Constraints on the pre-eruptive magmatic history of the Quaternary Laacher See volcano (Germany)

Abstract

Ba zonation patterns in sanidine phenocrysts from mafic and intermediate phonolite and crystal-rich cumulates from the Laacher See volcano (12.9 ka) in western Germany document diffusion times suggestive of periodic recharge events throughout the magma reservoir's entire lifespan of ~ 24 ky. Phenocrysts analysed from samples that formed late at the base of the compositionally zoned magma reservoir by mixing and mingling between a resident phonolite magma and recharging basanite show resorption and thin (2-10 μm) late-stage Ba-rich overgrowth. Short diffusion profiles across these boundaries give diffusion times of ~ 1.5-3 years at most, which are interpreted to be the maximum duration between the most recent recharge by the basanite and eruption. The lack of such late overgrowth in samples from other parts of the phonolite reservoir suggests that effect of this mixing and mingling was limited to the crystal-rich base. Sanidines in the cumulates, by contrast, are generally devoid of zoned crystals. Only rare cumulate crystals with resorbed outer boundaries and very thin overgrowths (a few microns) with very sharp compositional changes imply the remobilization of cumulates only months before eruption. Based on the diffusion timescales and storage temperatures obtained in a previous study, we present a genetic model for the conditions and timing of storage and (re-)activation of the magma system prior to the eruption of Laacher See, which is the largest volcanic event in Central Europe since the last glaciation.

Origin of carbonatites—liquid immiscibility caught in the act

“…Carbonatitic syenites, enclosing the Laacher See magma chamber as a mostly crystalline carapace 50 , 51 , occur as clasts in the middle and late erupted LST, and are consanguine to Laacher See phonolite magma as concluded from conjugate phonolite—carbonatite trace element patterns 50 , 52 as well as carbon- and oxygen isotopes 45 , 52 . While the exact mechanism of carbonatite melt formation remains unclear 52 , Schmitt et al 45 and Rout and Wörner 50 suggest liquid immiscibility between carbonatite and phonolite liquids with subsequent fast segregation of the carbonatite melt forming a carbonatite-syenite intrusive complex at the magma chamber margin 45 .…”

Mantle and Crustal Xenoliths in a Tephriphonolite From La Palma (Canary Islands): Implications for Phonolite Formation at Oceanic Island Volcanoes

“…It is likely that a recharge event ultimately caused ascent and eruption of the xenolith-rich tephriphonolite. Recharge by more primitive melts is a common eruption trigger, but is not necessarily apparent in the petrological record (Rout and Wörner, 2020). The actual mechanism for ultimate destabilization and ascent of the tephriphonolite is not known.…”

“…The record of the xenolith-rich tephriphonolite studied here provides a rare opportunity to constrain the frequency of these recharge events (cf. Rout and Wörner, 2020).…”

“…barometric data (Grant et al, 2013;Berthod et al, 2021) such an interpretation may be misleading. Recharge events during magma differentiation at shallower levels (e.g., Rout and Wörner, 2020) may also bring deep-seated fragments into an evolving melt. Here we present petrological data from a unique tephriphonolite body on La Palma (Canary Islands), which carries abundant mantle and crustal xenoliths in a phonolitic groundmass.…”

Nanoscale Chemical Imaging by Photo‐Induced Force Microscopy: Technical Aspects and Application to the Geosciences

“…2017). The PiFM mapping abilities may also expand the study of nanoscale diffusion profiles that are used, for example, to time events of magma‐chamber recharge leading towards volcanic eruptions (e.g., Rout and Wörner 2020). Similarly, we also see potential in the area of cosmochemistry, including nano‐imaging of chondrules, pre‐solar grains with unknown mineralogy, and extra‐terrestrial organics (Pignatari et al .…”