| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Journal of Petrology Volume 41 Number 5 Pages 667-691 2000
© Oxford University Press 2000
Volcanism at the Edge of the Hawaiian Plume: Petrogenesis of Submarine Alkalic Lavas from the North Arch Volcanic Field
1DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA 02139-4307, USA
2MONTEREY BAY AQUARIUM, RESEARCH INSTITUTE, MOSS LANDING, CA 95039-0628, USA
3SCHOOL OF OCEAN AND EARTH SCIENCE AND TECHNOLOGY, UNIVERSITY OF HAWAII, HONOLULU, HI 96822, USA
Received August 15, 1998; Revised typescript accepted October 28, 1999
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Submarine lavas erupted onto the Hawaiian arch 200–400 km north of Oahu show that the areal extent of Hawaiian volcanism is much larger than previously recognized. The North Arch volcanic field comprises 25 000 km2 of
0·5–1·15 Ma, volatile-rich, olivine-phyric alkalic lavas (alkalic basalt to nephelinite). These lavas are similar in composition to rejuvenated-stage lavas such as the Koloa Volcanics (Kauai) and Honolulu Volcanics (Oahu). North Arch lavas that encompass the compositional extremes have similar Sr, Nd and Pb isotopic ratios. Olivine accumulation and fractionation was the major post-melting process that affected the compositions of North Arch lavas. After correction for these processes, the inferred primary magma compositions show that they were derived by variable, factor of four, and relatively low extents of melting of garnet peridotite. Garnet and olivine were important residual phases during partial melting; in contrast to the Honolulu Volcanics, there is little evidence for residual hydrous phases, sulfides or Fe–Ti oxides. The mantle source for the North Arch lavas had Sr, Nd and Pb isotopic ratios intermediate between those of Pacific Ocean lithosphere and the inferred range for Hawaiian plume components. These data are consistent with a mixed lithosphere–plume source. Although the plume-derived component was probably from the Hawaiian plume, an alternative hypothesis is that during the middle Cretaceous, South Pacific lithosphere was contaminated by plumes that formed large oceanic plateaux (e.g. Ontong Java). This mixed source was subsequently partially melted as it passed near the Hawaiian plume. KEY WORDS: Hawaiian plume; North Arch; alkalic lavas; radiogenic isotopes; igneous geochemistry
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
The age progression of the volcanic chain forming the Hawaiian Ridge is consistent with the mantle plume hypothesis whereby the Pacific plate moves to the northwest over a hotspot fixed in the mantle (e.g. Clague & Dalrymple, 1987
). Moreover, as the site of an individual volcano approaches, overrides and moves away from the hotspot, a Hawaiian volcano evolves through a well-known sequence of stages (e.g. Clague & Dalrymple, 1987). The bulk of a Hawaiian volcano is tholeiitic basalt erupted during the shield-building stage when the volcano overlies the hotspot, but volcano growth begins and ends with alkalic volcanism; i.e. an early alkalic stage and a late alkalic rejuvenated (post-erosional) stage (Clague & Dalrymple, 1987). In addition to this well-established temporal change in lava composition, there is also a spatial control on lava composition (Wyllie, 1988; Clague et al., 2000). Specifically, alkalic submarine lavas are erupted on the flexural arch that surrounds the recently formed islands (Lipman et al., 1989; Clague et al., 1990). This arch and an associated trough closer to the islands (Fig. 1) result from lithosphere flexure caused by the volcanic loading of the Hawaiian volcanoes (Hamilton, 1957; Moore, 1987). Dredging in the vicinity of the arch has recovered alkalic lavas from water depths of 4–5 km in front of the plume track (the 14–20 ka lavas on the South Arch; Lipman et al., 1989; Clague et al., 2000) and along the north side of the plume track (the 0·5–1·15 Ma alkalic lavas covering 25 000 km2 north of Oahu, known as the North Arch field; Clague et al., 1990; Dixon et al., 1997). Age estimates for South Arch lavas are based on palagonite thickness; for North Arch lavas they are based on palagonite thickness and thickness of the overlying sediments. Although not voluminous relative to the volcanoes, the total area of alkalic volcanism discovered on the submarine arch greatly exceeds that of alkalic lavas exposed on nearby islands. The estimated 0·5–1·15 Ma age range for North Arch lavas overlaps with the younger part of the age range of rejuvenated-stage lavas on Kauai (3·65–0·52 Ma, Clague & Dalrymple, 1988) and Niihau (3·5–0·35 Ma, Clague & Dalrymple, 1987), and with the inferred age of rejuvenated-stage lavas erupted on the Koolau shield of Oahu (<1 Ma, Clague & Frey, 1982).
|
The major element compositions of these submarine alkalic lavas are broadly similar to those of the lavas forming the rejuvenated stages at Kauai (Koloa Volcanics), Niihau (Kiekie Basalt), and Koolau (Honolulu Volcanics) volcanoes (Lipman et al., 1989; Clague et al., 1990, 2000). These rejuvenated-stage lavas, ranging from alkalic basalt to nephelinite and melilitite, are characterized by the paradoxical features of a ‘depleted’ Sr and Nd isotopic signature (i.e. long-term evolution with relatively low Rb/Sr and high Sm/Nd), with high abundances of incompatible elements, including relatively high Rb/Sr and low Sm/Nd (Clague & Frey, 1982; Stille et al., 1983; Feigenson, 1984; Roden et al., 1984; Clague & Dalrymple, 1988; Maaloe et al., 1992; Reiners & Nelson, 1998). Chen & Frey (1983, 1985) proposed that: (1) the combination of incompatible element enrichment in lavas with a ‘depleted’ isotopic signature is best explained by low extents of melting of MORB (mid-ocean ridge basalt) related mantle; (2) the transition from tholeiitic shield to alkalic rejuvenated-stage volcanism is explained by a mixing model whereby the ratio of depleted (MORB source) to plume components increases as the volcano ages; i.e. the tholeiitic shield is largely derived from plume components, but important geochemical characteristics of rejuvenated-stage lavas are controlled by melts formed by low extents of melting of depleted (MORB-related) mantle.
Several types of mixing models have been evaluated for rejuvenated stage lavas. Roden et al. (1984) favored solid–melt mixing, and they suggested that the sources for the Honolulu Volcanics formed by mixing melts from a depleted wallrock (MORB-source) with the ascending plume. Specifically, they proposed that these mixed sources contain 2·5% of a melt derived from a MORB source by 0·3% melting; the limited isotopic variability of the Honolulu Volcanics indicates that the mixing process was efficient. Subsequently, this source was melted to varying extents to create alkalic lavas ranging from alkali olivine basalt to nephelinite and melilitite. Although the Koloa Volcanics are more heterogeneous in isotopic ratios than the Honolulu Volcanics (Reiners & Nelson, 1998), very similar petrogenetic models have been proposed. Feigenson (1984) and Clague & Dalrymple (1988) favored models involving mixing of melts derived from the plume by relatively large extents of melting with melts derived from a MORB source by much smaller extents of melting. In a recent study of the Koloa Volcanics, Reiners & Nelson (1998) suggested that variable amounts of melts formed by 0·1% melting of a MORB source infiltrate the ascending plume and form a heterogeneous metasomatized source. The Koloa Volcanics were subsequently formed by variable extents of melting that correlated with the degree of metasomatism.
Mixing is a process common to all of these hypotheses. A plausible physical setting for mixing is near the contact of an ascending plume with entrained asthenosphere or the overlying oceanic lithosphere. Maaloe et al. (1992) independently evaluated mixing models for the Koloa Volcanics, and concluded that a mixing model similar to that of Chen & Frey (1985) could explain the geochemical characteristics of the Koloa Volcanics. However, they also proposed an alternative model whereby the alkalic Koloa lavas are representative of the Hawaiian plume. This alternative model for rejuvenated-stage lavas is not consistent with the presence of geochemically similar alkalic lavas at the periphery of the plume.
Although submarine lavas erupted on the Hawaiian arch share some important characteristics with subaerial rejuvenated-stage lavas erupted on the Kauai and Koolau shields, there are important differences. First, the margins of submarine lavas were quenched to form glassy rinds. All of these glasses are degassed, but some with relatively high volatile (H2O, CO2, S, and Cl) contents were nearly closed systems with the degassed volatiles largely retained in the vesicles (Dixon et al., 1997). Second, the submarine arch lavas have not been affected by post-magmatic subaerial alteration, which leads to mobility of K and Rb in subaerial Hawaiian lavas (e.g. Frey et al., 1994). Therefore in the submarine lavas these elements can be used to evaluate the role of residual amphibole and phlogopite during melt segregation (e.g. Clague & Frey, 1982; Francis & Ludden, 1995; Späth et al., 1996; Class & Goldstein, 1997).
Dixon et al. (1997) concluded that lavas from the North Arch field evolved from parental magmas formed by variable extents of melting of a compositionally homogeneous source. During ascent olivine was fractionated (maximum of 34%) and partial degassing occurred upon eruption at 400 bar. Our goal in this paper is to use olivine and whole-rock compositions and isotopic ratios of Sr, Nd, Pb and He in the North Arch lavas to determine the mineralogy and composition of their source and to understand the partial melting process. To understand the processes leading to alkalic volcanism at the periphery of the Hawaiian hotspot, we compare the petrogenesis of North Arch alkalic lavas erupted 200–400 km north of the Koolau shield with that of the alkalic lavas erupted during the rejuvenated stage on the islands.
|
SAMPLING AND ANALYTICAL PROCEDURES |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Samples studied
The samples analyzed are four glasses and 23 whole rocks from 15 dredge locations in the North Arch field (Fig. 1). These rocks are associated with the glasses studied by Clague et al. (1990)
and Dixon et al. (1997).
Whole rocks
Major element analyses were obtained by X-ray fluorescence (XRF) at the US Geological Survey and were reported in table 3 of Clague et al. (1990). Abundances of V, Ni, Cu, Zn, Rb, Sr, Ba, Y, Zr and Nb (Table 1) were determined by XRF at the University of Hawaii following the procedures of Norrish & Chappell (1967). Abundances of Sc, Cr, Co, Cs, La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta and Th (Table 1) were determined by instrumental neutron activation analysis at the Massachusetts Institute of Technology following the procedures of Ila & Frey (1984).
|
Glasses
Sr, Nd and Pb isotopic ratios were determined and isotope-dilution measurements of Nd, Sm, Sr, Rb and Pb abundances were made at the University of Hawaii. The samples analyzed were 10–30 mg of glass, handpicked with the aid of a microscope for freshness and absence of phenocrysts. Following ultrasonic cleaning of these glasses in 2 M HCl and ultrapure water, chemical preparation and mass spectrometric procedures were similar to those described by Mahoney et al. (1991). The results are presented in Table 2 with information on analytical uncertainties, blanks, standard reference values, and the fractionation corrections employed.
|
Minerals
Minerals were analyzed on an SEMQ electron microprobe at the US Geological Survey in Menlo Park using natural and synthetic standards, 15 kV accelerating voltage, beam current of 15–30 nA, and a focused beam with a diameter of 1 µm. Representative analyses are presented in Table 3a–c.
|
|
RESULTS FOR NORTH ARCH LAVAS |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Petrography and mineral compositions
Major element abundances were determined for 345 olivine, 55 chromite and 22 augite crystals from 34, 26 and four samples, respectively. Most of the samples contain only skeletal to euhedral microphenocrysts of olivine (from <1 to 15%) that usually enclose very small euhedral chromite crystals. Minor amounts of kink-banded olivines, usually as angular crystal fragments, occur in 13 of the 36 flow units. Olivine xenocrysts are identified by these kink-bands or by low CaO contents [<0·20 wt %; see discussion by Clague & Denlinger (1994)
], although not all kink-banded crystals have low CaO contents. The olivine microphenocrysts and xenocrysts are usually smaller than 0·5 mm, with the largest 1 mm.
The olivine phenocrysts range from Fo80·7 to Fo87·8 (Fo is forsterite content). With increasing Fo, NiO increases from 0·13 to 0·39 wt % and CaO decreases from 0·69 to 0·17 wt %. At a given Fo content, especially in the range Fo80–85, the Ni abundances of North Arch olivine phenocrysts increase as the SiO2 content of the host glass increases (Fig. 2a). This trend is continued by the higher Ni contents of olivine phenocrysts in the more SiO2-rich Kilauea tholeiites (Fig. 2a). This general trend for the NiO content of olivine, at a given Fo content, to increase as the SiO2 content of the melt increases is consistent with a thermodynamic analysis of experimental data for Ni partitioning between olivine and silicate melt (Hirschmann & Ghiorso, 1994).
|
The inverse CaO–Fo trends for each lava type (i.e. alkalic basalt to nephelinite as indicated by the SiO2 groups in Fig. 2a) reflect the dependence of the olivine–melt partition coefficient for CaO on the activity of iron [see fig. 4 of Jurewicz & Watson (1988)
]. However, in Kilauea tholeiitic basalts CaO contents of olivine phenocrysts are independent of Fo content (Fig. 2a). At a given Fo content the increase of CaO in olivine from alkalic basalt to nephelinite reflects the concomitant increase in the CaO content of the melts.
The xenocryst cores form two compositional ranges: Fo86–92 and Fo76–79, with the rims on most kink-banded and low-CaO crystals having compositions similar to those of the phenocrysts in the same sample (Fig. 2b). The most forsteritic xenocrysts (>Fo90) average 0·38 wt % NiO, similar to the average olivine for lherzolite xenoliths from Hawaii (e.g. Goto & Yokoyama, 1988) and around the world (Carter, 1970). Most of these xenocrysts have cores that range from 0·01 to 0·11 wt % CaO (Fig. 2b). The low-forsterite xenocrysts average 0·14 wt % NiO and contain 0·02–0·05 wt % CaO. The high-forsterite xenocrysts are almost certainly broken crystal fragments from lherzolitic upper-mantle rocks whereas the low-forsterite xenocrysts are probably crystal fragments from recrystallized ocean crust layer 3 gabbro, as described by Clague et al. (1995) for a single small xenolith in the 1960 Kapoho lava from Kilauea Volcano, and by Clague & Chen (1986) for some two-pyroxene xenoliths from Hualalai Volcano. The presence of olivine xenocrysts from mantle lherzolite and ocean crust gabbro indicates rapid magma migration from mantle depths to eruption on the sea floor.
Chromite has a wide range of compositions, with Cr2O3 varying from 21·8 to 36 wt %, Al2O3 from 11·8 to 23·3 wt %, MgO from 15·7 to 10·5 wt %, FeO* (i.e. all iron as Fe2+) from 23·8 to 44·1 wt %, mg-number [100 x atomic Mg/(Mg + Fe) using the inferred stoichometric FeO contents from Table 3b] from 48·6 to 69·5, and TiO2 from 1·0 to 5·2 wt %, although 50 of 55 analyzed chromite crystals have TiO2 < 3·5 wt %. There are broad positive correlations of mg-number and Cr2O3 and Al2O3 content, and broad negative correlations of mg-number and Fe2O3 and TiO2. Thus, with decreasing mg-number, the ulvöspinel component of the spinel increases. There are broad positive correlations of mg-number in spinel and mg-number of the host glass and a better correlation of mg-number in spinel with Fo content of the host olivine. The spinels are cognate, and they were the first phase to crystallize.
Augite occurs in basanite and alkalic basalt samples from four flows (15D, 18D, 36D-a, and 37D) with glass MgO contents of 5·7–6·4 wt %, but is absent in nephelinite to alkalic basalt glasses with >6·4 wt % MgO. This indicates that augite joins olivine on the liquidus in these alkalic lavas at 6·4 wt % MgO. Augite varies in mg-number from 84 to 74·5, with TiO2 (0·9–2·9 wt %), Al2O3 (2·5–7·0 wt %), Na2O (0·29–0·43 wt %) and the Wo component (46·2–50·0 %) increasing, and SiO2 (51·4–45·6 wt %) decreasing with decreasing mg-number. There is no systematic relation between Cr2O3 and mg-number, nor between mg-number in augite and that in the host glass. Many of the augite crystals are slightly too magnesian to be in equilibrium with their host glasses using an Fe/Mg KD = 0·25 (Grove & Bryan, 1983; KD = (Fe/Mg)augite/(Fe/Mg)glass with all Fe as Fe2+).
Whole rocks—major element abundances
The major element abundances of glasses and associated whole rocks from the North Arch were reported by Clague et al. (1990). All of these lavas are alkalic; e.g. the 143 North Arch glasses analyzed by Clague et al. (1990), representing 36 distinct flow units, range in normative nepheline from 2·1 to 23%. Among the whole rocks analyzed, the extremes are sample 23-6 with 41·5 wt % SiO2 and 5·2 wt % (Na2O + K2O) and sample 22-2 with 47·1 wt % SiO2 and 3·0 wt % (Na2O + K2O); these two samples also have the highest (23-6) and lowest (22-2) abundances of Na2O, K2O, TiO2 and P2O5 (Fig. 3a). Both samples are from the central portion of the North Arch field (Fig. 1).
|
, calculated by incremental (1%) olivine addition to be in equilibrium with Fo91]. It should be noted that in the panels for Na2O, K2O, CaO, TiO2 and P2O5 there is a group of eight lavas (only six in TiO2 panel) with higher abundances of these oxides. These are lavas from Dredges 23, 24, 26 and 27. The measured Al2O3–MgO trend extrapolates to MgO 45·6 at 0% Al2O3. This corresponds to olivine of Fo85·6. 
, 
, measured and calculated data for submarine South Arch lavas, respectively (Clague et al., 2000The whole rocks range in MgO from 6·3 to 14·0 wt %, with 18 of 23 samples having >9·5 wt % MgO and only three samples having <7·2 wt % MgO. Clague et al. (1990)
concluded that olivine was the only silicate phase to crystallize from North Arch samples with >6·4 wt % MgO. Addition of 6–26 wt % olivine (in 1% increments of equilibrium olivine until the liquidus olivine is Fo91) to the observed whole-rock compositions leads to inferred parental magma compositions having 14–18 wt % MgO, which would be in equilibrium with olivine of Fo91 [Table 4; also see Dixon et al. (1997), for a similar calculation based on glass compositions]. In MgO variation plots the whole-rock compositions define scattered but inverse trends of Na2O, CaO, Al2O3 and TiO2 abundances vs MgO content (Fig. 3a). After addition of olivine to achieve a lava composition in equilibrium with Fo91 olivine, these trends, including those for K2O and P2O5 vs MgO, are better defined (Fig. 3a). The Al2O3–MgO trend is an exception; after olivine addition the Al2O3 content ranges from 10·3 to 11·9 wt %, but it is not correlated with MgO content (Fig. 3a).
|
Although in MgO–major oxide variation plots the North Arch lavas generally overlap with the fields for the rejuvenated-stage lavas at Kauai (Koloa Volcanics) and Koolau (Honolulu Volcanics), there are some important differences (Fig. 3b). Most of the lavas in these two rejuvenated stages are characterized by relatively high, >12 wt %, MgO contents. Relative to the North Arch lavas in the range of 10–14 wt % MgO, the fields defined by the Koloa and Honolulu Volcanics extend to much lower SiO2 contents (i.e. melilite-bearing lavas) than the North Arch lavas (Fig. 3b). Also, the Honolulu Volcanics field extends to higher P2O5 and Na2O content, and the Honolulu Volcanics and especially the Koloa Volcanics extend to higher TiO2 contents. In contrast to these differences, which reflect differences in magma composition, the extension of the fields for the Koloa and Honolulu Volcanics to lower CaO and Na2O contents (Fig. 3b) reflects the effects of post-magmatic, subaerial alteration (e.g. Clague & Frey, 1982).
Whole rock—trace element abundances
Abundances of Cr, Ni and Co are positively correlated with MgO content whereas abundances of Zn, Sc and V are inversely correlated (Fig. 4). The Koloa and Honolulu Volcanics also define positive trends of Ni, Cr and Co abundances vs MgO content, but their trends show much more scatter than the North Arch data. The increased scatter of these subaerial rejuvenated-stage lavas is even more apparent in the Zn, Sc and V vs MgO trends. We suspect that the scatter of the rejuvenated-stage lavas arises from three sources: (1) post-magmatic subaerial alteration; (2) imprecise data; (3) possibly variable source composition, especially for the Koloa lavas, which are isotopically heterogeneous (Reiners & Nelson, 1998).
|
Abundances of the incompatible elements Th, Ba, La, Ce, Sr and P are positively correlated in the North Arch lavas, and very similar trends are defined by the North Arch lavas and the rejuvenated-stage Koloa and Honolulu Volcanics (Fig. 5). All North Arch lavas have steep negative trends in chondrite-normalized rare-earth element (REE) plots (Fig. 6). Abundances of La range from 44x to 140x chondrites whereas Yb and Lu abundances range only from 5·0x to 7·8x chondrites. The lowest abundances of light REE (LREE), and all other highly incompatible elements, are in sample 22-2, but this sample has relatively high heavy REE (HREE) abundances. In contrast, sample 23-6 is the most enriched in highly incompatible elements, including LREE, and it has the lowest HREE content. These features lead to crossing REE patterns (Fig. 6).
|
|
Glasses—isotopes
Isotopic ratios of Nd, Pb, and Sr were analyzed for four North Arch glasses, including the compositionally extreme samples 22-2 and 23-6 (Figs 3a, 5 and 6). These two samples define the very small range of the four glasses in 143Nd/144Nd and 206Pb/204Pb (Table 2). The glasses display a very limited range in Sr and Nd isotopes, with 87Sr/86Sr = 0·70304–0·70311 and 143Nd/144Nd = 0·513062–0·513091, corresponding to 
Nd = +8·2 to +8·8. As shown in Fig. 7a, like the subaerial rejuvenated-stage lavas, the submarine lavas are offset from shield-stage lavas to much lower 87Sr/86Sr and higher 143Nd/144Nd; i.e. they occupy a region between the field for South Pacific MORB [note that the sea floor in the Hawaiian region was formed in the South Pacific during the middle Cretaceous; e.g. Waggoner (1993) and references therein] and fields for the various Hawaiian shields. This offset towards the MORB field has been used to argue that depleted mantle was a component in the source of rejuvenated-stage lavas (e.g. Chen & Frey, 1985; West et al., 1987). Significantly, the 87Sr/86Sr ratios of the North Arch and rejuvenated-stage lavas are shifted to values (3–5) x 10–4 higher, at Nd of +8 to +9, than those of modern Pacific MORB (see Basu & Faggart, 1999).
|
, results for two lavas dredged from the channel between Kauai and Oahu (Clague et al., 2000The North Arch glasses have only a small range in Pb isotopic ratios (Fig. 7c). For example, 206Pb/204Pb varies only by 0·098, from 18·142 to 18·240. The North Arch Pb isotopic field overlaps with that of the Honolulu, Hana and Lahaina Volcanics, and it is slightly above the Pacific MORB field in Fig. 7c. In the
Nd (and 87Sr/86Sr) vs 206Pb/204Pb diagram (Fig. 7b), the North Arch data lie between the fields for modern Pacific MORB and Hawaiian shield volcanoes. An important observation is that the Hawaiian alkalic suites are typically more homogeneous in isotopic ratios than the nearby shields [e.g. compare the fields for the Honolulu Volcanics and Koolau shield (Fig. 7)]. If a plume component contributes to the source of the alkalic lavas, it is more homogeneous than the sources contributing to the tholeiitic shield lavas.
The 3He/4He ratios of vesicle gases (i.e. in crushed rather than heated samples) in nine North Arch glasses range from 1·3 to 8·5 times the atmospheric ratio (Dixon et al., 1997). The two lowest ratios, 1·3 and 2·2, are in the two high-K2O glasses with the lowest He content (Fig. 8); thereby suggesting radiogenic ingrowth of 4He in the vesicle gases of these samples. Ratios for the other seven North Arch glasses range from 5·3 to 8·1 times the atmospheric 3He/4He ratio. The highest value overlaps with the range (7·8–8·2) of three rejuvenated-stage lavas from Haleakala (Kurz et al., 1987), and is similar to the typical value for MORB (Kurz et al., 1998). However, two South Arch lavas have much higher 3He/4He (Fig. 8), thereby providing evidence for a plume-derived component.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
North Arch lavas: post-melting processes
The diversity of North Arch lava compositions, alkalic basalt to nephelinite, coupled with their near homogeneity in Sr, Nd and Pb isotopic ratios, is consistent with the hypothesis that these lavas formed by varying extents of melting of a geochemically homogeneous source. Before assessing in detail the compositional effects of different extents of melting, it is necessary to determine the effects of post-melting processes on lava compositions. The compositions and petrography of North Arch lavas clearly show that accumulation and fractionation of olivine were important post-melting processes. Although the petrographic characteristics of olivine are complex, the correlation between glass and olivine compositions shows that the olivine phenocrysts were in equilibrium with the host melt (Fig. 2).
A significant amount of the compositional variation of North Arch lavas can be explained by olivine fractionation and accumulation. Figure 3a shows that much of the scatter in MgO variation plots is reduced to coherent trends by correcting for the effects of olivine fractionation. An alternative approach is to evaluate the effects of olivine addition, i.e. variable mixing proportions of magma and olivine of constant composition. For example, extrapolation of the linear MgO–Ni trend (Fig. 4) of the lavas intersects the center of the olivine phenocryst field at 45·6 wt % MgO (Fo85·6). Addition of Fo85·6 olivine is also consistent with extrapolation of the measured inverse trend between Al2O3 and MgO abundances (Fig. 3a). Compositional control by olivine with chromite inclusions is also consistent with the positive correlations among abundances of CaO, Na2O, K2O, TiO2 and P2O5 [see Fig. 3a, and fig. 4 of Clague et al. (1990)], the positive MgO–Cr trend, and the modest increases (20–30%) of Zn, Sc and V abundances with decreasing MgO content [Fig. 4; i.e. the partition coefficient between melt and olivine with chromite inclusions is >1 for Cr but between 0·1 and 1 for Zn, Sc and V (e.g. Beattie, 1994)]. Dixon et al. (1997) concluded that at eruption conditions some of the North Arch lavas were saturated with an immiscible Fe–S–O liquid. Zinc (Fig. 4) and Cu abundances, although widely scattered, increase with decreasing MgO, thereby providing no evidence for control of these elements by an immiscible sulfide melt during crustal evolution.
Another post-melting process that can significantly affect lava compositions is post-magmatic alteration. It is well known that exposure in a subaerial Hawaiian environment can lead to significant compositional changes in <1 Ma lavas (e.g. Clague & Frey, 1982; Frey et al., 1994). Earlier, we attributed the anomalously low CaO and Na2O contents of some rejuvenated-stage lavas to such alteration (Fig. 3b). Another manifestation of subaerial alteration in rejuvenated-stage lavas is the broad tendency for K2O/P2O5 to decrease with increasing volatile content, thereby showing the relative loss of K2O that typically occurs during subaerial alteration of Hawaiian lavas (Fig. 9). In contrast, K2O/P2O5 is not correlated with H2O content in the submarine North Arch lavas (Fig. 9).
|
North Arch lavas: constraints on the melting process
Melting reaction and range in extent of melting
Important aspects of the major oxide abundance variations cannot be explained by olivine control. Notably, incremental addition of equilibrium olivine to achieve lava compositions in equilibrium with Fo91 olivine does not result in a nearly uniform composition (Fig. 3a). The choice of Fo91 is arbitrary; normalization to other Fo contents does not affect our subsequent conclusions. These adjusted compositions, however, show systematic compositional variations; specifically, they define inverse correlations between MgO content and abundances of Na2O, K2O, TiO2 and P2O5, with the highest abundances of these typically incompatible oxides in the eight lavas from dredges 23, 24, 26 and 27 (Fig. 3a). These eight lavas also have the highest CaO/Al2O3, the highest abundances of CaO and incompatible trace elements, such as Rb, Nb and Th, and the lowest SiO2 contents (<43 wt %) (Figs 3a, 5 and 10). These samples were all recovered from small hills, interpreted as vents, rather than from the areally extensive horizontal flows. The Koloa Volcanics (Clague & Dalrymple, 1988; Maaloe et al., 1992), Honolulu Volcanics (Clague & Frey, 1982) and North Arch lavas show the same compositional trends; samples with the highest content of incompatible elements define the low SiO2, high CaO and high CaO/Al2O3 end of the compositional spectrum (Fig. 10a and b).
|
Given the very limited isotopic variability of the North Arch lavas (Fig. 7), we assume a homogeneous source composition (relative to the scale of melting) for all North Arch lavas. With this assumption, the factor of 3–4 range in abundance of highly incompatible elements, such as Rb, Nb and Th, in the North Arch lavas (adjusted to be in equilibrium with Fo91) indicates approximately a factor of four range in extent of melting. Based on the trend in Fig. 10b, melts formed at the lowest extents of melting are largely derived from SiO2-poor phases, such as olivine and garnet. The trend of decreasing CaO/Al2O3 with increasing extent of melting (Fig. 10a) is consistent with melt segregation in the garnet stability field [see Kinzler (1997), p. 873]. However, if a compositionally similar source is assumed for the Honolulu Volcanics and North Arch lavas, it is apparent that none of the Arch lavas were derived by the very low extent of melting that created the highly SiO2-undersaturated and Th-rich nepheline melilitites in the Honolulu Volcanics (Fig. 10b).
Clague & Frey (1982) summarized the early experimental evidence that highly SiO2-undersaturated lavas, such as the Honolulu Volcanics, are generated in the presence of CO2. Subsequent experimental studies have confirmed an important role for CO2 in generating the compositional characteristics of alkalic lavas (e.g. Adam, 1988). Most recently, Hirose (1997) using the diamond aggregate experimental approach showed that with increasing extent of melting of carbonated peridotite, abundance of SiO2 increases, CaO decreases and Al2O3 is relatively constant; i.e. producing trends similar to those of the North Arch and rejuvenated-stage lavas (Fig. 10a and b). Dixon et al. (1997) estimated that the vesicular vent samples from dredges 24 and 26 contained 5 wt % CO2, and they suggested that the mantle source contained 0·1–0·2 wt % CO2.
Important residual minerals
The compositional data for North Arch lavas provide constraints on the residual minerals that controlled primary magma compositions. Most notably, there is compelling evidence for garnet as an important residual phase. First, Al2O3 was not an incompatible oxide during partial melting. This is evident from the limited variation in Al2O3 content of the lava compositions calculated to be in equilibrium with Fo91 olivine; that is, the variable measured Al2O3 content of the erupted lavas resulted from olivine accumulation or fractionation (Fig. 3a). The compatible behavior of Al2O3 is also manifested by the absence of a positive correlation between Al2O3 and P2O5 abundances in the glasses [fig. 4 of Clague et al. (1990)] and adjusted whole-rock compositions (Fig. 3a). Finally, the positive correlation between Th content and CaO/Al2O3 (Fig. 10a) is explained because Th and CaO abundances decrease with increasing extent of melting whereas Al2O3 content was buffered by residual garnet (e.g. Hirose, 1997; Kinzler, 1997; Walter, 1998). Residual garnet is also implied by the crossing chondrite-normalized REE patterns (Fig. 6) and the positive trend between Tb/Yb and Th content (Fig. 10c). This inference for residual garnet based on REE abundances is consistent with the CaO/Al2O3 variation in North Arch lavas; i.e. sample 23-6 with relatively low HREE contents, high Tb/Yb, and high CaO/Al2O3 formed in equilibrium with residual garnet whereas sample 22-2, which has the lowest CaO/Al2O3 (similar to that of primitive mantle), lacks, or has a much smaller, residual garnet signature (Fig. 10a and c).
In contrast to the results for tholeiitic shield lavas (e.g. Hofmann et al., 1984), the normalization of North Arch lava compositions to a uniform olivine composition does not lower the dispersion of HREE contents; most notably, the eight North Arch lavas with the highest abundances of incompatible elements (lavas from dredges 23, 24, 26 and 27) define the maximum and minimum in Yb content (Fig. 10d). We infer that garnet was an important residual phase during generation of the North Arch lavas, but if the sources for these lavas had a similar Yb content, the proportion of residual garnet was not a simple function of extent of melting.
We also infer that olivine was a major residual phase. Clague & Frey (1982) presented the case for an olivine-rich source for the Honolulu Volcanics. Similar arguments are valid for North Arch lavas. They are:
- as expected of magmas derived from an olivine-rich source, North Arch lavas with >6·5% MgO are olivine-phyric, with phenocrysts ranging to Fo87·8. Moreover, the major element compositions of the lavas, after adjustment to be in equilibrium with a common olivine composition, are broadly consistent with derivation by low and variable extents of melting of garnet lherzolite (e.g. Table 4; Longhi, 1997; Walter, 1998). In particular, the decrease in CaO content with increasing extent of melting (i.e. the trend expected for an incompatible element) that is defined by North Arch lavas is a characteristic feature of partial melts of garnet peridotite (e.g. Hirose, 1997; Kinzler, 1997). As an aside, this trend contrasts with that for partial melts of spinel peridotite (e.g. Kinzler & Grove, 1992; Langmuir et al., 1992), and is further evidence for residual garnet. Although partial melting of pyroxenites has not been thoroughly studied (Hirschmann & Stolper, 1996), CaO is more likely to behave as a compatible oxide during partial melting of a clinopyroxene-rich source (Yasuda et al., 1994; Kogiso et al., 1998).
- Abundances of first transition series elements in North Arch lavas are also consistent with derivation from an olivine-rich source. For example, the Ni contents of North Arch lavas with 10–14 wt % MgO range from 300 to 475 ppm, which is consistent with an olivine-rich residue (Hart & Davis, 1978). Also, Chauvel et al. (1992) quantitatively evaluated melting of a mixed source of peridotite and recycled oceanic crust. They concluded that >70% peridotite is required to generate the high Ni and Cr (>300 ppm) typical of MgO-rich alkalic lavas, such as the North Arch lavas (Fig. 4). Although not as diagnostic as Ni, Zn is also preferentially incorporated into olivine relative to pyroxene and garnet; the Zn olivine–melt partition coefficient is 0·9–1 (Doe, 1995). By plotting Nb/Zn vs Nb for North Arch lavas and following the procedures of Clague & Frey (1982), we estimate a Zn bulk solid–melt partition coefficient of 0·4. This estimate is also consistent with an olivine-rich source.
As with abundances of the incompatible oxides Na2O, K2O, TiO2 and P2O5 in the North Arch lavas, a large abundance range for incompatible trace elements, e.g. Nb and Th, characterizes both the measured data and the compositions calculated to be in equilibrium with olivine of Fo91 (Fig. 11a). Using the slopes of data on plots of abundance ratios of moderately incompatible elements vs abundances of a highly incompatible element (e.g. Hofmann et al., 1986), we find that the North Arch lava compositions define the following order of bulk residue–melt partition coefficients: Th < Ba Rb Nb Ta < K < La Ce < Nd P < Sr Sm Zr < Ti Eu < Y. This order is consistent with a residual mineral assemblage dominated by olivine and pyroxenes (Sun & McDonough, 1989). The lavas of the Honolulu Volcanics, however, extend to much higher concentrations of incompatible elements than the North Arch lavas (Figs 5 and 11b). With the assumption of homogeneous abundances of highly incompatible elements in their respective sources, the range in extent of melting required to generate the Honolulu Volcanics is greater than a factor of five, whereas it is approximately a factor of four for North Arch lavas (i.e. abundances of Nb and Ta determined by two different analytical techniques vary by a factor of four; Table 3). Lavas of the Honolulu Volcanics with the highest Th contents have relatively low Ba/Th and P/Th (Fig. 5), which Clague & Frey (1982) interpreted as indicating that the extent of melting was comparable with that of the bulk solid–melt partition coefficients (D) for Ba and Th. For phosphorus the inferred D value is consistent with that of an apatite-free, olivine-rich residue, but based on the inferred D for barium, Clague & Frey (1982) suggested that phlogopite was a residual mineral during generation of the Honolulu Volcanics.
|
The relative abundance of potassium is important in evaluating the presence of residual amphibole or phlogopite. For example, depletion in potassium relative to other incompatible elements in some alkalic lavas from the Comores Archipelago has been used to argue for residual amphibole (Späth et al., 1996
; Class & Goldstein, 1997). The compositions of the North Arch lavas are well suited to evaluate the role of K-bearing phases in the melting process because these lavas have not been subjected to the alkali element mobilization processes that occur in subaerial Hawaiian environments (Fig. 9). Clague et al. (1990) used P2O5, K2O and TiO2 abundances in North Arch lavas to conclude that phlogopite, amphibole and Ti-oxide phases were not present in the residue. The trace element data for most of the North Arch lavas are consistent with this interpretation. For example, Francis & Ludden (1995) argue that with residual amphibole the bulk-solid–melt partition coefficient for K exceeds that of Ce; therefore, K/Ce increases with increasing extent of melting (e.g. the Honolulu Volcanics and Comores in Fig. 12). The absence of a systematic variation in K/Ce (Fig. 12) and positive correlations of K2O and Rb abundances with Th content (Fig. 5) confirm that, in general, the compositional variation of the primary North Arch magmas was not controlled by residual amphibole or phlogopite. In detail, however, there are four North Arch lavas (22-2, 24-3, 24-6 and 34-2) that are offset to lower K/Ce (Fig. 12). For samples from dredges 24 and 34, the lower K/Ce ratios are accompanied by relatively low Ti/Zr and Ti/Eu, and the dredge 34 sample also has low P/Nd (Fig. 13). These differences in abundance ratios could reflect differences in source composition or a role for residual K, P and Ti-rich phases when the primary melts for these three lavas were formed. Although both dredge 24 and 34 samples have low K/Ce, they differ significantly in Ba/Rb (Fig. 13). As DBa > DRb for phlogopite and DBa < DRb for amphibole (LaTourette et al., 1995), these Ba/Rb differences may reflect a varying role for these phases in the source and during partial melting.
|
|
The differences between the North Arch lavas and the Honolulu Volcanics are even more pronounced for the moderately incompatible elements Zr, Hf and Ti; in each case, abundances of these elements are positively correlated with Th abundance in lavas from the North Arch and Koloa Volcanics, but abundances of these elements are not correlated with Th abundance in the Honolulu Volcanics (Fig. 14). A similar difference between the fields for North Arch lavas and the Honolulu Volcanics is obvious for the Ta and Nb vs Th trends (Fig. 14). The relative compatibility of Ti, Zr, Hf, Nb and Ta in the Honolulu Volcanics led Clague & Frey (1982) to infer the presence of a residual Ti-rich phase at the lowest extents of melting. In contrast, all of these elements were highly incompatible during formation of the North Arch lavas and Koloa Volcanics [Fig. 14 and Clague & Dalrymple (1988)].
|
The relatively low Cu contents of the Honolulu Volcanics (typically <80 ppm) have been interpreted as indicating the presence of a residual sulfide during partial melting (Clague & Frey, 1982). The Cu contents of North Arch lavas are considerably higher (92–133 ppm), but it is intriguing that six of the seven lavas with the highest Nb content (samples from dredges 23, 24 and 27) have the lowest Cu contents (92–98 ppm); perhaps indicating that their primary melts formed in equilibrium with a sulfide phase.
In summary, during formation of the North Arch lavas, garnet was a residual phase during partial melting, and it controlled Al2O3 contents (Fig. 4), fractionated intermediate REE from HREE (Fig. 10c), and created crossing chondrite-normalized REE patterns (Fig. 6). Abundances of Ni and Zn and the major element compositions are consistent with melting of garnet lherzolite. In contrast to the melting processes leading to the Honolulu Volcanics (Clague & Frey, 1982; Class & Goldstein, 1997), the compositions of the North Arch lavas provide little evidence for residual phases, such as amphibole, phlogopite, Fe–Ti oxide or sulfides; the anomalous samples from dredges 24 and 34 may be exceptions (Fig. 13). An explanation for the difference between the North Arch and Honolulu Volcanics is that for the former the extent of melting was generally sufficient to eliminate minor phases from the residue; alternatively, higher abundances of elements such as Ti, K and P in the source of the Honolulu Volcanics led to larger amounts of accessory phases.
North Arch lavas: constraints on source mineralogy and composition
The evidence for residual olivine and garnet shows that these were important phases in the source. Also, the high CaO contents of the nephelinites require a CaO-rich mineral, such as clinopyroxene, in the source. Therefore, the compositional data for North Arch lavas are consistent with derivation by variable extents of melting of a garnet peridotite. Clague & Frey (1982) proposed a similar model for the rejuvenated-stage Honolulu Volcanics. As with rejuvenated-stage lavas, the apparent contradiction for North Arch lavas is that magmas derived from a long-term depleted source have relatively high abundances of incompatible elements. This seemingly paradoxical result is generally explained as reflecting very low extents of melting of a depleted source or larger extents of melting of a depleted source that was recently enriched in incompatible trace elements. The Honolulu Volcanics have been important in evaluating these alternatives. Their limited variation in Sr, Nd and Pb isotopic ratios (Fig. 7) and high MgO contents led to the hypothesis that these lavas were near-primary magmas derived from a compositionally homogeneous source. The incompatible element abundances in these lavas have been used to constrain the composition and mineralogy of their source and the extents of melting involved. Using the batch melting equation and approach of Treuil & Joron (1975), Clague & Frey (1982) concluded that the source was garnet-bearing (<10%) peridotite, enriched in highly incompatible elements (e.g. La 2·67 ppm) relative to primitive mantle (La 0·687 ppm, Sun & McDonough, 1989), and that this source was melted to 2–11% leaving residual garnet, amphibole or phlogopite and a Ti-rich phase. Albarède (1983) used a different inversion approach for batch melting and reached very similar conclusions. Also utilizing the data of Clague & Frey (1982), Class & Goldstein (1997) used a batch melting model to emphasize a role for residual phlogopite and a lithospheric source for the Honolulu Volcanics. The same incompatible element abundance data have been used to infer the source composition of the Honolulu Volcanics using a mixing model (Roden et al., 1984), a fractional melting model (Watson, 1993) and a dynamic melting model (Zou & Zindler, 1996). In each case, the conclusion is that the source of the Honolulu Volcanics was enriched in highly incompatible elements relative to primitive mantle. The inversion approach for dynamic melting used by Zou & Zindler (1996) yields conclusions that are remarkably similar to the conclusions of Clague & Frey (1982); i.e. ranges in extent of melting of 3·2–10·7% and 2–11%, and La contents of 1·59 and 2·67 ppm, respectively.
Sims et al. (1995), however, proposed much lower extents of melting for generation of rejuvenated-stage lavas. Based on 238U/230Th disequilibrium in three basanites of the Hana Volcanics, and assuming batch melting of garnet peridotite, they concluded that these basanites formed by 0·25% melting; presumably nephelinites would have formed by even lower extents of melting. With this factor of 10 decrease in inferred extent of melting, it is not necessary to have a source that is enriched in incompatible elements. A difficulty with this model is that the low melt fractions (e.g. 0·0025) are comparable with the bulk-solid–melt partition coefficients for incompatible elements. This results in non-linear trends among abundances of incompatible elements [e.g. fig. 11 of Reiners & Nelson (1998)] rather than the more typical observed linear trends (e.g. Fig. 5, this paper). Recently, Sims et al. (1999) have modified their melting models to incorporate timescales of melting, and they now favor larger degrees of melting.
Recent results showing isotopic heterogeneity within the Koloa Volcanics (Fig. 7), the rejuvenated-stage lavas on Kauai, have led to models involving mixing of different source components. Reiners & Nelson (1998) evaluated several mixing models and favored a scenario whereby an enriched (plume?) source was variably metasomatized by melts derived by low extents of melting of depleted mantle. In this model the Koloa Volcanics formed by melting this isotopically heterogeneous source with a positive correlation between the extents of metasomatism and melting. This model follows from the earlier mixing hypothesis used to explain the inverse trends of Rb/Sr vs 87Sr/86Sr (also Sm/Nd vs 143Nd/144Nd) that are defined by the transition from shield-stage tholeiitic magmas to alkalic magmas (e.g. Chen & Frey, 1985; Clague & Dalrymple, 1988).
Another important recent result for rejuvenated-stage lavas is that the Koloa and Honolulu Volcanics range widely in 187Os/188Os ratios (Lassiter et al., 1998), from values typical of Hawaiian shield lavas (0·130–0·148) to much higher ratios (up to 0·16). Lassiter et al. (1998) concluded that such high Os isotopic ratios require an aged high Re/Os source component, specifically a mafic rock, such as pyroxenite, derived from a partial melt. They proposed that these rejuvenated-stage lavas formed by mixing pyroxenite- and peridotite-derived melts, probably parts of the Pacific oceanic lithosphere mantle beneath the Hawaiian volcanoes. With this interpretation, rejuvenated-stage lavas may not contain a plume-related component; i.e. the Os isotopic differences between MORB and rejuvenated-stage lavas may largely reflect aging of oceanic lithosphere. The absence of high 3He/4He ratios in North Arch lavas [Fig. 8 and Dixon et al. (1997)] is consistent with this inference. However, as discussed earlier, derivation of magmas highly enriched in incompatible elements from a depleted source requires very low extents of melting and very specific constraints on the mixing process [see fig. 11 of Reiners & Nelson (1998)]. In addition, aging of normal and unaltered MORB lithosphere cannot explain the Sr, Nd and Pb isotopic differences between North Arch (and rejuvenated-stage) lavas and MORB (Fig. 7). Basu & Faggart (1996) noted that rejuvenated-stage lavas with Nd of +8 to +9 are offset from the MORB field to high 87Sr/86Sr. The North Arch lavas show this offset (Fig. 7). Basu & Faggart (1996) suggested that this offset reflects a role for seawater-altered upper lithosphere. Given our arguments that North Arch lavas ascended rapidly from a largely peridotite source at depths within the garnet-stability field, this interpretation is viable only if seawater alteration penetrates to well below subcrustal levels. In addition, with this hypothesis the source of rejuvenated-stage and North Arch lavas is restricted to oceanic lithosphere with relatively low Nd and Pb isotopic ratios.
Of course, metasomatic processes may have affected the aging oceanic lithosphere (e.g. Wright, 1984; Halliday et al., 1995; Wilson et al., 1995). Evidence consistent with aged metasomatized oceanic lithosphere as the source of rejuvenated-stage lavas is the correlation of Sr and Nd isotopic ratios with extent of source enrichment in incompatible elements for the Koloa Volcanics (Reiners & Nelson, 1998), and the presence of amphibole and phlogopite in the source of the Honolulu Volcanics (Clague & Frey, 1982; Class & Goldstein, 1997). Some of these metasomatic additions may have been plume derived. For example, given the age and South Pacific origin of the abyssal sea floor around the Hawaiian Islands (e.g. Waggoner, 1993), the oceanic lithosphere may have been contaminated by Middle Cretaceous mantle dispersed from the broad starting-plume heads that formed the 120–90 Ma Ontong Java, Manihiki, and Hess oceanic plateaux. This plume-derived component may form pockets, streaks, or veins in a matrix with a more normal-MORB-type mantle compositions. Isotopic data are limited for these plateaux; however, we note that the data fields for the North Arch and most rejuvenated-stage lavas in Fig. 7 lie in an appropriately intermediate position between the fields for modern South Pacific MORB and lavas from the Ontong Java and Manihiki plateaux.
|
SUMMARY AND CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
The North Arch volcanic field consists of submarine lavas, ranging from alkali basalt to nephelinite, occurring over a 25 000 km2 area 200–400 km north of Oahu. Inferred eruption ages of
0·5–1·15 Ma overlap with those of rejuvenated-stage lavas on Kauai, Niihau and Oahu. The North Arch lavas are unique because: (1) they erupted at the periphery of the Hawaiian hotspot; (2) some of the vesicular glasses are relatively undegassed; (3) they have not been altered by post-magmatic subaerial processes. Their compositional and isotopic (Sr, Nd and Pb) characteristics are broadly similar to those of rejuvenated-stage lavas, such as the Honolulu and Koloa Volcanics, which erupt on the tholeiitic shields as the final growth stage of a Hawaiian volcano. Like the Honolulu Volcanics, the North Arch lavas show only small variations in radiogenic isotopic ratios, and they have lower 87Sr/86Sr and higher 143Nd/144Nd than the Hawaiian tholeiitic shields. Olivine (with chromite inclusions) is the only phenocryst phase in glasses with >6·4% MgO. These phenocrysts range up to Fo88, and they coexist with mantle-derived olivine xenocrysts ranging to Fo92. Accumulation and fractionation of olivine were the major post-melting processes that affected the North Arch lava compositions. After correction for olivine fractionation, the compositional effects of variable extents of melting (factor of four) of a garnet peridotite source are evident. The importance of residual garnet is indicated by crossing chondrite-normalized REE patterns and systematic correlations between abundances of highly incompatible elements with SiO2 content and CaO/Al2O3; the incompatible behavior of CaO is distinctive for partial melting of garnet peridotite. Abundances of Sc, Cr, Co, Ni, and Zn are consistent with an olivine-rich source. Unlike the Honolulu Volcanics there is little or no evidence that amphibole, phlogopite, sulfides, or Fe–Ti oxides were important residual phases during generation of North Arch lavas. Although the North Arch alkalic lavas have low 87Sr/86Sr and high 143Nd/144Nd relative to tholeiitic Hawaiian shield lavas, these alkalic lavas were not derived solely from normal unaltered oceanic lithosphere. Their high abundances of incompatible elements reflect both derivation by low extents of melting and the influence of a plume component. The plume component may be locally derived from the Hawaiian plume. An alternative scenario is dispersion and incorporation of mid-Cretaceous plume material, e.g. related to formation of the Ontong Java Plateau, into the South Pacific lithosphere with subsequent northwest transport of this mixed lithosphere to the vicinity of the Hawaiian plume.
|
ACKNOWLEDGEMENTS |
|---|
We thank Drs P. Ila and K. Spencer for assistance in data acquisition. The success of the sampling program during US Geological Survey cruise F11-88-HW was due to the dedication of the ship and scientific staff on board, especially Captain John Cannon, Mike Torresan, Robin Holcomb, and Stephanie Ross. We also thank Chris Gutmacher of the US Geological Survey for her help with the GLORIA imagery used in Fig. 1. This research was supported by EAR and OCE NSF Grants, the US Geological Survey, and the David and Lucille Packard Foundation. We also thank R. Kinzler and J. Longhi for discussion of primary melt compositions derived from garnet peridotite, and M. Feigenson, P. Janney and especially J. Lassiter and P. Reiners for very helpful and detailed review comments. This is SOEST Contribution 4929.
|
FOOTNOTES |
|---|
*Corresponding author. e-mail: fafrey{at}mit.edu
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONSAMPLING AND ANALYTICAL...RESULTS FOR NORTH ARCH...DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Adam, J. (1988). Dry, hydrous, and CO2-bearing liquidus phase relationships in the CMAS system at 28 Kb and their bearing on the origin of alkali basalts. Journal of Geology 96, 709–719.
Albarède, F. (1983). Inversion of batch melting equations and the trace element pattern of the mantle. Journal of Geophysical Research 88, 10573–10583.
Bach, W., Hegner, E., Erzinger, J. & Satir, M. (1994). Chemical and isotopic variations along the superfast spreading East Pacific Rise from 6 to 30°S. Contributions to Mineralogy and Petrology 116, 365–380.
Basu, A. R. & Faggart, B. E. (1996). Temporal isotopic variations in the Hawaiian mantle plume: the Lanai anomaly, the Molokai fracture zone and a seawater-altered lithospheric component in Hawaiian volcanism. In: Basu, A. & Hart, S. (eds) Earth Processes: Reading the Isotopic Code. Geophysical Monograph, American Geophysical Union 95, 149–159.
Beattie, P. (1994). Systematics and energetics of trace element partitioning between olivine and silicate melts: implications for the nature of mineral/melt partitioning. Chemical Geology 117, 57–71.
Blundy, J. D., Robinson, J. A. C. & Wood, B. J. (1998). Heavy REE are compatible in clinopyroxene on the spinel lherzolite solidus. Earth and Planetary Science Letters 160, 493–504.[Web of Science]
Carter, J. L. (1970). Mineralogy and chemistry of the earth’s upper mantle based on the partial fusion–partial crystallization model. Geological Society of America Bulletin 81, 2021–2034.
Chauvel, C., Hofmann, A. W. & Vidal, P. (1992). HIMU-EM: the French Polynesian connection. Earth and Planetary Science Letters 10, 99–119.
Chen, C.-Y. & Frey, F. A. (1983). Origin of Hawaiian tholeiite and alkalic basalt. Nature 302, 785–789.
Chen, C.-Y. & Frey, F. A. (1985). Trace element and isotopic geochemistry of lavas from Haleakala volcano, East Maui, Hawaii: implications for the origin of Hawaiian lavas. Journal of Geophysical Research 90, 8743–8768.
Chen, C.-Y., Frey, F. A. & Garcia, M. O. (1990). Evolution of alkalic lavas at Haleakala Volcano, east Maui, Hawaii. Contributions to Mineralogy and Petrology 105, 197–218.
Chen, C.-Y., Frey, F. A., Rhodes, J. M. & Garcia, M. O. (1996). Temporal geochemical evolution of Kilauea volcano: composition of Hilina and Puna basalt. In: Basu, A. & Hart, S. (eds) Earth Processes: Reading the Isotopic Code. Geophysical Monograph, American Geophysical Union 95, 161–181.
Clague, D. A. & Chen, C.-H. (1986). Ocean crust xenoliths from Hualalai Volcano, Hawaii. Geological Society of America Abstracts 18(6), 565.
Clague, D. A. & Dalrymple, G. B. (1987). The Hawaiian–Emperor volcanic chain, Part 1, Geologic evolution. US Geological Survey Professional Paper 1350, 5–54.
Clague, D. A. & Dalrymple, G. B. (1988). Age and petrology of alkalic postshield and rejuvenated-state lava from Kauai, Hawaii. Contributions to Mineralogy and Petrology 99, 202–218.[Web of Science]
Clague, D. A. & Denlinger, R. P. (1994). Role of olivine cumulate in destabilizing the flanks of Hawaiian volcanoes. Bulletin of Volcanology 56, 425–434.
Clague, D. A. & Frey, F. A. (1982). Petrology and trace element geochemistry of the Honolulu Volcanics, Oahu: implications for the oceanic mantle below Hawaii. Journal of Petrology 23, 447–504.
Clague, D. A., Holcomb, R. T., Sinton, J. M., Detrick, R. S. & Torresan, M. E. (1990). Pliocene and Pleistocene alkalic flood basalts on the seafloor north of the Hawaiian islands. Earth and Planetary Science Letters 98, 175–191.
Clague, D. A., Moore, J. G., Dixon, J. E. & Friesen, W. B. (1995). Petrology of submarine lavas from Kilauea’s Puna Ridge, Hawaii. Journal of Petrology 36, 299–349.
Clague, D. A., Dixon, J. E., Frey, F. A., Kurz, M. D., Mahoney, J., Park, K.-H., Rhodes, J. M., Sinton, J. & Staudigel, H. (2000). The distribution of alkalic lavas around Hawaii and the geometry of the Hawaiian plume. Journal of Petrology (submitted).
Class, C. & Goldstein, S. L. (1997). Plume–lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth and Planetary Science Letters 150, 145–260.
Dixon, J. E., Clague, D. A., Wallace, P. & Poreda, R. (1997). Volatiles in alkalic basalts from the North Arch volcanic field, Hawaii: extensive degassing of deep submarine-erupted alkalic series lavas. Journal of Petrology 36, 911–939.
Doe, B. R. (1995). Zinc, copper and lead geochemistry of oceanic igneous rocks—ridges, islands and arcs. International Geology Review 37, 379–420.
Feigenson, M. D. (1984). Geochemistry of Kauai volcanics and a mixing model for the origin of Hawaiian alkalic basalts. Contributions to Mineralogy and Petrology 87, 109–119.
Francis, D. & Ludden, J. (1995). The signature of amphibole in mafic alkaline lavas, a study in the Northern Canadian Cordillera. Journal of Petrology 36, 1171–1191.
Frey, F. A., Wise, W. S., Garcia, M. O., West, H., Kwon, S.-T. & Kennedy, A. (1990). Evolution of Mauna Kea Volcano, Hawaii: Petrologic and geochemical constraints on postshield volcanism. Journal of Geophysical Research 95, 1271–1300.
Frey, F. A., Garcia, M. O. & Roden, M. F. (1994). Geochemical characteristics of Koolau Volcano: implications of intershield geochemical differences among Hawaiian volcanoes. Geochimica et Cosmochimica Acta 58, 1441–1462.[Web of Science]
Goto, A. & Yokoyama, K. (1988). Lherzolite inclusions in olivine nephelinite tuff from Salt Lake Crater, Hawaii. Lithos 21, 67–80.
Grove, T. L. & Bryan, W. B. (1983). Fractionation of pyroxene-phyric MORB at low pressure—an experimental study. Contributions to Mineralogy and Petrology 84, 293–309.
Halliday, A. N., Lee, D.-C., Tommasini, S., Davies, G. R., Paslick, C. R., Fitton, J. G. & James, D. O. (1995). Incompatible trace elements in OIB and MORB and source enrichment in the sub-oceanic mantle. Earth and Planetary Science Letters 133, 379–395.
Hamilton, E. L. (1957). Marine geology of the Southern Hawaiian Ridge. Geological Society of America Bulletin 68, 1011–1026.
Hart, S. R. & Davis, K. E. (1978). Nickel partitioning between olivine and silicate melt. Earth and Planetary Science Letters 40, 203–219.[Web of Science]
Hirose, K. (1997). Partial melt compositions of carbonated peridotite at 3 GPa and role of CO2 in alkali-basalt magma generation. Geophysical Research Letters 24, 2837–2840.[Web of Science]
Hirschmann, M. M. & Ghiorso, M. S. (1994). Activities of nickel, cobalt, and manganese silicates in magmatic liquids and applications to olivine/liquid and silicate/metal partitioning. Geochimica et Cosmochimica Acta 58, 4109–4126.
Hirschmann, M. M. & Stolper, E. M. (1996). A possible role for garnet pyroxenite in the origin of the ‘garnet signature’ in MORB. Contributions to Mineralogy and Petrology 124, 185–208.[Web of Science]
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.
Hofmann, A. W., Jochum, K. P., Seufert, M. & White, W. M. (1986). Nb and Pb in oceanic basalts: new constraints on mantle evolution. Earth and Planetary Science Letters 79, 33–45.[Web of Science]
Ila, P. & Frey, F. A. (1984). Utilization of neutron activation analysis in the study of geologic materials. In: Harling, O. K., Clark, L. & Von der Hardt, P. (eds) Use and Development of Low and Medium Flux Research Reactors. Atomkernenergie Kerntechnik 44(Supplement), 710–716.
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, 60–80.[Web of Science]
Jurewicz, A. J. G. & Watson, E. B. (1988). Cations in olivine, Part 1: Calcium partitioning and calcium–magnesium distribution between olivine and coexisting melts, with petrologic application. Contributions to Mineralogy and Petrology 99, 176–185.
King, A. J., Waggoner, D. C. & Garcia, M. O. (1993). Geochemistry and petrology of basalts from Leg 136, central Pacific Ocean. In: Wilkens, R. H., Firth, J., Bowler, J. et al. (eds) Proceedings of the Ocean Drilling Program, Scientific Results, 136. College Station, TX: Ocean Drilling Program, pp. 107–118.
Kinzler, R. J. (1997). Melting of mantle peridotite at pressures approaching the spinel to garnet transition: application to mid-ocean ridge basalt petrogenesis. Journal of Geophysical Research 102, 853–874.
Kinzler, R. J. & Grove, T. L. (1992). Primary magmas of mid-ocean ridge basalts. II: Applications. Journal of Geophysical Research 97, 6907–6926.
Kogiso, T., Hirose, K. & Takahashi, E. (1998). Melting experiments on homogeneous mixtures of peridotite and basalt: application to the genesis of ocean island basalts. Earth and Planetary Science Letters 162, 45–61.[Web of Science]
Kurz, M. D., Garcia, M. O., Frey, F. A. & O’Brien, P. A. (1987). Temporal helium isotopic variations within Hawaiian volcanoes: basalts from Mauna Loa and Haleakala. Geochimica et Cosmochimica Acta 51, 2905–2914.
Kurz, M. D., le Roex, A. P. & Dick, J. B. (1998). Isotope geochemistry of the oceanic mantle near the Bouvet Triple Junction. Geochimica et Cosmochimica Acta 62, 841–852.
Langmuir, C. H., Klein, E. M. & Plank, T. (1992). Petrological systematics of mid-ocean ridge basalts: constraints on melt generation beneath ocean ridges. In: Morgan, J. P., Blackman, D. K. & Sinton, J. M. (eds) Mantle Flow and Melt Generation at Mid-ocean Ridges. Geophysical Monograph, American Geophysical Union 71, 183–280.
Lassiter, J. C., Hauri, E. H., Reiners, P. W. & Garcia, M. O. (1998). Evidence for melting of garnet pyroxenite in the generation of Hawaiian post-erosional lavas: effects of a marble-cake mantle during melt generation. Goldschmidt Conference Abstract. Mineralogical Magazine 62A, 856–857.
LaTourette, T., Hernig, R. L. & Holloway, J. R. (1995). Trace element partitioning between amphibole, phlogopite and basanite melt. Earth and Planetary Science Letters 135, 13–30.[Web of Science]
Lipman, P. W., Clague, D. A., Moore, J. G. & Holcomb, R. T. (1989). South Arch volcanic field—newly identified young lava flows on the sea floor south of the Hawaiian Ridge. Geology 17, 611–614.
Longhi, J. (1997). Discrepancies in determination of mantle solidus temperatures in the garnet stability field. EOS Transactions, American Geophysical Union, 78(46), Fall Meeting Supplement, F812.
Maaloe, S., James, D., Smedley, P., Petersen, S. & Garmann, L. B. (1992). The Koloa Volcanic suite of Kauai, Hawaii. Journal of Petrology 33, 761–784.
Macdougall, J. D. & Lugmair, G. W. (1986). Sr and Nd isotopes in basalts from the East Pacific Rise: significance for mantle heterogeneity. Earth and Planetary Science Letters 77, 273–284.
Mahoney, J. J., Nicollet, C. & Dupuy, C. (1991). Madagascar basalts: tracking oceanic and continental sources. Earth and Planetary Science Letters 104, 350–363.
Mahoney, J. J., Storey, M., Duncan, R. A., Spencer, K. J. & Pringle, M. S. (1993). Geochemistry and age of the Ontong Java Plateau. In: Pringle, M. S., Sager, W. W., Sliter, W. V. & Stein, S. (eds) The Mesozoic Pacific. Geophysical Monograph, American Geophysical Union 77, 233–261.
Mahoney, J. J., Sinton, J. M., Kurz, M. D., Macdougall, J. D., Spencer, K. J. & Lugmair, G. W. (1994). Isotope and trace element characteristics of a super-fast spreading ridge: East Pacific Rise, 13–23°S. Earth and Planetary Science Letters 121, 173–193.
Moore, J. G. (1987). Subsidence of the Hawaiian Ridge. US Geological Survey Professional Paper 1350, 85–100.
Norrish, K. & Chappell, B. W. (1967). X-ray fluorescence spectrography. In: Zussman, J. (ed.) Physical Methods in Determinative Mineralogy. Orlando, FL: Academic Press, pp. 161–214.
Reiners, P. W. & Nelson, B. K. (1998). Temporal–compositional–isotopic trends in rejuvenated-stage magmas of Kauai, Hawaii, and implications for mantle melting process. Geochimica et Cosmochimica Acta 62, 2347–2368.
Roden, M. F., Frey, F. A. & Clague, D. A. (1984). Geochemistry of tholeiitic and alkalic lavas from the Koolau Range, Oahu, Hawaii: implications for Hawaiian volcanism. Earth and Planetary Science Letters 69, 141–158.
Sims, K. W. W., DePaolo, D. J., Murrell, M. T., Baldridge, W. S., Goldstein, S. J. & Clague, D. A. (1995). Mechanism of magma generation beneath Hawaii and mid-ocean ridges: uranium/thorium and samarium/neodymium isotopic evidence. Science 267, 508–512.
Sims, K. W. W., DePaolo, D. J., Murrell, M. T., Baldridge, W. S., Goldstein, S. & Clague, D. A. (1999). Porosity of the melting zone and variations in the solid mantle upwelling rate beneath Hawaii: inferences from 238U–230Th–226Ra and 235U–231Pa disequilibria. Geochemica et Cosmochemica Acta (in press).
Späth, A., le Roex, A. P. & Duncan, R. A. (1996). The geochemistry of lavas from the Comores Archipelago, western Indian Ocean: petrogenesis and mantle source region characteristics. Journal of Petrology 37, 961–991.
Stille, P., Unruh, D. M. & Tatsumoto, M. (1983). Pb, Sr, Nd, and Hf isotopic evidence of multiple sources for Oahu, Hawaii basalts. Nature 304, 25–29.
Sun, S.-S. (1980). Lead isotope study of young volcanic rocks from mid-ocean ridges, oceanic islands and island arcs. Philosophical Transactions of the Royal Society of London, Series A 27, 409–445.
Sun, S.-S. & McDonough, W. F. (1989). Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A. D. & Norry, M. J. (eds) Magmatism in the Ocean Basins. Geological Society, London, Special Publication 42, 313–345.
Tatsumoto, M., Hegner, E. & Unruh, D. M. (1987). Origin of the West Maui volcanic rocks inferred from Pb, Sr, and Nd isotopes and a multicomponent model for oceanic basalt. US Geological Survey Professional Paper 1350, 723–744.
Tejada, M. L. G., Mahoney, J. J., Duncan, R. A. & Hawkins, M. P. (1996). Age and geochemistry of basement and alkalic rocks of Malaita and Santa Isabel, Solomon Islands, southern margin of Ontong Java Plateau. Journal of Petrology 37, 361–394.
Todt, W., Cliff, R. A., Hanser, A. & Hofmann, A. W. (1996). Evaluation of a 202Pb–205Pb double spike for high-precision lead isotope analysis. In: Basu, A. & Hart, S. (eds) Earth Processes: Reading the Isotopic Code. Geophysical Monograph, American Geophysical Union 95, 429–437.
Treuil, M. & Joron, J.-L. (1975). Utilisation des éléments hydromagmatophiles pour la simplification de la modelisation quantitative des processus magmatiques: exemples de l’Afar et de la Dorsale Medioatlantique. Societa Italiana Mineralogia e Petrologia 31, 125–174.
Waggoner, D. C. (1993). The age and alteration of central Pacific Oceanic crust. In: Wilkens, R. H., Firth, J., Bowler, J. et al. (eds) Proceedings of the Ocean Drilling Program, Scientific Results, 136. College Station, TX: Ocean Drilling Program, pp. 119–132.
Walter, M. J. (1998). Melting of garnet peridotite and the origin of komatiite and depleted lithosphere. Journal of Petrology 39, 29–60.
Watson, S. (1993). Rare earth element inversions 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, 216–219.
White, W. M., Hofmann, A. W. & Puchelt, H. (1987). Isotope geochemistry of Pacific mid-ocean ridge basalt. Journal of Geophysical Research 92, 4881–4893.
Wilson, M., Rosenbaum, J. M. & Dunsworth, E. A. (1995). Melilitites: partial melts of the thermal boundary layer. Contributions to Mineralogy and Petrology 119, 181–196.[Web of Science]
Wright, T. L. (1984). Origin of Hawaiian tholeiite: a metasomatic model. Journal of Geophysical Research 89, 3233–3252.
Wyllie, P. J. (1988). Solidus curves, mantle plumes and magma generation beneath Hawaii. Journal of Geophysical Research 93, 4171–4181.
Yasuda, A., Fuji, T. & Kurita, K. (1994). Melting phase relations of an anhydrous mid-ocean ridge basalt from 3 to 20 GPa: implications for the behavior of subducted oceanic crust in the mantle. Journal of Geophysical Research 99, 9401–9414.
Zou, H. & Zindler, A. (1996). Constraints on the degree of dynamic partial melting and source composition using concentration ratios in magmas. Geochimica et Cosmochimica Acta 60, 711–717.[Web of Science]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  N. A. LEASE and A.-F. M. ABDEL-RAHMAN The Euphrates volcanic field, northeastern Syria: petrogenesis of Cenozoic basanites and alkali basalts Geological Magazine, September 1, 2008; 145(5): 685 - 701. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Vigouroux, P. J. Wallace, and A. J. R. Kent Volatiles in High-K Magmas from the Western Trans-Mexican Volcanic Belt: Evidence for Fluid Fluxing and Extreme Enrichment of the Mantle Wedge by Subduction Processes J. Petrology, September 1, 2008; 49(9): 1589 - 1618. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Keshav, G. Sen, and D. C. Presnall Garnet-bearing Xenoliths from Salt Lake Crater, Oahu, Hawaii: High-Pressure Fractional Crystallization in the Oceanic Mantle J. Petrology, September 1, 2007; 48(9): 1681 - 1724. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Zajacz, I. Kovacs, C. Szabo, W. Halter, and T. Pettke Evolution of Mafic Alkaline Melts Crystallized in the Uppermost Lithospheric Mantle: a Melt Inclusion Study of Olivine-Clinopyroxenite Xenoliths, Northern Hungary J. Petrology, May 1, 2007; 48(5): 853 - 883. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Laske, J. P. Morgan, and J. A. Orcutt The Hawaiian SWELL pilot experiment--Evidence for lithosphere rejuvenation from ocean bottom surface wave data Geological Society of America Special Papers, January 1, 2007; 430(0): 209 - 233. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. T. Leat, A. A. Dean, I. L. Millar, S. P. Kelley, A. P. M. Vaughan, and T. R. Riley Lithospheric mantle domains beneath Antarctica Geological Society, London, Special Publications, January 1, 2005; 246(1): 359 - 380. [Abstract] [PDF]
|
|
|
|
|
|
Z.-Y. REN, E. TAKAHASHI, Y. ORIHASHI, and K. T. M. JOHNSON Petrogenesis of Tholeiitic Lavas from the Submarine Hana Ridge, Haleakala Volcano, Hawaii J. Petrology, October 1, 2004; 45(10): 2067 - 2099. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A.-F. M. ABDEL-RAHMAN and P. E. NASSAR Cenozoic volcanism in the Middle East: petrogenesis of alkali basalts from northern Lebanon Geological Magazine, September 1, 2004; 141(5): 545 - 563. [Full Text] [PDF]
|
|
|
|
 |
|
 C.W. Devey, K.S. Lackschewitz, D.F. Mertz, B. Bourdon, J.-L. Cheminee, J. Dubois, C. Guivel, R. Hekinian, and P. Stoffers Giving birth to hotspot volcanoes: Distribution and composition of young seamounts from the seafloor near Tahiti and Pitcairn islands Geology, May 1, 2003; 31(5): 395 - 398. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H.-J. YANG, F. A. FREY, and D. A. CLAGUE Constraints on the Source Components of Lavas Forming the Hawaiian North Arch and Honolulu Volcanics J. Petrology, April 1, 2003; 44(4): 603 - 627. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A.-F. M. Abdel-Rahman and A.-F. M. ABDEL-RAHMAN Mesozoic volcanism in the Middle East: geochemical, isotopic and petrogenetic evolution of extension-related alkali basalts from central Lebanon Geological Magazine, November 1, 2002; 139(6): 621 - 640. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Agata and I. Hattori Chromite in greenstone lavas from the Kanakasu area, Nanjo Massif of the Mesozoic Mino terrane, central Japan Mineralogical Magazine, August 1, 2002; 66(4): 575 - 590. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. MATTIELLI, D. WEIS, J. BLICHERT-TOFT, and F. ALBAREDE Hf Isotope Evidence for a Miocene Change in the Kerguelen Mantle Plume Composition J. Petrology, July 1, 2002; 43(7): 1327 - 1339. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. E. DIXON and D. A. CLAGUE Volatiles in Basaltic Glasses from Loihi Seamount, Hawaii: Evidence for a Relatively Dry Plume Component J. Petrology, March 1, 2001; 42(3): 627 - 654. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||