Evolution of the winonaite parent body: Clues from silicate mineral trace element distributions

Abstract

Abstract-We have measured the trace element compositions of individual plagioclase, pyroxene, and olivine grains in 6 different winonaites that span the range of textures and mineralogies observed in these meteorites. Textural evidence in these meteorites, including the presence of a plagioclase/ clinopyroxene-rich lithology and coarse-grained olivine lithologies, suggests that they may have experienced some silicate partial melting. However, trace element distributions in these lithologies do not show any clear signatures for such an event. Pyroxene trace element compositions do exhibit systematic trends, with abundances generally lowest in Pontlyfni and highest in Winona. The fact that the same trends are present for both incompatible and compatible trace elements suggests, however, that the systematics are more likely the result of equilibration of minerals with initially heterogeneous and distinct compositions, rather than partial melting of a compositionally homogeneous precursor. The winonaites have experienced brecciation and mixing of lithologies, followed by varying degrees of thermal metamorphism on their parent body. These factors probably account for the variable bulk rare earth element (REE) patterns noted for these meteorites and may have led to re-equilibration of trace elements in different lithologies.

Reclassification of Villalbeto de la Peña—Occurrence of a winonaite‐related fragment in a hydrothermally metamorphosed polymict L‐chondritic breccia

“…7; Table 3). It is very similar to those of lunar anorthosites (like 60025 in Wiesmann and Hubbard 1975; http://curator.jsc.nasa.gov/lunar/lsc/60025.pdf) and plagioclase from other differentiated meteorites (e.g., eucrites, anomalous eucrites, and winonaites; e.g., Hsu and Crozaz 1996;Floss et al 2007Floss et al , 2008. However, REE-patterns of plagioclase are the result of crystal chemical controls and typically show such patterns thus bearing no unequivocal clue to the origin of the fragment.…”

“… REE ‐patterns of the black Villalbeto de la Peña bulk rock clast (black dots; 1σ‐error; compare Table ) in comparison with the lunar anorthosite 60025 (Wiesmann and Hubbard ), and plagioclase from the anomalous eucrite Ibitira (Hsu and Crozaz ) and from the winonaites Pontyfli and Hammadah al Hamra 193 (Floss et al. , ).…”

“…7. REE-patterns of the black Villalbeto de la Peña bulk rock clast (black dots; 1r-error; compare Table 3) in comparison with the lunar anorthosite 60025 (Wiesmann and Hubbard 1975), and plagioclase from the anomalous eucrite Ibitira (Hsu and Crozaz 1996) and from the winonaites Pontyfli and Hammadah al Hamra 193 (Floss et al 2007(Floss et al , 2008. Table 3 Sp-rich 300 lm (8) 0.05 0.04 0.008 0.007 0.04 0.03 0.008 0.008 0.08 0.05 0.13 0.04 0.05 0.03 0.013 0.011 0.12 0.08 0.010 0.007 0.003 0.002…”

Oxygen isotope variation in primitive achondrites: The influence of primordial, asteroidal and terrestrial processes

“…They are generally considered to represent meteorites that have experienced high-grade metamorphism, which in some cases resulted in partial melting (Benedix et al, 1998;Weisberg et al, 2006;Touboul et al, 2009). Consequently, primitive achondrites bridge the gap between chondrites and differentiated achondrites (Benedix et al, 1998;Weisberg et al, 2006;Floss et al, 2008;Touboul et al, 2009). In contrast to the more highly processed differentiated achondrites, primitive achondrites often retain compositional, isotopic and textural features that provide evidence about the nature of their precursor materials .…”

Petrogenesis of lunar meteorite Northwest Africa 2977: Constraints from in situ microprobe results

“…Concentrations of rare earth elements (REE) and other trace elements in minerals were measured at Washington University, St. Louis with the modified Cameca IMS-3f ion microprobe following the procedures of Floss (2000) and Floss et al (2008). We used an O ) primary beam of 1-5 nA (resulting in spot sizes of 10-30 lm) and energy filtering at low mass resolution to remove complex molecular interferences.…”