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Evolution Of Water Reservoirs In The Early Solar System Through Their Oxygen Isotopic Composition

By Lee Baker

Abstract

A new technique has been developed to enable analyses of δ<sup>17</sup>0 and δ<sup>18</sup>0 from small water samples extracted from meteorites. Isotopic measurements are made using a continuous-flow, isotope ratio mass spectrometer (Delta C, Finnigan Mat) utilising a helium carrier gas. Oxygen is extracted from water using the powdered, solid fluorinating agent CoF<sub>3</sub>, and is purified using a GC column (PLOT, 5Å). Reproducibility of the method, determined using solid standards and reference waters is ±.30%c for δ<sup>18</sup>O and +0.14%c for Δ<sup>I7</sup>O (1σ in each case).\ud \ud The technique has been applied to three suites of meteorites: Carbonaceous chondrites (CI and CM), SNC meteorites (four meteorites) and a selection of Antarctic samples, three eucrites and one ordinary chondrite. Results were used to constrain models of the origin of Solar System water and its subsequent interaction on the meteorite parent bodies. Results from carbonaceous chondrites suggest that water accreting to bodies in the early Solar System was enriched in both <sup>17</sup>O and <sup>18</sup>O and had a Δ<sup>17</sup>0 of at least +2%c The isotopic composition of water evolved during hydrothermal alteration on parent bodies toward lower Δ<sup>17</sup>O values, more similar to that of the host rocks. The complex release profile indicate that these meteorites experienced several periods of hydrothermal activity. SNC sample results have suggested the presence of two isotopically distinct reservoirs, the silicate crust and the hydrosphere each possessing distinct Δ<sup>17</sup>0 values. A third component with a large <sup>17</sup>O excess (+4%) was detected in ALH84001. The magnitude of this anomaly indicates an origin due to heterogeneous accretion or late stage veneer and cannot be produced by hydrodynamic escape. Results from the eucrites and ordinary chondrite also suggested isotopically distinct parent body silicate and hydrous reservoirs and may also be consistent with widespread late input of isotopically distinct water in the Solar System

Year: 2001
OAI identifier: oai:oro.open.ac.uk:19051
Provided by: Open Research Online
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