Plume-ridge interaction:constraints on melting dynamics from the Azores and Iceland

• Main Authors: Genske, F. S., Beier, C., Turner, S. P., Haase, K. M., Schaefer, B. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: /dk/atira/pure/mqoutputs/29; E3 - Conference Publication - published abstract or extract of paper; Mid-Atlantic Ridge; Iceland; Ocean Island
• Online Access: https://researchers.mq.edu.au/en/publications/e5a954c8-6563-40ab-b6bb-a3a90df48e08; http://goldschmidt.info/2011/index.html

Ocean Island Basalts (OIB) erupted in the vincinity of Mid-Ocean Ridges (MOR) provide important information on melting processes, melt movement and composition of the Earth's mantle. In particular the major element, trace element and Sr-Nd-Pb isotope ratios allow for constraints on the distinct melting behaviour of enriched and depleted mantle sources, their along and across axis distribution and potential changes in melting depth and melting temperatures. While the flow of melts into the Mid-Atlantic Ridge (MAR) in the Azores and Iceland has been the subject of several studies, both plumes exhibit active volcanism on the western side of the Mid-Atlantic Ridge away from the proposed plume locality. Such off-axis volcanism beneath the North-American plate is comparable for the two OIB settings in terms of trace element and isotopic source composition relative to the main plume centre. Incompatible trace element ratios of Nb/Zr, Ta/Hf and La/Sm are elevated by similar factors in the off-axis (western) lavas when compared to the lavas from the plume centre. We compare the melting dynamics (i.e. P-T conditions of basalt generation) underneath the Snaefelsness peninsula (Iceland) with those underneath Flores and Corvo islands (Azores); both examples of unusual off-axis and "off-plume" magmatism. We demonstrate that Iceland and the Azores exhibit comparable excess temperatures, but that melting underneath the western Azores islands is initiated deeper. The sources in the Azores are more enriched and degrees of partial melting are slightly lower than compared to Snaefellsness. This implies that for both cases melting dynamics are largely controlled by the geochemical composition of the source and possibly lithosphere thickness rather than upwelling rate. The differences between eastern and western (i.e. plume related vs. "off-plume") sources may reflect different proportions of enriched melts during binary mixing with depleted MORB mantle (DMM) sources.