An Amphibole Perspective on the Recent Magmatic Evolution of Mount St. Helens

Author:

Keller Franziska123ORCID,Wanke Maren4,Kueter Nico5,Guillong Marcel1,Bachmann Olivier1

Affiliation:

1. Institute of Geochemistry and Petrology, ETH Zürich Department of Earth Sciences, , Clausiusstrasse 25, 8092 Zürich, Switzerland

2. University of Oregon Department of Earth Sciences, , 100 Cascade Hall, 1272 Eugene, OR 97403, USA

3. Lehigh University Department of Earth and Environmental Sciences, , STEPS Building, 1 West Packer Ave, Bethlehem 18015, PA, USA

4. GEOMAR Helmholtz Centre for Ocean Research Kiel , Wischhofstr. 1-3, 24148 Kiel, Germany

5. Geological Institute, ETH Zürich Department of Earth Sciences, , Sonneggstrasse 5, 8092 Zürich, Switzerland

Abstract

Abstract Compositional variations of amphibole stratigraphically recovered from multiple eruptions at a given volcano have a great potential to archive long-term magmatic processes in its crustal plumbing system. Calcic amphibole is a ubiquitous yet chemically and texturally diverse mineral at Mount St. Helens (MSH), where it occurs in dacites and in co-magmatic enclaves throughout the Spirit Lake stage (last ~4000 years of eruptive history). It forms three populations with distinct geochemical trends in key major and trace elements, which are subdivided into a high-Al (11–14.5 wt% Al2O3), a medium-Al (10–12.5 wt% Al2O3), and a low-Al (7.5–10 wt% Al2O3) amphibole population. The oldest investigated tephra record (Smith Creek period, 3900–3300 years BP) yields a bimodal amphibole distribution in which lower-crustal, high-Al amphibole cores (crystallized dominantly from basaltic andesite to andesite melts) and upper-crustal, low-Al amphibole rims (crystallized from rhyolitic melt) document occasional recharge of a shallow silicic mush by a more mafic melt from a lower-crustal reservoir. The sudden appearance of medium-Al amphiboles enriched in incompatible trace elements in eruptive periods younger than 2900 years BP is associated with a change in reservoir conditions toward hotter and drier magmas, which indicates recharge of the shallow silicic reservoir by basaltic melt enriched in incompatible elements. Deep-crystallizing, high-Al amphibole, however, appears mostly unaffected by such incompatible-element-enriched basaltic recharge, suggesting that these basalts bypass the lower crustal reservoir. This could be the result of the eastward offset position of the lower crustal reservoir relative to the upper crustal storage zone underneath the MSH edifice. Amphibole has proven to be a sensitive geochemical archive for uncovering storage conditions of magmas at MSH. In agreement with geophysical observations, storage and differentiation have occurred in two main zones: an upper crustal and lower crustal reservoir (the lower one being chemically less evolved). The upper crustal silicic reservoir, offset to the west of the lower crustal reservoir, has captured compositionally unusual mafic recharge (drier, hotter, and enriched in incompatible trace elements in comparison to the typical parental magmas in the region), resulting in an increased chemical diversity of amphiboles and their carrier intermediate magmas, in the last ~3000 years of MSH’s volcanic record.

Funder

Swiss National Science Foundation

Publisher

Oxford University Press (OUP)

Reference78 articles.

1. Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids;Alonso-Perez;Contributions to Mineralogy and Petrology,2009

2. The effects of temperature and fO2 on the Al-in-hornblende barometer;Anderson;American Mineralogist,1995

3. The petrology of plutonic blocks and inclusions from the Lesser Antilles island arc;Arculus;Journal of Petrology,1980

4. Temperature-induced Al-zoning in hornblendes of the fish canyon magma, Colorado;Bachmann;American Mineralogist,2002

5. Mg/Mn partitioning as a test for equilibrium between co-existing Fe-Ti oxides;Bacon;American Mineralogist,1988

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