Geoscience: Beneath the Australian Alps

This is a snowy River National Park, it is a vast and magnificent landscape, but even everything we see here is just a small part of the earth's crust, we can walk around this country and study these rocks and imagine the massive forces that lift these mountains But unless we look miles deeper beneath the surface we will never know the full story of how our continent evolved. Yes, that's right, there are literally a hundred million years of geology in this part. It's like time travel. It's very well defined. It's critical that we have people with really strong, solid field experience who have seen these rocks, but we also have some of the newer second generation that are incredible.

We're taking some of these data sets and putting them together and it's that fusion of skills and knowledge that's helping. The interpretation that Cameron Cancer is talking about is the interpretation of a huge amount of new data. This data will help reveal the ancient origins of the earth. 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 have made it possible The Geological Survey has always been able to study near-surface rocks like these, but to truly understand the origins of the earth they needed to look deeper than ever, not just an A a few kilometers, but tens of kilometers deep, to do this they needed help, so the Geological Survey of Victoria brought together the resources and expertise of Geoscience Australia, a scientific group called Odd Scope, and the Geological Survey of New Wales of the South.

Together they share the common goal of understanding the The geological architecture of the southeastern part of our continent is one of the things that academics in Australia are particularly interested in the evolution of the Australian continent and, in order to analyze and research it, they need being able to get images of very, very deep parts. of the continent and look at how the building works, it came together to create the Australia we know today these geoscientists are investigating the origins of southeast Australia we have theories about how the continents came together and we have models placed on that based on what we can see at the surface but you don't know how they are connected at depth connections between the surface and buried rocks are commonly revealed using magnetic and gravity data dr.

Bob Musgrave is a senior geophysicist at the Geological Survey of New South Wales and saw something in the new magnetic data that was quite remarkable: a huge bend in rocks on a continental scale, which inspired Ross Cayley of the Geological Survey of Victoria to start to think big. Imagine that this edge of the water here is the east coast of Australia, where we are standing, so the coast is heading to Wilson's prom and milking. Melbourne Zin here, the Western Pictoris there, we began a survey north of Melbourne and continued up the east coast Ross realized that Bob's revelation might explain some puzzling rock structures recently mapped in Victoria and the idea we were making there was to test the idea that we have a geology that is wrapped up in a giant drop in Victorious Go when Ross combined Bob's data.

With Victorian mapping what he saw was almost unbelievable New South Wales and Victoria appeared to be part of a huge fold called the Klein the Lachlan aura, our Klein model suggests that about 430 million years ago these giant vertically sunken folds with amplitudes of more thousand kilometers were formed in eastern Australia, a byproduct of large folds on the scale of an ORAC line would be vertical faults and the Geological Survey has mapped some vertical faults on the surface, but if they were formed by an ORAC line they would be enormous and They would extend to the base of the crust so how does a geologist explore the Earth's crust at this scale?

He could look at the outcroppings on those mountains behind me to try to figure out what's immediately beneath my feet. It could even drill a diamond drill. hole of a kilometer or so, but to determine the structure of the deep crust up to say 40 kilometers then I need something very special and it is called a seismic reflection study, the trucks lower their platforms and begin to vibrate and this creates enough energy to send waves. They travel down through the earth up to 40 kilometers or more and the waves bounce layer after layer beneath us until they reach the surface in a matter of seconds.

This technology is like an ultrasound scan, but this scan is on a large scale and the power source is survivor-sized trucks or vibrations. These giants may be big, but they occupy a small footprint, so there are a series of microphones that we press into the ground, one every 10 meters, and they are distributed over six kilometers in front and behind. where the trucks that move the tiny companions of the giants are called geophones, specialized microphones that listen to the earth and although the tracks here were very difficult we have been very lucky because we are getting the acquisition and it has been absolutely perfect. weather and it is completely calm the only thing you can hear is the birds singing and the flies buzzing and that is not a problem for the geophone, without interference from wind and rain, the geophones can hear the small vibrations reflected in the buried rocks by combining all these reflections.

A gigantic vertical image of the rock strata is created and the team hopes to find evidence of the enormous folds already seen in magnetic and cartographic data and the formation of these files in the geology involved that is transported southwards thousands of kilometers and we should be able to see these patterns in the rock record up to 40 kilometers deep, so it's just a kind of preliminary interpretation, but you can see that there is a very distinctive reflectivity here, the change is markedly of westward character, so it is possible draw some. In fact, these massive faults have been a mystery since they were first mapped in the 1960s, but could now be explained by the ORAC line model, which theorizes massive southward movement as the crust creeps toward the South. began to envelop the much older Tasmanian crust, this movement forced adjacent areas to shear, thus creating deep vertical faults.

The team focused on features like these when planning the study, so if they can produce sufficiently detailed seismic images, there will be a powerful tool for examining the formation of southeastern Australia. There is only one problem: trucks must cross the most mountainous region of the continent the Great Dividing Range and the idea is that we want to shoot sighs let's go to the geology that gives us the best opportunity to solve the scientific questions with postal ecology There are hills here, so the rocks we want to study stick out of the ground, so We have already observed rocks directly as geologists and can now take seismic data to deepen understanding when the surface geology is well mapped and well.

I understand that it's easier to extend that knowledge using seismic data, so what we want to do is try to thread the needle between the geology that is significant and the extensions that allow us to visualize it in the best way possible to create images like this in places so mountainous country, the team needed new technology that was flexible and lightweight. no system can be easily mapped around here. There is a GPS receiver as well as seismic data. Each node records its own GPS position and time for the Tamiya loco, even every millisecond is very important The depth of the different strata is calculated using the time delay of the reflected waves The node characteristic is designed as hard in an endless task a great team keeps the nodes moving along with the vibrations the main choreographer these days is Ryan Newbould in his position at the head of the procession means that he is often the one meeting the general public for the last ten years , let's say, where all these little blue lines are.

They have carried out seismic studies and this is the last to reconstruct it. its enigma of what has been happening for the last half a billion years before, studies have already put western and central Victoria to the test, giving us a completely new understanding of the geological architecture of Victoria, so to complete the Victoria study, the 2018 line crossed the Australian Alps and ended on the east coast, this will build on previous work to help us understand the formation of southeastern Australia, it will also help with more modern scientific questions in the future and one of The reasons why we are not interested in sticking with the geometry of the faults is because they may contribute to understanding the earthquake that is heading for the region, so that could be important for developing management plans for reservoir dams and that type of infrastructure.

Surprisingly, the Victorian Alps are a young and dynamic landscape; Some uplift occurred as early as 80 million years ago, but most of the uplift is very recent and has been ongoing for the past 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 Australia is a very stable continent, but. We know that there have been some very significant earthquakes in Australia in recorded history and in human history; In fact, not far from where the study was carried out there was a very large earthquake about 40,000 years ago at the Murray River Dam, so deeper geology may allow us to better understand some of the faults that could be present. active in this shaky region so I'm checking and making sure the nodes are in the right order and all accounted for and if there are any problems catching them.

Compared to the usual lucky places we work this has been really lovely, we usually only get to see the flat parts of southern Australia so being in the Victorian Highlands is a nice change, walking from six to seven kilometers a day, the new nodal shaking. Technology meant that this survey collected more data than any previous land survey. This is the harvester truck, so this is where everything is unloaded and collected. We have the battery chargers here. The battery charging station in data download. Hundreds of nodes are processed every day once dismantled. the data from the nodes is downloaded and goes to Nelson to verify it with the Trimble GPS and timing data, it comes out of the rack and downloads, we verify that everything matches Nelson, then we pass the data to Lois for quality control and because the nodes are left out overnight, they also record natural seismic activity, which generates a huge amount of new information for the team and, if everything they say they brought me has been downloaded, that's it, the load is assembled, The main use of seismic data is assembled. visualize large-scale structures on earth, so features like mineral deposits are often too small to be seen, but by understanding the evolution of the continent it is possible to have a much better understanding of the formation of those resources, so there are reasons to do so.

This is in support of the exploration industry, but the research question is actually much bigger and really relates to how continents evolve, how mountains form, how commons break up during extension, whether the ORAC line is correct, another byproduct of its movement is the extension of the Earth's crust. and when that happens the crust becomes thinner, they can even create an area called a rift which could be a wide valley and because the crust beneath the rift is thin that allows volcanic material to come to the surface killing parts of the Rift and rift can subside and therefore the sea can invade depositing marine sediments and even limestone and this is exactly what happened in the Buckin rift area in 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 upside down reef, so we have some surface control over where the crack is and now with this seismic reflection data we can see the fairly reflective crack filling that continues to this position here marked in blue, so this is the first time we've actually had evidence that shows us what the shapes of this crack actually look like, so the seismic reflection gives us that incredibly detailed transect through the geology. You can understand the geology and history of a continent if you don't have those three. dimensional component is like trying to understand what the human body would look like without having x-rays or machinesMRI the type of scale seismic data we collect full crust you will have a three meter long section to view it from 1 to 100,000 scale if you want to get an overview you really need paper;

It's an old way of doing it, but it gives you much better control over large 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 out there. I'm learning things all the time and the interesting thing is that there are additional subvertical changes that we haven't really recognized in the geology before, including within the Tavor burrow site which we know from mapping that there is a terrain boundary between the ancient crust with the depth of Tasmania, if there is any, to the west and the younger cross with oceanic accretion affinity to the east and this interface which appears to be some sort of fault combination of the two different terranes pushed towards the surface and towards the west are simply world-class images and in seismic reflection data there is nothing better than walking through the maps and final sections with pencils in hand and having a robust debate with colleagues about what something might mean.

A technology as simple as colored pencil and paper seems to be the best way to synchronize the creative and very technical skills of the team, for example, the geophysicist.dr. Allison Kirkby is an expert in what is known as magnito a lurex, which measures the electrical properties of rocks at the scale of the continent. The image here tells us how well rocks reflect sound, but resistivity is a different property and tells us how they conduct. electricity so it is an independent constraint in the rock so you might have two different rocks that would be very similar seismically if you have the resistivity then that could highlight the differences between the two so they are used different geophysical techniques to measure different rock properties over large areas gravity data can be used to verify the density of rocks magnetic data can help distinguish packages of rocks in a seismic section that would otherwise look the same and, Therefore, all of these methods complement the seismic data and help build a more accurate picture.

Image of the bark in a much larger area. This has to have been one of the most challenging land seismic studies undertaken in Australia. Seismic expert Tonya Foeman had to carefully evaluate all the challenges when we looked at the map. I thought it wasn't possible to do it. When the team arrived 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 went well, so we have a very good team in Victoria. Very good team in New South Wales on camera at Justin's Australia, as well as people who really wanted to make it happen and would have a very experienced contractor.

Yesterday we discovered that there was a scene in our scene investigating the drug field, so we changed the university. because there was a bit of play oh cool it's a big challenge and it was a long job but we kept busy and it was quick why are you doing this job to give an idea on how to do earthworks on Monday Wednesday after the breeze? I quit, I go back to France and I say it took three months Frankie, pretty much a staple sandwich throughout Victoria and New South Wales, cheese chutney and cheese chutney, lamb, today's Johnny babe, oh look, it's a kind of a mix of excitement and relief in a It's a big relief that the project went so well.

We had to have a lot of things going for us. We were lucky to have really good weather. We had a fantastic team and the logistics worked really excellent. Latest. Latest. It is an honor for me. Leo is the last north now I was my thanks, yes, okay, break up the exciting science parties now that we have in the can lots and lots of fantastic deep seismic reflection data and we can use this data, that's what we anticipate, try all this geological and geochemical data for eastern Australia in Victoria, specifically the one we've been working on for years and years, it takes a lot of people to achieve something like this and you know, if someone drops a ball, it doesn't work as well. as I could and they all really get it right. ball out of the park with this one, just like at the beginning of the survey, we can see the results of these nodes, you compare them to the rocks sticking out of the ground, has been the purpose of the entire acquisition team. to the processing design, so we have to do it justice now with a really good geological interpretation with this data and results, the team can evaluate the Oricon model, they have seen the massive vertical thoughts and now they see something else that can have driven the own ORAC line now, the interesting thing about this is that this region is oceanic in character and is dominated by early westward dipping faults and you can see some of them in the seismic data and incredibly below the base of the crustal image here about 12 seconds we can see the faintest hints of possibly a fossil subduction zone trace dipping westward below and we need to do a little more work to confirm if that's the case so it's true this is a result really fantastic because that's the geodynamic drive.

Of all the structures, for the first time the team has extraordinary seismic images that extend more than 40 kilometers beneath southeastern Australia. These images will be combined with other geoscientific information and together will test the ORAC line model and its influence on the geology of our continent. This amazing data was collected by placing 63,000 geophones in the mountains of southeastern Australia. Applied Geoscience like this allows scientists and everyone to understand the faults, earthquakes, potential resources and evolution of the place we live in, just shave the static that we just traveled 629 kilometers. from the Murray Basin south of Banila across the Great Dividing Range and we are now on the east coast of Australia in the Tasman Sea we can really begin to put together the final pieces of the puzzle of how Victoria and south-east Australia has evolved from an ocean half a billion years ago to the landscapes we see today, including the mountains of the Great Dividing Range.