The magma body at Kilauea Iki lava lake: Potential insights into mid‐ocean ridge magma chambers

Abstract

Although geological and geophysical measurements at active ridges have provided indirect samples and remote images and ophiolites have provided fossil evidence, the lack of direct sampling of in situ physical and chemical properties severly hinders our understanding of subsurface magmatic systems at mid‐ocean ridges. In contrast with the ridge setting, substantial information has been gained from direct sampling of Kilauea Iki lava lake. We reanalyze time series physical and petrological data from both in situ sampling and remote seismic and electromagnetic imaging of this lava lake in order to gain insights into the evolution of an enclosed basaltic magma body with many characteristics similar to a mid‐ocean ridge magma chamber. Although the analogy is imperfect, our analysis of observations from Kilauea Iki suggests that at a mid‐ocean ridge (1) a fine structure exists at the top of the magma body in the form of horizontal segregation veins (i.e., sills), (2) sustained convection within the magma chamber is highly unlikely, (3) a “dry‐out” zone above the magma body and below the deepest penetration of hydrothermal circulation may exist, (4) with high magma supply (e.g., the East Pacific Rise), where quasi steady state melt zones are present, the magma chamber must be completely replenished very frequently (at least every 300–600 years), and (5) the onset of rigid behavior of the basaltic partial melt does not happen at a unique “critical” crystal fraction. These results also show that significant differences may occur in interpretation of the rheology of a magmatic system depending upon the type of petrologic, seismic, or drilling data analyzed.

Mécanismes de solidification des magmas basaltiques :

“…Absence of significant large-scale convection in the lava lake was proposed in previous studies (Barth et al, 1994;Gibb and Henderson, 1992;Helz et al, 1989). It accords with the conclusions of Marsh (1989) that convection is only possible when the crystal fraction is low, although no precise values can be easily estimated.…”

“…Consequently, Helz and Wright (1983) reported that the processes of large-scale internal differentiation occurring in the lake had stopped sometime between the 1979 drilling and 1981. Based on isotherm extrapolation, the lake is thought to have completely solidified in the mid-1990s, representing 35 years of cooling to reach the solidus throughout its maximum total thickness of 120-130 m (Barth et al, 1994;, and references therein).…”

Mid‐ocean ridge magma chamber processes: Constraints from olivine zonation in lavas from the East Pacific Rise at 9°30′N and 10°30′N

“…Recent seismic [e.g., Singh et al, 1998] and volcanological/geochemical studies (summarized by Perfit and Chadwick [1998]) indicate that the AMC beneath the East Pacific Rise (EPR) consists dominantly of crystal-liquid mush, even most portions of the melt ''lens'' or melt ''sill.'' However, it is not yet known whether the melt is present on millimeter-to centimeter-scale pockets in a rigid crystal network [Marsh, 1989] or on thin meter-scale sills [Barth et al, 1994]. In addition it is not clear whether the melt lens contains melt of ''average composition'' [Sinton and Detrick, 1992] or is more primitive than the average [Singh et al, 1998] or more fractionated than the average [Natland and Dick, 1996].…”

Solidification fronts and magmatic evolution

“…Chen, 1993a, b, andParmentier andPhipps Morgan, 1990). Barth et al (1994) have carefully pointed out the basic geophysical and petrological similarities between Kilauea lki lava lake and ocean ridge magmatism. Although they find the analogy imperfect, they infer a number of small scale processes and features of the ridge sill to be analogous to process in lava lakes.…”