How many plumes are there?

The objective of this paper is to quantitatively assess the role of mantle plumes in transporting heat to the base of the lithosphere. We first review the mechanisms responsible for mantle heat flow. We take the total global surface heat flow to be 4.43 x 10(13) W. Of this, we attribute 0.68 x 10(13 ) W (15%) to radiogenic heat production in the continental crust and 3.75 x 10(13) W (85%) to heat loss from the mantle. Of the heat loss from the man tle, 2.17 x 10(13) W (58%) is attributed to the subduction of the oceanic l ithosphere and the remainder, 1.58 x 10(13) W (42%), heats the base of the oceanic and continental lithosphere. Prior buoyancy studies of plumes give a plume heat flux of 0.24 x 10(13) W, which is only 15% of the total heal: flux associated with basal heating of the lithosphere. Thus, the amount tha t remains unaccounted for is a basal heat flux of 1.34 x 10(13) W. The miss ing heat flux can be attributed either to plumes that do not have a signifi cant surface expression, or to secondary mantle convection beneath the plat es. We show that the cumulative frequency-size distribution of the large an d intermediate size plume fluxes can be reasonably well approximated by a p ower-law distribution. We then extrapolate this distribution to smaller plu mes in order to estimate a total plume heat flux. This requires about 5200 plumes, with the smallest plume fluxes about 10(9) W. This compares with 12 x 10(9) W for the smallest plume fluxes previously reported in the literat ure. We suggest that the large number of seamounts represents surface evide nce for small plumes, and conclude that it is reasonable to attribute the e ntire basal heat flux to plumes. (C) 1999 Elsevier Science B.V. All rights reserved.