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Seismological Evidence for the Earliest Global Subduction Network at 2 Ga

Session: Recent Development in Ultra-Dense Seismic Arrays with Nodes and Distributed Acoustic Sensing

Type: Oral

Date: 4/20/2021

Presentation Time: 06:00 PM Pacific

Description: 

The theory of plate tectonics is one of the key scientific advances of the past century. It explains how Earth’s crust is made of enormous rocky “plates” floating on the planet’s molten interior, which slowly move around. When this happened, however, has remained controversial. The earliest evidence for subduction, which could have been localized, does not signify when plate tectonics became a global phenomenon. To test the antiquity of global subduction, we investigated Paleoproterozoic time, for which evidence is available from multiple continents. We studied an area geologists call the Ordos block, which is part of the North China craton, a very stable chunk of the Asian continent. In April 2019, we deployed 609 seismic recording stations spaced every 500 meters along a 300-kilometer line. By combining the earthquake data from these stations, we were able to form a detailed picture of Earth’s crust in this area. Beneath the city of Dongsheng, we found a feature called a dipping Moho in which the bottom of Earth’s crust dips from around 35km deep to more than 50km deep over a horizontal distance of only 40km. This dipping structure looks nearly identical to what is found beneath the Himalayan mountains, except it is around 2 billion years old.

Next, we collected seismic evidence from other studies around the world for similar dipping Moho structures that are about the same age. Putting observations from six continents together, we can form a picture of the creation of the ancient supercontinent Nuna. If Nuna was the first supercontinent, we can interpret these tectonic collisions that occurred around 2 billion years ago as the oldest evidence of plate tectonics in the global sense. Even though such collisions may have occurred here and there early on, it is likely that plate tectonics did not become a global network until this time. Global subduction by ~2 billion years ago can also explain why secular planetary cooling was not significant until Proterozoic time.

Presenting Author: Xusong Yang

Student Presenter: Yes

Authors