Geology topics

Research about Lassen Volcanic Center

Source-linked reports with geographic coverage including Lassen Volcanic Center.

4 recordsLinked to original sources

USGS2025

Persistent deep long-period seismicity near the Lassen Volcanic Center

Deep long-period (DLP) earthquakes have been observed at many volcanic settings around the world and linked to the magmatic processes that drive volcanic unrest. At the Lassen Volcanic Center (LVC) of the Cascade arc, limited detection of DLP activity hinders classification of anomalous seismic behavior and its relationship to the LVC magmatic system. This study uses a template matching approach with seismic data from temporary nodal and permanent stations to detect and locate DLP earthquakes near the LVC between 2017 and 2024. Within the DLP catalog of 611 events, a transition occurs from scattered (2017–2020) to oscillatory (2021–2024) occurrence rates. During the oscillatory period, regional earthquakes with large amplitude velocity waveforms observed near the LVC are associated with abrupt changes in DLP occurrence rates. Continued monitoring of DLP activity has the potential to better define the processes that drive volcanic unrest at the LVC in the future.

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USGS2014

Localized rejuvenation of a crystal mush recorded in zircon temporal and compositional variation at the Lassen Volcanic Center, northern California

Zircon ages and trace element compositions from recent silicic eruptions in the Lassen Volcanic Center (LVC) allow for an evaluation of the timing and conditions of rejuvenation (reheating and mobilization of crystals) within the LVC magmatic system. The LVC is the southernmost active Cascade volcano and, prior to the 1980 eruption of Mount St. Helens, was the site of the only eruption in the Cascade arc during the last century. The three most recent silicic eruptions from the LVC were very small to moderate-sized lava flows and domes of dacite (1915 and 27 ka eruptions of Lassen Peak) and rhyodacite (1.1 ka eruption of Chaos Crags). These eruptions produced mixed and mingled lavas that contain a diverse crystal cargo, including zircon. 238 U- 230 Th model ages from interior and surface analyses of zircon reveal ages from ~17 ka to secular equilibrium (>350 ka), with most zircon crystallizing during a period between ~60–200 ka. These data support a model for localized rejuvenation of crystal mush beneath the LVC. This crystal mush evidently is the remnant of magmatism that ended ~190 ka. Most zircon are thought to have been captured from “cold storage” in the crystal mush (670–725°C, Hf >10,000 ppm, Eu/Eu* 0.25–0.4) locally remobilized by intrusion of mafic magma. A smaller population of zircon (>730°C, Hf <10,000 ppm, Eu/Eu* >0.4) grew in, and are captured from, rejuvenation zones. These data suggest the dominant method to produce eruptible melt within the LVC is small-scale, local rejuvenation of the crystal mush accompanied by magma mixing and mingling. Based on zircon stability, the time required to heat, erupt and then cool to background conditions is relatively short, lasting a maximum of 10 s–1000 s years. Rejuvenation events in the LVC are ephemeral and permit eruption within an otherwise waning and cooling magmatic body.

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USGS2012

Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California

Hydrogen isotope ratio, water content and Fe 3 + /Fe 2 + in coexisting amphibole and biotite phenocrysts in volcanic rocks can provide insight into shallow pre- and syn-eruptive magmatic processes such as vesiculation, and lava drainback with mixing into less devolatilized magma that erupts later in a volcanic sequence. We studied four ~ 35 ka and younger eruption sequences (i.e. Kings Creek, Lassen Peak, Chaos Crags, and 1915) at the Lassen Volcanic Center (LVC), California, where intrusion of crystal-rich silicic magma mushes by mafic magmas is inferred from the varying abundances of mafic magmatic inclusions (MMIs) in the silicic volcanic rocks. Types and relative proportions of reacted and unreacted hydrous phenocryst populations are evaluated with accompanying chemical and H isotope changes. Biotite phenocrysts were more susceptible to rehydration in older vesicular glassy volcanic rocks than coexisting amphibole phenocrysts. Biotite and magnesiohornblende phenocrysts toward the core of the Lassen Peak dome are extensively dehydroxylated and reacted from prolonged exposure to high temperature, low pressure, and higher f O2 conditions from post-emplacement cooling. In silicic volcanic rocks not affected by alteration, biotite phenocrysts are often relatively more dehydroxylated than are magnesiohornblende phenocrysts of similar size; this is likely due to the ca 10 times larger overall bulk H diffusion coefficient in biotite. A simplified model of dehydrogenation in hydrous phenocrysts above reaction closure temperature suggests that eruption and quench of magma ascended to the surface in a few hours is too short a time for substantial H loss from amphibole. In contrast, slowly ascended magma can have extremely dehydrogenated and possibly dehydrated biotite, relatively less dehydrogenated magnesiohornblende and reaction rims on both phases. Eruptive products containing the highest proportions of mottled dehydrogenated crystals could indicate that within a few days prior to eruption, degassed vesiculated magma or lava had drained back down the volcanic conduit and mixed with less devolatilized magma. The vesiculated magma contained hydrous phenocrysts with lattice damage, which locally raised the effective H diffusion coefficient by ca 10–100 × and resulted in increased mineral dehydrogenation. Remobilization of dacite magma mush by relatively more reduced mafic magma appears to have generated further f O2 variations in May 1915 as oxidized magma from shallow levels circulated to depths where dehydrogenation of hydrous phenocrysts began. The δD Magmatic H2O expressed in LVC acid hot springs is likely a mixture derived from devolatilized ascending mafic magmas and crystallizing silicic magma mush.

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USGS2002

Osmium isotope constraints on lower crustal recycling and pluton preservation at Lassen Volcanic Center, CA

Osmium isotope compositions of intermediate- to silicic-composition calc-alkaline volcanic rocks from the Lassen volcanic region of the Cascade arc are significantly more radiogenic ( γ Os =+23 to +224) than typical mantle. These evolved arc rocks in the Lassen region have unradiogenic Sr, Nd, and Pb isotope compositions which overlap with those of contemporaneous mafic lavas. Crystal fractionation of mafic- to intermediate-composition magmas produces Re/Os ratios that are high enough to evolve to very radiogenic Os isotope compositions in only a few million years, providing a potential fingerprint for detecting the involvement of such young, relatively mafic crust in magmatic systems. However, the Sr, Nd, and Pb isotope compositions will remain constant over such short time intervals due to relatively low parent/daughter enrichment during magmatic evolution. The radiogenic Os isotope compositions in typically evolved Lassen rocks are interpreted to reflect significant interaction with lower crustal material that has radiogenic Os isotope compositions. Beneath this section of the Cascade arc, large amounts of such high- γ Os lower crust may have formed and been isolated from MASH zone mixing and homogenization processes during the Pliocene or Late Miocene. The results from this study indicate that Os isotopes may provide a unique glimpse into lower crustal processes, such as recycling, in primitive orogenic arcs.

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