Discovered: Sequence of Fossilized Volcanoes Spanning 400 Miles in Southern China Revealed by Geologists
Discovery of a Broad Volcanic Arc in Southern China Reveals Ancient Tectonic Activity
A team of researchers has uncovered a previously unknown volcanic chain in the Sichuan Basin, southern China, extending over 900 kilometers inland. This discovery sheds light on the ancient volcanic activity that took place during the early breakup of the supercontinent Rodinia about 800 million years ago.
The Yangtze volcanic arc, notably broader than other volcanic arcs such as the Cascades, is a result of the collision of the Yangtze Block with the China Ocean Plate. This collision led to subduction, a process in which the denser oceanic crust was forced beneath the lighter continental crust.
This shallow angle of subduction, known as flat-slab subduction, plays a critical role in shaping the geophysical characteristics of a region. It causes the subducting oceanic plate to descend at a shallow angle beneath the continental plate, resulting in volcanic activity occurring not only near the plate boundary but also further inland.
The airborne magnetic sensor, a key method used by the research team, allowed them to "see" underground rock formations beneath several kilometers of sedimentary rocks. The sensor revealed a continuous strip of iron-rich rock stretching 430 miles (700 km) from the northeast to the southwest of the Yangtze Block, providing evidence of the volcanic arc.
As the oceanic crust sank, it heated up and released water, which in turn generated magma. The borehole samples showed chemical signatures consistent with those found in rocks formed by volcanic activity, dating them to between 770 million and 820 million years ago. This magma then rose to the surface, forming a long, narrow chain of volcanoes along a volcanic arc.
The unique geological features of the Yangtze volcanic arc have sparked significant debate among researchers. Some propose that the two volcanic belts in this region might represent distinct yet time-equivalent systems later sutured together, but the flat-slab explanation remains a leading model for the arc’s unusual breadth.
Flat-slab subduction can influence crustal melting and magmatism by bringing water-rich fluids from the subducted slab into the overlying crust over a wide area, facilitating widespread volcanic activity and affecting crustal structure on a continental scale. This process has implications for crustal evolution and mineral deposit formation in these broad arcs.
The discovery of the Yangtze volcanic arc adds a new layer of complexity to our understanding of the climate transition during the Neoproterozoic era. Volcanoes release carbon dioxide (CO2) into the atmosphere, which can contribute to global warming. The extent of this volcanic activity in the Sichuan Basin during the Neoproterozoic era could have had significant implications for the Earth's carbon cycle and its climate at that time.
The research team used advanced geophysical techniques to detect the volcanic chain hidden beneath the Sichuan Basin, further confirming the volcanic origin of these rocks through analyses of rocks obtained from deep boreholes drilled into the uppermost crust of the Sichuan Basin.
References: [1] Yang et al., 2020 [2] Li et al., 2019 [5] Zhou et al., 2018
- The discovery of the Yangtze volcanic arc raises questions about its impact on medical-conditions during the Neoproterozoic era, as volcanic activity can release harmful gases into the environment.
- Further research in science, particularly medical-conditions and space-and-astronomy, can help determine whether the carbon dioxide released from the Yangtze volcanic arc had an influence on the Earth's climate or on potential life forms during the Neoproterozoic era, given the role of technology in uncovering geological phenomena like this arc.
