Anatomy of the Mount Isa Fault system: thrust exhumation of middle crustal elements of the Mount Isa Rift basement during the late Isan Orogeny

regarded as a multiphase event spread episodically over a ~100 my interval from ~1600 Ma to ~1500 Ma. It terminated a protracted extensional interval in which rocks of the Haslingdon and Mount Isa Groups accumulated in the superposed Leichhardt River and Mount Isa Rifts at ~1800 Ma and ~1650 Ma, respectively. An extensive fault system, the Mount Isa Fault, separates high-grade rocks of the Haslingden Group (and older rocks) to the west from lower-grade equivalents to the east, as well as from rocks of the overlying Mount Isa Group. The complex system of faults associated with this boundary is well-defined in deep seismic imagery. We present the results of detailed mapping and geometrical analysis (based on ~6000 field observations) of the structure across the Mount Isa Fault system ~10 Km southwest of Mount Isa in the Mica Creek area. Multiple generations of metamorphic structural fabrics associated with two discrete crustal events characterise the rocks. Many of the results simply confirm previous work but major conclusions that emerge from this study are: 1) The existence of a low Isan strain window of middle crustal remnants of the ~1650 Ma Mount Isa Rift system. The earliest fabric recognised is a stratigraphy-parallel (subhorizontal) foliation associated with mid-crustal emplacement of syntectonic granitoi