C. T. Foster

Tourmaline-rich pseudomorphs in sillimanite zone metapelites: Demarcation of an infiltration front

The mineralogical community lost a valued colleague and friend with the death of Eugene E. Foord. Gene, a Life Fellow of the Mineralogical Society of America, died at his home on January 8, 1998 at the age of 51 after a three-year battle with lymphoma. Gene was a career scientist at the U.S. Geological Survey where he worked from 1976 until his death in 1998. Gene was an outstanding mineralogist and he will be remembered for his significant contributions to the mineralogy and paragenesis of pegmatites from San Diego County, California. He will also be remembered for his boundless enthusiasm for mineralogy, his dedication to thorough and accurate mineral identifications and descriptions, and his willingness to work with both professional scientists and amateur collectors. Foordite, a tin-niobium oxide was named after Gene ( ̌ Cerný et al. 1988) in honor of his many contributions to the study of niobium-tantalum-tin minerals in pegmatites. Gene enjoyed practical jokes, having learned from the master himself, Richard H. Jahns. In fact, Gene was the “mystery” person responsible for “relocating” the bust of Theodore Hoover from the third floor of the Stanford geology building. Gene was an enthusiastic and animated storyteller and he loved to entertain his friends and colleagues with his outrageously funny stories of his escapades including backyard bouts with birds, avoiding landmines along the Pakistan-Afghanistan border, finding stashes of frozen hummingbirds in a Stanford professor’s freezer, nearly “starving” to death in Labrador, graphic descriptions of the Russian cuisine, toying with guards while in house arrest in China, and many more. Gene was born at Children’s Hospital in Oakland, California, November 20, 1946. Gene, a RH-factor baby, had the distinction of being one of the first survivors of a complete exchange transfusion. However, as a result of the RH incompatibility, Gene was born severely hearing impaired. He moved in 1947 with his parents, Elizabeth and Delbert Foord, and his older brother William, to West Hempstead, New York. When his parents realized that Gene was hearing impaired, they took him to the Manhattan Eye and Ear Infirmary. They were told that their only education option was to enroll Gene in a special school for the deaf. However, his parents were determined to provide Gene with a normal education in their own hometown. Consequently, they joined together with other parents of hearing impaired children in Long Island and formed the Long Island Hearing and Speech Society. This was one of the first

Metastable prograde mineral reactions in contact aureoles

Extrapolation of reaction paths and rates of metamorphic mineral growth from experimental to natural systems is complicated by a number of factors. Many of these factors are difficult to evaluate for natural systems. A combination of textural modeling and stable isotope analysis allows for a distinction between several possible reaction paths for olivine growth in a siliceous dolomite contact aureole. It is suggested that olivine forms directly from dolomite and quartz. The formation of olivine from this metastable reaction implies metamorphic crystallization far from equilibrium. Stable and metastable reaction paths predict the textures observed (calcite haloes around bladed olivine crystals) well. It is possible to discriminate between individual reaction paths only on the basis of the oxygen isotope compositions of the minerals involved. Products were found to be in stable isotope equilibrium, but in disequilibrium with the reactants. Only the metastable overall reaction dolomite + quartz → olivine + calcite + CO 2 produces no dolomite by local reactions, and hence agrees with the oxygen isotope data. Thus, significant mineral growth occurred far from equilibrium with respect to the thermodynamically stable reactions of the system. This amazing finding implies that metamorphism of contact aureoles has to be reinterpreted in a more complex, dynamic fashion, involving metastable reactions and metastable equilibria as well. The spatial distribution of metamorphic mineral assemblages in a contact aureole cannot be interpreted as a proxy for the temporal evolution of a single rock specimen, because each rock undergoes a different reaction path, depending on temperature, heating rate, and fluid-infiltration rate.

THE NEOGENE MARINE BIOTA OF TROPICAL AMERICA (''NMITA'') DATABASE: ACCOUNTING FOR BIODIVERSITY IN PALEONTOLOGY

Abstract The reliability of any survey of biodiversity through geologic time depends on the rigor and consistency by which taxa are recognized and samples are identified. The main goal of the Neogene Marine Biota of Tropical America (‘NMITA’) project is to create an online biotic database (http://nmita.geology.uiowa.edu) containing images and synoptic taxonomic information that are essential to collecting and disseminating high-quality taxic data. The database consists of an inventory of taxa collected as part of several large multi-taxa fossil sampling programs designed to assess marine biodiversity in tropical America over the past 25 m.y. In the first phase of the project, data for ∼1,300 taxa and ∼3,800 images are currently being entered into a relational database management system on an IBM RS6000 at the University of Iowa. Eleven taxonomic groups are represented: bivalves, gastropods (muricids, marginellids, strombinids), bryozoans (cheilostome, cyclostome), corals (azooxanthellate, zooxanthellate), benthic foraminifers, ostracodes, fish. The lowest taxonomic rank is species (genera/subgenera in mollusks) and the highest is family. Data that are collected and displayed on taxon pages include: (1) taxonomic authorship, synonyms, type specimens, and diagnostic morphologic characters; (2) images of representative specimens and associated museum catalog and measurement data; (3) distributional information including geologic ages, stratigraphic units, and spatial locations; and (4) higher level classification (genera and families) and bibliographic information. Illustrated glossaries of morphologic terms, character matrices, and identification tools are being developed for corals and mollusks. Interactive geographic maps and stratigraphic columns have been designed to provide information about taxa collected at different locations.

Prograde muscovite-rich pseudomorphs as indicators of conditions during metamorphism: An example from NW Maine

Abstract During metamorphism, evidence of the prograde path is commonly obliterated by continued recrystallization as temperatures increase. However, prograde pseudomorphs that are common in many terrains may provide insight into this portion of the metamorphic path if their mineralogy can be accurately interpreted. Seventeen sillimanite-zone metapelitic samples, each containing 2-5 muscovite-rich pseudomorphs, from the Farmington Quadrangle, Maine, U.S.A., were investigated to evaluate their use as indicators of conditions during prograde metamorphism. SEM-CL images, X-ray maps, image analysis, and electron microprobe analyses characterize the mineral distribution, modes, and compositions within the pseudomorph and the surrounding matrix. Based on modal mineralogy determined from image analyses, the muscovite-rich pseudomorphs are divided into four major types: muscovite-rich (>70% muscovite), quartz-muscovite (60-70% muscovite with 10-25% quartz), plagioclase-muscovite (58-72% muscovite with 10-20% plagioclase), and sillimaniteplagioclase- muscovite (50-60% muscovite with 10-20% each plagioclase and sillimanite). A biotiterich, muscovite-poor mantle surrounds many pseudomorphs. All pseudomorphs are interpreted to be prograde, based on their texture, and are after staurolite because of the partial replacement of staurolite by coarse muscovite at lower grades. Textural modeling of reaction mechanisms required to reproduce the observed mineralogy in the pseudomorphs indicates that each major pseudomorph type holds clues to the prograde path and represents a different mechanism of formation. Muscovite-rich and quartz-muscovite pseudomorphs formed by the breakdown of staurolite containing different modal amounts of poikiloblastic quartz. Quartz-muscovite pseudomorphs likely reflect a quartz-rich initial rock composition. Plagioclasemuscovite pseudomorphs require the infiltration of Na-bearing fluids. Sillimanite-plagioclase-muscovite pseudomorphs require a two-stage process; the infiltration of Na-rich fluids during staurolite breakdown followed by sillimanite growth. The subtle mineralogical differences recorded in the pseudomorphs studied here provide evidence of previously unrecognized controls along the prograde path during metamorphism.