Geochemical Journal, Vol. 51 (No. 1), pp. 31-43, 2017
Sara S. Russell,1* Jean-David Bodenan,1,2 Natalie A. Starkey,2 Teresa E. Jeffries,3 Anton Kearsley,3 John Spratt,3 Rosalind M. G. Armytage4 and Ian A. Franchi2
1Department Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, U.K.
2Department of Physical Sciences, Open University, Milton Keynes, MK7 6AA, U.K.
3Core Research Laboratories, Natural History Museum, London SW7 5BD, U.K.
4Department of Earth Sciences, University of Oxford, South Parks Rd, OX1 3AN, U.K.
(Received January 30, 2016; Accepted September 10, 2016)
We report the mineralogy, petrology, major, minor and trace element geochemistry, O and Si isotopes of a complex compound chondrule from the Allende meteorite. The chondrule contains zones of refractory (Ca, Al-rich) regions along with regions more similar to ferromagnesian chondrules. The bulk silicon isotopic composition of the object is δ30Si =
–0.71 ± 0.03‰. The oxygen isotopic composition of the different phases within the compound chondrules fall along the Allende chondrule line and range from Δ17O – 12.5 to –2‰. Rare earth element abundances are enriched compared to chondritic levels by up to 15× CI, and show a nebular condensate signature with depletions in Eu and Yb. Our data show that the object evolved in oxygen isotopes in a nebular environment, most likely due to formation from a mixture of diverse components combined with interaction with nebular gas. In addition, differences in olivine composition across the inclusion suggest isotopically distinct oxygen regions also existed in dust in the protoplanetary disk.
This object and other compound objects demonstrate that CAIs were present in the chondrule forming region, however they are not found in the majority of chondrules. We speculate that the bulk of the CAIs may have been added into the CV parent body after initial accretion of the body.
Key words: chondrule, calcium-aluminium rich inclusion, CV chondrite, oxygen isotopes, silicon isotopes