Showing papers by "Gary R. Huss published in 2003"

The Initial Abundance of 60 Fe in the Solar System

Abstract: 60Fe, which decays to radiogenic 60Ni (60Ni*), is a now extinct radionuclide. 60Fe is produced only in stars and thus provides a constraint on the stellar contribution to solar system radionuclides. Its short half-life [t1/2 = 1.49 × 106 yr (1.49 Myr)] makes it a potential chronometer for the early solar system. We found clear evidence for 60Ni* in troilite (FeS) grains from the Bishunpur and Krymka chondrites, two of the least metamorphosed (LL3.1) ordinary chondrites. The weighted means of inferred initial 60Fe/56Fe ratios [(60Fe/56Fe)0] for the troilites are (1.08 ± 0.23) × 10-7 and (1.73 ± 0.53) × 10-7 for Bishunpur and Krymka, respectively. We compare our data with upper limits established previously on (60Fe/56Fe)0 for a chondrule in an unequilibrated ordinary chondrite, Semarkona, and for troilites in a relatively metamorphosed chondrite, Ste. Marguerite, taking into account their 26Al-26Mg ages. The 60Fe and 26Al chronometers can be combined to produce a consistent chronology for Ca-Al-rich inclusions, which are thought to be the earliest solar system solids, chondrules, troilites, and Ste. Marguerite. The initial 60Fe/56Fe for the solar system is inferred from this chronology to have been 2.8 × 10-7 to 4 × 10-7. This is at or below the low end of predictions for a supernova source.

Al‐Mg systematics of CAIs, POI, and ferromagnesian chondrules from Ningqiang

Abstract: We have made aluminum-magnesium isotopic measurements on 4 melilite-bearing calcium-aluminum-rich inclusions (CAIs), 1 plagioclase-olivine inclusion (POI), and 2 ferromagnesian chondrules from the Ningqiang carbonaceous chondrite. All of the CAIs measured contain clear evidence for radiogenic ^(26)Mg^* from the decay of ^(26)Al (τ = 1.05 Ma). Although the low Al/Mg ratios of the melilites introduce large uncertainties, the inferred initial ^(26)Al/^(27)Al ratios for the CAIs are generally consistent with the value of 5 x 10^(−5). There is clear evidence of ^(26)Al^* in one POI and two chondrules, but with considerable uncertainties in the value of (^(26)Al/^(27)Al)0. The (^(26)Al/^(27)Al)_0 ratios for the POI and the chondrules are 0.3–0.6 x 10^(−5), roughly an order of magnitude lower than the canonical value. Ningqiang shows very little evidence of metamorphism as a bulk object and the (^(26)Al/^(27)Al)_0 ratios in its refractory inclusions and chondrules are consistent with those found in other unmetamorphosed chondrites of several different classes. Our observations and those of other workers support the view that ^(26)Al was widely and approximately homogeneously distributed throughout the condensed matter of the solar system. The difference in (^(26)Al/^(27)Al)0 between CAIs and less refractory materials seems reasonably interpreted in terms of a ∼2 million year delay between the formation of CAIs and the onset of formation of less refractory objects. The POI shows clear differences in ^(25)Mg/^(24)Mg between its constituent spinels and olivine, which confirms that they are partially reprocessed material from different sources that were rapidly quenched.

On the Nature and Origins of FeO-rich Chondrules in CR2 Chondrites: A Preliminary Report

Abstract: PRELIMINARY REPORT. Harold C. Connolly, Jr., Michael K. Weisberg, and Gary R. Huss. Dept. Physical Sciences, Kingsborough College of the City University of New York, 2001 Oriental Blvd., Brooklyn N.Y. 100235 (hconnolly@kbcc.cuny.edu); Dept. Earth Planetary Sciences, AMNH Central Park West, New York, N.Y. 110024; Dept. Geological Sciences, Rutgers University, 610 Taylor Rd. Piscataway, NJ 08854-8066; Dept. Geological Sciences & Center for Meteorite Studies, Arizona State University, Tempe, AZ 85287-1404.

Isotopic anomalies and presolar grains: Probes of nebular processes

Abstract: The solar system formed by gravitational collapse of a molecular cloud core composed of gas and dust. Some of the dust survived solar system formation to be incorporated into meteorites. Known types of presolar dust include diamond, SiC, graphite, Al2O 3, SiN, hibonite, spinel, organic compounds, and silicates. The chemical properties and thermal resistance of these materials cover a large range. Thus, different degrees or styles of chemical and thermal processing in the solar nebula should produce different fractionations among the presolar materials. Compositional classes of chondrites originated through processing in the solar nebular. Volatility-based and metalsilicate fractionations are the best-known signatures of this processing. The assemblage of presolar grains in a chondrite class correlates with the degree of volatility-controlled fractionation reflected in its bulk composition. For example, CI chondrites and CM2 matrices have bulk compositions most like the solar photosphere. They also have the highest abundances of thermally labile but chemically resistant presolar graphite and the P-3 noble-gas component in diamonds, they have the highest SiC abundances and among the highest diamond abundances, and they have D-rich organics and presolar oxides. Thus, they contain the widest variety of presolar materials and the highest abundances of labile components in meteorites. In contrast, CV3 and CO3 chondrites show some of the largest refractory lithophile element enrichments. These meteorites have no detectable presolar graphite, very low P3 contents in diamonds, little Drich organics and SiC, but among the highest matrixnormalized diamond abundances. Thus, CV3s and CO3s contain among the most fractionated assemblages of presolar materials in chondrites. Other meteorites show similar correlations. These correlations have important implications. First, presolar grains experienced the same processes that produced the volatility-controlled chemical fractionations among chondrite classes. Second, most of the material that makes up chondrites did not evaporate and recondense in the solar system. Instead, chondrites formed primarily from thermally processed presolar dust, only some of which remains recognizable. Third, assumed relationships among chondrite classes should be re-evalutated.