Ghost zircons from Easter Island challenge conventional beliefs about the Earth's mantle.

Easter Island is situated off the coast of South America and is part of the "Ring of Fire," a chain of volcanic islands encircling the Pacific Ocean. These formations are relatively young, dating back only a few million years. This is why the discovery of ancient zircons in the area has puzzled geologists. One possible explanation is that the mantle beneath is more stable than previously thought.

2024-10-20 07:30:11https://naked-science.ru/article/geology/tsirkony-prizraki-s-ostro

According to contemporary understanding, the Earth's crust is divided into plates. Those that support the continents are thick and very old, while those beneath the oceans are thin and young. Oceanic plates are in constant motion, and when they collide with a more rigid structure, they dive beneath it, sinking into the mantle and being remelted.

The oceanic crust is composed of basalts that have erupted onto the surface from numerous volcanoes. Easter Island serves as one such window into the mantle's depths. The discoveries of rather ancient zircons there, dating back 165 million years, add to the mystery.

Prior to this, zircons aged 180 million years were found on the underwater Southwest Indian Ridge. Even more ancient Paleozoic zircons have been encountered in the ocean. All of this demanded an explanation.

In scientific literature, the unusually ancient zircons from young oceanic "hot spots" have been dubbed "ghosts." It is possible that they are remnants of something much older that has long disappeared in subduction zones.

An international team of scientists led by geologist Yamirka Rojas-Agramonte, representing the Christian-Albrechts-University of Kiel and the University of Mainz in Germany, set out to investigate the issue.

“The presence of ghost zircons provides an opportunity to reconstruct the geological history of the Earth's mantle,” the researchers explained in a paper published on the ESS Open Archive platform, which has not yet undergone peer review.

According to Rojas-Agramonte, mantle plumes may exist for much longer than previously thought. This idea came to her after the discovery of zircons aged 164 million years on the Galapagos Islands.

The finding of ghost zircons on Easter Island is further confirmation. But how is this possible if this piece of land emerged at most four million years ago, and the oldest underwater mountain in this hot spot is dated at 48 million years?

The researchers proposed the following hypothesis. A mantle plume in the Easter Island region began its activity around 165 million years ago. The oldest zircons found are evidence of this active phase of melting in the Earth's crust.

The introduction of the plume led to the formation of traps—a large expanse of erupted basalts. According to modeling conducted by the authors, the traps originated on the hypothetical Paleozoic Phoenix Plate, which was hidden beneath the Antarctic Peninsula between 150 and 102 million years ago. It is possible that this is a remnant of the "Palmer Earth event," which caused the folding of the southern part of the peninsula.

Geological evidence of this tumultuous phase has not survived, except for the ghost zircons. If the mantle plume has been active for millions of years, then the upper part of the mantle from which it grows must have been stable for 165 million years. This contradicts current views that the asthenosphere—a liquid layer in the upper mantle—is actively mixing.