Heat flow in VC-2A and VC-2B, and constraints on the thermal regime of the Valles Caldera, New Mexico

Shear Velocity Evidence of Upper Crustal Magma Storage Beneath Valles Caldera

“…The location of the most delayed arrivals is consistent with previous P-wave studies that used seismographs with larger inter-station spacing but distributed over the area of the caldera rather than in one transect (Roberts et al, 1991;Steck et al, 1998). The along-transect distance of the most delayed arrivals, ∼0.5-0.65 s, coincides with the area of highest geothermal gradients (Morgan et al, 1996). More moderate lag times of ∼0.3 s extend south from Redondo Peak to ∼10 km beyond the southern edge of the caldera (Figure 2c).…”

“…Comparison of teleseismic P-wave tomography and Rayleigh tomography is complicated by differing resolution, but the existing results do not suggest a low Vp/Vs anomaly since the Vs reduction (−32%) is greater than the Vp reduction (−23%) reported by Steck et al (1998). A dominant role for exsolved volatiles in creating the low-velocity anomaly further seems unlikely because the high geothermal gradients in Valles Caldera are consistent with continued presence of melt (Morgan et al, 1996;Nielson & Hulen, 1984).…”

“…(1998). A dominant role for exsolved volatiles in creating the low‐velocity anomaly further seems unlikely because the high geothermal gradients in Valles Caldera are consistent with continued presence of melt (Morgan et al., 1996; Nielson & Hulen, 1984).…”

“…A lack of contemporary seismicity beneath Valles Caldera may indicate a stable cooling reservoir or primarily ductile deformation due to high crustal temperatures (House & Roberts, 2020; Nakai et al., 2017; Sanford et al., 1979). Boreholes drilled for geothermal exploration and basic science document high geothermal gradients of up to ∼350–450°C/km just west of the caldera's center (Figure 1; Morgan et al., 1996). Most boreholes within the caldera encountered high‐temperature alteration but a dearth of magmatic fluids suggesting a shrinking hydrothermal system (Goff & Gardner, 1994; Nielson & Hulen, 1984).…”

“…Blue triangles are nodal seismographs.A black dotted line shows the surficial trace of the ring fracture from the 1.23 Ma eruption. The green dotted line encloses the area with ≥350°C/km geothermal gradient(Morgan et al, 1996) and squares are borehole locations. Borehole B-12 is the deepest at ∼3.2 km(Nielson & Hulen, 1984).…”