This allows lots of Hf to decay to W, leading to epsilon-tungsten larger than zero. There are complicating factors that give cosmochemists the opportunity of delving more deeply into the processes involved in the initial differentiation of the planets. One of those is the behavior of the Hf and W left behind in the rocky portion. Shearer and Righter did experiments to quantify the behavior of W during the melting of silicates rocks. Iron meteorites like the one shown here formed when chondrites melted. The metal, because it was denser than the surrounding silicates, sank to form the core of a tiny planet in the asteroid belt.
Because the hafnium stayed behind, there was no source of W, giving a value of epsilon-tungsten less than 0. To determine the behavior of tungsten at high temperature and pressure, Kevin Righter used high-pressure apparatus at the University of Arizona. The samples to be studied were placed in the center of ceramic octahedral white and then squeezed between eight truncated tungsten carbide cubes grayish, metallic. The tungsten does not interfere with the experiments on the behavior of tungsten inside the ceramic octahedral.
Depending on the sizes of the octahedrons and the truncations on the tungsten carbide cubes, pressures between 3 and 30 billion pascals 30, to , times atmospheric pressure can be obtained. This corresponds to depths of about to km on Earth and to km on Mars. The assembled stack of eight cubes and the sample octahedron is placed in the center of this cylindrical module, between six wedges that are connected to a hydraulic system.
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The blue module is called a "multi-anvil module. The multi-anvil module is placed into a ton press in the laboratory of Professor Mike Drake right at the University of Arizona. Drake is a pioneer in determining partitioning behavior of trace elements from high-temperature and high-pressure experiments. Nancy Chabot left and Chris Capobianco right , then at the University of Arizona, observe a sample being pressurized.
The concentrations of tungsten were measured with the ion microprobe at the University of New Mexico. This complicated instrument consists of an ion source, mass spectrometer, and associated electronics and vacuum system. Such rocks could form late during the solidification of the lunar magma ocean. When rocks rich in ilmenite and high-calcium pyroxene melted, the magma would also have high epsilon-tungsten.
Residual elements were eluted sequentially with 5 c. A blank correction was applied to all samples, and the uncertainty of this correction is propagated in the final uncertainties of the isotope measurements reported in Table 1. Wasserburg for comments on an earlier version of this paper. We also thank Andy Davis and two anonymous referees for their constructive comments, which improved the quality of this paper.
The authors declare no conflict of interest. This article contains supporting information online at www. National Center for Biotechnology Information , U. Published online May Holst , a Mia B. Larsen , a James N. Connelly , a Jes K.
Author information Copyright and License information Disclaimer. Edited by Neta A. This article has been cited by other articles in PMC. Abstract Refractory inclusions [calcium—aluminum-rich inclusions, CAIs ] represent the oldest Solar System solids and provide information regarding the formation of the Sun and its protoplanetary disk. Open in a separate window. Supplementary Material Supporting Information: Click here to view. Acknowledgments We thank G.
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Footnotes The authors declare no conflict of interest. Short-lived radionuclides in the early solar system: Connelly JN, et al.
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Hf-w dating Mississippi
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