Top–down control on eruptive style at Masaya volcano inferred from melt composition.

Hlinka, Lisa, Longpré, Marc-Antoine, Pérez, Wendy, Kutterolf, Steffen and Monteleone, Brian (2021) Top–down control on eruptive style at Masaya volcano inferred from melt composition. Earth and Planetary Science Letters, 572 . Art.Nr. 117138. DOI 10.1016/j.epsl.2021.117138.

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Supplementary data:

Abstract

Highlights

• Regardless of eruptive style, Masaya magmas are compositionally similar.
• Volatile contents are higher in Plinian samples, but low compared to CAVA magmas.
• All Masaya magmas undergo extensive pre-eruptive degassing at low pressure.
• Initial volatiles are higher than observed, but do not control eruptive style.
• The state of the volcano's conduit modulates eruptive style in a top–down manner.

Abstract

Highly explosive Plinian eruptions of basaltic magma are enigmatic because low melt viscosities should inhibit such eruptive style. Masaya volcano, Nicaragua, is a persistently active basaltic system capable of a wide range of eruptive styles, from open-conduit lava lake activity to voluminous Plinian eruptions; it is thus an ideal natural laboratory to constrain potential controls on basaltic eruption style. Here we report the major, trace, and volatile (CO2, H2O, S, Cl, F) element composition of olivine-, plagioclase- and clinopyroxene-hosted melt inclusions as well as matrix glasses from lava lake ejecta and two Plinian tephra deposits—the 2.1 ka Masaya Triple Layer and the 1.8 ka Ticuantepe Lapilli—to test whether pre-eruptive volatile contents and degassing history may be linked to eruptive style. All samples display a relatively narrow and largely overlapping basaltic–basaltic andesitic compositional range (
wt.% SiO2, wt.% MgO) with similar trace element signatures (e.g., , ). However, lava lake and Plinian samples show systematic differences in pre-eruptive volatile contents, forming distinct groups with mean H2O contents of wt.% (lava lake), wt.% (Masaya Triple Layer), and wt.% (Ticuantepe Lapilli). Together, these groups generate broad positive correlations between S, Cl and H2O concentrations, with maximum values reaching 920 ppm, 1300 ppm and 2.3 wt.%, respectively, which are low compared to typical Central American arc magmas. Magma temperature estimates overlap and average at 30°C, while volatile saturation pressures are low, mainly <100 MPa, although only lava lake samples record pressures <31 MPa. These observations reiterate the compositionally buffered state of the volcano's magmatic system highlighted by previous work and demonstrate that — regardless of eruption style — all Masaya magmas undergo variable, but extensive, pre-eruptive degassing at low pressure. Geohygrometry, gas emissions, and H2O/Ce–Ba/La systematics suggest initial, undegassed H2O contents on the order of 3.9–5.5 wt.%. Our results imply that pre-eruptive volatile contents are not the culprit for Plinian events at Masaya. Instead, we propose that the volcano's vigorous magma supply is modulated in a top–down manner to produce a wide range of eruptive styles, whereby temporary sealing of the conduit may instigate a transition to explosive behavior. In this model, rapid magma ascent is triggered when the seal eventually breaks from degassing-induced pressurization, yielding high degrees of undercooling, rapid microlite growth, and a dramatic increase in magma viscosity and explosive eruption potential. There may thus be a thin line between open-conduit conditions and Plinian eruptions at Masaya.

Document Type: Article
Keywords: Masaya volcano, eruptive style, basaltic Plinian eruptions, lava lake, volatile degassing, melt inclusions
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Woods Hole
Main POF Topic: PT3: Restless Earth
Refereed: Yes
Open Access Journal?: No
Publisher: Elsevier
Date Deposited: 23 Aug 2021 06:42
Last Modified: 07 Feb 2024 15:39
URI: https://oceanrep.geomar.de/id/eprint/53817

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