QFL diagram

A QFL diagram or QFL triangle is a type of ternary diagram that shows compositional data from sandstones and modern sands, point counted using the Gazzi-Dickinson method. The abbreviations used are as follows:

• Q – quartz
• F – feldspar
• L – lithic fragments

Ternary diagram showing the relative abundance of quartz, feldspar, and lithic grains and views of what selected compositions would look like.

In general, the most contentious item counted is chert, which is usually counted as a lithic fragment, but is sometimes better suited in the Q pole. When this happens, the pole is renamed 'Qt' instead of Q.

QFL triangle showing schematic plots of common sand compositions

The importance of a QFL triangle is mainly demonstrated in tectonic exercises. As first demonstrated in the 1979 paper by Bill Dickinson and Chris Suczek, the composition and provenance of a sandstone is directly related to its tectonic environment of formation.

• Craton sands are clustered near the Q pole. As sandstones, these are known as quartz arenites.
• Transitional continental sands are along the QF line. As sandstones, these are known as arkoses.
• Basement uplift sands are near the F pole. This includes "thick-skinned tectonics." As sandstones, these are known as arkoses.
• Recycled orogen sands plot near the Q pole, but with significant F and L components. This includes "thin-skinned tectonics" common in subduction back-arc thrusting. As sandstones, these are known as lithic sandstones.
• Arc sands plot along the F and L line, with sometimes significant Q components. Clustering near the F pole indicates a dissected arc, and clustering near the L pole indicates an undissected, or new arc. As sandstones, these are known as arkoses and/or lithic sandstones.

See also

• Folk classification