Tantalum Isotope Compositions in Terrestrial and Meteoritic Materials

Markus Pfeifer, Carsten Münker, Nicholas S. Lloyd

Research output: Contribution to conferenceConference Abstract


Tantalum consists of two isotopes (180 and 181 amu) with
180Ta being the rarest stable isotope in the solar system.
Interestingly, 180Ta is only stable as an isomer in its excited
state. Thus, it hardly survives at harsh stellar conditions, which
in turn are needed for its production [1]. The exact
nucleosynthetic contributions from both p-process and
branching of the s-process pathway are still debated [2]. A
comparison of Ta isotope compositions with those of other
heavy elements with known nucleosynthetic anomalies
(e.g. 3-[5]) can help to solve this issue. Isotope ratio
measurements are analytically challenging, because the natural
180Ta/181Ta (ca. 0.00012) is very low. Here we report the first
high precision Ta data for terrestrial rocks from diverse
settings and for meteorites, also including refractory
All geological samples and bulk meteorites are
indistinguishable from our terrestrial AMES Ta standard. In
contrast, one refractory CAI from the Allende CV3 meteorite
displays a resolvable lower 180Ta/181Ta isotope ratio.
The homogeneity of terrestrial materials comprising a
range from primitive mantle melts to evolved ore deposits
suggests only minor stable Ta isotope fractionation on Earth
within our typical analytical uncertainty of ca. 3.5 e-units.
Therefore, mass dependent nuclear effects related to melting
processes are regarded unlikely for explaining the CAI
signature. Nevertheless, evaporation in the high-temperature
environment of CAI formation cannot completely be ruled out,
even for refractory elements. Alternatively, metastable 180Ta
may have been de-excited by γ-ray flux from the young sun.
However, such effects have not been observed for other
nuclides in meteorites. We therefore prefer a nucleosynthetic
origin for the Ta isotope anomaly in the CAI, supporting the
view of a compositionally heterogeneous solar nebula at the
time of CAI formation. The inherited Ta isotopic signature is
assumed to stem from presolar material that most likely had
either an r-process excess or a p-process deficit.
Original languageEnglish
Publication statusPublished - 1 May 2015
EventGoldschmidt 2015 - Prague , United Kingdom
Duration: 16 Aug 201521 Aug 2015


ConferenceGoldschmidt 2015
Country/TerritoryUnited Kingdom


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