Abstract
Diffusion profiles in olivine crystals from the final mafic eruption products of the compositionally zoned Laacher See tephra deposit were measured to identify recharge and eruption-triggering events prior to the eruption of the Laacher See volcano (12.9 kyr). These products represent the hybrids of mixing between phonolite and intruding basanite at the bottom of the reservoir, which is likely related to the eruption-triggering event. Additionally, olivine crystals from ten basanitic scoria cones and maar deposits (East Eifel) and two nephelinites (West Eifel) were analyzed to constrain histories of olivine in Quaternary basanite magmas. Olivine crystals from the Laacher See hybrids vary in core composition (Fo83–89) and show reversely zoned mantles with high Fo87.8–89 compared to olivine in East Eifel basanites erupted in nearby, older scoria cones. Towards the crystal margin, olivine in the hybrids develop a normally zoned overgrowth (Fo86.5–87.5). Olivine from East Eifel basanites show similar zonation and core compositions (Fo80–88) but have less forsteritic mantles (Fo83–88) indicating that these basanites are less primitive than those recharging the Laacher See reservoir (> Fo89). Olivine in the West Eifel nephelinites show mantles similar to those from Laacher See (Fo87.5–90), but have normal zoning and high-Fo cores (Fo88–92). This indicates that olivine in the Laacher See hybrids were entrained by a near-primary basanite from older cumulates just before hybridization of the basanite with the phonolite. Diffusion modeling indicates maximum timescales between entrainment and eruption of Laacher See of 30–400 days that are comparable to those calculated for olivine from basanitic scoria cones (10–400 days).
Highlights
The mitigation of potentially violent eruptions of evolved magmatic systems necessitates a better understanding of the pre-eruptive processes such as how fast magmas ascend from deep crustal reservoirs or mantle sources and how fast resident magmatic systems in the crust can be reactivated and triggered to erupt
We find that the olivine crystals analyzed here are antecrysts entrained from a basanitic crystal mush during ascent but prior to recharge of, and mixing with the resident phonolite magma
This study focuses on olivine in samples from the most mafic hybrid products from the uppermost part of the Laacher See tephra deposit (Fig. 1a, b) in order to constrain the time scale of mixing/mingling to eruption of the phonolite magma reservoir
Summary
The mitigation of potentially violent eruptions of evolved magmatic systems necessitates a better understanding of the pre-eruptive processes such as how fast magmas ascend from deep crustal reservoirs or mantle sources and how fast resident magmatic systems in the crust can be reactivated and triggered to erupt. 2011, 2013; Viccaro et al 2016; Rasmussen et al 2018; Ubide and Kamber 2018) Such studies have shown that the interaction of ascending mafic magmas with more evolved melts and crystal mush are a common process in many volcanic systems Processes that may lead up to eruption are preserved in chemically zoned crystals, either in phenocrysts from the recharging magmas or antecrysts disaggregated from older crystal mush. Crystal zoning provides information about chemical compositions of the interacting magmas and the timescales between this interaction and eruption. After the entrainment by a foreign magma, the crystals start to homogenize with the new composition to reach equilibrium. This homogenization will endure until (1) the crystal
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
