Ternary and Spider Diagrams for Austral Cook Volcanic Chain

Title: Ternary and Spider Diagrams for Austral Cook Volcanic Chain
Description: The AFM Ternary diagram shows composition of a representative subset of Ocean Island Basalts (based on wt% SiO2). These samples are tholeiitic, with little to no alkali evolution. This is to be expected, as magma at hotspots makes its way to the surface relatively quickly, allowing little time for fractional crystallization.

While the ternary diagram is similar to that of a MORB, the REE diagrams are quite different and tell an interesting story. In stark contrast to a MORB, the OIBs at the Austral Cook Volcanic Chain are very rich in incompatible elements. Like other REE diagrams, the line is sloping down, suggesting an increase in compatibility across the Lanthanide Series. This fits with Goldschmidt's rule, as ions with smaller radii are more compatible with solids, so are typically the last to melt.

The chondrite-normalized diagrams show a very high ratio of incompatibles in the OIB relative to the primitive mantle, the MORB-normalized diagram shows that OIB are also enriched in incompatibles relative to a MORB, but to a lesser extent than in a chondrite.
Subject: Petrology 2015 Final Project: Ocean Island
Creator: Devon Gorbey
Source: PetDB
Mediator: Tamara Carley