Meteorites calcium-aluminum-rich inclusions

Huss GR, MacPherson GJ, Wasserburg GJ, Russell SS, Srinivasan G (2001) Aluminum-26 in calcium-aluminum-rich inclusions and chondrales from unequilibrated ordinary chondrites. Meteorit Planet Sci... 

MacPherson GJ, Huss GR, Davis AM (2003) Extinct Be in type A calcium-aluminum-rich inclusions from CV chondrites. Geochim Cosmochim Acta 67 3615-3179 Matthews GJ, Cowan JJ (1990) New insights into the astrophysical r-process. Nature 345 491-494 McCulloch MT, Wasserburg GJ (1978a) Barium and neodymium isotopic anomalies in the Allende meteorite. Astrophys J 220 L15-L19... 

Laser ablation combined with LA-MC-ICPMS provides a new dimension to the analysis of Mg isotopes in calcium aluminum-rich inclusions from primitive meteorites. Dispersion in 26Mg - Al/ Mg evolution lines can be correlated with mass-dependent variahons in 5 Mg that distinguish open-system from closed-system processes. The ultimate product of such studies will be a better understanding of the chronological significance of variations in Mg in these objects. 

Russell SS, Huss GR, Fahey AJ, Greenwood RC, Hutchison R, Wasserburg GJ (1998) An isotopic and petrologic study of calcium-aluminum-rich inclusions from C03 meteorites. Geochim Cosmochim Acta 62(4) 689-714... 

McKeegan, K. D., Chaussidon, M. and Robert, F. (2000) Incorporation of short-lived 10Be in a calcium-aluminum-rich inclusion from the Allende meteorite. Science, 289, 1334-1337. 

Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001).

The terrestrial planets and the Moon are differentiated, with dense iron-rich cores and rocky mantles. The uncompressed densities of Earth and Venus are similar. Mercury has a high density which suggests it has relatively large core. Conversely, the Moon has a low density, indicating a very small core. There is little observational evidence that asteroids are differentiated except for Vesta and Ceres (Thomas et al. 2005). However, iron meteorites from the cores of differentiated asteroids are quite common, and the irons found to date come from several dozen different parent bodies (Meibom Clark 1999). Most meteorites come from asteroids that never differentiated. These chondritic meteorites consist of intimate mixtures of heterogeneous material millimeter-sized rounded particles that were once molten, called chondrules, similarly sized calcium-aluminum-rich inclusions (CAIs), and micrometer-sized matrix grains. 

Our description of meteorite mineralogy starts with the minerals characteristic of the calcium-aluminum-rich inclusions (CAIs). The mineralogy of CAIs varies systematically with their composition. The most Al-rich CAIs contain spinel, hibonite, and/or grossite. More rarely, corundum or calcium mono-aluminate is present. As the bulk composition becomes more Si-rich, the melilite solid solution becomes important. With additional Mg and Si in the bulk composition, fassaite and anorthite are present. 

The MIF phenomenon was first observed by Clayton in 1973 for the isotopic oxygen content in the earliest solids in the solar system, the so-called calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondritic meteorites [1]. The slope of versus plot for the CAIs was close to unity, the CAIs being equally deficient in the heavy O isotopes, deficient in the S notation sense, while the ozone is equally enriched in those isotopes in that sense, as in Figure 2.2. Both are examples of an MIF. Interest in this striking phenomenon for the CAIs is motivated by what it may reveal about the formation of the early solar system. Standard reaction rate transition state theory [3], and behavior of oxygen an other isotope fractionation in many other systems, would have led, instead, to the slope... 

Fagan T. J., McKeegan K. D., Krot A. N., and Keil K. (2001) Calcium, aluminum-rich inclusions in enstatite chondrites (2) oxygen isotopes. Meteorit. Planet. Sci. 36, 223 —230. 

RusseU S. S. (1998) A survey of calcium—aluminum-rich inclusions from Rumuritiite chondrites impUcations for relationships between meteorite groups. Meteorit. Planet. Sci. 33, A131-A132. 

Srinivasan G., Huss G. R., and Wasserburg G. J. (2000a) A petrographic, chemical and isotopic study of calcium— aluminum-rich inclusions and aluminum-rich chondrules from the Axtell (CV3) chondrite. Meteorit. Planet. Sci. 35, 1333-1354. 

Srinivasan G., Krot A. N., and Ulyanov A. A. (2000b) Aluminum-magnesium systematics in anorthite-rich chon-dmles and calcium-aluminum-rich inclusions from the reduced CV chondrite Efremovka. Meteorit Planet Sci. 35, A151-A152. 

Wark D. and Boynton W. V. (2001) The formation of rims on calcium-aluminum-rich inclusions Step 1. Flash heating. Meteorit. Planet. Sci. 36, 1135-1166. 

Calcium-Aluminum-rich Inclusions in Chondritic Meteorites... 

Calcium-aluminum-rich inclusions (CAIs) are submillimeter- to centimeter-sized clasts in chondritic meteorites, whose ceramic-like chemistry and mineralogy set them apart from other chondrite components. Since their hrst descriptions more than 30 years ago (e.g., Christophe Michel-Levy, 1968), they have been the objects of a vast amount of study. At hrst, interest centered on the close similarity of their mineralogy to the... 

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