Temperature ? composition relationships of authigenic micaceous minerals in the Los Azufres geothermal system (original) (raw)
Related papers
Cation Site Occupancy in Chlorites and Illites as a Function of Temperature
Clay Minerals, 1988
The relationships between the composition and the crystallization temperature of chlorites and illites have been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories, as the main changes in physical and chemical conditions and mineralogy are related to progressively increasing temperature with depth. Temperature was estimated from combined geothermometric approaches, and especially from fluid inclusion studies on quartz coexisting with clays. The Al(IV) content in the tetrahedral site of chlorites, and the K content and total interlayer occupancy of illites increase with temperature. These chemical changes are mainly related to the marked decrease in the molar fraction of the Si(IV)-rich end-members (kaolinite for chlorites, and pyrophyllite for illites) which become negligible at ∼300°C. Other chemical changes, such as the variation in Fe and Mg contents, are partly influence...
American Mineralogist, 2015
Oscillatory compositional zoning in minerals has been observed in hydrothermal, magmatic, and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth. Chemical zoning is a common feature of solid solutions, which has been rarely reported in phyllosilicates. In this study, oscillatory zoning in chlorite is described in samples from the Pic-dePort -Vieux thrust, a minor thrust fault associated to the major Gavarnie thrust fault zone (Central Pyrenees, Spain). The Pic-dePort -Vieux thrust sheet comprises a 1-20 m thick layer of Triassic red pelite and sandstone thrust over mylonitized Cretaceous dolomitic limestone. The thrust fault zone deformation comprises secondary faults and cleavage affecting the Triassic pelite and sandstone. An important feature responsible to this deformation is a set of veins filled by quartz and chlorite. Chlorite is present in crack-seal extension veins and in shear veins; both structures opened under the same stress conditions. In some shear veins, chlorite occurs as pseudo-uniaxial plates arranged in rosette-shaped aggregates. These aggregates appear to have developed as a result of radial growth of the chlorite platelets. Oscillatory zoning has been imaged by backscattered scanning electron microscopy and by X-ray quantitative micro-mapping. These oscillations correspond to chemical zoning with alternating iron-rich and magnesium-rich bands. The chlorite composition ranges from a Fe-rich pole to a Mg-rich pole. Fe 3+ /ΣFe values were measured in chlorite using m-XANES spot analyses and vary from 0.23 to 0.44. The highest values are in the Ferich area. Temperature maps, built from standardized microprobe X-ray images and redox state using the program XMapTools, indicate oscillatory variations from about 310 to 400 ± 50 °C during chlorite crystallization. These temperature variations are correlated with a Fe 3+ /ΣFe variation by Al 3+ Fe 3+-1 and ditrioctahedral substitutions highlighted by Mg and Fe Tot contents (Fe-Mg zoning). Chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock. It is however not excluded that kinetic effects influence the incorporation of Mg or Fe during chlorite crystallization.
Introduction to Minerals, Inclusions and Volcanic Processes
Reviews in Mineralogy and Geochemistry, 2008
Minerals are intrinsically resistant to the processes that homogenize silicate liquids-their compositions thus yield an archive of volcanic and magmatic processes that are invisible at the whole rock scale. Minerals and their inclusions record diverse magma compositions, the depths and temperatures of magma storage, the nature of open system processes, and the rates at which magmas ascend. The potential for understanding volcanic systems through minerals and their inclusions has long been recognized (Sorby 1858). Sorby's (1863) study of James Hall's reversal experiments helped resolve the "basalt controversy" in favor of a volcanic origin, while zirkel's (1863) discovery of quartz within a volcanic rock helped tip the balance in favor of a magmatic origin for granite (Young 2003). Studies of phenocrysts have also long illustrated the importance of wall rock assimilation and magma mixing (e.g., Fenner 1926; Finch and Anderson 1930; Larson et al. 1938), and the potential for geothermometry (Barth 1934). Darwin's (1844) mineralogical field-studies in the Galapagos archipelago, followed by King's (1878) studies at Hawaii, also inaugurated the establishment of fractional crystallization as an important evolutionary process (Becker 1897; Bowen 1915). Recent advances in micro-analytical techniques open a new realm of detail, building upon a long history of mineralogical research; this volume summarizes some of this progress. Our summary focuses on volcanologic and magmatic processes, but the methods reviewed here extend well beyond terrestrial applications. Samples from the Stardust return mission, for example, show that olivine, plagioclase and pyroxene pervade the solar system (Brownlee et al. 2006)-while the topics covered here surely apply to all terrestrial-like planetary bodies, relevance may extend to a cosmic scale. Our more modest hope is that this volume will aid the study of disparate fields of terrestrial igneous systems, and perhaps provide a catalyst for new collaborations and integrated studies. OVerVIeW OF the VOLuMe Our review begins by tracing the origins of mineral grains, and methods to estimate pressures (P) and temperatures (T) of crystallization. Key to such attempts is an understanding of textures, and in her review, Hammer (2008) shows how "dynamic" experiments (conducted with varying P or T), yield important insights into crystal growth. Early dynamic experiments (e.g., Lofgren et al. 1974; Walker et al. 1978) have shown that porphyritic textures can result from a single episode of cooling. More recent experiments demonstrate that crystals can form during ascent due to loss of volatiles (Hammer and Rutherford 2002). Hammer (2008) describes these and other advances, and additional challenges that require new experimental The next four chapters document insights obtained from isotopic studies and diffusion profiles. Ramos and Tepley (2008) review developments of micro-analytical isotope measurements, which now have the potential to elucidate even the most cryptic of open system behaviors. 87 Sr/ 87 Sr ratios, for example, can be matched to dissolution surfaces to identify magma recharge events (Tepley et al. 2000). And 87 Sr/ 86 Sr-contrasts within and between phenocrysts allow differentiation between the roles of wall rock assimilation and enriched mantle sources to explain elevated 87 Sr/ 86 Sr (Ramos and Reid 2005). In the next chapter, Cooper and Reid
Applied Clay Science, 2016
Two textural types of chlorite are identified in the mineralised veins at the Patricia Zn-Pb-Ag epithermal ore deposit (NE, Chile): massive and oscillatory-zoned radiated chlorites. Three main stages of mineralisation have been defined in the Patricia deposit: (1) pre-ore stage, (2) base-metal stage which is divided into two substages: substage 2a and substage 2b and (3) post-ore stage. Both types of chlorite are classified as chamosite and occur coeval to the sphalerite precipitation during the substage 2a. Massive chlorite shows an average content of 33 wt.% FeO, 4.9 wt.% MnO, and 4 wt.% MgO. Oscillatory zoning in radiated chlorites consists of concentric bands with different contents on FeO (from 26.45 to 41.41 wt.%), MgO (from 1.7 to 5.44 wt.%) and MnO (from 1.7 to 9.32 wt.%). Four different chlorite geothermometers based on the system SiO 2-Al 2 O 3-FeO-MgO-H 2 O were applied to both types of chlorites. The temperature estimations are in agreement with temperatures data of fluid inclusions previously measured in sphalerite of the sub-stage 2a. Despite the high content in Mn of chlorites, the study confirms the applicability of the chlorite geothermometers without the knowledge of the Fe 3+/ Fe ratio in low-pressure paragenesis and its usefulness as an important tool for characterising the thermal conditions in epithermal ore deposits.
Clays and Clay Minerals, 2004
Crystallization processes of the illite-smectite (I-S) mixed-layer mineral series during alteration of felsic vitric materials in volcaniclastic sediments through two drill holes (IT-2 and IT-8) near the Kakkonda active geothermal system, Japan, were examined by optical microscopy, scanning and transmission electron microscopy (SEM and TEM), electron microprobe analysis, X-ray diffraction (XRD), and oxygen isotope analysis. Temperatures measured through the drill holes increased nearly linearly with depth up to 317ºC at the bottom (1700 m) of IT-8. Homogenization temperature measurements of fluid inclusions indicated that the alteration occurred at temperatures similar to the present temperatures. In selected volcaniclastic rocks, excluding andesitic rocks and black shales, clay minerals occurred as glass replacements and pore fillings as seen under SEM and optical microscopy, and exhibited predominantly euhedral hexagonal and elongated forms under TEM, implying that they precipitated in situ through hydrolytic reactions of glass and fluid. Based on XRD examination, I-S minerals showed a sigmoidal variation in illite layer percentage (%I) in the range of~150 to 220ºC and R0 I-S minerals with intermediate %I between 20 and 40% rarely occurred (where R is the Reichweite parameter). The chemical composition also showed a specific variation with depth. Intermediate clays including smectite and I-S minerals are enriched in Al compared to those reported previously from hydrothermal alteration of almost equivalent parent rocks. The oxygen isotope data indicated that the reacting solution was percolating groundwater in the shallow levels and with fossil seawater in the deeper levels. Furthermore, calculating the fluid/rock (W/R) ratio from the isotope variations revealed that the alteration occurred at a nearly constant W/R ratio condition irrespective of %I. Consequently, the observed specific variations in structure and chemical composition of I-S minerals reflect the compositional variations of fluid participating in the crystallization at given temperatures under the conditions of a given original rock and constant W/R ratio. High pH and Na-rich solutions generated by progressive hydrolytic reactions between felsic glass and groundwater favored the precipitation of Al-rich smectite up to~150ºC and was followed by precipitation of an aluminous R1 I-S mineral with few intermediate R0 I-S minerals at higher temperatures. The crystallization obeys Ostwald's step rule behavior of smectite illitization processes under a high geothermal gradient.
Chemical variations of mineral inclusions -main
This paper details the mode of occurrence, petrography, and chemistry of mineral inclusions hosted in chromian spinels of the Neoproterozoic chromitites in the Southern Eastern Desert of Egypt. Neoproterozoic podiform chromitites from the Arais, Balamhindit, and Abu Dahr areas, in the Southern Eastern Desert, can be texturally and chemically classified into two main types: primary high-Al (spinel Cr# b 0.67) and high-Cr (spinel Cr# N 0.75) chromitites. The former, being free of primary-mineral inclusions, was crystallized mainly from the MORB-like tholeiitic melt generated during proto-forearc spreading at the initiation of subduction, whereas the latter was formed from boninitic melts resulting from the high-degree melting of the sub-arc depleted mantle in the presence of slab-derived fluids at a mature-arc stage. The primary mineral inclusions, such as Na-and Kphlogopites, pargasite-edenite and olivine with subordinate pyroxenes, millerite, and laurite, were trapped within the chromian spinel during the magmatic precipitation of the chromitites. The Abu Dahr chromitites are free of primary hydrous inclusions; on the other hand, Arais and Balamhindit high-Cr chromitites are enriched in Na-and K-phlogopites, respectively, as a result of a difference in the K/Na ratio of the magma responsible for chromitite crystallization at different mantle depths. This difference in the K/Na ratio can possibly be attributed to fractionation of the upward-migrating hydrous fluids/melts by the crystallization of K-or Na-rich minerals. The Balamhindit complex, where the chromitite showed K-phlogopite inclusions within the chromian spinel, was probably derived from a deeper part of the mantle than the other areas, where the chromitite shows inclusions of Na-rich hydrous phases. Both K-and Na-phlogopites were possibly formed from alkali-rich hydrous fluids/melts trapped within the chromian spinels during the chromitite formation at different mantle depths, where the K/Na ratio decreases upward through the incorporation of Na from the peridotite wall-rock, combined with the precipitation of K-rich phases at deeper depths. The chemistry of both primary mineral inclusions and chromian spinels suggests an arc-related tectonic setting for our chromitites that were crystallized at 1000°C
Applied Clay Science, 2016
In this research, we have investigated the illitization process in Quaternary calc-alkaline volcanic and volcaniclastic rocks in the active Tinguiririca geothermal field (Andean Cordillera, central Chile). XRD, SEM, and HRTEM/AEM techniques have been used to establish the illitization sequence and evaluate the influence of the factors controlling the mineral reaction and kinetics at low temperature (T). Analysed samples were collected through a slimhole core up to 815 m deep in which the T was measured in situ (up to 230°C at the bottom of the drill core). Textural information indicates that the dioctahedral clays have replaced most of the vitreous components. In contrast, plagioclase phenocrysts have only been partially and patchily albitized. The observed replacements imply dissolution-crystallization processes. The illitization sequence detected by XRD is apparently continuous from smectite to R3 IS through R0 and R1, with a progressive increase in illite layers. HRTEM data show a similar illitization trend. However, the high-resolution images reveal that the clays are more heterogeneous than the XRD patterns suggest, with the coexistence of different types of dioctahedral clays at the sample level. They also indicate that the most abundant dioctahedral clays are smectite, R1 IS , and illite. Therefore, the XRD patterns are probably the result of a mixture of these phases plus accessory IS mixed layers with higher ordering (R N 1). Increasing T with depth would enhance the kinetic conditions necessary for illitization and also favour the dissolution of the vitreous K-rich component and, locally the albitization of plagioclases. Both processes release K, which, with the concomitant increase in T and K availability, enhances the crystallization of clays progressively richer in K. Thus, at T ≤ 85°C smectite crystallizes, at T N 85°C the conditions are appropriate for the crystallization of R1 IS (with minor smectite + R0 IS), up to T ≥ 175°C, where illite is the most abundant and relatively stable phase.
Clay science, 2006
The transformations induced on argillaceous materials under thermal stress and the impact on their confining properties is a critical parameter, for example, in the nuclear waste storage. The samples were collected close to a basaltic intrusion in an argillaceous formation (argillites of Laumiere, Aveyron, France), which represents a natural analogue of thermal stress. The clay minerals characterization was conducted by the association of X ray diffractometry (XRD) and far infrared spectrometry (FIR) that allow to show an illitization of the highly illitic IS minerals at basalt contact. The illitization is a phenomenon primarily dominated by the thermal influence. The weak and nonmonotonous variation of IS crystallinity indexes corresponds to the influence of the geological context. The illitization is not monotonous because of superimposed processes. Those phenomena that had disturbed the heat transfer and the illitization are related to the geological context. Firstly, hydrothermalism was developing through the network of cracks. The high water/rock ratio had induced the basaltic chemical species transfers. Secondly, the presence of sedimentary heterogeneities as a limestone deposit had constraining the uniform dissipation of the heat. Laumiere study highlighted critical parameters that have influenced the evolution of argillaceous materials in thermal context.
Journal of Volcanology and Geothermal Research, 1996
Detailed X-ray diffraction of clay minerals from the less than 0.2 11m fraction of altered rocks has been carried out On cuttings and cores from three boreholes (CH7, CH9 and CH7B) from the geothennal field of Chipilapa (El Salvador, Central America). In most of the low-permeable horizons, the vertical distribution of l/S and CIS mixed-layers fairly agrees with the general scheme of di-smectite to illite and tri-smectite to chlorite conversion series with increasing depth (max. 2600 m) and temperature (max. 220°C). The deepest parts of the wells are characterized by chlorite and illite-rich illite/smectite mixed-layers (l/S R 2: 1) in close agreement with the measured temperature (170-220°C). Within fracture-controlled permeable horizons, the distribution of clay minerals strongly disagrees with the "classical pattern" of di-smectite to illite and tri-smectite to chlorite conversions observed in low-permeable horizons. Great amounts of smectites and/or smectite-rich mixed-layers occur at temperatures which strongly exceed the current range of smectite stability in natural systems (up to 205°C). Similar discrepancies may also be viewed from chlorite crystallinity in well CH9 and smectite content in smectite-rich chlorite/smectite mixed-layers in well CH7B. These high-temperature smectites are considered as present or very recent metastable phases representing the first step of kinetically controlled conversion series toward illite and/or chlorite. Such phenomena are restricted to the levels in which the present hydrodynamic conditions promote the crystallization process: boiling and mixing of fluids with contrasting temperatures. High-temperature smectites and smectite-rich mixed-layers may be of great interest for the understanding of the very recent evolution of geothermal reservoirs. They do not only indicate the present horizons of active fluid circulations in geothermal wells (smectite coatings at the wall of fractures), but they are also potential guides in the determination of the horizons in which permeability has recently decreased.