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

Abstract

The decline and renaissance over the past 50 years of the concept ‘space problem’ posed by large, predominantly calcalkaline, plutons which fuelled the ‘granite controversy’, that assimilation of crustal rocks may play a significant role in basalt genesis is reviewed and attention is drawn to the very restricted and partly in response to field and petrographic relationships observed at the margins of plutonic bodies, sampling of the potentially contaminated lavas which is available for most oceanic basalts. A simplified quantitative model of the which provided evidence of the operation of these processes. When the focus of attention switched to basalts behaviour of ideally behaved trace elements during the evolution of a hypothetical oceanic island volcano is explored and qualitative (Tilley, 1950), the implications of the space problem were largely ignored. The problem was less obtrusive and consideration given to the thermal and isotopic implications of this model. Three prominent features of the model are the importance of the uniformity and distinctive geochemical character of successive flows could be held to preclude extensive thermal contamination, which may be the clearest indicator of extensive country rock assimilation; the robustness of incompatible assimilation and contamination (Carmichael et al., 1974). Over the past 50 years, the rise, fall and renaissance trace element signals once these elements have been contributed to the magma chamber; and the apparent decoupling of output lava of appreciation of the importance of assimilation and contamination by the petrological community are chroncomposition from the concurrent input parental liquid composition, such that no closed system process can even approximately reproduce icled by the weight given or withheld in a succession of influential texts. Initially this appreciation was largely in the relationships. the context of the plutonic calc-alkaline and alkaline rocks, and was driven by the field relationships. It has only recently become extended first to continental, and