Geochimica d Cosmochimica Acla Vol. 56, pp. 1343-1363 Copyright 8 1992 Pergamon Press Ltd. Printed in U.S.A. 0016-7037/92/$5.00 + .oo Refractory inclusions with unusual chemical compositions from the Vigarano carbonaceous chondrite PAUL J. SYLVESTER,’ LAWRENCE GROSSMAN”*and GLENN J. MACPHERSON’ ‘Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA *Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA zyxwvutsrqpon (ReceivedJuly 15, 199 1; acceptedin revised form December 11, 199 1) Abstract-Ten inclusions, nine from Vigarano and one from Leoville, both members of the reduced subgroup of C3V chondrites, were analyzed for major and trace elements by neutron activation. Most have some refractory element characteristics that are common in refractory inclusions from Allende, a member of the oxidized subgroup of C3V chondrites. For instance, three (Leo 3537-2, Vig 1623-8, Vig 1623-11) are Type B inclusions with Group I or modified Group I REE patterns, three (Vig 1623-5, Vig 1623-10, Vig 1623- 13) are olivine-rich inclusions, each of which is rather uniformly diluted in most refractory elements compared to Group I inclusions, and two (Vig 1623-14, Vig 1623-16) are fine-grained inclusions with Group II REE patterns. Six of the Vigarano inclusions, however, have refractory element fractionations that are unusual in Allende inclusions. Vig 1623-11 has Cl chondrite-normalized enrichment factors for Th and refractory siderophiles that are lower than those for REE by 60% or more, a positive MO anomaly (Mo/Ir = 1.92 f 0.02 relative to Cl chondrites) and an unusually low Zr/Hf ratio (0.67 rt 0.06 relative to Cl). Relative to Cl chondrites, the Ir enrichment factor is 1.7 times greater than the mean enrichment factor for Re, OS, and Ru in Vig 1623- 10. Vig 1623- 13 has one of the lowest Ir/Sm ratios (0.00044 + 0.00007 relative to Cl) ever measured in an olivine chondrule. Vig 1623-16 has a modified Group II REE pattern which reflects removal of refractory REEs from the nebular gas at unusually low temperatures. Vig 477-S has a REE pattern with a small negative Ce anomaly (Cc/La = 0.79 + 0.01 relative to Cl), a large negative Yb anomaly (Yb/Lu = 0.57 + 0.02 relative to Cl) and no Eu anomaly. This inclusion also has a positive MO anomaly (Mo/Ir = 2.25 + 0.03 relative to Cl) and enrichment factors for Zr and Th that are lower than those for Lu by about 65%. Vig 477-B has a REE pattern that may be a mixture of five parts of a component with an ultrarefmctory REE pattern and ninety-five parts of another with a modified Group II REE pattern. Vigarano apparently sampled a different population of refractory inclusions from Allende, presumably because refractory nebular materials were not well mixed where and when C3V chondrites accreted. The Vigarano and Leoville coarse-grained inclusions studied here, like others analyzed previously, tend to have lower concentrations of Na and Au than Allende coarse-grained inclusions, but the two Vigarano fine-granted inclusions of this study have con- centrations of these elements that are comparable to those of Allende fine-grained inclusions. Thus, although coarse-grained inclusions in the reduced subgroup of C3V chondrites were altered under different conditions from those in the oxidized subgroup, some fine-grained inclusions in the reduced subgroup were altered under similar conditions as some in the oxidized subgroup. INTRODUCTION REFRACTORY,Ca-, Al-RICH inclusions (CAIs) in carbona- ceous chondrites are thought to be early, high-temperature condensates from a cooling solar nebular gas, modified by later partial melting, evaporation, and low-temperature al- teration. Recently, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA MAO et al. (1990) analyzed the bulk com- positions of five CAB from Leoville and Vigarano, members of the reduced subgroup of C3V chondrites (MCSWEEN, 1977). Three have refractory element characteristics that are rare in CAB from Allende, a member of the oxidized subgroup of C3V chondrites (MCSWEEN, 1977). They sug- gested, therefore, that Allende inclusions (those for which the most data exist) are not representative of all early nebular condensates that accreted into C3V chondrites, and that Vi- garano and Leoville are more likely than Allende to contain refractory inclusions that record undiscovered nebular frac- * Also Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA. 1343 tionations. Here, we determine the chemical compositions of nine additional Vigarano inclusions and one from Leoville by instrumental neutron activation analysis (INAA) in order to test the MAO et al. (1990) hypothesis. The idea that there are different CA1 populations in different C3V chondrites has also been suggested by LIU and SCHMITT (1988). It is important to determine if this is true, as it would imply that early condensates were distributed heterogeneously in the nebular region where and when C3V chondrites accreted. Petrographic and/or isotopic data have been reported for seven of the ten samples analyzed here. CAILLET et al. (199 1) determined the Mg isotopic composition of anorthite in Leo 3537-2. The mineralogy and petrography of Vig 477-B were described by CAILLET et al. (1988). In the same inclusion, ZINNER et al. (1989) measured 0 and Mg isotopic compo- sitions of periclase, spinel, and melilite, and EL GORESY et al. (1990a) determined Mg isotopic compositions of spinel, melilite, and hibonite. The mineralogy and petrography of Vig 477-5 were described by MACPHERSON (1985). Concen- trations of rare earth elements in fassaite and perovskite from