Page 421 - Global Tectonics

THE MECHANISM OF PLATE TECTONICS 403

convection (Section 12.5.2), the viscosity profile of the ably occurred independently of the supercontinent
mantle, and the amount of radioactive heat present. In cycle. Isley & Abbott (2002) used a series of plume
addition, their models suggest that, given an internally proxies, including massive dike swarms, high-Mg extru-
heated mantle, stresses generated at subduction zones sive rocks (e.g. Section 11.3.2), flood basalts, and layered

also may be sufficiently large to cause rifting in a station- intrusions, to identify mantle plume events through
ary supercontinent. time. At least two global scale events coincided with
Some geologic data suggest that plume-related continental assembly in Late Archean and Proterozoic
magmatism coincided with the assembly, rather than times. From these relationships, it seems that there
the break-up, of the supercontinents. Hanson et al. may be two types of mantle plume events, those asso-
(2004) showed that large-scale magmatic events ciated with supercontinental break-up and those asso-
occurred within continental interiors during the Pro- ciated with their formation (Condie, 2000). These
terozoic assembly of Rodinia (Section 11.5.3). These studies highlight the intriguing but uncertain relation-
authors also concluded that the impingement of mantle ships between mantle plumes and the supercontinent
upwellings on the base of continental lithosphere prob- cycle.