Magmatic history of the East Rift Zone of Kilauea Volcano, Hawaii based ondrill 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, geoch emical characteristics and accumulation rates of rocks from the continuousl y cored, similar to1.7 km deep Scientific Observation Hole (SOH) 1, which w as drilled into Kilauea's East Rift Zone. The uppermost similar to 750 m of this hole contain relatively unaltered subaerially quenched lavas; the low er 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 i s 351 +/- 12 ka for a sample from 1541 m. Eighty XRF major and trace elemen t analyses of lavas from throughout the section demonstrate that these lava s have the same compositional range as historical Kilauea lavas and that th ere was no systematic geochemical variation for the volcano over the last 3 50 ka. Kilauea's average yearly magma supply during this period was probabl y similar to 0.05 +/- .01 km(3), which is identical to its average historic al magma supply rate. Thus, Kilauea's overall source and melting conditions have remained remarkably constant for the last 350 ka despite its having d rifted similar to 42 km over the Hawaiian plume. These results require that the portion of the plume being melted to produce Kilauea magmas be relativ ely large and well mixed, which is inconsistent with models that place this source on the margin of a radially zoned plume. (C) 2000 Elsevier Science B.V. All rights reserved.