dipping foliation (12/298) that seems to be parallel to, and associated with the Sunrise Fault (a thrust west of the Wiagdon Fault Zone). In places, S4 is so strongly developed that it has the appearance of a very fissile slaty cleavage, yet it can be distinguished in outcrop because it buckles many small quartz veins parallel to S1. In thin section, a strong mineral differentiation can be seen along the cleavage zones, and limbs of buckled quartz veins have been partially removed by pressure solution. S5, is a weak, local crenulation cleavage that deforms S4 and occurs in only one locality in Two Mile Creek.