Relative timing of rifting and volcanism on earth and its tectonic implications

It is suggested that two basic types of rifting-volcanism relative timing might be related to two basic modes of rifting. In one sequence, volcanism and, usually, local doming predate major rift formation, while in the other type, rifts form first and volcanism follows. In the first mode of rifting, the mantle plays an active role and convection 'plumes' dome up and crack the lithosphere, while in the second case, the horizontal movements of plates give rise to extension of the lithosphere and induce rifting, and the mantle is passive. Since numerous local conditions complicate this simple pattern, detailed stratigraphic/structural analysis of individual rifts is recommended.