Geologists Uncover Massive Chain of Fossilized Volcanoes Hidden Under China’s Yangtze Block

Unraveling the Earth’s history is no easy feat, especially when much of it lies hidden deep beneath its surface. However, recent studies have shed light on some of the planet’s geological past buried beneath modern formations. A new research paper published in the Journal of Geophysical Research: Solid Earth highlights a remarkable 430-mile chain of extinct volcanoes uncovered in the Sichuan Basin of South China’s Yangtze Block. This discovery hints at significant volcanic activity that could have influenced ancient climate conditions, created during the tumultuous separation of the supercontinent Rodinia as tectonic plates collided.

The Ancient Volcanic Landscape of South China

About 800 million years ago, South China was part of Rodinia’s northwestern edge during the early Neoproterozoic era. The dynamics of shifting plate tectonics eventually led to the formation of the Yangtze Block plate, which came into contact with the China Ocean plate. This collision initiated a process called subduction, where the heavier oceanic crust slipped beneath the lighter continental crust. Consequently, the intense heat generated from this action facilitated magma formation, enabling it to well up and develop into a narrow volcanic chain along a curved alignment above the subduction zone, giving rise to new crust and transforming the existing landscape.

Digging into Sedimentary Evidence

Researchers, including Zhidong Gu from PetroChina and Junyong Li from Nanjing University, examined ancient volcanic arcs to gain insights into how the Earth’s crust formed during its infancy. They identified remnants of an extinct volcanic arc along the Yangtze Block and were keen to see if these volcanoes traced further inland. As fossils became enveloped by a layer of sedimentary rocks, the team utilized an airborne magnetic sensor allowing them to “visualize” the crust beneath. By employing magnetic signal variations, geophysicists were able to create bankable data about what lay underground, as each rock has its unique magnetic mineral signature.

Investigating Rock Samples

Their sensors unveiled a substantial igneous rock band measuring 430 miles long and 30 miles wide with hydrogen-rich minerals boasting stronger magnetic readings. This data substantiated the discovery of a larger Tonian magmatic arc belt concealed inside the Yangtze Block, as noted by the study highlighted in Interesting Engineering. Further investigation of rock samples gathered from seven deep drill holes into the Sichuan Basin indicated volcanic origins and revealed a chemical makeup typical of rocks birthed by volcanic activity. Radiometric dating confirmed that these samples dated between 770 and 820 million years, perfectly aligning with the timeline of Rodinia’s disintegration.

How Volcanoes Affect the Climate

Traditionally, most volcanic rocks are snuggled closely to continental edges, but this specific formation extends significantly inland, encompassing up to 500 miles. Researchers proposed that the phenomenon might involve an alternative tectonic mechanism known as flat-slab subduction— where the oceanic plate glides horizontally before descending. This could have fostered broader volcanic activity zones. Additionally, it’s plausible that multiple volcanic systems combined over eons, creating a vast volcanic network. Such a colossal volcanic backdrop bears striking relevance when exploring Earth’s ancient climate, likely integrating into the global carbon cycle and contributing to climate fluctuations during its time.