The Petermann Orogeny was an Australian intracontinental event that affected basement rocks of the northern Musgrave Province and Ediacaran (Proterozoic) sediments of the (now) southern Amadeus Basin between ~550-535 Ma. The remains are seen today in the Petermann Ranges.
Prior to the Petermann Orogeny, which resulted in exhumation of the Musgrave Block, the Amadeus Basin was contiguous with the Officer Basin in South Australia.
The extent and effect of the Petermann Orogen appears to be relatively confined, occurring most pervasively within the central northern-Musgrave Block. Here, older Musgravian (~1200-1150 Ma) fabrics are partially to completely overprinted by sub-eclogite-facies mineral assemblages (11-12 kbar at 650 °C).
The Woodroofe Thrust, Davenport Shear Zone and Mann Fault accommodated much of the 30–40 km exhumation. Exhumation of the Musgrave Block (and overlying sediments) resulted in successive unroofing and deposition of rock types such as arkose and conglomerate in localised sedimentary basins that now outcrop as Uluru and Kata Tjuta respectively. Beyond this region of intense Petermann-aged activity, deformation related to the Petermann Orogen is less pervasive and ductile.
Sedimentation associated with the Petermann Orogeny is responsible for the deposition of the Georgina Basin, Officer Basin, Ngalia Basin and Amadeus Basin sediments in the Cambrian. Sediments are a mixture of fluvial conglomerates, sandstones, and siltstones.
Several pull-apart structural grabens formed at flexures in the orogenic belt, forming the Levenger and Moorilyanna Grabens.
Dynamics
The Petermann Orogeny is dominated by south-over-north movement on several large, anastomosing curved thrust faults. The prime thrust fault is the Woodroffe Thrust, which is a laminated pseudotachlyte-schist zone up to 300 metres thick. This has accommodated up to 42 kilometres of vertical movement at an angle of about 15 to 20 degrees.
The structure of the Petermann Orogen within the Musgrave Block is considered to be a flower-structure, which is a set of vertically arcuate thrust faults which dip toward each other and accommodate vertical movement by essentially squeezing the central block up and out.
Several northeast trending discontinuities including the Mundrabilla lineament divide the Petermann orogeny, with extensive vertical offsets across them, usually west-side-up, though the timing of this event is unknown.
Deformations
Six deformations are known (to be completed) Folds of D1, D2 and D3 rare; D4 isoclinal upright, and D5 and D6 restricted to cleavage formation or small scale interference folds. Megascale Z folding of unknown provenance correlates with NE trending Mundrabilla Lineament parallel structures, and is probably D2 or D3.
Foliations
Foliations associated with the Petermann Orogeny are typically steeply to gently south-dipping and subparallel to the thrust faults upon which they were developed.
S regionally pervasive stretching lineation is potentially associated with some of these faults, especially in the deeper areas of the crust which have been exhumed, because these were within the temperature and pressure conditions for brittle-ductile and ductile deformation.
Tectonics
The tectonics of the Petermann Orogeny are extremely unusual, as it occurred in an intraplate setting in the centre of the Australian continental block.
Several theories about the causes and dynamics of the orogen are currently under investigation, including;
Transpression
The Transpression model (by SRK Ltd) considers the Petermann Orogen to be caused by transpressional strike-slip along a series of anastomosing crustal-scale strike-slip thrusts which included movements during the pan-African orogenies and tectonic events of the Cambrian-Ordovician.
The theory states that the degree of extreme uplift experienced in the Petermann Orogeny, specifically the ~42 km of uplift along the Woodroffe Thrust, occurred as a consequence of a crustal scale detachment surface forming a 'basement pop-up' as rock was thrust laterally along the detachment.
Problems with this model include lack of geochronology, and general lack of kinematics directly linked to transpression.