Sources and settings of granitic rocks

Abstract

Granitic rocks can have a wide range of sources, over all parts of the spectrum from pure mantle to pure crust. These sources show a significant correlation with tectonic setting. Granites from ocean ridges usually have characteristics that indicate depleted mantle sources. Granites in volcanic arcs usually have depleted mantle sources modified by a component from subducted oceanic crust and sediment. Granites from intraplate settings usually show evidence of enriched mantle (lithosphere and/or asthenosphere) sources together with rare crustal melts. Granites from syn-collision settings are usually characterised by pure crustal sources or by mantle sources containing large subducted crustal components. Granites from post-collision settings usually carry signs of enriched lithospheric mantle sources together with rare crustal melts. Further interaction between mantle-derived magmas and crust is a function of the thickness, temperature and composition of the crust and the residence time and temperature of the magma - variables that are also linked to tectonic setting. These relationships between source and setting provide the basis for the geochemical fingerprinting of granites which, when combined with geological considerations, enable granites to be assigned to their most probable setting of intrusion.