Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.529k&link_type=abstract
Meteoritics, vol. 30, no. 5, page 529
Computer Science
Chondrites, Ordinary, Condensation, Melting, Metal, Meteorites, Allan Hills 76009, Allan Hills 77011, Allan Hills 77231, Allan Hills 77299, Allan Hills 78109, Allan Hills 81024, Allan Hills 81251, Allan Hills 83007, Dhajala, Elephant Moraine 83213, Elephant Moraine 87778, Macalpine Hills 88174, Qingchen, Richardton, St. Severin, Wisconsin Range 91627, Yamato 74014, Yamato 791088, Yamato 791421, Yamato 791539, Yamato 792772, Yamato 91323, Yamato 91434, Redox State
Scientific paper
Bulk metals of 10 H, 6 L and 7 LL chondrites were analyzed by INAA. A significant difference in the metallic compositions between EOCs and UOCs is noted for the abundances of three lithophile elements, Cr, Mn and V, and three weakly siderophile elements, W, Mo and Ga. The abundances of W, Mo and Ga are increased and those of Cr, Mn and V are decreased with increase of petrographic type. According to condensation sequence [1], Fe condensed into a metal phase at high temperature. With temperature falling, metallic Fe was partly oxidized into silicates and partly transferred into troilite during equilibrium with the solar nebula. If Fe could equilibrate with the solar nebula, it is not expected that V, Cr and Mn still remain partly in the metal phases since they would be oxidized at higher temperatures than that for oxidizing Fe. Rapid formation of silicates around metal grains might preserve these elements but should keep W and Mo quantitatively present in the metals. Our results show that relative to Ir and Os, W and Mo are both depleted in the UOC metals to some extents, implying that portions of W and Mo are present in the non-metal phases. It is difficult to envision that the "being reduced" V, Cr and Mn can coexist with the "being oxidized" W, Mo and Ga in the metallic fractions if the metallic fractions were nebula condensates. W, Mo and Ga are enriched in the metallic fractions of the EOCs in order of W>Mo>Ga, while in those of the UOCs the order changes to Mo>W>Ga. We believe that the truly equilibrated distributions of W and Mo among different phases are preserved in the equilibrated chondrites, because the redox states of the elements must have been readjusted to reach equilibrium or near to equilibrium during the thermal metamorphism. So, if the UOC metals were equilibrated condensates, the relative distributions of W and Mo in the UOC metals should be similar to those in the EOC metals. However, this is not the case. If the metals were interstellar grains and have not changed their characteristics before the accretion of chondrites, the compositions of the metals should be uniform for all ordinary chondrites of different chemical groups. In fact, they have changed. If the compositions of the metals were adjusted according to the redox condition in places where chondrites formed, the contradictory states of "being reduced" V, Mn and Cr and "being oxidized" W, Mo and Ga preserved in the UOC metals must be erased. Thus, it seems implausible that the metals of ordinary chondrites were the interstellar grains before their accreting into chondrites. Formation of chondritic metals seems to be attributable only to the remaining melting mechanism. Experimental results showed that the metal/silicate partition coefficients of W were always lower than those of Mo at temperature 1300 degrees C and oxygen fugacities between 10^-13 to 10^-11 bars [2]. Moreover, partition behaviors of Cr, V and Mn [3] are similar to those found in the UOCs. The consistence of experimental partition coefficients of W, Mo, Ga, V, Cr and Mn with their abundance ratios between metal and silicate phases of UOCs suggests that the UOC metals were formed by a melting mechanism. It is thus concluded that the metals of ordinary chondrites were the melting remnants before they were accreted into chondritic parent bodies. References: [1] Wasson J. T. (1985) in Meteorites: Their Record of Early Solar-System History, Freeman, New York. [2] Schmitt W. et al. (1989) GCA, 53, 173-185. [3] Drake M. J. et al. (1989) GCA, 53, 2101-2111.
Ebihara Mitsuru
Kong Ping
No associations
LandOfFree
Metal Phases of Ordinary Chondrites: Melting Remnants or Nebular Condensates? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Metal Phases of Ordinary Chondrites: Melting Remnants or Nebular Condensates?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metal Phases of Ordinary Chondrites: Melting Remnants or Nebular Condensates? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-830077