TheRajmahal Traps is a volcanic igneous province inEastern India, covering the parts ofJharkhand,West Bengal andMeghalaya. TheRajmahal Hills ofJharkhand is the type area of this province. Multiple layers of solidified lava made the 608-metre-thick (1,995 ft) Rajmahal Traps which aredipping 2–5° towards the north-east. Individual layers vary in thickness from less than one metre (3 ft 3 in) to more than 70 metres (230 ft).[1]
These volcanic rocks were formed from the eruptions over theKerguelen hotspot in the earlyCretaceous.[2] The similarity between the geochemical data of Rajmahal volcanos and lavas of theKerguelen Plateau confirms this. According toplate tectonics, theIndian subcontinent was over this hot spot during theCretaceous Period.
The original lava flow covered an area of nearly 4,100 km2 (1,600 sq mi). Below the Bengal basin the flows cover 200,000 km2 (77,000 sq mi).[3]
The Rajmahal volcanics are predominantlytholeiitic basalt, quartz tholeiite,olivine tholeiite andalkali basalt. TheIntertrappean Beds are composed ofsedimentary rock such assiltstone,claystone andshale.[1]
The western boundary of the Rajmahal Traps is faulted and down-thrown towards the east. The eastern boundary of this trap has a North-South trending, fault-controlled basement. This basement connects the Purnea basin of the Ganga valley with the Bengal basin. These faulted contacts, along with the Damodar Gondwanagraben, form atriple junction at the mouth of the Bengal basin. The traps evolved along the then easterncontinental margin of India, following rifting ofGondwanaland. Over the epochs, the upper part of the lava deformed in a cold, brittle fashion and formedgraben structures.[3]
TheIntertrappean Beds contain an assemblage of LowerCretaceousplant fossils. The assemblage includesCladophlebis indica,Dictyozamites indicus,Taeniopteris spatulata, andBrachyphyllum rhombium.