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Pb and Hf isotope evidence for mantle enrichment processes and melt interactions in the lower crust and lithospheric mantle in Miocene orogenic volcanic rocks from Monte Arcuentu (Sardinia, Italy)
Get PDFMiocene (ca. 18 Ma) subduction-related basalts and basaltic andesites from Monte Arcuentu, southern Sardinia, Italy, show a remarkable correlation between 87Sr/86Sr (from ~0.705 to ~0.711) over a small range of SiO2 (~51–58 wt%) that contrasts with most other orogenic volcanic suites worldwide. New high-precision Pb and Hf isotope data help to constrain the petrogenesis of these rocks.\ud
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The most primitive Monte Arcuentu rocks (MgO >8.5 wt%) were sourced from a mantle wedge metasomatized by melts derived from terrigenous sediment, likely derived from Archean terranes of northern Africa. This gave rise to magmas with high 87Sr/86Sr (0.705–0.709) and 207Pb/204Pb (15.65–15.67) with moderate εHf (–1 to +8) and εNd (–6 to +1), but it does not account for the full range of compositions observed. More evolved rocks (MgO <8.5 wt%) have higher 87Sr/86Sr (up to 0.711) and 207Pb/204Pb (up to 15.68), with εHf and εNd as low as –8 and –9, respectively. Mixing calculations suggest that evolved rocks with low Rb/Ba and low 206Pb/204Pb interacted with lower crust similar compositionally to that exposed today in Calabria, Italy, which was formerly in crustal continuity with Sardinia. High Rb/Ba and high 206Pb/204Pb magmas interacted with lithospheric mantle similar to that sampled by Italian lamproites. Partial melting of lower crustal and upper mantle lithologies was facilitated by the rapid extension, and subsequent passive mantle upwelling, that occurred as Sardinia drifted away from the European plate during the Oligo-Miocene (ca. 32–15 Ma). Fractional crystallization under these PT conditions involved olivine + clinopyroxene with little or no plagioclase, such that differentiation proceeded without significant increase in SiO2. The Monte Arcuentu rocks provide insights into assimilation process in the lower crust and lithospheric mantle that may be obscured by upper crustal assimilation–fractional crystallization (AFC) processes in other orogenic suites
Garnet to Spinel facies transition and related metasomatism in the mantle wedge of Southern Patagonia (Pali Aike).
No full textThe Pali Aike volcanic field (longitude 67.7°W, latitude 52.1°S) is the only occurrence in extra-Andean Patagonia (back-arc) recording garnet- to spinel-peridotite facies transition.Garnet-facies peridotites are lherzolites with dominantly protogranular texture. In some cases garnet is accompanied by Cr-rich spinel. Spinel-facies peridotites are distinguished into: i) harzburgites with Cr-rich spinel and secondary recrystallised texture and ii) harzburgites and lherzolites with protogranular texture. Hydrous phases (phlogopite and pargasite) and glass may occur in all the peridotite facies. In the garnet-facies samples, garnet is always surrounded by a kelyphitic rim of minute crystals of opx, cpx and brown, euhedral Al-rich spinel, representing the breakdown reaction ol + gnt = sp + opx + cpx.The garnet peridotites equilibrated in the range 985 - 1190 °C and 2.2 - 2.7 GPa. When they contain Cr-spinel, equilibration range is 895 - 1165 °C and 1.7 - 2.3 GPa. Protogranular spinel peridotites have significantly lower temperatures of equilibration than the secondary recrystallised, but similar pressure (T = 730 - 970 °C and P = 1.43 - 1.9 GPa as compared with 1010 - 1143 °C and P = 1.2 -1.6 GPa) (Fig. 1).Major element variations with respect to fertility indexes display correlations consistent with melting and basalt extraction. Samples containing metasomatic phases deviate from the main trend toward lower CaO and higher TiO2 concentrations. The REE patterns vary from LREE depleted and flat from MREE to HREE, to variably LREE enriched. The LREE-enriched profiles vary from spoon-shaped, with inflections at Nd or Eu, to extremely fractionate. These latter predominate in the spinel-facies peridotites. In bulk rock Sr and HFSE (Nb, Hf, Ti, Zr) concentrations increase at decreasing MgO concentration, as expected from a depletion process caused by basalt removal. In most cases the HFSE anomalies are modest and vary from positive to negative. Only the samples which contain metasomatic phases show marked positive anomalies in HFSE (Ti/Ti* = 1.30 - 10.91, Zr/Zr* = 2.51 - 7.89). Sr and Nd isotopic composition of whole rocks, clinopyroxene and phlogopite separates show a variation range of Nd = 3.12 - 20.03 and Sr = -2.83 - -23.65, respectively (Fig. 2). Most of the samples plot within or close to the mantle array. The field of the host basalt is contained in the xenolith range but it is much less variable. Two samples deviate from the variation trend toward high 87Sr/86Sr values. Lead isotopic determinations on bulk rock and clinopyroxenes define an array overlapping the field of the host basalt, the Nazca sediment and the Pacific MORB.The observed REE profiles are traditionally explained by a chromatographic fractionation of fluid or melt percolating a previously depleted mantle. The LREE enrichment and the absence of significant HFSE anomalies in most peridotites suggest that these features are characteristics of the metasomatic component. They are typical of OIB melts and characterise also the host basalt, which has, furthermore, similar incompatible trace element ratios and isotope composition overlapping part of the peridotites. These evidences strongly support the hypothesis that the host basalt was an important metasomatic component. However, the different behaviour of some elements (mainly LILE) in modally metasomatised samples and the isotopic signatures suggest a contribution from slab-derived components.We suggest that the Pali Aike mantle column (straddling the garnet- spinel-facies boundary) has been repeatedly infiltrated by metasomatic agents, consisting of slab-derived components and, later on, alkali basalts. These latter underwent chromatographic fractionation under the observed T, P gradient and variously overprinted previous metasomatic signatures
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
Pervasive mantle plume head heterogeneity: Evidence from the late Cretaceous Caribbean-Colombian oceanic plateau
No full textVariations 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
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