Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.523h&link_type=abstract
Meteoritics, vol. 30, no. 5, page 523
Other
Chondrites, Ordinary, Chondrules, Macro, Differentiation, Igneous, Inclusions
Scientific paper
We present the results of a survey of large silicate objects in ordinary chondrites (OCs) from the collection of the Natural History Museum, London; 390 H-group, 386 L-group and 57 LL-group meteorites were examined. A total of 61 objects were identified (Table 1). Meteorites with light and dark, brecciated fabrics were excluded from our survey. Following Weisberg et al. [1], large silicate objects are taken to be >= 5mm in size. Macrochondrules have rounded outlines and textures - porphyritic, barred olivine, radiating pyroxene - that are indistinguishable from normal chondrules in OCs [1]. In addition, we also recognise igneous clasts and chondritic clasts. The largest macrochondrule in the collection is 4cm diameter, with a microporphyritic texture [2]. Igneous clasts are those objects whose properties indicate that they originated through melting and differentiation on a planetary body. Examples include a 2cm diameter clast, in Ness County (L6), which contains large (2mm) olivine and enstatite grains set in a plagioclase + olivine groundmass, cristobalite- and tridymite-rich clasts [3] and the FELINE feldspar-nepheline clast [4]. Chondritic clasts comprise a diverse group including a 1cm clast from Barwell (L6) which contains apparently remelted chondrules, microporphyritic clasts with K-rich mesostasis e.g. in Quenggouk (H4) and a 1cm single olivine grain with minor inclusions of anorthite and enstatite, in Julesburg (L3). The K-rich objects are similar to others described from a survey of LL-chondrites and may have an impact origin or have undergone exchange with a K-rich vapor [5]. Abundances of the three types of large silicate objects (Table 1) reflect the relative numbers of H, L and LL meteorite samples in the collection, although LL-group hosted clasts are over-represented as our work concentrated on sections of LL-chondrites. In total, 46% of the objects are macrochondrules, 18% are igneous clasts and 36% are in the indeterminate chondritic clast group. All three types of object occur in petrographic types 3-6, but none was found in H3 meteorites. Mineral compositions in large silicate objects in hosts of petrographic types 4-6 are usually equilibrated, although enstatite in H4-hosted samples and the cristobalite-rich igneous clasts from Farmington (L5) [3, 6] are exceptions to this. Clasts and chondrules from the same host-meteorite sometimes belong to different shock stages. References: [1] Weisberg M. K. et al. (1988) Meteoritics, 23, 309-310. [2] Binns R. A. (1967) Mineral. Mag., 36, 319-324. [3] Bridges J. C. et al. (1995) Meteoritics, submitted. [4] Bridges J. C. et al. (1995) Proc. NIPR Symp. Antarct. Meteorites, 8, in press. [5] Wlotzka F. et al. (1983) GCA, 47, 743-757. [6] Binns R. A. (1967) Science, 156, 1222-1226.
Bridges John C.
Hutchison Robert
No associations
LandOfFree
A Survey of Large Silicate Objects in Ordinary Chondrites 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 A Survey of Large Silicate Objects in Ordinary Chondrites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Survey of Large Silicate Objects in Ordinary Chondrites will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-830055