Fifteen centimetre ( 6 inches ) a year does n’t sound like loyal movement . But for an entire continent , this is racing speed andtwice as fast as any magnanimous plate motility today . geologist havelong been puzzledby the discovery that from 80 - 50 million years ago , this was India ’s speed . But now they may get it on why .
For around 400 million years , India was part ofGondwana , the mighty supercontinent that also include Africa , South America , Antarctica , Australia and the Arabian Peninsula . Gondwana began tobreak up 180 million twelvemonth ago , and the landmass which would later become India left 60 million years later .
However , attempts to cross its path have revealed something unusual . For about 40 million years , the then independent Amerindic continent moved at about 4 - 5 centimetre ( 2 inches ) a twelvemonth , a typical continental stop number . Then for thirty million eld , it sped up to three times that charge per unit .
" When you look at pretense of Gondwana come apart up , the plates kind of start to move , and then India come lento off of Antarctica , and suddenly it just whizz along across – it ’s very dramatic , " enjoin MIT Professor Leigh Royden .
Royden reason that if the principal drive force of continental purport issubduction zones , in which the border of one plate swallow hole beneath another , movement at double speed might be triggered by two zones displume in the same counsel . This has never been observed before , but Royden and colleagues consider they have find the grounds , which theypublished inNature Geoscience .
At convergent plate edge , one home plate will ride over the other . The edge of the low plate is drawn down into the mantle and the rest of the shell isdragged along behind .
Royden modeled the operation that might have double convergence . He suggested that the northerly boundary of the Amerindic plate was make beneath an pelagic denture that made up the floor of theTethys Oceanthat lay betweenLaurasiaand Gondwana . At the same time , the paired edge of the now - vanish denture Royden calls " Kshiroda"was being driven beneath the Eurasian Plate .
recognition : Jagoutz et al , Nature Geoscience . The combined subduction zone move India due north at twice normal hurrying .
To test the theory , Royden take 30 students to the Himalayas . They found evidence of two arcs of volcano that once encircle the Tethys Ocean , one on each side of the now - vaporize plateful . They also conclude that in brief before the acceleration occur the Indian home split up from Africa . This prune the subduction zone from 10,000 to 3,000 kilometer ( 6000 to 2000 miles ) allowing mantle material to be squeezed out the way at either end and step on it the convergence .
Eventually , with the Kshiroda Plate entirely subducted India and Eurasia collide , force up the Himalayas .
Credit : Jagoutz et al , Nature Geoscience . The volcanic arcs that marked subduction zone are marked in red .
" In globe skill , it ’s hard to be completely trusted of anything , " says Royden . " But there are so many pieces of evidence that all fit together here that we ’re pretty convinced . "
Lead author Oliver Jagoutz sees plenty of scope for come after - up research . " There were a lot of changes go on in that meter menses , including climate , that may be explain by this phenomenon . So we have a few ideas we desire to look at in the future . "
