Exploring the Eruptive Sequence and Chemical Evolution of the AD 1730—1736 Timanfaya Eruption, Lanzarote, Canary Islands

English Abstract:

The Timanfaya eruption is one of the largest historical basaltic fissure eruptions, producing an estimated 3—6 km³ of lava along a 15-km, E-W trending fissure. Previous work identified (I) a preliminary eruption sequence, and (II) an unusual progression of magma composition from basanite to tholeiite, based on mapping and geochemical analysis of distal lava flows [1, 2].

In this work, we present preliminary tephrostratigraphy results and geochemical analyses to better define the eruption (including its volume) and its mantle source. New X-ray fluorescence analyses of tephras sampled at the vents suggest edifices correlate strongly with distal flows, consistent with the associations proposed by [1]. Data also confirm the trends from highly alkaline (1.5 wt% K₂O, ~15 wt% MgO, 42 wt% silica) to tholeiitic (0.5 wt% K₂O, ~7.5 wt% MgO, and 51 wt% SiO₂) compositions. A 1-m-thick, bedded tephra sequence located at a section 4 km south of the fissure is chemically homogeneous. Correlating best with fall deposits from the Caldera de los Cuervos (first and most primitive) eruptive phase, the strata identified thus likely represent intra-phase pulses instead. The identification of these tephras confirms the involvement of that vent in the Timanfaya eruption, despite the edifice’s location off-axis of the fissure.

Incompatible trace element ratios, such as Zr/Y, display significant variations in the eruptive sequence that cannot be produced by fractional crystallization. Trace element data help test previous hypotheses on the origin of the syn-eruptive change in magma composition, including differing degrees of partial melting [1], different mantle source compositions [3], and crustal assimilation of sedimentary xenoliths [4].

[1] Carracedo et al., Estudios Geol., 46: 25-55 (1990).

[2] Carracedo et al., J. Volcanol. & Geotherm. Res., 53: 239-250 (1992).

[3] Sigmarsson et al., Earth Planet. Sci. Lett., 162: 137-151 (1998).

[4] Aparicio et al., Geol. Mag., 143 (2): 181-193 (2006).