LARAMIDE-STYLE BASEMENT BLOCK FAULTING AND FAULT INVERSION DURING THE MID-PALEOZOIC INTRAPLATE ALICE SPRINGS OROGENY, HUCKITTA REGION, NORTHERN TERRITORY, CENTRAL AUSTRALIA

In the Huckitta region in central Australia, the mid-Pz Alice Springs intraplate orogeny was characterized by basement block uplift on high-angle reverse faults, forming an array of predominantly north-northwest-trending, west-up, reverse faults with east-northeast-trending, south-up, cross faults. These reverse faults are interpreted here to reactivate previous normal faults in a style similar to that proposed for Laramide structures in the western US.

The mid-Pz Oomoolmilla reverse fault in the central study area is apparently a reactivated Neoproterozoic rift-bounding normal fault. The fault is 25 km in length, strikes N70E and dips 70 degrees to the south, juxtaposing Mesoproterozoic crystalline basement against Cambrian carbonate rocks with a minimum south-up vertical offset of 1400 m. Footwall strata adjacent to the fault are vertical to overturned. Neoproterozoic rift facies sediments are preferentially preserved in the hanging-wall block adjacent to the fault.

The paired Lucy Creek and Mount Playford faults in the eastern study area strike N30W and dip steeply to the west, with a strike length of greater than 45 km, and a combined west-up vertical offset of 2600 m. Prominent monoclinal folds are locally developed in Cambrian strata adjacent to the faults. The Lucy Creek fault displays west-up reverse offset of Pz rocks in the Jervois Range, but west-down normal offset of Neoproterozoic rift facies rocks in the Mount Cornish area to the south, interpreted together to indicate mid-Pz reactivation of a Neoproterozoic, rift-bounding normal fault. The younger Mount Playford fault likely formed as a footwall shortcut off the Lucy Creek fault during compressional inversion of the upward-steepening normal fault.

Fault-bounded, basement-cored uplifts formed by inversion of extensional fault systems are characteristic of intraplate cratonic deformation in the Huckitta region of central Australia, and (on a much larger scale) Laramide deformation in the western US. Whereas contractional inversion in these two regions was diachronous and depended on local tectonic conditions, the extensional fault systems that were reactivated may be largely synchronous, formed as Australia and North America were rifted apart during the Neoproterozoic breakup of Rodinia.