TY - CHAP
T1 - Iron and stony-iron meteorites
T2 - evidence for the formation, crystallization, and early impact histories of differentiated planetesimals
AU - Ruzicka, Alex M.
AU - Haack, Henning
AU - Chabot, Nancy L.
AU - Scott, Edward Robert Dalton
PY - 2017/1/1
Y1 - 2017/1/1
N2 - Introduction By far most of the melted and differentiated planetesimals that have been sampled as meteorites are metal-rich iron meteorites or stony-iron meteorites. The parent asteroids of these meteorites accreted early and differentiated shortly after the solar system formed, producing some of the oldest dated materials. The main heat source responsible for the melting and differentiation of asteroids was 26Al (Ghosh et al., 2006; Kleine et al., Chapter 11, this volume). Unlike the parent bodies of chondrites, the differentiated bodies accreted while 26Al was sufficiently abundant to cause melting. In this review, we summarize properties and interpretations for iron and stony-iron meteorites (Figure 7.1). Such meteorites provide important constraints on the nature of metal-silicate separation and mixing in planetesimals undergoing partial to complete differentiation. They include iron meteorites that formed by the solidification of cores (fractionally crystallized irons), irons in which partly molten metal and silicates of diverse types were mixed together (silicate-bearing irons), stony-irons in which partly molten metal and olivine from cores and mantles were mixed together (pallasites), and stony-irons in which partly molten metal and silicate from cores and crusts were mixed together (mesosiderites). Taxonomy and Associations Although differentiated meteorites are less common than chondritic meteorites, they are believed to sample a much larger number of parent bodies. Geochemical and isotopic data are useful for assigning iron and stony-iron meteorites into groups, which contain meteorites that probably originated on different parent bodies. Such data also allow evaluations of which groups might be associated, and what processes affected the meteorites in the groups. The most widely used parameters for taxonomy of iron and stony-iron meteorites are metal compositions (e.g. bulk Ni, Ir, Ga, Ge, Au), oxygen isotope compositions of silicates or oxide minerals (namely Δ17O = δ17O - 0.52δ18O, which should not vary during igneous processes), and, to a lesser extent, silicate mineral compositions (olivine Fa [fayalite] and low-Ca pyroxene Fs [ferrosilite]). Table 7.1 provides geochemical and isotopic data for selected iron and stony-iron meteorite groups, and Figure 7.2 shows plots for Ni-Ir-Ga metal compositions in these groups.
AB - Introduction By far most of the melted and differentiated planetesimals that have been sampled as meteorites are metal-rich iron meteorites or stony-iron meteorites. The parent asteroids of these meteorites accreted early and differentiated shortly after the solar system formed, producing some of the oldest dated materials. The main heat source responsible for the melting and differentiation of asteroids was 26Al (Ghosh et al., 2006; Kleine et al., Chapter 11, this volume). Unlike the parent bodies of chondrites, the differentiated bodies accreted while 26Al was sufficiently abundant to cause melting. In this review, we summarize properties and interpretations for iron and stony-iron meteorites (Figure 7.1). Such meteorites provide important constraints on the nature of metal-silicate separation and mixing in planetesimals undergoing partial to complete differentiation. They include iron meteorites that formed by the solidification of cores (fractionally crystallized irons), irons in which partly molten metal and silicates of diverse types were mixed together (silicate-bearing irons), stony-irons in which partly molten metal and olivine from cores and mantles were mixed together (pallasites), and stony-irons in which partly molten metal and silicate from cores and crusts were mixed together (mesosiderites). Taxonomy and Associations Although differentiated meteorites are less common than chondritic meteorites, they are believed to sample a much larger number of parent bodies. Geochemical and isotopic data are useful for assigning iron and stony-iron meteorites into groups, which contain meteorites that probably originated on different parent bodies. Such data also allow evaluations of which groups might be associated, and what processes affected the meteorites in the groups. The most widely used parameters for taxonomy of iron and stony-iron meteorites are metal compositions (e.g. bulk Ni, Ir, Ga, Ge, Au), oxygen isotope compositions of silicates or oxide minerals (namely Δ17O = δ17O - 0.52δ18O, which should not vary during igneous processes), and, to a lesser extent, silicate mineral compositions (olivine Fa [fayalite] and low-Ca pyroxene Fs [ferrosilite]). Table 7.1 provides geochemical and isotopic data for selected iron and stony-iron meteorite groups, and Figure 7.2 shows plots for Ni-Ir-Ga metal compositions in these groups.
U2 - 10.1017/9781316339794.007
DO - 10.1017/9781316339794.007
M3 - Book chapter
SN - 978-1-107-11848-5
T3 - Cambridge Planetary Science Series
SP - 136
EP - 158
BT - Planetesimals
A2 - Elkins-Tanton, Lindy T.
A2 - Weiss, Benjamin
PB - Cambridge University Press
ER -