HR: 0800h
AN: V51B-0569    [Abstracts]
TI: The mantle potential temperature anomaly beneath Iceland is insufficient for a thermal plume.
AU: * Foulger, G R
EM: g.r.foulger@durham.ac.uk
AF: University of Durham, Science Laboratories, South Rd., Durham, DH1 3LE United Kingdom
AU: Vinnik, L P
EM: vinnik@ifz.ru
AF: Institute of Physics of the Earth, Moscow, Moscow, LEV VIN Russian Federation
AU: Du, Z
EM: zd202@cam.ac.uk
AF: Institute for Theoretical Geophysics, Downing St., Cambridge, DB2 3EQ United Kingdom
AB: One of the few primary characteristics of mantle plumes is high temperature compared with surrounding mantle. A temperature anomaly of at least 200-300 K is thought to be required for an upper-mantle plume rising from the base of the mantle transition zone. More than 15 methods, many of them independent, have been applied to estimate the temperature anomaly beneath Iceland. Seismic methods include using the Vp/Vs ratio and attenuation to determine the temperature of the crust, and using P- and S-wave mantle tomography. P- and S-wave receiver functions have been used to estimate the depths to discontinuities, including those associated with the low-velocity zone and bounding the mantle transition zone. Seismic wave travel times have been used to estimate the velocities between the discontinuities. Petrological methods include olivine glass geothermometry, the study of melt inclusions in basalts, CMASNF geothermometry of high-MgO glasses, major element systematics of Icelandic MORB and the search for an olivine control line in Icelandic picrite cumulates. Other methods include modeling the bathymetry of the north Atlantic assuming it has a thermal origin, modeling the subsidence of the ocean crust and uplift of the Hebrides shelf, and studying ocean floor heat flow measurements. Virtually all results either require or are compatible with a temperature anomaly of no more than ~ 50-100 K beneath Iceland. The crust there is cooler than that beneath the East Pacific Rise. Seismic tomography is compatible with temperature anomalies of up to 200 K, decreasing to about 100 K at depths greater than 200 km, where the seismic anomaly is weaker. This assumes that compositional effects are zero and partial melt is absent, however. Other seismic results require the presence of partial melt, and this requires substantial downward-adjustment of the temperature anomaly estimate from tomography. P-wave receiver functions show that the 410-km discontinuity is warped downward but that the 650-km discontinuity is flat. These results are consistent with a temperature anomaly of about 100 K at 410 km and zero at 650 km. All petrological methods suggest relatively small temperature anomalies unless olivine control is assumed for Icelandic picrite cumulates. The validity of this assumption is questionable. Modeling of bathymetry and vertical motions suggests temperature anomalies of up to about 100 K or less. Virtually all temperature estimates for the Iceland region are thus consistent in suggesting that the temperature anomaly beneath Iceland is modest, and insufficient for a thermal mantle plume that rises through its own thermal buoyancy.
UR: http://www.mantleplumes.org
DE: 5134 Thermal properties
DE: 5418 Heat flow
DE: 3640 Igneous petrology
DE: 1025 Composition of the mantle
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting