Intraplate magmatism is the generation, ascent and emplacement of magma within the interior of a tectonic plate, away from most active plate boundaries. It includes both volcanic activity and intrusive bodies such as dikes, sills and plutonic complexes. Intraplate magmatism occurs in oceanic and continental settings and has been attributed to several processes operating in the mantle and lithosphere.
Occurrence Oceanic intraplate magmatism commonly forms volcanic islands, seamounts and age-progressive volcanic chains. Continental examples include isolated volcanic fields, alkaline complexes, dyke swarms, carbonatites and some large igneous provinces. The magma may erupt at the surface or crystallize within the crust, so the term magmatism covers a broader range of processes than volcanism.
Many intraplate magmas are basaltic, but evolved alkaline and silicic rocks also occur. Compared with typical mid-ocean ridge basalt, intraplate basalt commonly shows enrichment in incompatible trace elements, reflecting differences in mantle source, degree of partial melting and subsequent magma evolution.
Proposed mechanisms No single mechanism explains every occurrence. Proposed causes include deep mantle upwelling, deformation and extension of the lithosphere, small-scale convection in the asthenosphere, and melting of compositionally enriched mantle.
Mantle plumes The mantle plume model proposes that buoyant thermal or thermochemical upwellings rise from deep in the mantle and generate melt by decompression beneath the lithosphere. It was developed to explain hotspot tracks and flood-basalt events. Seismic imaging, geochemistry and plate reconstructions support a deep-mantle contribution at several major hotspots, although the structure, composition and surface expression of individual plumes remain active areas of research.
Lithospheric and shallow-mantle processes Other intraplate provinces lack the age progression, excess temperature or geophysical structure expected for a simple plume model. Extension and faulting can allow asthenosphere to rise and undergo decompression melting, while variations in lithospheric thickness can organize small-scale mantle flow. A comparison of intraplate basaltic volcanic fields found that shallow tectonic processes can account for many low- to high-flux fields, with eruption rate also influenced by mantle composition and source size.
Geochronological and geochemical work on contemporaneous provinces along the conjugate margins of Cameroon and northeastern Brazil found no age progression consistent with a moving plate over a fixed plume. The authors instead proposed decompression melting during drainage of enriched asthenosphere beneath thinner lithosphere.
Tectonic and economic significance Intraplate magmatic rocks preserve information about mantle composition, lithosphere–asthenosphere interaction and past plate motion. Age-progressive chains can record the relative motion between a plate and a mantle melting anomaly, whereas scattered volcanic fields may reflect regional stress and lithospheric structure.
Some continental intraplate systems are associated with mineral deposits. Alkaline complexes and carbonatites can host rare-earth and rare-metal mineralization, kimberlites can carry diamonds, and mafic–ultramafic intrusions may contain nickel, copper and platinum-group elements.
See also Hotspot (geology) Intraplate volcanism Mantle plume Large igneous province Rift
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