Computer Science
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..375j&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 375
Computer Science
Chondrules, Partition Coefficients, Pyroxenes, Rare-Earth Elements, Semarkona, Trace Elements
Scientific paper
The unequilibrated chondrite Semarkona (LL3.0) enables us to investigate primary properties of chondrules that have not been overprinted by secondary processes. Electron microprobe studies of the compositions and zoning properties of silicate phases in these chondrules have helped to interpret crystallization behavior and, hence, offer important insights into formation conditions [e.g., 1,2]. However, the behavior of trace elements in these systems has not been investigated, largely because of the difficulties encountered in analyzing such elements in chondrule silicates. Here we report preliminary ion microprobe data obtained on coexisting pyroxene and glass phases from a pyroxene-rich chondrule in Semarkona. Trace elements analyzed are REE (La, Ce, Nd, Sm, Eu, Dy, Er, Yb), Sr, Y, and Zr. The chondrule studied is a typical example of textural type IAB [2]. It contains phenocrysts of olivine (Fa(sub)3) and clinoenstatite and a glassy mesostasis occupying approximately 15 vol% of the chondrule. Augite (Fs(sub)3, Wo(sub)44) occurs as narrow (10-micrometer) rims on clinoenstatite phenocrysts. Clinoenstatite is FeO-poor (Fs(sub)3, Wo(sub)0.4) and shows little zoning in major and minor elements. Trace-element analyses have been carried out on clinoenstatite, augite, and glass in this chondrule. REE contents in clinoenstatite are extremely low, lying in the range 0.01-0.1 x CI, and show a smooth increase in abundance from La to Yb. REE abundances are enriched in both augite and glass at levels approximately 4-10 x CI, with a small negative Eu anomaly in augite and a small positive Eu anomaly in glass. Olivine is likely to contain REE abundances similar to low-Ca pyroxene [3]. These relative abundances are consistent with closed-system crystallization of the chondrule, assuming that its bulk composition has chondritic abundances of REE [4]. Trace-element partition coefficients (Ds) for the two pyroxene phases are shown in Fig. 1. Clinoenstatite Ds vary smoothly, increasing from 0.0006 (La) to 0.02 (Yb). These data are broadly consistent with equilibrium D values obtained experimentally [3]. However, chondrule Ds for the LREE and Sr are consistently higher than equilibrium experimental values. This could be attributed to the effect of rapid cooling in chondrules [3]. Values for D(sub)Y and D(sub)Zr are also consistent with the experimental data. For augite, the Ds we determined are approximately flat, at values around 1, with a decrease in the LREE and a negative Eu anomaly. The chondrule data are consistently higher than equilibrium experimental data for pyroxenes of composition Wo(sub)40 [5]. This may also be attributable to the effect of rapid cooling rate. However, the partitioning behavior of REE in Ca-rich pyroxene as a function of melt composition is not fully understood. D(sub)Sr, D(sub)Y, and D(sub)Zr are comparable with REE values, consistent with the data of [6]. In summary, trace-element partitioning among chondrule silicate phases appears to be entirely consistent with closed-system crystallization of the chondrule. Data such as these will be valuable in assessing the origins of, and relationships between, various chondritic components. They may also provide a valuable tool for studying metamorphism in ordinary chondrites. This work is supported by NASA grant NAGW-3347 (J. J. Papike). SIMS analyses were performed at the UNM/SNL Ion Microprobe Facility, a joint operation of the Institute of Meteoritics, UNM, and Sandia National Laboratories. References: [1] Jones R. H. (1990) GCA, 54, 1785-1802. [2] Jones R. H. (1992) LPS XXIII, 631-632. [3] Kennedy A. K. et al. (1993) EPSL, 115, 177-195. [4] Grossman J. N. et al. (1988) In Meteorites and the Early Solar System, 619- 659. [5] McKay G. et al. (1986) GCA, 50, 927-937. [6] Hart S. R. and Dunn T. (1993) CMP, 113, 1-8. Fig. 1 appears here in the hard copy.
Jones Rhian H.
Layne Graham D.
No associations
LandOfFree
Partitioning of Trace Elements Between Pyroxene and Liquid in a Porphyritic Pyroxene Chondrule in Semarkona 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 Partitioning of Trace Elements Between Pyroxene and Liquid in a Porphyritic Pyroxene Chondrule in Semarkona, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Partitioning of Trace Elements Between Pyroxene and Liquid in a Porphyritic Pyroxene Chondrule in Semarkona will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072356