Silicic Research Articles

Analysis of hydrochemical characteristics and genesis of water-deficient rivers in China: a case study of the Ciyao River Basin in Shanxi Province

In order to explore the chemical water characteristics of water-scarce rivers in China, the Ciyao River basin in Shanxi Province was taken as a case study. Water samples of the mainstream and its tributaries were collected in the wet, normal, and dry seasons of 2021. The composition and spatial variation of the main ions in the water body were analyzed using the ion chromatography (IC) instrument. In addition, Pearson correlation analyses were used to evaluate relevant correlation between ion concentrations. The results showed that the overall surface water in the study area was weakly alkaline, and the content of total dissolved solids (TDS) varied greatly, ranging from 702 to 5091 mg/L, with an average of 2897 mg/L. The TDS showed a middle stream > downstream > upstream trend, and the hydrochemical type was Cl • SO4 • HCO3 – Ca • Na. The contents of most ions were significantly changed based on differences in sampling sites and seasons. Natural and human factors influence the chemical characteristics of the river. According to the Gibbs diagram and Piper diagram (Figure 3), the ionic composition of the water body in the basin is mainly affected by the joint action of rock weathering and evaporative crystallization. Carbonate rocks constitute the most significant rock weathering, followed by evaporative and silicate rocks. Wastewater from industrial enterprises, agricultural wastewater, and activities of people’s daily living also have some influence on rock weathering. Cation exchange is also important in forming chemical water components in the Ciyao River. The research results can provide technical references and a basis for regional water environment protection, water resources development and utilization, and watershed eco-hydrology research.

Carbonates in the Critical Zone

AbstractEarth's Critical Zone (CZ), the near‐surface layer where rock is weathered and landscapes co‐evolve with life, is profoundly influenced by the type of underlying bedrock. Previous studies employing the CZ framework have focused primarily on landscapes dominated by silicate rocks. However, carbonate rocks crop out on approximately 15% of Earth's ice‐free continental surface and provide important water resources and ecosystem services to ∼1.2 billion people. Unlike silicates, carbonate minerals weather congruently and have high solubilities and rapid dissolution kinetics, enabling the development of large, interconnected pore spaces and preferential flow paths that restructure the CZ. Here we review the state of knowledge of the carbonate CZ, exploring parameters that produce contrasts in the CZ in different carbonate settings and identifying important open questions about carbonate CZ processes. We introduce the concept of a carbonate‐silicate CZ spectrum and examine whether current conceptual models of the CZ, such as the conveyor model, can be applied to carbonate landscapes. We argue that, to advance beyond site‐specific understanding and develop a more general conceptual framework for the role of carbonates in the CZ, we need integrative studies spanning both the carbonate‐silicate spectrum and a range of carbonate settings.

Magmatic Evolution of the Western Branch of the East African Rift System Melts: Evidence by Silicate Melt Inclusions, Rock Petrography and Geochemistry of the Nyiragongo 1977 and 2002 Lavas in DRC

Magmatic Evolution of the Western Branch of the East African Rift System Melts: Evidence by Silicate Melt Inclusions, Rock Petrography and Geochemistry of the Nyiragongo 1977 and 2002 Lavas in DRC

Prospects for the Use of the Silurian Carbonate Sequences of the Alakit-Markhinskiy Kimberlite Field for Drainage Water Injection

The development of the unique Yubileinaya pipe diamond deposit is accompanied by the formation of highly mineralized drainage waters, represented by practically unaltered natural brines of the Lower Ordovician and Upper Cambrian aquifers. Currently, drainage waters are injected into intrapermafrost collectors used as the main brine-absorbing structure. The lithofacies conditions of the Alakit-Markhinskoe kimberlite field has been chosen because of presence of the most representative Silurian sections in Western Yakutia, overlain by members of Carboniferous and Permian terrigenous deposits, as well as fairly thick trapp effusive fields (50–150 m). The study of cryohydrogeological conditions in the carbonate and terrigenous-carbonate rocks of the Silurian was carried out in the period 2014-2022 using standard methods to assess their potential for intrapermafrost reservoirs formation. In result of the studies, the main lithological types of the Silurian rocks, which are capable of forming an intrapermafrost technogenic aquifer due to the injection of drainage water and providing the safe development of the deposit to the entire design depth, are described.

Influence of Supercritical Water on the Composition and Distribution of Microelements in Resins, Asphaltenes, Kerogens, and Rocks of Tatarstan Domanik Deposits of Different Lithological Types

A comparative study of changes in the microelemental composition and distribution in resins, asphaltenes, and kerogens from Tatarstan Domanik rocks, occurring under the action of supercritical water (SCW) at 374°С and a pressure of 22–24 MPa, was made. The samples studied belong to different lithological types; they were taken from carbonate–siliceous deposits of the Romashkino and Tavel oilfields and from carbonate deposits of the Bavly oilfield. The specific features of distribution of different microelements (MEs) in rocks and rock organic matter (OM) components were revealed by inductively coupled plasma mass spectrometry (ICP-MS). The major MEs are Fe > Ti > Ni > Zn > V > Cr > Cu with the concentrations from 100 to 8600 ppm. The total ME content of rocks from these deposits is 1.14, 0.23, and 0.38%, respectively. The ME content of resins and asphaltenes does not exceed 0.3 and 2%, respectively. The highest ME content, 8%, is observed in kerogens. The carbonate–siliceous rocks from different deposits with Сorg 7.07 and 1.90% differ from the carbonate rock with low Сorg (0.33%) in that the ME concentration in them is maximal. On the other hand, the ME content of resins and asphaltenes from the carbonate rocks is higher compared to the carbonate–siliceous rock samples. The concentrations of Fe, Cu, As, Se, Pb, and Bi in kerogens of all the types decrease under the action of SCW. In the transformed resins and asphaltenes from carbonate–siliceous rocks, the V and Ni concentrations appreciably decrease, whereas in kerogens their concentrations do not change noticeably. The demetalation processes lead to the ME redistribution between the OM components and mineral surface of the rocks.

Rocha silicática com diferentes granulometrias como fonte de potássio para as culturas de alfafa e centrosema

Abstract The objective of this work was to evaluate the application of silicate ultramafic alkaline rock, with different granulometry, as an alternative potassium source on the increase of soil fertility and on the nutritional status and biomass yield of the alfalfa and centrosema crops. The used soil was a Typic Ultisol with 27.4 mg dm-3 K and 733 g kg-1 clay. The experimental design was completely randomized, in a 4 × 2 + 1 factorial arrangement. The treatments consisted of two granulometries (<0.3 and 0.3-2.0 mm) of alkaline ultramafic rock (4.0% K2O), four K rates (0, 100, 150, and 300 mg kg-1), and an additional treatment with the application of 150 mg kg-1 K in the form of KCl (58% K2O). Both legumes were grown in a greenhouse and subjected to five successive harvests. In comparison with KCl, the application of silicate rock has the potential to increase K uptake and root and shoot dry weight yield in alfalfa and centrosema. Granulometry does not affect rock use efficiency, and alfalfa presents a better K efficiency recovery in the soil after successive harvests compared with centrosema; the inverse is observed for K use and K uptake efficiencies.

Silica clay (opoka) as a promising raw material for unfired wall products by compression molding

The article is devoted to the actual problem of producing unburnt wall products of compression molding with improved and high efficiency in terms of thermal and engineering properties. The article notes the relevance, attractiveness, and wide use of unburnt pressed products in modern civil engineering. The raw material composition and production technology of unburnt wall products of compression molding are described. The traditionally used aggregates for unburnt wall products of compression molding are reviewed and their properties are analyzed. High average density and high thermal conductivity are noted in these products. The objective is to improve the thermal characteristics of these products while ensuring their strength properties. For this purpose, it is proposed to introduce a porous component of siliceous rock called opoka (silica clay) into the raw material composition of products as a mineral filler. Opoka collected from three different deposits was reviewed, its characteristics given, and the raw material analyzed. It is noted that the porosity and average density of opoka depend on its deposit. The effect of porosity and average density of opoka on the average density, compressive strength, and water absorption of unburnt wall products of compression molding based on opoka with different porosities from different deposits is described. The effect of the properties of opoka on the properties of unburnt wall products of compression molding is explained. It is confirmed that the use of opoka in the production of unburnt wall products reduces the average density of the products and improves their thermal and engineering properties. The appropriateness of manufacturing large-sized hollow wall blocks based on opoka is substantiated.

ЖЕРТВЕННЫЕ КОМПЛЕКСЫУСТЬ-ВАГИЛЬСКОГО ХОЛМА НА РЕКЕ ТАВДЕ (ПО МАТЕРИАЛАМ РАСКОПОК 1970 ГОДА)

Ust-Vagilsky Hill is an unusual cult site in the form of a hill with a diameter of about 50 m and a height of up to 6 m is located in the upper reaches of the Tavda river (Garinsky district of the Sverdlovsk region). All epochs from the Mesolithic to the Middle Ages are represented on the hill. Each epoch is characterized by its own features. For the Mesolithic, this is a geometric microlith and an arrowhead on a narrow plate. Ceramic vessels with anthropomorphic images stuck on their corollas were widely used in the Neolithic era. The Neolithic is also characterized by large nucleus and tools on wide (1.5–2.5 cm) plates of light gray weakly siliceous rock. The Eneolithic is represented by ceramic vessels decorated with a variety of geometric patterns from the impressions of a comb stamp, as well as polished arrowheads typical of this era, pendants made of dark red pyrophyllite slate, and the pommel of a mace. The transition period from late Bronze to Early Iron is characterized by ceramics of the Vagil type and remnants of metallurgical production in the form of pieces of slag, baked and crusted clay, and fragments of ceramics. This complex includes ornamental fishing sinkers, individual stone products and a clay stamp, which gives prints of a single-row fine-toothed wave. Among them are arrowheads in the form of wide isosceles triangles and scrapers, from the back and from the abdomen treated with flat retouching. The epoch of the Middle Ages is represented by ceramics of the Zelenogorsk type, an iron knife and bone tools (a dagger, a spearhead, arrowheads and points). The sacrificial character of the complexes is emphasized by the presence of ochre and non-utilitarian products: the pommel of a mace, pendants made of pyrophyllite slate, and individual clay products.

Degradacija planinskih šuma bukve (Fagetum moesiacae montanum B. Jov. 1953) u jugozapadnoj Srbiji

The degradation of mountainous beech forests in various habitat conditions in the territory of southwest Serbia is presented in this paper. Various forms of degradation on limestone and acid siliceous rocks are especially highlighted. Considering the different conditions relating to the parent rock and soil characteristics, the phases of degradation differ significantly. The research area is the wider area of Peštersko-sjenički plateau with the slopes of the surrounding mountains, so it can be said that it represents southwest Serbia.

Potential accumulation of toxic trace elements in soils during enhanced rock weathering

AbstractTerrestrial enhanced rock weathering (ERW) is a carbon dioxide removal technology that aims at accelerating one of the most powerful negative feedbacks on Earth's climate, the chemical weathering of silicates. To achieve this, ERW proposes to spread ground silicate rock on agricultural soils. According to many models, global application rates of 40 tonnes of ground basaltic rock per hectare and per year would be necessary to sequester a significant amount of CO2, representing up to 24% of the current net annual increase in atmospheric CO2. When assessing the viability of ERW as a global geo‐engineering strategy, a pivotal but overlooked question to address is whether ERW may lead to toxic trace element accumulation in soils at unauthorized and potentially harmful levels. This study evaluates the legal sustainability of ERW with regard to trace element contents in soils. We compare different trace element accumulation scenarios considering a range of rock sources, application rates and national regulatory limits. The results indicate that, at the suggested annual application rate of 40 tonnes per hectare, the first regulatory limits would be exceeded after 6 and 10 years for copper and nickel, respectively. This study argues in favour of close tailoring of ERW deployment to local conditions in order to tap into its climate mitigation potential while preserving long‐term soil uses.Highlights Terrestrial enhanced rock weathering (ERW) is a carbon sequestration technology that consists in applying rock powder to soils. This study evaluates whether rock powder application can lead to trace metals accumulation in soils beyond regulatory limits. ERW can lead to the overrun of some environmental regulatory limits within less than a decade. Specific site and rock selection will be necessary for this method to preserve long‐term soil uses.

Seasonal Variations in the Carbonate System of the Razdolnaya River

The values of pH, total alkalinity, humic substance, chlorophyll a were measured in water in the Razdolnaya R. within 13 months in 2013–2014 at a station near Razdolnyi Settl. Estimates of the carbonate system of river waters showed that the major portion of the year, the river water was a source of CO2 for the atmosphere with an annual emission flux of ~25 thousands tC/year. The chemical weathering of silicate rocks in the the Razdolnaya R. leads to withdrawal of atmospheric CO2. The mean annual export of the atmospheric CO2 in the form of dissolved inorganic and organic carbon by the Razdolnaya R. into the Amur Bay (the Sea of Japan) was 47 thousands tC/year. Therefore, the the Razdolnaya R. ecosystem in the study period absorbed CO2 (20 thousands tC/year). The period of 2003–2017 showed a tendency toward an increase in the export of alkalinity, dissolved inorganic and organic carbon by the Razdolnaya R.. Estimates of the rate of chemical weathering of rocks, composing the basin, lie within 12–24 t/(km2 year).

Petrogenesis and tectonic significance of two bimodal volcanic stages from the Ediacaran Campo Alegre-Corupá Basin (Brazil): Record of metacratonization during the consolidation of Western Gondwana

The Ediacaran Campo Alegre-Corupá Basin in South Brazil developed in two stages, the synorogenic passive rift (Basin Stage ∼605–590 Ma) and the post-collisional caldera volcano (Caldera Stage ∼583–577 Ma), respectively. Volcanic rocks from the Basin Stage show a bimodal compositional spectrum with dominant basalt and subordinate silicic rocks. The basaltic rocks are transitional to mildly alkaline, exhibiting Ocean Island Basalt-like (OIB-like) trace element enrichment patterns, with depletion in Nb and Ta, however, and crustal-like Sr-Nd isotopic signatures, suggesting that they were derived from low degrees (∼5%) of partial melting of an enriched lithospheric mantle source. The silicic rocks are transitional to mildly alkaline trachydacites associated with subordinate rhyolites, exhibiting trace element compositions typical of A2-type granitoids, produced by fractional crystallization of the coeval basalts in the Moho. Volcanic rocks from the Caldera Stage are constituted mainly by alkaline trachytes and rhyolites, occurring primarily as pyroclastic sequences coupled to minor effusive lava flows and domes, also exhibiting trace element compositions typical of A2-type granitoids. They are associated with subordinated effusive transitional to mildly alkaline basalts with Island Arc Basalt-like (IAB-like) trace element signatures. Compared to the Basin Stage, the basalts from the Caldera Stage result from higher degrees (∼15 %) of partial melting of possibly the same enriched lithospheric-mantle sources during the lithospheric root collapse of a cratonic terrane. The silicic rocks from the Caldera Stage are also derived from the coeval basalts by fractional crystallization in the Moho. However, an additional stage of differentiation in the upper crust is required to explain their silica-enriched compositions and eruptive styles. Results from this study support a connection between the silicic volcanic rocks from the Caldera Stage and the plutonic bodies from the nearby A-type Graciosa Province. Lu-Hf isotopes from detrital zircon suggest an Andean arc-type tectonic setting during the Paleoproterozoic (∼2,185 Ma) history of the Luis Alves Terrane (LAT) basement. This tectonic setting was responsible for the arc-like signatures of the intraplate lithospheric-derived rocks of both bimodal volcanic sequences. Crustal-like Sr-Nd-Hf isotopic characteristics result from a protracted isotope evolution of their enriched mantle sources, and each tectono-magmatic stage results from a different extensional setting, which has implications for the metacratonization of the LAT.

Lithofacies identification of shale reservoirs using a tree augmented Bayesian network: A case study of the lower Silurian Longmaxi formation in the changning block, South Sichuan basin, China

As important units for evaluating shale gas reservoirs, lithofacies exert obvious control on the abundance of shale organic matter and the enrichment degree of gas reservoirs. Therefore, it is of great significance to accurately identify the lithofacies of shale reservoirs relative to shale gas exploration and development. This paper takes the Longmaxi Formation shale in the Changning block, Sichuan Basin, China, as an example and uses a tree augmented Bayesian network for the quantitative classification and identification of lithofacies for the first time. First, based on thin section and scanning electron microscopy observations and X-ray diffraction, we can determine the shale lithofacies types of the Longmaxi Formation. Second, the logging response characteristics of different lithofacies were obtained by comparing conventional logging data. Finally, the tree augmented Bayesian network (TAN) was built according to the selected logging parameters and identified unknown lithofacies. The results are as follows: (1) Longmaxi Formation shale is rich in siliceous minerals. By comparing analysis of shale mineral composition and diagenetic characteristics, we divide the lithofacies into five types: siliceous rock, siliceous shale, argillaceous/siliceous mixed shale, calcareous/siliceous mixed shale and calcareous shale. (2) Based on the logging data, 6 logging curves (GR, AC, DEN, CNL, PE and RT) can sensitively indicate diagenesis and changes in mineral content. (3) The TAN model trained by logging information was used to identify 68 shale samples through the 5-fold cross validation method, with an accuracy rate of 95.58%. The results showed that the tree augmented Bayesian network not only can overcome the limitation of interdependence among well-logging properties but also represents an efficient and accurate new method for identifying shale lithofacies. This algorithm can be applied to lithofacies identification of shale reservoirs with only conventional well-logging data, which can help promote the development of lithofacies identification of unconventional oil and gas geology and provides a new method for shale gas reservoir evaluation.

Paleovolcanology, geochemistry, and zircon U-Pb-Hf isotopes of the volcano-sedimentary sequences from the Ediacaran Campo Alegre-Corupá Basin, southern Brazil: Linking volcanism and tectonics during Western Gondwana consolidation

The Campo Alegre-Corupá Basin (CACB) records a well-documented sequence of volcano-sedimentary episodes associated with specific periods of crustal extension during the late-convergent to post-collisional tectonic stages of the consolidation of Western Gondwana. Two main volcano-sedimentary stages were detailed through stratigraphic and lithofaciological studies, combined with whole-rock geochemistry and zircon U-Pb-Hf analysis, resulting in a more complete understanding of the tectono-magmatic cycles and volcanological evolution of the CACB. During the Basin Stage (605–590 Ma), regional collisional tectonics was responsible for initiating the basin as a syn-orogenic rift, during which the sedimentary cycle progressed from alluvial fans at the northern limit of the basin to braided rivers and into a lake to the south. U-Pb geochronology and Lu-Hf isotope signatures of detrital zircon revealed that the sediments were mainly derived from the Paleoproterozoic basement of the Luis Alves Terrane, which constitutes the direct basement of the CACB, with contributions from the nearby Piên Magmatic Arc and possibly from the Curitiba Terrane to the North. The sedimentary strata were progressively covered by transitional to mildly alkaline OIB-like basalts, occurring mostly as lava flows with structural aspects suggestive of subaqueous to subaerial environments, interbedded with trachydacites and surge-like pyroclastic deposits. Large volumes of widespread and densely-welded to rheomorphic ignimbrite sheets within the CACB attest to a second infilling period corresponding to the Caldera Stage (583–577 Ma). This stage was inaugurated by the outpouring of trachytic and very subordinated IAB-like basaltic lava flows at ∼583 Ma. The caldera eruption seems to have been initiated by the production of pumiceous fallouts during an early Plinian-like period of decompression of shallow magma chambers at ∼580 Ma, during which the rift-related structural framework of the Basin Stage probably controlled the collapse of a graben-like caldera. Compositional and isotopic signatures suggest lithospheric mantle sources for the magmas from both volcanic stages and support a connection between basic-intermediate and silicic rocks from both bimodal associations. They also suggest a cogenetic nature between the silicic rocks from the Caldera Stage and the A-type granitoids from the nearby plutonic Graciosa Province.

Agronomic Efficiency of Biotite in Soybean and Corn Silage Production

The aim of the present study is to assess the agronomic efficiency and potential of using biotite, a remineralizer, as nutrient source to both soybean (Glycine max (L.) Merrill and maize silage (Zea mays L.). These crops were grown in succession in different soils. The research was conducted due to the importance of adopting alternative sources of fertilizers for agriculture and the relevance of using ground silicate rock powders to maximize plant growth. The purpose was to also register this product in Ministry of Agriculture, Livestock and Supply (MAPA) as a soil remineralizer. Biotite (BE), a silicate rock powder used as soil remineralizer, was provided by Embu Mineral Company, Mogi das Cruzes, São Paulo State, Brazil. BE samples were used for particle size, mineralogical and geochemical analysis in order to assess its classification as a soil remineralizers based on Normative Instruction N. 5/2006, by MAPA. Two experiments, one with each crop, were conducted on a sandy loam texture Yellow Latosol (LA) and a clay Red Latosol (LV) soil. The experiments were zed block design with four replicates. Treatments consisted, witness, biotite (BE) remineralizer at four increasing K2O rates (30, 60, 120 and 240 kg K2O ha-1), KCl at 60 kg K2O ha-1, and FMX remineralizer (fine-graded mica schist from Pedreira Araguaia Mineral Company). Both KCl and FMX were used as reference K2O sources. Yield data have shown K release in the soil and absorption by the test plants resulted in yield increases. Biotite behavior in the soil is similar to that of FMX and in some cases, to that of KCl. Biotite has great potential to be used as potassium source in soybean and maize crops.

Genesis of Significance of Carbonated Thermal Water Springs in Xining Basin, China

There are 30 carbonate hot springs in Yaoshuitan geothermal field, Xining Basin, China, with a temperature of 18~41.5 °C; and there are 10 carbonate hot springs in Qijiachuan geothermal field, with a temperature of 10~19.5 °C. Both geothermal fields are carbonate hot springs containing large amounts of CO2 gas. In order to reveal the origin of the carbonated hot springs in Yaoshuitan and Qijiachuan of Xining Basin, this paper offers a comprehensive study of the regional deep geology, tectonic setting, total analysis of carbonated hot springs, δ2H, δ18O, δ13C isotopes, main gas composition, and geochemical characteristics of travertine dating, travertine δ13C, and rare earth elements. The geological process of carbonated hot spring formation and the evolution of H+ content from deep to shallow is revealed, and the genetic mechanism of the carbonated hot spring in Xining Basin is systematically summarized. The results show that: (1) The characteristics of δ2H and δ18O isotopes indicate that the recharge source of carbonated thermal water springs in Xining Basin is mainly atmospheric precipitation. The age of carbonated thermal water springs at 14C is more than 20 ka, indicating that some of them may come from deep fluid (gas) sources. The R/Ra in carbonated thermal water springs is mostly less than 1, indicating that the helium in geothermal water is mainly crustal source helium, and there is no deep mantle source material. (2) The Piper three-plot indicates that the direction of groundwater evolution from the recharge area at the edge of Xining Basin to Yaoshuitan and Qijiachuan carbonated thermal water spring area near the edge of the basin is opposite to the normal path of groundwater evolution in the basin, which is due to the large amount of CO2 gas mixed in the deep fault along the northern margin of Laji Mountain. The ratio of (Ca2+ + Mg2+) and (HCO3− + SO42−) in the Potan and Qijiachuan carbonated thermal water springs is close to 1, and the ratio of (Na+ + K+)/HCO3− is less than 1. It indicates that the chemical composition of the Yaoshuitan carbonated thermal water spring and the Qijiachuan carbonated thermal water spring in Xining Basin is dominated by the dissolution of calcite, dolomite, and gypsum in deep carbonate reservoirs, supplemented by the dissolution of silicate minerals. The relationship between the volume fraction of CO2 and the δ13C value of carbon isotope of CO2 indicates that the source of CO2 is inorganic, which is mainly formed by metamorphism and decomposition of deep carbonate and marble. The δEu < 1 and δCe > 1 of the rare earth elements in the calcium center of the carbonated thermal water springs indicate that the groundwater supplying the travertine material has been in the acidic environment receiving CO2 from the deep crust for a long time. (3) A series of tectonic activities, such as late collision and post-collision between the Indian and Eurasian plates, has led to the uplift, asthenosphere upwelling, and thermal invasion of the northern Tibetan Plateau and other deep dynamic processes. The deep faults in the northern margin of the Laji Mountain and other deep faults with obvious neotectonic activity have provided channels for the up-invasion of deep thermal materials, and local geothermal anomalies were formed near the deep faults. The hidden carbonate rocks and silicate rocks with large thickness undergo thermal metamorphism under high temperature and high pressure in the deep geothermal anomaly area and form a large amount of CO2, which is dissolved in water and enhances the acidity of water. At the same time, the dissolution reaction of acidic water to carbonate rocks consumes H+, which keeps the carbonated thermal water spring weakly acidic. (4) The composition of travertine in carbonated thermal water springs is dominated by calcite, indicating that travertine may be formed in a deep geological environment with a temperature of 150~200 °C, indicating that there are abnormal heat sources in shallow carbonate strata with a burial depth of 3000~4000 m. The abnormal heat source may be caused by the deep fault in the northern margin of Laji Mountain, as well as other deep and large faults channeled in the deep crust and mantle heat source, indicating that the deep fault in the northern margin of Laji Mountain has an obvious heat-controlling effect, and there is a good prospect of geothermal resources exploration near the fault.

MARBLE DIKES IN THE OLKHON COMPOSITE TERRANE (WEST BAIKAL AREA)

Linear or lens-like carbonate (marble) and carbonate-silicate bodies among gabbro and amphibolites within the Krestovsky subterrane of the Olkhon composite terrane (West Baikal Area) are identified as dikes. The dikes commonly dip almost vertically, range in thickness from 20 cm to a few meters, and are up to 100 m long. The Olkhon marble dikes quite often coexist with dolerite dikes and/or granite veins and show signatures of emplacement synchronously with the igneous bodies. The marble dikes differ from mantle carbonatites in mineralogy and chemistry and thus may be derived from sedimentary carbonate rocks molten during collisional events. The origin of the Olkhon carbonate and carbonate-silicate dikes may be explained with two possible geodynamic scenarios. They may be derived either from Neoproterozoic carbonate sediments upon the Early Precambrian basement of a cratonic block which was involved in collisional events, or from abundant carbonate sedimentary material in an island-arc terrane. Large-scale melting of silicate and carbonate rocks was maintained by heat released from mantle mafic magma intruding into the lower crust. The batches of both crustal (carbonate and granitic) and mantle (mafic) melts intruded late during the collision in a strike-slip tectonic setting.

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

New Insights Into the Petrogenesis of Voluminous Crustal‐Signature Silicic Volcanic Rocks of the Toba Eruptions (Indonesia)

AbstractThe formation of large‐volume silicic magmas in arc settings is fundamental for understanding trans‐crustal magmatic systems related to subduction zones. Here, we present an integrated study of the four Quaternary Toba eruptions and pre‐caldera Haranggaol Andesite on Sumatra, Indonesia. This rock suite has significantly enriched Sr‐Nd isotopes (87Sr/86Sr = 0.71220–0.71517, εNd = −8.9 to −10.6) compared with other volcanic rocks on Sunda‐Banda arc, but is similar to the post‐caldera (<74 ka) Sipisupisu basalts near the Toba Caldera. Thermodynamic modeling using Magma Chamber Simulator has revealed that the Toba silicic rocks can be produced by a two‐stage assimilation and fractional crystallization of mantle‐derived basaltic melts with compositions similar to the Sipisupisu basalts in the lower and upper crustal magma reservoirs. Binary modeling of Sr‐Nd isotopes suggests that the rocks near the Toba Caldera can be produced by mixing of 5%–10% of the subducting Nicobar Fan sediments (87Sr/86Sr = 0.73493, εNd = −14 on average) with depleted MORB mantle (DMM). Indeed, decompressional partial melting modeling of bulk mixtures of DMM with 7% subducting sediments using pMELTS indicates that the melts generated can have geochemical compositions similar to the Sipisupisu basalts. We therefore argue that hybridization of the subducting sediments with the mantle wedge could be an alternative scenario responsible for the enriched isotopic characteristics of the rocks near Toba. Prolonged fractionation of mantle‐derived enriched/depleted basaltic melts, accompanied by crustal assimilation and crystal‐melt segregation, could be common processes in generating large‐volume silicic magmas on continental arcs.

Late Permian radiolarians from the ‘Middle‐UpperDevonian’ in the Paqiu area of theChangning‐MenglianBelt, western Yunnan, China and their bearings on analysing the remains of thePalaeo‐Tethys

The Changning‐Menglian Belt in western Yunnan, China, is one of the key regions to decode the evolution of Palaeo‐Tethys. However, the work has been hampered considerably by the loose definition and composite nature of some stratigraphic units in the belt. These units normally have varied lithological components (slices of sequences), most of which yield scarce fossils. An example is the ‘Middle‐Upper Devonian (D2‐3)’ unit, which was established to accommodate a series of cherts, shales, siltstones and sandstones, occurring rather frequently in the central zone of the Belt. Its age assignment was mainly based on the Late Devonian conodonts from some siliceous shale intervals. However, the ‘D2‐3’ unit contains strata of ages other than Middle‐Late Devonian, as has been indicated by a few studies in the Chahe‐Manxin area. The Late Permian radiolarians have been obtained from bedded cherts of the ‘D2‐3’ in Paqiu area which provided the first solid evidence for the presence of Late Permian beds in the ‘D2‐3’ in this area. Radiolarians from two chert outcrops about 3 km apart can be assigned to two Wuchiapingian‐Changhsingian assemblages, namely, theAlbaillella levisandAlbaillella protolevisassemblages, respectively, with the former being slightly younger than the latter. Statistical analysis of Permian radiolarians from different localities in the Belt shows that Late Permian radiolarians are much commoner than Middle Permian radiolarians and Early Permian radiolarians. A review of the taxonomical composition of Late Permian radiolarians of the Belt shows that faunas from different localities can be classed into three groups, according to their contents of albaillellaians, latentifistularians, entactinarians and spumellarians, whose depositional environments correspond respectively to deep water (>500 m), intermediate water (200–500 m), and shallow water depths (<200 m). Such a composition indicates that the Late Permian radiolarian‐bearing siliceous rocks in the Changning‐Menglian Belt are slices from various palaeogeographic settings.