Lecture 10 - Volcanic Rocks

Tend to use chemical classification, but can use IUGS diamond for phenocrysts

I. Two series: Alkaline (includes peralkaline rocks) & Subalkaline (includes metaluminous & peraluminous rocks)

To determine alkalinity:

 

A. Alkaline - alkali olivine basalt series (mildly alkaline), nepheline or leucite series (highly alkaline)

If alkaline, decide between two suites based on normative chemistry

B. Subalkaline - tholeiitic, calcalkaline

If subalkaline, decide between two suites based on AFM diagram

 

This goes back to what I talked about on the first day. Fits in with plate tectonic setting.