Oxygen Isotope Composition of Almahata Sitta


Douglas Rumble, Geophysical Laboratory, Carnegie Inst. of Washington, Washington DC, USA
The results of analysis of 10 fragments of Almahata Sitta for oxygen isotopes, 16O-17O-18O, demonstrates unequivocally that it belongs to the ureilite meteorite group. The oxygen isotope composition of Almahata Sitta matches not only the range of compositions measured by Clayton and Mayeda (1988) in their study of ureiilite meteorites but also resembles the pattern of heterogeneity observed by them. Oxygen isotope compositions expressed in reference to Vienna Standard Mean Ocean Water Analyses range between 7.7 and 5.0 per mil for delta 18O, from 3.9 to 0.3 per mil for delta 17O, and from -0.4 to -2.3 in Capital Delta 17O. The composition data scatter along a linear trend parallel to the Carbonaceous Chondrite Anhydrous Mineral line (CCAM) when plotted on a diagram of delta18O (x-axis) and delta 17O (y-axis). The data measured for Almahata Sitta lie superimposed upon those of Clayton and Mayeda (1988) and are indistinguishable from them.