Mafic Magma Intraplating: Anatexis and Hybridization in Arc Crust, Bindal Batholith, Norway

Abstract

distinct, with Nd and O in the migmatites from −7·6 to −9·6 The dioritic Velfjord plutons (>448 Ma) were emplaced into and from +10·9‰ to +13·5‰, and in the contact granites regional migmatitic metapelitic and metacarbonate rocks at midfrom−5·2 to−7·5 and from+9·6‰ to+12·3‰, respectively. crustal levels, corresponding to pressures of >700 MPa. ExThus, the contact granites could have a source that is isotopically humation to >400 MPa began while the migmatites were in a distinct from, but mineralogically similar to the diatexites, or they partly molten state. With increasing proximity to the plutons, could result from mixing of magma similar to the high-K leucosomes regional stromatic migmatites change to diatexite, and diatexitic with dioritic magmas. Mass balance calculations are consistent dikes are common within 500 m of the contacts. We interpret these with the latter interpretation, with proportions of granitic to dioritic relationships to indicate that heat from the plutons resulted in contact magmas from 7:1 to 7:3. Emplacement and solidification of the migmatization in a zone up to 1 km wide. Typical residual dioritic plutons provided zones of structural anisotropy along which mineralogy in the diatexites is plagioclase + quartz + biotite high-K leucosome magmas and contact granite magmas collected. + garnet + sillimanite ± K-feldspar, consistent with biotite These magmas were injected by additional dioritic magma and dehydration melting. Podand dike-like leucosomes consist of two further hybridized. Because the solidi of the plutons were several types: earlier high-K (granitic) ones with mineral assemblages hundred degrees higher than that of the granitic magmas, the pluton identical to the migmatites and later low-K (tonalitic) ones in which walls acted as long-lived, hot, rigid surfaces along which magmas sillimanite is sparse and garnet absent. The high-K leucosome collected and migrated. magmas can be explained by biotite dehydration melting at 700 MPa. Within the aureole, mafic magmas were locally injected into, and hybridized with, the diatexites and the high-K leucosome