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Petermann Orogeny

From Wikipedia, the free encyclopedia

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.

Geological interpretation of the West Musgrave Block, Western Australia. 50x50km grid for scale.
Geological interpretation of the West Musgrave Block, Western Australia. 50x50km grid for scale.

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.

YouTube Encyclopedic

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  • Aussie English: Uluru | Learn Australian English

Transcription

G’day guys. Welcome to this episode. It’s finally the Uluru episode. I’ve gotten around to doing it today. I hope you guys enjoy it. I’m going to also try and record this as a podcast episode, hence this stuff here in front of me. Get a bit better quality audio. Anyway, without any further ado let’s just dive in. So, is it Ayers Rock or Uluru or both? Uluru’s actually the indigenous name for Ayers Rock, and it’s also the official name. So, Ayers rock is actually the European settlers name for Uluru, and it was named by William Gosse who stumbled upon Uluru in 1873, and he named it after Sir Henry Ayers who was the Chief Secretary of South Australia at the time. The landmark has actually been officially known as Uluru/Ayers Rock since 2002, and it’s one of the only very few dual-named locations or features in Australia. If you want to be politically correct I would probably refer to it as Uluru the indigenous name. Although if you use Ayers Rock people are going to know exactly what you mean and they shouldn’t be too offended especially if you’re travelling in Australia from overseas. That said, there isn’t just a single name for the rock, Uluru, at least in terms of indigenous names. There’s many names for the location and the different sites around the location including waterholes, caves and sacred sites. And although the local people consider Uluru to be sacred they actually distinguish between the rock itself and the numerous sacred all around the rock, hence the different names. So, what does it mean to be a sacred site to an indigenous person? All indigenous in Australia have a specific word in their language that means sacred site, and to an indigenous person when a place is considered to be a sacred site there are usually restrictions on who can visit that site, when they’re allowed to visit the site, and the rituals and songs that they have to know in order to visit that site. This means that some places on or around Uluru may only be visited by initiated men or by indigenous women. Places become sacred sites because Dreamtime beings visited those sites or travelled through those sites and performed a particular action in these places, and they’re still considered to be there performing those actions today. As a side note, Dreamtime or The Dreamtime is the indigenous Australians’ understanding of the world, of its creation and its great stories. So, it’s their version of religion. What does Uluru mean? Although you may find people or websites suggesting that Uluru isn’t just a place name but also means things like Big Rock, Mother Earth, Island Mountain or Rainbow Dreaming, this is actually false and Uluru is first and foremost just a place name with no other significant meaning. Where is Uluru? Uluru is located West of the Simpson Desert, pretty much smack bang in the centre of Australia, and the closest city or the closest town to Uluru is Alice Springs, and it’s about 463kms by road to the south west or 335kms as the crow flows, so, in a straight line. So, how big is Uluru? Uluru’s actually much bigger than even I thought before researching this episode. So, it’s actually taller than The Eiffel Tower. And I mean, I knew that it was big but I also appreciated just how high The Eiffel Tower was. So, it was a bit of a shock when I realised, when I found out that Uluru’s actually bigger than, taller than, The Eiffel Tower. So, it’s almost 350m tall, or metres high, it’s 863m above sea level, it’s 3.6km long and about 2km wide, and around the base it’s 9.4kms in circumference. So, it takes about 3.5hrs to walk the 10km track that’s called The Uluru Base Track or Base Walk, around the mountain. And the cool thing about Uluru is that it’s kind of like a land iceberg. So, you’ll know with icebergs that you can see a lot of it on the top, above the water, but the majority of the iceberg is below the water. And Uluru as a rock is actually similar to this where it actually dives down under the earth, the rock itself, for at least another 2.5 or 3km under the earth. So, it’s like a land iceberg. Who owns Uluru? There are several groups of people who own Uluru whose names I definitely can’t pronounce well but I’ll give it a try. The Pitjantjatjara, the Yankunytjatjara and the Ngangkaritjutaku. So, that was awful and I’m sorry to these people if any of these people are watching this video in the future. Collectively, these groups of people are known as The Anangu People or just Anangu, because the word “Anangu” actually just means “people”. I’ll refer to it as The Anangu People just to make things a little easier to understand. The Anangu people own all of Uluru and the surrounding area as well as obviously Kata Tjuta, which is a similar kind of sister monolith to Uluru itself that’s nearby. And they lease it to Parks Australia to be jointly managed as a national park. So, this arrangement began in October in 1985 in an historic moment known today as “Handback”. And the Anangu people consider Uluru to be an incredibly sacred site, or an incredibly sacred area, and while climbing the rock isn’t necessarily illegal, you can do it if you want, it’s considered disrespectful to the indigenous culture because they don’t really like people visiting these sacred sites and particularly walking on these sacred sites. So, I just mentioned Kata Tjuta, and Kata Tjuta, hopefully I’m pronouncing that correctly, is Uluru’s sister rock formation, which is found 25kms to the east [west*] of Uluru. It’s actually higher than Uluru, which surprised me, I mean I had heard of it but I had never really appreciated the size comparison. So, Kata Tjuta is 546m above the surrounding area, the surrounding plain, or 1066m above sea level. So, it’s about the same height as The One World Trade Center, which is currently under construction in New York. How long have indigenous people lived in Uluru, or in the surrounding area? The Anangu people have lived the country which surrounds Uluru for definitely thousands upon thousands of years and archaeological evidence shows that indigenous people have occupied Central Australia, so this region of Australia, for at least 30000 years. And to put that in context, at about the same time I think humans had only just gotten to northern parts of Europe and were actually interacting potentially with the Neanderthal at that same time. So, that’s crazy. How old is Uluru? Uluru’s estimated to be about 500 million years old. So, it’s probably older than that but that was the estimation for when it formed. And to put that in context, it actually formed before there were any plants on land. So, before any plants on land had evolved. How did Uluru form? This is a long story, and I’ve written it out in a detailed sort of list of dot points. So, I’ll try and go through it because I found it incredibly interesting, but yeah, it’s a detailed explanation. So, bear with me. So, it formed over 500 million years ago and at this time big crustal blocks, so big chunks of the earth’s crust, big crustal blocks, that formed the Australian continent came together. One of these blocks called the Musgrave Province pushed up from the south and created a mountain range called The Petermann Ranges. And The Petermann Orogeny is this sort of, the name for this event, and “orogeny” is the name for a mountain building event in geological terms. When The Petermann Ranges first formed they were incredibly high and they were sort of comparable with The Alps or The Himilayas today in height. So, very very very high. However, today we can only really see obviously the roots or the nubs of what once was a vast mountain range because they’ve all eroded away. At this time, so when this was happening remember there were no land plants and so the landscape was very different from today. The climate was also incredibly different, and without any of this plant cover The Petermann Ranges began to rapidly erode due to , you know, wind and rain and just exposure to the environment. There were no land plants to hold the topsoil together and protect these formations. So, they began to disappear pretty quickly, erode away. After this period of rapid mountain building followed by rapid erosion in the centre of Australia the place was also flooded and became an inland ocean, so an inland sea called The Amadeus Basin. So, a tropical seaway was formed due to this basin and it went through central Australia and out through the Kimberleys, and the Kimberleys is in the north east of Australia, the north east of the continent. And so, during this period, a phase of deposition began in this Amadeus Basin. So, a lot of soil, a lot of sand, was being deposited in this area. And so, it effectively buried what was left of The Petermann Ranges, and what would become in the future Uluru. So, Uluru was sort of submerged in mud, sand and limestone, and this happened at about 400 million years ago. And they were so deeply buried by these sediments that the pressure actually crushed them and fused them together into a solid rock. So, they went from sediment rock, so like sand and mud and limestone, you know, that sedimentary rock, and turned into solid rock, very very different density, strong, strong, strong solid rock. And so straight after this another mountain building event occurred, and this one was called The Alice Springs Orogeny, and that further folded the rock and compressed them. And in this process the original horizontal layers of sand and gravel that formed Uluru were actually flipped on their side, and this is why you see those vertical layers or stripes on Uluru today. They’re not horizontal they’re vertical. And so, Uluru and Kata Tjuta were incased in this softer sediment rock under which they had been buried. So, the mud and the sand and the limestone that surrounded them and buried them. This all happened below sea level. And once again, this whole sort of block including Uluru and the sand and mud that it was buried in was pushed above sea level. And then over the following millions of years all of the softer sedimentary rock around Uluru and Kata Tjuta eroded away due to exposure to the climate. So wind and rain eroded all of this away, which now lead to the much stronger rock below these sedimentary rocks being exposed again. So, this is what Uluru and Kata Tjuta are, and this is why it’s taken so long for them to erode away because they rock’s been turned into such strong solid rock. So, there you have it. That’s how Uluru formed in a nutshell, although a pretty detailed nutshell, over 100s of millions of years, and the primary reason it’s still there is because of this complicated process where it was buried, it was compressed into incredibly dense rock, strong rock, by the pressure when it was buried, and when it was eventually re-exposed all of the softer rock around it eroded away rapidly but because it had become such a strong rock it took a lot longer to erode, or it is taking a lot longer to erode, and that’s why we still see it there today. So, “Why is Uluru red?” is the next question. The reason that Uluru is red is due to oxidation or rusting. So, like if you were to leave your car out near the ocean for decades it would eventually turn red from rust. So, oxidisation from the air. So, Uluru, the rock that makes up Uluru, is full of iron-bearing minerals. So, there is a lot of iron mineral in the rock, and when this rock is exposed to oxygen in the air it rusts. So, that’s why Uluru is red. And the interesting thing is then if you actually get to the fresh rock below the outer layer, the outer red layer of Uluru, which hasn’t been exposed to the atmosphere, it’s actually grey in colour. How hot does it get at Uluru? In summer it can get incredibly hot with temperatures up to 47oC. And surprisingly, it actually still receives over 300mm of rainfall a year, and that temperatures can also drop to -7oC in winter. So, during the winter nights. And this is partly because it’s in the desert, there’s not much cloud cover at night, so all of the heat from the day escapes and it becomes incredibly cold. Has anyone ever died at Uluru? To date there have been at least 37 deaths since the 1950s that I found about Uluru, and apparently the majority of these deaths have been due to cardiac arrest, so heart attacks. And this is due to the first part of the climb, where people climb up onto the rock, being incredibly steep and incredibly strenuous and challenging to do. And so, the remainder of these deaths have actually just been from falls obviously. And yeah, so it was interesting to find out that most of these were due to heart attacks instead of falls. Who was the first European to see Uluru and Kata Tjuta? Kata Tjuta was seen first, and it was seen a year before Uluru in 1872 by the explorer Ernest Giles who travelled to Central Australia. His benefactor Baron Ferdinand Van Mueller named it Mount Olga. And the next year in 1873 William Gosse became the first European to sight Uluru, so to set eyes on Uluru, and he named it Ayers Rock, as we stated before, after the Chief Secretary of South Australia at the time Sir Henry Ayers. How many people visit Uluru each year? More than 250,000 people visit Uluru every year from all around the world. And the last, very last question is, “Is it ok to climb Uluru?” This is a bit of a contentious issue, meaning that it is one that people are likely to argue about, and I’m sure do argue about a lot. While there is a track that you can climb to the top of Uluru, and while it is not illegal to climb Uluru and see the top, it is considered somewhat offensive to the local Anangu people who consider the sites on Uluru and around Uluru to be sacred, and that they should remain undisturbed and only visited by certain initiated people within the tribes. Aside from the argument not to climb Uluru out of respect for the wishes of local indigenous people it’s also considered a dangerous climb. As we’ve stated 37 people have died during the climb on Uluru. And also there is a big issue of human waste accumulation. So, there’s actually no bins and no toilets, no facilities on the climb on Uluru. And so, human excrement, so I’m sure you know what that is, that’s if you go to the toilet on Uluru, nappies, general trash, all of that stuff accumulates on this monolith as tourists climb it and when it rains it gets flushed down into waterholes below. So, it’s relatively unsanitary to climb up there with there being no facilities. So, since the Handback of Uluru to the Anangu people in 1985 signs have been erected in many different languages by the local people asking that people respect the wishes of the Anangu people and don’t climb Uluru. And since doing so, it’s good because the number of people has reduced to only 20% of visitors now climbing the rock. Also, more recently, an unknown person climbed the rock and cut the safety chains along the first part of the walk, which has obviously made the Uluru walk a lot more dangerous if you want to get up on top of the rock. And he did this in an effort to try and discourage more people from doing this climb because it’s disrespectful to the local people. So, ultimately, if you go and visit Uluru the choice is up to you. If you want to climb it you can, ultimately, you just have to take into account that it is considered disrespectful to the local people to do so. So, that’s the episode for today. I hope you enjoy this video. It’s a bit a long but it’s full of information. I’m sure you guys will be able to listen to this multiple times and keep getting more out of it each time. If you have any suggestions for future episodes let me know in a comment below, and if I missed any interesting facts about Uluru that you guys have found out about, or that you guys know, also mention those in a comment below because I’m sure I would love to hear it and I’m sure everyone else would as well. Anyway, until next time guys. All the best!

Contents

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.

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 isotopic models.

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 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 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;

  • Magmatic Ni-Cu-PGE at the undeveloped Nebo-Babel Deposit, found by Western Mining Corporation, and now owned by BHP Billiton.
  • Podiform copper hosted in sheared basalts in the Warburton Ranges, near Warburton, Western Australia, worked in the 1960s and 1970s.
  • Laterite nickel, primarily at Wingelinna.

Exploration for Olympic Dam lookalikes and for magmatic nickel copper mineralisation is continuing.

In popular culture

There are only one or two geology oriented documentaries that trace Uluru and Kata Tjuta's origins with the Australian Petermann Ranges. The Time Traveller's Guide To Australia in 2012 is possibly the first documentary to make the connection with reasonable clarity.

See also

References

External links

This page was last edited on 21 March 2018, at 11:01
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