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The remote Pilbara region of northern Western Australia is one of Earth's oldest blocks of continental crust, and we now think we know how it formed, as explained in research published today in Nature Geoscience.
The region is well known for its rich, ancient Aboriginal history extending over at least 40,000 years. It also features an incredibly diverse ecosystem, with many species found nowhere else.
Architecture - Crust - Landscape - Oval - Features
The architecture of this ancient crust leads to a distinctive landscape as viewed from above, with light-coloured oval features that are granite domes surrounded by dark belts of volcanic and sedimentary rocks, known as greenstone belts.
This unique geological architecture bears witness to the history of our planet.
Pilbara - Region - Years - Research - Idea
The Pilbara region began to form more than 3.6 billion years ago and our research supports the idea that its rocks were not formed through the plate tectonics processes that we see in operation today.
In plate tectonics, the outermost layer of Earth consists of fragmented, stiff "tectonic plates" that drift across the planetary surface, interacting at their boundaries. New crust is generated and destroyed at plate boundaries and this process is associated with most of Earth's current volcanic and earthquake activity.
Plate - Boundaries - Segments - Hundreds - Kilometres
The plate boundaries are generally composed of fairly straight segments, hundreds of kilometres long. Witness the long chain of volcanoes along South America's west coast.
So why do the rocks in the Pilbara exhibit this unusual granite-greenstone geometry?
Research - Rocks - Series - Overturn - Events
In our research we detail how these rocks formed, describing a series of "gravitational overturn" events that affected the ancient crust in the East Pilbara well before plate-tectonic processes began around 3.2 billion years ago.
What is a gravitational overturn? The young Earth was roasting hot. Its large heat content resulted in widespread volcanism. It was too warm for the rigid plates required for plate tectonics to operate.
Earth - Piles - Basalt
The hot early Earth erupted thick piles of basalt...
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