Geophysical Research Abstracts, Vol. 10, EGU2008-A-07167, 2008 SRef-ID: 1607-7962/gra/EGU2008-A-07167 EGU General Assembly 2008 © Author(s) 2008 Non-hotspot volcano chains from small-scale sublithospheric convection (a 3D-numerical study) M. D. Ballmer (1), J. van Hunen (2), G. Ito (3), P. J. Tackley (1), and T. A. Bianco (3) (1) Institute of Geophysics, ETHZ, Zürich, (2) Dept. of Earth Sciences, University of Durham, (3) SOEST, University of Hawaii, Honolulu (ballmer@tomo.ig.erdw.ethz.ch) Although most of the intraplate volcanism in ocean basins is expressed in linear chains, not all of these can be attributed to a stationary hotspot. Many ridges do not show a linear age-distance relationship predicted by the hotspot hypothesis - such as the Cook-Austal, Magellan or Line Islands, and Pukapuka ridges. Small-scale sub- lithospheric convection (SSC) has been proposed to account for the volcanism at Puka- puka [Buck and Parmentier, 1986] and may also explain enigmatic geochronology at other intraplate ridges. In the Earth’s uppermost mantle SSC is likely to develop due to instabilities of the thickened thermal boundary layer below mature oceanic lithosphere. It is charac- terized by convective rolls aligning plate motion. Their onset is earlier (i.e. beneath younger and thinner lithosphere) for lower mantle viscosities (e.g. for hot or wet man- tle) or adjacent to lateral thermal or compositional heterogeneity. In these cases, par- tial melt potentially emerges in the upwelling limbs of SSC. Partial melting changes the compositional buoyancy owing to melt retention and additional depletion of the residue. Therefore, it promotes upwelling and allows for further melting. This self- energizing mechanism is able to sustain melt production in a once partially molten layer for a couple of million years [Raddick et al., 2002]. In this study [Ballmer et al., 2007], we take the step towards fully thermo-chemical 3D-numerical models of SSC (using the FEM-Code CITCOM) with a realistic, temperature- and depth-dependent rheology in order to quantitatively test the SSC- hypothesis on intraplate volcanism. We explore the 3D-patterns of melting associated with SSC, the age of seafloor over which it occurs, and the rates of melt generation by