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The Santa Lucía River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2. In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profile that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C. [ABSTRACT FROM AUTHOR]

The objective of this study is the analysis of the south of Chicontepec Paleocanyon (PC) and the relation of electromagnetic anomalies. For this purpose, we measured, processed, and interpreted 16 broadband magnetotelluric (MT) soundings, disposed of in an orthogonal profile that covers the inside and the boundaries of the Paleocanyon. We performed a 3-D inversion of the data set (ModEM) using the range of periods between 10−3–102 s. In addition, we compared the result of 3-D inversion and the interpolation of 1-D inversion in their invariant rotational along the profile, where it is watched that they are similar in the resistivity anomalies and geological structures. The interpretation of the 3D resistivity inversion model shows the heterogeneous geometry and boundaries of the Paleocanyon and the contact between sediments and the top of the basement. Furthermore, based on the resistivity contrast, the information from wells-drilled, and seismic sections, it is possible to delimitate some anomalies that perhaps have the probability of hydrocarbon existence. • Comparison of sections 3D MT inversion and seismic in the Chicontepec Paleocanyon. • Resistive contrasts were correlated to the geological structures and the basement. • 3D Magnetotellurics is a powerful technique for oil and gas exploration • MT surveying can help seismic information to detect oil/gas reservoirs [ABSTRACT FROM AUTHOR]

Water supply in semiarid areas in Mexico depends on water extraction from compartmentalized aquifers where large drawdown rates can be observed due to increasing demand from urban, industrial and agricultural users. Understanding the behavior of these aquifers is a necessity in order to improve the estimation of water balances. Accordingly, this study assembles both geochemical and isotopic data to identify the source of recharge to the San Juan del Río graben aquifer and to determine its dynamics. The geological model developed with the aforementioned data reveals a complex system composed of a heterogeneous multilayered compartmentalized aquifer. The San Juan del Rio basin is composed of (1) the Amealco perched aquifer, (2) a shallow granular aquifer, and (3) a fractured aquifer. Hydrogeochemical and isotopic data (δ2H, δ18O, δ13C and correct carbon activity (Δ14C)) allow for identification of three end-member sources: (1) local meteoric recharge, (2) old groundwater contained in the siliciclastic shallow aquifer, and (3) regional/local hydrothermal recharge. The contribution of both meteoric and regional hydrogeothermal flow to the different aquifer compartments is determined through a principal component analysis of the hydrogeochemical data. With the aforementioned analysis it was found that the dominant contribution source for all aquifer compartments is meteoric water (up to 60% with a median of 50%), while the regional hydrothermal groundwater contribution represents 15%, even for the shallow aquifer. [ABSTRACT FROM AUTHOR]

The western slope of Cerro Domuyo in northern Patagonia is characterized by thermal springs with boiling waters, Quaternary silicic domes, and pyroclastic deposits that suggest the existence of a geothermal reservoir. According to geochemical studies, the reservoir may have a temperature of 220 °C and one of the largest advective heat fluxes reported for a continental volcanic center. In this paper, we propose a more refined conceptual model for the Domuyo geothermal area, based on a geological survey supported by U Pb, U Th, and Ar Ar geochronology and by magnetotelluric and gravity surveys. Our study indicates that the Domuyo Volcanic Complex (DVC) is a Middle Pleistocene dome complex overlying middle Miocene to Pliocene volcanic sequences, which in turn cover: 1) the Jurassic-Early Cretaceous Neuquén marine sedimentary succession, 2) silicic ignimbrites dated at ~186.7 Ma, and 3) the Paleozoic metamorphic basement intruded by ~288 Ma granite bodies. The volcanic cycle in the DVC is distinctly bimodal, characterized by the emplacement of massive silicic domes and less voluminous olivine basalts on its southern slope. A major collapse of the central dome at ~600 ka produced a voluminous (19.4 km3 and 133 km2) block-and-ash flow, and associated pyroclastic flows, that filled a valley to the southwest at distances up to ~30 km from Cerro Domuyo summit. This was followed by a period of intense effusive activity that formed the Cerro Guitarra, Cerro Las Pampas, Cerro Domo, and Cerro Covunco silicic domes. The last two domes are the youngest and largest edifices, dated at 0.50 Ma (Ar Ar age) and 0.25 Ma (U Th age). Pre-Cenozoic successions were affected by N-S reverse and thrust faults that were later displaced by an ENE-WSW-trending transtensional belt. The basement rocks at the northern termination of the Cordillera del Viento anticlinorium were also displaced towards the east-northeast by this belt, which is observed NNW of Cerro Domuyo. The DVC was emplaced within this zone of crustal weakness. The integration of geologic observations with magnetotelluric and gravity data, allowed us to develop an updated conceptual model of the geothermal system. The geothermal reservoir is inferred at a depth of less than 2 km within pre-Pliocene fractured rocks, bounded by ~WSW-ENE trending faults and sealed by the pyroclastic deposits and rhyolitic lavas of the DVC. The location of most thermal springs is not directly controlled by faults. Instead, flows emerge at the contact between the fractured and faulted basement and the caprock. • The Domuyo Volcanic Complex (DVC) is a silicic dome complex formed in the Pleistocene. • The central dome collapsed at ~600 ka producing a voluminous (19.4 km3) pyroclastic deposit. • The youngest domes were emplaced at ~500 ka and 250 ka. • The DVC was emplaced within a ENE-WSW trending transtensional zone of crustal weakness. • The geothermal reservoir is hosted in pre-Pliocene rocks sealed by the DVC pyroclastics and lavas. [ABSTRACT FROM AUTHOR]

• The Juchipila graben is an unconventional geothermal system located in central Mexico. • Thermal water has anomalous concentrations of F, B, Li, and As. • δ2H and δ18O indicate a common meteoric source but different evaporation processes. • Mantle helium is transported into the system through deep-rooted faults. This work presents hydrochemical results for groundwater and dissolved gas samples collected from a thermal and cold aquifer in the Juchipila Basin, in southern Sierra Madre Occidental, central Mexico. Thermal springs in the Juchipila Basin reach temperatures of 60 °C, these manifestations are not related to recent or active volcanism as are all the known geothermal fields in Mexico. The thermal waters (>32 °C) are Na-HCO 3 and Na-SO 4 type, with an anomalous concentration of F, B, Li, and As. Their chemistry likely results from water-rock interaction processes. The cold waters (<32 °C) have a Ca-HCO 3 composition typical of recent infiltration and shallow flow, but they have an anomalous concentration of NO 3. The δ2H and δ18O indicate a common meteoric source for the warm and cold water plotting along an evaporation line. The waters have higher CO 2 and He concentrations than the air-saturated water. The helium composition is mainly atmospheric and terrigenous with a mantle helium contribution of up to 14%. This suggests that faults affecting the region are deeply rooted, permitting mantle helium uprise. Geothermometry gives mean reservoir temperatures of 58–102 °C. Based on these results, we propose a model of hydrothermal circulation in the Juchipila Basin, in which rainwater infiltrates deeply through the graben edges fault system, dissolves ions and crustal helium, incorporates mantle helium, while heated by the geothermal gradient, and eventually surges and mixes with the cold, shallow aquifer along faults cutting the whole succession within the graben. [ABSTRACT FROM AUTHOR]