The Tasmanian "Devil's Disguise" is an essential piece of the puzzle to understand supercontinents: UNM Newsroom

A new document recently published in geology by researchers Jacob Mulder, Karl Karlstrom and other Australian colleagues provides a new dataset that could resolve the debate of more than three decades on adjacent continents in southwestern United States. United in the supercontinent old of a billion years. Rodinia.

Funded by an Australian Stock Exchange, Mulder, of the School of Earth, Atmosphere and Environment at Monash University (Australia), has spent a year of her PhD. studied at the University of New Mexico and accompanied Karlstrom, a professor in the UNM's Department of Earth and Planet Sciences, on a research trip to the Grand Canyon. Their research, Devil Rodinian disguise: correlation of 1.25 to 1.10 Ga strata between Tasmania and Grand Canyon, aimed at testing geological connection patterns between rocks in the southwestern United States and Australia.

"The supercontinent's hypothesis is that all continents of the Earth congregate about every 700 million years in supercontinents, then separate into separate continents and then be reconfigured into supercontinents," Karlstrom said. "At the present time, the Atlantic Ocean is expanding and the continents are dispersing while 300 million years ago, all the continents were gathered in the supercontinent of Pangea, which is well documented by the match of the South American and African coasts and by magnetic tapes of the seabed. in the Atlantic Ocean that record the opening of the Atlantic and the dissolution of Pangea. "

Rodinia, Russian term for "homeland", was the second oldest supercontinent; it came together about 1 billion years ago and was separated about 750 million years ago. Its existence is well accepted, but its configuration has been controversial for more than two decades. Scientists have noticed that the Tasmanian Rocky Cape Group and Unkar groups in the Grand Canyon have strange bed-by-bed similarities.

"We started this work by examining Mesoproterozoic sedimentary rocks (about 1 billion years old) in Tasmania, a small island in southeastern Australia," said Mulder. "These rocks intrigued us for a long time, because they did not look much like the Mesoproterozoic rocks near Australia. We wanted to know where the old Tasmanian sedimentary rocks came from. So we analyzed grains the size of a sand, zircon, which represents only a small proportion of sedimentary rocks. "

By grinding the sandstones of each location, scientists found and dated hundreds of zircon grains in each estate to compare their "fingerprints". The ages and hafnium compositions of zircons in both locations agree very well and the authors suggest two zones were adjacent between 1.25 and 1.1 billion years ago.

To incorporate this into the Rodinia supercontinent debate, they hypothesized that these sediments were both eroded by a continental collision, called the "Grenville Mountains", which was similar to the collision between the Himalayas and the modern ones. . Tasmania and the Grand Canyon were both "front", in a foreland basin, and the rivers carried grains of sand from high mountains that existed in what is now the Texas region. Fragments of these mountains can also be found in the collapsing Kalahari block, currently in Africa.

"The new correlation was not enough on its own," said Karlstrom. "Given the long controversy surrounding Rodinia's configuration, we also synthesized all paleomagnetic data from the United States, Australia, Kalahari, and East Antarctica to determine if the Rodinian puzzle could be solved. like this. We found that the Tasmania-Grand Canyon connection could reconcile previous models (competitors) for Rodinia. "

"Not only are the Grand Canyon rocks similar to those of Tasmania and the same age, but the detritic zircons of the Grand Canyon sedimentary rocks (and the associated rocks of central Arizona and Texas) also share the same footprint. geochemical digital than the zircons of the Mesoproterozoic Tasmanian sequences, "said Mulder. "Together, these different lines of evidence support the interpretation that Tasmanian sedimentary rocks were once part of the same Mesoproterozoic basin system that is now exposed at Grand Canyon. Therefore, we have concluded that although it is now on the opposite side of the planet, Tasmania must be attached to the western United States by the Mesoproterozoic. "

Scientists propose a new evolutionary plaque configuration similar to the AUSMEX model (Australia and Mexico as neighbors) about 1.1 billion years ago, to the AUSWUS model (Australia and the western United States as neighbors) about 1.0 billion years ago, and at SWEAT. model (southwestern United States and eastern Antarctica as neighbors) about 0.9 billion years ago.

"The study is important to understand Rodinia's paleogeography because we have been able to show that the crustal block that makes up Tasmania, as well as a series of equally enigmatic little blocks now exposed in Antarctica and submerged under the sea. ocean south of Tasmania, provide major geological links between the major Australian, Antarctic and American continents are an important part of Rodinia, "said Mulder.

"Thus, the new document shows that Tasmania is an essential piece of the Rodinia puzzle," said Karlstrom. "In science, the devil is still in the details and this new" Tasmanian devil "seems to have revealed secrets of the Rodinian supercontinent that have remained mysterious for decades. The document also highlights the power of international collaborations in resolving geological debates. "