Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.497c&link_type=abstract
Meteoritics, vol. 30, no. 5, page 497
Astronomy and Astrophysics
Astrophysics
Scientific paper
Recent ion microprobe investigations have revealed large boron isotope variations (d11B values ranging between -50 and +40) in some chondrules from the Semarkona, Hedjaz and Allende chondrites [1].Up to 60 variations can be found in a single chondrule. The d11B values and the B/Si ratios (varying between 510-6 and 410-4) were found to be positively correlated. Since boron in the Universe cannot orginate from thermonuclear reactions in stars these isotopic variations are interpreted as the result of a mixing in the protosolar nebula between two different sources of spallogenic boron : (1) an interstellar source where boron results from reactions between high energy galactic cosmic rays (protons and alpha particles; >100 MeV) and interstellar nuclei yielding low B/Si and 11B/10B ratios (d11B -400) and (2) a molecular cloud source where boron results from reactions between low energy particles (C and O; <30 MeV) and low temperature H2 and He (as recently observed in Orion [3]) yielding high B/Si and 11B/10B ratios (d11B +110). The reactions producing 11B-rich boron would have occurred in the dense molecular cloud that predates the formation of the solar nebula. Detailed astrophysical calculations [4] are in agreement with this geochemical model. According to this model--and provided that the degree of isotopic homogenisation within the same chondrule is the same for Li and B--it can be shown that d7Li() and d11B() should be related by a 1:1 linear correlation with low d7Li values associated with high d11B values. Therefore, in order to test one of the clearest predictions of our interpretation, new ion microprobe determinations of Li-Be-B and major elements (Na, K, Ca, Mg, Si) concentrations and of the 11B/10B and 7Li/6Li isotopic ratios in meteoritic chondrules were performed. Considering all our measured chondrules, the Li/B ratio varies by 2 order of magnitude indicating that the two chemical elements were fractionated during the formation of chondrules. Therefore, the 7Li/6Li isotopic ratio was measured only in chondrules showing a homogeneous Li/B ratio and a value close to its spallogenic theoretical ratio (Li/B 1). References: [1] Chaussidon and Robert (1995) Nature, 374, 337-339. [2] Meneguzzi et al. (1971) Astron. Astrophys., 15, 337-359. [3] Bloemen et al. (1994) Astron. Astrophys., 281, L5-L8. [4] Ramaty et al., Astrophys. J., submitted.
Chaussidon Marc
Robert Frédéric
No associations
LandOfFree
Boron and Lithium Isotopic Composition in Chondrules 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 Boron and Lithium Isotopic Composition in Chondrules, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Boron and Lithium Isotopic Composition in Chondrules will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-830477