Geoscience: Beneath the Australian Alps

this is a snowy River National Park it is a vast and magnificent landscape but even all that we see here is just a tiny part of the Earth's crust we can walk this country and study these rocks and imagine the massive forces that raise these mountains but unless we look deeper kilometers below the surface we will never know the full story of how our continent evolved [Music] [Music] [Music] [Music] yep that's right there's literally a hundred million years of geology sitting in this bit it's like time travel it's really well defined [Music] it's pivotal that we've got people with really sound and solid field experience that have seen these rocks but we've also got some of the newer generation two which are unbelievable we're taking some of these datasets and pulling them together and it's that coalescence of skills and knowledge that is helping us get the most out of the into the interpret Cameron Cancer is talking about is the interpretation of a massive amount of new data this data will help to reveal the lands ancient origins understanding the composition of the deep crust has long been a quest for Australian geoscientists but now with new tools and a collaborative approach they've made it possible the Geological Survey have always been able to study rocks near the surface like these but to truly understand the origins of the land they needed to look deeper than ever before not just a few kilometers but tens of kilometres down to do this they needed help so the Geological Survey Victoria brought together the resources and expertise of Geoscience Australia a scientific group called odd scope and the Geological Survey of New South Wales together they share a common goal to understand the geological architecture of the southeastern part of our continent one of the things that academics in Australia are particularly interested in the evolution of the Australian continent and to be able to analyze that and do research into that they need to be able to image very very deep parts of the continent and look at what the building works out it came together to create the Australia that we know today these geo scientists are investigating the origins of Southeast Australia we have theories about how the continents put together and we have models placed on that based on what we can see on the surface but you don't know how they are connected at depth the connections between surface and buried rocks is commonly revealed using gravity and magnetic data dr. Bob Musgrave is a senior geophysicist with the Geological Survey of New South Wales and he saw something in new magnetic data that was quite remarkable a huge curve in the rocks on a continental scale this inspired Ross Cayley from the Geological Survey of Victoria to start thinking big imagine this edge of the water here is the East Coast Australia where we're standing play so the coastal heads down to wilson's prom and milk Melbourne Zin here the Western Pictoris over there we started a survey north of Melbourne and we proceeded all the way to the east coast ross realized that bob's revelation could explain some perplexing rock structures recently mapped in victoria and the idea we were doing there was to test the idea that we've got geology that's wrapped in a giant fall at Victorious go when ross combined bob's data with the victorian mapping what he saw was almost unbelievable New South Wales and Victoria seemed to be part of a huge fold called an aura Klein the Lachlan our Klein model suggests that about 430 million years ago these giant vertically plunging folds with amplitudes over over a thousand kilometers were formed in eastern Australia a by-product of large folds on the scale of an ORAC line would be vertical faults and the Geological Survey has actually mapped some vertical faults at the surface but if formed by an ORAC line they would be huge and extend all the way to the base of the crust so how does a geologist explore the Earth's crust on this scale I could look at the outcrops in those mountains behind me to try and work out what lies immediately beneath my feet I could even drill a diamond drill hole down a kilometer or so but to work out the structure of the deep crust down to say 40 kilometers then I need something very special and it's called a seismic reflection survey [Music] the trucks lower their pads and start vibrating and this creates energy enough to send waves down through the earth as far as 40 kilometers or more and the waves bounce back from layer upon layer beneath us until they reach the surface in a matter of seconds this technology is just like an ultrasound scan but this scan is on a huge scale and the source of energy is survivor sized trucks or vibes these giants may be large but they have a tiny footprint so there's an array of microphones we're pressing to the ground one every 10 meters and they're laid out for six kilometers in front and behind where the trucks operating the tiny companions to the giants are called geophones specialized microphones that listen to the earth and even though the tracks here were really difficult we've been really lucky because we're getting the acquisition done and we've got absolutely perfect weather and it's completely quiet the only thing you can hear are birds chirping and flies buzzing and that's not a problem for the geophone without interference from wind and rain the geophones are able to listen for the tiny vibrations reflected from buried rocks by combining all these reflections a gigantic vertical image of rock strata is created and the team is hoping they'll find evidence for the huge folds already seen in a magnetic and mapping data and the formation of these files in involved geology being transported south by thousands of kilometres and we should be able to see these patterns in the rock record right down to 40 kilometers depth so it's only sort of preliminary interpretation but you can see there's some very distinctive reflectivity here the change is markedly in character to the west and so it is possible to draw some vertical faults heading down right down into the lower crust in fact these huge faults have been a mystery since they were first mapped in the 1960s but now they might be explained by the ORAC line model which theorizes a massive southward motion as crust was drawn southward it began to wrap around the much older Tasmanian crust this movement forced adjacent areas to shear thus creating the deep vertical faults the team targeted features like these when planning the survey so if they can produce detailed enough seismic imagery there will be a powerful tool to examine the formation of southeastern Australia there's only one problem the trucks must cross the continents most mountainous region the Great Dividing range and the idea is that we want to shoot sighs we go to the geology that gives us the best chance of solving the scientific questions with postal ecology it's hilly here and so the rocks we want to study stick out of the ground so so we've already looked at the rocks directly as geologists and now we can take seismic data to take it understanding deeper when the surface geology is well mapped and well understood it is easier to extend that knowledge down using the seismic data so what we want to do is try and thread the needle between geology that's meaningful and tracts that allow us to image it in the best possible way to create images like this in such mountainous country the team needed a new technology that was both flexible and lightweight no system it can be plots easily around here there's a GPS receiver as well as the seismic data each node records its own GPS position and time for the tamiya crazy even every millisecond is very important the depth of different strata is calculated using the delay time of reflected waves the feature of node is designed as tough in a never-ending task a large crew keeps the nodes moving along with the vibes [Music] [Music] the chief choreographer this days is Ryan newbould in his position at the head of the procession means he is often the one who encounters the general public over the last say ten or so years where all these little blue lines are they've done seismic surveys and this is the last one to sort of pieced together their puzzle of what's been happening over the last say five hundred million years earlier surveys have already tested western and central Victoria giving us an entirely new understanding of Victoria's geological architecture so to complete the survey of Victoria the 2018 line crossed the Australian Alps and finished on the East Coast this will build on earlier work to help us understand the formation of Southeast Australia it will also help with more modern scientific questions back in the future and one of the reasons we interested none staying the geometry the faults is because um they can like they can contribute to understanding the earthquake headed for the region then that might be important for developing management plans for reservoir dams and and that sort of infrastructure surprisingly the Victorian Alps is a young and dynamic landscape some uplift happened as long as 80 million years ago but most uplift is very recent and is ongoing in the last six million years the Pacific plate along New Zealand has been pushing towards Australia the Australian Alps are rising further reactivating ancient faults and causing occasional earthquakes so we think of Australia as being a very stable continent but we do know that there have been some very significant earthquakes in Australia in recorded history and in human history in fact not too far from where the survey was taken there was a very very large earthquake about 40,000 years ago the dam the Murray River so understanding the deeper geology may allow us to get a better understanding of some of the faults that might be active in this region trembling so I'm going through and making sure the nodes in the correct order and all accounted for and if there's any issues catch'em compared to the usual luck places that we work out this has been really beautiful we generally just get to see the flat parts of South Australia so being in the Victorian Highlands is a nice change walking you know six to seven kilometers a day trembling the new nodal technology meant that this survey collected more data than any previous onshore survey this is the harvester truck so this is where everything gets downloaded and collected we have in here the battery chargers battery charging station in the data download hundreds of nodes are processed every day once disassembled the nodes data is downloaded and it goes to Nelson for cross-checking with the Trimble GPS and time data they come off the rack and they're downloaded we check to see that everything matches Nelson then passes the data to Lois for quality control and because the nodes are left out overnight they also record natural seismic activity resulting in a massive amount of new information for the team and if everything they say they brought me has been downloaded that's it the load gets put together assemble the main use of the seismic data is to visualize large-scale structures in the earth so features like mineral deposits are usually too small to be seen but by understanding the evolution of the continent it's possible to have a much better understanding of the formation of those resources so there is a case for doing this in support of from the exploration industry but the research question is are really much bigger and and really relate to how continents evolve how mountains form how Commons get torn apart during extension if the ORAC line model is correct another byproduct of its movement is crustal extension and when that happens the crust becomes thinner they can even create an area called a rift which could be a broad valley and because the crust under the rift is thin that allows volcanic material to come to the surface killing parts of the Rift and the rift can sink and so the sea can invade depositing marine sediments and even limestone and this is exactly what's happened in the buckin rift area of eastern Victoria 400 million years ago well this is the first time we've been able to have seismic reflection data available to test ideas like the formation of the backhand reef so we have some surface control on where the rift is and now with this seismic reflection data we can actually see the quite reflective rift fill continuing down to this position here marking blue so this is the first time we've actually had evidence that shows us what the shapes of this rift really looks like so the reflection seismic gives us that incredibly detailed transect through the geology you can understand the geology and the history of a continent if you don't have that three-dimensional component it's kind of like trying to understand what the human body would look like without having x-rays or MRI machines the sort of scale seismic data we collect full crustal you'll have a three meter long section to look at it one to 100,000 scale if you want to get the big picture you really need paper it's an old-fashioned way of doing it but it gives you much better control over the big structures which is what we're looking for all these surveys always give us surprises and that's why we do them because we don't know what's there am i learning stuff all the time and what's interesting is that there are additional sub vertical changes which we haven't actually recognized in the geology before even even within the Tavor a burrow site we know from the mapping that there's a terrain boundary between old crust with tasmanian if any lia depth into the west and younger cross with oceanic accretionary affinity to the east and this interface which seems to be some sort of fault combination of the two different terrains pushed towards the surface and towards the west that is just simply world-class imagery and in seismic reflection data there's nothing better than getting around the the maps and end sections with with pencils in hand and having a robust debate with with colleagues about what it might mean something as low-tech as colored pencil to paper seems to be the best way to synchronize the creative and very technical skills of the team for example geophysicist dr. Allison Kirkby is an expert in what's known as magnito to lurex which measures the electrical properties of rocks at the scale of the continent image here tells us about how well the rocks reflect sound but the resistivity is as a different property it tells us how they conduct electricity so it's an independent constraint on the rock so you might have two different rocks that'd be very similar in the seismic if you have the resistivity then that might be able to highlight differences between the two so different geophysical techniques are used to measure different properties of rocks over large areas gravity data can be used to check the density of rocks magnetic data can help to distinguish packages of rock in a seismic section that otherwise look the same and so all these methods complement the seismic data helping to build a more accurate picture of the crust over a much broader area this has to have been one of the most challenging onshore seismic surveys completed in Australia seismic expert Tonya foeman had to carefully assess all the challenges when we looked at the map I thought it's not possible to do it all when tenure in the team got on the ground they realized that with the help of land managers local experts and communities it was possible to design a safe route despite the rugged terrain everything has come together so we've got the very good team in Victoria very good team in New South Wales in the camera in the Justin's Australia as well people who actually wanted to actually make it happen plus would have very experienced contractor yesterday we found out there was a our scene digging on the drug course so we changed the uni because there was a little bit of play oh great it's great a challenge and you was a long job but we stayed busy and it went quick why are they doing this job to give a bit of an insight on to have earth moves Monday Wednesday after breezy left off I go back to France and I say I take three months Frankie pretty much a staple sandwich all across Victoria and New South Wales cheese chutney and cheese chutney lamb today's Johnny babe oh look it's a sort of a mixture of excitement and relief in a way so relief that the project went so well we had to have a lot of things go in our favor we were blessed with really good weather we had a fantastic crew and the logistics just panned out really superbly [Music] [Applause] the last the last one it's my honor to Leo's the last north now I was my thank you yeah all right dissolve the science exciting parties now we've got in the can heaps and heaps of fantastic deep seismic reflection data and we can use this data that's what we anticipated test all these geological and geochemical for eastern australia in victoria specifically that we've been working on for years and years takes lots of people to pull something like this together and you know if anyone drops a ball doesn't work as well as it could and everyone really hit the ball out of the park with this one just like at the start of the survey we get to see the results from these nodes you compare them to the rocks that stick out of the ground it's been the whole purpose of the whole thing from the acquisition crew to the design the processing so we have to sort of do justice to it now with a really good geological interpretation with these data and results the team can assess the oricon model they've seen the massive vertical thoughts and now they see something else that may have driven the ORAC line itself now what's exciting about this is that this region is of oceanic character and is dominated by early West dipping faults and you can see some of those in the seismic data and unbelievably below the base of the crust image here at about 12 seconds we can see the faintest hints of possibly a fossil subduction zone trace dipping to the west underneath and we have to do some more work to confirm if that's the case so that's true this is a really fantastic result because that is the Geo dynamic drive of all the structures for the first time the team have extraordinary seismic images that extend more than 40 kilometers below southeast Australia these images will be combined with other Geoscience information and together they will test the ORAC line model and its influence on the geology of our continent this amazing data was collected from the placement of 63,000 geophones across Mountains of southeastern Australia applied Geoscience like this enables scientists and everyone to understand faults earthquakes potential resources and the evolution of the place that we live in just absolutely rap the static we just traveled 629 kilometers from the from the murray basin south of banila across the Great Dividing range and we find ourselves now and the on the east coast of Australia on the Tasman Sea we can really start putting the final pieces of the jigsaw into place on how Victoria and southeastern Australia has evolved from an ocean five hundred million years ago to the the landscapes that we see today including those mountains of the Great Dividing range [Music] [Music]

Channel: Department of Jobs, Precincts and Regions

Views: 130,327

Rating: 4.8301315 out of 5

Keywords:

Id: _S-024Cb5VE

Length: 25min 27sec (1527 seconds)

Published: Sun Sep 22 2019

Reddit Comments

[u/SpiredRobin187]

This is a documentary about the Southeast Lachlan Deep Crustal Seismic Reflection Survey that was carried out by the Geologic Survey of Victoria, Geoscience Australia, Geological Survey of New South Wales, and AuScope as a part of The Eastern Victoria Geoscience Initiative. The aim of the initiative is to better understand the architecture and evolution of the geology of south-eastern Australia.

[u/WendyLoish]

Thank you