Some hotspots (e.g., Hawaii, Iceland) have been active for millions to tens of millions of years and are thought to be the surface manifestation of partial melting in a mantle plume. To understand the evolution of hotspot magmatisms it is necessary to determine how the compositions and productivity of magmatism vary with time. In this study, temporal geochemical variation in the Tertiary Icelandic magmatism is elaborated based on comprehensive analytical dataset. We revealed temporal changes in composition of magma sources and identified three distinct end-member components in this magmatism: one is the upper mantle peridotite and the other two are crustal lithologies. We also found the correlation between contribution from each end-member component and rate of magma production: higher magma productivity is coincident in time with larger contribution from recycled-crustal lithologies. The crustal lithologies have melting points lower than that of peridotite and should result in higher melt productivity at a given temperature in the melting region than melting of source dominated by peridotite. We therefore conclude that correspondence between productivity and the compositions of the Tertiary Icelandic lavas could be due to the periodic entrainment of recycled crustal lithologies into the pulses of Iceland mantle plume at its source region. (2, Jul., 2008)
Kitagawa, H., Katsura, K., Makishima, A., Nakamura, E., Multiple Pulses of the Mantle Plume: Evidence from Tertiary Icelandic Lavas., J. Petrol., 49, 1365-1396, 2008., doi:10.1093/petrology/egn029.
(Left) (a and b) The elemental Pb fractions from the E-1 and E-2 end-member components relative to the proportion from the D end-member component; (c) rate of lava accumulation for paleomagnetic sections in eastern and western Iceland; (d) profiles of gravity anomaly data obtained from the Irminger Basin with a time shift of +0·5 Myr. The gravity anomaly data are the short-wavelength anomalies relating to the thickness of the crust obtained by subtraction of the long-wavelength anomalies relating to dynamic support driven by the heat of the Iceland mantle plume.
(Right) Schematic diagrams showing the evolution of Icelandic magmatism from 13 to 2 Ma. (a) At c. 13 Ma, a mantle blob dominated by material with the E-1 geochemical signature arrived in the melting region, enhancing magma productivity. The tail of this blob may contain material with E-2 affinity, and thus the magmatism gradually changed from E-1- to E-2-influenced towards >10 Ma. (b) At c. 10 Ma, the mantle blob was partly consumed and the residue was incorporated into the lithosphere. The contribution from the D end-member component correspondingly increased, resulting in eruption of more geochemically depleted magmas and a decline in magma productivity. (c) At 8-7 Ma, a second mantle blob, dominated by the E-2 end-member component, ascended and began to melt, enhancing magma productivity. (d) After 6·5 Ma, the E-2 material rich domain was removed from the stem of mantle plume by extension, and the ensuing magmatism was less voluminous and more geochemically depleted.