Mo. Garcia et al., CRUSTAL CONTAMINATION OF KILAUEA VOLCANO MAGMAS REVEALED BY OXYGEN-ISOTOPE ANALYSES OF GLASS AND OLIVINE FROM PUN OO ERUPTION LAVAS, Journal of Petrology, 39(5), 1998, pp. 803-817
Oceanic island basalts have a large range in delta(18)O values (4.5-7.
5%) compared with the assumed primordial mantle values (5.5-6.0%) and
with mid-ocean ridge basalts (5.7 +/- 0.2%). Some Hawaiian tholeiitic
basalts have low O-18 values (4.6-5.2%), which have been interpreted t
o be either a primary source feature or caused by crustal contaminatio
n. This study, was undertaken to evaluate the cause of low delta(18)O
values in Hawaiian tholeiitic basalts. We determined the delta(18)O va
lues of glassy matrix material and coexisting olivines from pristine b
asalts produced during the current, 14-year-old Puu Oo eruption of Kil
auea Volcano. Our results show that the Puu Oo eruption lavas have sig
nificant ranges in matrix (0.7%) and olivine delta(18)O values (0.5%)
which do not correlate consistently with other geochemical Parameters
and that many of the lavas are out of oxygen isotopic equilibrium. The
se features probably reflect partial assimilation of and oxygen exchan
ge with metamophosed Kilauea rocks during the magma's 19 km transit th
rough the volcano's east rift tone. The parental magmas for Puu Oo lav
as had a delta(18)O value of at least 5.2% and perhaps as high as 5.6%
. Thus, Puu Oo lavas do not give a clear indication of the delta(18)O
value of Kilauea's mantle source but they do indicate that the oxygen
in these otherwise pristine basalts has undergone significant modifica
tion by interaction lentil crustal rocks.