Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites

The relative abundances and chemical compositions of the macroscopic components or "inclusions" (chondrules and refractory inclusions) and fine-grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion. We present new techniques for analysis of low count per pixel Si, Mg, Ca, Al, Ti and Fe x-ray intensity maps of rock sections, and apply them to large areas of CO and CV chondrites, and the ungrouped Acfer 094 chondrite. For many thousands of manually segmented and type-identified inclusions, we are able to assess, pixel-by-pixel, the major element content of each inclusion. We quantify the total fraction of those elements accounted for by various types of inclusion and matrix. Among CO chondrites, both matrix and inclusion Mg to Si ratios approach the solar (and bulk CO) ratio with increasing petrologic grade, but Si remains enriched in inclusions relative to matrix. The oxidized CV chondrites with higher matrix-inclusion ratios exhibit more severe aqueous alteration (oxidation), and their excess matrix accounts for their higher porosity relative to reduced CV chondrites. Porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized CV chondrites. We confirm that major element abundances among inclusions differ greatly, across a wide range of CO and CV chondrites. These abundances in all cases add up to near-chondritic (solar) bulk abundance ratios in these chondrites, despite wide variations in matrix-inclusion ratios and inclusion sizes: chondrite components are complementary. This "complementarity" provides a robust meteoritic constraint for astrophysical disk models

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

A TEM study of crystalline silicates in the matrices of MET 00426 and QUE 99177 CR3.0 chondrites: Constraints on the formation mechanisms of dust in the solar nebula

Understanding the constituents of fine-grained nebular dust prior to asteroidal accretion is a significant challenge in meteoritics. The key to understanding nebular dust lies in chondritic meteorites, which are composed of undifferentiated solar system materials. Chondritic matrices are a subnanometer mixture of amorphous material, silicate grains, sulfides, and other phases, that act as the “glue” for larger components. In the pristine chondrites (petrologic type 3.00) the matrix preserves some record of the primary characteristics of nebular dust. Two CR carbonaceous chondrites, MET 00426 (CR3.00) and QUE 99177 (CR3.00), are likely the most pristine meteorites ever described (Abreu and Brearley, 2010). The mineralogy of crystalline silicate grains in the matrices of these two chondrites has been studied here using focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Dark-field scanning transmission electron microscopy (STEM) imaging, along with bright-field TEM and energy dispersive X-Ray spectroscopy (EDS) techniques were used to understand mineralogical and chemical characteristics. FIB sections consist of extremely fine-grained, amorphous material (<50 nm in size). Additionally, each section contains crystalline or nanocrystalline silicate grains, varying in size from <100 to 1000 nm in diameter. These grains are MgO-rich or FeO-bearing olivines and pyroxenes. These crystalline silicates exhibit unequilibrated major and minor element compositions, but distinct compositional groupings of olivines and pyroxenes can be identified. We infer that the crystalline silicate materials in the matrices of these chondrites formed by different mechanisms that include nebular condensation under equilibrium and disequilibrium conditions, followed in some cases by annealing prior to accretion. Our data discount chondrule fragmentation as a significant source of the fine-grained matrix olivines. Although these chondrites have similar matrix mineralogy and chemistry, FeO-bearing crystalline silicates are more common in MET 00426 matrix than in QUE 99177, indicating that the matrices of these chondrites did not sample the same reservoir or source of crystalline silicate nebular dust. Nevertheless, in many cases, these grains have are similar in composition to other primitive silicates, like interplanetary dust particles (IDPs) and amoeboid olivine aggregates (AOAs), and could share a common formational mechanism or represent the nanoscale equivalent of these objects.Earth and Planetary SciencesMastersUniversity of New Mexico. Dept. of Earth and Planetary SciencesBrearley, AdrianJones, RhianSharp, ZacharyShearer, Charle

Physical-Chemical Characterization of Karst Waters Involved in the Vadose Zone of Diamond Caverns, Kentucky

This project was a preliminary investigation at Diamond Caverns, a private show cave located near Mammoth Cave National Park, Kentucky. The purposes of this research included establishing baseline compositional data for cave dripwaters, and examining the possible compositional influence of neighboring agriculture and pavement runoff. Objectives in this project were to obtain physical-chemistry characterization of karst waters and analysis in time and space of parameters such as pH, temperature, and electrical conductivity (EC). With this data, the relationship between the external atmosphere and soil cover, composition of drip waters, and the processes of precipitation/dissolution of carbonate minerals and the transfer of CO2 were extrapolated. A network of fifteen sampling sites, primarily along passageways throughout Diamond Caverns, was designed in order to incorporate various speleothem forms and to allow the assessment of spatial variations in drip rates throughout the cave. Samples were collected approximately every three weeks, and initial drip water volumes recorded in order to determine variations in rates of infiltration (temperature and CO2 also taken initially). Continuous flow was collected in calibrated vessels and the volume per unit time recorded (1 min drip rate). The pH and EC of freshly collected water samples were measured and all samples were titrated for bicarbonate and alkalinity. Preliminary analyses from five previous collections in the fall of 2006 and spring 2007 have been analyzed by OES-ICP at the ERTL Facility at the University of Kentucky. Variations in both element concentrations and element ratios (e.g. Ca/Sr, Mg/Sr, etc.) demonstrated anticipated spatial and temporal variation