Abstract
The eruptive activity of basaltic hotspot volcanoes displays major fluctuations on times scales of years to decades. Theses fluctuations are thought to reflect changes in the rate of mantle melt supply. However, the crustal filter generally masks the mantle processes involved. Here, we show that the cyclic and generally increasing activity of the Piton de la Fournaise volcano (La Réunion) since the mid 20th century is tightly linked to the fertility of its source, as recorded by 87Sr/86Sr and incompatible trace elements ratios of lavas. We identify a twofold control of source fertility on eruptive activity: melt extraction from fertile, incompatible element-enriched veins initiates decadal-scale eruptive sequences, so that vein distribution in the plume source directly controls the cyclic activity. Indirectly, reactive flow of enriched melts increases mantle porosity and promotes melts extraction from the peridotite matrix. This process is thought to have caused a fourfold increase in magma supply between 1998 and 2014 at Piton de la Fournaise, and could also explain magma surges at other frequently active hotspot volcanoes, such as Kilauea, Hawaii. The short-term eruptive activity of hotspot volcanoes appears to be ultimately linked to the distribution and size of lithological heterogeneities in mantle plumes.
Highlights
Ocean island basaltic shield volcanoes, such as Kilauea (Hawaii) or Piton de la Fournaise (La Réunion) are directly connected to zones of persistent melting in the Earth’s mantle[1,2]
Pyroxenite is probably a minor lithology of the Reunion mantle plume[23,26,27], its behaviour during melting has a twofold control on magma supply, and on the short-term eruptive activity of the Piton de la Fournaise volcano
Melting of fertile veins seems to trigger melt extraction, so that the distribution of veins in the melting region directly influences the timing of magma supply
Summary
Ocean island basaltic shield volcanoes, such as Kilauea (Hawaii) or Piton de la Fournaise (La Réunion) are directly connected to zones of persistent melting in the Earth’s mantle[1,2]. Their rates of lava production have varied by a factor of two to ten over timescales of years to decades[3,4] Such variations are difficult to explain solely by shallow magma chamber processes. Since the early 20th century, eruptions cluster into 12–24 years long sequences followed by three-to-six year-long reposes which, together, define the eruptive cycles[4,12] These decadal cycles could reflect the time needed to refill the plumbing system with mantle melts[12]. Such processes at Piton de la Fournaise are not readily seen in most geochemical and geophysical records, which are overprinted by higher frequency (
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