1,721,142 research outputs found
Origin and fate of refractory domains in the oceanic mantle - Secchiari A., Godard M., Montanini A.
No full textOrigin and fate of refractory domains in the oceanic mantle - Secchiari A., Godard M., Montanini A.</p
Les milieux polaires. A. Godard, M.-F. André, 1999, Les milieux polaires, Paris : Armand Colin, U Géographie
No full textUsselmann Pierre. Les milieux polaires. A. Godard, M.-F. André, 1999, Les milieux polaires, Paris : Armand Colin, U Géographie. In: Mappemonde 60, 2000/4. p. 46
Heterogeneous mantle domains in a modern OCT: new insights from the West Iberian margin (ODP Legs 149 and 173).
No full textNew constraints on the formation of heterogeneous oceanic crust at slow spreading ridges: a detailed petro-geochemical study of the olivine-rich troctolites from Atlantis Massif (MAR, IODP Hole U1309D, 30°N)
No full textMantle heterogeneity generated by melt depletion and melt-rock interaction: the West Iberian margin peridotites (ODP Legs 149 and 173).
No full textUnderstanding the nature and evolution of mantle sequences exhumed along modern magma-poor ocean-continent transition zones (OCTs) is crucial for deciphering the complex interplay of tectonic and magmatic processes during rifting, lithospheric breakup, and the genesis of oceanic lithosphere. However, the existing data pertaining to these specific tectonic settings remain limited.
In this study, we reassessed peridotites from the West Iberian margin (WIM) by performing a petrological and geochemical investigation of variably serpentinized mantle exposures sampled in the Iberia Abyssal Plain (ODP Holes 899B, 1068A and 1070A). The investigated samples exhibit a diverse spectrum of mineral modes, textures and chemistry. Hole 899B spinel harzburgites are coarse-grained granular peridotites (cpx content ~ 2-3 vol.%), displaying evidence of melt-rock interaction, evidenced by olivine-forming, pyroxene-dissolving microstructures. Mineral chemical variations, along with in-situ trace element analysis, reveal that these peridotites experienced moderate amounts of melt extraction, occurring partly within the garnet stability field, followed by reactive percolation of LREE-enriched melts.
Microtextural analysis combined with mineral major element compositions, including high Cr# and TiO2 in spinel, as well as Na2O- and Al2O3-enriched clinopyroxene, supports a derivation from melt impregnation processes for plagioclase peridotites of Holes 899B and 1068A. Geochemical modelling based on clinopyroxene REE compositions indicates that these peridotites originated through melt-rock reactions driven by chemically heterogeneous melts, ranging from depleted to MORB-like compositions.
Among the examined samples, Hole 1070A spinel harzburgites (cpx ~ 2-5 vol.%) exhibit the most distinctive features. The low modal clinopyroxene abundances, preserving a positive correlation between Cr#, Al2O3 and Yb, indicate that Hole 1070A peridotites represent a suite of residual mantle rocks recording variable degrees of melt extraction. However, the unusual Cr-Na enrichments, coupled to hump-shaped clinopyroxene REE patterns, cannot be solely ascribed to melt depletion. The counterintuitive features of these samples can be explained by a process of open-system melting occurring in the spinel stability field associated to contemporaneous percolation of an enriched melt.
Calculated equilibrium temperatures for the WIM peridotites are within the range of fossil OCTs (TCa-in-Opx= 921-1029 °C). They record a history of melt-rock interaction at high temperature (TREE-Y= 1098-1244 °C), followed by thermal re-equilibration at relatively low rates (TOl-Sp= 770-813 °C).
Our data provide new compelling evidence for a sub-continental lithospheric origin of the peridotite samples from ODP Holes 899B and 1068A. We show that the petrological and geochemical signature of the WIM peridotites reflect a polyphase history, which was achieved through the superimposition of rifting-related processes to melt extraction events, related to, or older than, the last Wilson cycle
GEOCHEMICAL VARIABILITY OF MANTLE ROCKS DRILLED IN AN OCEAN-CONTINENT TRANSITION: NEW INSIGHTS FROM THE IBERIAN MARGIN PERIDOTITES (ODP LEG 149 AND 173)
No full textMantle rocks exposed along ocean-continent transitions represent an exceptional archive for investigating processes occurring during lithospheric extension and break-up, providing important clues on the chemical heterogeneities in the Earth’s mantle.
In this contribution, we revisit the Iberian margin peridotites through a combined petrological and geochemical investigation performed on a new set of drilled samples (ODP Holes 899B, 1068A, 1070A).
Hole 899B peridotites are relatively fresh tectonic harzburgites, displaying variable clinopyroxene amounts (≈ 3-8 vol.%) and mineral chemisty (0.898≤Mg#[Ol]≤0.915; Al2O3[Opx]= 2.95-3.46 wt.%; 0.198≤Cr#[Spl]≤0.483). Holes 1068A and 1070A peridotites are characterized by higher serpentinisation degrees and wider compositional ranges (Hole 1068A: Al2O3[Cpx]= 3.77-6.79 wt.%; 0.253≤Cr#[Spl]≤0.376; Hole 1070A: Al2O3[Opx]= 2.65-3.70 wt.%; 0.378≤Cr#[Spl]≤0.452).
In-situ trace element analyses revealed a wide spectrum of geochemical signatures. Primary clinopyroxene was found only in Holes 1068A and 899B. The clinopyroxene yields abyssal-type patterns, with gently (LaN/SmN= 0.22-0.27) to steeply plunging (LaN/SmN= 0.02-0.03) LREE for Holes 1068A and 899B, respectively. Orthopyroxene of Hole 899B has low REE concentrations (HREEN≤ 1) and spoon-shaped patterns, excepted for one plagioclase-bearing sample, which exhibits a straight pattern (LaN/YbN =0.001-0.02) and negative Eu anomalies.
Hump-shaped REE patterns, yielding variable LREE-MREE fractionation (LaN/SmN= 0.003- 0.16) and flat HREE, were found in Hole 1070A. These patterns are atypical for mantle peridotites and cannot be explained by melt depletion.
Our new data shed light on the occurrence of different mantle domains exposed along the ocean-continent transition of the Iberian margin. These features cannot be accounted by margin
extension and oceanization, as samples with the most oceanic affinity (Holes 1068A and 899B) are preserved close to the Iberia continental margin, while hump-shaped patterns appear common offshore (Hole 1070A). We interpret these contrasting signatures as related to a complex interplay of depletion and melt-rock interaction, partly inherited from a previous Wilson cycle
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
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