Gilmour, I.

Pearson, V. K

Sephton, M. A.

English

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsThe macromolecular constitution of the CR chondritesConference or Workshop ItemHow to cite:Pearson, V. K; Sephton, M. A. and Gilmour, I. (2001). The macromolecular constitution of the CR chondrites. In:64th Annual Meeting of the Meteoritical Society, 10-14 Sep 2001, Vatican City, Italy.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/metsoc2001/pdf/5290.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukTHE MACROMOLECULAR CONSTITUTION OF THE CR CHONDRITES.  V. K. Pearson, M. A. Seph-ton and I. Gilmour.  Planetary and Space Sciences Research Institute, The Open University, Milton Keynes MK76AA, United Kingdom. (v.k.pearson@open.ac.uk)Introduction: In contrast to the extensive minera-logical, petrographic and isotopic studies [1,2,3] thathave been carried out on CR chondrites, their organicinventory remains poorly understood.   The organicassemblage is dominated by a high molecular weightmacromolecule.  Pyrolysis studies, which involve thethermal dissociation of the macromolecule, have beenused to determine the make-up of this component inother chondrites such as Murchison [4].  This studyutilises similar pyrolysis methods in order to determinethe macromolecular constitution of the CR chondritesAl Rais, Renazzo, EET87770 and Y790112.Experimental: Whole rock meteorite sampleswere powdered and ultrasonically extracted with a 93:7dichloromethane/methanol mixture (4×25min withadditional 15 min centrifugation following each soni-cation), the extract removed and the residue dried. 25mg of residue was loaded into a pre-cleaned quartzglass tube.  The sample was flash pyrolysed at 610°Cusing a CDS 1000 pyroprobe (CDS Analytical, Ox-ford, PA) for 15 s in a flow of helium. The heating rateof pyrolysis was 20°C ms-1. The interface was held at260°C. The pyrolysate was analysed on an AgilentTechnologies 5973 GCMS and the GC injector main-tained at 250°C.  GC conditions as in [4].Results:  Pyrolysates for all samples show themacromolecule to be composed of 1-2 ring, low mo-lecular weight compounds, including both alkylatedand hydroxylated forms (Al Rais is illustrated in Fig.1) The dominant product was naphthalene and its alkylderivatives. Generally, the products are consistent withreported pyrolysis fragments from CM and CI chon-drites [5].  In addition, 3 and 4 ring (Al Rais andEET87770 only) compounds were detected.  With theexception of benzonitrile, present in all samples butRenazzo, very few nitrogen compounds are evident.(Di)Benzothiophenes and their alkylated forms arefound in all samples, with thiophene being present inonly EET87770 where it elutes in the place of benzene.Discussion: The presence of phenolic and hy-droxylated species including fluorenone confirms theirsubjection to oxidising conditions during aqueous al-teration inferred by petrographic data [1,2,3]. The oc-currence of acetophenone and a high phenol content inAl Rais compared with other samples supports theproposal that it is the most aqueously altered sample[1].  Reports that CR chondrites have also experiencedreducing conditions [2] are strengthened by the pres-ence of 3-4 ring aromatics. Increased aromatisationinduced by anhydrous heating will lead to the conden-sation of these high molecular weight compounds suchas pyrene, particularly in Al Rais and EET87770. The2:1-methylnaphthalene ratio indicates that the thermo-dynamically stable 2-methylnaphthalene predominates.This produces a sequence from high to low thermalalteration of Al Rais> EET87770> Y790112 >Re-nazzo.Conclusion:  1. CR macromolecular material iscomposed of 1-4 ring compounds.  2. Oxidised speciesindicate their subjection to aqueous alteration.  3. Highmolecular weight fragments infer they have also un-dergone a period of thermal metamorphism.References:  [1] Weisberg M.K. et al. (1993)GCA, 57, 1567-1586.  [2] Bishoff A. et al. (1993)GCA, 57, 1587-1603.  [3] Kallemeyn G.W. and Was-son J.T. (1982) GCA, 46, 2217-2228.  [4] Gilmour I. etal. (2001) LPSC XXXII, 1993. [5] Sephton M.A. et al.(1999) GCA, 63, 321-328.SC2, C3, C4ONOHC2OC2, C3AbundanceRetention TimeFigure 1 Total ion Chromatogram of solvent extractedAl Rais CR chondrite64th Annual Meteoritical Society Meeting (2001) 5290.pdf

The macromolecular constitution of the CR chondrites

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The macromolecular constitution of the CR chondrites

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