JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 94, NO. B8, PAGES 10,525-10,538, AUGUST 10, 1989 MAJOR ELEMENT, VOLATILE, AND STABLE ISOTOPE GEOCHEMISTRY OF HAWAIIAN SUBMARINE THOLEIITIC GLASSES 1 ! Michael O. Garcia, David W. Muenow , and Kwesi E. Aggrey Hawaii Institute of Geophysics, University of Hawaii, Honolulu James R. O'Neil Department of Geological Sciences, University of Michigan, Ann Arbor Abstract. Tholeiitic glasses were dredged Introduct ion from the submarine rift zones of the five volcanoes comprising the island of Hawaii and Trace element, rare gas, and isotopic data Loihi Seamount. The major element composition indicate that Hawaiian lavas (including shield of the glasses follows a systematic trend that and posterosional lavas) and other oceanic is related to the stage of evolution of the island basalts (OIB) evolved by mixing melts volcano. Glasses from Loihi Seamount (the from several geochemically distinct sources. youngest Hawaiian volcano) are enriched in Fe, However, the number and compositions of the Ca, Ti, Na, and K and depleted in Si and A1 mixing end-members and the relationship of these relative to the glasses from the other, older components to specific mantle sources remain volcanoes. Kilauea is intermediate in age and points of controversy (see Zindler and Hart its glasses are intermediate in composition [1986] for a review). The source for Hawaiian between those from Loihi and Mauna Loa, the tholelites apparently consists of two principal largest and oldest of the active Hawaiian components based on Pb, Sr and Nd isotope data tholeiitic volcanoes. The volatile contents [Tatsumoto, 1978; Tatsumoto et al., 1987; West (H20, GO2, S, F, G1) of the glasses from these et al., 1987]. One of these components is volcanoes follow the same trend (highest in thought to be from a plume but there is little Loihi; lowest in Mauna Loa). Glasses from agreement on the nature of the nonplume Hualalai Volcano are similar in composition to component (for example, 100 Ma oceanic those from Mauna Loa; those from Kohala Volcano lithosphere [Stille et al., 1986]; recycled are similar to Kllauea; Mauna Kea glasses range oceanic lithosphere [Hofmann et al., 1986]). from Mauna Loa-like to Kilauea-like. The Isotopic end-members can be identified among observed systematic variation in composition of Hawaiian tholeiites. Kilauea is considered one Hawaiian tholelites may be related to the end-member and Koolau has been considered the progressive melting and depletion of the source other with tholelites from other volcanoes in of these volcanoes during their growth. Oxygen between. However, new data for Kahoolawe and and hydrogen isotope analyses were made on many Lanai tholelites show that Koolau is no longer of the glasses from each volcano. The 6180 unique (as suggested by Tatsumoto et al. [1987]) values of Hawaiian tholelites are distinctly and that the range of Hawaiian tholelites must lower than those of mid-ocean ridge basalt be extended [West et al., 1987]. (MORB) (averages: 5.1 versus 5.7). These low In order to complement previous studies and values are probably a distinct feature of hot more fully evaluate the nature of compositional spot lavas. The 6D values for these glasses variation among Hawaiian tholelites, we under- (-88 to -61) are typical of mantle and MORB took a comprehensive geochemical study of values. Thus the H20 in the Hawaiian glasses is submarine glasses from each of the five probably of magmatic origin. Previous isotopic volcanoes comprising the island of Hawaii (Mauna and trace element data indicate that the source Kea, Mauna Loa, Kilauea, Kohala and Hualalai) of Hawaiian tholelites contains two distinct and Loihi Seamount (Figure 1). This is the source components. Based on the results of this first such study where the geochemistry of a study, the plume component in the source for single suite of Hawaiian lavas is thoroughly Hawaiian tholelites is characterized by documented. Fresh submarine glasses were used moderate 87Sr/86Sr (0.7035-0.7037) and to avoid the effects of alteration and crystal 2ø6pb/2ø4pbratios (18.6-18.7), a low 6180 value accumulation. Such glasses may represent (~5.0), and greater contents of volatiles, Fe, virtually unmodtfied magmatic liquids. Ca, Ti, Na and K relative to the MORB source. Furthermore, submarine erupted glasses may contain preeruption concentrations of volcanic gases [Moore, 1970; Moore and Schilling, 1973] 1Also at Departmentof Chemistry, University which provide another important parameter in the of Hawaii, Honolulu. evaluation of the source of Hawaiian lavas. Finally, since all the glasses analyzed from Copyright 1989 by the American Geophysical each of the volcanoes are tholeiitic, we were Union. able to study lavas that are broadly repre- sentative of the shield-building stage of Paper number 89JB00894. development for each of the volcanoes. This 0148-0227/89/89JB-00894505.00 would not be possible if only subaerial lavas 10,525 10,526 Garcia et al.' Geochemistry of Hawaiian Submarine Tholeiitic Glasses 156 ø 155øW RD-2 • KO-2 MK-6 MK-4 20" N KIL-3 KIL-2 KIL-1 19 ø 0 25 50 KILOMETERS i i .J LO-1 NE CONTOUR INTERVAL ONE KILOMETER MAWA[!•O•o { report Fig. 1. Map of the island of Hawaii showing the five volcanoes that form the island and Loihi Seamount (the summit of each volcano is shown by a triangle). The rift zones of the volcanoes are shown by dashed lines. Dredge haul locations are shown by the plus symbol for each volcano. The bathymetric contour interval is 1 km. were used because alkalic lavas mantle the and Loihi Seamount. We dredged at various tholeiitic shields on most Hawaiian volcanoes. locations (Figure 1) along these rift zones at Those tholelites that are exposed are commonly water depths ranging from 1900 to 3700 m in altered (especially the contents of alkali order to sample as diverse an assortment of lava metals) due to groundwater percolation [Chen and compositions and ages as possible. The depth of Frey, 1985]. recovery of the samples is greater than the In this paper, we use major elements, depth they were erUPted at because the island of volatile abundances (H20, C02, C1, F, S), and Hawaii is sinking rapidly (-2.5 mm/y [Moore, hydrogen and oxygen isotope data of glasses to 1987]). Kohala has sunk approximately 1 km; further constrain the sources for Hawaiian Mauna Kea about 400-500 m; and Kilauea •100 m tholeiitic lavas. Separate studies are in [Moore, 1987]. Our dredging concentrated on progress on the trace element and radiogenic Mauna Loa and Mauna Kea since little fresh, isotopes [Garcia et al., 1986a, Gurriet et al., unaltered pillow rim glass was available from 1988] and rare gases [Lupron and Garcia, 1986] these volcanoes. We also obtained glassy in these lavas. samples from Kohala (RD-2) and Hualalai (HP) that were taken during engineering surveys of Samples these volcanoes. Pillowbasalts with well-develope• glass Most of the samples used in this study were rinds (>0.5 cm) were the focus for our study. obtained from dredges we made during a 1983 R/V For each dredge haul, we determined petrographic KANA KEOKI cruise around the isiand of Hawaii. groups and selected representative samples for Rocks with abundant fresh glass were obtained microprobe analyses; 41 distinct groups have from the deep submarine extensions of the major been defined. A major element analysis for a, rift zones of four of the five volcanoes representative sample from each group is given comprising the island of Hawaii (except Kohala) in Table 1. Garcia et al.: Geochemistry of Hawaiian Submarine Tholeitttc Glasses 10,527 TABLE1. Microprobe Analyses of Glasses from Mauna IDa, Mauna Kea, Kilauea, Hualalai, Kohala and Loihi Volcanoes, Hawaii Major Elements Modes Sample sio2 TiO2 Al•O3 FeO* Fz30 CaO Na20 K•O P•O$ Volatiles Total O1 Cpx Plag Total Number LoCi LO-1-4 48.69 2.82 13.44 11.82 6.81 11.68 2.54 0.54 0.32 0.87 99.53 4.6 0.1 0.0 4.7 LO-1-6 49.24 2.67 13.61 12.01 6.70 11.79 2.57 0.44 0.32 0.87 100.22 3.5 0.2 0.4 4.1 LO-1-9 49.27 2.79 13.96 12.23 6.28 11.41 2.61 0.45 0.31 0.92 100.23 3.0 0.2 0.1 3.3 Kilauea EIL-1-BR 51.50 2.57 13.71 10.67 6.40 11.20 2.30 0.43 0.26 0.73 99.77 12.2 0.0 0.0 12.2 EIL-I-1 51.02 2.56 13.64 10.62 6.47 11.26 2.29 0.44 0.28 0.74 99.32 10.4 0.0 0.0 10.4 EIL-1-4 51.23 2.58 13.89 10.58 6.41 11.13 2.24 0.44 0.27 0.77 99.54 3.6 0.1 0.0 3.7 EIL-1-5 50.78 2.86 13.95 11.02 6.20 10.89 2.36 0.49 0.31 0.87 99.73 1.4 0.4 1.4 3.2 EIL-1-9 51.07 2.42 13.57 10.52 7.23 11.27 2.20 0.42 0.24 0.80 99.74 15.0 0.0 0.0 15.0 EIL-2-1 51.72 2.66 14.10 10.11 6.37 11.07 2.28 0.46 0.30 0.64 99.71 29.6 0.1 0.0 29.7 EIL-2-8 51.76 2.73 14.02 10.17 6.34 10.98 2.28 0.47 0.29 0.78 99.83 28.6 0.1 0.0 28.7 EIL-2-9 51.38 2.64 13.73 10.11 6.64 11.15 2.41 0.47 0.26 0.73 99.52 28.6 0.0 0.0 28.6 EIL-3-9 51.71 3.25 13.94 10.64 5.77 9.95 2.56 0.60 0.34 0.83 99.59 27.8 0.8 0.0 28.6 EIL-3-19 51.75 3.33 13.98 11.30 5.85 10.02 2.49 0.55 0.36 0.91 100.54 16.0 0.1 0.2 16.3 Mauna IDa ML-I-1 52.03 2.16 13.89 9.69 7.05 10.99 2.28 0.33 0.24 0.65 99.31 29.4 0.4 0.0 29.8 ML-1-3 52.45 2.27 13.95 10.52 6.82 10.82 2.30 0.36 0.28 0.32 100.09 13.4 0.6 1.8 15.8 ML-l-10 52.38 2.83 13.58 11.05 6.01 9.86 2.49 0.54 0.33 0.52 99.58 11.4 2.2 1.0 14.6 ML-l-ll 52.46 2.20 14.21 9.91 6.39 11.50 2.28 0.34 0.25 0.49 100.04 12.8 0.0 0.0 12.8 ML-l-12 52.43 2.15 14.09 10.00 6.70 11.12 2.32 0.35 0.23 0.61 100.00 20.6 0.2 0.1 20.9 ML-2-1 52.24 2.62 13.84 11.04 6.32 10.76 2.46 0.49 0.30 0.44 100.19 12.4 0.8 1.4 14.6 ML-2-3 52.65 2.26 14.10 10.06 6.87 10.88 2.37 0.36 0.27 0.36 100.18 14.2 0.8 2.2 17.2 ML-2-8