Billion-year-old chunk of North America traced to Antarctica
A team of international researchers has discovered more proof that areas of North America and Antarctica were connected over a billion years ago. Their evidence predates the formation of the super continent Pangaea.
"I can go to the Franklin Mountains in West Texas and stand next to what was once part of Coats Land in Antarctica," said Staci Loewy, a geochemist at California State University, Bakersfield, who led the study. "That's so amazing."
Loewy and her coworkers found that rocks gathered from both locations have the same structure as lead isotopes. Studies conducted earlier also indicated the rocks were the exact same age and boast the same chemical and physical characteristics.
Their work, which is published online in the September issue of the academic journal Geology, gives more support to the supposed SWEAT hypothesis.
According to SWEAT, ancestral North America and East Antarctica were fused in an earlier supercontinent named Rodinia.
The roughly 1.1-billion-year-old North American Mid-continent Rift System stretches across the continent from the Great Lakes to Texas.
Volcanic rocks connected to the rift are uncovered in the Keweenaw Peninsula of the Upper Peninsula of Michigan from which they take their name, the Keweenawan large igneous province. The scientists think that the rift might be a tectonic attempt to divide the ancestral North American continent of Laurentia that was halted in the middle of the process.
The rift goes into the subsurface beneath Minnesota, Iowa, Nebraska, Kansas and Oklahoma to the Franklin Mountains near El Paso, Texas where similar rocks are visible.
This newest report from Loewy, Ian Dalziel, research professor at The University of Texas at Austin, Richard Hanson of Texas Christian University and colleagues from several overseas institutions, shows that rocks barely poking through the ice in Coats Land - an isolated part of the Antarctic continent south of the Atlantic Ocean basin - mirror a former continuation of the North American rift system.
Loewy and company used new lead isotopic data from the 1.1-billion-year-old rocks from Coats Land, to determine the positions of Laurentia (ancestral North America) and Kalahari (ancestral southern Africa) in the 1-billion-year-old supercontinent, Rodinia. The Coats Land rocks are indistinguishable in age to both the Keweenawan large igneous province of the North American mid-continent rift and the Umkondo large igneous province of southern Africa.
A comparison of the isotopic configurations indisputably links the Coats Land rocks with the Keweenawan province. Combined with the paleomagnetic data this puts forward the idea that the Coats Land block was a piece of Laurentia by west Texas 1.1 billion years ago.
Also, the Coats Land block crashed into the Kalahari Precambrian craton of Africa during a 1-billion-year-old impact. Based on this reimagining, Laurentia rammed into Kalahari along Antarctica’s Maud mountain belt, which would represent a perpetuation of the 1-billion-year-old Grenville mountain belt of eastern and southern North America.
Therefore, the small Coats Land piece of Antarctica is a "tectonic tracer" which gives important clues to the relationships between three of the major continents of the planet 1.1 – 1.0 billion years ago, this is before the opening of the Pacific Ocean basin, the conjectured "Snowball Earth" glaciations, and the rise of multi-cellular life.
As you might already be able to tell, this is an important find for many different scientific disciplines. It’s a piece of evidence that strongly reinforces some of the mainstream scientific beliefs about the history of our planet.