An international team of 30 scientists has traveled to the Philippine Sea to drill into the crust of the Izu–Bonin-Mariana (IBM) arc and discover a cause for the plate collision. The results of their research were published in Nature Geoscience Journal on August 24, 2015.
The researchers from around the globe traveled to the Philippine Sea in the summer of 2014 on JOIDES Resolution, a large drillship operated by the International Ocean Discovery Programme, to drill into the crust of the IBM arc and discover why the plates collide.
“Plate tectonics and seafloor spreading was a ground-breaking theory discovered in the mid-20th-Century that explained much of geology, and started our modern discipline today. Before it, there was no single accepted theory of why oceans and mountains formed, and why continents look like they used to be linked together. This latest discovery addresses one of the last links in the theory that explains how geology works – which is a really significant find,” Dr. Sev Kender, a Research Fellow in the School of Geography at the University of Nottingham, said.
Two main models are so far used to explain how subduction zones start. In the first, so-called "spontaneous" model, one side sinks due to higher density and in the second, "induced" models, the plates are forced together by pressure from other distant locations.
However, the models cannot be tested, as the processes involved are ongoing over many millions of years, and they cannot be observed happening today.
By drilling a long borehole into the ocean crust on the overlying plate, the scientists can gain some insight into the subduction process: “During our expedition to the IBM Arc, we successfully collected 1.5 km [0.93 miles] of borehole through the overlying sediments and into the crust itself, dating the rocks with microscopic fossils and magnetic field reversals that took place throughout Earth’s history."
“We found the crust to be much younger than expected, a stunning discovery indicating that we needed to readjust our ideas of how the subduction zone formed. The crust has chemical characteristics indicating it was formed at the time the subduction zone started, rather than much earlier. The crust may have formed in an extensional setting through seafloor spreading, in some ways similar to that formed at mid-ocean ridges today, although in this case near the newly-formed subduction zone,” Dr Kender explained.
Fresh new oceanic crust can be formed along the mid-ocean ridges which are the opposite of subduction zones. Numerous transform faults that form due to spreading plates can be found near the ridges today.
“One idea is that the subduction zone formed along a previous line of weakness in one of these fracture zones, although it is not proven. Our new records show that the initiation was probably ‘spontaneous’ rather than ‘induced’, as the crust was formed in an extensional setting and did not become uplifted before formation. This finding really takes us one step closer to discovering how plate tectonics really works.”
- "A record of spontaneous subduction initiation in the Izu–Bonin–Mariana arc" – Richard J. Arculus et al – Nature Geoscience Journal (2015) – doi:10.1038/ngeo2515
Featured image: Scientists discover how the plates collide. Image credit: The University of Nottingham
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