Superplumes or supercontinents?
I attribute the Cretaceous pulse of Pacific oceanic crust formation to a global plate reorganization associated with the breakup of Pangea and rapid growth and reorganization of the Pacific plate. The Cretaceous was characterized by widespread rifting, continental breakup, rapid spreading, and global magmatism. Tomography shows that the upper mantle of the Pacific and Indian oceans is hot. These large low-velocity regions contain most of the world's hotspots and ridges and were the sites of extensive plateau and continental flood-basalt magmatism. The formation and rapid expansion of the Pacific and Indian ocean plates took place in these regions that are hot because they have not been cooled or displaced by cold oceanic lithosphere for more than 200 m.y. Plumes are not required to explain such mantle. The Pacific hemisphere is isolated from the supercontinent hemisphere by a band of cool mantle over which continents collect and into which subduction preferentially occurs.
© 1994 Geological Society of America. Manuscript received June 14, 1993 Revised manuscript received October 5, 1993 Manuscript accepted October 13, 1993. I thank Eleanor and John R. McMillan and their family for support. This research was also supported by National Science Foundation Grant EAR-9218390. Contribution No. 5335, Division of Geological and Planetary Sciences, California Institute of Technology.