The structure of Kilauea's magmatic plumbing system: a geochemical perspective from historical rift lavas (1790-1980 A.D.)

Over 200 years of frequent and voluminous eruptions (4.5 km3) are documented at Kilauea Volcano, Hawaii providing a unique opportunity to probe this volcano's magmatic plumbing network. Kilauea magmas are thought to ascend through a primary conduit delivering melt to a shallow (2-6 km deep) magma reservoir beneath the volcano's summit, and Southwest (SWR) and East Rift Zones (ERZ). Previous geochemical studies suggest that Kilauea magmas are delivered to the rift zones first before feeding the summit reservoir, whereas others have argued that Kilauea magmas are processed through the volcano's summit reservoir before intruding the rift zones. These interpretations are based primarily on major element chemistry of lavas, which are also affected by variations in the degree of partial melting and shallow crystal fractionation and accumulation. Here, we present new high precision trace elements, and Pb, Sr, and Nd isotope ratios for a representative suite of historical (1790-1980 A.D.) Kilauea rift zone lavas to assess the petrogenic relationship among summit and rift parental magmas. Pb isotope and incompatible element ratios (e.g. Nb/Y) of rift lavas vary systematically over time (similar to summit temporal variations) suggesting historical summit and rift lavas are petrogenically related. Historical SWR eruptions (1823, 1868, 1919-20, 1971, and 1974) are rare and volumetrically minor (0.08 km3). The 1919-20 and 1971 lavas are chemically and isotopically identical to their summit counterparts suggesting SWR lavas are processed through the shallow summit reservoir and do not reside in the rift zone or only briefly before erupting. East Rift Zone eruptions have been frequent and voluminous (3.7 km3) since 1955. The systematic temporal Nb/Y variations (an indicator of parental magma composition) reveals that most 1955-1980 olivine-controlled ERZ lavas are generally offset to the left of contemporaneous summit lavas (except 1971 and 1974 summit lavas) confirming that late 20th century East Rift lavas may "appear" at the rift before the summit.