Journal of Petrology, Volume 39, Issue 5: May 1 1998.

Volcanic Plumbing and the Space Problem-Thermal and Geochemical Consequences of Large-Scale Assimilation in Ocean Island Development

M. J. O'HARA

DEPARTMENT OF EARTH SCIENCES, CARDIFF UNIVERSITY, P.O. BOX 914, CARDIFF CF1 3YE, UK

The decline and renaissance over the past 50 years of the concept that assimilation of crustal rocks may play a significant role in basalt genesis is reviewed and attention is drawn to the very restricted sampling of the potentially contaminated lavas which is available for most oceanic basalts. A simplified quantitative model of the behaviour of ideally behaved trace elements during the evolution of a hypothetical oceanic island volcano is explored and qualitative consideration given to the thermal and isotopic implications of this model. Three prominent features of the model are the importance of thermal contamination, which may be the clearest indicator of extensive country rock assimilation; the robustness of incompatible trace element signals once these elements have been contributed to the magma chamber; and the apparent decoupling of output lava composition from the concurrent input parental liquid composition, such that no closed system process can even approximately reproduce the relationships.

Keywords: assimilation; thermal contamination; oceanic islands; refilled magma chamber; space problem

Pages 1077-1089