Other
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.307w&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 307
Other
1
Scientific paper
INTRODUCTION. On April 7, 1990, a brecciated ordinary chondrite fell through the roof of a house near Glanerbrug in the Netherlands and was shattered to pieces. The total weight of the recovered fragments was about 800 g, the largest piece weighing 135 g. This main fragment clearly shows the inhomogeneous structure of the Glanerbrug: a dark-grey breccia occasionally containing blackish inclusions, separated from a light-grey breccia by a sharp boundary. Chondrules seem to be more common in the light grey parts. On the basis of earlier electron microprobe analyses of olivines and pyroxenes the light-grey portion was classified at the high Fa-Fs end of the L-field and the dark-grey part at the high Fa-Fs end of the LL-field [1]. Since it is not likely that the L and LL chondritic fragments originated on a single parent body, two alternative explanations were suggested: (i) The light-dark structure of the Glanerbrug is a characteristic feature of regolithic breccias, which once resided on or close to the surface of its parent body [2]. This lends some support to the idea that the light portion is an exotic clast in a dark host rock or vice versa; (ii) the two lithologies represent materials of a body having compositions between L and LL tentatively designated as L/LL [3,4]. Therefore additional electron microprobe analyses (EPMA) of silicates and kamacites in combination with neutron-activation analyses (INAA) of a light and a dark fragment and a noble gas analysis of a mixed light-dark fragment were undertaken. RESULTS and DISCUSSION. The light lithology in two thin sections shows olivine compositions in the L range (24.5+-0.3% Fa) and kamacite compositions (13.0+-1.3 mg/g Co) close to the LL range, plotting in the L/LL rather than in the L field on a kamacite-Co vs. olivine-Fa diagram [3,4]. Whereas only one aberrant olivine grain (out of 50) was found in the light portion, the dark portion is less homogeneous: one thin section shows olivine and kamacite compositions low in the LL field (27.0+-1.5% Fa and 15.0+-1.0 mg/g Co) whereas the olivines and kamacites in another thin section plot higher in the LL field (30.0+-1.0% Fa and 24+-4 mg/g Co). It also contains a small H chondritic inclusion (100 x 140 micrometers) and a blackish OC-fragment with widely varying silicate compositions and small (~10 micrometers) martensite grains a metal phase containing 97+-8 mg/g Ni typical for shock-reheated OCs [4]. Although this indicates that the dark portion once resided close to the surface of a parent body, no solar-wind implanted noble gases were found in a fragment consisting of both light and dark material [5] indicating that the Glanerbrug is a fragmental rather than a regolithic breccia [2]. The INAA study is still in progress but our first results on the light-grey sample show that the siderophiles are more like LL than L chondrites. These results leave two possible conclusions: (i) the Glanerbrug breccia originated on a single LL parent body, with the light and dark portions representing materials that formed from widely separated regions of the LL chondrite agglomeration zone; (ii) a light xenolithic L/LL fragment is incorporated into a dark LL chondritic host, while the latter was close to the surface of its parent body. The former would imply that at least some of the L/LL chondrites plotting in the upper part of the L/LL field on a kam-Co vs. ol-Fa diagram are a subgroup of the LL chondrites. However, since an olivine-Fa content of 24.5% is far below the LL range, such a conclusion can not be drawn solely on the basis of the Glanerbrug and therefore we prefer the second conclusion. From noble gas measurements [5] an average U,Th-He age of about 3.4 Ga was calculated, falling in the generally observed range of L/LL and LL chondrites [6], neither confirming nor rejecting our conclusions. Acknowledgements. We thank Dr. H.W. Weber and coworkers for the noble gas measurements. One of the authors (K.W.) is greatly indebted to Prof. Wasson and coworkers for their hospitality at UCLA. This work was financially supported by the "Nederlands Organisatie voor Wetenschappelijk Onderzoek" (NWO). References. 1. Lindner L. et al. (1990) Meteoritics 25, 379 (abs.); 2. Bunch T.E. and Rajan R.S. (1988) in Meteorites and the Early Solar System (eds. J.F. Kerridge and M.S. Matthews), pp. 144-164, Univ. Arizona Press, Tucson, Arizona; 3. Kallemeyn, G.W. et al. (1989) GCA 53, 2747-2767; 4. Rubin A.E. (1990) GCA 54, 1217-1232; 5. Schultz L. (pers. comm.); 6. Wasson J.T. and Wang S. (1991), Meteoritics 26, 161-167.
Kallemeyn Gregory W.
Lindner Louis
Poorter P. E. R.
Rubin Alan E.
Wasson John T.
No associations
LandOfFree
The Glanerbrug Breccia: Evidence for a Separate L/LL-Chondritic Parent Body? 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 The Glanerbrug Breccia: Evidence for a Separate L/LL-Chondritic Parent Body?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Glanerbrug Breccia: Evidence for a Separate L/LL-Chondritic Parent Body? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1210034