Journal of Petrology Volume 41 Number 7 Pages 967-990 2000
© Oxford University Press 2000
Magmatic Processes During the Prolonged Pu’u ’O’o Eruption of Kilauea Volcano, Hawaii
1HAWAII CENTER FOR VOLCANOLOGY, DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF HAWAII, HONOLULU, HI 96822, USA
2DEPARTMENT OF GEOSCIENCES, UNIVERSITY OF MASSACHUSETTS, AMHERST, MA 01003, USA
Received September 20, 1999; Revised typescript accepted February 8, 2000
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The Pu’u ’O’o eruption is exceptional among historical eruptions of Kilauea Volcano for its long duration (
17 years and continuing), large volume (2 km3), wide compositional range (5·6–10·1 wt % MgO) and the detailed monitoring of its activity. The prolonged period of vigorous effusion (300 000 m3/day) and the simple phenocryst mineralogy of the lavas (essentially only olivine) has allowed us to examine the volcano’s crustal and mantle magmatic processes. Here we present new petrologic data for lavas erupted from 1992 to 1998 and a geochemical synthesis for the overall eruption. The dominant crustal magmatic processes are fractionation and accumulation of olivine, which caused short-term (days to weeks) compositional variations. Magma mixing was important only during the early part of the eruption and during episode 54. The overall systematic decrease in MgO-normalized CaO content and abundances of highly incompatible elements, without significant Pb, Sr and Nd isotope compositional variation, is interpreted to be caused by mantle melting processes. Experimental results and modeling of trace element variations indicate that neither batch melting nor simple progressive melting can explain these compositional variations. Instead, a more complex progressive melting model is needed. This model involves two source components with the same isotopic composition, but one was melted 3% in the Hawaiian plume. The model results indicate that the amount of this depleted source component progressively increased during the eruption from 0 to 25%. Given the isotopic similarity of Pu’u ’O’o lavas to many lavas from Loihi Volcano and the small extent of prior melting to form the depleted source component, the melting region for Pu’u ’O’o magmas may partially overlap with that of the adjacent, younger volcano, Loihi. KEY WORDS: Kilauea Volcano; crystal fractionation; magma mixing; mantle melting processes
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The Pu’u ’O’o eruption is the longest-lived, best monitored (e.g. Wolfe et al., 1988
) and most voluminous historical eruption of Kilauea Volcano (Fig. 1). It started in January 1983 and, 17 years later, it is still continuing vigorously (300 000 m3/day). About 2 km3 of basaltic lava (dense rock equivalent) have been erupted, which destroyed 181 homes and a National Park visitor center on the south flank of the volcano (total losses $60 million). We previously documented the petrologic history of lavas from episodes 1 to 49 of this eruption (1983 to early 1992) utilizing petrography, mineral and whole-rock geochemistry [electron microprobe, X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) analyses], and Pb, Sr, Nd and O isotopes supplemented with field observations and geophysical data (Garcia & Wolfe, 1988; Garcia et al., 1989, 1992, 1996, 1998a). This paper chronicles the petrology and geochemistry (including ICP-MS trace element data, and Pb, Sr and Nd isotopic ratios) of Pu’u ’O’o lavas from episodes 50 to 55 (1992 to early 1998), a period when 0·9 km3 of lava was produced. In addition, we present the results of a time-series analysis of the entire eruption, which provides a rare opportunity to document both crustal magmatic processes (e.g. crystal fractionation, magma mixing and crustal assimilation) and to investigate mantle melting systematics. In contrast to the brief, small-volume, historical eruptions (1790–1982; see Macdonald et al., 1983), long-lived eruptions such as Pu’u ’O’o may have typified Kilauea’s prehistoric history (e.g. Holcomb, 1987).
|
Our results show that olivine fractionation and accumulation are the dominant crustal processes during the Pu’u ’O’o eruption, although crustal assimilation and magma mixing have played important secondary roles during the early part of the eruption and during episode 54. A progressive change in whole-rock CaO concentration and in incompatible trace element abundances and ratios with essentially no change in Pb, Sr and Nd isotopic ratios indicates that mantle partial melting was the primary factor controlling compositional variation in Pu’u ’O’o lavas erupted from 1985 to 1998. Modeling of this compositional variation requires melting of an isotopically homogeneous source with a component that was previously melted 3%. The model results suggest that the proportion of this component in the lavas increased from 0 to 25% during the Pu’u ’O’o eruption. The isotopic similarity of Pu’u ’O’o lavas to many Loihi lavas, the small extent of previous melting of one of the source components, the southward dip of Kilauea’s mantle conduit, and the indications from U-series data that Kilauea magmas are being derived from a large source area are all consistent with the possibility that these magmas were derived from the same source region that is supplying the adjacent, younger volcano, Loihi.
|
BRIEF HISTORY OF THE PU’U ’O’O ERUPTION |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The character of the Pu’u ’O’o eruption has changed markedly during 17 years of activity (see Table 1 for a summary). Episode 1 involved a ‘curtain of fire’ along a discontinuous fissure system of 8 km length, which was intermittently active for almost a month (Wolfe et al., 1987
). Episodes 2–47 (February 1983–June 1986) were short lived (5–100 h) with lava fountains of variable heights (10–400 m). These episodes were followed by repose periods of 8–65 days during which magma accumulated and fractionated in a shallow reservoir under the Pu’u ’O’o vent (Wolfe et al., 1988; Hoffmann et al., 1990; Garcia et al., 1992). In July 1986, the site of effusive activity shifted 3 km down-rift from the 255-m-high Pu’u ’O’o cone to form the Kupaianaha vent (Fig. 1). Magma rose up in the throat of the Pu’u ’O’o cone and degassed vigorously before passing through a shallow underground channel to the Kupaianaha vent (Garcia et al., 1996). This shift in the vent site marked a fundamental change in eruption style from episodic, high fountaining to nearly continuous, quiescent effusion. The Kupaianaha vent was active for 5·5 years during which it produced 0·5 km3 of lava (dense rock equivalent) and built a shield of 56 m height during this 48th episode of the Pu’u ’O’o eruption (Kauahikaua et al., 1996). Three months before the end of episode 48, a discontinuous fissure system of 1·7 km length opened up between the Pu’u ’O’o and Kupaianaha vents (episode 49). For approximately 21 days, this vent system produced lavas of the same composition as coeval lavas from the Kupaianaha vent (Garcia et al., 1996). Activity at the Kupaianaha vent diminished during episode 49 and ended 2 months later.
|
With the demise of the Kupaianaha vent in early 1992, effusive activity resumed 11 days later at Pu’u ’O’o from vents on its flanks. Episode 50 was short lived (15 days) but the eruption restarted (episode 51) along the same fissure after a 4 day hiatus (Table 1). Episode 51 was interrupted by 17 short pauses (8–90 h) and ended 7 months later following a magnitude 4·5 earthquake near Pu’u ’O’o (Heliker et al., 1998b). The next day, episode 52 began from two new vents on the southwest flank of the cone, 200–300 m from the episode 51 vent (which resumed erupting the next day). Episode 52 continued until a seismic swarm and a rapid summit deflation in February 1993 (Heliker et al., 1998b). Episode 53 started 9 days later and continued for almost 4 years until the Pu’u ’O’o lava lake suddenly drained and the cone collapsed on January 29, 1997. A few hours later, a 1 day eruption (episode 54) occurred along a discontinuous fissure system of 2 km length, 2–4 km up-rift from Pu’u ’O’o. Lava was produced during episode 54 from six, low fountaining (10–30 m high) vents (Harris et al., 1997). A 24 day hiatus followed episode 54. During this period, no lava was observed in or near the Pu’u ’O’o cone and many volcano watchers thought the eruption was finally over. This eruption, however, is continuing (episode 55) and shows no signs of ending in the near future despite occasional short (1–4 day) eruptive pauses.
|
SAMPLES |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
Ninety-three lava samples representing episodes 50–53, six from episode 54 and an additional 29 from episode 55 were collected for this study. Whenever possible, samples were collected in a molten state from active lava flows and water-quenched to minimize post-eruptive crystallization. The episode 54 samples were collected several weeks after their eruption, but from rapidly quenched vent deposits and are labeled according to their eruptive vent (A–F). All other samples are labeled with the date that they were collected (day-month-year), which is probably within a day of their eruption. During episodes 50–52, lava samples were mostly collected within 100 m of the eruptive vent. Following the onset of episode 53, lava drained directly into tubes and only rarely were overflows and skylights available for sampling. Therefore, most of our samples from episode 53 and all from episode 55 were collected on the coastal plain, 10–12 km from the Pu’u ’O’o vent, as the lava discharged from lava tubes. Splits of our Pu’u ’O’o samples are available to anyone interested in performing additional analyses.
|
PETROGRAPHY |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
Episode 50–53 and 55 lavas, like the vast majority of other Pu’u ’O’o lavas we have studied, are glassy, strongly vesicular, friable and weakly to moderately olivine-phyric (0·4–6·2 vol. % phenocrysts; Table 2). Olivine is the only phenocryst in these samples; it is usually small (
0·1–1 mm in diameter), euhedral, undeformed and contains spinel and glass inclusions. Olivine is somewhat more common (1 vol. %) in these lavas compared with those from the preceding 5·5 years of eruptive activity at the Kupaianaha vent (episode 48), despite identical ranges in MgO contents (7–10 wt %; Garcia et al., 1996) for the lavas from the two periods. Olivine abundance in episodes 50–53 and 55 lavas is generally correlated positively with whole-rock mg-number, although olivine phenocryst abundance can vary as much as 5 vol. % for a given mg-number (Table 2).
|
Clinopyroxene (cpx) microphenocrysts occur in 65% of the episode 50–53 lavas and in many of the early episode 55 lavas that we examined but always in low abundance (<1·7 vol. %). Commonly, these small (0·1–0·3 mm) crystals occur in clusters of 3–12 grains and some have sector zoning. Plagioclase microphenocrysts (0·1–0·5 mm) are absent in the episode 50–52 samples we examined but rare (
0·4 vol. %) crystals occur in 33% of the episode 53 samples. Tiny crystals (<0·1 mm) of plagioclase, olivine, spinel and clinopyroxene occur in a matrix of honey brown glass or black cryptocrystalline material in nearly all samples. Episode 55 samples collected after April 21, 1997, when surface activity became more vigorous, do not contain cpx or plagioclase microphenocrysts.
The episode 54 lavas are among the most aphyric samples from the Pu’u ’O’o eruption. They contain only rare (0·2 vol. %) phenocrysts of olivine and plagioclase. Rare microphenocrysts of plagioclase, olivine and clinopyroxene are also present in these lavas.
Xenoliths are rarely reported in Kilauea lavas but are present in six of the samples we studied in thin section. These small basalt xenoliths contain ‘black’ olivine. Black olivines are created by high-temperature oxidation as forsteritic olivine (>90%), magnetite and hypersthene replace the original olivine (Macdonald, 1944).
|
MINERAL CHEMISTRY |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
Olivine and clinopyroxene compositions were determined for a suite of episode 50–55 lavas that span nearly the entire range of whole-rock MgO contents (6·1–10·1 wt %). Plagioclase compositions were determined for the two episode 54 lavas with plagioclase phenocrysts. The University of Hawaii, five-spectrometer, Cameca SX-50 electron microprobe with SAMx automation was used for the mineral analyses. Operating conditions were 15 kV, a minimum spot size of 1 µm and a beam current of 20 nA for olivine and pyroxene, and 10 nA for plagioclase. Each element was counted for 30–45 s on the peak and 15 s on the background. Concentrations were determined using a ZAF–PAP correction scheme. Analytical error is estimated to be
0·2% forsterite, and 1–2% relative for major elements and 5–10% relative for minor elements (<1 wt %) based on repeated analyses of standards. Three spot analyses were made in the core and one on the rim of each crystal to check for compositional zoning.
Olivine
Over 200 olivine crystals were analyzed from 19 episode 50–55 lavas. Most of the analyzed olivine crystals are normally zoned with <3% variation in forsterite (Fo) from core to rim. The forsterite content of the olivine cores from the episode 50–53 and 55 lavas range from 79·7 to 84·4% (Table 3) with a few notable exceptions (e.g. black olivines with Fo >90%). Phenocrysts and microphenocrysts in episode 50–53 lavas overlap in composition (average Fo contents of 81·0%) and have somewhat lower Fo contents than the olivines from episode 48 lavas (82·5% average; Garcia et al., 1996). Olivines from episode 55 lavas have somewhat higher forsterite contents then episode 50–53 olivine (average 82·4%) and have a compositional distinction between phenocrysts and microphenocrysts (average 83·5 vs 81·7% Fo, respectively).
|
Cores of olivines from lavas with a wide range of mg-numbers (56–61) have olivine compositions in equilibrium with the bulk rock (Fig. 2). Many episode 50–53 and 55 lavas, especially those with higher mg-numbers, contain olivines with forsterite contents too low to be in equilibrium with melts corresponding to their whole-rock composition (Fig. 2). The olivines in these rocks are identical in appearance to those in Pu’u ’O’o lavas with lower mg-numbers. The positive correlation between olivine abundance and mg-number in Pu’u ’O’o lavas (Table 2) indicates that these lavas probably accumulated olivine. Sample 11-May-98 contains olivine crystals with forsterite contents up to 89%, which are too high to be in equilibrium with the host rock mg-number. These high-Fo crystals show no signs of deformation and are probably relics from a Pu’u ’O’o parental magma.
|
, phenocrysts (0·5–2 mm in diameter); small •, microphenocrysts (0·1–0·5 mm). The date below each vertical set of olivine data is the sample number. The diagonal stippled field is the low-pressure equilibrium field for basaltic magma (Fe/Mg Kd = 0·30 ± 0·03; Roeder & Emslie, 1970Episode 54 olivines are more variable in composition, with cores ranging from 78 to 85% Fo. Most of the rare olivines in these lavas are too forsteritic to be in equilibrium with the differentiated composition of their host rock (Fig. 2), although they are strongly zoned with rims in equilibrium with their bulk composition. These high-Fo olivines were probably derived from a more MgO-rich magma shortly before eruption.
The black olivines in the basalt xenoliths from episode 51 and 53 lavas have some of the highest forsterite contents ever reported for Hawaiian rocks (up to 97·6%; Table 3).
Clinopyroxene
Compositions were determined for 70 cpx crystals in 12 lavas from episodes 53 and 54 (Table 4). The crystals are compositionally unzoned or weakly normally zoned. Microphenocryst compositions in these lavas range in cpx end-member components from 10 to 17% ferrosilite, 28 to 43% wollastonite and 47 to 53% enstatite. Matrix crystals have a wider range in iron content (e.g. 8–24% ferrosilite). Cr2O3 contents of Pu’u ’O’o cpx are from 0·1 to 1·3 wt %, Al2O3 contents range from 1·3 to 3·8 wt % and Na2O and TiO2 contents are low (<0·25 wt % and <1·5 wt %). These compositions are typical of cpx from Hawaiian tholeiites (Fodor et al., 1975). Many of the cpx crystals have low and variable CaO contents (e.g. 14·1–19·1 wt % for rim to core) but nearly constant mg-numbers (80·4–81·1; Table 4). These features are indicative of disequilibrium growth (see Lofgren, 1980). Disequilibrium cpx was also noted in the early, evolved Pu’u ’O’o lavas but its presence was ascribed to magma mixing (Garcia et al., 1992). No petrographic or mineral chemical evidence for magma mixing was observed in the episode 50–53 and 55 lavas.
|
Plagioclase
Compositions were determined for phenocrysts and microphenocrysts in two episode 54 D vent samples (Table 5), which are the only Pu’u ’O’o lavas we have sampled since episode 3 to contain plagioclase phenocrysts. These plagioclase crystals are strongly reversely zoned (7–8% anorthite) from core to near the rim (30 µm) but are normally zoned at the rim.
|
|
WHOLE-ROCK GEOCHEMISTRY |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
XRF major and trace element analyses
Ninety-two samples from episode 50–55 lavas (
1·2 samples/month over a 6·7 year period) were analyzed by XRF spectrometry in duplicate at the University of Massachusetts for major and trace elements (Rb, Sr, Y, Nb, Zr, Zn, Ni, Cr and V; Table 6). For details of the methods used and for analytical precision estimates, the reader is referred to Rhodes (1996). With these new analyses, our XRF dataset for Pu’u ’O’o lavas includes 395 samples (a full dataset of these analyses is available on the Journal of Petrology Web page, at http://www.petrology.oupjournals.org).
|
The lavas from episodes 50 to 55 extend the compositional range for the Pu’u ’O’o eruption (Fig. 3). A lava from episode 53 (19-Jan-96) is the most MgO rich of any Pu’u ’O’o lava (10·1 wt %) and an episode 54 lava (Vent F) has the lowest MgO (5·6 wt %). Overall, the episode 50–55 lavas are similar in composition to the other Pu’u ’O’o lavas, especially for Al2O3. In detail, the K2O and CaO trends are offset to lower values, with the episode 55 lavas having the lowest values. Also, the K2O–MgO trend is linear for episode 50–53 and 55 lavas compared with the curved trend observed for the earlier episodes of the eruption and expected from crystal fractionation (Fig. 3). This linear trend is probably related to mantle melting processes, which are discussed below. The episode 54 lavas are petrographically and geochemically similar to lavas from episodes 1 to 3 with low MgO contents (5·6–6·3 wt %) and are readily distinguished from other Pu’u ’O’o lavas by their relatively low CaO/Al2O3 (<0·78 vs >0·82).
|
Cr, Ni and Zn are compatible trace elements in the episode 50–55 Pu’u ’O’o lavas (Table 5). Cr and Ni show the most variation of any element in Pu’u ’O’o lavas (factors of 6·4 and 3·3, respectively). Plots of these elements relative to a highly incompatible element (e.g. K) define steep negative trends for episode 50–53 and 55 lavas that overlap with and extend beyond the field for older Pu’u ’O’o lavas (Fig. 4). There is a systematic decrease in K at a given Ni abundance indicating a progressive variation in parental magma composition during the eruption. Among the incompatible trace elements, Rb and Nb varied by a factor of two for episode 50–55 lavas, with less variation for Zr (1·65), Y (1·45), Sr (1·4) and V (1·3). Element–element and element-ratio plots of the highly incompatible elements demonstrate that the episode 50–53 and 55 lavas overlap in composition with previous Pu’u ’O’o lavas and thus were derived from compositionally similar mantle sources. The episode 54 lavas are similar to early Pu’u ’O’o lavas in Cr and Sr but have distinctly lower Ni and Nb for their K concentration (Fig. 4). These differences indicate that the episode 54 lavas are probably not related to the same batch of magma that was tapped during episodes 1–3 despite the close spatial relationships of their vents. The relatively small Sr variation (Table 5) and the decrease in Al2O3 with decreasing MgO for the most evolved rocks, especially episode 54 lavas (Fig. 3), indicates that the evolved lavas underwent plagioclase fractionation.
|
ICP-MS analyses
Twenty-eight samples from episodes 50 to 55 were analyzed for trace elements by ICP-MS in the same laboratory (Washington State University; Table 7) as the 32 lavas from episodes 1 to 48 (Garcia et al., 1996). For a summary of the methods used, the reader is referred to King et al. (1993) and Pietruszka & Garcia (1999a). The analytical precision (1
) is estimated to be 1–3% based on repeated analyses of a Kilauea basalt standard [Kil1919; for information on this standard, see Rhodes (1996) for XRF data and Pietruszka & Garcia (1999a) for ICP-MS data]. Plots of highly incompatible elements show excellent linear trends for the overall Pu’u ’O’o suite with the episode 50–55 lavas extending the range of the suite to both significantly higher and lower concentrations (Fig. 5). Plots of ratios of highly over moderately incompatible elements vs highly incompatible elements (e.g. La/Yb vs Ba) show an overall linear trend with the scatter reflecting variable amounts of crystal fractionation. The episode 54 lavas have distinctly higher La/Yb ratios compared with all previously analyzed Pu’u ’O’o lavas except for an episode 1 lava (Fig. 5). On ratio–ratio plots of highly incompatible elements (with the most incompatible element in the numerator; e.g. Ba/Ce and La/Ce) the episode 50–53 and 55 lavas form fields that overlap with the field for episode 1–48 lavas but extend to lower values for the more recent lavas (1995–1998; Fig. 5). The overall decrease in La/Yb with time could be caused by an increase in the degree of partial melting during the eruption. The decrease in ratios of highly incompatible trace elements cannot be explained by an increase in partial melting and instead indicates that there was a minor change in the mantle source composition for the more recent lavas.
|
|
Pb, Sr and Nd isotopes
Ratios of Pb, Sr and Nd isotopes were determined on selected Pu’u ’O’o samples at the University of Hawaii using a VG Sector mass spectrometer [see Pietruszka & Garcia (1999a) for a summary of methods used]. Isotope fractionation corrections, standard values, total procedural blanks, and analytical uncertainties are given in Table 8. Five samples, one each from episodes 51 and 55, and three from 53, were analyzed for isotope ratios; the data for two of these samples (29-Dec-92 and 25-Apr-94) were presented by Garcia et al. (1996). Our previous work showed that Pb and Sr isotope ratios changed somewhat during the first 2 years of the eruption, a period of extensive magma mixing and crustal contamination (Garcia et al., 1992, 1998a), but remained nearly constant for the next 7 years (Garcia et al., 1996).
|
The new isotopic data for episode 51, 53 and 55 lavas show slight temporal increases in Pb and Sr isotope ratios, although the Sr isotope variation is essentially within analytical error (Fig. 6). Pu’u ’O’o lavas deviate from the good negative correlation observed for Pb and Sr isotope ratios in most Hawaiian tholeiites (e.g. West et al., 1987), as do Loihi tholeiites (Fig. 7). The Pb and Sr isotopic data for tholeiites erupted during the last 20 years from the three adjacent, active Hawaiian volcanoes are distinctly different (Fig. 7) and demonstrate that the Hawaiian plume source must have at least three distinct components [as suggested by Staudigel et al. (1984)]. Compared with other historical Kilauea lavas analyzed in the same laboratory (Pietruszka & Garcia, 1999a), Pu’u ’O’o lavas have the lowest 206Pb/204Pb ratios and plot within the Loihi field (Fig. 7). Nd isotope ratios have not varied beyond analytical error for the entire eruption (Garcia et al., 1996; Table 7).
|
|
|
MAGMATIC CONDITIONS FOR THE PU’U ’O’O ERUPTION |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The Pu’u ’O’o eruption provides an excellent opportunity to examine the details of magmatic processes at an active basaltic volcano because we have a wealth of background information on Kilauea’s basic magmatic processes (e.g. Tilling & Dvorak, 1993
). Seismic evidence has documented a vertical conduit of 60 km length that supplies magma to Kilauea (Tilling & Dvorak, 1993). For the Pu’u ’O’o eruption, magma in this conduit is thought to bypass the summit reservoir and feed directly into the east rift zone conduit (based on the rapid change in trace element geochemistry for Pu’u ’O’o lavas compared with Kilauea summit lavas; Garcia et al., 1996). Seismic and ground deformation studies indicate that the east rift zone supplies a shallow (0·5–2·5 km depth) magma reservoir under the Pu’u ’O’o vent (Koyanagi et al., 1988; Hoffmann et al., 1990; Gillard et al., 1996). From 1983 to 1986, this reservoir was a narrow (3 m wide), dike-like body (1·6 km long and 2·5 km deep) that belched out much of its contents during brief (1 day), monthly eruptions (Hoffmann et al., 1990). The crown of the Pu’u ’O’o magma reservoir is open, which allows heat and gases to escape readily (Wolfe et al., 1988). The high surface area and open top of this magma reservoir is thought to have caused rapid crystal fractionation (5%) during the 20–30 day pauses between episodes 4–47 (Garcia et al., 1992). There are no data to constrain the current size or shape of the Pu’u ’O’o reservoir since episode 47 but it is assumed to have remained small (e.g. Heliker et al., 1998b). Its shape may have changed to a more thermally efficient form with the change from episodic to continuous effusion in mid-1986.
The temperature of Pu’u ’O’o magma just before eruption can be inferred from the MgO contents of glasses (Helz & Thornber, 1987), clinopyroxene compositions (Putirka et al., 1996) and from thermocouple measurements of molten lava. Temperatures of 1145–1160°C have been determined for Pu’u ’O’o glasses (Mangan et al., 1995; Heliker et al., 1998b), which agree well with measured lava temperatures (1135–1160°C). Temperatures calculated from cpx matrix and microphenocryst rim compositions yield similar to higher temperatures (1158–1212°C; Table 4). Cpx microphenocryst cores yield consistently high temperatures (1187–1212°C), which might be considered more representative of magmatic rather than eruption temperatures. Experiments on Kilauea lava compositions indicate that lower temperatures (1160–1172 ± 9°C) are more appropriate for low-pressure growth of cpx (Helz & Thornber, 1987).
Crystallization pressures for the Pu’u ’O’o reservoir can be inferred from several lines of evidence. Seismic and ground deformation studies indicates that the reservoir is shallow (<3 km depth) corresponding to pressures of <0·10 GPa (Hoffmann et al., 1990). Thermobarometry calculations for cpx microphenocryst cores yield much higher pressures for episode 53 magmas (0·51 ± 0·09 GPa; Table 4). Similar values were also reported for cpx microphenocrysts in lavas from episodes 9 and 10 (Putirka, 1997). Surprisingly, high pressures were also calculated for some matrix and microphenocryst rim compositions (0·55 and 0·68 GPa; Table 4). These mantle depth estimates (the Moho is 13 km, 4 GPa, at its deepest point under Kilauea; Klein et al., 1987) are inconsistent with petrographic, field, experimental and geochemical evidence, which indicates that cpx forms late in Pu’u ’O’o lavas.
The liquidus mineralogy of a MgO-rich Pu’u ’O’o lava was modeled using the MELTS program (Ghiorso & Sack, 1995) to better understand the cause of the anomalous cpx pressure estimates. It was assumed for this modeling that the magma underwent equilibrium crystallization, contained 0·3 wt % H2O and 0·1 wt % CO2, and that its redox state was one log unit below the FMQ (fayalite–magnetite–quartz) buffer (models were also run at FMQ with no significant change in the results). The model results indicate that olivine is the liquidus phase only at low pressures (<0·3 GPa). At moderate pressures (0·3–0·6 GPa), orthopyroxene is the liquidus phase, rather than cpx, and olivine is unstable. Euhedral olivine is ubiquitous in all but the most evolved Pu’u ’O’o lavas and orthopyroxene has not been observed in any of the Pu’u ’O’o lavas. Previous studies have consistently shown that cpx phenocrysts are rare in Kilauea lavas, except those with MgO contents <6·8 wt % (e.g. lavas with 5 wt % MgO from the 1955 eruption contain cpx; Macdonald & Eaton, 1964). Therefore, the calculated moderate pressure for cpx crystallization in Pu’u ’O’o magmas is probably an artifact of their rapid growth (as discussed above). The moderate CaO content of the Pu’u ’O’o olivines (0·25–0·32 wt %, except in the black olivines; Table 3) is consistent with results of the MELTS calculations that olivine formed at low pressures (e.g. Ulmer, 1989). Thus, it is our conclusion that the minerals in the Pu’u ’O’o lavas record only the effects of low-pressure processes (<0·3 GPa).
If the shallow magmatic processes in the rift zone and Pu’u ’O’o reservoir can be identified and their compositional effects removed from the geochemistry of Pu’u ’O’o lavas, then the geochemical signature of mantle melting and source heterogeneity can be identified. In the following sections, we present an analysis of the crustal and mantle magmatic processes affecting Pu’u ’O’o lavas.
|
CRUSTAL MAGMATIC PROCESSES FOR THE PU’U ’O’O ERUPTION |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
Olivine fractionation and accumulation
The importance of olivine in controlling compositional variation in Hawaiian tholeiitic lavas has been recognized for many years (e.g. Powers, 1955
). This observation is reaffirmed in Pu’u ’O’o lavas by the presence of only normally zoned, olivine phenocrysts and the relatively high and nearly constant whole-rock CaO/Al2O3 (0·83) in all Pu’u ’O’o lavas erupted since episode 20 in 1984 (except those from episode 54). In addition to olivine fractionation, olivine accumulation is important in these weakly to moderately olivine-phyric lavas. For example, during a 4 month period of episode 53, the lavas exhibit the largest MgO variation (7·1–10·1 wt %) since the onset of continuous effusion in 1986 but have essentially the same olivine composition (81·0 ± 0·5% Fo). The overall MgO variation for the two extreme lavas from this period (samples 11-Sep-95, which has olivine in equilibrium with a melt of its whole-rock composition, and 19-Jan-96, the most MgO-rich lava from the entire eruption) can be explained by accumulation of 6·9 vol. % olivine with 81% Fo. This result is consistent with the relatively large difference in olivine abundance in these two samples (5·8 ± 1·5 vol. %). Good agreement between predicted and observed olivine differences is also found for the less MgO-rich sample 14-Oct-95 (8·9 wt %) and sample 11-Sep-95 (predicted 3·9 vol. % vs observed 3·6 ± 0·8 vol. %). These results are consistent with the observation that most of the MgO-rich, episode 50–53 lavas have olivine forsterite contents too low to be in equilibrium with their host rocks (Fig. 2). Thus, the episode 50–53 melts probably accumulated olivine and were less MgO rich than the episode 48 magmas.
Crustal assimilation
Pu’u ’O’o lavas have relatively low matrix oxygen isotope ratios (4·6–5·2
) and the oxygen isotope ratios for olivines in many of these lavas are out of equilibrium with the matrix (Garcia et al., 1998a). This disequilibrium is thought to have occurred after the growth of olivine because some of the olivines have oxygen isotope values consistent with growth from a ‘normal’ mantle-derived magma (5·5; Garcia et al., 1998a). The size of the oxygen isotope disequilibrium between olivine and matrix does not correlate with major and trace element concentrations or ratios, or with the Pb, Sr or Nd isotope compositions of Pu’u ’O’o lavas. Therefore, Pu’u ’O’o magmas probably partially assimilated and exchanged oxygen with a high-temperature metamorphosed Kilauea basalt (Garcia et al., 1998a). The presence of basaltic xenoliths with black olivines in some Pu’u ’O’o lavas may be related to this process. The amount of crustal assimilation was greatest (perhaps up to 12%) during the early period of magma mixing with rift-zone stored magmas but decreased dramatically or stopped following the shift to continuous effusion in 1986 (Garcia et al., 1998a).
Magma mixing: episode 54 lavas
Previous studies of Kilauea’s historical eruptions have focused on the products of short-lived eruptions and found that magma mixing involving a differentiated, rift zone-stored magma and the influx of a more MgO-rich magma is a common process (e.g. Wright & Fiske, 1971). The lavas from the first 2 years of the Pu’u ’O’o eruption display ample petrographic, mineral and whole-rock chemical evidence of magma mixing (Garcia et al., 1992). Except for the rare high-Fo (87–89%) olivines, which may be relics from the influx of new magma, there is no evidence of magma mixing in Pu’u ’O’o lavas erupted from episodes 30 to 54 (a 12 year period).
Episode 54 marked an abrupt change in lava mineralogy and composition when evolved lavas with rare plagioclase phenocrysts (Tables 2 and 4) erupted a few kilometers up-rift from the Pu’u ’O’o cone (Fig. 1). The start of episode 54 was accompanied by rapid subsidence of Kilauea’s summit and an intrusion into the rift zone (Heliker et al., 1998a). The episode 54 lavas have distinct differences in mineralogy and whole-rock geochemistry from early 1983, evolved lavas (Figs 3–5), which were erupted from the same area. These differences indicate that they were derived from compositionally distinct magmas. The mixing event for episode 54 lavas probably occurred shortly before eruption. Otherwise, the high Fo content olivines in the hybrid lavas would have been partially or completely re-equilibrated by diffusion. No suitable mixing end members are evident among the Pu’u ’O’o lavas for the episode 54 lavas because the F vent sample does not lie on a mixing trend with the other episode 54 lavas (Fig. 3). These results suggest that Kilauea’s east rift zone, a site of frequent intrusions over the last 50 years (Klein et al., 1987), contains many closely spaced pockets of compositionally distinct magma that can be forced to erupt by intruding dikes as suggested by Ho & Garcia (1988).
In summary, the dominant crustal processes modifying the geochemistry of Pu’u ’O’o magmas are fractionation and accumulation of olivine. Crustal assimilation and magma mixing have been important only during the early part of the eruption and during episode 54.
|
MANTLE-RELATED TEMPORAL GEOCHEMICAL VARIATIONS |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The whole-rock compositions of the non-hybrid Pu’u ’O’o lavas from 1985 to 1998 were normalized to the same ‘parental’ MgO content to allow an evaluation to be made of the mantle-related geochemical variations for this eruption. A value of 10 wt % MgO was selected for normalization because it corresponds to the most MgO-rich Pu’u ’O’o lava composition. Furthermore, the higher forsteritic olivines (85%) from this eruption are in equilibrium with a melt of this MgO content, assuming 90% of the total iron is Fe2+. Because olivine is the only phenocryst in these lavas, the normalization was performed using a mixture of 98·5% equilibrium olivine and 1·5% Cr-spinel, a typical proportion of these minerals in Kilauea lavas (Wright, 1971
), added in small increments (0·02%) to the liquid.
The results of this normalization procedure indicate that highly incompatible elements (e.g. K) and CaO decrease systematically with time (Fig. 8), Al2O3, Y and Yb remain essentially constant, whereas Fe2O3 and SiO2 slightly increase. These results extend the trends that were identified for the 1985–1992 period of the Pu’u ’O’o eruption (Garcia et al., 1996) and clearly demonstrate a long-term systematic compositional variation for the eruption. A systematic decrease in the abundance of incompatible elements was also noted for the 1969–1974 Mauna Ulu eruption of Kilauea (Hofmann et al., 1984).
|
|
MANTLE MELTING MODELS FOR TWO PROLONGED KILAUEA ERUPTIONS |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The magmas for the Pu’u ’O’o and Mauna Ulu rift zone eruptions of Kilauea are thought to have partially bypassed the volcano’s summit magma storage reservoir (Ryan et al., 1981
; Garcia et al., 1996). Thus, these eruptions potentially offer a more direct view of the processes that generate tholeiitic basalts in the Hawaiian mantle plume compared with Kilauea’s historical summit lavas, which are thought to have been stored in the summit reservoir for 30–120 years (Pietruszka & Garcia, 1999b). Unlike these summit lavas (Pietruszka & Garcia, 1999a), lavas from these two rift zone eruptions display a rapid decrease in the abundance of highly incompatible elements (e.g. K, Nb) and in ratios of highly to moderately incompatible trace elements (i.e. Ce/Yb) with little or no change in Pb, Sr and Nd isotope ratios (Hofmann et al., 1984; Figs 6 and 8). There are, however, important geochemical differences between these two eruptions. The CaO contents of the Pu’u ’O’o eruption lavas decreased over time (Fig. 8), whereas no change in the CaO abundance of the Mauna Ulu lavas erupted from 1969 to 1971 was observed (Hofmann et al., 1984). Furthermore, ratios of highly incompatible trace elements (e.g. Ba/Ce) also decreased slightly over time for the Pu’u ’O’o lavas, whereas these ratios are constant in the Mauna Ulu lavas (Hofmann et al., 1984; Fig. 8). The incompatible trace element ratio changes for both eruptions are consistent with the relative incompatibility of these elements during mantle melting (e.g. Hauri et al., 1994). This suggests that partial melting processes, rather than source heterogeneity, are the dominant controls on the compositional variation for these lavas. Below, we evaluate two models that have been proposed to explain the large compositional variation in prolonged Kilauea eruptions with little or no change in Pb, Sr and Nd isotopes: batch melting of a homogeneous source (Hofmann et al., 1984) and progressive source depletion through mantle melting (Garcia et al., 1996).
Both melting models require an estimate of the degree of partial melting for the earliest Pu’u ’O’o lavas. We chose an initial melt fraction of 10% for Pu’u ’O’o lavas based on our previous results of modeling Kilauea historical lavas (Pietruszka & Garcia, 1999a). This estimate is derived from the systematic temporal variations in Pb, Sr and Nd isotope and incompatible trace element ratios at this volcano over the last 200 years, which are thought to result from the short-term changes in the composition of the mantle source and the degree of partial melting. In the context of this model, Pu’u ’O’o lavas formed at relatively high melt fractions compared with other historical Kilauea lavas, on the basis of their low ratios of highly over moderately incompatible trace elements (e.g. Ce/Yb). The source mineralogy and the melting mode for the melting model are essentially the same as used by Hofmann et al. (1984) for the Mauna Ulu eruption. We found that the modeling results were rather insensitive to the melting mode, which was also pointed out by Hofmann et al. (1984).
Batch melting of a homogeneous source
The temporal decrease in ratios of highly over moderately incompatible trace elements for Mauna Ulu lavas can be explained by a 20% relative increase in the degree of batch partial melting during the eruption (Hofmann et al., 1984). This model is consistent with the relatively constant ratios of Sr and Nd isotopes and of highly incompatible trace elements (e.g. Ba/Ce) in lavas from this eruption. A similar model for Pu’u ’O’o lavas (see Table 9 for model parameters) also requires an 20% relative increase in the degree of partial melting to explain the variation in ratios of highly over moderately incompatible trace element (Ce/Yb; Fig. 8). However, a simple increase in the degree of partial melting cannot account for the slight temporal decrease of highly incompatible trace element ratios observed for Pu’u ’O’o lavas (e.g. Ba/Ce; Fig. 8) as a result of the relatively high melt fraction expected for Kilauea tholeiites (5–10%; Pietruszka & Garcia, 1999a). Furthermore, this batch melting model is inconsistent with experimental results (Kushiro, 1996) for partial melting of a fertile garnet lherzolite source at 3 GPa (the mantle source conditions that are thought to be needed for generation of Kilauea magmas; Hofmann et al., 1984), which show that CaO should increase with increasing degrees of partial melting up to 20% (when cpx disappears). This expected increase in CaO content with increasing degree of partial melting was not observed for the Mauna Ulu eruption (Hofmann et al., 1984) and a decrease with time was observed for the Pu’u ’O’o eruption (Fig. 8).
|
Progressive melting and source depletion
Alternately, the temporal decrease in the incompatible trace element ratios (e.g. Ce/Yb and Ba/Ce) of Pu’u ’O’o lavas may result from an increase in the proportion of melt derived from a depleted source component. The relatively constant Pb, Sr and Nd isotope ratios of Pu’u ’O’o lavas suggest that this depletion is a recent consequence of melting within the Hawaiian plume. In this context, Garcia et al. (1996) proposed that the geochemical variations of Pu’u ’O’o lavas were caused by an eruption-related modification of the Kilauea’s mantle source through progressive mantle melting and depletion. Their model assumed that the later Pu’u ’O’o lavas formed by a simple remelting of the same source that produced the early lavas (e.g. at a constant melt fraction of 10% throughout the eruption). In testing this model, however, we discovered that it fails to explain the overall chemistry of Pu’u ’O’o lavas because the magmas generated from a remelted source would have incompatible trace element abundances and ratios much lower than observed.
To overcome this problem, we considered a more complex progressive melting model using two source components (an ‘initial’ and a ‘depleted’) with the same isotopic composition. The ‘depleted’ source component is assumed to have experienced a relatively small amount of prior melt removal (compared with the total melt fraction). The ‘depleted’ source was mixed with the ‘initial’ source, and this mixed source was partially melted to form the subsequent Pu’u ’O’o lavas. To determine the possible extent of previous melting for the ‘depleted’ source component, we evaluated a range of values from 0·1 to 10% (i.e. slightly to strongly depleted sources, respectively). Good residuals are obtained for incompatible element abundances and ratios using this model only if this parameter is <10%. If the amount of previous melting is 3%, the total degree of partial melting during the eruption remains nearly constant at 10 ± 1% (Table 9). For smaller or larger amounts of recent melt removal, the model predicts that the degree of partial melting during the Pu’u ’O’o eruption increases or decreases over time, respectively. The maximum amount of recent melt removal permitted by the model is 7% because, at higher values, the total melt fraction for the late Pu’u ’O’o lavas would be <5%, which is outside the range expected for Hawaiian shield lavas (5–20%; Watson, 1993). In all cases, the model results suggest that the relative amount of the ‘depleted’ source component increased progressively during the eruption, although magnitude depends on the amount of recent melt removal to form the ‘depleted’ source. For 3% recent melt removal, which gave the lowest residuals, the amount of the ‘depleted’ source increases from 0 to 25% (Table 9). Although the assumptions used in this modeling are based on previous studies, they may seem somewhat arbitrary. None the less, the modeling results demonstrate that the progressive melting model provides a better explanation for the geochemical variation of the Pu’u ’O’o lavas than other models we considered.
We favor 3% recent melt removal to form the ‘depleted’ source component (Table 9) because (1) the overall lava output rate has not changed during the Pu’u ’O’o eruption and (2) a small value for this factor is required to account for the subtle temporal decrease in the Th/U, Ba/Th, and Ba/U ratios of Pu’u ’O’o lavas (as determined by high-precision isotope dilution methods; A. Pietruszka, unpublished data, 1999). Physically, this removed melt could have been incorporated into the early eruptive products of Pu’u ’O’o, a previous Kilauea eruption, or, possibly, an eruption from the adjacent younger volcano, Loihi. If the amount of melt removal was 3%, then it is unlikely to be related to a Kilauea eruption during its shield stage (last 400 ky; Quane et al., 2000) because the range in melt fractions for Hawaiian tholeiitic basalts is expected to be higher (5–20%; Watson, 1993). Kilauea’s melting region may have progressively encroached upon a source that was melted to form Loihi’s alkalic and transitional lavas, which are thought to have formed by lower degrees of melting than tholeiitic lavas (e.g. Watson, 1993). Three additional lines of evidence favor a Loihi source: (1) Pu’u ’O’o lavas are isotopically similar to some Loihi lavas (Fig. 7); (2) U-series model results suggest that Pu’u ’O’o is tapping a relatively large mantle source region, which may overlap with that of Loihi (Pietruszka et al., 2000); (3) the mantle conduit for Kilauea dips south towards Loihi Volcano (Tilling & Dvorak, 1993).
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
The Pu’u ’O’o eruption is noteworthy in the historical eruption record of Kilauea for its long duration, large volume, and substantial lava geochemical variation. These features, and the simple mineralogy and pristine nature of the Pu’u ’O’o lavas, have allowed us to examine both crustal magmatic and mantle melting processes. The dominant crustal processes influencing compositional variations in Pu’u ’O’o lavas are olivine fractionation and accumulation. Shallow magma mixing and crustal assimilation were important only during the early part of the eruption and episode 54. The short-term (days to weeks) geochemical variations caused by olivine fractionation and accumulation are superimposed on longer-term variations that are probably related to partial melting processes in the mantle plume. The small but systematic decrease in ratios of highly incompatible elements cannot be explained by batch melting of a homogeneous source, as was invoked for the Mauna Ulu eruption, nor can a simple progressive melting model explain them. Instead, Pu’u ’O’o magmas appear to have been produced by melting a mixed source with both components having the same isotopic composition. The depleted source component was probably previously melted by
3% relative to the initial source component. The percentage of the depleted component in Pu’u ’O’o lavas progressively increasing during the eruption from 0 to 25%. The depleted source must have formed recently to have avoided a change in its Pb, Sr and Nd isotope composition but is probably not related to a Kilauea shield stage eruption because its extent of melting was too low. Given the isotopic similarity of lavas from Pu’u ’O’o to many from the adjacent, younger volcano, Loihi, the melting region for the two volcanoes may partially overlap. Prolonged eruptions such as Pu’u ’O’o offer an opportunity for a better understanding of crustal and mantle magmatic processes within active volcanoes. It will be interesting to see if the lessons learned from this eruption are applicable to eruptions at other oceanic island volcanoes.
|
ACKNOWLEDGEMENTS |
|---|
This paper is dedicated to the memory of Keith Cox, an icon of modern petrology. His friendship to students of petrology was much appreciated. Our study would not have been possible without the assistance of many individuals who collected samples (especially Frank Trusdell, Tom Hulsebosch, Scott Rowland and Marc Norman), and prepared and ran them for geochemical analysis (P. Dawson, M. Vollinger, M. Chapman, B. Martin, J. Rayray, J. Parker, R. Magu and K. Kolysko-Rose). We would like to thank Friederike Klinge for assisting with microprobe analyses of episode 53 lavas, K. Putirka for help in using his thermobarometer, and the staff at the Hawaiian Volcano Observatory for their diligent efforts in monitoring the Pu’u ’O’o eruption and their cooperation. Constructive reviews by W. Bohrson, G. Fitton, A. Klugel and M. Wilson are gratefully acknowledged. This work was supported by NSF grants to M.G. (EAR-9315750 and EAR-9614247). This is SOEST Contribution 5073.
|
FOOTNOTES |
|---|
*Corresponding author. Telephone: +1-808-956-6641. Fax: +1-808-956-5512. e-mail: garcia{at}soest.hawaii.edu
Present address: Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
Extended data set can be found at: http://www.petrology.oupjournals.org
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONBRIEF HISTORY OF THE...SAMPLESPETROGRAPHYMINERAL CHEMISTRYWHOLE-ROCK GEOCHEMISTRYMAGMATIC CONDITIONS FOR THE...CRUSTAL MAGMATIC PROCESSES FOR...MANTLE-RELATED TEMPORAL...MANTLE MELTING MODELS FOR...CONCLUSIONSREFERENCES |
|---|
Fodor, R. V., Keil, K. & Bunch, T. E. (1975). Contributions to the mineral chemistry of Hawaiian rocks. IV. Pyroxenes in rocks from Haleakala and West Maui volcanoes. Contributions to Mineralogy and Petrology 50, 173–195.
Garcia, M. O. & Wolfe, E. W. (1988). Petrology of the erupted lava. US Geological Survey Professional Paper 1463, 127–143.
Garcia, M. O., Ho, R. A., Rhodes, J. M. & Wolfe, E. W. (1989). Petrologic constraints on rift zone processes: results from episode 1 of the Pu’u ’O’o eruption of Kilauea volcano, Hawaii. Bulletin of Volcanology 52, 81–96.
Garcia, M. O., Rhodes, J. M., Ho, R. A., Ulrich, G. & Wolfe, E. W. (1992). Petrology of lavas from episodes 2–47 of the Pu’u ’O’o eruption of Kilauea Volcano, Hawaii: evaluation of magmatic processes. Bulletin of Volcanology 55, 1–16.
Garcia, M. O., Jorgenson, B., Mahoney, J., Ito, E. & Irving, T. (1993). Temporal geochemical evolution of the Loihi summit lavas: results from ALVIN submersible dives. Journal of Geophysical Research 98, 537–550.
Garcia, M. O., Foss, D., West, H. & Mahoney, J. (1995). Geochemical and isotopic evolution of Loihi Volcano, Hawaii. Journal of Petrology 36, 1647–1674.
Garcia, M. O., Rhodes, J. M., Trusdell, F. A. & Pietruszka, A. P. (1996). Petrology of lavas from the Pu’u ’O’o eruption of Kilauea Volcano: III. The Kupaianaha episode (1986–1992). Bulletin of Volcanology 58, 359–379.[Web of Science]
Garcia, M. O., Ito, E., Eiler, J. & Pietruszka, A. P. (1998a). Crystal contamination of Kilauea Volcano magmas revealed by oxygen isotope analysis of glass and olivine from the Pu’u ’O’o eruption lavas. Journal of Petrology 39, 803–817.
Garcia, M. O., Rubin, K. H., Norman, M. D., Rhodes, J. M., Graham, D. W., Muenow, D. & Spencer, K. (1998b). Petrology and geochronology of basalt breccia from the 1996 earthquake swarm of Loihi Seamount, Hawaii: magmatic history of its 1996 eruption. Bulletin of Volcanology 59, 577–592.
Ghiorso, M. S. & Sack, R. O. (1995). Chemical mass transfer in magmatic systems IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid–solid equilibria in magmatic systems at elevated temperatures and pressures. Contributions to Mineralogy and Petrology 119, 197–212.[Web of Science]
Gillard, D., Rubin, A. & Okubo, P. (1996). Highly concentrated seismicity caused by deformation of Kilauea’s deep magma system. Nature 384, 343–346.
Harris, A. J. L., Keszthelyi, L., Flynn, L. P., Mouginis-Mark, P. J., Thornber, C., Kauahikaua, J., Sherrod, D., Trusdell, F., Sawyer, M. W. & Flament, P. (1997). Chronology of the episode 54 eruption at Kilauea Volcano, Hawaii, from GOES-9 satellite data. Geophysical Research Letters 24, 3281–3284.
Hauri, E. H., Wagner, T. P. & Grove, T. L. (1994). Experimental and natural partitioning of Th, U, Pb and other trace elements between garnet, clinopyroxene and basaltic melts. Chemical Geology 117, 149–166.[Web of Science]
Heliker, C. C., Kauahikaua, J. P., Sherrod, D. R. & Thornber, C. R. (1998a). The rise and fall of the Pu’u ’O’o cone, Kilauea Volcano, 1983–1998. EOS Transactions, American Geophysical Union 79, F956.
Heliker, C., Mangan, M. T., Mattox, T. N., Kauahikaua, J. P. & Helz, R. T. (1998b). The character of long-term eruptions: inferences from episodes 50–53 of the Pu’u ’O’o–Kupaianaha eruption of Kilauea Volcano. Bulletin of Volcanology 59, 381–393.
Helz, R. T. & Thornber, C. R. (1987). Geothermometry of Kilauea Iki lava lake, Hawaii. Bulletin of Volcanology 49, 651–668.
Ho, R. A. & Garcia, M. O. (1988). Origin of differentiated lavas at Kilauea Volcano, Hawaii: implications from the 1955 eruption. Bulletin of Volcanology 50, 35–46.
Hoffmann, J. P., Ulrich, G. E. & Garcia, M. O. (1990). Horizontal ground deformation patterns and magma storage during the Pu’u ’O’o eruption of Kilauea volcano, Hawaii: episodes 22–42. Bulletin of Volcanology 52, 522–531.
Hofmann, A. W., Feigenson, M. D. & Raczek, I. (1984). Case studies on the origin of basalt, III. Petrogenesis of the Mauna Ulu eruption, Kilauea 1969–1971. Contributions to Mineralogy and Petrology 88, 24–35.
Holcomb, R. (1987). Eruptive history and long-term behavior of Kilauea Volcano. US Geological Survey Professional Paper 1350, 261–350.
Johnson, K. T. M. (1998). Experimental determination of partition coefficients for rare earth and high-field strength elements between clinopyroxene, garnet, and basaltic melt at high pressures. Contributions to Mineralogy and Petrology 133, 60–68.[Web of Science]
Kauahikaua, J., Mangan, M., Heliker, C. & Mattox, T. (1996). A quantitative look at the demise of a basaltic vent: the death of Kupaianaha, Kilauea Volcano, Hawaii. Bulletin of Volcanology 57, 641–648.
King, A., Waggoner, G. & Garcia, M. O. (1993). Geochemistry and petrology of basalts from ODP Leg 136. Ocean Drilling Program Scientific Results, 136. College Station, TX: Ocean Drilling Program, pp. 107–118.
Klein, F. W., Koyanagi, R. Y., Nakata, J. S. & Tanigawa, W. R. (1987). The seismicity of Kilauea’s magma system. US Geological Survey Professional Paper 1350, 1019–1185.
Koyanagi, R. Y., Tanigawa, W. R. & Nakata, J. S. (1988). Seismicity associated with the eruption. US Geological Survey Professional Paper 1463, 183–235.
Kurz, M. D., Kenna, T. C., Kammer, D., Rhodes, J. M. & Garcia, M. O. (1995). Isotopic evolution of Mauna Loa volcano: a view from the submarine southwest rift. American Geophysical Union Monograph 92, 289–306.
Kushiro, I. (1996). Partial melting of a fertile mantle peridotite at high pressures: an experimental study using aggregates of diamond. American Geophysical Union Monograph 95, 109–122.
Lofgren, G. (1980). Experimental studies on the dynamic crystallization of silicate melts. In: Hargraves, R. B. (ed.) Physics of Magmatic Processes. Princeton, NJ: Princeton University Press, pp. 487–551.
Macdonald, G. A. (1944). Unusual features in ejected blocks at Kilauea Volcano. American Journal of Science 242, 322–326.
Macdonald, G. A. & Eaton, J. P. (1964). Hawaiian volcanoes during 1955. US Geological Survey Bulletin 1171, 1–85.
Macdonald, G. A., Abbott, A. T. & Peterson, F. L. (1983). Volcanoes in the Sea. Honolulu, HI: University of Hawaii Press, pp. 89–81.
Mangan, M. T., Heliker, C. C., Mattox, T. N., Kauahikaua, J. P. & Helz, R. T. (1995). Episode 49 of the Pu’u ’O’o–Kupaianaha eruption of Kilauea volcano—breakdown of a steady-state eruptive era. Bulletin of Volcanology 57, 127–135.
Moore, J. G. & Ault, W. U. (1965). Historic littoral cones in Hawaii. Pacific Science 19, 3–11.
Pietruszka, A. P. & Garcia, M. O. (1999a). A rapid fluctuation in the mantle source and melting history of Kilauea Volcano inferred from the geochemistry of its historical summit lavas (1790–1982). Journal of Petrology 40, 1321–1342.
Pietruszka, A. P. & Garcia, M. O. (1999b). The size and shape of Kilauea Volcano’s summit magma storage reservoir: a geochemical probe. Earth and Planetary Science Letters 167, 311–320.
Pietruszka, A. P., Rubin, K. H. & Garcia, M. O. (2000). 226Ra–230Th–238U disequilibria of historical Kilauea lavas (1790–1982) and the dynamics of mantle melting within the Hawaiian plume. Earth and Planetary Science Letters (submitted).
Powers, H. (1955). Composition and origin of basaltic magma of the Hawaiian Islands. Geochimica et Cosmochimica Acta 7, 77–107.
Putirka, K. (1997). Magma transport at Hawaii: inferences based on igneous thermobarometry. Geology 27, 69–72.
Putirka, K., Johnson, M., Kinzler, R., Longhi, J. & Walker, D. (1996). Thermobarometry of mafic igneous rocks based on clinopyroxene–liquid equilibria, 0–30 kbar. Contributions to Mineralogy and Petrology 123, 92–108.[Web of Science]
Quane, S. L., Garcia, M. O., Guillou, H. & Hulsebosch, T. P. (2000). Magmatic history of the east rift zone of Kilauea Volcano, Hawaii based on drill core from SOH 1. Journal of Volcanology and Geothermal Research (in press).
Rhodes, J. M. (1996). The geochemical stratigraphy of lava flows sampled by the Hawaii scientific drilling project. Journal of Geophysical Research 101, 11729–11780.
Rhodes, J. M. & Hart, S. (1995). Episodic trace element and isotopic variations in historical Mauna Loa lavas: implications for magma and plume dynamics. American Geophysical Union Monograph 92, 263–288.
Roeder, P. L. & Emslie, R. F. (1970). Olivine–liquid equilibrium. Contributions to Mineralogy and Petrology 29, 275–289.[Web of Science]
Ryan, M. P., Koyanagi, R. Y. & Fiske, R. S. (1981). Modeling the three-dimensional structure of macroscopic magma transport systems. Journal of Geophysical Research 86, 7111–7129.
Salters, V. J. M. & Longhi, J. (1999). Trace element partitioning during the initial stages of melting beneath mid-ocean ridges. Earth and Planetary Science Letters 166, 15–30.[Web of Science]
Shaw, D. M. (1970). Trace element fractionation during anatexis. Geochimica et Cosmochimica Acta 34, 237–243.[Web of Science]
Shimizu, N. & Kushiro, I. (1975). The partitioning of rare earth elements between garnet and liquid at high pressures: preliminary experiments. Geophysical Research Letters 2, 413–416.[Web of Science]
Staudigel, H., Zindler, A., Hart, S. R., Leslie, T., Chen, C.-Y. & Clague, D. A., (1984). The isotope systematics of a juvenile intraplate volcano: Pb, Nd, and Sr isotope ratios of basalts from Loihi seamount, Hawaii. Earth and Planetary Science Letters 69, 13–29.
Tilling, R. I. & Dvorak, J. J. (1993). Anatomy of a basaltic volcano. Nature 363, 125–133.
Todt, W., Cliff, R. A., Hanser, A. & Hofmann, A. W. (1984). 202Pb and 205Pb double spike for lead isotopic analyses. Terra Cognita 4, 209.
Ulmer, P. (1989). The dependence of the Fe2+–Mg cation-partitioning between olivine and basaltic liquid on pressure, temperature and composition. Contributions to Mineralogy and Petrology 101, 261–273.
Ulrich, G. E., Wolfe, E. W., Heliker, C. C. & Neal, C. A. (1987). Pu’u ’O’o IV: evolution of a plumbing system. Hawaii Symposium 1987 Abstracts Volume, p. 259.
Watson, S. (1993). Rare earth element inversion and percolation models for Hawaii. Journal of Petrology 34, 763–783.
West, H. B., Gerlach, D. C., Leeman, W. P. & Garcia, M. O. (1987). Isotopic constraints on the origin of Hawaiian lavas from the Maui Volcanic complex, Hawaii. Nature 330, 216–220.
Wolfe, E. W., Garcia, M. O., Jackson, D. B., Koyanagi, R. Y., Neal, C. A. & Okamura, A. T. (1987). The Pu’u ’O’o eruption of Kilauea volcano, episodes 1 through 20, January 3, 1983, to June 8, 1984. US Geological Survey Professional Paper 1350, 471–508.
Wolfe, E. W., Neal, C. A., Banks, N. G. & Duggan, T. J. (1988). Geologic observations and chronology of eruptive events. US Geological Survey Professional Paper 1463, 1–97.
Wright, T. L. (1971). Chemistry of Kilauea and Mauna Loa lavas in space and time. US Geological Survey Professional Paper 735, 1–45.
Wright, T. L. & Fiske, R. S. (1971). Origin of the differentiated and hybrid lavas of Kilauea Volcano, Hawaii. Journal of Petrology 12, 1–65.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  J. P. Marske, M. O. Garcia, A. J. Pietruszka, J. M. Rhodes, and M. D. Norman Geochemical Variations during Kilauea's Pu'u 'O'o Eruption Reveal a Fine-scale Mixture of Mantle Heterogeneities within the Hawaiian Plume J. Petrology, July 1, 2008; 49(7): 1297 - 1318. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. O. Garcia, E. Ito, and J. M. Eiler Oxygen Isotope Evidence for Chemical Interaction of Ki lauea Historical Magmas with Basement Rocks J. Petrology, April 1, 2008; 49(4): 757 - 769. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. J. Falloon, D. H. Green, and L. V. Danyushevsky Crystallization temperatures of tholeiite parental liquids: Implications for the existence of thermally driven mantle plumes Geological Society of America Special Papers, January 1, 2007; 430(0): 235 - 260. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Norman, M. O. Garcia, and A. J. Pietruszka Trace-element distribution coefficients for pyroxenes, plagioclase, and olivine in evolved tholeiites from the 1955 eruption of Kilauea Volcano, Hawai'i, and petrogenesis of differentiated rift-zone lavas American Mineralogist, May 1, 2005; 90(5-6): 888 - 899. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. VLASTELIC, T. STAUDACHER, and M. SEMET Rapid Change of Lava Composition from 1998 to 2002 at Piton de la Fournaise (Reunion) Inferred from Pb Isotopes and Trace Elements: Evidence for Variable Crustal Contamination J. Petrology, January 1, 2005; 46(1): 79 - 107. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. GAFFNEY, B. K. NELSON, and J. BLICHERT-TOFT Geochemical Constraints on the Role of Oceanic Lithosphere in Intra-Volcano Heterogeneity at West Maui, Hawaii J. Petrology, August 1, 2004; 45(8): 1663 - 1687. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. AMMA-MIYASAKA and M. NAKAGAWA Evolution of Deeper Basaltic and Shallower Andesitic Magmas during the AD 1469-1983 Eruptions of Miyake-Jima Volcano, Izu- Mariana Arc: Inferences from Temporal Variations of Mineral Compositions in Crystal-Clots J. Petrology, December 1, 2003; 44(12): 2113 - 2138. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. O. GARCIA, A. J. PIETRUSZKA, and J. M. RHODES A Petrologic Perspective of Kilauea Volcano's Summit Magma Reservoir J. Petrology, December 1, 2003; 44(12): 2313 - 2339. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. R. THORNBER, C. HELIKER, D. R. SHERROD, J. P. KAUAHIKAUA, A. MIKLIUS, P. G. OKUBO, F. A. TRUSDELL, J. R. BUDAHN, W. I. RIDLEY, and G. P. MEEKER Kilauea East Rift Zone Magmatism: an Episode 54 Perspective J. Petrology, September 1, 2003; 44(9): 1525 - 1559. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. NAKAGAWA, K. WADA, and C. P. WOOD Mixed Magmas, Mush Chambers and Eruption Triggers: Evidence from Zoned Clinopyroxene Phenocrysts in Andesitic Scoria from the 1995 Eruptions of Ruapehu Volcano, New Zealand J. Petrology, December 1, 2002; 43(12): 2279 - 2303. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||