From Wikipedia, the free encyclopedia Petermann Orogeny
Petermann Orogeny
The Petermann Orogeny was an intracontinental event Deformations
that affected basement rocks of the northern Musgrave
• Six deformations are known (to be completed)
Province and Proterozoic sediments of the (now) south-
• Folds of D1, D2 and D3 rare; D4 isoclinal upright,
ern Amadeus Basin between ~550-535 Ma.
and D5 and D6 restricted to cleavage formation
Prior to the Petermann Orogeny, which resulted in
or small scale interference folds. Megascale Z
exhumation of the Musgrave Block, the Amadeus Basin
folding of unknown provenance correlates with
was contiguous with the Officer Basin in South Australia.
NE trending Mundrabilla Lineament parallel
The extent and effect of the Petermann Orogen ap-
structures, and is probably D2 or D3.
pears to be relatively confined, occurring most perva-
sively within the central northern-Musgrave Block. Here,
older Musgravian (~1200-1150 Ma) fabrics are partially
Foliations
to completely overprinted by sub-eclogite-facies mineral Foliations associated with the Petermann Orogeny are
assemblages (11-12 kbar at 650 °C). typically steeply to gently south-dipping and subparallel
The Woodroofe Thrust, Davenport Shear Zone and to the thrust faults upon which they were developed.
Mann Fault accommodated much of the 30-40 km ex- S regionally pervasive stretching lineation is poten-
humation. Exhumation of the Musgrave Block (and over- tially associated with some of these faults, especially in
lying sediments) resulted in successive unroofing and de- the deeper areas of the crust which have been exhumed,
position of rock types such as arkose and conglomerate because these were within the temperature and pressure
in localised sedimentary basins that now outcrop as Ulu- conditions for brittle-ductile and ductile deformation.
ru and Kata Tjuta respectively. Beyond this region of in-
tense Petermann-aged activity, deformation related to Tectonics
the Petermann Orogen is less pervasive and ductile.
Sedimentation associated with the Petermann Oroge- The tectonics of the Petermann Orogeny are extremely
ny is responsible for the deposition of the Georgina Basin, unusual, as it occurred in an intraplate setting in the cen-
Officer Basin, Ngalia Basin and Amadeus Basin sediments tre of the Australian continental block. Several theories
in the Cambrian. Sediments are a mixture of fluvial con- about the causes and dynamics of the orogen are current-
glomerates, sandstones, and siltstones. ly under investigation, including;
Several pull-apart structural grabens formed at flex-
ures in the orogenic belt, forming the Levenger and Moo- Transpression
rilyanna Grabens. This 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
Dynamics included movements during the pan-African orogenies
The Petermann Orogeny is dominated by south-over- and tectonic events of the Cambrian-Ordovician.
north movement on several large, anastomosing arcuate The theory states that the degree of extreme uplift ex-
thrust faults. The prime thrust fault is the Woodroffe perienced in the Petermann Orogeny, specifically the
Thrust, which is a laminated pseudotachlyte-schist zone ~42 km of uplift along the Woodroffe Thrust, occurred
up to 300 metres thick. This has accommodated up to 42 as a consequence of a crustal scale detachment surface
kilometres of vertical movement at an angle of about 15 forming a ’basement pop-up’ as rock was thrust laterally
to 20 degrees. along the detachment.
The structure of the Petermann Orogen within the Problems with this model include lack of geochronology,
Musgrave Block is considered to be a flower-structure, and general lack of kinematics directly linked to trans-
which is a set of vertically arcuate thrust faults which dip pression.
toward each other and accommodate vertical movement
by essentially squeezing the central block up and out. Intraplate thermal depression-rebound
Several northeast trending discontinuities including Another theory for the causes of the deep and extremely
the Mundrabilla lineament divide the Petermann oroge- rapid exhumation of the Petermann Orogen is that it is
ny, with extensive vertical offsets across them, usually due to isostatic instabilities caused by thermal events in
west-side-up, though the timing of this event is un- the deep crust, causing accumulated stress to be released
known. by violent thermal rebound (Sandiford, et al. 2001). This
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From Wikipedia, the free encyclopedia Petermann Orogeny
is envisaged as a kind of feedback loop between sedimen- exploration tenements. This has created uncertainty
tation and isostatic orogenic events. However, some au- about tenure and land access for mineral exploration.
thors (Camacho et al.) have called this into question with There are three main known forms of mineralisation
isotopic models. in the Petermann Orogen;
• Magmatic Ni-Cu-PGE at the undeveloped Nebo-Babel
Impact triggered deformation Deposit, found by Western Mining Corporation, and
This theory purports that a massive impact ~545Ma was now owned by BHP Billiton.
the triggering event. There is evidence of an impact,on • Podiform copper hosted in sheared basalts in the
the scale of the Vredefort crater proximal to the Mus- Warburton Ranges, near Warburton, Western
grave block. The center of this suspected buried impact Australia, worked in the 1960s and 1970s.
encloses most of the area between Uluru/Ayers rock and • Laterite nickel, primarily at Wingelinna.
Mt. Conner. Exploration for Olympic Dam lookalikes and for magmat-
The basic facts, however, remain the same. The Peter- ic nickel copper mineralisation is continuing.
mann Orogeny was unusually violent, and has resulted in
a rare window into the lower crust. See also
• Geology of Australia
Economic Geology • Eclogite
The Petermann Orogeny exposes deep crustal roots of • Granulite
the previous Musgrave Orogen and lkely parts of several • Thrust fault
poorly exposed Proterozoic orogenic belts and igneous • Laterite
provinces. As such, the rocks of the Petermann Orogen • Ore genesis
are considered prospective territory for mineral explora-
tion. References
The history of mineral exploration in the Petermann
Orogen extends back to the last half of the 19th century, • Sandiford M., Hand M., Sandra McLaren, S., 2001.
with a series of prospectors and exploring pioneers tran- Tectonic feedback, intraplate orogeny and the geochemical
siting the area. Most famously was Lasseter, who alleged- structure of the crust: a central Australian perspective. In
ly found Lasseter’s Reef, a near-mythical gold lode of "Polyphase tectonism and reactivation mechanisms
such richness and scale that it has fired imaginations for in metamorphic belts", Geological Society of London,
over a century, but remains undiscovered. Special Publication
In the mid and late 20th century, government mis- • Connelly D., 2009 "The case for a massive Australian
sionaries brought to the indigenous Aborigines of the Precambrian/Cambrian impact structure (MAPCIS)"
area European law, European culture and the concept of The Geological Society of America, Northeastern section
salaried work, previously unknown to the hunter-gather- annual meeting,2009
er inhabitants. In order to provide work, subsidised ex-
ploration was undertaken by the Western Mining Corpo- External links
ration, resulting in the discovery of podiform copper at
• Musgrave Eclogites
Warburton Range, and eventually the Wingelinna nickel
• Tectonic feedback, intraplate orogeny and the
laterite resource.
geochemical structure of the crust: a central
The advent of the Mabo Decision and land rights
Australian perspective
movements has seen aboriginal land rights improved,
with the result that they now control access to land and
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Categories: Orogeny, Geology of Western Australia
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