Los dendrogramas y su uso en la petrografía

  • Gerardo Sánchez-Rubio Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, México 20, D. F.
Keywords: tree diagrams, petrographic data, Probability Theory, relative abundances, mineral assemblage


A new method for handling petrographic data is introduced. The method is based on "tree diagrams", commonly used in Probability Theory and Numerical Taxonomy.

The method can be applied to a set of rock specimens, representative of a particular geological unit, for which relative mineral abundances have been determined. The particular case of the andesitic "Calixtlahuaca" volcanics, Mexico, is used as an example.

Petrographic tree diagrams can be used as a support for the more time consuming modal analyses. However, it is "relative mineral abundances" that forms the basis for tree diagrams and hence must be considered separate from diagrams based on modal analyses, which deal with exact percentages of minerals.

Tree diagrams are of great help for presenting every single mineral assemblage whilst highlighting the most important ones.