Petrogenesis of Ultramafic Xenoliths from the 1800 Kaupulehu Flow ...

168 CHEN-HONG CHEN ET AL.10nKaupulthu duniti xtnolithsKaupulehu wthrlite & clinopyroxtnitt xtnolitht20-io 15 -cnn-1 10-u.Hawaiian tholti5 -I--rm n rr-i• 1 •10^5 - Hawaiian alkalic basaltsn n90 80 70 60 50 40nMole % Fo in olivineFIG. 2 Histogram of olivine compositions in Hawaiian rocks. Data for Hawaiian tholeutic and alkalic basalts arefrom Lofgren et al. (1981). Xenolith data are from Tables 2 and 3.exists between Mg/(Mg -I- Fe 2 + ) in spinel and the forsterite content of coexisting olivine(Tables 2-5), which indicates equilibrium between spinel and coexisting olivine (Sigurdsson,1977). This correlation is similar to that observed for Mid-Atlantic Ridge basalts (Sigurdsson& Schilling, 1976), for Hawaiian basalts (Evans & Wright, 1972; Clague et al, 1980a;Lofgren et al., 1981), and in the Stillwater complex (Jackson, 1969). The only zoned spinel isin sample X2 (Table 5), which shows increasing Mg/(Mg + Fe 2 + ) from core to rim.ClinopyroxeneWithin a single thin section, compositions of clinopyroxene grains in the Hualalaiultramafic xenoliths (Tables 6 and 7) are identical within analytical uncertainty. Figure 3