RECONCILING TECTONIC AND GEODYNAMIC MODELS FOR THE ASSEMBLY AND BREAKUP OF PANNOTIA

The Late Neoproterozoic-Early Paleozoic amalgamation of Gondwana is an important component in the formation of the supercontinent, Pannotia. Gondwana’s amalgamation necessitates the subduction of oceanic lithosphere between converging continental blocks. Tomographic images from Mesozoic-Cenozoic orogens imply that this subducted oceanic lithosphere probably congregated in “slab graveyards” along the core-mantle boundary. Numerical mantle convection models indicate that plumes are preferentially and frequently produced along the edges of such graveyards and that hot mantle trapped for long periods of time beneath the slabs may evolve into a ‘‘mega-plume”, as long wavelength mantle convection evolves from a degree-1 to a degree-2 planform pattern.

The relocation of subduction zones to the periphery as Gondwana assembled indicates that along much of Gondwana’s margin, rising plume material may have interacted with peripheral subduction zones. Most geodynamic models indicate that the ascent of plumes is either stalled or destroyed at subduction zones. This has focused attention on the exploitation of structures that permit the flow of plume material into the upper plate (e.g. through gaps, tears, breaks or windows in the subducted slab) and on processes such as “plume-assisted delamination” which can be further exploited by ascending plume material. This presentation examines the potential of such dramatic change in mantle convection patterns to provide new ways of investigating the processes responsible for the opening of the Iapetus and Rheic oceans, as well as some of the enigmatic tectonothermal events that characterize the Late Neoproterozoic-Early Paleozoic tectonic evolution of the northern margin of Gondwana.