Academic literature on the topic 'Chlorite geothermometry'

Chlorite, a 2:1:1 phyllosilicate, has all the required attributes to form the basis of a geothermometer: this mineral is ubiquitous in metamorphic, diagenetic, and hydrothermal systems with a broad field of stability and a chemical composition partly dependent on temperature (T) and pressure (P) conditions. These properties led to the development of a multitude of chlorite thermometers, ranging from those based on empirical calibrations (linking T to AlIV content) to thermodynamic or semi-empirical models (linking T to chlorite + quartz + water equilibrium constant). This present study provides an overview of these geothermometers proposed in the literature for low-temperature chlorite (T < 350 °C), specifying the advantages and limitations of each method. Recent analytical developments that allow for circumventing or responding to certain criticisms regarding the low-temperature application of thermometers are also presented. The emphasis is on micrometric and nanometric analysis, highlighting chemical intracrystalline zoning—which can be considered as evidence of a succession of local equilibria justifying a thermometric approach—and mapping ferric iron content. New perspectives in terms of analysis (e.g., Mn redox in Mn-chlorite) and geothermometer (molecular solid-solution model, oxychlorite end-member) are also addressed.

AbstractChlorites from Cambrian basaltic vesicular lavas, characterized by relatively highXc (0.81-0.98), gave temperatures of formation of 285 to 350°C (Cathelineau's empirical geothermometer). Both theXcand temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy. The HRTEM and XRD studies indicate the absence of smectite layers in these chlorites; i.e. according to lattice images, the actual value ofXcis 1. The chlorite composition in these basaltic lavas must, therefore, be explained in relation to their whole-rock geochemistry, with which a good correlation has been found. The basaltic lavas are characterized by relatively high FeO/M ratios (3.28±1.66) and must be considered as an Fe-rich system, with similar chemical behaviour to pelitic rocks. In these cases, direct chlorite formation, without a previous smectite precursor, is a normal occurrence and theXccalculation and empirical geothermometric calculations are inadequate.

The pre-Alpine basement of the Ios Island involves large Variscan granitoid bodies intruded into metasediments that had already been metamorphosed under upper amphibolite facies conditions, as it is indicated by residual migmatitic textures and deformed muscovite pegmatites. The Alpine HP-metamorphism, documented on various cycladic islands, has, also, affected the basement rocks of Ios. Pressures of '25 Kbar and temperatures of '540 °C, are estimated for the Alpine HP event, applying the chloritoid-chlorite and garnetclinopyroxene geothermometers, and the garnet-phengite-omphacite and garnet-rutile-quartz-sphene-clinozoisite geobarometers. Garnet-hornblende geothermometry yielded temperatures of '520 °C and garnet-chlorite geothermobarometry yielded temperatures of 450 °C at 15 Kbar. This suggests that, at least the first stages of decompression were accompanied by cooling, indicating a rapid exhumation, related to tectonic processes.

Abstract. This study reports on reaction processes in a transition zone from contact to regional metamorphism by using Raman spectroscopy on carbonaceous matter (RSCM), illite “crystallinity” (Kübler index, KI), chlorite geothermometry, and thermal modeling. The thermal effect due to the emplacement of the Torres del Paine intrusion (TPI, assembly time of ca. 150 kyr) had different consequences for inorganic and organic compounds of the host rock. The thermal alteration of the pre-intrusive regional metamorphosed host rock is documented by elevated RSCM temperatures, high-temperature chlorite generations, and the appearance of epidote and retrograde Fe-rich chlorite. Microprobe analysis on chlorite indicates incomplete re-equilibration as evidenced by various chlorite populations of individual contact metamorphic samples. This study indicates that the maturity of organic matter is the most reliable and unequivocal indicator on timescales of several thousand years to determine the lateral extension of the TPI contact aureole. Raman geothermometry reveals that the lateral extension of the contact-influenced zone expands up to a distance of 1.5 km and, thus, expands to ca. 1.1 km further out than the macroscopically mappable hornfels contact aureole. The best match between measured (Raman geothermometry) and calculated (thermal modeling) ΔTmax values (ΔT=54 ∘C) is achieved with a total intrusion assembly time of 150 kyr, a magmatic temperature of 800 ∘C, a two-batch model (batch repose time of 10 kyr) with five pulses per batch, short heating durations (3 kyr), and long pulse repose times (15 kyr).

Abstract This work deals with scarce chlorite schists scattered through the Ronda peridotites (Betic Cordilleras, Spain). These schists have unusually high zircon contents, which contrast with the usual lack of this mineral in ultramafic rocks. From field data and detailed petrographic, geochemical, and geothermometric studies, we focused on the origin of the zircon, a relevant issue for the interpretation of geochronological results. The chlorite schists appear as concordant sheets with granite dikes and as blackwall zones between dikes and serpentinized peridotites. As the intrusion age of the dikes and chlorite schist zircon crystallization (ca. 22 Ma) is slightly older than the age of serpentinization and related chlorite schist formation (ca. 19 Ma), we propose that the chlorite schists are tied to the intrusion of the granite dikes and the subsequent serpentinization of peridotites. Trace and rare earth elements alone are not indicative of the magmatic or hydrothermal origin of the zircon, but the combination of information about zircon morphology, melt inclusions, geothermometry, and the structural relationships between granite dikes and chlorite schists points to late magmatic melts for the zircon origin. We suggest that high-temperature melts saturated in F and Cl acted as Zr carriers under low-pH conditions. A change of the pH conditions, due to hydrothermal alkaline fluids incoming for the concomitant peridotite serpentinization, would have led to zircon crystallization and concentration at the apical zones of the dikes, and to rodingitization before the extensive observed chloritization.

The study of the metamorphism of Proterozoic units of the Quadrilátero Ferrífero is revisited in terms of the historical evolution and the application of the carbonate geothermometry method. Previous work indicates an eastward increase of the metamorphic grade and the relative distribuition of the chlorite, biotite, kyanite and staurolite zones. Oxygen isotope and carbonate geothermometry values corroborate previous investigations. Microprobe analysis of coexisting calcite and dolomite indicate attainment of exchange equilibrium for samples of Aguas Claras, Morro Agudo mines and Dom Bosco area. Temperatures of equilibrium obtained from calcite-dolomite pairs range from 283ºC to 547º.

ABSTRACTClay minerals and organic matter occur frequently in fault zones. Their structural characteristics and their textural evolution are driven by several formation processes: (1) reaction by metasomatism from circulating fluids; (2)in situevolution by diagenesis; and (3) neoformation due to deformation catalysis. Clay-mineral chemistry and precipitated solid organic matter may be used as indicators of fluid circulation in fault zones and to determine the maximum temperatures in these zones. In the present study, clay-mineral and organic-matter analyses of two major fault zones – the Adams-Tinui and Whakataki faults, Wairarapa, North Island, New Zealand – were investigated. The two faults analysed correspond to the soles of large imbricated thrust sheets formed during the onset of subduction beneath the North Island of New Zealand. The mineralogy of both fault zones is composed mainly of quartz, feldspars, calcite, chabazite and clay minerals such as illite-muscovite, kaolinite, chlorite and mixed-layer minerals such as chlorite-smectite and illite-smectite. The diagenesis and very-low-grade metamorphism of the sedimentary rock is determined by gradual changes of clay mineral ‘crystallinity’ (illite, chlorite, kaolinite), the use of a chlorite geothermometer and the reflectance of organic matter. It is concluded here that: (1) the established thermal grade is diagenesis; (2) tectonic strains affect the clay mineral ‘crystallinity’ in the fault zone; (3) there is a strong correlation between temperature determined by chlorite geothermometry and organic-matter reflectance; and (4) the duration and depth of burial as well as the pore-fluid chemistry are important factors affecting clay-mineral formation.

La situation géodynamique de la Basse-Terre de Guadeloupe sur l’arc des Petites Antilles marquée par un volcanisme actif, est favorable au développement de la géothermie haute-enthalpie. Ainsi, en 1986, la centrale géothermique de Bouillante a été mise en production. Le programme Geotref (plate-forme pluridisciplinaire d’innovation et de démonstration pour l’exploration et le développement de la GEOThermie haute énergie dans les REservoirs Fracturés), financé par l’ADEME dans le cadre des Investissements d’Avenir, vise à explorer les possibilités de développer la géothermie au Sud de Bouillante, dans le secteur de Vieux-Habitants. Cependant, en raison de la présence de nombreuses coulées volcano-clastiques récentes, peu d’indices de surface de la présence d’un réservoir géothermique y sont visibles. L’île de Terre-de-Haut (archipel des Saintes) est considérée comme un analogue exhumé du système géothermique de Bouillante (Verati et al., 2016) et représente une zone clef pour étudier les paléo-altérations hydrothermales. Afin de déterminer les critères pétrographiques et minéralogiques des paléo-altérations hydrothermales et aussi caractériser les paléo-fluides en termes de composition et de température, cette étude propose de coupler les approches pétrographique, minéralogique, géochimique et géothermométrique menées par diffraction des rayons X, analyses microsondes, thermométrie sur chlorite et étude d’inclusions fluides dans des quartz néoformés. Les minéraux argileux présentent une distribution concentrique à l’échelle de l’île (chlorite au centre, smectite en périphérie, et illite entre les deux). La similitude de cette zonation avec celle observée en profondeur à Bouillante, permet d’interpréter cela comme une section horizontale affichant un gradient de température latéral. La géothermométrie sur chlorite est basée sur un modèle développé pour les contextes de basse température et basse pression (T<350°C et P < 4 kbar ; Bourdelle et al., 2013). Elle a été appliquée sur les chlorites identifiées à Terre-de-Haut ainsi que sur les chlorites de Bouillante grâce aux analyses chimiques de la littérature (Mas et al., 2006). Les résultats montrent une grande différence des températures estimées entre les chlorites de Terre-de-Haut (environ 120°C) et celles de Bouillante (environ 230°C, en accord avec les températures mesurées dans les forages de Bouillantes ; Mas et al., 2006). La microthermométrie des inclusions fluides sur les quartz ont montré deux épisodes de croissances enregistrés dans le cœur du cristal et sa périphérie. Ces quartz ont cristallisé à partir de fluides de basse salinité (≤ 2% NaCl, typique des eaux météoriques) avec une température minimum de piégeage de 250-280°C dans le cœur et de moins de 70°C dans les zones de croissance externes. Ces deux évènements peuvent être interprétés comme un enregistrement du refroidissement des fluides durant l’évolution du système géothermal. Les inclusions fluides d’un second échantillon de quartz, indiquent un épisode de circulation peu profond à CO2 et basse température (≤70°C). Cette étude montre que la zonation des minéraux argileux à l’affleurement à Terre-de-Haut est similaire à celle observée dans les forages du système actif de Bouillante. Cependant, les températures estimées pour la formation de certains minéraux néoformés (chlorite notamment) indiquent que certains épisodes d’altérations se produisent à des températures plus faibles que la circulation de fluide dans le système géothermique actif de Bouillante, et pourraient représenter des témoins de la fin de vie du système géothermal de Terre-de-Haut.Les résultats de cette thèse montrent que l’étude des minéraux argileux et les données de géothermométrie sur les minéraux néoformés (chlorite et quartz), permettent par conséquent d’apporter de nouvelles contraintes dans la caractérisation du paléo-système de Terre-de-Haut et son évolution, en particulier sur la fin de vie du système géothermal
Due to its geodynamic location on the Lesser Antilles arc, Basse-Terre of Guadeloupe displays an active volcanism which is favorable to the development of geothermal energy associated to power generation. Thus, thirty years ago, the Bouillante geothermal field was brought into production and now produces 15 MWe (Bouchot et al., 2010).The Geotref program (a multidisciplinary platform for innovation and demonstration activities for the exploration and development of high geothermal energy in fractured reservoirs) funded by ADEME in the frame of “Les Investissements d’Avenir” program, aims to investigate the high enthalpy geothermal potential in the Vieux-Habitants area, located south of Bouillante. However, because of recent volcano-clastic deposits, surfaces showing the presence of a geothermal reservoir are rare. Terre-de-Haut island (Les Saintes archipelago) is considered as an exhumed analog of the deep geothermal system of Bouillante (Verati et al., 2016) which represents a key area to study the paleo-hydrothermal alterations. To characterize the paleo-hydrothermal alterations in terms of composition and temperature, and to determine the mineralogical and petrographic features of the paleo-hydrothermal alterations, we propose to couple petrographic, crystallographic, geochemical and geothermometric approaches, i.e. X-ray diffraction (XRD), microprobe analysis (EMPA), chlorite thermometry and in-quartz fluid inclusion study (FI) on selected samples. A link is also established with the petrophysical properties of the altered.The clay minerals display a specific concentric distribution at the scale of the island, with chlorite crystallization in the core, smectite in the surroundings, and illite in an intermediate halo. Considering the data obtained in boreholes in Bouillante, which show that illite and chlorite are in the deeper parts, chlorite being located in the heart of the geothermal reservoir (Bouchot et al., 2010), the clay distribution allows to identify the temperature profile. Hence, thanks to the exhumation, we are looking to a horizontal section through the paleo-system of Terre-de-Haut, where we observe a lateral temperature gradient.Chlorite geothermometry, based on a model specifically developed for low temperature contexts (T < 350°C) and pressures below 4 kbar (Bourdelle et al., 2013), has been applied on chlorites from both Terre-de-Haut paleo-system and from the active geothermal system of Bouillante. The results show a strong difference between the temperature estimates for chlorite formation on Terre-de-Haut (around 120°C) and for Bouillante (around 230°C, in agreement with the temperature measured in boreholes in Bouillante; Mas et al., 2006).Fluid inclusions microthermometry on quartz show two growth stages recorded in the crystal core and clear overgrowths. Data indicate very low salinity (≤ 2% NaCl), and a minimum trapping temperature of around 250-280°C in inclusions located in the core, and around 70°C or less in the outer growth zones. These two events can be interpreted as a record of the fluid cooling during system evolution. Moreover, fluid inclusions from a second quartz sample indicate a shallow CO2 paleo-circulation episode.This study shows that the clay mineral zonation cropping out in Terre-de-Haut is similar to that found by drilling in the active system of Bouillante. However, the temperatures of formation of some newly formed minerals (especially chlorite) indicate that some alteration episodes occurs at lower temperature than the fluid circulation occurring in Bouillante’s active geothermal system and could represent the end of life of the Terre-de-Haut geothermal system.Hence, these results show that clay minerals study and geothermometry of newly formed minerals (chlorite and quartz) are key steps to provide new thermal constrains on the paleo-geothermal reservoir of Terre-de-Haut and its evolution, particularly the end of life of the geothermal system

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The newly-discovered Oberon gold deposit, Tanami Goldfields, represents a Paleoproterozoic mesothermal orogenic gold deposit hosted in the Tanami Group. Recent drilling has intersected extensive mineralised zones at various positions within the lower stratigraphy. Studying drillhole TID0065 using a number of different techniques, the project set out to understand the lithostratigraphy of the sequence and its relationship with gold mineralisation, constraints on depositional environments and associated hydrothermal alteration, along with correlations to other deposits in the region. The sequence consists of a dolomitic mudstone, grading up into a phyllite, with a siltstone protolith. This meta-sandstone represents the main host for gold mineralisation and is similar to that seen in the Coyote deposit. Conformably overlying this unit is a rapidly-deposited well-defined turbidite sequence. Gold is also hosted in the overlying Boudin Chert unit, a graphitic, pyrite rich rock that has hosts distinctive diagenetic boudin structures. The Boudin Chert represents a transition into an anoxic sediment-starved environment. Increased clastic input along with a drop in sea level further defines the rest of the sequence, with a siltstone, mudstone and sandstone package and intercalated volcaniclastics and ignimbrites noted in the upper part of the drillhole extending into the Killi Killi Formation. Mineralisation is predominantly stratabound but thrust stacking provides a secondary control to the gold distribution pattern. Gold mineralisation is associated with Na-enrichment and K-depletion; albite is the dominant feldspar in the gold-hosting assemblage. This demonstrates a possible sodic metasomatism of an alkali assemblage. The wide variation in chlorite composition, expressed as varying proportions of chamosite and clinochlore end-members between lithologies, is suggestive of multiple fluid phases and/or alteration events, including possible „seafloor metamorphism‟ prior to hydrothermal activity. Primary alteration in the deposit is represented by an earlier chlorite-sericite assemblage and a later stage calcite-dolomite alteration in certain lithologies at the base of the sequence. Using chlorite thermometry, peak metamorphic temperatures were calculated to be at 366 ± 21 °C (i.e. greenschist facies); conditions reach amphibolite grade less than a kilometre away. Electron probe microanalysis suggests the mineralising fluids were volatile-rich, as demonstrated by the high F content of biotite and apatite. Future exploration potential for deposits of this type should focus on identification of Fe-enriched turbiditic sequences, chlorite-albite-muscovite assemblages and the presence of arsenopyrite. Graphitic oxygen-deprived beds enriched in a range of trace elements with strong pyrite alteration are also good indicators of gold mineralisation.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2011