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ThePetermann Orogeny was an Australian intracontinental event that affected basement rocks of the northernMusgrave Province andEdiacaran (Proterozoic)sediments of the (now) southernAmadeus Basin between 630-520Ma.[1] The remains are seen today in thePetermann Ranges.[2]
Prior to the Petermann Orogeny, which resulted inexhumation of theMusgrave Block, the Amadeus Basin was contiguous with theOfficer Basin inSouth 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-faciesmineral assemblages (11-12 kbar at 650 °C).
TheWoodroofe Thrust,Davenport Shear Zone andMann Fault accommodated much of the 30–40 km exhumation. Exhumation of the Musgrave Block (and overlying sediments) resulted in successiveunroofing anddeposition ofrock types such asarkose andconglomerate in localisedsedimentary basins that now outcrop asUluru andKata Tjuta respectively. Beyond this region of intense Petermann-aged activity,deformation related to the Petermann Orogen is less pervasive andductile.
Sedimentation associated with the Petermann Orogeny is responsible for the deposition of theGeorgina Basin, Officer Basin,Ngalia Basin andAmadeus Basin sediments in theCambrian. Sediments are a mixture of fluvial conglomerates,sandstones, andsiltstones.
Several pull-apart structuralgrabens formed at flexures in the orogenic belt, forming the Levenger and Moorilyanna Grabens.
The Petermann Orogeny is dominated by south-over-north[3] movement on several large,anastomosing curvedthrust faults. The prime thrust fault is the Woodroffe Thrust, which is a laminatedpseudotachlyte-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 aflower-structure, which is a set of vertically arcuate thrust faults which dip toward each other and accommodate vertical movement by essentiallysqueezing the central block up and out.
Several northeast trendingdiscontinuities 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.
Six deformations are known (to be completed)
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 stretchinglineation is potentially associated with some of these faults, especially in the deeper areas of thecrust which have been exhumed, because these were within thetemperature andpressure conditions forbrittle-ductile and ductile deformation.
The tectonics of the Petermann Orogeny are extremely unusual, as it occurred in an intraplate setting in the centre of theAustralian continental block.
Several theories about the causes and dynamics of the orogen are currently under investigation, including;
TheTranspression model (bySRK Ltd) considers the Petermann Orogen to be caused bytranspressional strike-slip along a series of anastomosing crustal-scale strike-slip thrusts which included movements during thepan-African orogenies andtectonic events of the Cambrian-Ordovician.
The theory states that the degree of extremeuplift 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 ofgeochronology, and general lack ofkinematics directly linked to transpression.
The unusual geometry of this east-west tending orogenic belt suggests that during the formation of the supercontinentGondwana 550 million years ago, India collided with Western Australia from the northwest, rather than from the west, with deformation accommodated along a zone of crustal weakness and pre-existing fault lines.[4]
Another theory for the causes of the deep and extremely rapid exhumation of the Petermann Orogen is that it is due to isostatic instabilities caused by thermal events in the deep crust, causing accumulated stress to be released by violent thermal rebound (Sandiford, et al. 2001). This is envisaged as a kind of feedback loop between sedimentation andisostatic orogenic events. However, some authors (Camacho et al.) have called this into question withisotopic models.
The dramatic north-south difference in gravity across the Woodroffe Thrust-Mann Fault Zone, regarded as the largest continental gravity gradient in the world, is attributed to an upthrust of densemantle material 30 km closer to the present land surface.[5]
The Petermann Orogeny exposes deep crustal roots of the previous Musgrave Orogen and likely parts of several poorly exposed Proterozoic orogenic belts andigneous provinces. As such, the rocks of the Petermann Orogen are considered prospective territory formineral exploration.
The history of mineral exploration in the Petermann Orogen extends back to the last half of the 19th century, with a series of prospectors and exploring pioneers transiting the area. Most famously wasLewis Lasseter, who allegedly foundLasseter's Reef, a near-mythicalgold lode of such richness and scale that it has fired imaginations for over a century, but remains undiscovered.
In the mid and late 20th century, government missionaries brought to the indigenousAboriginal people of the areaEuropean law,European culture and the concept of salaried work, previously unknown to thehunter-gatherer inhabitants. In order to provide work, subsidised exploration was undertaken by theWestern Mining Corporation, resulting in the discovery ofpodiformcopper at Warburton Range, and eventually theWingelinnanickellaterite resource.
The advent of theMabo Decision and land rights movements has seen aboriginal land rights improved, with the result that they now control access to land and exploration tenements. This has created uncertainty about tenure and land access for mineral exploration.
There are three main known forms of mineralisation in the Petermann Orogen;
Exploration forOlympic Dam mine lookalikes and for magmatic nickel coppermineralisation is continuing.
There are only one or two geology oriented documentaries that traceUluru andKata Tjuta's origins with the AustralianPetermann Ranges. The 2012 documentaryAustralia: The Time Traveller's Guide is possibly the first to make the connection with reasonable clarity.