Proportions, Timing, and Re-equilibration Progress during the 1959 Summit Eruption of K ılauea: an Example of Magma Mixing Processes Operating ...
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Journal of Petrology, 2022, Vol. 63, No. 1, 1–22
https://doi.org/10.1093/petrology/egab091
Advance Access Publication Date: 4 November 2021
Original Manuscript
Proportions, Timing, and Re-equilibration
Progress during the 1959 Summit Eruption of
Kı̄lauea: an Example of Magma Mixing
Processes Operating during OIB Petrogenesis
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Rosalind Tuthill Helz *
Florence Bascom Geoscience Center, US Geological Survey, Reston, VA 20192, USA
*Corresponding author. Telephone: 1-703-648-6096. E-mail: rhelz@usgs.gov
Received 15 December 2020; Revised 21 October 2021; Accepted 25 October 2021
Abstract
Petrographic and chemical analysis of scoria samples collected during the 1959 Kı̄lauea summit
eruption illustrates the progress of thermal and chemical homogenization of the melts, and the
gradual growth and/or re-equilibration of olivine phenocrysts, over the course of the eruption.
Glass compositions show that thermal equilibration was largely complete within the span of
the eruption, whereas chemical homogenization was a work in progress. The olivine phenocryst
population, known to contain conspicuous antecrystic components, is also hybrid within the
euhedral population. The bulk of the olivine reached the level of the erupting magma on November
18–19, 1959. Zoning patterns in olivine phenocrysts show that initially unzoned grains developed
normal zoning by the end of the eruption. Reverse zoning in relatively Fe-rich olivine phenocrysts
(interpreted as cognate to the stored magma) was progressively eliminated from November 21 to
December 19, 1959, by diffusive re-equilibration between crystals and melt. Toward the end of the
eruption, the only olivine composition in direct contact with the melt was Fo84–86 , with the original
rim compositional heterogeneity gone in 4–5 weeks’ time. Activity in December 1959 differed from
that in November, as high fountaining events were more closely spaced and almost all samples
were picritic, with bulk MgO ≥16·5 wt%. Three different levels were in play during the 1959 eruption:
a deep source for high-MgO melts and forsteritic (Fo87–89 ) olivines, an intermediate source for the
bulk of the stored magma, and a shallower source for the most differentiated magma. This model
is consistent with geophysical, petrological and chemical observations. Comparison of the 1959
eruption with results from older explosive deposits suggests that stored and recharge melts and
olivine from the deeper parts of Kı̄lauea’s plumbing are similar in composition to those observed
or inferred in the 1959 eruption, so they behave similarly during extrusive and explosive periods
alike.
Key words: magma mixing; olivine zoning; glass; olivine content
INTRODUCTION The 1959 scoria samples contain olivine + chromite + glass,
The 1959 summit eruption is unique in Kı̄lauea’s historical record with other phases (immiscible sulfide, clinopyroxene, plagioclase)
for its highly magnesian, olivine-rich lavas (Murata & Richter, 1966) rarely present and only in trace amounts. Glasses have MgO contents
and high fountains (up to 580 m, Richter et al., 1970). The eruption ranging from 6·4 to 10·2 wt% (Helz, 1987, 2009; Helz et al., 2017).
was closely observed, and many scoria samples were collected in real Olivine crystals vary in composition, appearance, size, and state of
time as the eruption progressed. This study focuses on what can aggregation. This paper presents data for all available samples of
be learned from these time-stamped samples, especially seeking to 1959 scoria collected in real time, and helps quantify the timing of
define possible constraints on the time needed for mixing and re- magma mixing and subsequent homogenization, and re-equilibration
equilibration to occur. of olivine with the enclosing melts, that occurred during the eruption.
Published by Oxford University Press 2021.
1
This work is written by US Government employees and is in the public domain in the US.
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Fig. 2. Plot showing the time of collection of scoria samples (black dots),
collected in real time during the 1959 eruption, plotted on the curve showing
the gradual filling of Kı̄lauea Iki lava lake (modified from Fig. 3 of Richter &
Moore, 1966). The time gaps between early phases were several days long,
whereas those after phase 4 were mostly shorter than 2 days.
scoria (Schwindinger & Anderson, 1989). More recently, work has
Fig. 1. Index map of the summit area of Kı̄lauea volcano, as it was until 2018,
focused on samples from the ejecta blanket that lies south and east of
showing the location of Kı̄lauea Iki lava lake and the 1959 cinder cone relative the cinder cone that fed the 1959 eruption and lava lake, including
to the main caldera. Modified from Helz (1987). studies by Stovall et al. (2011, 2012), Sides et al. (2014), and Rae
et al. (2016), plus further investigations of the CO2 contents of melt
inclusions in the olivine (Sides et al., 2014; Moore et al., 2015; Tuohy
et al., 2016), and of volatile loss from melt embayments in olivine
(Ferguson et al., 2016). Bradshaw et al. (2018) have investigated trace
PREVIOUS WORK ON THE 1959 SUMMIT
element zoning in olivine phenocrysts in scoria and dip samples from
ERUPTION
the lava lake.
The 1959 summit eruption of Kı̄lauea volcano involved 16 distinct
phases of pyroclastic fountaining, occurring over a period of 5 weeks.
The eruption was very accessible (the lava fountains were visible
SAMPLE CHARACTERIZATION AND ANALYTICAL
from the Hawaiian Volcano Observatory, as can be inferred from
Fig. 1) so there are detailed logs of the activity (Richter et al., 1970).
METHODS USED
The eruption was also among the first to be monitored seismically: The samples that form the basis for this paper, as well as those in the
Eaton & Murata (1960) were able to track earthquakes as they earlier studies (Murata & Richter, 1966; Wright, 1973; Helz, 1987;
ascended from mantle depths, in the weeks prior to the eruption, to Helz et al., 2017), were collected at known times during the eruption.
the summit reservoir, where their arrival coincided with the onset of Figure 2 shows when these samples were collected, plotted along the
the eruption in Kı̄lauea Iki pit crater, on the evening of November curve that shows the gradual filling of Kı̄lauea Iki lava lake. Spatter
14. The 1959 samples were characterized chemically (Murata & from the initial fissure is included, and there are nine samples from
Richer, 1966) and petrographically (Richter & Murata, 1966). This later in phase 1. Other phases are represented by one or two samples;
allowed Wright (1973) to recognize that the erupted material was a no samples were taken during phases 10–14, however, and the spatter
mixed magma, with two components distinguishable by their CaO collected after phase 17 of the eruption was not investigated in this
content. study.
The eruptive samples next were revisited and their complex The scoriae are pristine, with little post-eruptive re-equilibration
olivine load was described by Helz (1987). Fo contents showed or alteration of the glasses or olivine in the samples. Details for the
that individual olivine crystals are not consistently in equilibrium samples are given in Table 1, including time of eruption and fountain
with their host glasses nor with nearby olivine crystals in the same height (from Richter et al., 1970), and data on the number of thin
section. This pervasive disequilibrium, documented by Helz (1987) sections (43) and scoriae (approximately 100) examined. The table
for 15 scoria samples, was further explored using micro X-ray also gives references to all available analyses of bulk major-element
absorption near-edge structure spectroscopy (μ-XANES) analyses on chemical compositions.
eight 1959 scoriae (Helz et al., 2017), three of which were not in the Analytical data on glass and olivine compositions were obtained
1987 study. in the US Geological Survey (USGS) electron microprobe laboratory
Other work on 1959 eruption samples includes studies by A. in Reston, VA, using the techniques and conditions described by
T. Anderson, Jr and his students on melt inclusions in olivine from Helz et al. (2017) and Helz (2020). In all cases, the glass compo-
the eruption (Harris, 1983; Anderson & Brown, 1993; Wallace & sitions were collected on clear, undevitrified areas within the thin
Anderson, 1998) and on the state of aggregation of olivine in the sections investigated. In addition to the olivine spot analyses taken as
Journal of Petrology, 2022, Vol. 63, No. 1 3
Table 1: Scoria samples from the 1959 eruption of Kilauea Volcano collected during the eruption
Sample Eruptive Date Time of day Nature of Fountain Whole-rock analysis No. polished thin NMNH
field no. phase erupted sample height (m) no., references sections, scoria catalogue
pieces∗ number
Iki-58 1 14-Nov-59 2130–2215 flow, vent H up to 30 S-1 (Murata & Richter, 1, 1 116111–57
(easternmost) 1966)
Iki-1 1 14-Nov-59 2035– flow, vent A up to 30 S-2 (Murata & Richter, 1, 1 116111–1
∼2400 1966)
M-59-15 1 15-Nov-59 1610 spatter, vent E up to 30 1, 1 116113–5
Iki-2 1 17-Nov-59 1500 pumice† 80–100 S-4 (Murata & Richter, 2, 12 (1, 2) 116111–2
1966)
Iki-65 1 18-Nov-59 1230 pumice 230–240 1, 1 116111–64
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Iki-22 1 18-Nov-59 1700 pumice 320 S-5 (Murata & Richter, 4, 22 (1, 2) 116111–22
1966); Gunn (1971)
Iki-3 1 19-Nov-59 800 pumice 320–350 Gunn (1971); Helz & 2, 10 (1, 1) 116111–3
Taggart (2010)
Iki-71 1 19-Nov-59 1415 pumice 300 1,4 116111–70
Iki-44 1 20-Nov-59 700 pumice 240–300 S-7 (Murata & Richter, 1, 1 (1, 1) 116111–44
1966)
Iki-74 1 20-Nov-59 1500 pumice 240–300 1, 4 116111–73
Iki-5 1 21-Nov-59 710 pumice 240 S-8 (Murata & Richter, 1, 1 (1, 1) 116111–5
1966)
Iki-7 1 21-Nov-59 2000 pumice 215 S-9 (Murata & Richter, 1, 1 116111–7
1966)
Iki-11 2 26-Nov-59 1530–1635 pumice 240–300 S-11 (Murata & Richter, 1, 1 116111–11
1966)
Iki-9 3 28-Nov-59 1815 pumice 200 S-12 (Murata & Richter, 2, 3 116111–9
1966)
Iki-10 3 29-Nov-59 2100 pumice 180 S-13 (Murata & Richter, 1, 1 (1, 1) 116111–10
1966)
Iki-13 4 5-Dec-59 930 pumice 90–150 S-15 (Murata & Richter, 1, 8 +? 116111–13
1966)
Iki-14 5 6-Dec-59 1630 pumice 300 S-16 (Murata & Richter, 1, 1 116111–14
1966); Gunn (1971);
Helz & Taggart (2010)
Iki-15 5 7-Dec-59 100 pumice 300 S-17 (Murata & Richter, 2, 1 116111–15
1966)
Iki-17 6 7-Dec-59 2330 pumice 125 1, 4 116111–17
Iki-19 7 8-Dec-59 1830 pumice 430 S-18 (Murata & Richter, 1, 2 116111–19
1966)
Iki-20 7 8-Dec-59 pumice 260–430 1, 2 116111–20
Iki-21 8 11-Dec-59 600 pumice 180–300 S-19 (Murata & Richter, 1, 1 116111–21
1966)
Iki-24 9 13-Dec-59 1400 pumice 60–180 1, 1 116111–24
Iki-25 10 14-Dec-59 1200 pumice 300 1, 1 116111–25
Iki-26 10 14-Dec-59 1400 pumice 180–330 S-21 (Murata & Richter, 2, 4 (1, 1) 116111–26
1966)
Iki-32 15 17-Dec-59 1445 pumice 580 S-22 (Murata & Richter, 1, 2 (1, 1) 116111–32
1966)
Iki-33 16 19-Dec-59 630 pumice 185 S-24 (Murata & Richter, 1, 1 116111–33
1966)
∗ The first number is the number of polished thin sections available and the second is the number of individual pieces of scoria. Section for Iki-13 contains some
crushed fragments, so count is uncertain. Numbers in parentheses are for the XANES mounts described by Helz et al. (2017).
† Frothy scoria was referred to as ‘pumice’ by Murata & Richter (1966), also in the field notes. That term is retained in this table to distinguish scoria from high
fountains from flow or spatter samples.
described above, a set of automated step traverses of selected olivine and olivine traverse data, is included in the Supplementary Material
crystals has been made, again using the USGS electron microprobe (supplementary data are available for downloading at http://www.pe
laboratory. A description of the analytical techniques, plus all glass trology.oxfordjournals.org).
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Fig. 3. (a) CaO vs MgO for glass compositions in scoria from phases 1–3, erupted from November 14 to 29, 1959. The field of composition of whole-rock analyses
(Wright, 1973) is shown for comparison. Glasses included in olivine are not plotted. Cross indicates uncertainties in MgO (±0·15 wt%) and CaO (±0·25 wt%)
according to Helz et al. (1995). (b) CaO vs MgO for glass compositions in scoriae from phases 4–16, erupted from December 4 to 19, 1959, overlain by compositional
fields from (a). All other features as in (a).
GLASS COMPOSITIONS IN 1959 SCORIA east end of the initial eruptive fissure, hence designated 1959E; see
SAMPLES Table 1) plus the low-CaO component S-2 (sample Iki-1, from the
west end of the initial fissure, designated 1959W; see Table 1), plus
Glass analyses from the scoria fall into two groups, as follows.
olivine and chromite.
(1) Matrix glasses: these include far-field glasses (those at some
The variation of CaO vs MgO in 1959 scoria glasses for sam-
distance from olivine), glasses next to euhedral olivine, and low-MgO
ples from phases 1–3, erupted between November 14 and 29, is
enclave glasses (mostly found next to resorbed olivine, as discussed
shown in Fig. 3a. Glasses in these samples occupy distinct composi-
by Helz, 1987, 2020).
tional fields, in line with their distinct bulk compositions: the 1959E
(2) Glasses closely associated with olivine and olivine aggregates,
November samples contain 60–70 wt% of the high-CaO (1959E)
found as inclusions and embayments in olivine, and interstitial glasses
component, whereas the 1959W November samples contain 89–
within clusters of olivine crystals.
100 wt% of the low-CaO component (Wright, 1973). The glasses
lie along two parallel trends that mostly fall within the boundaries
Magmatic components of the 1959 eruption of the olivine-controlled 1959 compositions as defined from bulk
Initial work on whole-rock chemistry by Murata & Richter (1966) chemistry (Wright, 1973). The parallel arrays show that the low-
allowed Wright (1973) to recognize two distinct chemical batches, CaO glasses were not produced by fractionation of augite from the
distinguishable most readily by differences in bulk CaO contents high-CaO glasses: augite begins to crystallize from Kı̄lauea melts only
at constant MgO content. Wright (1973) described each sample as at MgO = 7·4 wt% (Thompson & Tilley, 1969; Helz & Thornber,
consisting of a mixture of the high-CaO component, represented in 1987), and most of the low-CaO glasses have higher MgO contents
the calculations by the composition of S-1 (sample Iki-58, from the (Fig. 3a).
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Fig. 4. MgO content of matrix glasses in 1959 scoria plotted in the sequence in which the scoria were erupted, with eruptive phases for each sample indicated
below. Blanks in the sequence indicate pauses in the eruption and/or gaps in collection. Most matrix glasses have MgO contents lying between 8 and 9 wt%, as
emphasized by the shaded field. Continuous lines connect samples adjacent in time: dashed lines indicate non-adjacent samples. Upper line of symbols (gray
squares) shows estimated MgO content of 100 % 1959E in selected 1959E-rich samples, as discussed in text.
Two small sets of glasses in Fig. 3a show other processes at work. followed by seven samples with 88–100 wt% 1959W, including four
First, glasses with
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Table 2: Comparison of 1954 and 1959W glasses and whole-rock compositions (in wt%)
Sample: 1954 lava, Wright (1971) 1954 lava, Wright (1971) Iki-1, Murata & Richter (1966)
Analysis type: Gravimetric Gravimetric Gravimetric
SiO2 50·20 50·09 50·07
TiO2 2·72 2·68 2·75
Al2 O3 13·73 13·79 13·70
FeO 11·21 11·23 11·26
MnO 0·17 0·17 0·17
MgO 7·20 7·31 7·23
CaO 11·56 11·51 11·55
Na2 O 2·25 2·28 2·30
K2 O 0·57 0·53 0·60
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P2 O5 0·28 0·26 0·28
Sum 100·13 100·01 100·02
Given the component fractions of Wright (1973), and microprobe OLIVINE CONTENT OF THE 1959 SCORIA:
analyses of glasses obtained subsequently, we can estimate the MgO TIMING AND SIGNIFICANCE
content of the pure 1959E melt component, for many of the 1959E-
The 1959 eruption produced the most olivine-rich Kı̄lauea lavas in
rich samples by solving pairs of equations such as
the last 200 years (Wright, 1971), in addition to having the highest
pyroclastic fountains of any summit eruption over the same period.
For Iki-22: 0.68X + 0.32Y = 10.04 (observed Mg O in glass) (1) Here we evaluate the relationships between bulk MgO content, glass
MgO content, fountain height and volatile (sulfur) content over the
course of the eruption.
For Iki-44: or Iki-7: 0.06X + 0.94Y = 8.55 (observed Mg O in glass) There is a positive correlation (Fig. 5) between bulk olivine con-
(2) tent (reflected in bulk MgO) and glass MgO content in the November
(phases 1–3) samples, where the most magnesian melts (Iki-22, 3 and
where X is the MgO content of the pure 1959E melt, Y is 71, erupted on November 18–19) have entrained abundant olivine
the MgO content of the pure 1959W melt, and the component (bulk MgO = 17·3–19·5 wt%, corresponding to about 20–25 wt%
fractions are taken from Wright (1973). The maximum average olivine). In the December samples (phases 4–16), this correlation
glass MgO found in 1959W-rich samples is ∼8·55 wt%, which is weak: virtually all December samples have high olivine contents
thus represents the highest-temperature part of the nearly pure (16·5–19·5 wt% bulk MgO), regardless of the MgO contents of their
stored magma, and so was used to represent the 1959W component glasses or their chemical affinity.
in all calculations. Solving these paired equations for Iki-22 (and
similar pairs for other 1959E-rich samples) produces a minimum Fountain heights and sulfur contents of 1959 scoriae
estimate for MgO content of the pure 1959E component in Pyroclastic fountains are produced by degassing of the melt during
Iki-22. the last stages of ascent and eruption. The main components of the
The inferred MgO content of the 1959E melt component is gas phase in Kı̄lauea basalts are H2 O, CO2 , and various sulfur species
10·5–10·8 wt% in the earliest samples (Iki-22, Iki-3), or ∼ 25◦ C (see e.g. Dixon et al., 1991; Gerlach, 1993; Edmonds et al., 2013;
hotter than the melts observed in those samples, using the slope Sides et al., 2014; Ferguson et al., 2016; Moussallam et al., 2016), so
found by Helz & Thornber (1987). The estimated MgO contents one or all of these must be responsible for the high fountaining seen
for pure 1959E decline irregularly with time (Fig. 4) so that, by in almost all phases of the eruption.
the end of the eruption, Iki-32 (phase 15), which contains 39 wt% The variation of bulk MgO content (equivalent to olivine content)
1959E, has only a slightly higher estimated 1959E MgO content with fountain height is plotted in Fig. 6. There is a slight increase
than the prevailing average melt. This pattern suggests that the in maximum fountain heights (from 200 to 380 m) as bulk MgO
excess heat associated with the newer 1959E component when it increases. However, the data are noisy, and some phases of the
first intruded the stored magma had dissipated by the end of the eruption (notably phase 4, represented by sample Iki-13) showed
eruption. consistently low fountaining, although the scoria was very MgO-rich.
Glass contents in the 1959W December samples fall within the There were three episodes of distinctly higher fountaining, during
same 8–9 wt% MgO range as many of the 1959W November phases 3 and 7 (both 430 m) and phase 15 (580 m). There is no
samples, which suggests that the volume of the 1959W component correlation between bulk MgO contents and these episodes of higher
was larger than the volume of 1959E magma that invaded the fountaining, nor is there any correlation with glass MgO content, nor
chamber. Many of the later hybrids consist of ∼20 wt% 1959E and with chemical affinity. However, the length of the events decreases
80 wt% 1959W, consistent with the new magma being a subordinate from 7 h in phase 3, to 2–3 h in phase 7, to ∼10 min in phase 15
component of the eruption. Thermal homogeneity was well advanced (Richter et al., 1970), suggesting a decrease in the amount of the
by phase 10 of the eruption, although the erupting magma was still propellant gas over the course of the eruption.
chemically heterogeneous, as bulk compositions of scoria from the Of the three main volatile components (H2 O, CO2, sulfur), the
last two high-fountaining phases (15 and 16) have 39 % and 19 % variation of sulfur in the melt is the most easily documented. Sulfur
of the 1959E component respectively. contents for a wide range of glasses from the 1959 scoria are shown
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Fig. 5. MgO in matrix (far-field) glasses plotted against the bulk MgO content of the corresponding 1959 scoria sample (Murata & Richter, 1966; Wright, 1973).
Fig. 6. Fountain height (meters) vs bulk MgO in scoria (wt%). Vertical lines indicate variable fountain heights (Table 1). Symbols surrounded by black circles
correspond to episodes of unusually high fountaining.
in Fig. 7, plotted in eruptive sequence as in Fig. 4. Sulfur contents in Helz et al. (2017) for a smaller sample set, each high-fountaining
of matrix glasses are consistently low, with most
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Fig. 7. Sulfur contents of glasses (in ppm) in the 1959 scoria plotted in chronological sequence Each point corresponds to an individual microprobe analysis.
Phase numbers (3, 7, 15) mark episodes of unusually high fountaining, shown in Fig. 6. Inclusion glasses with unusually low sulfur contents (Iki-7 and Iki-32) are
marked by ovals. Dashed line encloses interstitial glasses with unusually high sulfur contents found in olivine clots in three phase 1 samples.
Olivine content and its significance OLIVINE CHARACTERISTICS: STATE OF
The amount of olivine entrained in the 1959 lavas is conspicuously AGGREGATION AND COMPOSITIONS
large. Early samples Iki-22 and Iki-3, for example, contain melts There are many distinct subpopulations of olivine in the 1959 lavas
with MgO ∼10 wt%, and contain 20–25 wt% olivine [assuming (Helz, 1987) but this study focuses on with the euhedral (class 2)
an average composition of Fo86–87 , as was documented by Wright olivine. The class 1 olivine (large, blocky, commonly deformed) and
(1971, 1973)]. The question arises: how much Fo87 olivine can a the class 5 olivine (enclosing swarms of sulfide-bearing inclusions),
melt crystallize? and aggregates of both were interpreted as not closely related to the
To evaluate this, the thermodynamically based computer models 1959 melts. Recent work by Bradshaw et al. (2018) on the class 1
of Ghiorso & Sack (1995) and Ghiorso et al. (2002) were used to olivines confirms that they formed in a different environment from
model the equilibrium crystallization of 1959 bulk compositions Iki- the euhedral olivine; those researchers further suggested that, because
2 (MgO = 11·5 %) and Iki-22 (MgO = 19·52 %), plus experimental of their size, the class 1 olivine makes up half the olivine present. Even
sample KI75-143.8 (MgO = 12·15 %; Helz & Thornber, 1987) over at that level, however, classes 1 and 5 do not make up two-thirds of
a range of oxidation conditions [fayalite–magnetite–quartz (FMQ) the olivine load, so cannot be the only excess olivine crystals present.
or nickel–nickel oxide (NNO)], pressures (0·1–100 MPa) and water Thus the population of class 2 euhedral olivine must itself be hybrid.
contents (0·0–0·7 wt%). The results show that, to reach the Fo Petrographic examination of the 1959 scoria shows two popu-
contents observed, the oxidation state must approximate NNO con- lations of euhedral olivine crystals, distinguishable by their degree
ditions. This is consistent with recent XANES work on glassy Kı̄lauea of aggregation and composition (Figs 8 and 9). The first population
samples (Moussallam et al., 2016; Helz et al., 2017) that shows (Fig. 8) is typically found in olivine clusters, which enclose some void
relatively high Fe3+ /total Fe ratios in Kı̄lauea melts The amount of space, in marked contrast to the tight dunitic aggregates of (mostly)
olivine seen in the calculations at melt MgO = 10 wt% (to match the deformed class 1 olivine (Helz, 1987). The olivine grains are often
most magnesian observed glasses in the 1959 eruption) is 3–4 wt%, crystallographically oriented relative to each other, as described by
and its composition is Fo85·5–86·0 , so the amount of Fo86 –87 that Schwindinger & Anderson (1989), with their c-axes being either
can be produced is less. parallel or roughly perpendicular to each other. Such olivine typically
Thus ∼3 wt% Fo86–87 is produced where the bulk composition has core compositions of Fo86·5–88·0 and contains melt inclusions,
is 11·5–12·1 wt% MgO, and the melt has reached 10 wt% MgO. although not swarms of inclusions. These clusters occur in almost all
If one assumes a higher initial melt MgO content, then the amount scoria samples.
of Fo86–87 that can crystallize increases by roughly 2 % per 1 % A second population of olivine crystals (Fig. 9) comprises either
increase in MgO. Therefore a melt with MgO = 14·5 wt% [like isolated grains or small clusters, enclosing little or no interstitial
the unique glass fragment in the uppermost Pahala Ash reported space. These crystals may contain melt inclusions, but often do not.
by Helz et al. (2015)] could crystallize an additional 4–5 wt% Core compositions are typically Fo84·5–86·0 and these crystals either
olivine, for a total of 7–8 % olivine. Given the observed olivine show fairly strong reverse zoning, or, more rarely, are unzoned.
load of 20–25 wt% in Iki-22, Iki-3 and other comparably magne- The frequency distribution of core and rim compositions for 63
sian samples, we see that the 1959 scoriae contain three times as class 2 olivine phenocrysts (>1 mm) is shown in Fig. 10a. The cores
much olivine as could have crystallized from the amount of lava are weakly bimodal, with a large peak at Fo87 (corresponding to the
erupted. Therefore, the lavas are cumulates, as reviewed by Helz compositions of the olivine in clusters as in Fig. 8) and a low peak
et al. (2014). at Fo85 (corresponding to the olivine crystals illustrated in Fig. 9). A
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Fig. 8. Selected clusters of euhedral olivine from 1959 scoria samples, labeled by sample number and eruptive phase. Melt inclusions in such olivines are
common, and the clusters usually enclose some intercrystalline pore space as well (as in circled area). Olivine crystals are often oriented crystallographically,
but the starburst cluster in Iki-10 (phase 3) should be noted.
similar spread in core compositions was observed earlier in the class is similar to the distribution of phenocryst rim compositions seen in
1 olivine populations (Helz, 1987), and has been found in olivine Fig. 10a, and presumably also reflects equilibration with the post-
phenocrysts in the 1959 ejection blanket (Rae et al. 2016). The rim mixing melts and their narrow range of MgO.
compositions in Fig. 10a have a single peak at Fo86 , presumably
reflecting progressive equilibration of olivine with the mixed melts
produced during the eruption, with their narrow range (8–9 wt%) of
MgO; this is in marked contrast to the rim distribution reported by
OLIVINE ZONING IN THE 1959 REAL-TIME
Rae et al. (2016). SCORIA SAMPLES
Given that the grain size of olivine in the 1959 scoriae varies The histories of the various olivine populations in the 1959 scoria
continuously (Mangan, 1990; Bradshaw et al., 2018), it is useful to samples are reflected in their zoning patterns. The overall variation
look at the compositions of the microphenocrystic and groundmass in rim compositions can be seen in Fig. 11, which displays rim
olivine as well. Their compositions are shown in Fig. 10b, where they compositions for 63 olivine phenocrysts (>1 mm) plotted in eruptive
are divided into those from samples erupted in November (phases 1– sequence. These data show that (1) there is a gradual decline in the
3) versus those erupted in December (phases 4–16). The November maximum observed Fo content of phenocryst rims over the course of
population shows three peaks: the largest is at Fo87 , the second at the eruption, (2) the mix of olivine zoning patterns varies over the
Fo85 , and the third at Fo83 . The first two correspond to the peaks course of the eruption, and (3) rim compositions more Fe-rich than
in Fig. 10a and again are consistent with there being two different ∼Fo84 are rare.
magmas involved. The third peak is defined by olivine from the more The bulk olivine composition of the 1959 lavas lies between
differentiated phase 3 samples (see Fig. 4). Fo87 and Fo86 (Wright, 1973), and is shown by the shaded band
The smaller olivines in the December samples, in contrast, show a running through the array of rim compositions in Fig. 11. Rim
single peak at Fo85 ± 1 , with a slight tail out to Fo80 . The distribution compositions falling above the range of average olivine composition
10 Journal of Petrology, 2022, Vol. 63, No. 1
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Fig. 9. Olivine crystals interpreted as being phenocrystic to the 1959W (stored) component, labeled by sample number and eruptive phase. Such grains may
occur as single crystals or in pairs. Melt inclusions are relatively uncommon, and there is little or no intercrystalline pore space involved.
in samples from phases 1 and 2 indicate the presence of reversely (3) olivines with more subdued (rounded) normal zoning, with
zoned crystals, as well as of unzoned olivine with Fo87–88 , in the Fo87–88 cores zoned out to rims of Fo85·0–87·0 . This style is observed
population analyzed. In the phase 4 and 5 samples, most olivine in nine traverses, but only in the December samples;
phenocrysts show little or no zoning, with core and rim compositions (4) olivines with less forsteritic cores (Fo84·5–86·0 ) and wide
alike being Fo86·6–87·0 . From phase 7 on, most olivine phenocrysts (≥150 μm) reversely zoned rims (maximum Fo87·8 ), observed in 10
have normal zoning. traverses throughout the eruption, with the extent of zoning declining
A set of 42 traverses on olivine phenocrysts was made as part over the course of the eruption;
of this study; full descriptions are included in the Supplementary (5) olivines with forsteritic (Fo87–88 ) cores and shallow reverse
Material, especially in File 1, which shows the traverses together with zoning out to Fo88·1–88·5 (two traverses in phases 1 and 2);
photomicrographs of the olivines analyzed. The consistency of rim (6) olivines (Fo87–88 as cores) with shallow reverse zoning that
compositions and the general reproducibility of the traverses suggests appears to result from infilling (Shea et al., 2015) associated with
that the data, although somewhat noisy, represent the compositions melt inclusions (three traverses in phase 1 samples).
of the olivine to ±0·25 mol% Fo. Because of the size of these crystals, Another notable characteristic is that most complete traverses
the points analyzed were usually spaced at 10 μm, and some earlier (rim to rim) are symmetrical, with opposite rim compositions match-
traverses had steps of 15–30 μm. ing (26 out of 42). Asymmetrical traverses (10 of 42) are observed
Forsterite zoning patterns in these traverses are summarized in where either the presence of an adjacent olivine grain in a cluster or
Table 3 and include the following: the presence of a vesicle limited interaction with melt on one side
(1) unzoned or very slightly zoned crystals, seen in 10 traverses of the crystal. The pattern suggests that the zoning in most crystals
in phase 1 (all Fo87–89 ), plus two traverses in phases 4–8 (both developed in a melt-rich environment.
Fo86·5–87·0 );
(2) olivines showing sharp normal zoning, with Fo87–88 cores Fo profiles vs NiO and CaO contents
zoned out to Fo83·5–85·0 , observed in six traverses in five grains The sharp normal zoning style is illustrated in Fig. 12, which shows
throughout the eruption; traverses for two crystals in Iki-2 (phase 1). The Fo core profilesJournal of Petrology, 2022, Vol. 63, No. 1 11
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Fig. 10. (a). Frequency distribution of compositions of 63 olivine phenocrysts (>1 mm long) in 1959 scoria samples, in mol% Fo. Core compositions include the
maximum Fo and average values for most crystals. Rim points are within 10 μm of the edge of the grain. Data from Helz (1987), Helz et al. (2017), and this paper.
(b) Frequency distribution of compositions for small olivines (12 Journal of Petrology, 2022, Vol. 63, No. 1
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Fig. 11. Forsterite composition (mol%) of rims on 63 olivine phenocrysts (crystals >1 mm in length) plotted in sequence erupted. Eruption phase numbers are
shown below the samples. This figure includes all phenocryst rim compositions analyzed to date, taken within 10 μm of the rim. The shaded field indicates
the average bulk olivine composition for the 1959 eruption, which lies between Fo86 and Fo87 (Wright 1973). Vertical lines connect compositions within a single
sample. Dash–dot line connects to data from the tip of a single olivine phenocryst in Iki-25. Data from Helz (1987), Helz et al. (2017), and this paper.
Table 3: Characteristics of overall forsterite zoning patterns in olivine traverses shown in Supplementary Material File 1
Phase Phase 1 Phase 1 Phase 2 Phase 3 Phases 4, 5 Phases 7, 8 Phase 10 Phase 15 Phase 16 No.
traverses
Date erupted: Nov 17–19 Nov 20–21 Nov 26 Nov 29 Dec 5–6 Dec 8–11 Dec 14 Dec 17 Dec 19
Unzoned Iki-22-1, Iki-5 Iki-14 Iki-21 5
Iki-3X-2 skeletal
Narrow rim Iki-3-2 (1, R) Iki-44X-1 (1), 7
normal (one Iki-5X-2
or two steps) (short, R),
Iki-7 (sm, lg)
Sharp normal Iki-2-2, Iki-10 (1, Iki-19 Iki-33-1 6
Iki-2X-2 short)
Rounded Iki-13 Iki-21 (1, R) Iki-26X-3 Iki-32X-1 9
normal (1, R) (1, R),
Iki-32 cir 1
(1, R)
Reverse Iki-22-1, Iki-7 pair Iki-11 Iki-21 (1, R) Iki-26-2 Iki-33-3 10
(Fo84–86 ) Iki-22-3 (1, R) (1, R)
Reverse Iki-44 cir 2 Iki-11 2
(Fo87–89 ) (class 2)
Infill reverse Iki-22X-2 Iki-44X-1 (R) 3
(1, R)
Symmetrical 10 1 2 3 3 2 2 2 25
Asymmetrical 1 4 1 3 1 10
Incomplete 4 1 2 7
for Ni and Ca in olivine as reviewed by Chakraborty (2010), with Ni in these otherwise strongly zoned crystals, so MnO plots have not
diffusing at rates very similar to Fe and Mg, whereas Ca is about an been included.
order of magnitude slower.
Inspection of the whole suite of traverses shows that zoning
patterns for the three components (Fo, NiO, and CaO) are similar Elimination of reversely zoned rims with time
to those observed in Figs 12 and 13. Although MnO was analyzed in Traverses for most of the reversely zoned low-Fo olivine phenocrysts
all traverses, the results showed no variation across the grains, even shown in Fig. 9 are presented together in Fig. 14. The profile fromJournal of Petrology, 2022, Vol. 63, No. 1 13
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Fig. 12. Traverses of two normally zoned olivines from Iki-2 (phase 1), with photomicrographs showing location of traverses. Plots include the Fo content of the
olivines (mol%), plus NiO and CaO contents (wt%). The horizontal lines in the upper plot are marked with the MgO content of the glass in the thin sections and
show that opposite rims have the same composition. (See also Supplementary Material File 1, p. 5.)
Iki-11 (reviewed in Fig. 13) shows reverse zoning cresting at Fo87·8 Syneruptive effects in traverses
with only thin outer rims (one or two steps wide) having lower Fo A μ-XANES study on the Fe3+ /FeT ratio in glasses from the 1959
contents. In the next profile (from Iki-21, erupted on December 11, eruption (Helz et al., 2017) found that (1) the redox state of the
or 15 days later than Iki-11), the roll-over near the edges of the grain glasses varies, (2) the decrease in redox state correlates with sulfur
is wider, with rim compositions of Fo86·2–86·3 . The crest of the profile loss in the glasses, and (3) the degassing and reduction were hap-
is Fo86·6–86·9 , or 1 % lower than the rims in the earlier samples, so pening in real time, during fountaining. This result is consistent with
the overall profile is flatter. earlier work (Anderson & Wright, 1972), and also with the more
Three days later (December 14), the width of the roll-over in Iki- recent study of Moussallam et al. (2016) on samples from Kı̄lauea’s
26 is similar to that seen in the Iki-21 sample, but Fo contents are 2008–2018 summit eruption.
lower, with rims Fo85·5–85·7 and the crest Fo86·5–86·6 . The latest The question is: to what extent can these rapid syneruptive
profile, for the olivine from Iki-33 (erupted December 19, 5 days processes (reduction + cooling) be seen in the olivine traverse data?
later than Iki-26) is incoherent. Rim compositions (Fo84·6–84·7 ) are Many traverses were asymmetric (Table 3), often where a vesicle is
the same as the core composition of this grain, but a scattering of adjacent to one side of the olivine crystal. For traverses with normal
individual points (about 200 μm from the edge) retain higher Fo zoning, the asymmetry exists in only one or two steps in the traverse,
contents, suggesting that this grain formerly had reverse zoning. suggesting that the vesicle was present and blocking access to the host
The succession of profiles suggests that the reverse zoning seen melt for only the last stage of crystal growth. In two of the broad,
in olivines in phases 1 and 2 was erased by diffusion of Fe from the reversely zoned profiles (Iki-7 pair, Iki-21), a single point (having
melt into the edge of the crystals, and diffusion of Mg into the melt, FeO higher than either the glass or the interior of the olivine) was
without obvious effects inboard of ∼150 μm, and that the process detected in the first step of the traverse (Supplementary Material
has run to completion over 28 days. File 3), but this layer was too thin to analyse cleanly, so its exact14 Journal of Petrology, 2022, Vol. 63, No. 1
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Fig. 13. Traverses of two reversely zoned olivines, from Iki-7 (phase 1) and Iki-11 (phase 2), with photomicrographs showing location of traverses. Plots include
the Fo content of the olivines (mol%), plus NiO and CaO contents (wt%). The arrow marks the position of the grain boundary between the pair of grains. (See
also Supplementary Material File 1, p. 13.)
composition is not known. All these narrow asymmetric rims are This can be rearranged to give
inferred to have grown during ascent, fountaining and rapid cooling
+ reduction during the eruption.
Mg (melt) = (Fe2 /Mg)olivine /(KD )(Fe2+ )melt . (4)
By contrast, most traverses in samples from phases 10–16 are
symmetric: they have rims with similar compositions on opposite
sides of the grains, and all rim compositions fall in a relatively This arrangement shows that given data on olivine core
narrow range within each sample. Thus internal equilibration was compositions, a relevant KD value, information on bulk FeOT in
well advanced in these later samples, as noted earlier by Helz et al. the melt and information on the Fe3+ /FeT in the melt, then the Mg
(2017). content (and hence the MgO content) in the parental melt can be
estimated. The olivine and glass compositions are shown in the
Supplementary Material. Previous work on selected 1959 samples
ESTIMATED PARENTAL MELT COMPOSITIONS by Helz et al. (2017) [modified according to the results of Zhang
et al. (2018)] found that, in the 1959 scoria, the olivine–melt
The data on olivine core compositions in the real-time scoria samples,
exchange KD = 0·28. The Fe3+ /FeT in olivine melt inclusions,
plus previous studies on these samples, allow us to estimate the
determined by XANES analysis to be 0·165, is assumed to be the
amount of MgO in the melt needed to precipitate the phenocryst
pre-degassing value for the 1959 magmas.
cores. The calculation uses the familiar Fe–Mg exchange reaction
In most cases, the sulfur contents of melt inclusions provide direct
evidence that the XANES determination of Fe3+ /FeT is relevant, and
also suggest that the crystallization pressures were high enough that
KD = (Fe2 /Mg)olivine /(Fe2 /Mg)melt . (3) any sulfur loss that may have occurred did not cause reduction ofJournal of Petrology, 2022, Vol. 63, No. 1 15
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Fig. 14. Forsterite traverses (mol%) for five reversely zoned olivine phenocrysts; photomicrographs are shown in Fig. 9b–f. The vertical dashed line at 150
emphasizes the similarity in rim thicknesses in these crystals.
ferric iron (see de Moor et al., 2013). For crystals having inclusions by sulfur loss. For these, the Fe3+ /FeT value used in the calculation
with lower sulfur contents, as observed for two of the three reversely was lowered using the relationship shown in fig. 11 of Helz et al.
zoned olivines included in Fig. 15, Fe3+ /FeT may have been modified (2017), but including the −2 % correction recommended by Zhang16 Journal of Petrology, 2022, Vol. 63, No. 1
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Fig. 15. Glass MgO content of scoriae, plotted in sequence erupted. Open circles, estimated melt MgO contents based on mixing ratios; open circles, estimated
melt MgO contents based on core compositions in Fo87–89 phenocrysts; open triangles, estimated melt MgO contents based on core compositions in Fo84·5–86
phenocrysts. Vertical lines join melt MgO estimates reflecting variable Fo content within single cores. Lower box (8–9 wt% MgO) highlights the dominant range
of MgO content in scoriae; upper box (10–11 wt% MgO) shows the dominant range of MgO contents estimated by the two independent methods.
et al. (2018). The original work of Roeder & Emslie (1970) reported samples. Third, chemical homogenization proceeded more slowly
KD = 0·30; use of that value would shift all points up by about than thermal homogenization. The December glasses contain much
1 % MgO. material with intermediate compositions, but small domains of near-
The calculated values (Fig. 15), using constraints obtained directly endmember glass compositions persist in matrix glasses dominated
from samples of the 1959 scoria, suggest that parental melts with by the opposite component (Fig. 3b). Grosser chemical heterogeneity
10–11 wt% MgO would be in equilibrium with most of the olivine also persisted to the end of the eruption, as can be seen in phases 15
core compositions observed. There are some exceptionally magnesian and 16 (Wright, 1973), where the fraction of the 1959E component
olivines in Iki-22 and Iki-3 that require slightly higher MgO. Also, varies from 39 % in Iki-32 to 19 % in sample Iki-33.
three reversely zoned olivines that have melt inclusions (and so The suite of real-time scoriae shows when the olivine arrived in
allow a calculation of parental MgO to be made) show lower MgO shallow storage and how its zoning changed with time during the
results, two of them consistent with the MgO contents of the stored eruption. The only picritic November samples were those erupted
(1959W) liquid. The MgO estimates for the high-Fo olivine cores are on November 18–19 (Fig. 5), which suggests that the dominant
very similar to the MgO estimates for the pure 1959E component forsteritic (Fo87–89 ) phenocrysts and olivine clusters were mostly
calculated above (Fig. 4). These calculations are independent of each brought up in that one magma pulse. Also, zoning in the forsteritic
other, so the agreement suggests that the immediate source melts for phase 1 and 2 olivine is limited, consistent with those crystals
the bulk of the high-Fo olivine found in the 1959 scoria did indeed being newly arrived from depth. A few crystals in phases 1 and 2
contain 10–11 wt% MgO. show smooth, minor reverse zoning out to >Fo88·0 (Table 3); these
presumably interacted with highly magnesian liquids at depth, prior
to entrainment and eruption. Rare phase 1 crystals showing evidence
of infilling, associated with melt inclusions (Shea et al., 2015), show a
DISCUSSION: INSIGHTS FROM REAL-TIME different kind of reverse zoning, initially resulting from growth rather
SCORIA SAMPLES than diffusion.
The 1959 eruption has long been recognized (Wright, 1973) as a The subordinate population of low-Fo olivine phenocrysts, with
mixed-magma eruption. Microprobe data on glasses and olivines thick, reversely zoned rims, are interpreted as cognate to the 1959W
from the expanded set of real-time scoriae provide insight into the (stored) component. Their high-Fo rims were progressively elimi-
processes that occurred. First, the two components were erupted nated between November 21 and December 19 (Fig. 14). The process,
sequentially in November, whereas in December they alternated in presumably diffusive re-equilibration, occurred where the thermal
rapid succession. Second, the resolvable thermal effect of intrusion effect of the 1959E recharge had dissipated, and the ambient melts
of the (more juvenile or recharge) 1959E component of the eruption returned to MgO contents of 8–9 wt%.
(Fig. 4) diminished over time, stalling at the temperature of the stored The time needed for the reverse zoning to disappear (4–5 weeks)
1959W magma after 4 weeks. Thus the latter was the dominant may place constraints on the timing of intrusion of new magma into
component, consistent with an overall mixing ratio of 20 % 1959E to Kı̄lauea’s summit reservoir. If the zoning took about the same length
80 % 1959W, as observed by Wright (1973) for most of the December of time to develop as to disappear, then intrusion of new magmaJournal of Petrology, 2022, Vol. 63, No. 1 17
into the stored body should have occurred in mid- to late October, Constraints from embayment and interstitial glasses in
2–3 weeks before the eruption of Iki-7 and Iki-11 (on November olivine clusters
21, 1959 and on November 26, 1959 respectively). This proposed In addition to the larger-scale constraints on the timing of intrusion
timing is consistent with the tilt results of Eaton et al. (1987), which and mixing summarized above, glass compositions in embayments in
show a major increase in summit inflation between October 16 and olivine or in interstices within olivine clusters offer further insights
November 13, 1959. into pre-eruptive processes.
Both crystal growth and diffusive re-equilibration occurred The interstitial glasses from most olivine clusters plot within the
throughout the 1959 eruption. Diffusion rates may be definable but compositional fields of the dominant components of the host melt
crystal growth rates are less constrained. One notable observation (Fig. 3a), as do glasses in olivine aggregates in the December scoriae
is that the normally zoned rims on the Fo87–89 olivine are thinner (Fig. 3b). However, in two phase 1 olivine clusters the interstitial
than the reversely zoned rims found on the Fo84–86 olivine. The glasses have CaO/MgO ratios like the CaO-rich 1959E component
latest sharp-normal olivine (in Iki-33, Table 3) would have had 30– (‘interior’ glasses in Fig. 3a), even though the host bulk composi-
60 days to grow its 80–120 μm thick rims, given the timing of the tions (Iki-44, Iki-7) contain 94 wt% 1959W (Wright, 1973). These
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1959E intrusive events (Eaton et al., 1987). The thinner normal rims interstitial glasses with high CaO/MgO contents also retain high
may reflect the fact that the ∼30–40 ◦ C cooling undergone by the sulfur contents more typical of inclusions (Fig. 7). The Iki-7 cluster
new magma was not enough to trigger extremely high olivine growth contains an interstitial melt pocket with highly vesicular, sulfur-rich
rates, and that needed olivine precipitation was partly accommodated glass (circle in Fig. 8c), which is locked inside the cluster, although
by nucleation of new, small olivines. adjacent melt channels have leaked sulfur to the host glass. However,
Incorporation of the November 18–19 olivine load into lower- the interstitial glass in the Iki-44 circle 2 cluster (shown in the upper
temperature melts resulted in both crystal growth and progressive photomicrograph in Supplementary Materials File 1, p. 10) is equally
re-equilibration of rim compositions over the course of the eruption. sulfur-rich but is not so confined. Their MgO contents extend to
Overall thermal stability later in the eruption led to narrower ranges lower values than those in any 1959E-rich samples especially in thin
of rim compositions (Fo84–86 ) especially within samples Iki-26, Iki- interstices, perhaps from olivine overgrowth during quenching.
32 and Iki-33 (see Fig. 11 and Supplementary Material File 1). The high CaO/MgO ratio of melts in these two olivine clusters
The tight clustering of Fo contents of small olivines in December confirms that it was the 1959E magma that sampled them at depth
samples compared with the spread in small olivine compositions and brought them to the surface. The Iki-7 clot and a cluster in Iki-22
in November samples (Fig. 10b) further indicates that significant (the third with high-sulfur glasses in Fig. 7) are well cemented, and
reworking of olivine compositions occurred during the eruption. The the Iki-44 cluster shows mild reverse zoning in the olivine. Thus all
overall pattern shows that the olivine (Fo87–89 ) brought in by the three clots, although brought up by the 1959E magma, are antecrystic
recharge magma was not in equilibrium with the melts in the storage to it; that is, the 1959E melt is the carrier magma but not the parent.
chamber, and did not survive in contact with the stored melts for The survival of the 1959E carrier melt in the Iki-44 and Iki-7
more than 4–5 weeks. This may have implications for olivine–melt clusters implies that the interstitial melts in other olivine clusters,
interactions in other ocean island basalt (OIB) systems. which match their host liquids, may reflect later exchange of melt
with their present hosts. For example, the olivine cluster from Iki-
5X (shown in Fig. 9b; studied by Helz et al., 2017), has interstitial
Complexity of mixing processes melt with MgO = 7·8 wt% and CaO/MgO that matches the matrix
Early sample Iki-2 (erupted on November 17, so before the main glass in that sample. However, the olivines in the cluster are unzoned
picritic pulse on November 18–19), offers additional insight into Fo87·5–88·0 , and so have rim compositions that require 10–11 wt%
the October pre-eruptive phase 1 mixing event. Overall, rims on MgO in the host melt. Also, the melt inclusion is rich in the 1959E
the normally zoned olivine crystals thicken from phase 3 to phase component (Helz et al., 2017). Thus this crystal clot may be cognate
16. Assuming constant crystal growth rates, the Iki-2 rims (Fig. 12) to the 1959E magma. If so, its present interstitial melt is neither the
would have developed over c. 23 days, consistent with their starting carrier nor parent magma, but is stored, slightly hybrid magma that
on October 25–26, and consistent with the timing of the first arrival has infiltrated the clot more recently. The ubiquity of elevated sulfur
of the 1959E component intruding the stored magma. However, contents in interstitial glasses in all these aggregates, including those
Iki-2 (containing 63 % 1959E, according to Wright, 1973) is het- in December scoriae, suggests that the exchange of melt between
erogeneous in both its melt MgO content and the character of its interstices and the host (matrix) melt took place at depth, before
olivine phenocrysts. Other phenocrysts (besides the two normally vesiculation and sulfur degassing, immediately after mixing of the
zoned olivines in Fig. 12) include three additional high-Fo olivine 1959E and 1949 W components began.
phenocrysts (one unzoned plus two with minor reverse zoning) plus
an unzoned Fo84 crystal. None of these four crystals had ‘seen’
the rapidly cooling 1959E-rich magma that encloses them for long
enough to react, unlike the crystals in Fig. 12. The inconsistent inter-
THE 1959 ERUPTION—MODEL AND TIMELINE
action between olivine and the hybridizing melts, plus the variability A sketch of Kı̄lauea’s plumbing∗∗ (Fig. 16a) shows a configuration
of glass MgO seen from one thin section to the next, shows that consistent with the spatial constraints that we have, both for the
there is more internal disequilibrum in Iki-2 than in most 1959 scoria 1959 eruption and the precursor 1954 eruption. Features include the
samples. Iki-2 thus exhibits piecemeal mixing behavior as modeled by following.
Bergantz et al. (2015) and Cheng et al. (2020). The 1959 eruption (1) The body that fed the 1954 eruption, which erupted along a
is more complicated than their models, as the incoming recharge NE-trending fissure in the middle of the caldera, follows what Poland
magma has its own crystal load, the melts vary both in composition et al. (2014) referred to as the ‘Kı̄lauea Iki trend’. Its location, plus its
and temperature, and the resulting mixed samples contain olivine differentiated melt and olivine compositions indicate a shallow source
crystals from both the new and stored magmas. centered under the caldera, which did not erupt again in 1959.18 Journal of Petrology, 2022, Vol. 63, No. 1
because it was significantly cooler (Figs 4 and 15) than any lava other
than spatter from the initial fissure and, second, because it contains
none of the 1959E component, whereas other samples erupted from
November 17 to 26 contain resolvable amounts of both components
(Wright, 1973).
In Fig. 16a, the participating source regions and feeder dike are
shown along the NE side of the magma reservoir, where magma
ascent presumably was facilitated by the faults bounding the caldera
(Poland et al., 2014; Helz et al., 2015). Although their depths are
approximate, the relative positions of these regions are constrained
by the MgO content of their melts and the Fo content of olivine
crystallizing from those melts, with melt MgO and Fo contents
decreasing in parallel as the magmas move up through Kı̄lauea’s
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plumbing system.
Time constraints on the events of the 1959 eruption are sum-
marized in Table 4. The earliest seismicity associated with the 1959
eruption began in February 1959 (Eaton & Murata, 1960), but major
inflation between October 16 and November 13 was interpreted
(Eaton et al., 1987) as marking the first arrival of the new (1959E)
magma in the intermediate-level reservoir. Thus the time available
for the properties of the scoria samples to develop, including most
changes in melt and olivine compositions observed, runs from mid-
October 1959 to the end of the eruption.
Phase 1 of the eruption proceeded as described by Richter et al.
(1970), with the opening of a fissure and its collapse to a single vent.
This was followed by a steep rise in melt MgO content (Figs 4 and
15) as the conduit developed; the earliest example of hotter material
is the very heterogeneous sample Iki-2 described above.
Phase 1 next saw the eruption of very hot 1959E-rich mate-
rial (melt MgO = 10 wt%); these picritic samples were erupted on
November 18–19, and contain a large and very heterogeneous pop-
ulation of olivine crystals and aggregates. The minimum ascent rate
required to successfully entrain the load of olivine they carried is 0·6–
0·8 cm s–1 or 0·2–0·3 km h–1 (assuming a simple Newtonian melt; see
Fig. 16. Sketch of Kı̄lauea’s summit reservoir showing approximate locations
Helz, 1987). If the source of this material was 8–10 km down, as
of melt bodies involved in the 1959 eruption, plus the location of the 1954
eruptive source and the approximate outline of the aseismic zone (after Ryan, seems reasonable from their melt compositions, the ascent time from
1988). (a) The configuration on November 18–19, 1959, when the conduit first that depth to the surface was 30–45 h. Thus this pulse rose from depth
operated at maximum efficiency. (b) The configuration as of December 4, independently of, and more quickly than, the batch of 1959E magma
1959, the beginning of the December activity. that arrived in mid-October. The character of the olivine phenocrysts
in these scoriae (highly forsteritic, unzoned) is consistent with their
having spent negligible time in storage in the intermediate chamber
(2) The hotter and less evolved 1959E component is shown as prior to eruption.
a dike-like body rising from below 10 km along the NE side of After this highly picritic pulse was spent, the conduit was occupied
Kı̄lauea’s aseismic volume (Eaton et al., 1987; Ryan, 1988), following by 1959W-rich magma from November 20 to 26. Samples from this
the caldera-bounding faults near the surface. This corresponds to period contain the same high-Fo olivine types as the November 18–
the eruption on November 18–19, 1959. Olivine core compositions 19 scoriae (Table 3), but their melt MgO contents (7·8–8·6 wt%)
associated with this magma are Fo87–88 , with their parental melt were lower. They also contain two low-Fo reversely zoned crystals
MgO estimated to be 10–11 wt% (Fig. 15). These melt and olivine (Table 3) interpreted as cognate to the 1959W magma body.
compositions are inferred to occur at depths equivalent to the base All late phase 1 and phase 2 scoriae contain 89–94 wt% 1959W,
of the aseismic bulb shown by Ryan (1988). and 12–6 wt% 1959E component (Wright, 1973). The intermediate
(3) The 1959W (stored) component, the main volume of which magma chamber (Fig. 16a), having been invaded twice by 1959E
is shown as a large body of magma stored at ∼3–4 km depth, was magma from mid-October on, produced only hybrids. The lack of
intersected and/or intruded repeatedly by the 1959E magma during detectable 1959E component in the phase 3 scoriae (Wright, 1973)
the ascent of the latter. Characteristic olivine core compositions are thus requires that those samples have come from a separate magma
Fo84·5–86·0 . This magma (MgO = 8–9 wt%) mingled with and/or was body (as shown in Fig. 16a), although they did use the same conduit.
entrained by the 1959E magma to produce the phase 1 and 2 lavas, as Eaton et al. (1987) documented that by the beginning of phase 4,
well as the December lavas. This depth is consistent with the results after the longest pause of the eruption, the summit reservoir had fully
of Ferguson et al. (2016) on the depth of origin of a partially degassed recovered to its pre-eruptive state of inflation. Other observations
embayment in a 1959 olivine phenocryst. (Murata & Richter, 1966; Richter et al., 1970) show that all sub-
(4). The phase 3 magma is shown in Fig. 16a as a separate sequent activity (from December 4 on) differed from the November
body, stored somewhat higher in the edifice. This is required, first, activity in that gaps between high fountaining phases were brief andYou can also read
