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Drilling core with a length of 1,6 km coming from a depth of nearly 5 km under sea level

Segments of the drill core obtained on IODP expedition 351. Photo: Philipp Brandl, Geomar

An international team of scientists is making steps to understand the process of subduction of one continental plate under another

The movements of Earth’s tectonic plates shape the face of our planet. The sinking of one plate beneath another, known as subduction, causes volcanism and earthquakes. Subduction zones lie, for example, off the coast of Indonesia, Chile and Japan. But how exactly did this process begin? As part of the International Ocean Discovery Program, an international science team was able to drill and investigate the origin of a subduction zone for the first time in 2014. The team has published its data in the scientific journal Earth and Planetary Science Letters.

About 2000 km east of the Philippine Islands lies one of the most famous topographical peculiarities of the oceans: the Mariana trench. Reaching depths of up to 11,000 meters below sea level, it holds the record as the deepest point of the world’s ocean. This 4000-km-long trench extends from the Mariana Islands in the south through the Izu-Bonin Islands to Japan in the north. Here, the Pacific Plate is subducted beneath the Philippine Sea Plate, resulting in intense volcanic activity and a high number of earthquakes.

The entire area is part of the „Pacific Ring of Fire.”

But when and how exactly did the subduction of the Pacific Plate begin? This is a controversial topic among scientists. An international team led by the Geomar Helmholtz Center for Ocean Research Kiel, the Japan Agency for Marine Earth Science and Technology (JAMSTEC) and the Australian National University investigated this early phase of subduction along the Izu-Bonin-Mariana trench, with findings published in the March edition of the scientific journal Earth and Planetary Science Letters.

Diagram showing the shallow subduction of a tectonic plate that formed the Rocky Mountains. Author: Melanie Moreno / Wikimedia Commons

The study is based on a drill core that was obtained by the International Ocean Discovery Program (IODP) in 2014 with the US research drilling vessel Joides REsolution some 600 kilometers west of the current Izu-Bonin Trench. „For the first time, we were able to obtain samples of rocks that originate from the first stages of subduction,” says Dr. Philipp Brandl from Geomar, first author of the study.

The team of the Joides Resolution was able to drill more than 1600 m deep on the seabed, starting at a water depth of around 4700 m below sea level. That is at the limit of the technically feasible.

The researchers found evidence that volcanism was only beginning to gain momentum. The volcanic activity intensified with the rollback of the subduction zone towards the east and the huge explosive stratovolcanoes formed, similar to those present nowadays, for example along the western rim of the Pacific Ring of Fire.

The question of how subduction zones develop is not only interesting to understand the history of the earth. Such areas are the drivers for the chemical exchange between the earth’s surface and the earth’s interior.

The drill core on which the study is based was obtained during Expedition 351 of the International Ocean Discovery Program (IODP). The study included scientists from the Geomar, the Australian National University, Japan Agency for Marine Earth Science and Technology (JAMSTEC), California State University Northridge (USA), University of Leeds (UK), Geological Survey of Japan and the Chinese Academy of Science. (MOdS)

Earth and Planetary Science Letters, 461, 73-84

Source: Geomar

Japan lying at the rim of the „Pacific Ring of Fire“ has many volcanoes among them the Fuji, here at sunrise. Source: Wikimedia Commons

(16.02.2017, USA: 02.16.2017)