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Twenty new heat flow measurements in southern Mexico are presented. These measurements document a very broad zone of low heat flow between the coastline and the Trans‐Mexico volcanic belt. At the Trans‐Mexico volcanic belt, heat flow increases to high values and remains high into central Mexico. Heat flow values in the Trans‐Mexico volcanic belt and northward are in excess of 80 mW m−2 (1.9 μcal/cm2 s) and typical of values observed in the high heat flow regions of the western United States. The average heat flow in the Sierra Madre del Sur is 26 mW m−2 (0.6 μcal/cm2 s), in the Sierra Madre Oriental is 89 mW m−2 (2.1 μcal/cm2 s), and in the Trans‐Mexico volcanic belt is 91 mW m−2 (2.2 μcal/cm2 s). A surface heat flow profile was constructed perpendicular to the trench, and the data were matched with a simple thermal subduction model. The resulting final model parameter set suggests that the angle of subduction is low and that convective heat transfer in the back arc region is probable. For data south of the Trans‐Mexico volcanic belt, reduced heat flow values (upper crustal radioactive effect removed) are less than 15 mW m−2 (0.4 μcal/cm2 s). Thus essentially the total mantle heat flow is being absorbed by the subducting block. The values are lower than the heat flow observed in the Sierra Nevada Mountains of California and support the hypothesis that the heat flow couple associated with the Sierra Nevada Basin and Range province is a relic subduction zone thermal pattern.

Geothermal data from 248 wells and drill holes, a thermal model for the effects of the Snake Plain aquifer on observed heat flow, an estimate of the regional heat flow in the eastern Snake River Plain, a detailed moving source, regional thermal model, and a discussion of the origin and the relationship of the eastern and western halves of the Snake River Plain are included in this paper. In order to determine the thermal structure of the eastern Snake River Plain, an extensive geothermal gradient and heat flow survey was carried out. Data from 248 holes show high heat flow values along the margins but low values along the center because of effects of the extensive Snake Plain aquifer. Based on a thermal model of the aquifer, a heat budget was derived from which a mean heat flow for the eastern Snake River Plain of 190 mW m -2 was calculated. This value can be compared to observed values along the margins of 120 mW m -2 and two values in deep holes along the northeastern margin of 110 and 109 mW m -•. The areas of highest expected values, in the Island Park caldera region, have not been sampled by heat flow measurements, however. Based on the heat flow results from the eastern and the western Snake River Plain and other geophysical and geological data, a finite-width movingsource-plane thermal model is developed for the Snake River Plain. Even though the geological and geophysical characteristics of the eastern and western Snake RiVer Plain are somewhat different, they are attributed to the same moving heat source, and the spatial geological and geophysical differences are explained by different stages in a time-related sequence of thermally driven geological and tectonic events. The Snake River Plain is due to a strong thermal source interacting with the crust with the resulting complete chemical reorganization of the crust. The major immediate driving mechanism is a thick mafic intrusive emplaced in the midlevels of the crust. Associated with this thermal event are regional uplift of a kilometer or sO as the heating occurs, associated melting of the upper crust, and subsequent rapid subsidence of approximately 1/2 to 1 km because of the change in density of the crust and upper mantle section associated with the emplacement of the basic intrusive and the disruption of the granitic upper crust. After the heat source moves eastward, continued subsidence occurs due to cooling of the lithospheric section (similar to that seen for oceanic regions). Along with the subsidence and soon after completion of the extensive silicic volcanism, basalts began to be extruded. Thermal contraction also generates faulting on the sides and perhaps in the center of the hot spot track. The subsidence causes reversal of the dips of the silicic ash flows from their initial away-from-the-source configuration, to the toward-the-source configuration observed in the Snake River Plain. Continued subsidence and cooling cause the formation of the basin which is then filled by sediments, causing additional subsidence due to isostatic adjustment ...

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Roughly 90% of the geothermal power resource in the United States is thought to reside in Enhanced Geothermal Systems (EGS). While realization of EGS development on the 100+ GWe scale would make geothermal a significant component of the renewable energy portfolio, hurdles to commercial development still remain in accessing and characterizing, creating, monitoring, operating, and sustaining engineered reservoirs. In August 2011 the Geothermal Technologies Office (GTO), U.S. Department of Energy (DOE), convened a workshop in San Francisco, CA, to outline opportunities for advancing EGS technologies on five-to 20-year timescales. Community input charted technology needs categorized within the functional stages of Characterizing, Creating, and Operating EGS reservoirs. In this paper we present technical paths identifying, creating, and managing fractures and flow paths; monitoring flow paths and fracture evolution; zonal isolation; drilling; models; and tools that encompass the underlying technology needs identified at the workshop as critical to optimizing and ultimately commercializing EGS. We develop the chronological evolution of these paths, tying the past and current status of each to the active GTO EGS research and development (R&D) portfolio, anticipating milestones that strategic initiatives could help to realize on a five-year timescale, and projecting to target capabilities for 2030. The resulting structure forms the basis for an EGS Technology Roadmap to help guide priorities for future GTO EGS R&D investments. State of EGS Since the early 1970s, several large-scale EGS field projects reached varying degrees of success, though the majority of EGS developers and researchers would conclude that EGS has yet to be validated as an optimized technology on a commercial scale. Fenton Hill, Rosemanowes, Le Mayet, Hijiori, Soultz, and Cooper Basin (Wyborn, 2011) targeted granitic reservoir host rocks at depths in excess of 2 km to achieve temperatures sufficient for electric power production. With the exception of the Landau project in Germany, past projects have not successfully sustained commercial production rates (50-100 kg/sec). Note that the characteristics of Landau suggest that it is a stimulated hydrothermal reservoir and not a "green-field" EGS development (e.g., Baria and Petty, 2008). Each of these historic EGS projects, however, has played an integral role in informing the future direction of EGS research and development, having added significantly to our understanding of micro to macro-scale issues associated with EGS.