Original: The source of the Siberian Traps basalt has variously been attributed to a mantle plume which impacted the base of the crust and erupted through the Siberian Craton, or to processes related to plate tectonics.
Simplified: The source of the Siberian Traps basalt was, probably, a mantle plume at the base of the crust which erupted through the Siberian craton (the oldest part of the Siberian continental plate).