The size and shape of Kilauea Volcano's summit magma storage reservoir: a geochemical probe

One of the most important components of the magmatic plumbing system of Kil auea Volcano is the shallow (2-4 km deep) magma storage reservoir that unde rlies the volcano's summit region. Nevertheless, the geometry (shape and si ze) of Kilauea's summit reservoir is controversial. Two fundamentally diffe rent models for the reservoir's shape have been proposed based on geophysic al observations: a plexus of dikes and sills versus a single, 'spherical' m agma body. Furthermore, the size of the reservoir is poorly constrained wit h estimates ranging widely from 0.08 to 40 km(3). In this study, we use the temporal variations of Pb, Sr, and Nd isotope and incompatible trace eleme nt (e.g., La/Yb and Nb/Y) ratios of Kilauea's historical summit lavas (1790 -1982) to probe the geometry of the volcano's summit reservoir. These lavas presence a nearly continuous, 200-year record of the changes in the compos ition of the parental magma supplied to the volcano. The systematic tempora l variations in lava chemistry at Kilauea since the early 19th century sugg est that the shape of the volcano's summit reservoir is relatively simple. Residence time analysis of these rapid geochemical fluctuations indicates t hat the volume of magma in Kilauea's summit reservoir is only similar to 2- 3 km(3), which is smaller than most geophysical estimates (2-40 km(3)). Thi s discrepancy can be explained if the volume calculated from lava chemistry represents the hotter, molten core of the reservoir in which magma mixing occurs, whereas the volumes estimated from geophysical data also include po rtions of the reservoir's outer crystal-mush zone and a hot, ductile region that surrounds the reservoir. Although our volume estimate is small, the a mount of magma stored within Kilauea's summit reservoir since the early 19t h century is an order of magnitude larger than the magma body supplying Pit on de la Fournaise Volcano, another frequently active ocean-island volcano. (C) 1999 Elsevier Science B.V. All rights reserved.