Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution

Mafic dykes of the Antarctic Peninsula continental-margin arc are compositionally diverse, comprising calc-alkaline (dominant), shoshonite, tholeiite, and OIB-like varieties. Their compositions give information about different mafic magma sources tapped during arc evolution. The compositional groups represent partial melts of at least five distinct mantle sources: a low-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (older calc-alkaline); a high-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (shoshonites); a high-ɛNd subduction-modified, spinel-bearing, asthenospheric mantle (younger calc-alkaline); E-MORB-like spinel-bearing asthenosphere depleted by a previous melting event (tholeiites); and within-plate non-subduction modified, garnet- and spinel-bearing, asthenosphere (OIB-like). Slab-derived fluids, subducted sediment, and arc crust also contributed to the magmas. Consideration of previous work in the light of our new compositional and geochronological data enables presentation of a summary of arc evolution. For most of the Cretaceous and Tertiary, the tectonic regime of the Antarctic Peninsula arc was transtensional, and calc-alkaline magmas intruded. An oceanic spreading centre collided with the trench during the Late Cretaceous and induced tectonic changes which caused tapping of different magma sources. A pulse of shoshonitic, tholeiitic, and OIB-like mafic magmatism resulted. Three ridge-trench collisions are now recognized during the history of the arc, in Mid–Late Jurassic, Late Cretaceous, and Early–Mid Tertiary times.