Mixed-layer Chlorite-smectite Research Articles

Clay Mineral Assemblages in the Cretaceous Volcanogenic–Sedimentary Rocks of the North-Western Part of the Transition Zone from the Asian Continent to the Pacific Ocean

In this study, clay and non-clay minerals in the cement of Cretaceous volcanogenic–sedimentary rocks from the bottom of the marginal seas of the north-western Pacific Ocean and adjacent areas were studied. Corrensite and mixed-layer chlorite–smectite, rectorite and mixed-layer illite–smectite, chlorite, swelling chlorite (?), illite, kaolinite, smectite (?), calcite, ankerite, barite, gypsum, epsomite, zeolites (laumontite, analcime, and stilbite), cristobalite, and quartz were determined. The following are the indicative properties: (a) minerals: corrensite and rectorite; (b) associations: corrensite–chlorite, corrensite–chlorite–laumontite, corrensite–epsomite–authigenic calcite, and quartz–illite. Such minerals indicate that the thickness of the accumulated sediments in the studied basins could reach three to five kilometers and that the temperature of their formation could be higher than 150 °C. Transformations in the process of diagenesis and epigenesis occur in two directions: smectite–rectorite–mica, with an excess of potassium, and smectite–corrensite–chlorite, with an excess of magnesium. The chlorite–corrensite association may indicate conditions favorable for seawater evaporation, and the presence of laumontite in the corrensite–chlorite association suggests a periodic supply of calcium to the sedimentation basin. The illite–kaolinite association is probably associated with coal accumulation in epicontinental conditions and a warm humid climate in nearby areas. Periods of sedimentation, possibly associated with global climate events, were identified: 113–120, 110–113, 105–110, 93–95, 72–83 and 61–72 Ma. The established time intervals and mineral associations can serve as benchmarks for stratigraphic constructions in reconstructing the physicochemical, climatic parameters, and conditions of Cretaceous volcanogenic–sedimentary strata accumulation.

Geochemical and mineralogical evidence of an offset in the Andean arc recorded in the Upper Cretaceous marine deposits of the Austral-Magallanes basin, Argentina

The Austral-Magallanes Basin covers the southernmost region of Patagonia, South America. South of Lago Argentino, the Calafate Formation documents part of the foreland stage of the evolution of this basin. Here, sandstones from the Calafate Formation were characterized using petrographical, X-ray diffraction (XRD) and geochemical data in order to establish their tectonic setting and sediment source areas. Based on our results, three intervals (lower, middle, and upper) were distinguished according to their composition. The lower and upper intervals are composed of felsic volcanic lithics, abundant quartz and orthoclase. A shift in the composition was observed in the middle interval, with an increase in the modal abundance of plagioclase as well as other accessory minerals such as pyroxene. In addition, XRD data reveal that the middle interval is dominated by smectite in the clay-fraction, whereas the lower and upper intervals present mixed-layer chlorite-smectite and chlorite assemblages. Similar differences are observed using major and trace elements: data from the lower and upper intervals point to source rocks of intermediate to acid composition, while the middle interval had source rocks of intermediate composition and a lower degree of weathering. With regard to the provenance studies, the three intervals have a strong affinity to intermediate compositions of the Tobífera Formation (El Quemado Complex) and with the diorite/andesite of the Patagonian Batholith, which implies an exclusive contribution from the western edge of the basin. However, the shift in the composition towards the middle interval indicates a sediment supply from the juvenile Andean arc, suggesting contemporaneous magmatic activity during the deposition of the Calafate Formation sandstones. This peak of magmatic activity may have been caused by an eastward migration of the arc, driven by a switch in the tectonic setting south of 48°S.

Clay Minerals in Sediments from the Central Part of the Guaymas Basin, the Gulf of California, Hole 478

The clay minerals in the Upper Pleistocene sediments from DSDP Hole 478 (a drilled depth of 464 m) located in the central area of the Guaymas Basin, Gulf of California, are studied. The composition of the clay minerals and their quantitative proportions in natural mixtures are determined by modeling of X-ray diffraction patterns for oriented specimens of finely dispersed particles. The terrigenous clay minerals are mainly dioctahedral (mixed-layer smectite–illite is dominant, the amount of illite is smaller) with admixtures of chlorite and kaolinite. They are distributed throughout the entire sedimentary section, except for thermally altered sediments from the contact zones with the top of the sills, where terrigenous dioctahedral clay minerals disappear, except for illite, and are substituted by trioctahedral mixed-layer chlorite–smectite and corrensite–chlorite; trioctahedral smectite also appears. Terrigenous illite is missing in the sediments at the base of the sedimentary cover exposed by the hole, on the top of the sill complex with a thickness of no less than 125 m.

Clay minerals in sediments from contact zones with basalt sills

Clay minerals (fraction <0.001 mm) of Upper Pleistocene clayey-sandy-silty sediments recovered by DSDP Holes 481 and 481A in the Northern Trough, Guaymas Basin, Gulf of California, were studied by X-ray based on the modeling of diffraction patterns and their comparison with experimental diffractograms. Terrigenous clay minerals are represented mainly by dioctahedral micaceous varieties (mixed-layer disordered illite-smectites, illite) with the chlorite admixture and by kaolinite in the upper section of unaltered sediments. Intrusion of hot basalt sills (total thickness of the complex is about 27 m) provoked alterations in the phase composition of clay minerals in sediments (7.5 m thick) overlying the sill complex. These sediments include newly formed triooctahedral layered silicates (mixed-layer chlorite-smectites, smectite). Sediments inside the sill complex include trioctahedral mixed-layer mica-smtctite-vermiculite or trioctahedral smectite. The trioctahedral mixed-layer chlorite-smectite coexisting with smectite was found in a single sample of the same complex.

Clay Minerals in Sediments from Contact Zones with Basalt Sills

Clay minerals (fraction <0.001 mm) of Upper Pleistocene clayey–sandy–silty sediments recovered by DSDP Holes 481 and 481A in the Northern Trough, Guaymas Basin, Gulf of California, were studied by X-ray methods based on the modeling of diffraction patterns and their comparison with experimental diffractograms. Terrigenous clay minerals are represented mainly by dioctahedral micaceous varieties (mixed-layer disordered illite–smectites, illite) with the chlorite admixture and by kaolinite in the upper section of unaltered sediments. Intrusion of hot basalt sills (total thickness of the complex is about 27 m) provoked alterations in the phase composition of clay minerals in sediments (7.5 m thick) overlying the sill complex. These sediments include newly formed trioctahedral layered silicates (mixed-layer chlorite–smectites, smectite). Sediments inside the sill complex include trioctahedral mixed-layer mica–smectite–vermiculite or trioctahedral smectite. The trioctahedral mixed-layer chlorite–smectite coexisting with smectite was found in a single sample of the same complex.

Reservoir descriptions of the K\xf6m\xfcrl\xfc and Penek Formations near Erzurum, East Anatolia, Turkey

In the work presented here, core and cutting samples from a single well were studied with the aim of understanding the diagenesis and reservoir properties of the Kömürlü and Penek Formation sandstones in the Aşkale sub-basin in East Anatolia. Based on petrological and hydrocarbon saturation analyses [attenuated total reflectance-Fourier-transform infrared spectroscopy] of the samples, we discuss the relationships between diagenetic alterations and reservoir quality. The diagenetic alterations include quartz, feldspar overgrowth, calcite, smectite, chlorite, mixed-layer illite–smectite, mixed-layer chlorite–smectite, illite, kaolinite, and pyrite. After the diagenetic mineral phases formed, secondary porosity formed via dissolution of late carbonate cement in these sandstones. Diagenesis in the Kömürlü and Penek Formation sandstones commonly destroyed much of the original intergranular porosity, dissolved grains, and produced clay-filled pores. The pore throats typically range in size from 1 to 5 µm and represent only a small portion of the total porosity. This study is the first attempt to make petrophysical data available from the well logs of the reservoir sandstones (Kömürlü and Penek Formations) in the Aşkale sub-basin of the East Anatolia Basin. The results of this study will clarify the characterization of the reservoir sandstones.

Clay minerals in sediments of the hydrothermally active southern trough in the Guaymas Basin (Gulf of California)

The results of the study of clay mineral alterations in Upper Pleistocene sediments of the southern trough in the Guaymas Basin (Gulf of California) due to the influence of hydrothermal solutions and heat produced by sill intrusions are discussed. Core samples from DSDP Holes 477 and 477A were taken for the analysis of clay minerals. Application of the method of modeling X-ray diffraction patterns of oriented specimens of the finely dispersed particles made it possible to establish the phase composition of clay minerals, determine their structural parameters, and obtain reliable quantitative estimates of their contents in natural mixtures. The modeling data allowed us to characterize reliably the transformation of clay minerals in sediments of the hydrothermally active southern trough in the Guaymas Basin. In Upper Pleistocene sandy–clayey sediments of the southern trough, changes in the composition of clay minerals occurred under the influence of a long-living hydrothermal system. Its lower part (interval 170.0–257.5 m) with maximum temperatures (~300°C) was marked by the formation of chlorite. Terrigenous clay minerals are not preserved here. Saponite appears at a depth of 248 m in the chlorite formation zone. Higher in the sedimentary section, the interval 146–170 m is also barren of terrigenous clay minerals. Sediments of this interval yielded two newly formed clay minerals (chlorite and illite), which were formed at lower temperatures (above 180°C and below 300°C, approximately up to ~250°C), while the relatively low-temperature upper part (110–146 m) of the hydrothermal system (from ~140°C to ~180°C) includes the mixture of terrigenous and newly formed clay minerals. Terrigenous illite is preserved here. Illitization of the mixed-layer illite–smectite was subjected to illitization. The terrigenous montmorillonite disappeared, and chlorite–smectite with 5–10% of smectite layers were formed. In the upper interval (down to approximately 110 mbsf), the composition of terrigenous clay minerals remains unchanged. They are composed of the predominant mixed-layer illite–smectite and montmorillonite, the subordinate illite, mixed-layer chlorite–smectite with 5% of smectite layers, mixed-layer kaolinite–smectite with 30% of smectite layers, and kaolinite. This composition of clay minerals changed under the influence of sill intrusions into the sedimentary cover at 58–105 m in the section of Hole 477. The most significant changes are noted in the 8-m-thick member above the sill at 50–58 m. The upper part of this interval is barren of the terrigenous mixed-layer illite–smectite, which is replaced by the newly formed trioctahedral smectite (saponite). At the same time, the terrigenous dioctahedral smectite (montmorillonite) is preserved. The composition of terrigenous clay minerals remains unchanged at the top of the unit underlying the sill base.

Mineral reactions associated with hydrocarbon paleomigration in the Huincul High, Neuquén Basin, Argentina

Bleaching of red beds by the migration of reducing pore fluids is a widespread phenomenon, with most previous work on the topic focused on detailed studies in the southwestern United States, and to a lesser extent Germany. Herein, we report on widespread bleaching of Cretaceous red beds in the Neuquen Basin and the relationship of this bleaching to hydrocarbon migration. In the Cerro Granito area of the Huincul High, Neuquen Basin, the basal deposits of the Neuquen Group (Candeleros and Huincul Formations) are bleached. This alteration was apparently controlled by fluid and host-rock composition as well as by the intensity and span of the fluid-rock interaction. Red, fine-grained sandstones and mudstones of the Candeleros Formation were deposited in fluvial and swamp environments and contain authigenic hematite, Na-rich corrensite, micro- and mesoquartz, calcite, and analcite. Coarse-grained sandstones and mudstones of the Huincul Formation, which overlie the Candeleros Formation, were deposited in a braided fluvial system, under more humid and acidic conditions than the Candeleros Formation. Sandstones are similar in composition and texture to the Candeleros sandstones, except they contain less basic volcanic detritus and lack corrensite. Bleached facies in both formations contain bitumen and clusters of calcite + bitumen concretions, and partially dissolved detrital clasts and most cements, including early Fe-oxides, which resulted in an increase in secondary porosity and bleaching of the red beds. Alteration of the Candeleros Formation is confined to medium- to coarse-grained sandstone in which corrensite is partially dissolved and its interlayer charge is satisfied by Ca instead of Na, as in corrensite from the red sandstones. Extensive dissolution occurred in the Huincul Formation, which favored the precipitation of new authigenic minerals such as smectite, mixed-layer chlorite-smectite, and pyrite. Bleaching and associated alteration most likely resulted from interaction of hydrocarbons with the red beds. Hydrocarbon paleomigration in the Cerro Granito area occurred in higher-permeability portions of the Candeleros and Huincul Formations. The seal provided by the Lisandro Formation was breached during uplift driven by Tertiary tectonism, resulting in the exhumation of the Huincul and Candeleros Formations. This study highlights the importance of a variety of alterations, including complex clay mineral paragenesis, contemporaneous with bleaching of the red beds. Such alterations can potentially be used to provide evidence for the passage of chemically reducing fluids associated with hydrocarbons in other regions, including cases where the original red color has been completely removed.

An Integrated Methodological Approach for Source-Clay Determination of Ancient Ceramics: The Case of Aegina Island, Greece

AbstractA new model is proposed for analysis of the source clays used to create ceramics, based on geographic, petrographic, mineralogical, mineral-chemistry, and geochemical criteria. The development of this model became feasible after the discovery of a Pliocene volcanic clay horizon on NWAegina Island, Greece. The volcanic clay contains smectite, mixed-layer chlorite-smectite, biotite, and palygorskite and has greater feldspar content than the underlying Pliocene marls, which contain R0 mixed-layer illitesmectite, mica, dolomite, serpentine, talc and gypsum, and, in some places, palygorskite. The two units have distinct geochemical characteristics. In general the Pliocene volcanic clay is richer in SiO2, Al3O3, and Fe2O3 and poorer in Na2O, MgO, and P2O2 than the Pliocene marls. The Nb, Zr, Hf, Th, and rare earth element (REE) contents are also significantly greater in the Pliocene volcanic clay and comparable to those of the dacitic rocks of the island, reflecting the volcanic origin of the clay.The proposed model was used to identify the source-clay materials that were used for the production of ceramics on the island of Aegina (Aeginetan Ware). All five criteria should be considered in any provenance study. The use of individual criteria on their own can lead to ambiguous conclusions. In the present study the geochemical criterion was particularly helpful. It provided robust evidence for the nature of the source clay. The Pliocene volcanic clay horizon and the underlying Pliocene marls are the candidate raw materials for Aeginetan Ware. Although the Pliocene marls have been invoked as raw materials for Greek Bronze Age (~3000–1100 BC) Aeginetan ceramics and are used as raw materials by modern Aeginetan ceramists, the geochemical characteristics of a large set of Bronze Age Greek Aeginetan sherds with fine and coarse fabrics coincide with those of the Pliocene volcanic clay. This comparative and cumulative evidence suggests that the Pliocene volcanic clay was the main source clay for ancient Aeginetan ceramics, regardless of the fabric (coarse or fine) and that admixture of different sources might not be necessary for fine-grained ceramics.

Genesis and Classification of Soils in Segzi Plain (Iran)

A study was carried out to investigate the genesis and classification of soils in Segzi plain in the eastern of Isfahan province (center of Iran). Due to its specific geographic condition, Iran is located in the dry and semidry climatic zone. Aridisols are soils of the aridic moisture regime which occur normally in arid climates. For this study, a sum of 15 profiles was studied. Soil colors were defined using the Munsell soil color chart. Electrical conductivity, soil reaction, organic matter (OM) and the percentage of gypsum and calcium carbonate were measured. Mineralogical properties of the soils were analysed. The evidence provided by this experiment indicated that most of the soils were classified as Gypsic Aquisalids sub groups according to the Soil Taxonomy and as in Hypersalic Solonchaks soil units according to WRB classification systems. According to micromorphological analysis the studied soils have clay coatings (clay film), calcite infillings and gypsic infillings in selected soil profiles. Mineralogical properties showed that there were Mica, Palygorskite, Smectite, Vermiculite, Chlorite, Kaolinite, irregular mixed layer Mica-Smectite mineral, irregular mixed layer Chlorite-Vermiculite mineral, irregular mixed layer Chlorite-Smectite mineral and Quartz in the soils of Segzi plain.

Mineralogical Evolution of a Claystone After Reaction With Iron Under Thermal Gradient

AbstractThe design of the repository for high-level nuclear waste (HLW) in France consists of a multiple-barrier system including steel canisters in a clay host rock. The system will undergo temperature variations in time and space, the heat source being the HLW within the canisters. The effect of a thermal gradient in space on the Fe-claystone interaction was investigated here by applying a thermal gradient (150–300°C and 80–150°C) to a mix of claystone, Fe, and an aqueous chloride solution over periods of 3 and 6 months. Following the reaction, the starting clay minerals (mostly illite and mixed-layer illite-smectite) evolved toward chlorite, Fe-serpentine, Fe-saponite, mixed-layer chlorite-smectite, or mixed-layer serpentine-smectite as a function of temperature. Iron corrosion made the medium basic and reductive. Magnesium enrichment of clay minerals was observed in the hottest part of the experiment due to Mg migration under the thermal gradient. Reaction progress was enhanced at the lowest temperatures, compared to batch experiments.

Low-Temperature Hydrothermal Metamorphic Mineralization of Island-Arc Volcanics, South Apuseni Mountains, Romania

AbstractThe island-arc volcanics situated in the eastern part of the Căpîlnaş-Techereu nappe (South Apuseni Mountains, Romania) were studied to evaluate the temperature, fluid properties, and mineral chemistry during low-temperature metamorphism. Detailed observations of metamorphic mineral assemblages were conducted using powder X-ray diffraction and electron microprobe. The metamorphism involved albitization of plagioclase feldspar and the formation of mafic phyllosilicates, zeolites, and other hydrous Ca-Al-silicate minerals. Mafic phyllosilicates consisted of transitional dioctahedral-trioctahedral smectites, mixed-layer chlorite-smectite (C/S, 6–96% chlorite), and discrete chlorite. The zeolites were analcime, stilbite ± stellerite, heulandite, laumontite, epistilbite, and mordenite. Also present, as secondary minerals filling amygdales and veins, are prehnite, pumpellyite, and secondary amphibole. Two mineral assemblages were identified which provide important information about metamorphic conditions (temperature, reaction progress, and fluid properties): (1) heulandite + analcime + quartz; and (2) laumontite + albite + quartz + prehnite + pumpellyite ± amphibole. The types of and relations between minerals in the first assemblage suggest the occurrence of low-temperature hydrothermal metamorphism in the zeolite facies at ~125°C, whereas the second assemblage was metamorphosed at 200°C. The composition and variability of the mineral assemblages in the study area suggest that, due to slow reaction rates, the low-temperature transformations and mineral assemblages were influenced not only by temperature but also by local rock composition, fluid-rock ratio, and fluid chemistry.

Illitization of Early Paleozoic K-Bentonites in the Baltic Basin: Decoupling of Burial- and Fluid-Driven Processes

AbstractThe mineralogical characteristics of Ordovician and Silurian K-bentonites in the Baltic Basin were investigated in order to understand better the diagenetic development of these sediments and to link illitization with the tectonothermal evolution of the Basin. The driving mechanisms of illitization in the Baltic Basin are still not fully understood. The organic material thermal alteration indices are in conflict with the illite content in mixed-layer minerals. The clay fraction of the bentonites is mainly characterized by mixed-layered illite-smectite and kaolinite except in the Upper Ordovician Katian K-bentonites where mixed-layer chlorite-smectite (corrensite) occurs. The variation in expandability plus other geological data suggest that the illitization of Ordovician and Silurian K-bentonites in the Baltic Basin was controlled by a combination of burial and fluid driven processes. The illitization in the south and southwest sectors of the basin was effected mainly by burial processes. The influence of the burial process decreases with decreasing maximum burial towards the central part of the basin. The advanced illitization of the shallowburied succession in the north and northwest sectors of the basin was enhanced by the prolonged flushing of K-rich fluids in relation to the latest phase of development of the Scandinavian Caledonides ≈420–400 Ma.

Clay alteration of volcaniclastic material in a submarine geothermal system, Bay of Plenty, New Zealand

The Calypso Hydrothermal Vent Field (CHVF) is located along an offshore extension of the Taupo Volcanic Zone (TVZ), an area of abundant volcanism and geothermal activity on the North Island of New Zealand. The field occurs within a northeast-trending submarine depression on the continental shelf approximately 10–15 km southwest of the White Island volcano in the Bay of Plenty. The graben has been partially filled by tephra from regional subaerial volcanic eruptions, and active hydrothermal venting occurs at several locations along its length. The vents occur at water depths of 160 to 190 m and have temperatures up to 201 °C. Recovered samples from the vent field include variably cemented and veined volcaniclastic sediments containing an assemblage of clay minerals, amorphous silica, barite, As–Sb–Hg sulfides, and abundant native sulfur. The volcanic glass has been altered primarily to montmorillonite and mixed-layer illite–montmorillonite; illite, and possibly minor talc and mixed-layer chlorite–smectite or chlorite–vermiculite are also present. A hydrothermal versus diagenetic origin for the smectite is indicated by the presence of both illite and mixed-layer clays and by the correlation between the abundance of clay minerals and the abundance of native sulfur in the samples. The mineralization and alteration of the volcanic host rocks are similar to that observed in near-neutral pH geothermal systems on land in the TVZ (e.g., Broadlands–Ohaaki). However, the clay minerals in the CHVF have a higher concentration of Mg in the dioctahedral layer and a higher interlayer Na content than clay minerals from Broadlands–Ohaaki, reflecting the higher concentrations of Mg and Na in seawater compared to meteoric water. Minerals formed at very low pH (e.g., kaolinite and alunite), typical of steam-heated acid-sulfate type alteration in the TVZ geothermal environment, were not found. Mixing with seawater likely prevented the formation of such low-pH mineral assemblages. The occurrence of illite and mixed-layer illite–smectite close to the seafloor in the CHVF, rather than at depth as in the Broadlands system, is interpreted to reflect the higher pressures associated with submarine venting. This allows hotter fluids to be discharged before they boil, and thus minerals that are encountered mainly at depth in subaerial geothermal systems can form close to the seafloor.

Metamorfismo de facies prehnita-pumpellyita en la franja oriental de la Formacion Abanico, Cordillera de los Andes de Chile central (33°50'S): controles qumicos y de escala sobre las asociaciones minerales, el progreso de la reaccion y el estado de equili

In the El Volcan and Rodeo de los Bueyes areas, Andean Principal Cordillera (east of Santiago; 33o50'S), an Upper Oligocene-Lower Miocene volcanic series belonging to the Abanico Formation (Late Eocene-Early Miocene) is exposed. The rock successions outcropping in both areas, ca. 3,300 m total thickness, have been affected by very low-grade, non-deformative metamorphism in the prehnite-pumpellyite facies. This is represented by the widespread development of secondary mineral assemblages composed of epidote, mixed-layer chlorite-smectite, albite, quartz, white mica, and titanite. These mineral assemblages also contain pumpellyite, prehnite or prehnite+actinolite in a few samples. Chemical characteristics, such as low compositional variability of mixed-layer chlorite-smectite and actino- lite independent from the metadomain where these phases are hosted, along with a high proportion of chlorite layers in the former, suggest that these phases closely represent the whole rock effective bulk composition. On the contrary, pumpellyite compositions show a higher variability and a strong metadomain control evidencing its lower equilibration kinetics and leaving only those that grow in the rock matrix as the more closely representative of a whole rock effective bulk compositional control. Mineral assemblages from both areas show evidence of having been formed during the same metamorphic event where reactions have ocurred equivalently between them. However, local differences in chemical variables controlling this process are recognizable. A higher CO 2 concentration in the fluids during the metamorphism in the El Volcan area than in the Rodeo de los Bueyes area is suggested by the scarce development of prehnite and the ubiquitous presence of calcite in the metamorphic assemblages of the former. Pressure and temperature of this meta- morphic event have been roughly estimated to be lower than 2-3 kbar and 320oC, respectively.

Lithology and mineralogy of the Permo-Triassic raw materials used in the tile industry of Castellón (Spain): the Moró clay

The aim of this work is to establish the mineralogical (XRD) composition of the Permo-Triassic claystone known as Moro clay. Particular emphasis is placed on the compositional variations along the litostratigraphic section. Bulk rock XRD analysis shows a homogeneous composition dominated by quartz, phyllosilicates and hematite. Minor components (< 5%) include potassium feldspar, dolomite and calcite. The clay minerals assemblage is formed by illite +/- kaolin +/- chlorite +/- mixed-layer +/- illite-smectite +/- mixed-layer chlorite-smectite and reveals a sedimentary distribution pattern. The study of the lithological section allows the identification and valuation of changes in the mineralogical characteristics of the raw material. Results provide evidence for the importance of mineralogical analysis in the control of raw materials and hence their use in industrial processes.

Regional very low-grade metamorphism of basaltic lavas, Disko–Nuussuaq region, West Greenland

The thick Paleocene basaltic lava succession exposed on Disko Island and Nuussuaq Peninsula, central West Greenland, experienced regional metamorphism shortly after volcanism followed by several events of localized hydrothermal alteration. Regional metamorphism resulted in well-developed lower zeolite facies mineral assemblages consisting primarily of mafic phyllosilicates and zeolites. In the upper Paleocene lava formation, the Maligât Formation, alteration is dominated by early mixed dioctahedral–trioctahedral smectite followed by chabazite and thomsonite. This same assemblage persists into the upper portions of the underlying Vaigat Formation. Within the Vaigat Formation, the chabazite–thomsonite assemblage is replaced at depth by an assemblage dominated by mafic phyllosilicates followed by thomsonite + chabazite + analcime + natrolite + gonnardite. Mafic phyllosilicate compositions within the latter zone become systematically more rich in the trioctahedral component with depth; the highest-grade mafic phyllosilicates consist of purely trioctahedral, mixed-layer chlorite–smectite. The mineral assemblage developed in the Vaigat Formation is distinct from similar grade assemblages formed in most large igneous provinces as a consequence of the unusually olivine-rich lava compositions that dominate this formation. The zeolites developed in the Vaigat Formation tend to be more Na-rich and somewhat Si-depleted relative to those that form in feldspar-phyric lavas such as the Maligât Formation. Late hydrothermal alteration led to a wide variety of low-grade metamorphic mineral assemblages largely confined to mineralized veins and their immediate surroundings. The distribution of regional alteration assemblages on Disko and Nuussuaq suggests relatively low geothermal gradients (< 45 °C/km) during metamorphism. The highest regional metamorphic grades occur at the base of the exposed succession on northern Disko, suggesting uplift of this area relative to the rest of the island, consistent with recent seismic data.

Chloritization of Late Ordovician K-bentonites from the northern Baltic Palaeobasin–influence from source material or diagenetic environment?

The Baltic Ordovician–Silurian sedimentary succession embodies numerous altered volcanic ash beds that are illite–smectite dominated. Only a few beds rich in chlorite–smectite are known from the Upper Ordovician Pirgu Stage of Estonia. Mixed-layer chlorite–smectite occurs commonly in low-grade metamorphic and hydrothermal environments. However, chloritic K-bentonites of the Pirgu Stage have never been buried deeply and lack signs of metamorphic overprinting. In order to understand the origin of chloritization, three distinct beds were sampled in 14 drillcores from Estonia and Latvia and analysed by means of XRD and SEM. The principal authigenic assemblage of the bulk samples consists of chlorite–smectite (corrensite) together with illite–smectite and K-feldspar. The actual mineral composition of K-bentonites though varies from sample to sample. The clay mineral assemblages range from virtually pure chlorite–smectite to illite–smectite dominated assemblages with minor or no chlorite–smectite. The proportion of chlorite–smectite in K-bentonites shows systematic lateral variations: the share of chloritic phases is highest in the shallower-water part of the palaeobasin and decreases towards the deeper part of the basin. Such regular lateral variations suggest a possible link between chloritization and the configuration of ancient palaeobasin. The present study suggests that the chloritization of primary felsic ashes occurred during early diagenesis and that it was caused by an influx of Mg-rich water probably from a marine sabkha-type environment.

Characterization of the formed from kaolinite expandable clays at 200°C

The hydrothermal reaction of kaolinite in the system Na2O-K2O-MgO-Al2O3-SiO2- H2O-HCl, at near-neutral pH conditions, has been investigated at 200ºC, for times from 12 h to 180 days. X-ray diffraction (XRD) study of the solid products indicates that the phases formed from 15 days’ reaction time are randomly ordered mixed-layer chlorite-smectite, dioctahedral on average, with a chlorite:smectite ratio of ∼1:2. No structural evolution was observed with increasing reaction time. Investigation by transmission electron microscopy revealed, on the contrary, that very thin packets with basal spacing of either 10 Å (smectite) or 14 Å (chlorite) are dominant. In addition, packets with periodicities of 12 –13 Å are also observed. Only rarely, randomly to ordered sequences of 10 and 14 Å are observed in the packets. These observations indicate that the mixture of these phases behaves in XRD as randomly ordered mixed-layer chlorite-smectite. Chemical analysis of the solutions suggests that the neo-formed phases are metastable and would evolve, at longer reaction times, toward ordered mixed-layer chlorite-smectite or to clinochlore.

Characterization of the expandable clays formed from kaolinite at 200ºC

AbstractThe hydrothermal reaction of kaolinite in the system Na2O-K2O-MgO-Al2O3-SiO2- H2O-HCl, at near-neutral pH conditions, has been investigated at 200ºC, for times from 12 h to 180 days. X-ray diffraction (XRD) study of the solid products indicates that the phases formed from 15 days’ reaction time are randomly ordered mixed-layer chlorite-smectite, dioctahedral on average, with a chlorite:smectite ratio of ∼1:2. No structural evolution was observed with increasing reaction time. Investigation by transmission electron microscopy revealed, on the contrary, that very thin packets with basal spacing of either 10 Å (smectite) or 14 Å (chlorite) are dominant. In addition, packets with periodicities of 12 –13 Å are also observed. Only rarely, randomly to ordered sequences of 10 and 14 Å are observed in the packets. These observations indicate that the mixture of these phases behaves in XRD as randomly ordered mixed-layer chlorite-smectite. Chemical analysis of the solutions suggests that the neo-formed phases are metastable and would evolve, at longer reaction times, toward ordered mixed-layer chlorite-smectite or to clinochlore.