Trace element abundance in glass-bearing inclusions in Chassigny

MARIA EUGENIA VARELA; ZINNER ERNST,; KURAT GERO,

Houston

Congreso; XXXVIII Lunar and Planetary Science Conference.; 2007

The Chassigny achondrite belongs to the SNC (Shergottite- Nakhlite- Chassigny) group of meteorites and consists mainly of Fe-rich olivine (Fo68) with anhedral to euhedral shape, suggestive of a cumulate origin [1]. The classical genetic scenario considers Chassigny as a recrystallized cumulate dunite, which possibly formed from a fractionated melt rather than a residual rock after partial melting [2]. The parent magma from which the SNC meteorites could have formed seems to resemble terrestrial tholeiitic magmas (but somewhat poorer in Al2O3) [e.g., 3-5]. In the case of Chassigny, the glass-bearing inclusion phase assemblages are consistent with an initial trapped melt that resembles terrestrial boninite lavas with ~1.5 wt% H2O [6] or with the evolution of a liquid from silica-saturated hawaiitic (with > 0.4 wt% H2O) to trachy-andesite to sodic, alkali-rich rhyolite with P> 4.3 kbar [7]. The parent melt was LREE-enriched with a REE pattern parallel to that of the whole rock [8]. The study of all types of glass inclusions in Chassigny and Nakhla minerals suggests a non-classical scenario with low temperatures prevailing during their formation [9-11]. In Chassigny, the heterogeneous trapping of the mineral assemblages at sub-solidus temperatures suggests a non-igneous origin for the primary glass-bearing inclusions in olivine [9]. Here we report the results of a SIMS study on glass-bearing inclusions in Chassigny olivines that give support to our previous view. The Chassigny achondrite belongs to the SNC (Shergottite- Nakhlite- Chassigny) group of meteorites and consists mainly of Fe-rich olivine (Fo68) with anhedral to euhedral shape, suggestive of a cumulate origin [1]. The classical genetic scenario considers Chassigny as a recrystallized cumulate dunite, which possibly formed from a fractionated melt rather than a residual rock after partial melting [2]. The parent magma from which the SNC meteorites could have formed seems to resemble terrestrial tholeiitic magmas (but somewhat poorer in Al2O3) [e.g., 3-5]. In the case of Chassigny, the glass-bearing inclusion phase assemblages are consistent with an initial trapped melt that resembles terrestrial boninite lavas with ~1.5 wt% H2O [6] or with the evolution of a liquid from silica-saturated hawaiitic (with > 0.4 wt% H2O) to trachy-andesite to sodic, alkali-rich rhyolite with P> 4.3 kbar [7]. The parent melt was LREE-enriched with a REE pattern parallel to that of the whole rock [8]. The study of all types of glass inclusions in Chassigny and Nakhla minerals suggests a non-classical scenario with low temperatures prevailing during their formation [9-11]. In Chassigny, the heterogeneous trapping of the mineral assemblages at sub-solidus temperatures suggests a non-igneous origin for the primary glass-bearing inclusions in olivine [9]. Here we report the results of a SIMS study on glass-bearing inclusions in Chassigny olivines that give support to our previous view.