Genesis of magmas from the Tres Vírgenes Volcanic Complex, Baja California Sur, Mexico
Macías, J. L.
Avellán, D. R.
Arce, J. L.
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The late Pleistocene Tres Vírgenes Volcanic Complex (TVVC), Baja California Sur, Mexico, is formed by 3 volcanic edifices: El Viejo, El Azufre and La Vírgen. Although the TVVC is emplaced in a tectonic environment where subduction was terminated, its volcanic products are calc-alkaline. In addition to its typical-arc calc-alkaline nature, we classified the TVVC rocks as adakitic. Typical-arc calc-alkaline rocks are widely described in Baja California, so we focus on the adakitic rocks. Relatively high-silica adakitic rocks (57–64 SiO2wt.%; Sr/Y = 30–49; La/Yb = 4–8) from the TVVC are constrained between 110–90 ka and could be produced when typical-arc calc-alkaline magmas partially melt the lower crust. Alternatively, these high-silica adakitic rocks could be formed by mixing between typical-arc calc-alkaline magmas and low-silica adakitic rocks. Low-silica adakitic rocks (50–55 SiO2wt.%; Sr/Y = 50–65; La/Yb = 3–7) are produced when the metasomatized mantle wedge is partially melted. With the exception of La Vírgen Tefra, a Plinian eruption where typical-arc calc-alkaline magmas are involved, mineral composition and lack of xenocrysts suggest mixing and assimilation are not dominant processes at the TVVC upper crust reservoir. In contrast, mineral textures in some rocks suggest that magma reservoirs were heated. We propose that the low-silica adakitic magmas are the heating-mixing elements modifying the reservoir-plumbing system.