Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.417p&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 417
Other
6
Chondrules, Condensation, Matrix
Scientific paper
We have recently shown that in Allende, chondrules and matrix are complementary in composition. Chondrules have low Fe/Cr ratios and matrix has high Fe/Cr ratios; the bulk meteorite has the CI ratio. Chondrules on the average have Ca/Al ratios below the solar system ratio of 1.10, which is also the bulk Allende ratio; matrix and related dark inclusions have ratios above 1.10. It was therefore concluded that chondrules and matrix formed from a single reservoir characteristic of the bulk Allende composition [1,2]. Recent reports on the CV meteorite Y-86751 [3,4] indicated the opposite relationship, with high Ca/Al ratios in chondrules and low ratios in matrix. Different compositions of individual components of Y-86751 and of Allende but similar bulk compositions of both meteorites may reveal important details on the preaccretionary evolution of the carbonaceous chondrites. We have therefore begun chemical analyses of the bulk of Y-86751 and its individual lithic components, chondrules, matrix, amoeboid olivine inclusions, Ca,Al-rich inclusions, etc. Results of the bulk analysis of Y-86751 show that this meteorite has (within the accuracy of the analysis) the same bulk composition as Allende. In particular, the Ca/Al ratio is within 3% of the average solar system ratio of 1.1 (by weight). The only statistically resolvable difference is the 50% higher content of Zn in Y-86751. Major-element INA analyses indicate a Ca/Al ratio above the chondritic ratio for several chondrules and opposite to that of average Allende chondrules [1]. Matrix samples have a tendency for low Ca/Al ratios, confirming EMP-matrix analyses [4]. The separates are presently analyzed for a large number of trace elements. After the analyses, separates will be investigated petrographically. The apparent disequilibrium among Allende components and the strong compositional zoning of olivine grains constrain the thermal history of the Allende parent body [e.g., 5]. Any metamorphic redistribution of Ca or Al between chondrules and matrix can be virtually excluded. Therefore, the complementary relationship in the distribution of Ca and Al between matrix and chondrules must be of nebular origin and must reflect conditions of formation of chondrules and matrix. Early condensation and separation of spinel may be responsible for the high Ca/Al in Y-86751 chondrules. The early separated spinel grains were later collected with the matrix and are responsible for the low Ca/Al ratio in Y-86751 matrix [3,4]. A different evolution, where chondrules incorporated less Ca than Al, must have occurred for Allende. Perhaps conditions were more oxidizing and some Ca remained as Ca(OH)(sub)2 in the gas before matrix was formed, as suggested by Hashimoto [6]. Allende dark inclusions representing matrix have excess Ca while all other refractory elements occur in CI proportions, suggesting a unique behavior of Ca [7]. A different nebular history for two members of the same group (CV) would indicate strong local differences in formation conditions for chondrules and matrix from two identical nebular reservoirs. In addition, if both meteorites come from the same parent body there could only be limited mixing on the parent body to retain the different signatures. References: [1] Palme H. et al. (1992) LPS XXIII, 1021-1022. [2] Palme H. (1992) 17th Symp. Antarc. Met., Tokyo, 71-1-3. [3] Murakami T. et al. (1992) 17th Symp. Antarc. Met., Tokyo, 11-1-2. [4] Murakami T. and Ikeda Y. (1993) in preparation. [5] Weinbruch S. et al. (1990) Meteoritics, 25, 115-125. [6] Hashimoto A. (1992) GCA, 56, 511-532. [7] Palme H. et al. (1989) Z. Naturforsch., 44a, 1005-1014.
Ikeda Yasufumi
Palme Herbert
Spettel Bernhard
No associations
LandOfFree
Origin of Chondrules and Matrix in Carbonaceous 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 Origin of Chondrules and Matrix in Carbonaceous Chondrites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Origin of Chondrules and Matrix in Carbonaceous Chondrites will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1073085