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Perspectives on Magma Mush Deformation: Textural and Geochemical Constraints on Compaction and Melt Extraction in a Granitic Magma Body
No full textMagmatic textures and compositions illuminate magma dynamics, such as compaction and melt extraction. Preserved textures in plutons (crystallized magma bodies) or magma mush fragments (crystal-rich, melt bearing clasts potentially genetically related to the erupted magmas) can provide important perspective on mush processes in both inactive and active magmatic systems respectively. The emplacement of a large (2 m diameter) felsic enclave (LFE) within granitic mush in Aztec Wash pluton (15.7 Ma, NV-USA) is preserved within a granitic body. The LFE is an ellipsoidal microgranite mass inferred to have been nearly solid when it settled at the top of a crystal-rich zone of the magma body. Backscattered Electron (BSE) imaging, Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and X-ray Fluorescence whole-rock data for samples from the granite surrounding the LFE show key textural and compositional differences between granite immediately beneath the LFE and granite located more distant and to the side (“far-field”). Alkali feldspar crystals beneath the enclave have well-defined euhedral rims, while those in the far-field have irregular overgrowths, suggesting continuing growth into larger melt pools. The samples underneath the enclave (69.6-70.0% SiO2, 1100-1170 ppm Ba, 400-430 ppm Sr) are less felsic than the far-field sample (72.1% SiO2, 750 ppm Ba, 330 ppm Sr), also suggesting less retained melt. We conclude that impingement of the LFE led to enhanced melt extraction. The composition of the far-field sample is typical of Aztec Wash pluton samples interpreted to represent cumulate mush (70.0-72.4% SiO2, 640-1100 ppm Ba, 250-440 ppm Sr; Harper et al. 2004 and our new data). For comparison, “non-cumulate” Aztec Wash samples that may represent input magma are distinctly more felsic (72.3-73.9% SiO2, 570-690 ppm Ba, 170-270 ppm Sr). Our beneath-LFE compositions indicate the greatest melt depletion identified among Aztec Wash granites, substantially more than in the typical cumulates. We calculate that emplacement of the LFE in a magma mush enhanced melt extraction, segregating 10-20% melt from the crystal-rich framework.
Magma mush fragments – crystal-rich, glass bearing clasts potentially genetically related to the erupted magmas – can provide important perspective on mush processes in active magmatic systems. Granitoid clasts from the Rotoiti Ignimbrite, Taupō Volcanic Zone (TVZ), include magma mush fragments that can provide insights on magmatic systems of one of the most active areas of rhyolitic volcanism in the world. This study focuses on a large (35 cm) clast found within a lag-breccia of the 64 ka Rotoiti Ignimbrite, one of the largest eruptions from the Ōkataina Volcanic Center (TVZ). This fragment is layered and can be divided into 5 zones based on compositions and textures. Backscattered Electron (BSE), Cathodoluminescence (CL), and Energy Dispersive Spectrometry (EDS) techniques highlight the textural and mineralogical differences between the zones. In this study, we focus on a fine-grained, biotite granite zone with microcrystalline patches and sparse granophyric texture. Quartz grains range from euhedral to subhedral, with complex zoning patterns that are visible in both BSE and CL. Some feldspar grains are zoned, others are not. The microcrystalline patches make up less than 10% of the sample and they are surrounded by subhedral grains (both quartz and feldspar). The interstitial texture and distribution of the microcrystalline patches indicate that this fragment is representative of a magma mush with <10% trapped melt. The average compositions of this microcrystalline material range from 72-77% SiO2 and 4-6% K2O and yield rhyolite-MELTS model pressures of ~100 MPa. This melt composition does not correspond with Rotoiti eruptive products; this mush fragment may illuminate non-eruptive sequences of the TVZ. Tying textures and compositions in both active and inactive magmatic systems can provide key perspective on the generation of eruptible magma bodies
Squashing Crystals with the Big Felsic Enclave: Magma Dynamics in the Aztec Wash Pluton
No full textAnalyzing magmatic fabrics in the Aztec Wash Pluton (~15.5 Ma) illuminates magma dynamics during the emplacement of a big felsic enclave (BFE) in a granitic pluton. Evidence suggests that the BFE settled at the boundary between crystal-rich and crystal-poor zones of the magma body at the time of impingement. Textural and compositional analysis using a Scanning Electron Microscope (SEM) allow visualization of a deforming crystal mush. Four thin sections sampled from the granite surrounding the BFE (three located underneath, one in the far field) show a change in alkali feldspar foliation around the enclave. Using the SEM, imaging using Backscatter Electron (BSE) imaging, Energy Dispersive Spectrometry (EDS), and Electron Backscatter Diffraction (EBSD) show the textural and compositional differences between the samples located underneath the BFE and the sample from the far field granite, specifically the existence of an oriented fabric directly underneath the enclave. BSE images show multiple instances of broken feldspar grains in the samples located underneath the enclave. BSE and EDS display large euhedral alkali feldspar crystals located underneath the enclave, while the far field sample has alkali feldspar grains with irregular outermost rims. EBSD data indicate that there is an oriented foliation of the alkali feldspar underneath the BFE that does not exist in the far field. This evidence suggests that a crystal mush was deformed during the emplacement of the BFE, causing the alkali feldspars to reorient and causing some feldspars to break. This deformation indicates that compaction occurred underneath the enclave and may have been paired with melt extraction
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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