To better understand the origin of the waters in these meteorites, we are currently working on understanding the mineralogical constraints on storage and release of water. The existence of heterogeneity in the Δ 17O' values of water extracted at different temperature intervals from Tissint and Zagami supports the possible existence of isotopically distinct reservoirs on Mars. Since both Tissint and Zagami were observed falls, we would not expect extensive terrestrial contamination, although trace amounts of hydration could affect the 'water' data, but not the bulk rock data. At temperatures above 400☌ the Δ 17O' values of the extracted water begin to get more negative (0.17‰ for Tissint and 0.09 for Zagami). The highest Δ 17O' values were measured for water extracted between 200 and 400☌ (0.21‰ for Tissint and 0.1‰ for Zagami). This is likely due to terrestrial contamination of the absorbed water portion. The lowest Δ 17O' values (<0.1‰) are measured in waters extracted below 150☌. Both samples also show a similar trend in the Δ 17O' values of the waters released at different temperature steps. This supports the previous observations of isotopic disequilibrium (or terrestrial contamination) between the two sites of oxygen (water and bulk rock). Δ 17O' values of water extracted from Tissint and Zagami are distinctly elevated relative to that of Earth but are lower than the corresponding bulk rock Δ 17O' values (0.33‰). The O 2 gas was then purified in a GC column and measured for the triple oxygen isotope value. Water was extracted from samples using stepwise heating and converted to O 2 by fluorination. So far we have measured the oxygen isotope composition of water extracted from martian shergottites Tissint and Zagami and are presently working on analyzing other shergottites as well as a variety of nakhlites, chassignites and the basaltic breccia NWA 7034. A broader and more detailed sampling is the goal of this study. (1992) has thus far been the only systematic study of oxygen isotopic compositions of water extracted from martian meteorites and their data cannot be easily interpreted. By analyzing the isotopic composition of oxygen in the water extracted from a variety of martian meteorites we hope to identify distinct oxygen isotope reservoirs on Mars (mantle, crust and hydrosphere), and attempt to link them to certain geological processes experienced by the different types of martian meteorites.

Previous studies have shown that the oxygen extracted from water in martian meteorites is generally not in isotopic equilibrium with the bulk silicate rock. The presence of water in martian meteorites provides a unique glimpse into the evolution of water on Mars.

Compositions of water