Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..525k&link_type=abstract
Meteoritics, vol. 30, no. 5, page 525
Other
4
Chondrites, Carbonaceous, Classification, Meteorites, Bells, Composition Of, Essebi, Neutron Activation
Scientific paper
The Bells and Essebi carbonaceous chondrites have long been associated with the CM group, although petrographic and isotopic observations have questioned that relationship. Samples of Bells and Essebi were obtained for bulk compositional study by neutron activation analysis (INAA) in an attempt to further fuel the debate on this issue. The current INAA work for Bells is complete, but analysis of Essebi is ongoing, and therefore the data is preliminary. Although CM chondrites typically contain <3 wt% magnetite, Bells and Essebi contain approximately 16 wt% and 11 wt% magnetite, respectively [1]. Both Bells and Essebi seem to have suffered more intense aqueous alteration than typical CM chondrites [2]. Bells has a phyllosilicate matrix composition closer to CI chondrites than CM chondrites [3]. The delta 15N value for Bells is much higher than any of the established carbonaceous chondrite groups[4]. Carbonate material in Essebi has delta 13C compositions (+62 per mil to +80 per mil) higher than the CM mode of +40 per mil to +50 per mil [5]. Both Bells and Essebi have whole rock O-isotope compositions in the CM chondrite range, but Essebi has separated matrix and magnetite values similar to whole rock and magnetite values in CI chondrites [6]. Samples of Bells were from two different stones collected after the fall. One stone was collected the day after the fall, the other was collected several days later after a hurricane went through the area. The samples will be referred to as 'normal' Bells and 'weathered' Bells, respectively. The 'normal' and 'weathered' Bells samples are very similar in composition with a few notable exceptions. The Mg-normalized abundances of Na, K and Br in 'weathered' Bells are markedly depleted relative to 'normal' Bells. The abundance of Ca is also lower to a smaller extent. One must be cautious of compositional studies of late-collected Bells specimens as they may have been altered by the affects of rainwater. Refractory lithophile abundances (Mg-normalized) in Bells are at CI chondrite levels, not CM, but volatile lithophile abundances follow a normal CM depletion pattern relative to CI chondrites. Common siderophile (Fe, Co, Ni) abundances are also at CI chondrite levels, but normalized refractory siderophile abundances are elevated relative to CI chondrites, and greater than even CM chondrite abundances. The Au abundance in Bells is lower than those of the common siderophiles, a pattern unlike CM chondrites where the abundances are all very similar. On a Zn/Mn vs. Al/Mn diagram Bells plots just outside the tight cluster of CM chondrites in the direction of CI chondrites. Bells does not easily fall into any classification scheme. It does not appear to be a CM chondrite, though. Only preliminary data is available for Essebi. Refractory siderophile abundances (Ni-normalized) are similar to CM, but volatile siderophile and chalcophile element abundances appear to be noticeably lower, a pattern similar to the anomalous chondrite Al Rais. On a Zn/Mn vs. Al/Mn diagram Essebi plots just outside the CM chondrite cluster on the side opposite Bells and very near Al Rais. Essebi may be related to the same clan as Al Rais, an idea that is also supported by their very similar whole-rock O-isotope compositions [6,7]. It is also probably not closely related to Bells. The picture on Essebi may become clearer once the INAA analysis is complete (including key lithophile elements). References: [1] Hyman M. and Rowe M. W. (1983) LPS XIV, 341-342. [2] Metzler K. et al. (1992) GCA, 56, 2873-2897. [3] Davis A. M. and Olsen E. (1984) LPS XV, 190-191. [4] Kerridge J. F. (1985) GCA, 49, 1707-1714. [5] Grady M. M. et al. (1988) GCA, 52, 2855-2866. [6] Rowe M. W. et al. (1994) GCA, 58, 5341-5347. [7] Weisberg M. K. et al. (1993) GCA, 57, 1567-1586. _
No associations
LandOfFree
Bells and Essebi: To Be or Not To Be (CM) 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 Bells and Essebi: To Be or Not To Be (CM), we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bells and Essebi: To Be or Not To Be (CM) will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-829698