PETROLOGY AND GEOCHEMICAL EVOLUTION OF LAVAS FROM THE ONGOING AND VOLUMINOUS PUU OO ERUPTION OF KILAUEA VOLCANO, HAWAII

Puu Oo eruption is the longest lived (34+ years) and most voluminous (4+ km³) historic eruption of Kilauea Volcan on the Island of Hawaii. The lavas from this eruption have taught us much about the processes of magma generation and differentiation. The continually changing composition of the new lavas produces unique insights into the dynamic processes within a single magmatic event. We have monitored the compositional and isotopic signatures of its lavas since its start in 1983. Puu Oo lavas have shown remarkable variations resulting from diverse crustal and mantle processes including crystal fractionation, magma mixing and storage, assimilation of crust and melting of a heterogeneous plume source. Small, systematic variations in isotopes of Pb and Sr, incompatible trace element ratios and MgO-normalized major element abundances document rapid changes in the parental magma composition unrelated to crustal processes. Lavas erupted between 1985-2012 continued Kilauea’s post-1924 composition trend towards more depleted composition that was heralded by the collapse of summit crater during a period of exceptionally low magma supply. There was a systematic temporal evolution towards historical Mauna Loa lava composition from 1998-2003. This trend reversed in 2003 and again in 2008 creating a cyclic pattern of geochemical variations. These reversals in composition are contrary to previous models for sustained basaltic eruptions. The cyclic variations of Pb isotopic and some trace element ratios during the Puu Oo eruption suggest melt extraction from a mantle source with thin strands of vertically-oriented source heterogeneities. This continuing eruption provides a dynamic laboratory for evaluating models of the generation and evolution of basaltic magmas.