Masahiko Tanaka^1,*, Tomoki Nakamura², Takaaki Noguchi³, Aiko Nakato², Hatsumi Ishida², Toru Yada⁴, Kei Shirai⁴, Akio Fujimura⁴, Yukihiro Ishibashi⁴, Masanao Abe⁴, Tatsuaki Okada⁴, Munetaka Ueno⁴, Toshifumi Mukai⁴

¹Synchrotron X-ray Station at SPring-8, National Institute for Materials Science (NIMS), Sayo, Hyogo, Japan
²Department of the Earth and Planetary Material Science, Tohoku University, Sendai, Miyagi, Japan
³Department of Materials and Biological Sciences, Ibaraki University, Mito, Ibaraki, Japan
⁴JAXA-ISAS, Sagamihara, Kanagawa, Japan

The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131-index required for the thermometer, which is the difference in X-ray diffraction peak positions between the 131 and 131 reflections of plagioclase, was obtained by a high-resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring-8. Crystallization temperatures were successfully determined from the Δ131-indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.

Reference
Tanaka M, Nakamura T, Noguchi T, Nakato A, Ishida H, Yada T, Shirai K, Fujimura A, Ishibashi Y, Abe M, Okada T, Ueno M and Mukai T (in press) Crystallization temperature determination of Itokawa particles by plagioclase thermometry with X-ray diffraction data obtained by a high-resolution synchrotron Gandolfi camera. Meteoritics & Planetary Science
[doi:10.1111/maps.12215]
Published by arrangement with John Wiley & Sons

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W. Akram^1,2, M. Schönbächler^1,2, P. Sprung³, and N. Vogel^2,4

¹School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
²Institute for Geochemistry and Petrology, ETH, Clausiusstrasse 25, 8092 Zürich, Switzerland
³Institut für Planetologie, Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster, Germany
⁴Eawag, Swiss Federal Institute of Aquatic Science and Technology, Water Resources and Drinking Water, Ueberlandstrasse 133, 8600 Dübendorf, Switzerland

Recent work based on analyses of meteorite and terrestrial whole-rock samples showed that the r- and s- process isotopes of Hf were homogeneously distributed throughout the inner solar system. We report new Hf isotope data for Calcium-Aluminum-rich inclusions (CAIs) of the CV3 carbonaceous chondrite Allende, and novel high-precision Zr isotope data for these CAIs and three carbonaceous chondrites (CM, CO, CK). Our Zr data reveal enrichments in the neutron-rich isotope ⁹⁶Zr (≤1ε in ⁹⁶Zr/⁹⁰Zr) for bulk chondrites and CAIs (~2ε). Potential isotope effects due to incomplete sample dissolution, galactic and cosmic ray spallation, and the nuclear field shift are assessed and excluded, leading to the conclusion that the ⁹⁶Zr isotope variations are of nucleosynthetic origin. The ⁹⁶Zr enrichments are coupled with ⁵⁰Ti excesses suggesting that both nuclides were produced in the same astrophysical environment. The same CAIs also exhibit deficits in r-process Hf isotopes, which provides strong evidence for a decoupling between the nucleosynthetic processes that produce the light (A ≤ 130) and heavy (A > 130) neutron-rich isotopes. We propose that the light neutron-capture isotopes largely formed in Type II supernovae (SNeII) with higher mass progenitors than the supernovae that produced the heavy r-process isotopes. In the context of our model, the light isotopes (e.g. ⁹⁶Zr) are predominantly synthesized via charged-particle reactions in a high entropy wind environment, in which Hf isotopes are not produced. Collectively, our data indicates that CAIs sampled an excess of materials produced in a normal mass (12-25 M_☉) SNII.

Reference
Akram W, Schönbächler M, Sprung P and Vogel N (2013) Zirconium—Hafnium Isotope Evidence from Meteorites for the Decoupled Synthesis of Light and Heavy Neutron-rich Nuclei. The Astrophysical Journal 777:169.
[doi:10.1088/0004-637X/777/2/169]

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