Las Tres Research Articles

Thermal conductivity of igneous rock cores estimated from shallow wells drilled within the Las Tres Vírgenes volcanic complex, BCS, Mexico

Thermal conductivity of igneous rock cores estimated from shallow wells drilled within the Las Tres Vírgenes volcanic complex, BCS, Mexico

Comprehensive investigation on the geothermal energy sector in México

Factors such as fossilisation, diversification of energy resources, sustainable development, and energy security are attracting global attention for the development and expansion of renewable energy sources. Environmental issues arising from fossil fuel consumption are being addressed, but concerns remain about the renewability and availability of new energy sources. Mexico is one of the ten countries in the exploitation of geothermal energy, with a history of approximately five decades. This study examines Mexico's five major geothermal fields: Cerro Prieto, Los Azufres, Los Humeros, Las Tres Vírgenes, and Domo San Pedro. Currently, Mexico is working with international geothermal companies. However, there are more power plants and substantial cooperation to obtain this energy for industry and homes. This study is focused on the potential of geothermal exploitation in Mexico and its position worldwide after the introduction of geothermal energy in Mexico. Next, five geothermal fields are introduced in Mexico, and the potential and capacities of each are discussed. Finally, the future energy scenarios in Mexico are reviewed, with an emphasis on geothermal energy.

The bromine and chlorine isotopic composition of the mantle as revealed by deep geothermal fluids

Chlorine (Cl) and bromine (Br) are rare elements when considering the whole Earth. However, being highly volatile elements, their delivery and retention processes during planetary accretion and chemical differentiation provide important clues about the formation of the Earth. Variations in Cl and Br isotopic systems (37Cl/35Cl or δ37Cl and 81Br/79Br or δ81Br) among terrestrial reservoirs could trace these processes. While the Br isotopic value of the mantle remains entirely unknown, the measurement of mantle Cl isotopic values is a controversial subject, with measured δ37Cl values ranging from −3 to 0‰ in mid-ocean-ridge basalts (MORBs) and from −2 to +3‰ in oceanic island basalts (OIBs). Here, we report newly-determined δ81Br and δ37Cl values, together with noble gas 3He/4He (R) ratios, measured in geothermal fluids from production wells of three Mexican fields: Cerro Prieto, Las Tres Vírgenes, and Los Azufres. Relationships between 3He/4He ratios and both δ37Cl and δ81Br suggest that geothermal fluid volatiles have three distinct sources: (1) a local crustal source, enriched in radiogenic 4He (R = 1.7–1.9Ra, where Ra is the atmospheric 3He/4He ratio), and halogens from brines with δ37Cl and δ81Br of +0.1 and +0.3‰ respectively; (2) the mantle wedge, with 3He/4He ratios of 6–6.5Ra, typical of arc volcanism, and δ37Cl and δ81Br of −0.4 and −1.0‰ respectively, typical (for Cl) of fluids derived from the dehydration of serpentinite in the subducting slab; and (3) a mantle source, with 3He/4He ratios of 7.7–8.2Ra, typical of MORBs, and δ37Cl and δ81Br of +0.9 and +0.7‰ respectively. These results suggest that the primitive mantle Cl isotopic composition was positive – possibly ≥+3‰, as measured in some OIBs – and inherited during the Moon forming impact. The progressive subduction of isotopically lighter halogens over the last 2–3 Ga could have progressively lowered this initial value to those currently measured in the depleted mantle beneath Mexico. It is speculated that the different isotopic values measured in mantle rocks and fluids could reflect the heterogeneous regassing of subducted halogens and the inefficient homogenization of recycled material in the MORB source, as suggested in other studies by the heterogeneous isotopic compositions of the heavier Ar and Xe of the convective mantle.

Imaging of the magmatic system feeding Las Tres Virgenes Geothermal field (Baja California Sur, Mexico) using Enhanced Seismic Tomography

The Las Tres Vírgenes volcanic field (Baja California Sur, Mexico) hosts one of the five active geothermal power plants operating in Mexico. The volcanic system is considered still active and has been extensively studied during and after the development of the geothermal activities. However the volumes and locations of the magmatic sources, as well as the size of the geothermal reservoir are still poorly known. In this work we use the records of 177 local earthquakes recorded in 2012 by a temporary local seismic network to characterize compressional (Vp) and shear (Vs) wave seismic velocities of the volcanic system from the surface down to 8–10 km of depth. We applied the Enhanced Seismic Tomography method, which incorporates the Double Difference tomography and the post processing Weighted Average Method. Results describe for the first time that the magmatic source reaches at least 4–5 km of depth beneath La Virgen Volcano, feeding a widespread reservoir confined in the first 2–3 km of depth, which is much larger than the currently exploited region.

Marine controlled-source electromagnetics with geothermal purposes; central Gulf of California, Mexico

We acquired and interpreted data from two controlled-source electromagnetic profiles, in the Gulf of California off the coast of Santa Rosalía, Baja California Sur, Mexico. This area is interesting from the geothermal point of view due to its proximity to the Guaymas Basin, the La Reforma Caldera, and the Las Tres Vírgenes volcano, the first with intense submarine hydrothermal manifestations and the final one with a geothermal field in production. The survey consisted of the deployment of 10 Ocean Bottom Electromagnetic receivers, distributed along two ~14 km-long profiles. These sensors recorded the two horizontal components of the electric and magnetic fields. The source consisted of a horizontal 200 m electric dipole towed behind the vessel. The processed data were inverted to estimate the subsurface distribution of electrical resistivity using a finite-element two-dimensional multi-frequency program, resulting in adequate fits between observed and calculated data. To estimate how well the models are constrained by the data, sensitivity tests were applied to the models. The tests were based on the Jacobian matrix and a perturbation analysis of selected features of the model. They show that the model in its central part is well constrained by the data down to a depth of about 2.5 km. With the perturbation approach, 16 resistivity features out of the 19 tested turned out to be well constrained by the data. The estimated resistivity distribution was compared with the information obtained from other geophysical methods (bathymetry, gravity, and 2D multi-channel seismic reflection), resulting in reasonably good correlations between them. For the first profile, we find a remarkable similarity with the current conceptual models proposed in the literature for a volcanic geothermal system, where an altered conductive clay cap overlays another with higher electrical resistivity. The second profile shows agreements with anomalies detected with echo-sounder bathymetry suggesting the existence of hydrothermal manifestations.

Thermodynamic Analysis of a Half-Effect Absorption Cooling System Powered by a Low-Enthalpy Geothermal Source

A thermodynamic analysis of a half-effect absorption cooling system powered by a low-enthalpy geothermal source was carried out. This paper presents modeling of the half-effect absorption cooling system operating with an ammonia/lithium nitrate mixture and based on the first and second laws of thermodynamics, using as energy inputs real data from two geothermal wells located at Las Tres Vírgenes volcanic complex, Baja California Sur, México. Plots of coefficients of performance and exergy efficiency against condenser, evaporator, and generator temperatures are presented for the half-effect cooling system. The results showed that the system was able to operate at generation temperatures between 56 and 70 °C, which were supplied by the geothermal wells in order to produce cooling at temperatures as low as −16 °C, achieving coefficients of performance between 0.10 and 0.36, while the exergy efficiency varied from 0.15 to 0.40 depending on the system operating temperatures.

Origin of fluids in Las Tres Vírgenes Geothermal Field

A geochemical survey of fluids in the Las Tres Vírgenes geothermal field (LTVGF) in Baja California Sur, Mexico, was carried out to describe their origins and evolution within the reservoir. Major and minor elements and noble gas isotopes (He, Ne, Ar, Kr, and Xe) were measured in fluids from three production wells, one injection well, and one fumarole (El Azufre). Stable isotopes of water (δD and δ18O) show mixing between Quaternary recharge, lighter than present-day rainfall, and a deep fluid of andesitic origin. The Na/Br and Cl/Br ratios indicate that deep brines from the LTVGF are seawater having leached evaporite deposits (i.e., halite). These deposits are presently absent in the area, but likely occurred during the Miocene, prior to the breakup of the Gulf of California, suggesting that the saline fluid end-member of the LTVGF is several million year old. Measured 3He/4He ratios of greater than 6.5 Ra (where Ra is the atmospheric ratio of 1.384 x10-6) show that LTVGF fluids are a mixture of meteoric waters and deep magmatic fluids, with the hotter and more pristine mantle fluids found in the southern part of the exploitation zone.

Variability of deep carbon sources in Mexican geothermal fluids

A sampling campaign for collecting geothermal fluids was carried out between 2014 and 2016 at the Cerro Prieto (CP), Los Azufres (LA), Los Humeros (LH), and Las Tres Vírgenes (LTV) geothermal fields (GFs) in Mexico. The aim of this study was to determine the CO2 carbon origin and behavior in geothermal reservoirs. The LA-GF and LH-GF are situated in an arc magmatism context related to the subduction of the Cocos plate under the North American one. The CP-GF and LTV-GF are located in an extensional pull-apart context related to the San Andreas Fault System and the opening of Gulf of California. The most interesting observation of this study was that the measured isotopic composition of CO2 (13C/12C and 18O/16O ratios) is distinct and unique for each sampled geothermal field. The C isotopic variability is controlled mainly by its sources (i.e., δ13C is −6 ± 2‰ in the mantle; −20‰ in carbon organic matter-rich sediment; and 0 ± 2‰ in marine carbonates) and possibly secondary processes such as calcite precipitation. The δ13C in the CP-GF and LA-GF are compatible with a dominant mantle carbon source. LTV-GF and LH-GF show lower (−10.7 ± 0.5‰) and higher (−3.5 ± 0.9‰) values than that of the mantle respectively. The lower δ13C of carbon in LTV-GF fluids could be due to calcite precipitation (carbonate scaling), a well-known phenomenon in this field. However, calcite precipitation should lower the CO2/3He ratios from an initial mantle value of 2 × 109. Calculated CO2/3He ratios of 1.72 and 5.49 × 1010 in LTV-GF fluids suggest that the addition of sedimentary carbon rather than calcite precipitation might be the main process. Based on the isotopic composition of helium (3He/4He ratios, or R, from 3.2 to 7.9 times the atmospheric ratio, Ra = 1.384 × 10−6) and carbon (δ13C from −11 to −2‰ vs PDB) in the fluids, the δ13C variability could be caused by the addition of carbon organic matter-rich sediments from an ancient subducting plate in the LTV-GF and from leaching of marine carbonates located underneath the basement in the LH-GF. The oxygen isotopic variability is related to the degree of isotopic re-equilibration between steam (H2O) and CO2, which, in the case of fluids extracted from production wells, may be incomplete.

“La Plaza era una trampa”: Emotional Violence of Tlatelolco 1968 in Luis Spota’s La Plaza

The massacre of a student demonstration in La Plaza de las Tres Culturas in the Tlatelolco district of Mexico City, on 2 October 1968 has been the subject of many texts aiming to keep “2 de octubre” alive in the collective memory. The apparent discord in the representation of the massacre in the state discourse (including media) and popular discourse can be seen as a representation of a conflict between hegemonic and posthegemonic order. The two structures are often seen as existing in an uneasy truce, where one is unable to fully realize itself and the other is not allowed to do so. This study will examine Luis Spota’s controversial novel La plaza (1972) as an example of posthegemonic text. We will focus upon the three components of posthegemonic order – affect, habit and multitude – and consider how they are represented in the interaction between the narrator/protagonist Domingo and the hostage. We will examine the relationship between affect and emotions in this interaction and consider what effect this has on the “consoling” role of fiction, as defined by Paul Ricoeur (Time and Narrative, vol. 3, 27).

Los paratextos de la <em>Cima del Monte Parnaso Español</em> (1672) de José Delitala: diálogo intertextual con <em>El Parnaso Español</em> (1648) y <em>Las Tres Musas Últimas Castellanas</em> (1670) de Quevedo

El trabajo pretende explicar e interpretar el diálogo intertextual establecido entre los paratextos de la Cima del Monte Parnaso Español del poeta sardo en lengua española José Delitala y Castelví, publicada en Cagliari en 1672, y las dos partes de la edición póstuma de la poesía de Francisco de Quevedo, El Parnaso Español de 1648 y Las Tres Musas Úlltimas Castellanas de 1670. El análisis permite reconocer la importancia de Quevedo a finales del siglo XVII no solo como modelo de inspiración poética sino como ejemplo editorial para la construcción organizada de un libro de poemas.

Origin and evolution of geothermal fluids from Las Tres Vírgenes and Cerro Prieto fields, Mexico – Co-genetic volcanic activity and paleoclimatic constraints

Major and trace elements, noble gases, and stable (δD, δ18O) and cosmogenic (3H, 14C) isotopes were measured from geothermal fluids in two adjacent geothermal areas in NW-Mexico, Las Tres Vírgenes (LTV) and Cerro Prieto (CP). The goal is to trace the origin of reservoir fluids and to place paleoclimate and structural-volcanic constraints in the region. Measured 3He/4He (R) ratios normalized to the atmospheric value (Ra = 1.386 × 10−6) vary between 2.73 and 4.77 and are compatible with mixing between a mantle component varying between 42 and 77% of mantle helium and a crustal, radiogenic He component with contributions varying between 23% and 58%. Apparent U–Th/4He ages for CP fluids (0.7–7 Ma) suggest the presence of a sustained 4He flux from a granitic basement or from mixing with connate brines, deposited during the Colorado River delta formation (1.5–3 Ma). Radiogenic in situ4He production age modeling at LTV, combined with the presence of radiogenic carbon (1.89 ± 0.11 pmC – 35.61 ± 0.28 pmC) and the absence of tritium strongly suggest the Quaternary infiltration of meteoric water into the LTV geothermal reservoir, ranging between 4 and 31 ka BP. The present geochemical heterogeneity of LTV fluids can be reconstructed by mixing Late Pleistocene – Early Holocene meteoric water (58–75%) with a fossil seawater component (25–42%), as evidenced by Br/Cl and stable isotope trends. CP geothermal water is composed of infiltrated Colorado River water with a minor impact by halite dissolution, whereas a vapor-dominated sample is composed of Colorado River water and vapor from deeper levels. δD values for the LTV meteoric end-member, which are 20‰–44‰ depleted with respect to present-day precipitation, as well as calculated annual paleotemperatures 6.9–13.6 °C lower than present average temperatures in Baja California point to the presence of humid and cooler climatic conditions in the Baja California peninsula during the final stage of the Last Glacial Pluvial period. Quaternary recharge of the LTV geothermal reservoir is related to elevated precipitation rates during cooler-humid climate intervals in the Late Pleistocene and Early Holocene. The probable replacement of connate water or pore fluids by infiltrating surface water might have been triggered by enhanced fracture and fault permeability through contemporaneous tectonic–volcanic activity in the Las Tres Vírgenes region. Fast hydrothermal alteration processes caused a secondary, positive δ18O-shift from 4‰ to 6‰ for LTV and from 2‰ to 4‰ for CP geothermal fluids since the Late Glacial infiltration.

Seismic activity and stress tensor inversion at Las Tres Vírgenes Volcanic and Geothermal Field (México)

We analyze local earthquakes occurring between 2003 and 2012 at the Las Tres Vírgenes Volcanic and Geothermal Field (TVVGF) to establish their temporal and spatial distribution, and relationships with local and regional fault systems, water injection, acid stimulation and steam production tests. We obtained focal mechanisms and inverted data for the stress tensor to understand the local and regional stress fields. We analyzed 423 local earthquakes with magnitudes between 0.1 and 2.9Mc and hypocentral depths from 0.2 to 7.4km b.s.l. The cutoff depth at ~7.4km possibly delineates the brittle–ductile transition zone. We identified seven swarms (from 1 to 7). Swarms 1 (December 2009), 2 (May 2010), 3 (June–July 2010) and 7 (December 2012) are strongly correlated with injection processes; whereas swarms 5 (April 2012) and 6 (September 2012) are correlated with local tectonic faults. Stress inversion showed NW–SE, E–W and NE–SW extensional orientations (Shmin), in agreement with the local tectonic stress field; while NE–SW compressional orientations (SHmax) are correlated with the regional tectonic stress field.

The 1968 Tlatelolco Massacre: The Cold War's Politicization and Internationalization of Everyday Life

Although the colossal ideological struggle between the U.S. and the Soviets raged and ravished the peripheral nations of the world and left no space unaffected, perhaps no other country in the world responded, reacted to, and altered the context of the Cold War in a more complex fashion than Mexico. Within this encompassing global context, the mindsets of both the students murdered and those directing the killings in the Plaza of the Three Cultures were molded less by the dictates of Moscow or Washington than by the more decentralized and localized ideologies, plans of action, and policies which evolved in the shadow of the macro level of the titanic superpower struggle. In this shadow world, the discontent of students grew to be global, disaffected, and revolutionary. The consequences of Mexico's Cold War politicization and internationalization of everyday life unfolded throughout the summer of 1968 and culminated on the night of October 2nd at La Plaza de las Tres Culturas at Tlatelolco, Mexico City. On this night a student demonstration was to end in a hail of bullets. When the shooting ended, hundreds of people would lay dead or wounded; Army and police forces apprehended many of the survivors; now subjected to interrogation.

Mechanisms of arsenic enrichment in geothermal and petroleum reservoirs fluids in Mexico

The lack of chemical similarity between thermal fluids in geothermal and petroleum reservoirs in Mexico indicates a distinct origin for arsenic in both types of reservoirs. Deep fluids from geothermal reservoirs along the Transmexican Volcanic Belt (TMVB) are characterized by elevated arsenic concentrations, within a range between 1 and 100 mg L −1 at a depth from 600 to 3000 m b.s.l. Based on hierarchical cluster analysis (HCA), arsenic is linked to typical geothermal species like lithium, silica, and boron. The lack of correlation between arsenic and salinity reflects the importance of secondary water-rock interaction processes. The predominance of arsenic compared to Fe- and Cu-concentrations, and the occurrence of secondary minerals (sulfides and clay minerals) in temperature-dependent hydrothermal zones, supports this hypothesis. Neither magmatic fluids input, nor As mineralization is a prerequisite for As enrichment in Mexican geothermal fluids. In contrast, petroleum reservoir waters from sedimentary basins in SE-Mexico show maximum As concentrations of 2 mg L −1, at depths from 2900 to 6100 m b.s.l. The linear chloride–arsenic correlation indicates that evaporated seawater represents the major source for aqueous arsenic in oil reservoirs, and only minor arsenic proportions are derived from interaction with carbonate host rock. Speciation modeling suggests the lack of arsenic solubility control in both geothermal and petroleum reservoirs, but precipitation/co-precipitation of As with secondary sulfides could occur in petroleum reservoirs with high iron concentrations. Geothermal fluids from magmatic-type reservoirs (Los Azufres and Los Humeros at the TMVB and Las Tres Vírgenes with a granodioritic basement) show relative constant arsenic concentrations through varying temperature conditions, which indicates that temperatures above 230–250 °C provide optimal and stable conditions for arsenic mobility. In contrast, temperature conditions for sedimentary-type reservoirs are irrelevant for water-rock interaction processes, as suggested by low arsenic aqueous concentration for both Cerro Prieto geothermal fluids (high temperature – sedimentary type) and oil field formation water (low temperature – sedimentary type).

An Inverse Method for Estimation of Initial Temperatures in Geothermal Reservoirs: Part 2. Inverse Control Algorithm and Results of Application

A method based on proportional control was used to solve the inverse heat transfer problem of estimating geothermal reservoir initial formation temperatures from temperatures logged in geothermal wells. The proportional control computes the error between logged and simulated well temperatures during shut-in and feeds back this information to the initial proposal of the initial formation temperature until the error is a minimum. In this sense, an inverse problem is solved since the initial formation temperature represents the initial conditions, which are unknown a priori, to solve the set of partial differential equations that govern heat transfer in the wellbore and surrounding formation during drilling. The mathematical model of the well and the formation is described in Part 1 of this article, while Part 2 described the application of the method to the estimation of the initial formation temperatures of well LV-3 from the Las Tres Virgenes, Mexico geothermal field. Estimated initial formation temperatures compare within ±15°C, which is an acceptable result from an engineering point of view.

Solute geothermometry of springs and wells of the Los Azufres and Las Tres Vírgenes geothermal fields, Mexico

Subsurface reservoir temperatures of two important Mexican geothermal systems (Los Azufres and Las Tres Vírgenes) were estimated by applying all available solute geothermometers for 88 and 56 chemical data measurements of the spring waters and fluids of the deep geothermal wells, respectively. Most of the chemical data for spring water of these two geothermal fields are for HCO3 water, followed by SO4 and Cl types. For the Los Azufres geothermal field (LAGF), the reservoir temperatures estimated by Na-K geothermometers for springs of HCO3 and SO4 waters, and by Na-Li and Li-Mg geothermometers for Cl water, are close to the average bottom-hole temperature (BHT) of the geothermal wells. However, all reservoir temperatures for spring waters from the Las Tres Vírgenes geothermal field (LTVGF) estimated by all solute geothermometers indicated significantly large differences (low temperatures) compared to the BHT. Evaluation of inferred reservoir temperatures for spring waters of the LAGF and LTVGF suggests that not all springs nor all solute geothermometers provide reliable estimation of the reservoir temperatures. Even though chemical equilibrium probably was not achieved in the water–rock system, Na-K geothermometers for HCO3 water (peripheral water mainly of meteoric origin with little geothermal component) and SO4 water (geothermal steam heated) and Na-Li and Li-Mg geothermometers for Cl-rich spring water (fully mature geothermal water) of the LAGF indicated reservoir temperatures close to the BHT. However, in comparison with the geothermometry of spring water of the LAGF and LTVGF, fluid measurements from geothermal wells of these two fields indicated reservoir temperatures in close agreement with their respective BHTs. For the best use of the solute geothermometry for spring water, it is advisable to: (1) chemically classify the springs based on water types; (2) identify and eliminate the discordant outlier observations by considering each water type as a separate sampled population; (3) apply all available solute geothermometers employing a suitable computer program such as SolGeo instead of using some specific, arbitrarily chosen geothermometers; and (4) evaluate the temperatures obtained for each solute geothermometer by considering the subsurface lithology, hydrological conditions, and BHTs or static formation temperatures whenever available.

An Inverse Method for Estimation of Initial Temperatures in Geothermal Reservoirs: Part 1. Mathematical Model of the Well and Formation

An inverse method is presented for the estimation of geothermal reservoir initial temperatures based on a control theory algorithm in which computed well temperatures are fitted to well-logged temperatures. The method and results are presented in a two-part paper. Part I deals with the mathematical model of the well and the formation while Part II presents the inverse control algorithm and results of application. Well temperatures are obtained by simulating the circulation and shut-in processes in the presence of lost circulation using macroscopic balances to describe momentum and energy transport. Transport processes in the formation consider the reservoir as an isotropic porous medium with Darcian flow. Computed well temperatures are fed to the inverse control algorithm to estimate the initial formation temperatures. The method was applied to the estimation of the initial formation temperatures of well LV-3 from the Las Tres Virgenes, Mexico, geothermal field, as described in Part II of this paper.

SolGeo: A new computer program for solute geothermometers and its application to Mexican geothermal fields

The freely available computer program Solute Geothermometers (SolGeo) was written and tested using geochemical data and reported geothermometric temperatures from several geothermal wells from around the world. Subsurface temperatures for the Mexican geothermal fields of Cerro Prieto, Las Tres Vírgenes, Los Azufres, and Los Humeros were estimated based on different solute geothermometers and found to be generally in close agreement with measured well temperatures when considering errors in the calculations and measurements. For Los Humeros wells it was concluded that a better agreement of chemical geothermometric temperatures is observed with static formation than with bottom-hole temperatures (BHTs). It was also found that the widely used Na–K geothermometric equations generally give more consistent and more reliable temperature estimates than the other geothermometers, which should therefore be applied with caution.

Fluid chemistry and temperatures prior to exploitation at the Las Tres Vírgenes geothermal field, Mexico

Generation of electricity at the Las Tres Vírgenes (LTV) geothermal field, Mexico, began in 2001. There are currently nine geothermal wells in the field, which has an installed electricity generating capacity of 10 MW e. The chemical and temperature conditions prevailing in the field prior to its exploitation have been estimated, including their central tendency and dispersion parameters. These conditions were computed on the basis of: (i) geochemical data on waters from springs and domestic wells, and on geothermal well fluids (waters and gases); most of the sampling took place between 1995 and 1999; (ii) fluid inclusion studies; (iii) geothermometric data; and (iv) static formation temperatures computed using a modified quadratic regression Horner method. Fluid inclusion homogenization temperatures (in the 100–290 °C range) suggest that there is a high-temperature fluid upflow zone near wells LV3 and LV4 in the southern part of the field. Computed average chemical equilibrium temperatures for the geothermal fluids are ∼260 °C, based on the Na/K and SiO 2 geothermometers, and ∼265 °C, based on the H 2/Ar, and CO 2/Ar geothermometers. In general, the fluid inclusion homogenization temperatures are consistent with geothermometric data, as well as with static formation temperatures. Some of the observed differences could be related to well interference effects and different fluid production/sampling depths. The deeper geothermal waters show higher concentrations of Cl, Na, K, B, Ba, but lower concentrations of SO 4, Ca, and Mg than the shallower waters. Fluid inclusion salinities are also higher in the deeper rocks. The measured Na/Cl ratios of the geothermal well waters are more or less uniform throughout the field and are very similar to that of seawater, strongly suggesting a seawater component in the fluid of the LTV system. The heat stored in the LTV geothermal system was estimated to be at least 9 × 10 12 MJ, of which some 4 × 10 11 MJ (equivalent to about 148 MW e for 30 years of operation, assuming a conversion efficiency of ∼35%) might be extracted using wells. These results indicate that the installed capacity at LTV could be safely increased from the current 10 MW e.

The Echo of Tlatelolco in Contemporary Mexican Protest Poetry

The shooting of a student demonstration in La Plaza de las Tres Culturas in the Tlatelolco district of Mexico City on 2 October 1968 has been the subject of many literary works, among which the Tlatelolco poetry addresses not only the event itself but also the aftermath of the massacre. Both approaches examine the relationship between the ‘yo’/‘nosotros’ and ‘ellos’ constructs, focusing on the ‘nosotros’ construct as the result of this interaction. The following analysis of this process is based on the theory of self and Other, especially Rene Girard's theory of the mimetics of violence and the process of scapegoating as a basis for the relationship between the individual and society within the context of a violent conflict.