Discovered in China: A 400-mile-long chain of ancient volcanoes petrified within the earth
In a groundbreaking discovery, a research team led by geophysicist Zhu Lei has unearthed a 400-mile-long chain of extinct fossilized volcanoes deep below South China. The findings, published in the Journal of Geophysical Research: Solid Earth on June 30, 2023, shed new light on the region's geological history and could redefine our understanding of the Earth's past climate.
The volcanoes, which date back to between 770 million and 820 million years ago, were discovered using an airborne magnetic sensor to "see" the crust beneath sedimentary rocks in the Sichuan Basin. The strip of iron-rich rock found beneath the Sichuan Basin is approximately 430 miles long and 30 miles wide, stretching from the northeast to the southwest of the Yangtze Block and reaching as far as 550 miles inland.
The team proposed that a different style of tectonics, called flat-slab subduction, may have formed the wide Yangtze arc. In flat-slab subduction, the oceanic plate moves horizontally beneath the continental plate at a shallow angle for hundreds of miles before sinking into the Earth, producing two distinct volcanic ridges. As oceanic crust subducts, it heats up and releases water, which generates magma. This magma rises to the surface, creating a long, narrow chain of volcanoes in a volcanic arc above the subduction zone.
The volcanoes formed during the breakup of the supercontinent Rodinia hundreds of millions of years ago. South China sat at the northwestern margin of Rodinia about 800 million years ago. Geologists previously discovered remnants of an extinct volcanic arc along the edge of the Yangtze Block. However, the new findings extend the region of past volcanism in this area by several hundred miles, suggesting that the volcanic activity was more widespread than previously thought.
The study presents an "exciting new set of data" in a region that has been difficult to study. The impact on Earth's past climate of the magmatic activity along this boundary should be evaluated, as scientists think the global carbon cycle underwent a major shift during this time interval. It remains unclear how the rings of fire in South China could have contributed to this perturbation and any resulting climate instability.
Peter Cawood, an Earth scientist, suggested an alternative explanation that the inland volcanoes could represent two independent but time-equivalent systems that were sutured together. Further research is needed to confirm this hypothesis and to understand the full implications of this discovery for our understanding of the Earth's history.
In conclusion, the discovery of the 400-mile-long chain of extinct fossilized volcanoes beneath South China offers a fascinating glimpse into the region's geological past and could provide valuable insights into the Earth's climate history. The findings could also have implications for our understanding of plate tectonics and the formation of continents.
