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Martinsville, VA, United States

Frost C.D.,University of Wyoming | Frost B.R.,University of Wyoming | Beard J.S.,Virginia Museum of Natural History
American Mineralogist | Year: 2016

Silica-rich granites and rhyolites are components of igneous rock suites found in many tectonic environments, both continental and oceanic. Silica-rich magmas may arise by a range of processes including partial melting, magma mixing, melt extraction from a crystal mush, and fractional crystallization. These processes may result in rocks dominated by quartz and feldspars. Even though their mineralogies are similar, silica-rich rocks retain in their major and trace element geochemical compositions evidence of their petrogenesis. In this paper we examine silica-rich rocks from various tectonic settings, and from their geochemical compositions we identify six groups with distinct origins. Three groups form by differentiation: ferroan alkali-calcic magmas arise by differentiation of tholeiite, magnesian calc-alkalic or calcic magmas form by differentiation of high-Al basalt or andesite, and ferroan peralkaline magmas derive from transitional or alkali basalt. Peraluminous leucogranites form by partial melting of pelitic rocks, and ferroan calc-alkalic rocks by partial melting of tonalite or granodiorite. The final group, the trondhjemites, is derived from basaltic rocks. Trondhjemites include Archean trondhjemites, peraluminous trondhjemites, and oceanic plagiogranites, each with distinct geochemical signatures reflecting their different origins. Volcanic and plutonic silica-rich rocks rarely are exposed together in a single magmatic center. Therefore, in relating extrusive complements to intrusive silica-rich rocks and determining whether they are geochemically identical, comparing rocks formed from the same source rocks by the same process is important; this classification aids in that undertaking. © 2016 by Walter de Gruyter Berlin/Boston. Source

Ivanov K.,Cleveland State University | Keiper J.,Virginia Museum of Natural History
Biodiversity and Conservation | Year: 2010

The effects of forest edge on ant species richness and community composition were examined within an urbanized area of northeast Ohio. The ground-dwelling ant fauna was inventoried in three deciduous forest fragments that have resulted from human disturbance. We surveyed ants via leaf-litter extraction along 150 m transects positioned perpendicular to the forest edge. We collected 4,670 individuals from 14 genera and 29 species. Samples closest to the forest edge contained more species and accumulated species at a higher rate than did samples located in the forest interior. Our rarefied and expected richness estimates revealed a decline of species richness from edge to forest interior. The higher ant richness at the forest edge was due mostly to the presence of species characteristic of the neighboring open habitats. Although most of the typical forest ant species were represented equally at the edge and at the forest interior, a few responded to the presence of edges with changes in their relative abundance and frequency of occurrence. Forest edges had a higher proportion of opportunistic species and a lower proportion of cryptic ants, whereas interior locations exhibited a more even distribution among ant functional groups. In addition, we documented a community composition shift between the edge and the forest interior. Consistent with previous findings, we suggest that the edge effects are most pronounced within 25 m of the forest edge, which may have implications for the overall conservation of forest-dwelling fauna. © 2010 Springer Science+Business Media B.V. Source

Hoffman R.L.,Virginia Museum of Natural History
Zootaxa | Year: 2011

The name Rondostreptus kiellandi is proposed for an undescribed genus and species of Spirostreptidae apparently endemic to the Rondo Plateau in southeastern Tanzania. It appears to have no close relatives among the known spirostreptid fauna of East Africa. Copyright © 2011. Magnolia Press. Source

Frost B.R.,University of Wyoming | Evans K.A.,Curtin University Australia | Swapp S.M.,University of Wyoming | Beard J.S.,Virginia Museum of Natural History | Mothersole F.E.,Curtin University Australia
Lithos | Year: 2013

Dunite from New Caledonia displays three types of serpentine-dominated veins. The earliest, type 1 veins are narrow (50-100μm wide) and rarely extend across more than a single olivine grain. They are lizardite, contain abundant brucite and never contain magnetite. Type 2 veins are 0.01 to 0.1mm wide, extend across several olivine grains and cut across the type 1 veins. They are lizardite, contain magnetite, often in vein interiors, and contain less brucite than type 1 veins. Type 3 veins are dominantly chrysotile, cm-scale, have a magnetite-rich core, and extend for meters or more. Analyses of two representative samples indicate that the type 1 veins have relatively Fe-rich serpentine (XMg=0.92) and brucite (XMg=0.82). These minerals are less magnesian than those in the type 2 veins; serpentine has XMg=0.93-0.94 and brucite has XMg=0.84. In the magnetite-rich core to the type 3 vein both serpentine (XMg=0.94-0.97) and one of the two brucite populations (XMg=0.94) are Mg-rich. Opx in harzburgite layers in these samples is cut by serpentine veins that are on the order of 0.05mm wide. The serpentine veins after Opx lack talc or magnetite and, as with veins cutting olivine, the older veins are more Fe rich (XMg=0.84) than the younger veins (XMg=0.90). We conclude that the formation of magnetite was accompanied by the extraction of iron from the early-formed serpentine and brucite.Thermodynamic calculations suggest that the type 1 veins formed in a rock-dominated system where the activities of FeO, MgO, and SiO2 were dictated by the compositions of olivine and orthopyroxene. In contrast the type 2 veins were formed in a more fluid-dominated system where the infiltrating fluid was relatively oxidizing and out of equilibrium with the original brucite-serpentine assemblage. Reduction of this fluid was accompanied by reaction of brucite and serpentine to magnetite and hydrogen. By producing magnetite, this reaction extracted iron from brucite and serpentine, making them both more magnesian. This would drive the brucite-serpentine-magnetite assemblage to higher oxygen fugacity, progressively decreasing the efficiency of the magnetite-forming reactions. © 2013 Elsevier B.V. Source

Vieira L.M.,University of Sao Paulo | Winston J.E.,Virginia Museum of Natural History | Fehlauer-Ale K.H.,University of Sao Paulo
PLoS ONE | Year: 2012

Background: Bugula is a speciose genus of marine bryozoans, represented by both endemic and cosmopolitan species distributed in tropical and temperate waters and important to marine biologists because of the occurrence of many species in harbor and fouling communities, therefore as potential invaders. The southeastern Brazilian coast in the southern Atlantic hosts the highest known diversity of the genus, a status intimately associated with the intensity of collecting efforts. Methodology: Morphological data based on the examination of living specimens, scanning electron and light microscopic images, and morphometric analyses were used to assess the diversity of Bugula along the coastal areas of southern, northeastern, and southeastern Brazil. In this study, morphological species boundaries were based mainly on avicularian characters. For two morphologically very similar species, boundaries are partially supported by 16 S rDNA molecular data. Results: Nine species are newly described from Brazil, as follows: Bugula bowiei n. sp. (= Bugula turrita sensu Marcus, 1937) from the southern, northeastern, and southeastern coasts; Bugula foliolata n. sp. (= Bugula flabellata sensu Marcus, 1938), Bugula guara n. sp., Bugula biota n. sp. and Bugula ingens n. sp from the southeastern coast; Bugula gnoma n. sp. and Bugula alba n. sp. from the northeastern coast; Bugula rochae n. sp. (= Bugula uniserialis sensu Marcus, 1937) from the southern coast; and Bugula migottoi n. sp., from the southeastern and southern coasts. Conclusion: The results contribute to the morphological characterization and the knowledge of the species richness of the genus in the southwestern Atlantic (i.e., Brazil), through the description of new species in poorly sampled areas and also on the southeastern coast of that country. Additionally, the taxonomic status of the Brazilian specimens attributed to B. flabellata, B. turrita and B. uniserialis are clarified by detailed studies on zooidal and avicularia morphology. © 2012 Vieira et al. Source

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