Magmatic processes during the prolonged Pu'u 'O'o eruption of Kilauea Volcano, Hawaii

The Pu'u 'O'o eruption iss exceptional among historical eruptions of Kilaue a Volcano for its long duration (similar to 17 years and continuing), large volume (similar to 2 km(3)), wide compositional range (5.6 10.1 wt % MgO) and the detailed monitoring of its activity. The prolonged period of vigoro us effusion (similar to 300 000 m(3)/day) and the simple phenocryst mineral ogy of the lavas (essentially only olivine) has allowed us ti examine the v olcano's crustal and mantle magmatic processes. Here we present new petrolo gic data for lavas erupted from 1992 to 1998 and a geochemical synthesis fo r the overall eruption. The dominant crustal magmatic processes and fractio nation and accumulation of olivine, which caused short-term (days to weeks) compositional variations. Magma mixing was important only during the early part of the eruption and during episode 54. The overall systematic decreas e in MgO-normalized CaO content and abundance of highly incompatible elemen ts, without significant Pb, Sr and Nd isotope compositional variation, is i nterpreted to be caused by mantle melting processes. Experimental results a nd modeling of trace element variations indicate that neither batch melting nor simple progressive melting can explain these compositional variations. Instead, a more complex progressive melting model is needed. This model in volves two source components with the same isotopic decomposition, but one was melted similar to 3% in the Hawaiian plume. The model indicate that the amount of this depleted source component progressively increased during th e eruption from 0 to similar to 25%. Given the isotopic similarity of Pu'u 'O'o lavas to many lavas from Loihi Volcano and the small extent of prior m elting to form the depleted source component, the melting region for Pu'u ' O'o magmas partially overlap with that of the adjacent, younger volcano, Lo ihi.