THREE-DIMENSIONAL DENSITY STRUCTURE OF THE

HAWAIIAN MANTLE-PLUME-HOT-SPOT

SCHMIDT, P., JANLE, P., Institut f. Geo-

physik, Univ. Kiel, 24098 Kiel, Germany

The classical hot spot of Hawaii has been

frequently explained by a mantle plume. The

regional swell, progressive aged seamounts

and petrological constraints suggest the

origin to be a plume from the D"-layer.

Theoretical and laboratory models of mantle

plumes have been presented. Recent tomogra-

phic results seem to support the plume-

hypothesis. Up to now, only crustal models

of Hawaii mainly constrained by seismology

and gravity have been presented.

We calculated the regional Bouguer-ano-

maly and modelled a three-dimensional den-

sity structure that well includes the plume

and its interaction with the lithosphere in

order to explain the observed swell. The

plume is of reduced density, mushroom-

shaped and extends to about 1000 km in dia-

meter. We obtained the following conclu-

sions:

The mantle plume produces a significant

contribution to gravity. Moreover there

must be any kind of plume-lithosphere-in-

teraction that leads to a so-called altered

lithosphere. The maximum effect of this

plume-lithosphere-interaction arises not

direct above the plume center but well

downstream of the swell due to the high ve-

locity of the Pacific plate. Thus, at Ha-

waii the processes of alteration of the li-

thosphere and volcanic features are separa-

ted in space and time.