A Comprehensive Study of Major, Minor, and Light Element Abundances in Over 100 Interplanetary Dust Particles

Details A Comprehensive Study of Major, Minor, and Light Element Abundances in Over 100 Interplanetary Dust Particles A Comprehensive Study of Major, Minor, and Light Element Abundances in Over 100 Interplanetary Dust Particles

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.587t&link_type=abstract

Meteoritics, vol. 30, no. 5, page 587

Mathematics

Logic

2

Anhydrons, Carbon, Cluster Particles, Hydrated, Interplanetary Dust Particles

Scientific paper

Chondritic interplanetary dust particles (IDPs) are samples of material that are believed to have formed very early in the history of our solar system. These particles are some of the most pristine extraterrestrial materials we have to study because of their primitive mineralogies, chemistries, and isotopic compositions. In general, IDPs have a chondritic composition within a factor of two of CI for most major and minor elements with the exception of carbon, which has been reported to average ~3xCI for anhydrous [1] and hydrated [2] IDPs, and ~2xCI for one cluster IDP [3]. The high carbon abundance in some IDPs is incompatible with an origin from known chondritic meteorites. The presence of carbonaceous materials in IDPs has broad implications for the processes involved in the formation and evolution of the early solar system. We have concentrated on determining the abundance and distribution of carbon in IDPs; we also have preliminary data on the nature of carbon-bearing materials [4, 5]. This is the first comprehensive report summarizing carbon and oxygen, along with major element abundances, in over 100 IDPs. Nearly 50% were collected as individual particles while the remaining fragments are from cluster particles. We have classified IDPs into groups based on chemistry and available mineralogy and have summarized chemical trends for these groups. Our data are compared with previous analyses of 200 IDPs in which particles were categorized based on bulk chemistry and surface morphology [6]. Samples Since 1987, we have analyzed a total of 129 IDPs for major element chemistry and modal mineralogy; these IDPs were requested from the Cosmic Dust Catalogs and are C-type (chondritic). Individual particles include anhydrous (40) and hydrated (13) IDPs. We were also allocated IDPs from several cluster particles: anhydrous clusters (2; one with 53 fragments and the other with 5 fragments), one hydrated cluster (4 fragments), and one mixed cluster (anhydrous and hydrated fragments; 4 fragments). Ten IDPs have unknown mineralogy. Methods All IDPs were placed on beryllium substrates for analysis at NASA/JSC using a JEOL 35 CF scanning electron microscope (SEM) equipped with a thin window PGT X-ray energy dispersive spectrometer (EDS); this spectrometer allows detection of elements with Z>5. Following the initial bulk chemical analyses, most IDPs were thin sectioned and examined with a transmission electron microscope (TEM). Procedures for SEM light element analysis and TEM mineralogical analyses of IDPs are described in detail elsewhere [1 & 7, resp.]. Results Some chemical trends are not unique (previously described by [6]) while others are notable: (1) carbon abundances range from ~1-47 wt.% for all anhydrous IDPs, 1-29 wt% within a single anhydrous cluster particle (53 IDPs), and from 2-22 wt% for hydrated IDPs. Carbon abundances range from ~0.3-13xCI; some IDPs contain more carbon by wt. than any other element. The C-rich material is amorphous or poorly crystalline and in some instances exhibits vesicular textures [5,8]; it acts as a matrix holding individual grains together. We have recently found significant nitrogen in this amorphous carbon phase [9]. (2) One anhydrous cluster particle (53 IDPs) has a greater range of major element abundances than all individual anhydrous IDPs combined. (3) A higher percentage of hydrated IDPs (~20%) compared with anhydrous IDPs (~10%) show mineralogical evidence of being heated (e.g., magnetite rims) during atmospheric entry. In conclusion, chondritic IDPs, including anhydrous, hydrated, and cluster particles, have C contents that average ~2-3xCI indicating that they are more chemically primitive than the carbonaceous chondrites. Some IDPs have the highest bulk C abundances of any extraterrestrial samples. References: [1] Thomas et al. (1992) GCA, 57, 1551. [2] Keller et al. (1993) LPS XXIV, 785. [3] Thomas et al. (1995) GCA, in press. [4] Keller et al. (1995) IAU Symp. 50, in press. [5] Keller et al. (1994) Meteoritics, 29, 480. [6] Schramm et al. (1989) Meteoritics, 24, 99. [7] Kl"ck et al. (1989) Nature, 339, 126. [8] Thomas et al. (1993) AIP Conf. Proc. 310, 165. [9] Keller et al., this volume.

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