Sequence and kinematics of multiple deformation around Taemas Bridge, Eastern Lachlan Fold Belt, New South Wales

Abstract

The area around Taemas Bridge in the Gilgandra‐Cowra‐Yass Zone, southwest of Yass, contains Devonian limestone, silicic volcanics and terrestrial sedimentary rocks that are folded by four deformations of inferred Carboniferous age. Interference between folds is well developed, mainly as Type 1 and Type 2 interference patterns. The two most prominent fold trends can be found more widely throughout the Lachlan Fold Belt as northwest/north‐northwest and north/north‐northeast regional trends. Early folds may be more localised. The fold axes associated with consecutive generations display an anticlockwise directional sequence, suggesting that incremental strain axes rotated anticlockwise during the Carboniferous deformation. North‐northwest‐trending faults in the area are inferred to have moved by both sinistral strike‐slip and reverse mode at different times. Small‐scale structures, such as veins, vein arrays and tectonic stylolites, are well developed in the Lower Devonian limestones. These structures can be correlated with, and indicate the 3-D incremental strain directions and kinematics of, the fold events. Early folding shows a predominantly wrench style of deformation and appears to be related to wrench motion on the bounding faults. North‐northeast‐trending F2 folds are 30° clockwise to faults and, together with associated small‐scale wrench indicators, suggest sinistral shear on these faults. Northwest‐trending F3 folds are associated mainly with reverse faulting, indicating a change in kinematic style. These are in turn overprinted by wrench motion associated with ?minor north/north‐northwest compression. The results of this study suggest a multiphase contraction and wrench history that is more complex than previously proposed for this part of the Eastern Lachlan Fold Belt.