ENDEMIC Ru ISOTOPIC ANOMALIES IN IRON METEORITES AND IN ALLENDE
نویسندگان
چکیده
Small variations for Mo isotopes have been observed recently in the Allende meteorite and in iron meteorites, mesosiderites, and pallasites, using ICP-MS [1]. Large effects for Mo have been reported for leaches of Orgueil [2] and in SiC and graphite from Murchison [3-5]. Variations for Mo in bulk Allende and in Murchison have also been presented by NTIMS [6]. Effects in Ru isotopes can define further the preserved exotic r, s, and p contributions in this mass region , and possible effects in 98 Ru and 99 Ru from 98 Tc (4.2 Ma half-life) and 99 Tc (0.21 Ma half-life). Previous attempts at determination of Ru isotopes yielded no resolved effects [7-10]. The present work represents a substantial improvement in precision over the earlier work. We have developed chemical and mass spectromet-ric analytical techniques to determine the Ru isotope compositions in terrestrial standards and in meteorites. Because the Mo isotope interferences can affect 96 Ru and 98 Ru, we have used 99 Ru/ 101 Ru for the mass frac-tionation correction and applied the exponential law. Through improved chemical separations, we have reduced the Mo interference to 98 Mo/ 98 Ru<0.00002. All measurements were obtained in the new mass spec-trometry laboratory at JPL, using the ThermoFinnigan Triton, in static mode. The results on terrestrial standards of different chemical composition show external precision (reproducibility) of isotope ratio measurements to better than 0.3εu (2σ) for 100 Ru/ 101 Ru, 0.6εu for 102 Ru/ 101 Ru and 104 Ru/ 101 Ru, and 1εu to 2εu for 96 Ru/ 101 Ru and 98 Ru/ 101 Ru. The range of reproducibil-ity for normal Ru is shown as dashed lines in Fig. 1. The results are shown in Fig. 1. The y-axis lists the sample sequence number. Ordinary chondrites meas-These ordinary chondrites plot within the error envelopes of the terrestrial standards for all Ru isotopes. The minor isotopes 96 Ru and 98 Ru, show slightly larger uncertainties and scatter, but no anomalies. In contrast, analyses of two whole rock samples of the Allende carbona-ceous chondrite (#6-7) show hints of enrichments in 96 Ru, 98 Ru and 104 Ru and well-resolved depletions in 100 Ru of 1.2 and 1.6 εu. The measurements on Allende were obtained after the ordinary chondrite and iron meteorite analyses. Iron meteorite metal from Canyon Diablo (IA, #8) and Pitts (IB, #9) show normal values. For three IIAB irons, Bennett County (#10), Negrillos (#11) …
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