TY - JOUR
T1 - Opaque minerals in the matrix of the Bishunpur (LL3.1) chondrite
T2 - Constraints on the chondrule formation environment
AU - Lauretta, Dante S.
AU - Buseck, P R
AU - Zega, Thomas J.
N1 - Funding Information:
This work was supported by NASA grant NAG5-4308. C. Moore and the Center for Meteorite Studies at ASU provided the samples of Bishunpur. We thank J. Clark and G. Benedix for assistance with the JEOL 8600 microprobe. We also thank A. Higgs and S. Myhajlenko for use of and assistance with the Hitachi 4700 field-emission SEM. We are grateful to S. Mostefaoui, H. C. Connolly, Jr., and X. Hua for interesting discussions. H. C. Connolly, Jr., A. N. Krot, and S. Mostefaoui provided constructive reviews. Also, the comments of the Associate Editor, H. Palme, were very helpful in revising the manuscript.
PY - 2001
Y1 - 2001
N2 - The chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the Bishunpur LL3.1 ordinary chondrite provide insight into the nebular environment in which they formed. The assemblages consist of a kamacite (Fe,Ni) core that is rimmed by troilite (FeS) and fayalite (Fe2SiO4). Accessory phases in the rims include silica (SiO2), chromite (FeCr2O4), whitlockite (Ca3(PO4)2), maricite (FeNaPO4), magnetite (Fe3O4), and tetrataenite (FeNi). We suggest that the metal melted in and equilibrated with an igneous chondrule under high-temperature, reducing conditions. In this environment the molten alloys incorporated varied amounts of Si, Ni, P, Cr, and Co, depending on the oxygen fugacity and temperature of the melt. Some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas. As the temperature dropped, the alloy solidified and volatile elements corroded the metal. The main reaction products were troilite and fayalite. Thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula. Kinetic factors are used to place a lower limit on the formation temperature. We determine that the metal corroded between 1173 and 1261 K at a total pressure in the range of 10-5.0 to 10-4.1 bars and a dust/gas ratio of 302 to 355 x relative to solar composition. These conditions are consistent with our model that the metal corroded in a dust-rich region of the solar nebula that was cooling after a chondrule formation event.
AB - The chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the Bishunpur LL3.1 ordinary chondrite provide insight into the nebular environment in which they formed. The assemblages consist of a kamacite (Fe,Ni) core that is rimmed by troilite (FeS) and fayalite (Fe2SiO4). Accessory phases in the rims include silica (SiO2), chromite (FeCr2O4), whitlockite (Ca3(PO4)2), maricite (FeNaPO4), magnetite (Fe3O4), and tetrataenite (FeNi). We suggest that the metal melted in and equilibrated with an igneous chondrule under high-temperature, reducing conditions. In this environment the molten alloys incorporated varied amounts of Si, Ni, P, Cr, and Co, depending on the oxygen fugacity and temperature of the melt. Some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas. As the temperature dropped, the alloy solidified and volatile elements corroded the metal. The main reaction products were troilite and fayalite. Thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula. Kinetic factors are used to place a lower limit on the formation temperature. We determine that the metal corroded between 1173 and 1261 K at a total pressure in the range of 10-5.0 to 10-4.1 bars and a dust/gas ratio of 302 to 355 x relative to solar composition. These conditions are consistent with our model that the metal corroded in a dust-rich region of the solar nebula that was cooling after a chondrule formation event.
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U2 - 10.1016/S0016-7037(00)00615-3
DO - 10.1016/S0016-7037(00)00615-3
M3 - Article
AN - SCOPUS:0035034174
SN - 0016-7037
VL - 65
SP - 1337
EP - 1353
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 8
ER -