Tholeiitic glasses were dredged from the submarine rift zones of the five volcanoes comprising the island of Hawaii and Loihi Seamount. The major element composition of the glasses follows a systematic trend that is related to the stage of evolution of the volcano. Glasses from Loihi Seamount (the youngest Hawaiian volcano) are enriched in Fe, Ca, Ti, Na, and K and depleted in Si and Al relative to the glasses from the other, older volcanoes. Kilauea is intermediate in age and its glasses are intermediate in composition between those from Loihi and Mauna Loa, the largest and oldest of the active Hawaiian tholeiitic volcanoes. The volatile contents (H20, CO2, S, F, Cl) of the glasses from these volcanoes follow the same trend (highest in Loihi; lowest in Mauna Loa). Glasses from Hualalai Volcano are similar in composition to those from Mauna Loa; those from Kohala Volcano are similar to Kilauea; Mauna Kea glasses range from Mauna Loa‐like to Kilauea‐like. The observed systematic variation in composition of Hawaiian tholeiites may be related to the progressive melting and depletion of the source of these volcanoes during their growth. Oxygen and hydrogen isotope analyses were made on many of the glasses from each volcano. The δ18O values of Hawaiian tholeiites are distinctly lower than those of mid‐ocean ridge basalt (MORB) (averages: 5.1 versus 5.7). These low values are probably a distinct feature of hot spot lavas. The δD values for these glasses (−88 to −61) are typical of mantle and MORB values. Thus the H2O in the Hawaiian glasses is probably of magmatic origin. Previous isotopic and trace element data indicate that the source of Hawaiian tholeiites contains two distinct source components. Based on the results of this study, the plume component in the source for Hawaiian tholeiites is characterized by moderate 87Sr/86Sr (0.7035–0.7037) and 206Pb/204Pb ratios (18.6–18.7), a low δ18O value (∼5.0), and greater contents of volatiles, Fe, Ca, Ti, Na and K relative to the MORB source.

No abstract

INTRODUCTION.Since discovery of apparent carbonate carbon in Naldala [1], significant evidence has accumulated for occurrence of volatile compounds in shergotfites and nakhlites. Gooding and Muenow [2] showed that at least one shergottite (EETA79001) contains substantial sulfur in a highly oxidized form and that the oxidation must have occured on the shergottite parent planet. Burgess et al. [3] also found oxidized sulfur in ALHA77005, Shergotty, Nakhla, and Chassigny. Kerridge [4] reported carbon and deuterium of apparent pre-terrestrial origin in Shergotty and Lafayette (a nakhlite). In addition, discrete grains of salt minerals have been documented in EETA79001 and Nakhla [5][6][7]. Here we present final results from our study of volatile compounds [8] in three shergottites, one naldalite, and three eucrite control samples. SAMPLES AND METHODS. Antarctic meteorites included Allan Hills specimens ALHA77005 (shergottite) and ALHA81001 (eucrite), as well as Elephant Moraine specimens EETA79001 (shergottite; lithologies A, B, and C), and EETA79004 (eucrite). A Pasamonte eucrite specimen (USNM-897) was obtained from the U. S. National Museum and a Nakhla specimen (BMNH-1911,369) from the British Museum (Natural History). A Shergotty specimen (GSI-179) was sub-divided from material allocated by the Geological Survey of India to Duke [9]. Samples from the exterior (0-0_5-era depth, including fusion crust) and interior (> 1-cm depth) of each meteorite were individually analyzed so that terrestrial weathering and contamination could be recognized and not misinterpreted as parent-body effects. Each sample (20-80 rag) was pyrolyzed by continuous heating to 1500 K at 5-6 K/rain under 10-7 torr vacuum in a Knudsen cell fitted with a high-purity aluminum oxide liner. Evolved gases were analyzed by a quadrupole mass spectrometer that was continuously scanned over m/e = 2-100 to simultaneously measure abundances of H20, CO 2, CO, SO2, S2, H2S, HCI, C1, and hydrocarbons. RESULTS. WATER. For interior samples of shergottites, H20-release profiles and total water concentrations (< 0.1%), are not obviously correlated with similar data for other volatile species. A typical H20-release profile consists of a single broad peak at 350-700 K that suggests desorption of loosely bound water. Although Nakhla was previously suspected to contain hydrous phases [7,10,11], its measured water content was less than anticipated and its H20-release profile was similar to those of shergottites. As discussed below for chlorine, however, it is possible that much of Nakhla's indigenous water reacted to form HCI during pyrolysis. Therefore, the actual water content of Nakhla may be significantly higher than the 0.007% measured as evolved H20. Kerridge [4] reported a total of 13.3 ppm H in Shergotty and 58.3 ppm H in the nakhlite, Lafayette, but discarded as terrestrial contamination all gases extracted at < 723 IC Judging from our results for Nakhla, however, HCI evolution (and, by inference, water loss) begins at < 700 K in nakhlites. Therefore, it...