Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

Bergfeld, D.; Evans, William C.; Howle, James F.; Hunt, Andrew G.

doi:10.1016/j.jvolgeores.2015.01.008

Cited by 14 publications

(12 citation statements)

References 57 publications

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“…This is in agreement with recent work by Bergfeld et al . [] which examined degassing from Mono Lake and the Mono‐Inyo chain of domes. They propose that magmatic δ 13 C (~−4.5‰) and 3 He/ 3 He (5–6 R A ) ratios in soil gases from the North Coulee reflect the presence of a degassing basaltic intrusion, perhaps associated with Holocene volcanism [ Bray , ].…”

Section: Resultsmentioning

confidence: 83%

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

2015

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We present a degassing study of Long Valley Caldera that explores the structural controls upon emissions of magmatic carbon dioxide gas. A total of 223 soil gas samples were collected and analyzed for stable carbon isotopes using a field-portable cavity ring-down spectrometer. This novel technique is flexible, accurate, and provides sampling feedback on a daily basis. Sampling sites included major and minor volcanic centers, regional throughgoing faults, caldera-related structures, zones of elevated seismicity, and zones of past and present hydrothermal activity. The classification of soil gases based on their δ 13 C and CO 2 values reveals a mixing relationship among three end-members: atmospheric, biogenic, and magmatic. Signatures dominated by biogenic contributions (~4 vol %, À24‰) are found on the caldera floor, the interior of the resurgent dome, and areas associated with the Hilton Creek and Hartley Springs fault systems. With the introduction of the magmatic component (~100 vol %, À4.5‰), samples acquire mixing and hydrothermal signatures and are spatially associated with the central caldera and Mammoth Mountain. In particular, they are concentrated along the southern margin of the resurgent dome where the interplay between resurgence-related reverse faulting and a bend in the regional fault system has created a highly permeable fracture network, suitable for the formation of shallow hydrothermal systems. This contrasts with the south moat, where despite elevated seismicity, a thick sedimentary cover has formed an impermeable cap, inhibiting the ascent of fluids and gases to the surface.

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Section: Resultsmentioning

confidence: 83%

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

2015

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“…The low resistivity of this feature suggests an active path of hydrothermal fluid flow. Ongoing emission of magmatic fluids (CO 2 and He) near North Coulée and along the southern edge of Mono Lake support this interpretation [ Bergfeld et al , ]. Assuming the saturated rock resistivity is on the order of 2–5 Ω m, a fluid resistivity of 0.5 Ω m [ Nesbitt , ], and a cementation factor of 2, the porosity of this hydrothermal zone is estimated from Archie's equation to be on the order of ∼30%.…”

Section: Discussionmentioning

confidence: 99%

“…Tizzani et al [] used InSAR to detect ground motion between 1992 and 2000, suggesting that the area southeast and east of the Mono Craters is uplifting at 0.3–0.5 cm/yr (in the line of site direction). Recently, Bergfeld et al [] reported elevated CO 2 emissions of ∼29 t/d from Mono Craters and 3 He/ 4 He of 5.1–6.0 R A consistent with a magmatic source under Mono Craters. These studies confirm the existence of a magmatic source beneath the Mono Craters, but to date the geometry and location are not well constrained.…”

Section: Previous Geophysical Work In Mono Basinmentioning

confidence: 99%

Imaging the magmatic system of Mono Basin, California, with magnetotellurics in three dimensions

et al. 2015

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A three‐dimensional (3‐D) electrical resistivity model of Mono Basin in eastern California, unveils a complex subsurface filled with zones of partial melt, fluid‐filled fracture networks, cold plutons, and regional faults. In 2013, 62 broadband magnetotelluric stations were collected in an array around southeastern Mono Basin from which a 3‐D electrical resistivity model was created with a resolvable depth of 35 km. Multiple robust electrical resistivity features were found that correlate with existing geophysical observations. The most robust features are two 300 ± 50 km3 near‐vertical conductive bodies (3–10 Ω m) that underlie the southeast and northeastern margin of Mono Craters below 10 km depth. These features are interpreted as magmatic crystal‐melt mush zones of 15 ± 5% interstitial melt surrounded by hydrothermal fluids and are likely sources for Holocene eruptions. Two conductive east dipping structures appear to connect each magma source region to the surface. A conductive arc‐like structure (< 0.9 Ω m) links the northernmost mush column at 10 km depth to just below vents near Panum Crater, where the high conductivity suggests the presence of hydrothermal fluids. The connection from the southernmost mush column at 10 km depth to below South Coulée is less obvious with higher resistivity (200 Ω m) suggestive of a cooled connection. A third, less constrained conductive feature (4–10 Ω m) 15 km deep, extending to 35 km is located west of Mono Craters near the eastern front of the Sierra Nevada escarpment and is coincident with a zone of sporadic, long‐period earthquakes that are characteristic of a fluid‐filled (magmatic or metamorphic) fracture network. A resistive feature (103–105 Ω m) located under Aeolian Buttes contains a deep root down to 25 km. The eastern edge of this resistor appears to structurally control the arcuate shape of Mono Craters. These observations have been combined to form a new conceptual model of the magmatic system beneath Mono Craters to a depth of 30 km.

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“…The δ 13 C values corresponding to the helium concentrations calculated above for the preexisting reservoir (9.1 ppmv) and fresh magmatic (34.0 ppmv) gas end‐members are −5.28‰ and −3.41‰, respectively. Interestingly, these values nearly coincide with the range of δ 13 C values (−5.03‰ to −3.46‰) reported for magmatic CO 2 at five other degassing sites in the region around Mammoth Mountain (Bergfeld et al, ). The earliest samples (through January 1990) plot well above the left end of the mixing line, as expected if CO 2 scrubbing only minimally fractionates the carbon isotopes.…”

Section: Discussionmentioning

confidence: 99%

Rate of Magma Supply Beneath Mammoth Mountain, California, Based on Helium Isotopes and CO₂ Emissions

Lewicki

Evans

Montgomery-Brown

et al. 2019

Geophysical Research Letters

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Mammoth Mountain, 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 beneath Mammoth Mountain pose a challenge for estimating magma supply rate. Here, we use the record of fumarolic 3He/4He ratios and CO2 emissions to estimate that of the ~5.2 Mt of CO2 released from Mammoth Mountain between 1989 and 2016, 1.6 Mt was associated with active intrusion and degassing of ~0.05–0.07 km3 of basaltic magma. Intrusion at an average rate of ~0.002–0.003 km3/year into a postulated zone of partial melt at ~15‐km depth could occur without detection by local Global Navigation Satellite System stations.

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Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

Cited by 14 publications

References 57 publications

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

Imaging the magmatic system of Mono Basin, California, with magnetotellurics in three dimensions

Rate of Magma Supply Beneath Mammoth Mountain, California, Based on Helium Isotopes and CO₂ Emissions

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Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

Cited by 14 publications

References 57 publications

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

Structural controls on the emission of magmatic carbon dioxide gas, Long Valley Caldera, USA

Imaging the magmatic system of Mono Basin, California, with magnetotellurics in three dimensions

Rate of Magma Supply Beneath Mammoth Mountain, California, Based on Helium Isotopes and CO2 Emissions

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About

Rate of Magma Supply Beneath Mammoth Mountain, California, Based on Helium Isotopes and CO₂ Emissions