Origins and Scales of Compositional Variations in Crustally Derived Granitic Rocks: The Example of the Dartmoor Pluton in the Cornubian Batholith of Southwest Britain

The ca. 280 Ma, postorogenic, S-type Dartmoor pluton was assembled from numerous sheets of granitic magma, emplaced into the shallow crust. main magma source lies in middle crust and is most probably Proterozoic metagreywackes, with minor metapelites metavolcanic or plutonic rocks, possibly formed a syncollisional environment. Partial melting this may have occurred under fluid-deficient conditions, magmas likely had relatively high initial H2O contents. contains substantial, whole-rock-Sr quartz-O isotope heterogeneities on scales down to meter less, such small-scale are common intrusions derived heterogeneous protoliths. Thus, variations terranes not be fully captured sample numbers commonly applied studies plutons. preservation both large- isotopic suggests that were never efficiently homogenized by flow-driven mechanical mixing. This implies terrane lithological tens meters less. rocks form five texturally, chemically, isotopically distinct groups, each which somewhat different sources mixtures sources. chemical cannot been through fractionation any combination major minerals rocks. Instead, entrainment variable proportions peritectic plagioclase, orthopyroxene, ilmenite responsible, together local crystal fractionation. Low-density, late-magmatic melts aqueous fluids produced patchy enrichment light elements extreme some highly silicic, two-mica microgranites. However, although they also enriched elements, “aplites” seem independent magmatic origins.