G. Jiracek1, P. Zablowski2, B. Castro3, F. Le Pape4, B. Biagini1, M. Kennedy5, D. Feucht6, L. Pellerin7, P. Bedrosian8, D. Hasterok9, S. Biehler10, D. McPhee8, and J. Ferguson11 1San Diego State Univ., 2Boston Univ., 3Univ. Rochester, 4Dublin Inst. Adv. Stu., 5So. Methodist Univ., 6Univ. , 7Green Engineering, 8US Geol. Surv., 9Univ. Calf. San Diego,, 10Univ. Calif. Riverside, 11Univ. Dallas

1. SAGE Program Sample SAGE Magnetotelluric (MT) Results in Central RGR • Recently published borehole temperature gradients http://www.sage.lanl.gov/ 3. exceed central RGR background of ~30oC/km . • Depth to midcrustal conductor (MC) is a proxy for the A four-week-long, field-based program in the central a • depth of ~500oC isotherm: 27 to 7 km from west to b rift (RGR), near Santa Fe, New featuring “hands-on” land-based geophysics for 25- east under the Valles (Fig. 3) and 17 km deep 30 students per year. north of Santa Fe (Fig 4). 58oC/km

W E MC 17 km Fig. 1. B 1.6 km “Hands-on” 24oC/km geophysics o MC 7 km 40 C/km at SAGE. o MC 27 km Fig. 9. a) Map of shallow temperature gradients ( C/km) and Fig. 4. 1-D MT TE inversion. b) Selected temperature/depth profiles of 24 to 58oC/km.2 a 2. Central RGR Geothermal Indications Fig. 3. 2-D MT TM inversion. • High heat flow (80 to >300 mW/m2). • Defining basin freshwater, brine, and clay zones and CR G Young volcanism (e.g., Valles caldera (0.13-1.75 low-permeability, resistive basement depth (B) are • b Ma) and Cerros del Rio (1.14-2.8 Ma) critical for conventional geothermal and EGS (Fig. 6). with >50 exposed vents). • High 3He/4He fluids along with numerous, rift-related SL Fig. 10. . faults and volcanic vents indicate high-temperature B Fig. 11. Proposed hydrothermal settings: a) Basement magmatic/mantle fluid component. horst constriction model and b) Up-flow through deep B • Thick (>2 km) Española Basin sediments with low- faults or volcanic pipes and along shallow fault barriers.2 porosity, impermeable basement rocks below. B Fig. 5. Simplified geologic map of central .2 b a B (km) MC (km) -220 TE 2.3 14 • Shallow (<15 km deep) midcrustal conductor 2.1 12 -240 2.1 12 detected by SAGE magnetotelluric (MT) soundings. 2.3 10 Fig. 6. 2-D interpretation of ~13.5 km-long MT-derived geoelectric section across Santo Domingo Basin. -260 Midcrustal low resistivity (high conductivity) zones MT Density (Mg/m3) E (m ) indicate: 1) electrical conductors such as graphite or W 4.Caja del Rio Geothermal Prospect (CR in Fig. 5 red area) Elev sulfide minerals, 2) H O brines, and/or 3) magma. 2 • The combination of a thick hydrologically permeable, Santa Fe Group aquifer and a relatively shallow basement, both at ~2 km with temperatures projected to be >150oC, makes this region the most attractive geothermal prospect in the central RGR outside of the Valles caldera. Fig. 12. SAGE 2011 a) Gravity (Fig. 5,G) and b) MT modeling do not support Fig. 11a constriction model alone because: a) S-N SL Gravity high is too far west and b) MT-derived basin depths (B = 2.1 to 2.3 km) are nearly uniform across region of proposed basement horst. Santa Fe Group 5. Conclusions • Depth to midcrustal conductor is potentially a very valuable regional geothermal assessment tool in western U.S. Fig. 2. Schematic interpretation of prominent • Caja del Rio thermal source is mostly from deep up-flow. midcrustal conductor (MC) beneath Eastern Great Area has viable geothermal direct use and EGS potential. Basin-Transition Zone-Colorado Plateau (EGB-TZ- Fig. 7. Cenozoic stratigraphy in central RGR. Santa Fig. 8. S-N industry seismic line (Fig. 5, SL) time- CP). MC is physically interpreted to be high section. N-end ~2 s TWTT yields ~2 km-thick Santa 6. References Fe Group above Espinaso Formation is key aquifer. 1Wannamaker et al., 2008, in Geochemistry Geophysics temperature H20 brine above basaltic and silicic melts Fe Group aquifer above top of Espinaso Formation. • with MC top at 500oC.1 Geosystems, AGU Electronic Journal, 38 p. • 2Johnson et al., 2011, in GSA Special Paper 2021, in press.