Geology of Australia

Australia is both a country and a continent. It is located southeast of Asia in the Southern Hemisphere, between the Indian and Pacific Oceans. Australia’s geological formations are among the oldest in the world, with some rocks dating from as much as three billion years ago, around the same time that Earth’s continental crust was being formed. Other geological features were created later by events such as volcanic eruptions, continental drift, and erosion. This diversity of geological formations makes Australia a fascinating object of study for paleontologists, geologists, and mineralogists.

Brief History

The shape of Australia was determined primarily by the continent’s tectonic plates and its separation from Antarctica, the process of which began around eighty-five million years ago and concluded about thirty-four million years ago. Remnants of Australia’s connection to Antarctica remain in the Finke River, which is one of the oldest rivers in the world and is believed to have once been part of a larger river system in Antarctica. Similarly, a chain of salt lakes about 170 kilometers (105 miles) long, found in the Yilgarn Craton (an old, stable part of the continental crust) of western Australia, was once part of a drainage channel that predated Australia’s separation and drift away from Antarctica. Geologists believe that this channel formed before the Jurassic period and was filled with water from now-frozen headwaters in Antarctica.

As Australia moved and the glaciers covering the continent began to melt, new basins were formed. One such basin is the Eromanga Basin, which covers an area of approximately 1,000,000 square kilometers (about 386,000 square miles) in central and eastern Australia. The basin was formed by sediment from glacier melting and contains minerals such as sandstone, coal, and shale. It has been mined for natural gas since the 1970s.

Later, approximately thirty-three million years ago, Australia drifted over a volcanic hot spot. New volcanoes erupted at this time, and new mountains were formed. As a result of this process, the world’s largest continental volcano chain was formed in Australia. This chain, which was first identified as such in 2015 and has been dubbed the Cosgrove track, is about 2,000 kilometers (1,243 miles) long and was last active between thirty-three million and nine million years ago. Many of these volcanoes are now extinct, meaning that they no longer erupt, but their structures are still visible. Modern researchers study them to learn more about how volcanoes emerge in different types of rock and how they change over time. While these scientists have found some evidence of seismic activity in this region, they do not expect the volcanoes to become active again.

The melting of glaciers and Australia’s gradual movement north opened new spaces to erosion, developed new rivers, and encouraged plants to grow. Volcanoes also contributed to changes in Australia’s topography, particularly in eastern Australia, where lava once covered much of the land. The resulting volcanic soil that exists there today is among the best in the world for growing crops.

Much of the western Australian landmass consists of the Australian Shield (also known as the Western Plateau), an example of a continental shield. In geology, a shield is an exposed region of once-molten rock that formed during the Precambrian, somewhere between 570 million and 3.5 billion years ago. Because shields are part of the continental crust, they are often very solid and do not support dense vegetation. The Australian Shield covers most of western Australia and contains within it the Yilgarn and Pilbara Cratons, as well as a number of smaller individual plateaus.

Off the coast of eastern Australia are two large islands—Tasmania to the south and New Guinea to the north—that were once part of the mainland. The last glacial period of the Quaternary glaciation (the current ice age) reached its peak around 22,000 years ago; by about 11,700 years ago, enough of the ice had melted for rising sea levels to separate Tasmania and New Guinea from mainland Australia.

Australia, or rather the Australian continental plate on which it resides, is still moving north at a rate of about seven centimeters per year, making it the fastest-moving of all the major continental tectonic plates. Between 1994 and 2016, the continent moved approximately 1.5 meters north, putting it out of sync with satellite positioning and navigation systems. To correct the discrepancy, the Australian government announced in July 2016 that it would adjust Australia’s official latitude and longitude coordinates to reflect a northward shift of 1.8 meters, an overcorrection intended to match the continent’s predicted location in 2020.

Overview

Geologists often use seismic surveys, a method of using ultrasound to create a picture of underground rock formations, to map out a region’s geology. These images have uncovered large deposits of fossils and minerals throughout Australia. Before seismic technology was available, Australians were discovering deposits of fossils and minerals by exploring the land by foot and mining by hand.

Some of the oldest fossils discovered in Australia are trilobites, small marine arthropods that lived during the Paleozoic era, between about 542 million and 251 million years ago. Trilobites have been found near Victoria and in other coastal regions, indicating that parts of Australia were once under seawater and have since moved to the surface, or that rocks that were under seawater and embedded with trilobite fossils have broken off and appeared in Australian waterways. Finding trilobites is one way that scientists were able to understand Australia’s geology before the development of seismic technology.

Even older evidence of Australia’s geographic past has been found near Lake George and the Yass River in the form of limestone outcrops. An outcrop is a spot where bedrock is visible on Earth’s surface, having been either exposed by erosion or pushed to the surface by the movement of tectonic plates. Studying these outcrops allows geologists to understand what kinds of rock formations are beneath Australia. Before the development of seismology, this was one of the few ways to determine geological makeup of an area without mining a region.

Mining and Mineral Deposits

Metal mining began in Australia in 1841, shortly after the discovery of lead ore in Glen Osmond, South Australia. Copper was discovered in the same region the following year, and the 1850s saw a series of gold rushes in New South Wales and Victoria. Iron ore was mined in South Australia beginning in the late nineteenth century, but it was not considered a significant resource until exploration began in earnest in the 1960s, leading to the discovery of large deposits in Western Australia. Uranium ore was mined on a small scale beginning in 1906 in South Australia, though at the time miners were primarily looking for radium. Intentional uranium extraction began in the 1950s, was briefly halted in the 1970s during a government inquiry, and commenced again near the end of the decade.

In contemporary Australia, mining companies operate throughout the country, and minerals are Australia’s largest export. Because of Australia’s extensive geographic diversity, the country has deposits of many of the minerals used in modern technologies and manufacturing, such as gold, iron ore, silver, coal, and uranium. These minerals are primarily exported to markets in China, Japan, South Korea, and India.

Australia also has large deposits of minerals necessary for construction and industrial products. As of 2015 it was the world’s largest producer of bauxite, a type of aluminum ore. High-quality iron ore is found in abundance in the Pilbara region of Western Australia, but in 2010 the Australian Bureau of Agricultural and Resource Economics predicted that if extraction continued at the same rate, the Pilbara ore would be depleted in thirty to fifty years.

Beyond metals, Australia also has large zircon mines. Zircon is a mineral that can be found in many different colors, from colorless to brown, blue, yellow, and green. The colorless stones are commonly used as a substitute for diamonds. Small particles of colored zircon are also used in ceramics and in the production of titanium. Some rare zircon crystals found in Australia within much younger rocks have been dated to 4.4 billion years ago, making them older even than the continent’s oldest rock formations.

The majority of Australia’s lithium comes from pegmatite deposits in Western Australia. The most commonly known use of lithium is in lithium batteries, which are required for modern cell phones and many laptops. These batteries are also used in electric cars, the demand for which is increasing the price of lithium and the desire for miners to increase extraction from Australian lithium mines. Lithium is also used to make glass and ceramics that can resist high heat.

Australia was the fourth-largest nickel producer in 2015. Again, the majority of deposits—about 95.3 percent of demonstrated reserves—are found in Western Australia; the remaining nickel deposits are in Queensland (4.5 percent) and Tasmania (0.2 percent). These deposits are rather large, though it is uncertain if Australian geologists will be able to find new deposits. While they expect that more nickel does exist, in possibly larger deposits, it is believed to be buried within other minerals, making it difficult to uncover through current exploration techniques.

Australia had the world’s second-largest deposits of silver in 2014, approximately 16 percent of known silver deposits worldwide, and was the fourth-largest producer. Silver is often found in conjunction with zinc and lead, as was the case in 1885, when large amounts of silver were found in the Broken Hill deposit in New South Wales. This region has since become famous for the large lead-zinc-silver deposits that are found in the area. The orebody was discovered in 1883 and was first believed to be tin but was later found to be lead–zinc sulfide deposits, with silver produced as a by-product. Mines were quickly set up, and the town of Broken Hill emerged to support the mining efforts. Today, most mining is done by machines, which require far fewer employees.

Energy Sources

Australia was the world’s third-largest producer of uranium in 2015, although estimated in-ground deposits far exceed those of any other country. Uranium was first discovered in 1906 at Radium Hill in South Australia by miners looking for radium. As there was little known use for uranium before World War II, extraction was minimal until the 1950s. Due to government support for mining projects, new deposits were subsequently found in the Northern Territory and Queensland. Mining efforts were briefly halted in 1976 for a government inquiry into the environmental effects of uranium mining. Around the same time, the movement for Indigenous Australian land rights was gaining traction, leading to conflict when uranium deposits were identified in Indigenous lands. While both the environmental inquiry and the subsequent land-rights inquiry resulted in a resumption of mining activities, many Australians have continued to oppose uranium mining because of concerns for the environment and for Indigenous land rights, as well as a belief that it is not ethical to participate in the proliferation of nuclear power and weapons.

Australia also plays a large role in coal production. As the world’s fourth-largest coal producer as of 2015, Australia is heavily invested in coal-mining projects in Queensland, New South Wales, and Victoria. More than half of Australia’s energy comes from burning coal, and additional coal is exported to other countries. While these mines bring in a large amount of money, they are commonly opposed by environmental movements, which point to scientific evidence linking the burning of coal to climate change.

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