Tungsten isotopes in bulk meteorites and their inclusions—Implications for processing of presolar components in the solar protoplanetary disk

Abstract

We present high precision, low-and high-resolution tungsten isotope measurements of iron meteorites Cape York (IIIAB), Rhine Villa (IIIE), Bendego (IC), and the IVB iron meteorites Tlacotepec, Skookum, and Weaver Mountains, as well as CI chondrite Ivuna, a CV3 chondrite refractory inclusion (CAI BE), and terrestrial standards. Our high precision tungsten isotope data show that the distribution of the rare p-process nuclide 180 W is homogeneous among chondrites, iron meteorites, and the refractory inclusion. One exception to this pattern is the IVB iron meteorite group, which displays variable excesses relative to the terrestrial standard, possibly related to decay of rare 184 Os. Such anomalies are not the result of analytical artifacts and cannot be caused by sampling of a protoplanetary disk characterized by p-process isotope heterogeneity. In contrast, we find that 183 W is variable due to a nucleosynthetic s-process deficit/r-process excess among chondrites and iron meteorites. This variability supports the widespread nucleosynthetic s/r-process heterogeneity in the protoplanetary disk inferred from other isotope systems and we show that W and Ni isotope variability is correlated. Correlated isotope heterogeneity for elements of distinct nucleosynthetic origin ( 183 W and 58 Ni) is best explained by thermal processing in the protoplanetary disk during which thermally labile carrier phases are unmixed by vaporization thereby imparting isotope anomalies on the residual processed reservoir.

Origin of the analytical 183W effect and its implications for tungsten isotope analyses

“…2, these variations are best described as pure deficit in 183 W, where the largest measured anomalies correspond to a deficit of ∼2.3 per 10 5 atoms of 183 W. These observations were not only made throughout the analyses at the IfP (Kruijer and Kleine, 11 and references in Section 2.1), but similar systematics were also reported for processed terrestrial standards in high-precision MC-ICP-MS studies conducted in numerous other laboratories ( e.g. , Cook and Schönbächler, 14 ETH Zürich; Holst et al , 29 University of Copenhagen; Shirai and Humayun, 30 Florida State University; Takamasa et al , 31 JAMSTEC; Tusch et al , 15 University of Cologne; Willbold et al , 13 University of Bristol).…”

“…2), which is contrary to the effect of organic interferences on mass 183 that occasionally occurred in some studies. 5,29,34 Moreover, the generation of W hydrides, as suggested by Breton and Quitté, 35 cannot explain Fig. 2 W isotope diagrams for kimberlite samples (blue) and geological reference materials (green) obtained by MC-ICP-MS.…”

High-precision measurement of W isotopes in Fe–Ni alloy and the effects from the nuclear field shift

“…External precisions (2SD) for the other ratios are 3 182 W (6/3) AE 0.07, 3 184 W (6/3) AE 0.05, 3 182 W (6/4) AE 0.08, and 3 183 W (6/4) AE 0.08. These results, as well as the uncertainties on individual samples, are comparable to previous studies 5,6,20,22,23 of metallic samples for which samples were analyzed multiple times (i.e., n > 1).…”

“…19 The external reproducibilities (2SD), obtained from the 20 replicates of SRM 129c, for 3 180 W (6/4) and 3 180 W (6/3) are AE 0.49 and AE 0.48, respectively. These values represent an analytical resolution that is better by a factor of z2.4 or more compared to previous studies 6,7,9,20,21 of W isotopes using MC-ICPMS (Fig. 1).…”

“…1 Isotopes of W measured in meteorites have also been used to dene the level of isotopic heterogeneity among the building materials within the protoplanetary disk and to ascertain the stellar origins of these materials. [2][3][4][5][6] Several recent studies [7][8][9] reported variations in the relative abundance of 180 W in iron meteorites, which is the least abundant W isotope (0.1198% (ref. 10)).…”