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Magnetic Sensors Reveal Chain of Extinct Volcanoes Almost 800 Km Hidden Below Deep Rocks in the Sichuan Basin in China
Researchers from Nanjing University in China identified a chain of extinct volcanoes extending approximately 640 kilometers.
This set was found deep within the Sichuan Basin, located in the Yangtze Block in the south of the country. The formation is associated with the Tonian magmatic arc belt, created between 820 and 770 million years ago.
The study provides new clues about the region’s geological history. According to the scientists, the so-called “fossilized volcanoes” were hidden about 6.5 kilometers below the Earth’s surface.
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They are buried under kilometers of sedimentary rocks and were only detected with the help of airborne magnetic sensors.
Sensors Reveal Iron-Rich Belt
These sensors revealed a band of rock with high iron content, measuring 690 kilometers in length and 48 kilometers in width.
The presence of iron is a strong indication of past volcanic activity. The magnetic field generated by these rocks was stronger than that of the surrounding formations, reinforcing the evidence.
According to the researchers, the volcanic chain would have emerged during the breakup of the supercontinent Rodinia, approximately 800 million years ago.
The movement of tectonic plates during this period caused southern China to drift away from the supercontinent. This resulted in the formation of the Yangtze Block plate.
Collision and Subduction Led to Magma Formation
Later, this plate collided with the plate of the Indian Ocean. This process generated what is known as subduction: the denser oceanic crust sank beneath the continental crust.
This movement produced heat and pressure, leading to the creation of magma. As the magma rose, it gave rise to a long chain of volcanoes — the so-called volcanic arc.
The resulting formations altered both the existing crust and the new crust in development. However, these structures became invisible over the millennia, buried beneath the Sichuan Basin.
Drilling Confirms Volcanic Origin
In addition to the magnetic data, the scientists collected samples from seven deep wells, ranging from 3,600 to 6,500 meters deep.
The analysis confirmed that the extracted rocks were magmatic, meaning they were formed from volcanic material. The chemical composition of these samples was compatible with that of rocks created in volcanic arcs.
Radiometric dating placed these rocks between 770 and 820 million years ago. This time coincides with the period of fragmentation of the supercontinent Rodinia, reinforcing the link between the events.
An Unusual and Extensive Volcanic Arc
The most surprising aspect was the size of the newly identified chain. Most volcanic arcs tend to emerge in narrower bands along continental margins.
However, this arc stretches about 800 kilometers into the interior of the continent, deviating from the more common pattern.
The researchers suggest two possibilities to explain this unusual dimension. One is the occurrence of a special type of subduction called flat-slab subduction.
In this case, the oceanic plate slides horizontally beneath the continental plate over a long distance before sinking. This may have generated a more extensive area of volcanic activity.
Another hypothesis considered is that two different volcanic systems may have merged over millions of years, creating a single belt of large proportions.
Possible Impact on Ancient Earth’s Climate
The study highlights that this chain of volcanoes may have played a significant role in Earth’s climate during that period.
Large-scale volcanic activity in southern China may have disrupted the global carbon cycle. This, in turn, could have contributed to climate instability at a crucial moment in the planet’s history.
These new findings help reconstruct geological events from almost 800 million years ago and may change the understanding of the evolution of the Earth’s crust in that region.
With information from Interesting Engineering.
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