Plate tectonics may stop at least once again in Earths history

January 4th, 2008 - 3:26 pm ICT by admin  


Washington, January 4 (ANI): Carnegie Institution researchers say that Plate tectonics the geological process responsible for creating the Earths continents, mountain ranges, and ocean basins may have stopped at least once in the planets history, and that it may happen again.

A key aspect of plate tectonic theory is that on geologic time scales ocean basins are transient features, opening and closing as plates shift. Basins are consumed by a process called subduction, where oceanic plates descend into the Earths mantle.

Subduction zones are the sites of oceanic trenches, high earthquake activity, and most of the worlds major volcanoes.

Paul Silver of the Carnegie Institutions Department of Terrestrial Magnetism and former postdoctoral fellow Mark Behn say that most of the subduction zones are currently located in the Pacific Ocean basin.

Writing in the journal Science, they revealed that the Pacific basin may close in about 350 million years, when the westward-moving Americas collide with Eurasia.

Silver and Behn believe that that most of the planets subduction zones will disappear at that moment, effectively stopping plate tectonics unless new subduction zones start up.

The experts have also highlighted present geochemical evidence from ancient igneous rocks, which indicate that around one billion years ago there was a lull in the type of volcanic activity normally associated with subduction.

They say that a Pacific-type ocean basin had closed at that time, welding the continents into a single supercontinent, known to geologists as Rodinia. According to them, it might also have stopped subduction for a while.

Rodinia finally split apart when subduction and plate tectonics resumed.

Plate tectonics is driven by heat flowing from the Earths interior, and a stoppage would slow the rate of the Earths cooling, they add.

The experts believe that intermittent plate tectonics may explain why the Earth has lost heat slower than current models predict, and that the build-up of heat beneath stagnant plates may explain the occurrence of certain igneous rocks in the middle of continents away from their normal locations in subduction zones.

If plate tectonics indeed starts and stops, then continental evolution must be viewed in an entirely new light, since it dramatically broadens the range of possible evolutionary scenarios, says Silver. (ANI)

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