A rapid fluctuation in the mantle source and melting history of Kilauea Volcano inferred from the geochemistry of its historical summit lavas (1790-1982)

The geochemical variations of Kilauea's historical summit lavas (1790-1982) document the short-term magmatic evolution of one of the Earth's most acti ve volcanoes. Most of these lavas are thought to have erupted directly from the shallow (2-4 km deep) magma reservoir that underlies the volcano's sum mit region. This paper details a remarkable variation of lava chemistry tha t spans nearly the entire known compositional range of the volcano in only 200 years. The Pb, Sr, and Nd isotope and incompatible trace element ratios (e.g. La/Yb or Nb/Y) of the lavas vary systematically over time with an ab rupt reversal after 1924. This rapid geochemical fluctuation records the te mporal changes in the parental magma composition delivered to Kilauea's sum mit reservoir since 1790. The isotope and incompatible trace element ratio systematics suggest that the source region of historical Kilauea magma is b oth isotopically and chemically heterogeneous. These source variations can be explained by the melting of small-scale heterogeneities within the Hawai ian mantle plume. Model calculations suggest that the degree of partial mel ting decreased from the early 19th century until the mid-20th century, whic h correlates with a lower eruption rate (and presumably a lower magma suppl y rate) for the volcano between 1840 and 1959. This interval of declining o utput from the Hawaiian plume culminated with an explosive summit eruption in 1924 and the longest quiescent period in Kilauea's historical record (19 34-1952). Lavas erupted just after 1924 are geochemically anomalous and may have been contaminated by the assimilation of country rock into the volcan o's magma reservoir during the explosions. Subsequently, the inferred degre e of partial melting and the volcano's eruption rate have increased, with t he highest values since the early 19th century observed during the current Puu Oo rift zone eruption.