Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain

No abstract available

Atomic Scale Depth Profile of Space Weathering in an Itokawa Olivine Grain

No abstract available

Atom scale element and isotopic investigation of 25Mg-rich stardust from a H-burning supernova

We have discovered a presolar olivine from ALH 77307 with the highest 25Mg isotopic composition measured in a silicate to date (δ25Mg = 3025.1‰ ± 38.3‰). Its isotopic compositions challenge current stellar models, with modeling of magnesium, silicon, and oxygen showing a closest match to formation in a supernova (SN) where hydrogen ingestion occurred in the pre-SN phase. Presolar grains within primitive astromaterials retain records of processes and environmental changes throughout stellar evolution. However, accessing these records has proved challenging due to the average grain size (∼150 nm) of presolar silicates, their sensitivity to extraction agents, and instrumental restrictions, limiting the range of isotopic and chemical signatures which can be studied per grain volume. Here, we present the first known detailed geochemical study of a presolar silicate from a hydrogen-burning SN, studied in 3D without contributions to the analysis volume and at unprecedented spatial resolutions (<1 nm), essential for constraining physical and chemical processes occurring within this recently proposed stellar environment. From our results, we infer either (i) condensation within an environment depleted of heavy elements compatible with the olivine lattice under the pressure and temperature conditions during condensation, or (ii) during periods of limited mixing either near the end of the pre-SN phase or from a collapse so rapid localized pockets of different gas compositions formed

Hidden secrets of deformation: Impact-induced compaction within a CV chondrite

The CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1—essentially unshocked—using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample

The parental care behaviour of Paratilapia polleni (Perciformes, Labroidei), a phylogenetically primitive cichlid from Madagascar, with a discussion of the evolution of maternal care in the family Cichlidae

The parental behaviour of the Madagascan cichlid, Paratilapia polleni , was studied in the laboratory. According to current hypotheses of phylogenetic intrarelationship for the family Cichlidae, Paratilapia is a representative of a phylogenetically primitive cichlid lineage, and as such is of particular interest in comparative evolutionary studies. Given the basal phylogenetic placement of Paratilapia it seems reasonable to expect that, if maternal participation in brood care arose within the extant Cichlidae, then the proposed plesiomorphic system of extensive male care of eggs and embryos may be retained in this taxon. This is not the case, and already by the fertilized-egg interval male and female roles in Paratilapia are strongly differentiated with the female as the primary care giver. In addition to specialized behavioural roles, a unique egg morphology and mobile egg mass is described for Paratilapia . The results of the study are discussed in the context of theories of the evolution of maternal brood care within the Cichlidae.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42636/1/10641_2004_Article_BF00004768.pd

Garnet porphyroblast timing and behaviour during fold evolution: implications from a 3-D geometric analysis of a hand-sample scale fold in a schist

Detailed 3-D analysis of inclusion trails in garnet porphyroblasts and matrix foliations preserved around a hand-sample scale, tight, upright fold has revealed a complex deformation history. The fold, dominated by interlayered quartz–mica schist and quartz-rich veins, preserves a crenulation cleavage that has a synthetic bulk shear sense to that of the macroscopic fold and transects the axis in mica-rich layers. Garnet porphyroblasts with asymmetric inclusion trails occur on both limbs of the fold and display two stages of growth shown by textural discontinuities. Garnet porphyroblast cores and rims pre-date the macroscopic fold and preserve successive foliation inflection/intersection axes (FIAs), which have the same trend but opposing plunges on each limb of the fold, and trend NNE–SSW and NE–SW, respectively. The FIAs are oblique to the main fold, which plunges gently to the WSW. Inclusion trail surfaces in the cores of idioblastic porphyroblasts within mica-rich layers define an apparent fold with an axis oblique to the macroscopic fold axis by 32°, whereas equivalent surfaces in tabular garnet adjacent to quartz-rich layers define a tighter apparent fold with an axis oblique to the main fold axis by 17°. This potentially could be explained by garnet porphyroblasts that grew over a pre-existing gentle fold and did not rotate during fold formation, but is more easily explained by rotation of the porphyroblasts during folding. Tabular porphyroblasts adjacent to quartz-rich layers rotated more relative to the fold axis than those within mica-rich layers due to less effective deformation partitioning around the porphyroblasts and through quartz-rich layers. This work highlights the importance of 3-D geometry and relative timing relationships in studies of inclusion trails in porphyroblasts and microstructures in the matrix

A Morphologic and Crystallographic Comparison of CV Chondrite Matrices

No abstract available

High Resolution Chemical Analysis of Grains From the Itokawa Asteroid by FIB-ToF-SIMS

No abstract available

High Resolution Chemical Analysis of Grains From the Itokawa Asteroid by FIB-ToF-SIMS

No abstract available

Nanoscale Characterisation of Grains From the Itokawa Asteroid by FIB-ToF-SIMS, APM and TEM

No abstract available