Magmatic history of the East Rift Zone of Kilauea Volcano, Hawaii based on drill core from SOH 1

Deep drilling has allowed for the first time an examination of most of the shield stage of a Hawaiian volcano when it is centered over the hotspot and most of its volume is produced. We determined the lithologies, ages, geochemical characteristics and accumulation rates of rocks from the continuously cored, ∼1.7 km deep Scientific Observation Hole (SOH) 1, which was drilled into Kilaueaʹs East Rift Zone. The uppermost ∼750 m of this hole contain relatively unaltered subaerially quenched lavas; the lower portion is a mixture of weakly to moderately altered hyaloclastites and massive basalts intruded by dikes. Unspiked K–Ar dating was attempted on 14 lavas but only four yielded geologically reasonable ages. The oldest age is 351±12 ka for a sample from 1541 m. Eighty XRF major and trace element analyses of lavas from throughout the section demonstrate that these lavas have the same compositional range as historical Kilauea lavas and that there was no systematic geochemical variation for the volcano over the last 350 ka. Kilaueaʹs average yearly magma supply during this period was probably ∼0.05±.01 km3, which is identical to its average historical magma supply rate. Thus, Kilaueaʹs overall source and melting conditions have remained remarkably constant for the last 350 ka despite its having drifted ∼42 km over the Hawaiian plume. These results require that the portion of the plume being melted to produce Kilauea magmas be relatively large and well mixed, which is inconsistent with models that place this source on the margin of a radially zoned plume.