Geochemical characteristics of Koolau Volcano: Implications of intershield geochemical differences among Hawaiian volcanoes

Frey, Frederick A.; Garcia, Michael O.; Roden, Michael F.

doi:10.1016/0016-7037(94)90548-7

Cited by 190 publications

(161 citation statements)

References 59 publications

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“…The present model also indicates that garnet is consumed during melting, while aggregate melts retain a garnet signature. This result may help to resolve the apparent conflict between trace element abundances, which indicate garnet in the source region [Budahn and Schmitt, 1985;Frey et al, 1994], and experimental studies which indicate that some primitive Kilauea basalts are not garnet saturated at P < 3.5 GPa [Eggins, 1992].…”

Section: Discussionmentioning

confidence: 90%

Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Putirka¹

1999

J. Geophys. Res.

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Abstract. Mantle melting calculations are presented that place constraints on the mineralogy of the basalt source region and partial melting depths for oceanic basalts. Melting depths are obtained from pressure-sensitive mineral-melt partition coefficients for Na, Ti, Hf, and the rare earth elements (REE). Melting depths are estimated by comparing model aggregate melt compositions to natural basalts from Hawaii and the East Pacific Rise (EPR). Variations in melting depths in a peridotite mantle are sufficient to yield observed differences in Na/Ti, Lu/Hf, and Sm/Yb between Hawaii and the EPR.Initial melting depths of 95-120 km are calculated for EPR basalts, while melting depths of 200-400 km are calculated for Hawaii, indicating a mantle that is 300øC hotter at Hawaii. Some isotope ratios at Hawaii are correlated with Na/Ti, indicating vertical stratification to isotopic heterogeneity in the mantle; similar comparisons involving EPR lavas support a layered mantle model. Abundances of Na, Ti, and REE indicate that garnet pyroxenite and eclogite are unlikely source components at Hawaii and may be unnecessary at the EPR. The result that some geochemical features of oceanic lavas appear to require only minor variations in mantle mineral proportions (2% or less) may have important implications regarding the efficiency of mantle mixing. Heterogeneity required by isotopic studies might be accompanied by only subtle differences in bulk composition, and material that is recycled at subduction zones might not persist as mineralogically distinct mantle components. IntroductionFundamental questions in the Earth sciences concern the mineralogy of the basalt source region and the temperatures and depths at which basalts form. It has been proposed that isotopic and other compositional differences between basalts reflect mineralogical heterogeneity differentiate between heterogeneity with respect to mineralogy, isotope ratios, or differences in major or minor element composition. To examine issues of heterogeneity and the conditions of partial melting, alkalic and tholeiitic basalts from Hawaii and tholeiites from the EPR are compared. Hawaii is the type example for a mantle plume, while EPR basalts are representative of mid-ocean ridges [Langmuir, 1988]

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Section: Discussionmentioning

confidence: 90%

Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Putirka¹

1999

J. Geophys. Res.

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“…Potassium/uranium ratios can be lowered by alkali leaching during subaerial weathering [cf. Frey et al, 1994], as well as during fractionation of plagioclase or K-feldspar phases in more evolved melts. Therefore averages for individual chains were determined from literature data (compiled data available from the GEOROC Web site (http://georoc.mpch-mainz.…”

Section: Influence Of Recycled Eclogite On Estimates Of the Earth's Kmentioning

confidence: 99%

Role of recycled oceanic crust in the potassium and argon budget of the Earth: Toward a resolution of the “missing argon” problem

Lassiter¹

2004

Geochem Geophys Geosyst

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The K content of the Silicate Earth is commonly estimated at ∼250 ppm on the basis of K/U ratios of ∼12,000–13,000 in mid‐ocean ridge basalts and continental crust, and assuming a chondritic U content for the Earth. Given this K content, only ∼50% of the 40Ar generated over Earth history from the decay of 40K currently resides in the atmosphere. Because the upper mantle is thoroughly degassed and contains little 40Ar, the “missing” Ar has long been taken as evidence for a gas‐rich (and therefore convectively isolated) lower mantle. An alternative solution of the “missing Ar” problem is that the K content of the Silicate Earth is substantially lower than 250 ppm. Previous estimates have failed to take into account the composition of recycled oceanic crust, which could comprise up to 6–9% of the mantle by mass and contain up to 40% of the Earth's U. Because K is more soluble than U in subduction‐generated hydrous fluids, recycled, dehydrated oceanic crust is characterized by extremely low K/U ratios. This is evidenced in the low K/U ratios of eclogites (∼1000), and in HIMU‐type basalts (∼4000), which are thought to derive from sources containing significant quantities of recycled crust. Ocean island basalts, which are generated from mantle containing varying amounts and types of recycled material, possess highly variable K/U ratios, but average K/U ratios from individual island chains are negatively correlated with 206Pb/204Pb, indicating that the low K/U in some ocean‐island basalts is a long‐lived source feature. Inclusion of a recycled crust reservoir in K and U mass balance calculations results in an estimate of the Bulk Silicate Earth K/U of ∼7000–9000, or a K content of ∼150–195 ppm. As a result, much of the “missing” 40Ar thought to be stored in the deep mantle may not exist, with ∼60–90% of the Earth's 40Ar residing in the atmosphere or continental crust. The remaining 40Ar can be accommodated in the convecting mantle without isolation of a deep, undegassed reservoir.

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“…Roden et al (1984) provided the first modern geochemical studies of Koolau tholeiitic basalts, and Clague and Frey (1982) reported the compositional details of the Honolulu Volcanics. Stille et al (1983), Frey et al (1994), Roden et al (1994), Lassiter and Hauri (1998), and Jackson et al (1999) addressed the trace-element and isotopic compositions of the Koolau tholeiitic shield from exposures in the upper several hundred meters of the southeastern shield, and Tanaka et al (2002) examined submarine landslide blocks. Finally, Garcia (2002) showed that abundant picritic shield lavas occupy the submarine flank of Koolau.…”

Section: Background Information and Samplingmentioning

confidence: 99%

“…It comes from Makapuu Point on eastern Oahu (Fig. 1), a region thoroughly analyzed by Frey et al (1994).…”

Section: Background Information and Samplingmentioning

confidence: 99%

Koolau shield basalt as xenoliths entrained during rejuvenated-stage eruptions: perspectives on magma mixing

Weinstein

Fodor

Bauer³

2004

Bulletin of Volcanology

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Rejuvenated-stage tuff cones (Honolulu Volcanics) on Koolau volcano, Oahu, Hawaii, contain xenoliths of Koolau shield basalt. Because Koolau subaerial shield lavas represent a Hawaiian geochemical 'end member', and submarine shield lavas have compositions with some affinities to Mauna Loa and Kilauea, we analyzed 28 xenolithic basalts from Salt Lake and Koko Head cones to determine how these seemingly random samplings of the Koolau profile compare to established Koolau geochemistry. Analyses reveal that 24 are shield tholeiitic basalt-the focus of this study-and 4 are rejuvenated-stage basaltic rocks. The tholeiitic xenoliths represent largely upper Koolau shield lavas, as these samples (8.3 to 5.8 wt% MgO) have, with one exception, overall major-and trace-element compositions that overlap those of Koolau subaerial shield lavas. Secondary processes, however, created some distinctions-namely, enrichments/depletions in K, Ba, Sr, SiO 2 , and FeO, and, due to zeolitization (chabazite with attending okenite and apophyllite), elevated CaO. One xenolithic basalt with 8.2 wt% MgO has higher Ti, Zr, Nb, and Sc, and lower Zr/Nb than subaerial lavas, and appears to represent relatively early, deeper shield-thereby reinforcing that the Koolau shield source varied temporally. Olivine, orthopyroxene, and plagioclase are the phenocrysts (clinopyroxene is rare), and their core compositions range widely across the suite-Fo 87.872 , orthopyroxene Mg#s 85-72, and An 74-60 . Several xenolithic basalts have both normally and reversely zoned orthopyroxene and plagioclase with a variety of core compositions (e.g., orthopyroxene-core Mg#s 82, 77, and 72, all in one sample). These compositions and zonations record evidence for wide compositional ranges of replenishment (MgO~13-8 wt%) and reservoir (MgO~7 to <5 wt%) magmas mixing in varying proportions; however, extreme MgO lavas (~13 and <5 wt%) are not observed as either subaerial or xenolithic basalt, but are indicated by phenocryst cores of Fo 87.8 and orthopyroxene-Mg# 72. The Koolau magma-mixing history resembles that of Kilauea, and is unlike the 'steady-state' mixing known for Mauna Loa. Finally, these basalt samples show that any xenolithic occurrence of Koolau lava is subject to the zeolitization prevalent in the tuff-cone hosts.

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Geochemical characteristics of Koolau Volcano: Implications of intershield geochemical differences among Hawaiian volcanoes

Cited by 190 publications

References 59 publications

Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Melting depths and mantle heterogeneity beneath Hawaii and the East Pacific Rise: Constraints from Na/Ti and rare earth element ratios

Role of recycled oceanic crust in the potassium and argon budget of the Earth: Toward a resolution of the “missing argon” problem

Koolau shield basalt as xenoliths entrained during rejuvenated-stage eruptions: perspectives on magma mixing

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