182 Hf– 182 W systematics in eucrites: the puzzle of iron segregation in the early solar system

Tungsten Nuclear Anomalies in Planetesimal Cores

“…Subsequent melting induced differentiation (i.e., segregation of metal and silicate), the timing of which can be determined by measuring the abundance of 182 W, a decay product of short-lived 182 Hf (t 1 = 2 ¼ 8:9 AE 0:09 Myr; Vockenhuber et al 2004). Using this extinct radioactivity, it is possible to establish the accretion timescales of Earth and Mars, date the Moonforming impact, and date magmatic differentiation events in meteorite parent bodies (e.g., Quitté et al 2000;Yin et al 2002;Kleine et al 2002;Schoenberg et al 2002;Lee et al 2002;Foley et al 2005;Markowski et al 2006a).…”

“…Excluding 180 W, which has too low of an abundance to be measured with sufficient precision, and 186 W and 183 W, which are used for correcting the measurements for instrumental mass fractionation in both this study and previous work (e.g., Yin et al 2002;Quitté et al 2000;Markowski et al 2006a), the only other abundant W isotope besides 182 W remaining to quantify the degree of mixing of nucleosynthetic sources in the solar nebula is 184 W. In order to document the degree of homogenization of the solar nebula for the products of stellar nucleosynthesis, we have measured the W isotopic compositions of some magmatic iron meteorites that are thought to be remnants of planetesimal cores. The ultimate goals are to refine the s-process path in the W mass region and correct for any nucleosynthetic anomalies that could affect 182 Hf-182 W chronology in meteorites.…”

Dating the First Stage of Planet Formation

“…Chambers 2004). Using planet-wide metalsilicate segregation and core formation as a tool to monitor the rate of late-stage accretion processes, the stage II (Vesta to Mars) and stage III (Earth-Moon system) formation timescales are now well established (e.g., Lugmair & Shukolyukov 1998;Quitté et al 2000;Yin et al 2002;Foley et al 2005;Jacobsen 2005; Kleine et al 2005). Stage I is the least understood among the three stages because there are very few observational constraints and the physics of grain growth in the solar nebula from micron-sized particles to kilometer-sized bodies is not well understood (Youdin & Shu 2002).…”

182Hf‐182W chronometry and the early evolution history in the acapulcoite‐lodranite parent body

“…The short-lived chronometer 182 Hf-182 W, t 1/2 = 8.90 ± 0.09 million years (Vockenhuber et al 2004), has been shown to be one of the best tools for studying the metal-silicate differentiation and thermal history of early planetary bodies (Harper et al 1991;Harper and Jacobsen 1996;Halliday 1996, 1997;Horan et al 1998;Schoenberg et al 2002;Yin et al 2002;Kleine et al 2002Kleine et al , 2004Kleine et al , 2005aKleine et al , 2005bQuitté et al 2000Quitté et al , 2005Quitté and Birck 2004;Lee 2005;Markowski et al 2006aMarkowski et al , 2006b). This is due largely to the different chemical behavior between Hf and W, with Hf tending to concentrate in the silicate mantle, while W goes into the metal core during metal-silicate segregation (Lee and Halliday 1996;Kleine et al 2005aKleine et al , 2005bLee 2005;Quitté et al 2005;Markowski et al 2006aMarkowski et al , 2006b).…”