Many minerals form only under specific conditions, therefore it is possible to identify sourceland composition with some confidence. Specific rock fragments indicate directly what the sourceland is made of. The composition (QFL) of sandstones can reveal where they came from. For example, sandstone samples collected from each of four tectonic regimes have been plotted on a QFL ternary diagram (see illustration below). The shaded fields on the ternary diagram represent the sediment compositions associated with each tectonic regime: stable Craton, block faulted continent (including continental rifts), volcanic arcs, and recycled orogens (arc-continent and continent-continent collision mountains). As the ternary diagram indicates, these fields tend to be distinct, indicating that sandstone composition can be used, judiciously, to make tectonic interpretations.
Contributed by Lynn Fichter