Baker, Lee

Franchi, Ian

Morris, Adam

Watson, Jonathan

Wright, Ian

English

Open Research Online

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsDeterming the effects of aqueous alteration on thedistribution of oxygen isotopes in carbonaceouschondritesConference or Workshop ItemHow to cite:Morris, Adam; Franchi, Ian; Baker, Lee; Watson, Jonathan and Wright, Ian (2006). Determing the effects ofaqueous alteration on the distribution of oxygen isotopes in carbonaceous chondrites. In: 69th Annual MeteoriticalSociety Meeting, 6-11 Aug 2006, Zurich, Switzerland.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/metsoc2006/pdf/5041.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.ukDETERMING THE EFFECTS OF AQUEOUS ALTERATION ON THE DISTRIBUTION OF OXYGEN ISOTOPES IN CARBONACEOUS CHONDRITES.  A. A. Morris, I. A. Franchi, L. Baker, J. Watson and I. P. Wright. Plane-tary and Space Sciences Research Institute, The Open University, Milton Keynes, MK7 6AA. E-mail: a.a.morris@open.ac.uk.   Background: Carbonaceous chondrites (particularly the CI, CM and CR meteorites) have the most diverse range of high and low temperature mineral phases, and display the widest range of oxygen-isotopic compositions [1,2]. There are then inherent problems when trying to interpret early Solar System history. One is identifying the isotopic signature of oxygen from specific component compounds in a complex mixture of materials that existed in the solar nebular, and deconvoluting this from signa-tures developed during parent body processing, of which aqueous alteration is the most wide spread. Models to account for the variations in oxygen-isotopic compositions in carbonaceous chondrites e.g. [3,4] generally involve mixing of a solid anhy-drous silicate component, with an isotopic composition enriched in 16O, with liquid water depleted in 16O along with mass-dependent isotopic fraction between various phases at low tem-perature [5]. Isotopic evolution of the fluids involved in these reactions would be expected to lead to significant isotopic het-erogeneity within the components e.g. [4]. Research: We have employed a number of approaches to better determine the distribution of oxygen isotopic components within these complex meteorites. Much of our work has been involved with characterizing the products from artificial hydro-thermal alteration of olivine. Olivine was reacted with neutral, acidic and alkaline solutions at 330oC and 50 bar pressure with the aim of producing phyllosilicates of serpentine composition (lizardite, chrysotile and antigorite); the products were character-ised using Raman spectroscopy, SEM, XRD and thermal analy-sis. Stepped heating extraction to liberate water and structural (OH)- has also been undertaken [6]; this technique permits iso-topic measurements of resolved components, the identification of which has been established by detailed study of the thermal re-lease temperature of water (OH)- components and a range of ter-restrial analogues. This method has been used to trace the loca-tion of different oxygen reservoirs as alteration proceeds in fur-ther artificial hydrothermal alteration reactions of olivine using isotopically labeled water. Stepped heating extraction of water and (OH)- have also been used to characterise the oxygen iso-topic composition of liberated, indigenous, water (OH)- from a range of carbonaceous chondrites (CI, CM2, CR2).  Summary: The initial stepped heating experiments for car-bonaceous chondrites revealed considerable variation in δ18O [5]. Much of our new work has been aimed at determining the extent of isotopic fractionation associated with the formation of the common phyllosilicates found in meteorites, and identifying the specific minerals liberating (OH)- at each temperature. This will be used ultimately to better constrain the isotopic composi-tion of the fluids involved in the alteration process on carbona-ceous chondrite parent bodies. References: [1] Clayton R. N. & Mayeda T. K. (1999) GCA, 63, 2089–2104. [2] Brearley A. J. & Jones R. H. (1998) Planetary Materials, 36, 3-01-3-370. [3] Clayton R. N. & Mayeda T. K. (1984) EPSL, 67, 151-161. [4] Young E. D. et al. (1999) Science, 286, 452-455. [5] Franchi. et al (2001) Phil. Trans. R. Soc. Lond. A 359, 2019–2035. [6] Baker. et al. (2002) Analyl. Chem. 74 1665-1673. 69th Annual Meteoritical Society Meeting (2006) 5041.pdf

Determining the effects of aqueous alteration on the distribution of oxygen isotopes in carbonaceous chondrites

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Determing the effects of aqueous alteration on the distribution of oxygen isotopes in carbonaceous chondrites

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