22-Jan-2018: A Remote Australian Region was once part of North America

Geologists have found a series of rocks which suggests that, part of Australia could have once been connected to part of Canada on the North American continent, around 1.7 billion years ago.

Speculation about such a connection has existed since the late 1970s, when a paper proposed a connection dating back to the continent of Rodinia, around 1.13 billion years ago. However, an exact time and location for the connection has remained under debate.

Found in Georgetown, north east of Australia, the rocks are unlike other rocks on the Australian continent. Instead, they show similarities to ancient rocks found in Canada, in the exposed section of the continental crust called the Canadian Shield. This unexpected finding reveals something about the composition of the ancient supercontinent Nuna.

About 1.7 billion years ago, Georgetown rocks were deposited into a shallow sea when the region was part of North America. Georgetown then broke away from North America and collided with the Mount Isa region of northern Australia around 100 million years later. This was a critical part of global continental reorganization when almost all continents on Earth assembled to form the supercontinent called Nuna.

The last time the continents were close to one another was the major supercontinent known as Pangea, which broke apart around 175 million years ago. However, before Pangea, the planet went through a number of supercontinent configurations - one of which was Nuna, also called Columbia, which existed from around 2.5 billion to 1.5 billion years ago.

According to the research, when Nuna started breaking up, the Georgetown area remained permanently stuck to Australia. This challenges the current model that suggests the Georgetown region was part of the continent that would become Australia prior to 1.7 billion years ago. The research also found new evidence that Georgetown and Mount Isa mountain ranges were formed when the two regions collided.

Ongoing research by the team shows that this mountain belt, in contrast to the Himalayas, would not have been very high, suggesting the final continental assembling process that led to the formation of the supercontinent Nuna was not a hard collision like India's recent collision with Asia.

14-Aug-2017: Malpelo tectonic plate: a new tectonic microplate discovered off the coast west of Ecuador.

Scientists from Rice University have discovered a microplate off the west coast of Ecuador which adds another piece to Earth’s tectonic puzzle. Geophysicist Richard Gordon discovered the microplate, which they have named “Malpelo,” while analyzing the junction of three other plates in the eastern Pacific Ocean.

The Malpelo Plate, named for an island and an underwater ridge it contains, is the 57th plate to be discovered and the first in nearly a decade. There are more to be found.

Misfit plates in the Pacific led Rice University scientists to the discovery of the Malpelo Plate between the Galapagos Islands and the South American coast. Geologists carefully studied the movements of other plates and their evolving relationships to one another as the plates move at a rate of millimeters to centimeters per year to discover the new plate.

The Pacific lithospheric plate that roughly defines the volcanic Ring of Fire is one of about 10 major rigid tectonic plates that float and move atop Earth’s mantle, which behaves like a fluid over geologic time. Interactions at the edges of the moving plates account for most earthquakes experienced on the planet. There are many small plates that fill the gaps between the big ones, and the Pacific Plate meets two of those smaller plates, the Cocos and Nazca, west of the Galapagos Islands.

One way to judge how plates move is to study plate-motion circuits, which quantify how the rotation speed of each object in a group (its angular velocity) affects all the others. Rates of seafloor spreading determined from marine magnetic anomalies combined with the angles at which the plates slide by each other over time tells scientists how fast the plates are turning.

The angular velocities of these three plates ought to sum to zero, but in this case, the velocity doesn’t sum to zero at all. It sums to 15 millimeters a year, which is huge. That made the Pacific-Cocos-Nazca circuit a misfit, which meant at least one other plate in the vicinity had to make up the difference. Misfits are a cause for concern – and a clue.

Knowing the numbers were amiss, the researchers drew upon a Columbia University database of extensive multibeam sonar soundings west of Ecuador and Colombia to identify a previously unknown plate boundary between the Galapagos Islands and the coast.

Previous researchers had assumed most of the region east of the known Panama transform fault was part of the Nazca plate, but the Rice researchers determined it moves independently. If this is moving in a different direction, then this is not the Nazca plate and the scientists realized this is a different plate and it’s moving relative to the Nazca.

Evidence for the Malpelo plate came with the researchers’ identification of a diffuse plate boundary that runs from the Panama Transform Fault eastward to where the diffuse plate boundary intersects a deep oceanic trench just offshore of Ecuador and Colombia. A diffuse boundary is best described as a series of many small, hard-to-spot faults rather than a ridge or transform fault that sharply defines the boundary of two plates. Because earthquakes along diffuse boundaries tend to be small and less frequent than along transform faults, there was little information in the seismic record to indicate this one’s presence.