Geothermal Exploration of Newberry Volcano, Oregon

Waibel, Albert F.; Frone, Zachary; Blackwell, David

doi:10.2172/1182676

Cited by 5 publications

(14 citation statements)

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“…Our model shows that this resistive zone wraps around the volcano through the northwest to the west and south (Figures d–f and ). We uphold the interpretation of previous workers (Waibel et al, ) that the resistive body represents a pluton that is the heat source for geothermal targets on the west flank. Such impermeable, crystalline rock would have too little interconnected porosity for the fluids to contribute significantly to the rock conductivity while also resisting the formation of clay minerals.…”

Section: Interpretation and Discussionsupporting

confidence: 90%

“…Gravity data acquired in 2006 to 2010 on a dense array covering Newberry (Waibel et al, ) combined with regional gravity data (Roberts et al, ) were used to infer subsurface density from Bouguer anomaly mapping (Waibel et al, ). This was followed by additional data collection in 2012 by Zonge International Inc. With the full data set of 1,418 stations, 3‐D forward and inverse modeling was done to create a density model of the volcano (Bonneville et al, ).…”

Section: Previous Geophysical Studiesmentioning

confidence: 99%

“…Nonetheless, this well log demonstrates that extremely high temperatures are reached at modest depths at Newberry. Outside of the caldera, deep (>2 km) geothermal exploration wells drilled 1.5 km from the caldera rim reached conductive thermal gradients of 124 and 141°C/km, while gradients of 98 and 109°C/km were observed in wells 3 km from the rim (Bargar & Keith, 1999;Blackwell, 1994;Bonneville et al, 2016;Frone, 2015;Spielman & Finger, 1998;Waibel et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Composition of Magma and Characteristics of the Hydrothermal System of Newberry Volcano, Oregon, From Magnetotellurics

Bowles-martinez

Schultz

2020

Geochem Geophys Geosyst

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We use 3‐D magnetotellurics to improve our understanding of the structure and magma composition of Newberry Volcano in Oregon, USA. Newberry is a broad shield volcano with a summit caldera and strongly bimodal magmatism. Newberry has long been the subject of geothermal exploration research, but that work has focused on the volcano's west flank, leaving the caldera largely unstudied with geophysical methods until recently. Our modeling shows a relatively resistive magma reservoir of approximately 50 Ωm. Our work builds upon recent seismic models and petrological analysis to interpret Newberry's magma reservoir as a dry rhyolite with 8–11% partial melt, which matches the seismically determined melt fraction. Finding the conditions within the magma reservoir that allow the resistivity and seismic analysis to come to the same melt fraction helps us narrow down the magma temperature and composition. From this we infer a dry rhyolitic magma at 850 °C. We also image a prominent vertical conductive anomaly along the south rim below the vent that produced the most recent eruption. The anomaly extends from magma reservoir depths of 3 km to 1 km below the surface where it disperses into the caldera fill. We interpret this as the main conduit for magmatic fluids to reach Newberry's hydrothermal system. Other features that our model shows include higher conductivity along the caldera rim and a resistive older pluton on the west flank.

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Section: Interpretation and Discussionsupporting

confidence: 90%

Section: Previous Geophysical Studiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Composition of Magma and Characteristics of the Hydrothermal System of Newberry Volcano, Oregon, From Magnetotellurics

Bowles-martinez

Schultz

2020

Geochem Geophys Geosyst

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“…In contrast, higher velocities on the east flank, >6.1 km/s at 3–4 km depth, are consistent with predominately mafic material, mirroring gravity results [ Gettings and Griscom , ]. The intrusives may reflect earlier distinct magma bodies [ Waibel et al ., ] that were intruded at slightly different locations or alternatively may be the solidified remnants of what was once a single larger magmatic system. Thermal modeling shows that the measured high temperatures at depth on the west flank of the volcano are not the result of the imaged magma body [ Frone et al , ; Sammel et al , ] and that these anomalous temperatures may be the result of conductive cooling of larger intrusive bodies on the flanks that were potentially emplaced 100s of kyr ago [ Frone et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Imaging the magmatic system of Newberry Volcano using joint active source and teleseismic tomography

Heath

Hooft

Toomey

et al. 2015

Geochem Geophys Geosyst

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In this paper, we combine active and passive source P wave seismic data to tomographically image the magmatic system beneath Newberry Volcano, located east of the Cascade arc. By using both travel times from local active sources and delay times from teleseismic earthquakes recorded on closely spaced seismometers (300–800 m), we significantly improve recovery of upper crustal velocity structure (<10 km depth). The tomographic model reveals a low‐velocity feature between 3 and 5 km depth that lies beneath the caldera, consistent with a magma body. In contrast to earlier tomographic studies, where elevated temperatures were sufficient to explain the recovered low velocities, the larger amplitude low‐velocity anomalies in our joint tomography model require low degrees of partial melt (∼10%), and a minimum melt volume of ∼2.5 km3. Furthermore, synthetic tests suggest that even greater magnitude low‐velocity anomalies, and by inference larger volumes of magma (up to 8 km3), are needed to explain the observed waveform variability. The lateral extent and shape of the inferred magma body indicates that the extensional tectonic regime at Newberry influences the emplacement of magmatic intrusions. Our study shows that jointly inverting active source and passive source seismic data improves tomographic imaging of the shallow crustal seismic structure of volcanic systems and that active source experiments would benefit from longer deployment times to also record teleseismic sources.

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“…Background colors are fractional change in velocity from the Heath et al () tomography, taken along A to A′ in Figure a. Red, magenta, and green lines show the top and bottom of an electrical conductor (Fitterman et al, ; Waibel et al, ) and the top of a resistive layer (Fitterman et al, ) respectively. The autocorrelation traces for 6 Hz ambient noise (Figure a) are hung from the topography and converted to depth using a 1‐D velocity model, assuming a vertically propagating wave.…”

Section: Discussionmentioning

confidence: 99%

Autocorrelation of the Seismic Wavefield at Newberry Volcano: Reflections From the Magmatic and Geothermal Systems

Heath

Hooft

Toomey

2018

Geophysical Research Letters

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We show that seismic autocorrelations provide new depth constraints on upper crustal magmatic systems. Autocorrelations of both ambient noise recorded on seismometers and geophones and teleseismic earthquake coda recorded on seismometers elucidate the structure of Newberry Volcano. These autocorrelations result in the two‐way, body wave Green's function beneath a station. Within the caldera, a reproducible, coherent P wave reflection is inferred to come from the top of a magma body at ~2.5 km depth and maps with the lateral extent of an anomalously low‐velocity body imaged tomographically. On the west flank of the volcano, a reflection that deepens with distance from the caldera is inferred to result from a temperature‐dependent change in metamorphic facies and may map the thermal structure of the edifice. Our results show that the autocorrelation of diffuse seismic energy reconstructs reflections from seismically sharp boundaries associated with the upper crustal magmatic structure.

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Geothermal Exploration of Newberry Volcano, Oregon

Cited by 5 publications

References 0 publications

Composition of Magma and Characteristics of the Hydrothermal System of Newberry Volcano, Oregon, From Magnetotellurics

Composition of Magma and Characteristics of the Hydrothermal System of Newberry Volcano, Oregon, From Magnetotellurics

Imaging the magmatic system of Newberry Volcano using joint active source and teleseismic tomography

Autocorrelation of the Seismic Wavefield at Newberry Volcano: Reflections From the Magmatic and Geothermal Systems

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