India off to the racesAbout 100 million years ago, the Supercontinent Gondwana, composed of what are

India off to the racesAbout 100 million years ago, the Supercontinent Gondwana, composed of what are today the continents of Africa, Australia, Antarctica, South America, and the Indian Subcontinent, broke apart. Most of the continents moved slowly, sliding away as mid-ocean ridges developed, but India did something remarkable. About 80 million years ago, India suddenly raced to the North, crossing the entire Tethys Ocean in only 30 million years at 2-3 times the speed of the other continents (see animated gif at our blog here: http://tmblr.co/Zyv2Js1kb5DXy)A paper just published by Dr. Jagoutz’s group at MIT offers an explanation for how India moved so rapidly. We already know there was a subduction zone at the northern side of the Tethys Ocean; that subduction zone left remnants in the rocks currently forming the Himalayas today. Subduction is the engine that drives plate tectonics; although other forces can have an impact, the strongest driving force in plate motion is the desire of oceanic crust to sink into the Earth. Once oceanic crust gets about 100km deep, the pressure causes it to convert to a rock type called Eclogite (http://tmblr.co/Zyv2Js1ggzLcN, http://tmblr.co/Zyv2Js1UUiNx8) that is denser than the mantle and sinks, pulling along the ocean and any attached continents with it.India was pulled northward as a subduction zone formed beneath southern Eurasia, but according to Dr. Jagoutz, that wasn’t the only subduction zone pulling on India. Based on evidence from rocks in a few places in India that show evidence of ocean-ocean subduction as well as plate-motion reconstructions, they hypothesize that there was a second subduction zone in-between India and Eurasia during the time India moved at double-speed. Two sinking slabs would pull the Indian subcontinent north much faster than one, explaining India’s rapid race to the North.Other scientists have worked on another important plate tectonic problem, when India actually hit Eurasia and had difficulty. Scientists have disagreed whether the faults in India started growing 40 or 50 million years ago or somewhere in-between; this model also has implications for that work. If an island arc was forming over the subduction zone in the middle of the Ocean and India ran into that island arc, it would start forming faults and slow India’s motion down before it ran into Eurasia, making the history of the Himalayas even more complicated.This intriguing model therefore explains several of the long-debated details of the India/Eurasia collision: why did India move so fast, when did the collision start, and why are there different ages for when the faults start forming depending on where we look? A particularly interesting contribution with a lot of explanatory power.-JBBImage credit/more info:http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2418.htmlJagoutz et al., 2015. -- source link

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