The cause of the Siberian Traps is far from certain. I think you are confusing them with the Deccan Traps of India. They, according to some scientists, *may* have been triggered by the K/T, 'dinosaur killer', asteroid impact on the opposite side of the world (Yucatan Peninsula).
Nope - they found the remains of a giant crator under (mostly) the ross ice shelf.
Actually, I think the Siberian Traps were, or may have been, the result of a ‘Mantle Plume’.
My bad. Of course, I meant the Deccan Trapps, not the Siberian, although I will not be surprised if they do eventually find an exterrestrial cause for the Siberian as well. The Siberian outflow was a lot larger than the very impressive Deccan, but being more than 3 times older it is harder to find a boloid signature. Of course, if something crashed into the Siberian Trapps area, it could have been completely covered up by the magma.
Did volcanic eruptions kill the dinosaurs?
Note in particular the last paragraph. It's unlikely that the Deccan Traps were triggered by the Chicxulub impact; this is the first I've heard of a second impact hypothesis.