72 Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains (Posters)

This session highlights research across geoscience disciplines to advance understanding of the deformation, magmatism, seismicity, topography, and sedimentation processes governing trench to retroarc evolution during ocean-continent plate convergence.

Sunday, 19 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

Pluton Emplacement Style of Exposed Shallow Arc Spirit Lake Pluton, WA

Paper number: 72-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Volcanoes are underlain by extensive plumbing systems that facilitate movement of magma from the mantle and deep crust toward the Earth’s surface. The crust must deform to accommodate this movement, generating crustal inflation and seismic activity. Many geophysical studies and volcanic hazards programs utilize these signals to constrain the volumes of magma emplaced at subvolcanic depths and predict eruptions. However, the emplacement style of magmatic intrusions will strongly affect how crustal deformation manifests at the Earth’s surface. Processes that concentrate deformation above the intrusion (i.e., laccolithic emplacement) will lead to strong signals at the Earth’s surface, while processes that concentrate deformation below the intrusion (i.e., cauldron subsidence) will lead to weak, or nonexistent, signals at the Earth’s surface. Studies of subvolcanic pluton emplacement are, consequently, an important component of understanding the geophysical signatures of volcanic hazards.

The Oligocene Spirit Lake Pluton is a well-exposed, well-mapped arc pluton located north of the modern Mt. St. Helens volcanic edifice. Excellent geologic mapping of the pluton has identified three distinct intrusive phases. The youngest phase is a granite that forms a bell-shaped feature in the northeastern part of the pluton. We hypothesize this bell-shape is the cross-sectional view of a large block of phase two sinking during the emplacement of phase three magmas. Here we investigate the relationship between the second and third phases of the pluton using new, small-scale mapping of its margins and U-Pb zircon geochronology to better understand its emplacement style.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412463

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