Anatomy of intraplate monogenetic alkaline basaltic magmatism. Clues from magma, crystals, and glass

Intraplate basaltic systems, often occurring as fields of small monogenetic volcanoes, are dominated by eruption of alkaline basaltic rocks, ranging from nephelinite/basanite to transitional/subalkaline. Their primitive erupted compositions imply limited crustal modification, thus providing an important probe into deep, lithospheric mantle processes. The whole-rock chemical variability within single eruptions is controlled by the characteristics of the primary melting source, as well as near-source percolative/reaction processes. Complex crystal textures and compositions have so far demonstrated that basaltic magmas are principally processed and modified within the lithospheric mantle with minor modification en route through the crust. Fractional crystallization and magma mixing modify melts throughout ascent, and can imprint secondary chemical intra-eruptive variability. Quantifiable temperature and pressure parameters constrain the depth of formation, and hence provide information about the role of different mineral phases in deep versus shallow chemical evolution. Volatile components in the melt can be quantified on glass and melt inclusions. These analyses may help to reconstruct initial dissolved volatile content to further constrain the source characteristics and magmatic ascent dynamics. Integrated studies of crystals and melt paint a picture of extended lithospheric mantle to minor crustal processing resulting from the complex deep plumbing of monogenetic basaltic systems. This highlights the need for improved resolution to characterize true primary signatures and hence elucidate the formation of intraplate alkaline basalts