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DIAGRAMME ARAIGNEE [1 record]

Filter results by subject field Alphabetical list of terms

Filter results by subject field

Alphabetical list of terms

Record 1 2009-09-29

English

Subject field(s)
  • Petrography
  • Statistical Graphs and Diagrams
DEF

A useful plot, used in igneous petrology to show variations between two rocks or rock types for a wide range of elements.

CONT

Usually, one rock is a standard type, e.g. a mid-oceanic-ridge basalt or a carbonaceous chondrite meteorite. Data for the test rock are "normalized" to the standard by dividing the abundance for each element by the abundance in the standard and plotting the quotient, usually in order of atomic number. Elements which have the same abundance in the test rock as in the standard yield a quotient of 1; if the two compositions were identical the plot would be a straight line through 1 on the y axis. Elements more abundant in the test rock yield numbers greater than 1; those less abundant yield numbers less than 1. By connecting the points plotted by a single line, a spidery diagram of peaks and troughs is obtained which illustrates immediately systematic differences in composition, e.g. relative enrichment in incompatible elements.

CONT

Extended rare earth element (REE) spidergram of rocks classified using modal opaque oxide percentage as "oxide-free" gabbro and olivine gabbro.

OBS

spidergram: term used at Natural Resources Canada - Earth Sciences Sector.

Key term(s)
  • spiderlike graph

French

Domaine(s)
  • Pétrographie
  • Diagrammes et graphiques (Statistique)
CONT

Afin de mieux comprendre l'origine des différences entre MORBs [pour «Mid Oceanic Ridge Basalts»] et OIBs [pour «Oceanic Island Basalts»], on peut étudier les arachnogrammes comparés de ces deux types de basaltes. Dans les arachnogrammes, on représente certains éléments incompatibles par degré d'incompatibilité décroissante de la gauche vers la droite, chaque concentration étant normalisée au manteau primitif. L'étude de ces arachnogrammes ou spidergrams montrent que la dualité manteau supérieur-manteau inférieur ne suffit pas à expliquer la différence MORBs-OIBs.

CONT

Sur un diagramme arachnide, les teneurs en terres rares sont d'environ 15 fois celles des chondrites dans l'unité Apan1, alors que dans les formations d'Urban et de Lacroix elles sont de 10 fois les chondrites [...]

OBS

diagramme arachnide; arachnogramme : termes en usage à Ressources naturelles Canada - Secteur des sciences de la Terre.

Spanish

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