Sandstone compositions are a function of provenance and depositional basin and both of these are determined by plate tectonics. Modal analyses of major framework grain types--quartz, polycrystalline quartz, potassium feldspar, plagioclase, volcanic lithic grains, and sedimentary lithic grains--plotted on a series of four triangular diagrams can be used to distinguish between the main provenance types.

Quartz-rich sands come from cratonal sources and are deposited in basins on the craton and at quiet continental margins (miogeoclines and opening ocean basins). Arkosic sands are shed from uplifted blocks on continental basement into rift troughs and wrench basins associated with transform faults. Volcanic lithic sands have volcanic arc provenances and are deposited in trenches, forearc basins, and marginal seas. Undissected arcs produce very lithic-rich sand; more mature and eroded arcs produce a mixture of volcanic lithic and plutonic (mainly quartz and feldspar) detritus. Sands rich in quartz or chert plus sedimentary lithic grains come from subduction complexes, collision orogenic belts, and foreland uplifts and are deposited in closing ocean basins, successor basins, and foreland basins.

Data from both modern sands and ancient sandstones of known tectonic settings fit the above picture; influence of climate and diagenesis on sand composition must be less important than that of tectonic setting. Hence knowing the detrital modes of sandstones provides a way of determining the original tectonic setting of the rocks, and framework grain composition of sands can be predicted from their tectonic setting.

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