TY - JOUR
T1 - Crystal and magma residence at Kilauea Volcano, Hawaii
T2 - 230Th-226Ra dating of the 1955 east rift eruption
AU - Cooper, Kari M.
AU - Reid, Mary R.
AU - Murrell, Michael T.
AU - Clague, David A.
N1 - Funding Information:
This work was supported by the Institute of Geophysics and Planetary Physics at Los Alamos National Laboratory (M.T.M. and M.R.R.), and a U.S. Department of Energy, Office of Basic Energy Sciences, Geosciences Research Program grant to M.T.M. D.A.C. thanks the David and Lucile Packard Foundation for their generous support. Sample collection was supported by a Geological Society of America Research grant to K.M.C., and K.M.C. also thanks D. Swanson and J. Kauahikaua for help during field work, R. Roback for help with Ra chemistry, and C. Coath and K. McKeegan for help with the ion microprobe analyses. The manuscript benefited from constructive comments and suggestions by T. Wright, R. Helz. and K. Cashman, by reviewers A. Pietruszka, T. Elliott, and by an anonymous reviewer. [FA]
PY - 2001
Y1 - 2001
N2 - Previous estimates of crustal storage time of magmas at Kilauea Volcano, Hawaii, range from a few years to a few thousand years, leading to considerable uncertainty in the time scales of processes of magmatic storage and differentiation. We present a new approach for determining minimum magma residence times which involves dating phenocrysts in a magma using 226Ra-230Th disequilibria, and apply this approach to the early phase of the 1955 east rift eruption at Kilauea. When fractionation of Ra from Ba (a proxy for initial Ra in the crystals) during crystal growth is considered along with the effects of inclusions in the minerals, the data are consistent with co-precipitation of plagioclase and clinopyroxene from a melt represented by the groundmass at a mean age of 1000-400+300 a. Unless a significant fraction (> 30%) of the crystals are remnants from an earlier batch of evolved magma in the system, these data constrain the minimum magmatic residence time to be ∼ 550 yr, considerably longer than most previous estimates of storage time at Kilauea as well as those for some other basaltic systems. For the temperature interval of augite+plagioclase growth in the early 1955 magma, a maximum constant cooling rate of 0.1°C/yr (1 x 10-5°C/h) is derived from the minimum magmatic residence time of 550 yr. The total magma storage time would be > 2500 yr if this cooling rate applied to the entire thermal history of the magma, although a more complex cooling history where cooling rates were more rapid early in the storage history is permissive of a total residence time which is not much longer than 550 yr. The disparate estimates of magma residence at Kilauea may reflect the uncertainties in the methods of estimation in addition to true variations in storage time for different batches of magma. More work is necessary in order to determine whether a long residence time is characteristic of rift zone lavas and/or of Kilauean lavas in general.
AB - Previous estimates of crustal storage time of magmas at Kilauea Volcano, Hawaii, range from a few years to a few thousand years, leading to considerable uncertainty in the time scales of processes of magmatic storage and differentiation. We present a new approach for determining minimum magma residence times which involves dating phenocrysts in a magma using 226Ra-230Th disequilibria, and apply this approach to the early phase of the 1955 east rift eruption at Kilauea. When fractionation of Ra from Ba (a proxy for initial Ra in the crystals) during crystal growth is considered along with the effects of inclusions in the minerals, the data are consistent with co-precipitation of plagioclase and clinopyroxene from a melt represented by the groundmass at a mean age of 1000-400+300 a. Unless a significant fraction (> 30%) of the crystals are remnants from an earlier batch of evolved magma in the system, these data constrain the minimum magmatic residence time to be ∼ 550 yr, considerably longer than most previous estimates of storage time at Kilauea as well as those for some other basaltic systems. For the temperature interval of augite+plagioclase growth in the early 1955 magma, a maximum constant cooling rate of 0.1°C/yr (1 x 10-5°C/h) is derived from the minimum magmatic residence time of 550 yr. The total magma storage time would be > 2500 yr if this cooling rate applied to the entire thermal history of the magma, although a more complex cooling history where cooling rates were more rapid early in the storage history is permissive of a total residence time which is not much longer than 550 yr. The disparate estimates of magma residence at Kilauea may reflect the uncertainties in the methods of estimation in addition to true variations in storage time for different batches of magma. More work is necessary in order to determine whether a long residence time is characteristic of rift zone lavas and/or of Kilauean lavas in general.
KW - Kilauea
KW - Residence time
KW - Th-230/RA-226
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U2 - 10.1016/S0012-821X(00)00341-1
DO - 10.1016/S0012-821X(00)00341-1
M3 - Article
AN - SCOPUS:0035076469
SN - 0012-821X
VL - 184
SP - 703
EP - 718
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
IS - 3-4
ER -