
doi: 10.1007/bf01163243
Rapakivi granites, recently redefined as A-type granites showing rapakivi texture at least in the larger batholiths, occur on all continents and presumably represent the most voluminous continental silicic intraplate magmatism on Earth. Most of the rapakivi granites are Proterozoic (mainly 1.0 to 1.7 Ga) but also Archean (2.8 Ga) and Phanerozoic (0.05 to 0.4 Ga) are known. The magmatic association is bimodal comprising anorthosite to gabbro, diabase, minor Fe-enriched intermediate rocks, and monzonite, beside granite; mingling of silicic and mafic magmas is typical. Geochemically and otherwise, rapakivi granites show the characteristics of the Phanerozoic A-type granites, except that they encompass relatively few peralkaline rocks and that they may occur as very large (up to 40,000 km2) batholiths. Some of the rapakivi granite complexes host important Sn-polymetallic and Fe-Cu deposits. The rapakivi granites crystallized from relatively hot, restite-poor magmas at low (epizonal-subvolcanic) pressure, $$a_{H_2 O} $$ , and $$a_{O_2 } $$ . Mineral assemblages are indicative of a multiphase crystallization history; the conspicuous mantling of the perthite ovoids with plagioclase can be explained by changes in magma composition and/or, P, T, and $$a_{H_2 O} $$ affecting the stabilities of feldspars. The isotopic composition of rapakivi granites is generally compatible with a lower crustal protolith. The latter could have been either a melt-depleted residue or otherwise relatively anhydrous igneous or metaigneous rock. Melting of the protolith commenced under vapor-absent conditions and was induced by heat from the contemporaneous mantle-derived mafic magmas. The widespread rapakivi granite magmatism in the Middle Proterozoic may have been related to the establishment of a major continental mass (supercontinent).
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