Petermann Orogeny
Encyclopedia
The Petermann Orogeny was an intracontinent
al event that affected basement rocks of the northern Musgrave Province and Proterozoic
sediment
s of the (now) southern Amadeus Basin
between ~550-535 Ma.
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) fabric
s 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 basin
s 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, sandstone
s, and siltstone
s.
Several pull-apart structural graben
s formed at flexures in the orogenic belt, forming the Levenger and Moorilyanna Grabens.
thrust fault
s. 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.
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.
al strike-slip along a series of anastomosing crustal-scale strike-slip thrusts which included movements during the pan-Africa
n 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.
models.
proximal to the Musgrave block. The center of this suspected buried impact encloses most of the area between Uluru/Ayers rock
and Mt. Conner.
The basic facts, however, remain the same. The Petermann Orogeny was unusually violent, and has resulted in a rare window into the lower crust.
.
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 was Lasseter
, who allegedly found Lasseter's Reef
, a near-mythical gold 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 indigenous Aborigines
of the area European law, European culture and the concept of salaried work, previously unknown to the hunter-gatherer
inhabitants. In order to provide work, subsidised exploration was undertaken by the Western Mining Corporation, resulting in the discovery of podiform copper
at Warburton Range, and eventually the Wingelinna nickel
laterite
resource.
The advent of the Mabo 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 for Olympic Dam
lookalikes and for magmatic nickel copper mineralisation
is continuing.
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
al event that affected basement rocks of the northern Musgrave Province and Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s of the (now) southern Amadeus Basin
Amadeus Basin
The Amadeus Basin is a large intracratonic sedimentary basin in central Australia, lying mostly within the southern Northern Territory, but extending into the state of Western Australia. It is named after Lake Amadeus which lies within the basin...
between ~550-535 Ma.
Prior to the Petermann Orogeny, which resulted in exhumation of the Musgrave Block
Musgrave Block
The Musgrave Block is an east-west trending belt of Proterozoic granulite-gneiss basement rocks approximately 500km long. The Musgrave Block extends from western South Australia into Western Australia....
, the Amadeus Basin was contiguous with the Officer Basin
Officer Basin
The Officer Basin is a large intracratonic sedimentary basin in Australia, lying across the states of South Australia and Western Australia. It is named after Officer Creek which is a watercourse that drains a small part of the basin. Deposition of up to 10 km of marine and non-marine sedimentary...
in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
.
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) fabric
Fabric (geology)
In geology, a rock's fabric describes the spatial and geometric configuration of all the elements that make it up.-Types of fabric:* Primary fabric — a fabric created during the original formation of the rock, e.g...
s are partially to completely overprinted by sub-eclogite
Eclogite
Eclogite is a mafic metamorphic rock. Eclogite is of special interest for at least two reasons. First, it forms at pressures greater than those typical of the crust of the Earth...
-facies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
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
Deposition (geology)
Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...
of rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
types such as arkose
Arkose
Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
and conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
in localised sedimentary basin
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
s that now outcrop as Uluru
Uluru
Uluru , also known as Ayers Rock, is a large sandstone rock formation in the southern part of the Northern Territory, central Australia. It lies south west of the nearest large town, Alice Springs; by road. Kata Tjuta and Uluru are the two major features of the Uluṟu-Kata Tjuṯa National Park....
and Kata Tjuta
Kata Tjuta
Kata Tjuta, sometimes written Tjuṯa , and also known as Mount Olga , are a group of large domed rock formations or bornhardts located about southwest of Alice Springs, in the southern part of the Northern Territory, central Australia...
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
Georgina Basin
The Georgina Basin is a large intracratonic sedimentary basin in central and northern Australia, lying mostly within the Northern Territory and partly within Queensland. It is named after the Georgina River which drains part of the basin. Deposition of locally up to ca...
, Officer Basin, Ngalia Basin
Ngalia Basin
The Ngalia Basin is a small intracratonic sedimentary basin in central Australia, lying within the southern Northern Territory. Deposition of locally up to about six km of marine and non-marine sedimentary rocks took place from the Neoproterozoic to the late Paleozoic...
and Amadeus Basin sediments in the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
. Sediments are a mixture of fluvial conglomerates, sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s, and siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s.
Several pull-apart structural graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s 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 arcuateArcuate
Arcuate can refer to:* Arcuate delta, a type of river delta* Arcuate fasciculus* Arcuate line * Arcuate artery* Arcuate nucleus* Arcuate nucleus * Internal arcuate fibers of the brain...
thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
s. The prime thrust fault is the Woodroffe Thrust, which is a laminated pseudotachlyte-schist
Schist
The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
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)
- FoldsFold (geology)The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
of D1, D2 and D3 rare; D4 isoclinal upright, and D5 and D6 restricted to cleavageCleavage (geology)This article is about rock cleavage, for cleavage in minerals see Cleavage Cleavage, in structural geology and petrology, describes a type of planar rock feature that develops as a result of deformation and metamorphism. The degree of deformation and metamorphism along with rock type determines the...
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.
- Folds
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
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
which have been exhumed, because these were within the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
and pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
conditions for brittle
Brittle
A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...
-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
This model (by SRK Ltd) considers the Petermann Orogen to be caused by transpressionTranspression
Transpression is a geological term used to describe a region of the Earth's crust that experiences strike-slip shear and a component of shortening, resulting in oblique shear. Transpression typically occurs at a regional scale, such as plate boundaries that have an oblique convergence. More...
al strike-slip along a series of anastomosing crustal-scale strike-slip thrusts which included movements during the pan-Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
n orogenies and tectonic events of the Cambrian-Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
.
The theory states that the degree of extreme uplift
Tectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic 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
Geochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
, and general lack of kinematics
Kinematics
Kinematics is the branch of classical mechanics that describes the motion of bodies and systems without consideration of the forces that cause the motion....
directly linked to transpression.
Intraplate thermal depression-rebound
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 and isostatic orogenic events. However, some authors (Camacho et al.) have called this into question with isotopicIsotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
models.
Impact triggered deformation
This theory purports that a massive impact ~545Ma was the triggering event. There is evidence of an impact,on the scale of the Vredefort craterVredefort crater
Vredefort crater is the largest verified impact crater on Earth. It is located in the Free State Province of South Africa and named after the town of Vredefort, which is situated near its centre. The site is also known as the Vredefort dome or Vredefort impact structure...
proximal to the Musgrave block. The center of this suspected buried impact encloses most of the area between Uluru/Ayers rock
Uluru
Uluru , also known as Ayers Rock, is a large sandstone rock formation in the southern part of the Northern Territory, central Australia. It lies south west of the nearest large town, Alice Springs; by road. Kata Tjuta and Uluru are the two major features of the Uluṟu-Kata Tjuṯa National Park....
and Mt. Conner.
The basic facts, however, remain the same. The Petermann Orogeny was unusually violent, and has resulted in a rare window into the lower crust.
Economic Geology
The Petermann Orogeny exposes deep crustal roots of the previous Musgrave Orogen and lkely parts of several poorly exposed Proterozoic orogenic belts and igneous provinces. As such, the rocks of the Petermann Orogen are considered prospective territory for mineral explorationMineral exploration
Mineral exploration is the process of finding ore to mine. Mineral exploration is a much more intensive, organized and professional form of mineral prospecting and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is much more involved.-Stages...
.
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 was Lasseter
Lewis Hubert (Harold Bell) Lasseter
Lewis Hubert Lasseter, or Lewis Harold Bell Lasseter as he later referred to himself, was born on 27 September 1880 at Bamganie, Victoria, Australia. Though self-educated, he was literate and well-spoken, but commonly described as eccentric and opinionated...
, who allegedly found Lasseter's Reef
Lasseter's Reef
Lasseter's Reef refers to the purported discovery, in 1897, of a fabulously rich gold deposit in a remote and desolate corner of central Australia...
, a near-mythical gold lode
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
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 indigenous Aborigines
Indigenous Australians
Indigenous Australians are the original inhabitants of the Australian continent and nearby islands. The Aboriginal Indigenous Australians migrated from the Indian continent around 75,000 to 100,000 years ago....
of the area European law, European culture and the concept of salaried work, previously unknown to the hunter-gatherer
Hunter-gatherer
A hunter-gatherer or forage society is one in which most or all food is obtained from wild plants and animals, in contrast to agricultural societies which rely mainly on domesticated species. Hunting and gathering was the ancestral subsistence mode of Homo, and all modern humans were...
inhabitants. In order to provide work, subsidised exploration was undertaken by the Western Mining Corporation, resulting in the discovery of podiform copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
at Warburton Range, and eventually the Wingelinna nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
laterite
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
resource.
The advent of the Mabo Decision
Mabo v Queensland
Mabo v Queensland was a landmark High Court of Australia decision recognising native title in Australia for the first time...
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;
- MagmaMagmaMagma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
tic Ni-Cu-PGEPlatinum groupThe platinum group metals is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table.These elements are all transition metals, lying in the d-block .The six...
at the undeveloped Nebo-Babel Deposit, found by Western Mining Corporation, and now owned by BHP BillitonBHP BillitonBHP Billiton is a global mining, oil and gas company headquartered in Melbourne, Australia and with a major management office in London, United Kingdom...
. - Podiform copper hosted in sheared basalts in the Warburton Ranges, near WarburtonWarburton, Western AustraliaWarburton or Warburton Ranges is an Indigenous Australian community in Western Australia, just to the south of the Gibson Desert and located on the Great Central Road and Gunbarrel Highway...
, Western Australia, worked in the 1960s and 1970s. - Laterite nickel, primarily at Wingelinna.
Exploration for Olympic Dam
Olympic Dam, South Australia
Olympic Dam is a mining centre in South Australia located some 550 km NNW of Adelaide, the capital city of South Australia. It is the site of an extremely large iron oxide copper gold deposit producing copper, uranium, gold and silver. The site hosts an underground mine as well as an...
lookalikes and for magmatic nickel copper mineralisation
Mineralization (geology)
In geology, mineralization is the hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".The first scientific studies of this process took place in Cornwall, United Kingdom by J.W.Henwood FRS and later by R.W...
is continuing.
See also
- Geology of AustraliaGeology of AustraliaAustralia is a continent situated on the Indo-Australian Plate.The geology of Australia includes virtually all known rock types and from all geological time periods spanning over 3.8 billion years of the Earth's history.-Components:...
- EclogiteEclogiteEclogite is a mafic metamorphic rock. Eclogite is of special interest for at least two reasons. First, it forms at pressures greater than those typical of the crust of the Earth...
- GranuliteGranuliteGranulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...
- Thrust faultThrust faultA thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
- LateriteLateriteLaterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
- Ore genesisOre genesisThe various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....