Tracing hydrothermal mineral thenardite in geysers/hot springs of North-western Himalayan belt,Ladakh Geothermal Province,India by hydrogeochemistry,fluid-mineral equilibria and isotopic studies

The present study highlights the first evidence of hydrothermal mineral Thenardite (Na₂SO₄) from Puga geothermal area, North-western Himalayan belt in Ladakh Geothermal Province, India, which is unequivocal evidence for the presence of high-temperature hydrothermal fluid activity from one of the thickest crust areas of the Earth. The Puga geothermal belt illustrates a fault-bounded hydrothermal system with a clearly defined conductive zone, coinciding with Kiagar Tso fault typically exemplifying a shallow-level medium enthalpic geothermal reservoir. The hydrogeochemistry suggests that thermal and non-thermal waters are of Na-Cl-HCO₃ and Ca-Mg-HCO₃ type, respectively, with neutral to near alkaline pH. The silica and cation geothermometry reveal sub-surface temperatures around 150 °C and 250 °C, respectively, at shallow depth; however, >250 °C is anticipated at the deepest levels (~3 km). Stable isotope (δD and δ¹⁸O) studies explicate depletion of isotopic content for thermal waters over Puga river water and radiogenic isotope (³H) suggests matured thermal waters with ongoing water-rock interactions. The recharge altitude estimation and physiographic studies put forth that geothermal reservoir is recharged with the ice masses located at an altitude of 6458 m above mean sea level (msl) in the west of Puga valley, probably from the highest peak of Polokong La mountain. The two key processes participating in regulation of proportions of the dissolved salts in the thermal waters are silicate weathering and ion-exchange kinetics. The powder X-ray diffraction study reveals a major occurrence of hydrothermal mineral thenardite in the hot spring deposits for the first time along with huge encrustations of trona, borax, calcite and elemental sulfur. The high-temperature fluids encounter thenardite, pyrite, and jarosite-bearing minerals in basement rock causing enrichment of SO₄²⁻ and Cl⁻ in geothermal waters. The temperature-dependent speciation modelling (50 °C–200 °C) for major ion Na⁺ reveals the composition of the reservoir fluid (~150 °C): Na⁺ > NaCO₃⁻ > NaSO₄⁻ > NaHCO₃ > NaF > NaOH. A conceptual evolution model of thermal waters involving the recharge-deep circulation-mixing-discharge of thermal springs is hence put forth in the study using various hydrogeochemical insights.     

Hydro-geochemical and isotopic fluid evolution of the Los Azufres geothermal field,Central Mexico

Hydrothermal alteration at Los Azufres geothermal field is mostly propylitic with a progressive dehydration with depth and temperature increase. Argillic and advanced argillic zones overlie the propylitic zone owing to the activity of gases in the system. The deepest fluid inclusions (proto-fluid) are liquid-rich with low salinity, with NaCl dominant fluid type and ice melting temperatures (T_mi) near zero (0 °C), and salinities of 0.8 wt% NaCl equivalent. The homogenization temperature (T_h)  = 325 ± 5 °C. The boiling zone shows T_h = ±300 °C and apparent salinities between 1 and 4.9 wt% NaCl equivalent, implying a vaporization process and a very important participation of non-condensable gases (NCGs), mostly CO₂. Positive clathrate melting temperatures (fusion) with T_h = 150 °C are observed in the upper part of the geothermal reservoir (from 0 to 700 m depth). These could well be the evidence of a high gas concentration. The current water produced at the geothermal wells is NaCl rich (geothermal brine) and is fully equilibrated with the host rock at temperatures between T = 300 and 340 °C. The hot spring waters are acid-sulfate, indicating that they are derived from meteoric water heated by geothermal steam. The NCGs related to the steam dominant zone are composed mostly of CO₂ (80–98% of all the gases). The gases represent between 2 and 9 wt% of the total mass of the fluid of the reservoir.The authors interpret the evolution of this system as deep liquid water boiling when ascending through fractures connected to the surface. Boiling is caused by a drop of pressure, which favors an increase in the steam phase within the brine ascending towards the surface. During this ascent, the fluid becomes steam-dominant in the shallowest zone, and mixes with meteoric water in perched aquifers. Stable isotope compositions (δ¹⁸O–δD) of the geothermal brine indicate mixing between meteoric water and a minor magmatic component. The enrichment in δ¹⁸O is due to the rock–water interaction at relatively high temperatures. δ¹³C stable isotope data show a magmatic source with a minor meteoric contribution for CO₂. The initial isotopic value δ³⁴S_RES = −2.3‰, which implies a magmatic source. More negative values are observed for shallow pyrite and range from δ³⁴S (FeS₂) = −4‰ to −4.9‰, indicating boiling. The same fractionation tendencies are observed for fluids in the reservoir from results for δ¹⁸O.     

天津地热资源评价与综合研究

以4 000 m以浅的主要热储层为研究对象,通过总结天津地热资源特征及勘查现状,利用热储法结合水均衡法和数值耦合优化管理模型计算天津市主要热储层30 a热流体可采资源量及可采热量。结果表明: 到2045年底,热储法结合水均衡法计算的热流体可采资源量和可采热量分别为27.012×10¹⁸ m³和47.0×10¹⁶ J; 数值耦合优化管理模型计算的热流体可采资源量和可采热量分别为26.6×10¹⁸ m³和49.74×10¹⁶ J; 2种方法计算结果基本一致。该计算结果可为天津市地热资源合理开发及科学管理提供依据。     

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 (R_a = 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 situ ⁴He 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.     

The use of O,H, B,Sr and S isotopes for tracing the origin of dissolved boron in groundwater in Central Macedonia,Greece

The groundwater B concentration in Mesozoic karst, Neogene and alluvial aquifers in the West part of Chalkidiki province in Central Macedonia, Greece reaches 6.45 mg L⁻¹, which exceeds the limit of 1 mg L⁻¹, set by the European Union for drinking water. The high B contents have been detected in this area, not only near the shoreline, where seawater intrusion occurs, but also in the inland part of the basin. Multi isotope (²H, ¹⁸O, ³⁴S, ¹⁸O_(SO4), ¹¹B, ⁸⁷Sr/⁸⁶Sr) data from borehole and thermal water springs allow identification of the possible B sources. The B dissolved in groundwater in the Chalkidiki area is mainly geogenic. The low δ¹¹B values, 0–1‰, similar to those of thermal fluids from continental geothermal fields, and the low Cl/B ratio compared to seawater both indicate a geothermal origin for B and reflect deep circulation and interaction with igneous rocks. The ⁸⁷Sr/⁸⁶Sr ratio also indicates that the deep-aquifer granodiorite is the predominant rock source of Sr, while the shallow limestone unit has negligible effects on the dissolved Sr budget in these thermal karst waters which O and H isotopes show to be of meteoric origin. The main source of high B in borehole water is mainly mixing with B-rich geothermal water. The mixing between geothermal water and water from the Neogene aquifer is also reflected by isotopic contents of SO₄.     

O,H, and Sr isotope evidences of mixing processes in two geothermal fluid reservoirs at Yangbajing,Tibet, China

The Yangbajing geothermal field with the highest reservoir temperature among Chinese hydrothermal systems is located about 90 km northwest to Lhasa City, capital of Tibet, where high temperature geothermal fluids occur in two reservoirs: a shallow one at a depth of 180–280 m and a deep one at 950–1,850 m. In this study, Oxygen-18 and deuterium isotope compositions as well as ⁸⁷Sr/⁸⁶Sr ratios of water samples collected from geothermal wells, cold springs and surface water bodies were characterized to understand the genesis of geothermal fluids at Yangbajing. The results show that the deep geothermal fluid is the mixing product of both magmatic and infiltrating snow-melt water, whereas the shallow geothermal fluid is formed by the mixing of deep geothermal fluid with cold groundwater. Using a binary mixing model with deep geothermal fluid and cold groundwater as two endmembers, the mixing ratios of the latter in most shallow geothermal water samples were calculated to be between 40 and 50%. The combined use of O, H, and Sr isotopes proves to be an effective approach to depict the major sources of geothermal fluids and the mixing processes occurring in two reservoirs at Yangbajing.     

Hydrogeochemistry of thermal and mineralized waters in the Diyadin (Ağri) area,Eastern Turkey

The Diyadin Geothermal area, located in the eastern part of Anatolia (Turkey) where there has been recent volcanic activity, is favorable for the formation of geothermal systems. Indeed, the Diyadin geothermal system is located in an active geodynamic zone, where strike-slip faults and tensional cracks have developed due to N–S regional compression. The area is characterized by closely spaced thermal and mineralized springs, with temperatures in the range 30–64 °C, and flowrates 0.5–10 L/s. Thermal spring waters are mainly of Ca(Na)-HCO₃ and Ca(Mg)-SO₄ types, with high salinity, while cold groundwater is mostly of Ca(Na, Mg)-HCO₃ type, with lower salinity. High contents of some minor elements in thermal waters, such as F, B, Li, Rb, Sr and Cs probably derive from enhanced water–rock interaction.Thermal water samples collected from Diyadin are far from chemical equilibrium as the waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters. The temperatures of the deep geothermal reservoirs are estimated to be between 92 and 156 °C in Diyadin field, based on quartz geothermometry, while slightly lower estimates are obtained using chalcedony geothermometers. The isotopic composition of thermal water (δ¹⁸O, δ²H, δ³H) indicates their deep-circulating meteoric origin. The waters are likely to have originated from the percolation of rainwater along fractures and faults to the deep hot reservoir. Subsequent heating by conduction due to the presence of an intrusive cupola associated with the Tendurek volcano, is followed by the ascent of deep waters to the surface along faults and fractures that act as hydrothermal conduits.Modeling of the geothermal fluids indicates that the fluid is oversaturated with calcite, aragonite and dolomite, which matches travertine precipitation in the discharge area. Likewise, the fluid is oversaturated with respect to quartz, and chalcedony indicating the possibility of siliceous precipitation near the discharge areas. A conceptual hydro-geochemical model of the Diyadin thermal waters based on the isotope and chemical analytical results, has been constructed.     

Elemental and isotopic geochemistry in the hydrothermal area of Chaves,Vila Pouca de Aguiar (northern Portugal)

Chaves thermal waters (76°C) are the most important external manifestations of low-temperature geothermal systems occurring in Portuguese mainland. They are related to crystalline granitic rocks. This paper describes the use of the environmental isotopic composition (oxygen-18, deuterium, and tritium) of hot and cold waters of the Chaves area as an important hydrogeological tool to solve specific problems arising in the appraisal of the geothermal resources of the area (e.g., origin and age of waters, recharge area, and underground flow paths).¹⁸O and D analyses seem to confirm the meteoric origin of Chaves thermal waters. The local altitude dependence of meteoric waters was determined by¹⁸O and D analyses of superficial and shallow groundwaters of the Chaves plain and its bordering mountains. Chaves thermal waters seem to be related to meteoric waters, infiltrated on the highest topography areas (Bolideira granitic outcrop NE Chaves), that percolate at great depth and emerge in a discharge area at lower altitude (Chaves plain). Chaves thermal waters showing little oxygen-18 shift and low tritium concentrations could be considered external manifestations of an old geothermal system in which the isotopic water-rock interaction is adjusted to equilibrium.     

δ<Superscript>18</Superscript>O shifts of geothermal waters in the central of Weihe Basin,NW China

The thermal-waters resources in Weihe Basin of Shaanxi province, NW China are historically classified as middle- to low- temperature thermal-waters in China. Recent exploitation of the deep thermal reservoir in the centre part of the basin (i.e. Xi’an and Xianyang) had observed plentiful supply of thermal fluid with higher measured maximum temperature (120°C) and higher hydraulic pressure (80.50 MPa) in the deeper (more than 4,000 m deep) sedimentary basin. A recent isotope study shows that deep geothermal waters in the cities of Xi’an and Xianyang are characterized by an observable horizontal oxygen-18 (δ¹⁸O) shift and minor deuterium (²H) enrichment. The considerable oxygen shift is possibly due to the following four reasons: water–rock interaction at high temperature, slow circulation rate of water, low water-to-rock ratio, and old age. On the end number of the δ¹⁸O shift, minor δ²H enrichment occur when there is higher concentrations of H₂S, CH₄, I and Br with lower rate of rSO₄ ²⁻/rCl⁻ and r _Na⁺/r _Cl⁻ suggesting relatively isolated geological environment. In a few thermal waters points, r\textNa^\text+ \text/r\textCl^-r{\text{Na}}^{{\text{+}}} {\text{/}}r{\text{Cl}}^{-} < 0.85. This shows possible presence of formation waters. Combining the results from isotopic study and chemical analysis, we can classify the types of geothermal waters into three groups, the shallow and fast circulating system, the semi-circulating system and the deep and slow circulating system.     

Geochemical constraint on origin and evolution of solutes in geothermal springs in western Yunnan,China

Geothermal resources are very rich in Yunnan, China. However, source of dissolved solutes in geothermal water and chemical evolution processes remain unclear. Geochemical and isotopic studies on geothermal springs and river waters were conducted in different petrological-tectonic units of western Yunnan, China. Geothermal waters contain Ca–HCO₃, Na–HCO₃, and Na (Ca)–SO₄ type, and demonstrate strong rock-related trace elemental distributions. Enhanced water–rock interaction increases the concentration of major and trace elements of geothermal waters. The chemical compositions of geothermal waters in the Rehai geothermal field are very complicated and different because of the magma chamber developed at the shallow depth in this area. In this geothermal field, neutral-alkaline geothermal waters with high Cl, B, Li, Rb Cs, As, Sb, and Tl contents and acid–sulfate waters with high Al, Mn, Fe, and Pb contents are both controlled by magma degassing and water–rock interaction. Geothermal waters from metamorphic, granite, and sedimentary regions (except in the Rehai area) exhibit varying B contents ranging from 3.31 mg/L to 4.49 mg/L, 0.23 mg/L to 1.24 mg/L, and <0.07 mg/L, respectively, and their corresponding δ¹¹B values range from −4.95‰ to −9.45‰, −2.57‰ to −8.85‰, and −4.02‰ to +0.06‰. The B contents of these geothermal waters are mainly controlled by leaching host rocks in the reservoir, and their δ¹¹B values usually decrease and achieve further equilibrium with its surrounding rocks, which can also be proven by the positive δ¹⁸O-shift. In addition to fluid–rock reactions, the geothermal waters from Rehai hot springs exhibit higher δ¹¹B values (−3.43‰ to +1.54‰) than those yielded from other areas because mixing with the magmatic fluids from the shallow magma. The highest δ¹¹B of steam–heated waters (pH 3.25) from the Zhenzhu spring in Rehai is caused by the fractionation induced by pH and the phase separation of coexisting steam and fluids. Given the strong water–rock interaction, some geothermal springs in western Yunnan show reservoir temperatures higher than 180 °C, which demonstrate potential for electricity generation and direct-use applications. The most potential geothermal field in western Yunnan is located in the Rehai area because of the heat transfer from the shallow magma chamber.     

Geochemical assessment,mixing behavior and environmental impact of thermal waters in the Guelma geothermal system,Algeria

A study of thirteen geothermal springs located in the geothermal field of Guelma, northeastern Algeria, was conducted. Samples were collected during the period between January 2014 and February 2016. Geochemical processes responsible for the chemical composition of thermal and mineralized water were evaluated. The hydrochemical analysis shows that the thermal waters are characterized by the presence of two different chemical facies, the first type SO₄–Ca in the east, west and south of Guelma, the second type HCO₃–Ca in the south. This analysis also attributed to sodium, chlorides, and sulfates to an evaporitic terrigenous origin by the molar ratio Sr²⁺/Ca²⁺. The thermal spring waters from Guelma geothermal system have a meteoric origin, and all samples are immature with strong mixing between hot and shallow waters with 19–38.5% rate of mixing. The silica geothermometer shows that these thermal waters have a temperature varying from 84 to 122 °C and that the water came from a depth of 2100–3000 m through a fault system that limits the pull-apart basin of Guelma. Potential environmental effluent from thermal spas could pollute in both the irrigation and drinking waters, and which imposes danger on the health of the inhabitants of the region.

     

Surface and groundwater pollution by organochlorine compounds in a typical soybean system from the south Pampa,Argentina

Organochlorine pesticides (OCPs) use has been restricted or forbidden in Argentina since 1998 and technical endosulfan is the last currently used OCPs on the soybean-wheat production. As they persist in soil for several years after application, OCPs constitute a source of environmental pollution. This work aims to assess OCPs contamination of groundwater (Gw) and streamwater (Sw) in the Quequén Grande River watershed from south Argentinean Pampas in relation to the hydrogeological characteristics. OCPs were analyzed in Sw, Gw, surface bottom sediments, soils and borehole cutting sediments (Cs) by gas chromatograph-electron capture detector. Pesticide distribution in Cs was dependent on the characteristic of the non-saturated zone. Leached pesticides over 3 m in Cs showed the pattern: HCHs = endosulfan > chlordanes > DDTs, and from 3 to 6 m heptachlor was the main group as a consequence of the past use of this compound in the area, mainly on potato crops. Endosulfan reaches Gw during application season as well as during flooding events while a retard effect was observed for Sw. Levels of α- and β-isomers were in certain cases above national (7 ng L⁻¹) and international (3 ng L⁻¹) limits for aquatic biota protection. As the endosulfan sulfate metabolite was present in Gw and Sw and due to its high toxicity, it should be considered in the establishment of water quality criteria for human and environmental protection.     

A multi-isotope approach (O,H, C,S, B and Sr) to understand the source of water and solutes in some the thermal springs from West Coast geothermal area,India

The West Coast belt, consisting of nearly 60 thermal springs, is one of the most diversified geothermal fields in India. The present work describes the multi-isotopic (O, H, C, S, B and Sr) characterization of thermal waters carried out in the Tural-Rajwadi geothermal field, situated in southern sector of the west coast geothermal area. The aim of this study is to delineate the origin of thermal water as well as to ascertain the sources of carbon, sulphur, boron and strontium dissolved in those thermal springs. The stable isotopes (δ²H and δ¹⁸O) and tritium data indicate that these thermal springs are not recently recharged rain water rather, it contains very old component of water. Oxygen-18 shift is observed due to rock-water interaction over a long period of time. Carbon isotopic composition of DIC points out to the silicate weathering with soil CO₂ coming from C₃ type of plants whereas δ³⁴S of dissolved sulphate confirms the marine origin of sulphate. This marine signature is basically derived from paleo-seawater possibly entrapped within the flows. Boron isotopic data reveals that both the seawater and rock dissolution are the sources of boron in the thermal waters whereas high ⁸⁷Sr/⁸⁶Sr ratios (0.7220–0.7512) of the thermal waters conclusively establishes that archean granitic basement is the predominant rock source of strontium, not the Deccan flood basalts. In addition, like strontium, concentrations of lithium, rubidium and caesium are also governed by the rock-water interaction. Thus, the combined use of this multi-isotope technique coupled with trace element concentrations proves to be an effective tool to establish the sources of solutes in the thermal water.     

Andalusite and Na- and Li-rich cordierite in the La Costa pluton, Sierras Pampeanas, Argentina: textural and chemical evidence for a magmatic origin

The La Costa pluton in the Sierra de Velasco (NW Argentina) consists of S-type granitoids that can be grouped into three igneous facies: the alkali-rich Santa Cruz facies (SCF, SiO₂ ~67 wt%) distinguished by the presence of andalusite and Na- and Li-rich cordierite (Na₂O = 1.55–1.77 wt% and Li₂O = 0.14–0.66 wt%), the Anillaco facies (SiO₂ ~74 wt%) with a significant proportion of Mn-rich garnet, and the Anjullón facies (SiO₂ ~75 wt%) with abundant albitic plagioclase. The petrography, mineral chemistry and whole-rock geochemistry of the SCF are compatible with magmatic crystallization of Na- and Li-rich cordierite, andalusite and muscovite from the peraluminous magma under moderate P–T conditions (~1.9 kbar and ca. 735°C). The high Li content of cordierite in the SCF is unusual for granitic rocks of intermediate composition.     

我国建立第一个地热资源数据库

Demonstrative geothermal resources data-base consists of 3 subsystems ; 1) Geotemperature&rock thermo一physical property ; 2 ) Hydrogeological testing parameters of thermal water&thermal water sites;3)Chemical composition of thermal fluids in geothermal areas. Data-base system is accompanied with software set including various programs for calculation on geothermal gradient, radioactive heat productivity and hydrogeological parameters,for identification of thermal water chemical type,for comparision of different geothermometers and for ploting lithological colum，geotherms , histograms ofthermal conductivity&. heat productivity, chemical composition of thermal waters, isotherms as well as curves of water table and flow rate.
     

Metamorphism, isotopic ages and composition of lower crustal granulite xenoliths from the Cretaceous Salta Rift, Argentina

Crustal xenoliths from basanitic dikes and necks that intruded into continental sediments of the Cretaceous Salta Rift at Quebrada de Las Conchas, Provincia Salta, Argentina were investigated to get information about the age and the chemical composition of the lower crust. Most of the xenoliths have a granitoid composition with quartz-plagioclase-garnet-rutile ± K-feldspar as major minerals. The exceedingly rare mafic xenoliths consist of plagioclase-clinopyroxene-garnet ± hornblende. All xenoliths show a well equilibrated granoblastic fabric and the minerals are compositionally unzoned. Thermobarometric calculations indicate equilibration of the mafic xenoliths in the granulite facies at temperatures of ca. 900 °C and pressures of ca. 10 kbar. The Sm-Nd mineral isochron ages are 95.1 ± 10.4 Ma, 91.5 ± 13.0 Ma, 89.0 ± 4.2 Ma (granitoid xenoliths), and 110.7 ± 23.6 Ma (mafic xenolith). These ages are in agreement with the age of basanitic volcanism (ca. 130–100 and 80–75 Ma) and are interpreted as minimum ages of metamorphism. Lower crustal temperature at the time given by the isochrons was above the closure temperature of the Sm-Nd system (>600–700 °C). The Sm-Nd and Rb-Sr isotopic signatures (¹⁴⁷Sm/¹⁴⁴Nd = 0.1225–0.1608; ¹⁴³Nd/¹⁴⁴Nd_{t 0} = 0.512000–0.512324; ⁸⁷Rb/⁸⁶Sr = 0.099–0.172; ⁸⁷Sr/⁸⁶Sr_{t 0} = 0.708188–0.7143161) and common lead isotopic signatures (²⁰⁶Pb/²⁰⁴Pb = 18.43–18.48; ²⁰⁷Pb/²⁰⁴Pb = 15.62–15.70; ²⁰⁸Pb/²⁰⁴Pb = 38.22 –38.97) of the granitoid xenoliths are indistinguishable from the isotopic composition of the Early Paleozoic metamorphic basement from NW Argentina, apart from the lower ²⁰⁸Pb/²⁰⁴Pb ratio of the basement. The Sm-Nd depleted mantle model ages of ca. 1.8 Ga from granitoid xenoliths and Early Paleozoic basement point to a similar Proterozoic protolith. Time constraints, the well equilibrated granulite fabric, P-T conditions and lack of chemical zoning of minerals point to a high temperature in a crust of nearly normal thickness at ca. 90 Ma and to a prominent thermal anomaly in the lithosphere. The composition of the xenoliths is similar to the composition of the Early Paleozoic basement in the Andes of NW Argentina and northern Chile. A thick mafic lower crust seems unlikely considering low abundance of mafic xenoliths and the predominance of granitoid xenoliths. Received: 21 July 1998 / Accepted: 27 October 1998     

河南省地热资源综合评价

河南省地热资源类型按照所处的大地构造环境分为沉积盆地型和隆起山地型。计算结果表明,沉积盆地区4 000 m以浅储存的地热水总量为82 063.23×10~8 m~3,储存热能总量为7 734 086.01×10~(12) kJ。不考虑回灌时,全省沉积盆地型地热可采流体量为92 223.93×10~4 m~3/a,可利用热能量196.6×10~(12) kJ/a;考虑回灌时,全省沉积盆地型地热流体可开采量5 931 841.92×10~4 m~3/a,可利用热能量为13 003.47×10~(12) kJ/a。统计分析显示,按地热流体可采量为92 223.93×10~4 m~3/a、地热流体可开采热量196.46×10~(12) kJ/a计算,即使按50%利用,其经济效益也是十分可观的。另外,地热开发可带动第三产业经济的发展,产生的间接经济效益更加巨大。     

Determination of the origin of the Helvadere drinking springs by means of hydrochemical and isotopic techniques, Aksaray, Central Anatolia, Turkey

The main aquifer of the Helvadere springs that emerges on the strike-slip of the Hasanda?? fault set alongside the Tuzgölü (salt lake) fault zone, and trends in a NW–SE direction of Aksaray city, in the western part of Central Anatolia, is the exposed rocks of Hasanda?? which are volcanics that have distinct hydrogeological properties. The meteoric origin of the spring waters is deduced from hydrochemical and environmental isotope (¹⁸O, ²H, ³H) studies. The springs have high discharge (Q>100?l/s) and low ion concentrations because of fast circulation along the groundwater flow path in the aquifer. Furthermore, because it has Ca-Na-Mg-HCO₃ hydrochemical facies, it conforms to high standards of drinking and irrigation water.     

Differential timing of vertical-axis block rotations in the northern Ryukyu Arc: Paleomagnetic evidence from the Koshikijima Islands,Japan

Over 300 samples for paleomagnetic analysis and K–Ar dating were collected from 27 sites at NW–SE and NE–SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D = ? 37.7^°, I = 51.8^°, α₉₅ = 9.6^°, and κ = 40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D = 16.1^°, I = 57.7^°, α₉₅ = 7.1^°, and κ = 41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40^° of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F₁ faults) without vertical-axis block rotation, (2) strike-slip reactivation of F₁ faults and oblique-normal displacement on NE–SW-trending faults (F₂ faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F₂ faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.     

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C₃ forest browsers in the Amazon (mean δ¹³C = −13.4‰), to mixed C₃ grazers and/or browsers living either in C₃ grasslands, or mixed C₃ forested and grassland habitats in Honduras (mean δ¹³C = −9.3‰), Buenos Aires province, Argentina (δ¹³C = −8.7‰), and Bahia, Brazil (mean δ¹³C = −8.6‰), to predominantly C₄ grazers in northern Argentina (δ¹³C = −4.4‰), to specialized C₄ grazers in the Chaco of Bolivia (δ¹³C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C₃-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.