Tuesday, December 7, 2010

Remotely India # 2: Dyke Swarms Of Northern Deccan Traps

Around Nandurbar in northern Maharashtra are spectacular outcrops of a dyke swarm intruding the Deccan volcanics.

Source: IRS-Resourcesat-1

 Models of Deccan volcanism envision that most the lava came out of vents and fissures localized along two major rift zones, the roughly east-west trending Narmada Tapi Satpura rift zone along which today the Narmada and Tapi rivers flow westwards and which initially developed in the Proterozoic but has been active intermittently since and the north-south trending West Coast rift zone which developed during the mid-late Cretaceous as India broke away from Madagascar around 90 mya. There are dyke clusters along these major rift zones and they are thought to be lava feeders, remnants of the pipes through which magma from deep magma chambers was brought up to the surface.

The dykes in the image belong to the Narmada rift zone cluster. They are mostly tholeiitic basalts in composition. Variations in chemical composition shows that the Deccan lava pile was built up through several major eruptive episodes. A comparison of this dyke cluster suggests that many of these dykes were likely feeders to the older and middle eruptive phases of the lave pile, although a feeder relationship with a lava flow is rarely seen in the field.


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