The chemically zoned 1949 eruption on La Palma (Canary Islands): Petrologic evolution and magma supply dynamics of a rift zone eruption

The 1949 rift Zone eruption along the Cumbre Vieja ridge on La Palma involv ed three eruptive centers, 3 km spaced apart, and was chemically and minera logically zoned. Duraznero crater erupted tephrite for 14 days and shut dow n upon the opening of Llano del Banco, a fissure that issued first tephrite and, after 3 days, basanite. Hoyo Negro crater opened 4 days later and eru pted basanite, tephrite, and phonotephrite, while LIano del Banco continued to issue basanite. The eruption ended with Duraznero erupting basanite wit h abundant crustal and mantle xenoliths. The tephrites and basanites from D uraznero and Llano del Banco show narrow compositional ranges and define a bimodal suite. Each batch ascended and evolved separately without significa nt intermixing, as did the Hoyo Negro basanite, which formed at lower degre es of melting. The magmas fractionated clinopyroxene + olivine +/- kaersuti te +/- Ti-magnetite at 600-800 MPa and possibly 800-1100 MPa. Abundant reve rsely zoned phenocrysts reflect mixing with evolved melts at mantle depths. Probably as early as 1936, Hoyo Negro basanite entered the deep rift syste m at 200-350 MPa. Some shallower pockets of this basanite evolved to phonot ephrite through differentiation and assimilation of wall rock. A few months prior to eruption, a mixing event in the mantle may have triggered the fin al ascent of the magmas. Most of the erupted tephrite and basanite ascended from mantle depths within hours to days without prolonged storage in crust al reservoirs. The Cumbre Vieja rift zone differs from the rift zones of Ki lauea volcano (Hawaii) in lacking a summit caldera or a summit reservoir fe eding the rift system and in being smaller and less active with most of the rift magma solidifying between eruptions.