29-07-2025
Scientists discover 400-mile-long chain of fossilized volcanoes buried beneath China
Researchers have uncovered a massive, 400-mile-long chain of extinct,
fossilized volcanoes
deep under
South China
, revealing a surprising new chapter in
Earth
's geological history. This
ancient volcanic arc
formed around 800 million years ago during the early
Neoproterozoic era
, when two
tectonic plates
collided during the breakup of the supercontinent Rodinia, according to a recent study published in the
Journal of Geophysical Research: Solid Earth
.
Formation and geological significance
About 800 million years ago, South China sat on the northwestern margin of Rodinia. Shifting tectonic forces caused the landmass, now known as the Yangtze Block, to break off and move toward the China Ocean plate. This collision caused the denser oceanic crust to subduct beneath the continental crust — a process that generated magma as the oceanic plate heated up and released water. The magma rose through the crust, forming a long volcanic arc along the subduction zone.
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Unlike typical narrow volcanic arcs seen along continental margins (such as the Cascade Range in North America), this chain is unusually broad, stretching approximately 430 miles (700 km) long and about 30 miles (50 km) wide, extending as far as 550 miles (900 km) inland. This extensive width is linked to a tectonic process called flat-slab subduction, where the oceanic plate moves horizontally at a shallow angle beneath the continent before descending deeper. This shallow subduction produces two volcanic ridges—one near the plate boundary and another further inland—explaining the wide spatial extent of the fossilized volcanic arc beneath the Yangtze Block.
Methodology and findings
Because fossil volcanoes erode over millions of years and become buried under thick sedimentary layers (up to several kilometers thick in the Sichuan Basin), they are challenging to detect. The research team, led by Zhidong Gu (PetroChina) and Junyong Li (Nanjing University), employed airborne magnetic sensing technology to map magnetic minerals beneath these sedimentary layers, revealing iron-rich rocks with strong magnetic signals consistent with volcanic arc magmatism approximately 4 miles (6 kilometers) below the surface.
Rocks taken from seven deep boreholes drilled in the Sichuan Basin showed geochemical signatures similar to crust formed by volcanic arcs, and uranium-lead dating confirmed that these magmatic rocks formed between 770 million and 820 million years ago, placing them firmly in the early Neoproterozoic.
Broader implications
This discovery has significant implications for understanding Earth's crustal evolution. Volcanism and related mountain building in arc systems create new crust and alter existing crust. The volume and extent of magmatic activity revealed by this study suggest that ancient volcanic arcs were more extensive than previously realized in this region.
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Geologist Peter Cawood from Monash University, who was not involved in the study, pointed out alternative possibilities, such as the idea that the two volcanic belts revealed might be separate, contemporaneous systems joined together later in geological time. Nevertheless, he emphasized that the study provides "exciting new data" in a traditionally difficult-to-study area.
