Calcium-aluminum inclusions

Broken surface of the Allende meteorite, a chondrite that fell in Mexico in 1969. Note the abundant round chondrules and white calcium-aluminum inclusions. 

Oxygen 3-isotope plot showing excesses of 160 in minerals from calcium-aluminum inclusions (CAIs). All samples from Earth rocks plot along the terrestrial fractionation line. Mass-dependent fractionation processes cannot move a composition off of this line, so the excesses of 160 were clearly isotopic anomalies. After Clayton et al. (1977). 

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

Clayton et al. (1973) observed that the high-temperature calcium-aluminum inclusions (CAIs) present in the carbonaceous chondrite Allende possess an oxygen isotope composition of rather than the expected mass-dependent = 0.56 O. It was suggested that this anomalous isotopic composition must derive from a nuclear, rather than chemical process. In general, an equality may arise in... 

Calcium—Silicon. Calcium—silicon and calcium—barium—siUcon are made in the submerged-arc electric furnace by carbon reduction of lime, sihca rock, and barites. Commercial calcium—silicon contains 28—32% calcium, 60—65% siUcon, and 3% iron (max). Barium-bearing alloys contains 16—20% calcium, 9—12% barium, and 53—59% sihcon. Calcium can also be added as an ahoy containing 10—13% calcium, 14—18% barium, 19—21% aluminum, and 38—40% shicon These ahoys are used to deoxidize and degasify steel. They produce complex calcium shicate inclusions that are minimally harm fill to physical properties and prevent the formation of alumina-type inclusions, a principal source of fatigue failure in highly stressed ahoy steels. As a sulfide former, they promote random distribution of sulfides, thereby minimizing chain-type inclusions. In cast iron, they are used as an inoculant. 

Fig. 14.3 Three isotope plot of calcium-aluminum oxide inclusions in chrondrite meteorites compared with the terrestrial fractionation TFL line. For TFL m 0.5, the meteoric line shows m 0.9 (The data are from Clayton, R. N. et al., Earth Planet. Sci. Lett. 34,209 (1977) Geochim. Cosomochim Acta 63, 2089 (1999). Thiemens, M., Ann. Rev. Earth Planet. Sci. 34, 217 (2006))... 

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. 

Richter EM, Davis AM, Ebel DS, Hashimoto A (2002) Elemental and isotopic fractionation of type B calcium-aluminum-rich inclusions Experiments, theoretical considerations, and constraints on their thermal evolution. Geochim Cosmochim Acta 66(3) 521-540... 

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... 

Richter FM, Davis AM, Ehel DS, Hashimoto A (2002) Elemental and isotopic fractionation of Type B calcium-, aluminum-rich inclusions Experiments, theoretical considerations, and constraints on their thermal evolution. Geochim Cosmochim Acta 66 521-540 Richter FM, Davis AM, DePaolo DJ, Watson EB (2003) Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim Cosmochim Acta 67 3905-3923 Rudnick RL, Fountain DM (1995) Nature and composition of the continental crust—a lower crustal perspective. Rev Geophys 33 267-309... 

Figure 5-9 Al- Mg isochron for a calcium-aluminum-rich inclusion (CAI) E60. The initial isotopic ratio of (26ai/27ai)o 4,52 X 10 . Adapted from Amelin et al. (2002).

Amelin Y., Krot A.N., Hutcheon I.D., and Ulyanov A.A. (2002) Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions. Science 297, 1678-1683. 

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. 

MacPherson, G. J., Simon, S. B., Davis, A. M., Grossman, L. and Krot, A.N. (2005) Calcium-aluminum-rich inclusions major unanswered questions. In Chondrites and the Protoplanetary Disk, ASP Conference Series, 341, eds. Krot, A. N., Scott, E. R. D. and Reipurth, A. San Francisco Astronomical Society of the Pacific, pp. 225-250. 

Calcium-aluminum-rich inclusions The CAIs reveal a lot of isotopic action in calcium. But 4°Ca itself is taken as a reference for other isotopes because it is the most abundant. What is measured is the ratio of the other Ca isotope abundances to that of 4°Ca therefore attribution of an anomalous isotopic ratio to an anomaly in 4°Ca abundance is seldom made. Because of systematic linear variations with isotopic mass of the measured isotopic abundances, moreover, it is common to remove that effect by defining the ratio 44Ca/4°Ca as normal, a doubtful procedure, but common. Anomalies in other Ca isotopes thus appear as deviations from the linear slope set by the 44Ca/4°Ca ratio. All this is to say that a self-consistent analysis of the entire Ca suite is required. 

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