Chemical Composition Of Rocks Research Articles

A geochemical model for the transformation of gabbro into vesuvianite-bearing rodingite

Rodingite is a Ca-rich and Si-poor metasomatic rock commonly occurring in association with serpentinites. This rock is characterized by specific mineral assemblages consisting of hydrated garnet, diopside, vesuvianite, epidote-zoisite, chlorite, or prehnite. However, natural rodingites are significantly heterogeneous in mineral composition and vesuvianite occurs only in some extensively rodingitized rocks. Major factors controlling the mineral diversity as well as details on fluid-rock interactions leading to the evolution of mineral and chemical composition during rodingitization have not yet been fully constrained. In this work, we use PHREEQC software to present a geochemical model for the transformation of a mafic rock into vesuvianite-bearing rodingite at a temperature of 300 °C. Through these simulations, we investigate the effect of fluid composition and progress of the metasomatic process on rodingite formation. Our results show that rodingitization requires an open system with a high input of hydrothermal fluid. Additionally, a decrease in the Si/Ca ratio in the metasomatized rock is correlated to an increase in the volume of incoming fluid. Whole rock chemical and mineral composition in natural rodingites are well reproduced by the model. Furthermore, the diversity of mineral parageneses results mainly from different degrees of transformation and only to a lesser extent to the chemical composition of hydrothermal fluid or protolith. The hydrothermal fluid doesn't need to be especially rich in calcium to transform a mafic rock into rodingite, but it must be low in magnesium, silicon, and have a high pH, which is naturally controlled by serpentinization of surrounding ultramafic rocks.

Changes in the magmatic plumbing system associated with the Gotemba sector collapse at Mount Fuji, Japan

It is well known that magmatic plumbing systems change over time, but there is much debate as to why and how. We studied volcanic ejecta continuously deposited in an outcrop at Kagosaka Pass at the eastern base of Mount Fuji to investigate the factors responsible for changes in the magmatic plumbing system. The sample consisted of pyroclastic sediments from explosive eruptions for approximately 3000 y, which sandwiched the time of the Gotemba sector collapse at approximately 2500 BP. Chemical analyses of whole rocks, minerals, and matrix glasses, as well as mode measurements of glass and bubbles, were performed on samples collected from approximately 30 layers; significant changes were observed before and after the collapse. For example, before and after the collapse, matrix glass area increased around 60% to over 80% and anorthite content (Ca / (Ca + Na) * 100) of phenocryst plagioclase decreased from over 80 to below 65. For a period after the collapse, possibly hundreds of years, the plagioclase and olivine phenocrysts exhibited characteristics indicative of crystallization at low temperatures and pressures, and the pyroclast matrix became highly vitreous. Eruptions with ejecta of these characteristics continued more than a dozen times, lasting about 500 years. In addition, the trend in the distribution of the bulk rock chemical composition changed significantly, showing a differentiation trend with only plagioclase and clinopyroxene crystal separation. An investigation using the MELTS software revealed that the phenomenon of direct eruptions from deep magma chambers to the surface, bypassing shallow magma reservoirs, continued for several hundred years after the collapse. This can be interpreted as a decrease in confining pressure associated with the collapse, facilitating the eruption of magma from the depths. Furthermore, based on an examination of the water content in the magma during this period, we posit that the trigger for the rise of magma from the deep magma chamber of Mount Fuji is the acquisition of excess pressure by the injection of magma from a deeper level.

GEOCHEMISTRY AND PETROGRAPHY OF METAMORPHIC SOLE AMPHIBOLITES FROM THE SLATINA QUARRY, MT. ZRINSKA GORA, CROATIA

The investigated Mt. Zrinska Gora amphibolites are a part of the metamorphic sole of the Banovina ophiolite complex. Mineral composition and other petrographic characteristics of amphibolites and adjacent peridotite were investigated by polarised microscopy and chemical analyses of rocks were obtained by a combination of inductively coupled plasma mass and emission spectrometry. The main minerals in these garnet-bearing amphibolites are amphibole and plagioclase with accessory garnet, sphene, spinel, opaque mineral ± clinopyroxene ± quartz ± actinolite ± zoisite-clinozoisite ± prehnite ± pumpelyite and ± clay minerals. Kelyphitic corona is developed around garnet. The amphibolites have nematoblastic, nematogranoblastic, porphyroblastic and porphyroclastic textures and homogenous to foliated structures. The presence of clinopyroxene in some of the investigated amphibolites points to their possible formation under P‒T conditions of upper amphibolite facies. The greenschist facies retrograde metamorphism and subsequent surface weathering of amphibolites is also evident. The chemical composition of rocks indicates that protoliths of most amphibolites were tholeiitic basalts, initially formed in island arcs and the adjoining back-arc basins. During the intraoceanic subduction in Jurassic Neotethys Ocean basalts/basaltic tuffs of island arc tholeiite affinity and back-arc basin basalts, positioned on the top of the down-going oceanic slab, were welded to the base of the hot over-riding mantle wedge, metamorphosed to amphibolite rocks and obducted together with ophiolites on the Adria continental margine. The new described amphibolite type having peridotite protolith characteristics originated as the consequence of the hydration of the bottom part of the overlying mantle wedge.

Extensive two-tier structure and breccia stockwork formation by hydrothermal processes in the first Paraná lava flow covering the Botucatu paleoerg-turned-Guarani Paleoaquifer

The Catalán Flow in the southernmost Paraná Volcanic Province exhibits two extensive red and gray to white tiers and an areally vast breccia stockwork, both of which are unique within intraplate large igneous provinces. To comprehend the processes responsible for the formation of these structures, we integrated the study of satellite images with field surveys and the interpretation of published geochemical analyses. During the Early Cretaceous, a 30-m-thick layer of quartz andesite known as the Catalán Flow covered the 160-m-thick Botucatu + Guará formations, which had transformed into the Guarani Paleoaquifer. This flow consists of a lower Tier 1, which appears gray in satellite images and medium gray to white in the field, and an upper Tier 2, which is red in both images and in the field. Amethyst and agate geodes are present in Tier 1 but are absent in Tier 2. Within an area exceeding 100 by 100 km, a breccia stockwork composed of quartz andesite fragments can be found. These fragments either include silicified sandstone or hydrothermal zeolites. The chemical composition of rocks from Tier 2 features a loss on ignition (LOI) of less than 1.5 wt% and a composition similar to the original lava. In contrast, Tier 1 underwent significant alteration, particularly a reduction in SiO2 and K2O, along with an increase in Fe2O3T, with LOI exceeding 1.5 wt% and reaching up to 8 wt%. The formation of hematite and the reddening of the rock in Tier 1 were a result of heated, oxidizing aquifer water percolating through the lava. Subsequently, reducing, aquifer hot water percolated, causing intense chemical and mineralogical alteration in the previously oxidized flow, resulting in a gray to white color and the formation of amethyst and agate deposits. Tier 1 represents the reduced lower layer of the flow, while Tier 2 is the remaining red upper portion. Comparative fluid activity is observed in red and white dunes in the Etendeka, as well as in basalts from various environments. The breccia stockwork was formed through explosive hydrothermal processes beneath the upper crust, where overpressured fluids came into direct contact with the atmosphere, leading to flash vaporization. The structures observed are the outcome of the distant influence of paleodune patterns on the Catalán Flow, which corresponds to the presence of higher dunes in the two tiers and sand sheets in the breccia stockwork. The processes responsible for the two-tier (oxidation and reduction) and breccia formation (explosive pressure release and sand injection near the surface) are recognized in various hydrothermal systems worldwide. However, the extensive areal coverage and homogeneity of these features, coupled with the presence of world-class amethyst deposits, make the Paraná Volcanic Province unique among large igneous provinces worldwide.

Hydro-geochemical characterization of the main European mineral water brands

The history of the mineral water consumption goes back to early legends. Already then, in addition to physiological needs, their beneficial effects were also used in medicine. Mineral water contains a complex of components, the composition of each mineral water varies according to its origin, the minerals, salts, gases and radioactive elements it contains and the quantities of the components. In our research, statistical methods were used to analyze the chemical composition of the macro-parameters indicated on the labels of European bottled and commercial mineral waters. A total of 692 mineral waters from 13 countries were analyzed: Austria (15), Belgium (8), Greece (10), France (33), Poland (34), Portugal (7), Spain (66), Slovakia (11), United Kingdom (9), Hungary (33), Germany (309), Italy (123), Romania (34), United Kingdom (9). Furthermore, mineral waters were classified according to their evaporation residue and ionic content. Correlation coefficients were used to study the relationship between the chemical composition of rocks and mineral waters. Statistical analysis was carried out on the cations Ca2+, Mg2+, Na+, K+, and on the anions HCO3-, Cl-, SO42-. Piper diagrams of the studied mineral waters were prepared at country level, as well as box-plots and Spearman correlations and heat maps.

Timing of Carbonatite Ultramafic Complexes of the Eastern Sayan Alkaline Province, Siberia: U–Pb (ID–TIMS) Geochronology of Ca–Fe Garnets

In this study, we present the results of U–Pb (ID-TIMS) geochronological studies of calcic garnet from the alkaline ultramafic complexes of Eastern Sayan province (eastern Siberia). New U–Pb ID–TIMS garnet ages obtained from different rocks of Bolshaya Tagna (632 ± 2 Ma) and Srednaya Zima intrusions (624 ± 5 Ma), as well as previously published garnet ages of the Belaya Zima complex (646 ± 6 Ma), allow us to constrain the timing and duration of episodes of alkaline ultramafic magmatism in Eastern Sayan province (619–651 Ma). Variations in the chemical compositions of rocks from three massifs indicate that the parental melts were separated from different magmatic chambers generated during the same episode of mantle melting. This study further highlights garnet U–Pb dating as a potentially robust, high-resolution geochronometer to constrain the evolution of the main pulse of alkaline ultramafic magmatism in the large magmatic provinces.

Petrology of the Kureika Graphite Deposit in the Roof of the First-Rapid Trap Intrusion (Siberian Platform)

Abstract —The leading role of lithostratigraphic, structural/tectonic, magmatic, metamorphic, and fluid geologic factors in the formation of a graphite deposit is substantiated. We present the petrographic and chemical compositions of rocks and minerals of igneous rocks, the δ13С values of graphites and calcitites, the δ18O values of carbonates, the δ34S values of sulfides, and the 87Sr/86Sr and 87Rb/86Sr ratios in calcitites and microdolerite injections. The thermal effect of magmatic melt on coal led to its degassing and graphitization. The steaming of microdolerite injections with hydrocarbon fluids was probably accompanied by the removal of iron from them and the crystallization of low-Fe clinopyroxene, and the interaction of fluids with basaltic melt in the upper endocontact zone of the intrusion led to the segregation of the melt and the formation of a globular structure of rocks. The presence of a calcitite lens and a sulfide vein between the roof of the intrusion and the graphite bed is due to the earlier intrusion of sulfate salt melt and its subsequent interaction with hydrocarbon fluids, which resulted in sulfate reduction and the formation of calcitites. The sulfate reduction terminated with iron sulfurization in the basaltic melt and the formation of a sulfide vein. Sulfate salt melt was a source of heavy sulfur isotope (δ34S = 14.9–17.5‰) for sulfides and of calcium for calcitites. The similar isotope compositions of calcitites (δ13СPDB = –22.5 to –23.5‰), coals (–22.6 to –25.5‰, n = 25), and graphites (–23.5 to –25.0) suggest that coal is a source of carbon for calcitites. In the isotopic compositions of strontium (87Sr/86Sr ≈ 0.70834–0.70885) and oxygen δ18O ≈ 15‰) the calcitites are similar to the Devonian evaporites of the Siberian Platform. The isotope data (δ34S, δ18O, δ13С, and 87Rb/86Sr) point to the participation of the coal seam and anhydrite as sources of substance in the formation of calcitite and sulfide mineralization.

MANAGING THE HORIZON-ORIENTED IN-SITU LEACHING FOR THE URANIUM DEPOSITS OF MONGOLIA

This paper summarizes the results of evaluating uranium in-situ leaching (ISL) parameters for hydrogenous deposits in eastern Mongolia. This method, also known as in-situ recovery (ISR) or solution mining was proposed for mining used to extract uranium from underground deposits without physically removing the ore. The studies included drilling, geophysical surveying, evaluations of rock properties and chemical composition of rocks and groundwater, as well as modelling coupled flow and transport for the “Ul’zit” deposit as a case study. The proposed horizon-oriented approach to process separate ore bodies at different depths allows for the mining process to be adapted to layered heterogeneity and allows successive leaching by wells of varying diameter and special design. This approach may reduce drilling costs and shorten the time for mining uranium deposits in Mongolia by 2 times on average. It was proven that this method is an environmentally friendly and cost-effective alternative to traditional underground or open-pit mining for uranium ore bodies. The economic evaluation confirms the effectiveness of the proposed solutions.

Holocene volcanic eruptions of the Malpaís de Zacapu and its pre-Hispanic settlement history

AbstractThe Michoacán-Guanajuato volcanic field (MGVF) hosts >1,400 monogenetic structures younger than 5 Ma. Here we focus on the Malpaís de Zacapu Late Holocene cluster located in the western part of the Zacapu lacustrine basin, situated in the heart of native Purepecha province. The Malpaís de Zacapu comprises four distinct eruptions: the Infiernillo lava flow emitted at ~1450 b.c.; Malpaís Las Víboras, a purely effusive eruption at ~1000 b.c.; the Capaxtiro compound lava flow at ~150 b.c.; and the most recent eruption, the Malpaís Prieto lava flow at ~a.d. 900. Although these lava flows are not inhabited today, they were densely populated in pre-Hispanic times (before a.d. 1521), especially during the Milpillas phase (a.d. 1200–1450). Volcanological studies (geochemical studies and detailed mapping using high-resolution DEM from LiDAR) allowed us to characterize these eruptions in terms of their magma source (rock chemical composition, mineral assemblage), age (radiocarbon and paleomagnetic dating), magnitude and dynamics (volume, morphology of the deposits), as well as lava flow emplacement duration. The findings allow us to infer the potential impact that these eruptions had on the pre-Hispanic settlement history of the area.

Some geological and petrological characteristics of the Eocene trachybasalt-trachyandesite- basalt-phonolite formation of the Talysh zone (Azerbaijan)


 
 
 This article discusses the stages of crystallization of the Eocene trachybasalt-tra- chyandesitebasalt-phonolith formation of the Talysh zone. Determination of the composi- tion of the primary magma, evolution and melting fraction of the initial melt of the Eocene volcanism of the Talysh zone within Azerbaijan. Eocene volcanism of the trachybasalt-tra-chyandesitebasalt-phonolith formation of the Talysh zone. Petrographic, petrochemical, geochemical studies of rocks, typomorphic features of mineral paragenesis, chemical composition of rocks were carried out by X-ray spectral and X-ray fluorescence analysis. The analyzes of the conducted studies show that the Talysh zone was formed in the Eocene time. Stages of evolution of the original magma and typomorphic features of mineral parageneses have been established. The distributions of microelements in mineral parageneses, which are direct participants in the crystallization processes that took place in intermediate chambers at different depths, have been studied. At present, the question arises of the need to clarify the typomorphic features of igneous complexes, as factors that determine the geodynamic regimes of their formation, and to determine the potential ore content. The petrographic and petrochemical characteristics of the volcanic rocks are given. It was found that if the process of differentiation in the Early-Middle Eocene was more distinct with the initial formation of more magnesian rock varieties (picrite-trachybasalts), and subsequently more ferruginous ones (trachyandesites and trachyandesitebasalts), then such accumulation of iron is not observed in porphyritic trachyandesites. This petrochemical feature is obviously associated with the duration of the break in volcanism, caused by the formation of a thick sedimentary-tuffaceous stratum, accompanied by the initiation and manifestation of an intermediate chamber of medium composition. Volcanism in the Late Eocene was undifferentiated and was not accompanied by the formation of medium differences. The appearance in the late Eocene of leucite phonolites, which represent an alkaline branch, and the absence of transitional varieties indicate the autonomous development of vit- robasalts and leucite phonolites. It is concluded that from the early phases of the manifestation of Eocene volcanism to the later phases, the change in the material composition along the lateral is expressed in the manifestation of more alkaline facies with a significant predominance of K over Na and with a greater correspondence to the differentials of the shoshonite series.
 
 

Reactive transport investigations of the long-term geochemical evolution of a multibarrier system including bentonite, low-alkali concrete and host rock

The Canadian concept for a deep geological repository for used nuclear fuel includes highly-compacted and homogenized bentonite (HB) and low-alkali concrete such as Low-Heat High-Performance Concrete (LHHPC) as engineered barrier materials. The initial mineralogy and pore water compositions are different for bentonite, LHHPC and potential host rocks, such as granite and limestone. Consequently, chemical alterations are expected at the interfaces between these materials. Two scenarios were simulated to investigate the alterations at the material interfaces: 1) HB/LHHPC/host rock; 2) HB/host rock. For both scenarios, excavation damage zones (EDZs) were taken into consideration. Because of the low reactivity of bentonite compared to LHHPC, for the second scenario, only relatively minor mineral volume fraction and porosity changes were predicted for the HB/granite and HB/limestone host rock cases, with limited impact on radionuclide migration. For the first scenario; however, due to the relatively high pH of pore water in LHHPC, substantial mineral dissolution and precipitation were predicted to occur at the HB/LHHPC and/or LHHPC/host rock interfaces, leading to porosity reduction or even pore clogging in close proximity (<1 cm) of the interfaces. The predicted geochemical evolution depends mainly on the mineralogy and pore water chemical composition of the host rock. In the case of granitic host rock, Calcium Silicate Hydrate (C–S–H) phases initially present in LHHPC are predicted to transform into tobermorite, phillipsite, saponite and gypsum within 1,000 years. The simulations indicate a complex evolution of porosity, with an initial reduction, followed by a slight increase, and subsequent pore clogging. In the case of limestone host rock, saponite and sepiolite are the dominant minerals formed in the LHHPC. A sensitivity analysis shows that higher initial effective diffusion coefficients in the LHHPC enhance the diffusive fluxes of ions and result in earlier pore clogging in the host rock. The simulations illustrate that reactive transport modelling accounting for barrier reactivity and pore clogging provides a useful tool for assessing the migration of radionuclides across material interfaces for various canister failure scenarios.

Chemické složení křemene a světlé slídy z komplexu ortoruly, granitu, pegmatitů a křemenných žil v Přibyslavicích jako indikátor jejich příbuznosti

The complex of leucocratic granitoid rocks at Přibyslavice (Fig. 1), composed of muscovite-tourmaline orthogneiss, muscovite granite and several types of pegmatites, is well known for numerous finds of interesting minerals like large almandine crystals (Breiter et al. 2005b), Li-Fe-Mn phosphates (Povondra et al. 1987), nigerite (Čech et al. 1978), columbite and cassiterite (Šrein et al. 2004, Breiter et al. 2006), lepidolite (Šrein et al. 2004) and oxy-schorl (Bačík et al. 2013). Less attention has been paid so far to the petrology of orthogneisses, granite and pegmatites and their genetic relationships. This study aims, based on the chemical composition of quartz and muscovite, to assess possible genetic links among all these rocks of granitoid composition including an associated cassiterite-bearing quartz vein with a B, Ta-rich metasomatic halo. Major elements in micas were analyzed using electron microprobe, and trace elements in both quartz and mica were determined using laser ablation-ICP-MS according to methods described in Breiter et al. (2017, 2020). About 550 spot analyses of quartz and 220 spot analyses of mica allow reliable definition of the typical composition of quartz and mica from all types of studied rocks (Tables 2, 3). Some genetic relationships are visualized in Figs. 2 and 3. The Přibyslavice orthogneiss is geochemically more evolved than petrographically similar orthogneisses through entire Moldanubicum as expressed not only in bulk rock chemical composition but also in trace element composition of quartz (higher Al, Ge and Li contents, Fig. 2) and muscovite (higher Li, Nb, Ta, Sn and W contents, Fig. 3). Pegmatoids at Přibyslavice and nearby Březí, forming small nests in orthogneisses with a gradual mutual transition, are interpreted as in situ anatexites. The direct genetic link between the granite intrusion and the quartz vein with cassiterite and B, Ta-rich metasomatites (tourmaline + Ta-rutile) is supported by the Sn, Nb and Ta enrichment of granite. It is highlighted by the relative distribution of Nb and Ta, with Nb preferentially bonded to muscovite in granite and Ta segregated into a fluid (see e.g. Stepanov et al. 2014). Chemical and mineral similarity between the granites and the orthogneiss suggests a common source lithology located deep below the present surface. During the first melting of the protolith in the late Cambrian (Vrána – Kröner 1995), a boron-rich melt was formed, which extracted most boron from the source and facilitated the origin of tourmaline orthogneiss. The second, Variscan melting of the same or a very similar protolith produced a melt slightly enriched in F and Li. We assume that the Přibyslavice granite represents only a small proportion of this melt, strongly enriched in Sn, W, Nb and Ta due to fractionation. Chemistry and mineralogy of several types of associated pegmatites suggest their relation rather to the granite melt than to the anatexis of the orthogneiss. The difference in their chemical composition including the content of water, F, and Li reflects the timing of separation from the parental magma and the distance of the melt transport upwards. During the transport, internal fractionation culminated in the “Li-pegmatite” by crystallization of its quartz-lepidolite core.

Geology, mineralogy, geochemistry and conditions of forming the Tukan gold-quartz deposit (Khudolaz trough, South Urals)

Research subject. Detailed mineralogical and geochemical studies of rocks of the Tukan gold-quartz deposit (quartz veins, dolerites, gabbro-diorites) were carried out. The deposit is one of numerous small gold-quartz occurrences in the Khudolaz trough of the West Magnitogorsk zone.Methods. The morphology and composition of native gold was studied using an Axios kop 40 A optical microscope and Tescan Vega 3 and JEOL-6390LV scanning electron microscopes. The chemical composition of rocks was determined by X-ray fluorescence (Carl Zeiss VRA-30) and atomic emission (Shimadzu ICPE-9000) analyzes. Fluid inclusions were analyzed using Linkam TMS-600 thermostage equipped with Link-System 32 DV-NC software and an Olympus BX51 optical microscope. The gas composition of fluid inclusions was examined by Raman spectroscopy (Horiba LabRam HR800 Evolution).Results. Gold-bearing quartz veins and dolerites intersect ing the gabbrodiorite intrusion of the Khudolaz complex are associated with submeridional strike-slip faults. Native gold has a various morphology and is confined to cracks in quartz veins and altered dolerites. The composition of gold is stable, with the average fineness of 871 ± 8.3‰. An analysis of fluid inclusions in a gold-bearing quartz vein showed that gold was formed at temperatures of no less than 186–230°С from a fluid with a salinity of 4–8 wt % NaCl-eq. The presence of gases СО2, N2 and CH4 was found in fluid inclusions. Dolerites and gabbrodiorites hosting gold-bearing veins contain sulfides (pyrite, pyrrhotite, chalcopyrite, pentlandite, violarite), sulfoarsenides (cobaltite and its analogs), as well as mine rals of Ag (hessite) and Pb (kuranakhite and phases similar in composition to minerals of the dugganite group and burckhardtite). Conclusions. The sustained composition of native gold and a narrow range of salinity and homogenization temperatures of fluid inclusions indicate the formation of gold during a single stage of mineralization. The main source of gold could have been the dolerite dikes of the Ulugurtau complex. The presence of CO2, N2 and CH4 gases in fluid inclusions from goldbearing quartz indicates that not only magmatic fluid, but also fluid from the host rocks took part in mineral formation. The low value of the ratio X(CO2)/X(CH4) ≤ 0.7 indicates a moderately reduced ore-forming fluid. Low Au concentrations (0.1– 0.4 ppm) in quartz veins, dolerites, and gabbro-diorites, including those containing visible gold, indicate a weak commercial potential of the deposit

Geochemical features of the devonian plutonic rocks of the Reftinsky massif (Middle Urals)

This article examines the Devonian plutonic rocks of two massifs – Khomutinsky and Yuzhno-Khomutinsky, which are located in the western part of the Reftinsky massif. The rocks of the Khomutinsky and Yuzhno-Khomutinsky massifs are divided into gabbroid and granitoid associations. Their chemical composition, the content of pertrogenic, rare and trace elements were studied. Based on the data obtained, the rocks were assigned to the calc-alkaline series, according to the ratio of sodium and potassium, they are rocks with a sodium type of alkalinity. The peculiarity of the studied formations lies in the differences in the nature of alkalinity, thus the rocks of the gabbroid association in terms of the K2 O content are transitional from low to moderate potassium varieties, and the rocks of the granitoid association are characterized by a sufficiently high potassium content and correspond to the high potassium calc-alkaline series. Comparative analysis with basalts and granites of island arcs allows us to conclude that the Khomutinsky and YuzhnoKhomutinsky massifs were formed in an island arc geodynamic setting. Relevance. The geochemical features of the rocks of the Devonian intrusions in the Eastern zone of the Middle Urals have been studied very poorly to date, which makes it difficult to restore the geodynamic conditions of their formation and compare the processes of magmatism in the East of the Middle Urals with other regions of the mobile belt. The data presented in the work will make it possible to fill the existing gap to some extent and thereby help to clarify the patterns of magmatism evolution and the history of the formation of the Urals. The purpose of the work. Study of the contents of petrogenic, rare and trace elements of the Khomutinsky and Yuzhno-Khomutinsky massifs. Comparison of the geochemical features of the rocks of these intrusions with similar formations formed in island-arc geodynamic conditions. Research methodology. The chemical composition of rocks was studied by the X-ray fluorescence method, which was performed on a multichannel spectrometer SRM-35 with the determination of losses on ignition by the gravimetric method and the determination of the content of ferrous iron by the titrimetric method. Analysis of the content of rare and trace elements in rocks was carried out on inductively coupled plasma mass spectrometers ELAN 9000 and NexION 300S. Analytical data are presented in the form of discrimination diagrams. Results. The rocks of the Khomutinsky and Yuzhno-Khomutinsky massifs are divided into gabbroid and granitoid associations. Based on the obtained geochemical data, the rocks were assigned to the calc-alkaline series. According to the ratio of sodium and potassium, they are rocks with a sodium type of alkalinity. It is shown that the rocks of the gabbroid and granitoid associations differ in the character of alkalinity. The former in terms of K2O content are transitional from low to moderate potassium varieties, the latter are characterized by a fairly high content of potassium and correspond to the high potassium calc-alkaline series. Conclusion. Comparison of the studied rocks in terms of geochemical features with basalts and granites of island arcs allows us to conclude that the Khomutinsky and Yuzhno-Khomutinsky massifs were formed in an island-arc geodynamic setting.

Two-stage regional rare-element pegmatite formation at Tysfjord, Norway: implications for the timing of late Svecofennian and late Caledonian high-temperature events

Pegmatite fields within granite plutons are commonly considered to have formed from residual melts of their host. This is not always true as demonstrated by the Tysfjord granite gneiss and its two groups of pegmatites. The Tysfjord granite gneiss, exposed in a tectonic window of the Caledonides of northern Norway, is part of the transscandinavian igneous belt (TIB) that includes several phases of granitic magmatism. In the northern Hamarøy area (Drag-Finnøy), where most rare-element pegmatites occur, Paleoproterozoic and metamorphosed Group 1 allanite–(Ce)–fluorite metapegmatites have similar bulk rock chemical composition as the TIB granite gneiss rocks, indicating that these pegmatites are residual melts. Group 1 metapegmatites, which are up to 400 m in size, are among the largest known intra-plutonic pegmatites with Nb–Y–F (NYF) signature. The formation of these unusually large granite-hosted NYF pegmatites may have been facilitated by the overall high F content of TIB granite gneisses. Undeformed Group 2 amazonite–tourmaline pegmatites yield columbite and zircon U–Pb ages in the range 400–379 Ma. These pegmatites are interpreted to be anatectic melts that formed from the partial melting of Tysfjord granite gneiss. Group 2 pegmatites, including those from Træna Island and the Sjona tectonic window (400 and 414 Ma), formed during late Caledonian ductile shearing and incipient unroofing of the central Scandinavian Caledonides and record progressively younger ages of this event from SW to NE.

БЛОК ЭДИАКАРСКИХ ВУЛКАНИЧЕСКИХ ПОРОД В СТРУКТУРЕ ЮЖНО-МОНГОЛЬСКО–ХИНГАНСКОГО ОРОГЕННОГО ПОЯСА

The publication presents the results of studies on chemical composition of rocks from the volcanogenic part of the Shirokopadinskaya Formation in the Bereya River basin of the Amur fragment of the northeastern flank of the South Mongolia–Khingan orogenic belt, as well as the results of geochronological (U-Th-Pb, LA-ICP-MS) and isotopic (Lu-Hf) studies on zircons from crystalloclastic tuff. Metaandesite-basalts, their tuffs and tuffites dominate among the volcanic and volcano-sedimentary rocks from the Shirokopadinskaya Formation. The geochemical features of the rocks and Hf-isotopic composition of zircons from volcanic rocks indicate their suprasubduction origin. The concordant age of the youngest zircon population from crystal tuff is 589 ± 5 Ma (MSWD = 0.60, concordance probability = 0.90 %), which corresponds to the Ediacaran. These zircons are characterized by well-preserved crystal faceting without traces of roundness. In our opinion, the age of the tuffs reflects the age of volcanism and the studied volcanic rocks. The data are rather unexpected, because the most ancient rocks of the oceanic crust of the South Mongolia–Khingan orogenic belt are Ordovician in age, which means the studied volcanic rocks are more than 100 million years older and cannot be part of the South Mongolia–Khingan belt. Ediacaran volcanic rocks, considering their structural position, are located at the boundary between the South Mongolia–Khingan orogenic belt and the Mamyn (Xing’an) terrane. They are a fragment of the Mamyn (Xing’an) terrane, which was tectonically placed into the modern structure of the South Mongolia–Khingan orogenic belt. This conclusion is supported by the occurrence of formations in the Mamyn (Xing’an) terrane that are similar in age and geochemical features.

TECTONOMAGMATIC EVOLUTION OF THE EOCENE VOLCANISM OF THE TALYSH ZONE (AZERBAIJAN)

Link for citation: Karimov V.M. Tectonomagmatic evolution of the Eocene volcanism of the Talysh zone (Azerbaijan). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2021, vol. 332, no. 11, рр. 200-211. In Rus. The relevance. At present, the question arises of the need to clarify the typomorphic features of magmatic complexes, as factors that determine the geodynamic regimes of their formation and to clarify the potential ore content. In this regard, the article examines the features of the Talysh magmatic complexes, which makes it possible to elucidate the tectonomagmatic evolution of this complexly constructed region in the Caucasus. Purpose of research is to clarify the tectonomagmatic evolution of the Eocene volcanism of the Talysh zone within Azerbaijan. Objects: Eocene volcanism, volcanogenic trachybasalt-trachyandesite-basalt-phonolite formation, petrochemical composition of rocks, evolution of the primary melt. Methods: petrographic studies of rocks, chemical composition of rocks by X-ray spectral analysis, isolation of magmatic complexes. In addition, the results of analyzes of the studied samples for petrogenic elements were used, both published in the literature and obtained by X-ray fluorescence analysis on a multichannel X-ray spectrometer SRM-25 at the Institute of Geology and Geophysics, Baku. Minerals were analyzed on a JXA-8200 JEOL (Japan) electron microprobe at the Karpinsky All-Russian Geo-logical Research Institute (St. Petersburg). Results. The analysis of the conducted studies shows that during the period from the Paleozoic to the Quaternary, inclusive, in the development of the structures of the Talysh fold zone, there is a certain sequence in its inception. In the structure of the zone, there are structural stages corresponding to the pre-collisional (Cretaceous–Eocene) and collisional (Oligocene–Miocene) periods of the region's development. Paleogene volcanic formations of Talysh make up the southeastern segment of the northern volcanoplutonic belt, in the structure of which the volcanic trachybasalt-basaltic trachyandesite-phonolite (Early-Middle and Late Eocene) and intrusive subalkaline ultrabasic (Late Eocene–Oligocene) formations are distinguished. The volcanic formation includes two complexes: (Early-Middle Eocene) absarokite-shoshonite-alkaline basaltic and (Late Eocene) basaltic trachyandesite-phonolite. The petrographic and petrochemical characteristics of the volcanic rocks that make up the first formation are given. It was found that if the process of differentiation in the Early-Middle Eocene had more distinct character with the initial formation of more magnesian rock varieties (picrite-trachybasalts), and subsequently more ferruginous (trachyandesites and basaltic trachyandesites), then such accumulation of iron is not observed in porphyry trachyandesites. This petrochemical feature is obviously associated with the duration of the break in volcanism caused by the formation of a thick sedimentary-tuffaceous sequence, accompanied by the formation and manifestation of an intermediate chamber of average composition. Volcanism in the Late Eocene was undifferentiated and had a contrasting character, i. e. was not accompanied by the formation of average differences. The appearance in the Late Eocene of leucite phonolites, which are an alkaline branch, and the absence of transitional differences indicate the autonomous development of vitrobasalts and leucite phonolites, possibly associated with the process of early decomposition of the initial melt under subcrustal conditions. It is concluded that from the early phases of the manifestation of Eocene volcanism to the later, the change in the material composition laterally is expressed in the manifestation of more alkaline facies with a significant predominance of K over Na and with a greater correspondence to the differentiates of the Shoshonite series.

Fluid-Rock Interactions in a Paleo-Geothermal Reservoir (Noble Hills Granite, California, USA). Part 1: Granite Pervasive Alteration Processes away from Fracture Zones

Only few data from geothermal exploited reservoirs are available due to the restricted accessibility by drilling, which limits the understanding of the entire reservoir. Thus, analogue investigations are needed and were performed in the framework of the H2020 MEET project. The Noble Hills range, located along the southern branch of the Death Valley pull-apart (CA, USA), has been selected as a possible granitic paleo-reservoir. The aim is to characterize the pervasive alteration processes affecting this granite, away from the influence of the faults, in terms of mineralogical, petrophysical and chemical changes. Various methods were used as petrographic, geochemical and petrophysical analyses. Mineral changes, clay mineralogy, bulk rock chemical composition, calcite content and porosity were determined on different granite samples, collected in the Noble Hills granite, far from the faults and in the Owlshead Mountains, north of the Noble Hills, considered as its protolith. In order to complete the granite characterization, the metamorphic grade has been studied through the Noble Hills granite body. This complete characterization has allowed distinguishing the occurrence of three stages of alteration: (1) a pervasive propylitic alteration characterized by calcite-corrensite-epidote-K-white mica assemblage, (2) a more local one, only present in the Noble Hills granite, producing illite, kaolinite, illite/smectite, calcite and oxides, characteristic of the argillic alteration, which overprints the propylitic alteration and (3) weathering evidenced by the presence of montmorillonite in the Owlshead Mountains, which is considered as negligible in both granites. Alteration was also outlined by the correlation of the loss on ignition, representing the hydration rate, to porosity, calcite content and chemical composition. Moreover, the Kübler Index calculated from illite crystals allowed to identify a NW-SE temperature gradient in the Noble Hills.

AGE AND COMPOSITION OF THE EARLY PALEOZOIC MAGMATIC ASSOCIATIONS AND RELATED RARE-ELEMENT PEGMATITES IN THE SOUTH-EASTERN PART OF THE SANGILEN BLOCK, TUVA-MONGOLIAN MASSIF

The article presents new data on ages (U-Pb zircon dating, SIMS SHRIMP-II) and chemical compositions of rocks from gabbro-granitic and granite-leucogranitic magmatic associations. These rocks preceded the formation of Li-enriched spodumene pegmatites of the Tserigiyngol-Burchin ore cluster (Russian: ЦБРУ), one of the main clusters in the South Sangilen pegmatite belt (SSB) located in the Tuva-Mongolian massif being a part of the Central Asian Fold Belt. We investigated the rocks from the Upper Tserigiyngol, Uchuglyk and Temenchulu plutons, and pegmatites from two neighbouring fields. We distinguish three impulses of granitic magmatism (517±7, 508±7, and 488±6 Ma), which are attributed to different stages of the Early Paleozoic collision orogeny (520-480 Ma). The period when the Li-enriched pegmatites were formed (494±7 Ma) is close to the magmatism impulse at 488±6 Ma. Differences are discovered in compositional and isotopic (Sm-Nd) features of granites dominating at the following stages of collisional orogeny: (1) early collision (517±7 Ma) – I-type granites, eNd(T)=0–1.5, TNd (DM-2st)=1.2–1.1 b.y., and (2) late collision (488±6 Ma) – A-2-type granites, eNd(T)=–3.0…–1.6, TNd (DM-2st)=1.5–1.4 b.y., which are due to different sources. Our study shows that facies transitions are absent between the late-collision granites (488±6 Ma) and the spodumene pegmatites from the Tserigiyngol-Burchin ore cluster (494±7 Ma), although these rocks are close in age. In terms of geochemical features, the spodumene pegmatites from the cluster are strongly different from both the late-collision granites and spodumene pegmatites from other SSB fields, including the large Tastyg lithium deposit. We have analysed the role of interactions between the crustal and mantle materials in the formation of granitoid sources in the Tserigiyngol-Burchin ore cluster, and described their evolution in time and the influence on the pegmatite rare-element specialization.

Martian Meteorites Shed Light on Solar System’s Early Dynamics

Chemical compositions of rocks from Mars indicate that the earliest orbits of Jupiter and Saturn were more circular than they are today.