Magma supply rate beneath Mammoth Mountain, California estimated from helium isotopes and CO2 emissions
Abstract
The rate at which magma is supplied to a volcano exerts a fundamental control on its activity. Mammoth Mountain, a dacitic dome complex (~100-50 ka) within a field of mafic vents (~230-8.5 ka) on the southwestern rim of Long Valley Caldera, California has exhibited unrest over the past ~30 years, characterized by seismicity over a broad range of depths, elevated 3He/4He ratios in fumarolic gas and large-scale diffuse CO2 emissions. This activity has been attributed to magmatic intrusion, but minimal ground deformation and the presence of a shallow-crustal gas reservoir that traps rising CO2 for unknown periods of time pose a challenge for estimating magma supply rate. In this study, we use the record of 3He/4He ratios (3.04-6.72 R/RA) at Mammoth Mountain fumarole and CO2 emissions (based on direct soil CO2 flux and proxy tree-ring radiocarbon measurements) to estimate that of the ~5.2 Mt of CO2 released from Mammoth Mountain between 1989 and 2016, 1.6 Mt were associated with active intrusion and degassing of ~0.05-0.07 km3 of basaltic magma. Based on ground deformation source modeling, we find that intrusion at an average rate of ~0.002-0.003 km3 yr-1 into a postulated zone of partial melt at ~15 km depth could occur without detection by local Global Navigation Satellite System stations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V24C..06L
- Keywords:
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- 1030 Geochemical cycles;
- GEOCHEMISTRY;
- 1031 Subduction zone processes;
- GEOCHEMISTRY;
- 8414 Eruption mechanisms and flow emplacement;
- VOLCANOLOGY;
- 8485 Remote sensing of volcanoes;
- VOLCANOLOGY