Tuff Samples Research Articles

Microstructural Characterization and Mechanical Properties of Volcanic Tuff (Malatya, Turkey) Used as Building Stone for the Restoring Cultural Heritage

Old stone buildings constitute a significant percentage of the residential buildings in many countries. These structures are highly vulnerable, and important losses in masonry structures occur even in moderate earthquakes. Therefore, safety evaluations of these structures have gained significant attention in recent years. In this study, the mechanical, physical and microstructural characteristics of tuff samples used in the old buildings were investigated in Battalgazi within the boundaries of Malatya Province during the Seljuk time. The characteristics of the building materials were examined in detail using in-situ and laboratory tests. Because adequate samples could not be obtained from the historical buildings, quarry areas with the same characteristics were identified. First, original building stone (OBS) used in construction was taken from fallen and unusable blocks. Then, the properties of the restoration building stones (RBS) brought from the quarries were investigated. The RBS samples were also examined using in the laboratory, and the mechanical and microstructural properties of the building components were determined. The dynamic and static moduli of elasticity were determined using ultrasonic pulse velocity and uniaxial compression test. The OBS and RBS samples yielded similar results after the microstructural analyses. Our results showed that the dynamic elastic modulus value was higher than the static elastic modulus value. The results revealed by both methods showed that the static and dynamic elastic moduli were closely linked. The OBS and RBS samples exhibited microlitic porphyritic and vesicular textures and nearly the same mineralogical and textural characteristics.

Experimental test of the cooling rate effect on blocking temperatures in stepwise thermal demagnetization

SUMMARYUpon cooling, most rocks acquire a thermoremanent magnetization (TRM); the cooling rate at which this happens not only affects palaeointensity estimates, but also their unblocking temperatures in stepwise thermal demagnetization experiments, which is important, for example, to estimate volcanic emplacement temperatures. Traditional single-domain (SD) theory of magnetic remanence relates relaxation times to blocking temperatures— the blocking temperature is the temperature at which the relaxation time becomes shorter than the experimental timescale—and therefore strictly only applies to remanence acquisition mechanisms at constant temperatures (i.e. viscous remanent magnetizations, VRMs). A theoretical framework to relate (constant) blocking temperatures to (time-varying) cooling rates exists, but this theory has very limited experimental verification—partly due to the difficulty of accurately knowing the cooling rates of geological materials. Here we present an experimental test of this ‘cooling rate effect on blocking temperatures’ through a series of demagnetization experiments of laboratory-induced TRMs with controlled cooling rates. The tested cooling rates span about 1 order of magnitude and are made possible through (1) extremely accurate demagnetization experiments using a low-temperature magnetic properties measurement system (MPMS) and (2) the use of a ‘1-step-only’ stepwise thermal demagnetization protocol where the relaxation process is measured over time. In this way the relaxation time corresponding to the blocking temperature is measured, which can be done to much higher accuracy than measuring the blocking temperature directly as done in traditional stepwise thermal demagnetization experiments. Our experiments confirm that the cooling rate relationship holds to high accuracy for ideal magnetic recorders, as shown for a synthetic weakly interacting SD magnetoferritin sample. A SD-dominated low-Ti titanomagnetite Tiva Canyon Tuff sample, however, showed that natural samples are unlikely to be sufficiently ‘ideal’ to meet the theoretical predictions to high accuracy—the experimental data agrees only approximately with the theoretical predictions, which may potentially affect blocking temperature estimates in stepwise thermal demagnetization experiments. Moreover, we find a strongly enhanced cooling rate effect on palaeointensities for even marginally non-ideal samples (up to 43 per cent increase in pTRM for a halving of the cooling rate).

Sedimentary and geochronological studies on tuff levels from Triassic strata in the Nanzhao Basin, North Qinling Orogenic Belt, and their geological significance

The Ordos Basin is the second largest oil‐ and gas‐bearing sedimentary basin in China. This basin formed during the Triassic. At present, the location of the basin margins is still highly debated in the literature, especially its eastern and southern margins. The Triassic Yanchang Formation extensively outcrops in the Ordos Basin, and its distribution can provide a significant constraint on the basin extension. In this study, we focus on the measurement and correlation of the Middle–Late Triassic sedimentary strata from Nanzhao Basin, which is located to the south‐east of the present‐day Ordos Basin. The results of this study indicate that the sedimentary sequence of Triassic strata from Taizishan Formation and Taishanmiao Formation in the Nanzhao Basin is comparable with that of the Yanchang Formation in the Ordos Basin. Tuff intercalations in clastic rocks from Taizishan Formation in the Nanzhao Basin were studied with zircon chronology and Hf isotope analysis. The results show that the tuff sample has concord U–Pb age of 234.6 ± 1.5 Ma, which is considered as the boundary age between Middle and Late Triassic with a similar age in respect to that of the Yanchang Formation. The TDM2 values for the studied sample range from 1.0 to 1.4 Ga with the peak at 1.2 Ga, which is also similar to TDM2 values for tuffs encountered in the Yanchang Formation. On the other hand, the corresponding εHf(t) values of tuff in Nanzhao Basin range from −1.1 to +4.2 with an average of 1.2 and peak at 2, which are different with respect to those of the Yanchang Formation. According to the geochronological data, the tuffs in Nanzhao Basin might be mainly derived from a depleted‐mantle source from Late Meso‐Proterozoic period, and contaminated by a continental Early–Middle Meso‐Proterozoic crust. Therefore, we suggest that in Middle–Late Triassic, the southeastern margin of the Ordos Basin may have extended to Nanzhao area and the different εHf(t) values between tuffs in Nanzhao Basin and present Ordos Basin may be the result of scissor‐type collision of North China Block and South China Block during the Triassic.

Physical and mechanical characteristics of saturated tuff under the freeze–thaw cycle

The freeze–thaw cycle of rocks is a research hotspot in the field of geotechnical engineering, and it significantly affects the eastern part of the Zhejiang Province in China. In this study, we test 40 occurrences of freeze–thaw cycles on tuff from the Ningbo area and investigate the variation of the physical and mechanical properties. The results show that only a small amount of debris falls off the saturated tuff samples during the freeze–thaw cycle. The overall quality of the rock sample gradually decreases with the increase in the number of freeze–thaw cycles. However, the average loss rate of the quality is extremely low, accounting for only 0.07% of the rock sample quality. The wave velocity of the rock sample gradually decreases, and the extent of reduction decreases when the number of cycles increases. In the uniaxial compression test, a failure surface appears for the rock samples with low freeze-thaw cycles. The complete failure surface of the samples gradually disappears. Moreover, the compressive strength of the samples progressively decreases with the increase of the number of freeze–thaw cycles.

Zircon U[sbnd]Pb age constraints on the mid-Cretaceous Hkamti amber biota in northern Myanmar

Hkamti amber contains exquisite fossils, but the age of the amber biota is unclear. In this study, we documented the characteristics of fossils hosted in the amber, and we present zircon UPb ages of tuff layers from the Kachin and Hkamti sites (i.e., the “new mine”). We also present a compilation of arthropod and echinoderm syn-inclusions from the mid-Cretaceous Hkamti amber of Myanmar, indicating a humid tropical or subtropical forest paleo-environment. Zircon analyses (n = 143) of four tuff samples that host the amber deposit in different pits yielded a weighted-mean age of 109.7 ± 0.4 Ma. Zircon rare earth element data demonstrate the zircons are of igneous origin. Therefore, the age of the Cretaceous amber biota from Hkamti is ca. 110 Ma. This means that the Hkamti assemblage should be treated as distinct from other Burmese amber collections, as it represents a significantly older source within a different depositional environment. The commercial sources of Burmese amber are variable and encompass multiple mining regions, which makes maintaining distinctions between deposits important if their faunal contents are to be studied in a proper temporal or ecological context. The refined understanding of amber deposits in Myanmar highlights the importance of distinguishing sources, but it also offers an opportunity to study a series of deposits from ~110 to ~72 Ma, instead of just one snapshot of terrestrial ecology around ~99 Ma.

The role of different salt solutions and their concentration ratios in salt crystallization test on the durability of the Döğer tuff (Afyonkarahisar, Turkey) used as building stones of cultural heritages

Volcanic tuff is widely used in Anatolian architecture and represents building stones of cultural heritage. The present study included a relevant assessment of the effect of four salt types and their four different concentrations on the durability of the Doger tuff used as building stones of cultural heritages, which is subjected to salt crystallization tests. For this purpose, an investigation was conducted on their chemical, mineralogical-petrographical (polarized microscopy, XRD, SEM analyses, pore size distribution), and physical and mechanical properties as well as their deterioration behavior in the salt crystallization test by different salt solutions (and their different concentrations). In salt crystallization tests, sodium sulfate (Na2SO4·10H2O), magnesium sulfate (MgSO4·7H2O), sodium chloride (NaCl), and potassium chloride (KCI) solutions were used, and 2, 5, 10, and 14% concentration ratios were used for each salt solution. In this work, it was observed some physical and mechanical values decreased along with weight loss in samples. The ultrasound pulse velocity (UPV) and uniaxial compression strength (UCS) values of the Doger tuff samples in all the salt solutions and concentrations decreased after the 15 test cycles. The tested Doger tuff samples completely broke down in the 10% and 14% concentrations in the sodium sulfate, magnesium sulfate, and potassium chloride solutions.

Geochronology of the Volyn volcanic complex at the western slope of the East European Craton – Relevance to the Neoproterozoic rifting and the break-up of Rodinia/Pannotia

Thick Neoproterozoic rift sequences along the western margin of the East European Craton (EEC) are classically attributed to rifting leading to break-up of super-continent Rodinia/Pannotia. Rifting was associated with intense, mainly mafic, volcanism, known as the Volyn Series, in the Lublin-Podlasie Basin (LPB) and in the Orsha-Volyn Aulacogen. Legacy deep boreholes in Poland provide continuous section through the volcanic series. Zircon from nine samples of tuff layers interbedded with basalt, from four boreholes, were dated with the U–Pb method with SHRIMP. The samples contain syn-eruptive zircons, together with zircon recycled from previous ash falls and zircon from the surrounding Proterozoic basement. The youngest volcanic zircon cluster from each sample of the studied tuff samples yielded concordia ages stratigraphically consistent, which document eruption events that took place between 567.1 ± 4.7 Ma and 551.0 ± 4 Ma. The most intense development of lavas and pyroclastics took place at ca. 557–555 Ma and ca. 567–560 Ma. Older volcanogenic zircon grains, inherited from previous phases of volcanic activity, preceding actual eruptions, were are dated at 588.0 ± 8 Ma to 580 ± 8.1 Ma. Age spectrum of xenocrysts zircon grains, inherited from the crystalline basement rocks of the LPB, ranges from ca. 1830 Ma to ca. 1480 Ma, coherent with the known late Paleoproterozoic and Mesoproterozoic age of crust-forming events in the western part of the EEC. The late Ediacaran syn-rift igneous activity in the LPB continued over a time span of approx. 37 My. It developed along both the SW margin of emerging Baltica and in the western the Orsha-Volyn Aulacogen. The study area was located at the intersection of these regional structures, being thus a site of development of an incipient triple junction, related to Rodinia/Pannotia break-up. Further extension along the SW margin of Baltica led to its separation from the plate adjacent to the west, and to the subsequent development of continental passive margin. Final emergence of Baltica, as an individual palaeocontinent, took place at ca. 550 Ma.

Adsorption of lead and cadmium from aqueous solution by Gunungkidul zeolitic tuff, Indonesia

This study focuses on utilizing zeolitic tuff as a novel adsorbent for lead and cadmium solution. Two zeolitic tuff samples were obtained from Tegalrego and Bantengwareng village, Gunungkidul, Yogyakarta, Indonesia. Zeolitic tuff sample characterization was carried out by conducting microscopic and X-ray diffraction analysis, cation exchange capacity, and chemical measurement. Batch adsorption tests were carried out for the study of isotherms with the Langmuir model. The results of characterization showed that the Bantengwareng and Tegalrejo zeolitic tuff sample consist dominantly of mordenite mineral and other impurities. Bantengwareng zeolitic sample revealed had higher mordenite and smectite content compared to Tegalrejo zeolitic tuff sample which effects to the adsorption capacity. The batch adsorption test showed the adsorption ability of the Bantengwareng zeolitic tuff sample achieved for 76% of lead and 69% of cadmium; however, the Tegalrejo zeolitic tuff sample achieved for 51% of lead and 26% of cadmium. The result of isotherm study based on Langmuir equation revealed that the adsorption capacity of Bantengwareng and Tegalrejo zeolitic tuff samples has a value of 416.67, 384.61 and 277.77, 243.91 mg/g for lead and cadmium, respectively. The correlation coefficient based on Langmuir model varied from 0.866 to 0.956, which suggests that isotherm models fit very well. The reusability study revealed that the efficiency decreased reduce up to 30% after third cycles; however, the zeolitic tuff samples in study area are considered as part of its adsorption potential for lead and cadmium solution.

Phase-field fracture modelling of crack nucleation and propagation in porous rock

In this work, we suggest a modified phase-field model for simulating the evolution of mixed mode fractures and compressive driven fractures in porous artificial rocks and Neapolitan Fine Grained Tuff. The numerical model has been calibrated using experimental observations of rock samples with a single saw cut under uniaxial plane strain compression. For the purpose of validation, results from the numerical model are compared to Meuwissen samples with different angles of rock bridge inclination subjected to uni-axial compression. The simulated results are compared to experimental data, both qualitatively and quantitatively. It is shown that the proposed model is able to capture the emergence of shear cracks between the notches observed in the Neapolitan Fine Grained Tuff samples as well as the propagation pattern of cracks driven by compressive stresses observed in the artificial rock samples. Additionally, the typical types of complex crack patterns observed in experimental tests are successfully reproduced, as well as the critical loads.

Geochronology and geochemistry of late Paleozoic volcanic rocks from eastern Inner Mongolia, NE China: Implications for igneous petrogenesis, tectonic setting, and geodynamic evolution of the south-eastern Central Asian Orogenic Belt

Here we report new petrography, geochemistry, UPb zircon geochronology, and Hf isotope results for volcanic rocks of the Dashizhai Formation in the Dashizhai area, Keerqin Right Wing Front Banner, Inner Mongolia. The volcanic rocks have mafic to felsic bulk-rock compositions and include basalt, rhyolite, basaltic andesite, andesite, dacite, and rhyolitic tuff. Two dacite and rhyolitic tuff samples yield laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) 206Pb/238U zircon ages of 332 ± 1 Ma and 300 ± 1 Ma, respectively, suggesting that the timing of felsic volcanism ranged from the early to late Carboniferous. Mafic volcanic rock samples are enriched in large-ion lithophile elements (LILE) and light rare earth elements (LREE; La/Nb = 1.58–4.84), and are depleted in high-field-strength elements (HFSE; Th/Yb ratios <2.2) and heavy rare earth elements [HREE; (Tb/Yb)N ratios 1.27–1.91]. Based on these trace element characteristics, we propose that the mafic volcanic rocks represent fractionated, high-degree partial melts that were sourced from the subduction-modified and melt-depleted mantle wedge. The felsic volcanic rocks yield LILE- and LREE-rich compositions and arc-like HFSE- and HREE-poor signatures. Magmatic zircons recovered from the dated rhyolitic tuff and dacite samples yield positive εHf(t) values (+1.21 to +14.85) and two-stage Hf model ages of 1236 and 391 Ma, suggesting that arc-like felsic volcanism was sourced from, and/or interacted with, the older juvenile lower-crust underlying the Dashizhai Formation. Therefore, the mafic to felsic volcanic rocks from the Dashizhai area likely formed in a Carboniferous magmatic arc at a continental margin. Based on the isotopic and geochemical signatures of the Carboniferous–Permian volcanic rocks in the Dashizhai area, we preliminarily divide central and eastern Inner Mongolia into three zones: (i) North Zone, which formed at the magmatically active continental margin; (ii) Middle Zone, which formed in a magmatic arc peripheral to the continental marginal; and (iii) South Zone, which formed in an oceanic island arc. The age and geochemical signature of the Dashizhai Formation points to active, northward subduction during the early Carboniferous to the early Permian and suggests that the Paleo-Asian Ocean closed after the early Permian.

Pore property as an indicator of macro-deterioration in slightly weathered tuffs

Tuff rock is highly heterogeneous due to volcanic activity, hydrothermal alteration, and weathering. It is difficult to explain the deterioration mechanisms of the weathered rocks merely based on mineralogical and chemical parameters. It has been reported that subtle weathering can modify pore structure and subsequently affect the rock mechanical behavior of tuffs. In this work, the pore characteristics in slightly weathered tuffs and fresh tuffs are systematically analyzed based on Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Porosimetry (MIP) tests. Additionally, meso-level uniaxial compression tests were conducted on the tuff samples by utilizing the MTI–LM (miniature tensile instrument–light microscope) system to detect the crack propagation and deformation process. The results demonstrated that additional mesopore (10–50 nm) increases with pore throat expansion during weathering, and the change of pore structure influences the tuff failure mode. Specifically, for the slightly weathered tuff, crack initiates in the altered minerals or matrix and results in shear failure. However, as for the fresh tuff, crack usually initiates in the intact and fresh minerals and matrix, and eventually leads to tensile failure. Therefore, we propose that tuff pore property can serve as potential indicator of the micro-mechanism of substantial macro-deterioration due to weathering.

SHRIMP U–Pb ages of zircons from the Lengshuikeng ore field, North Wuyi Mountains, South China: Implications for dating volcaniclastic rocks

AbstractThe Lengshuikeng Ag‐Pb‐Zn ore field is located in the North Wuyi Mesozoic volcanic belt south of the Qinzhou–Hangzhou suture zone between the Yangtze and Cathaysia paleo‐plates. Previous zircon U–Pb geochronological studies on ignimbrites and tuffs from this area have yielded conflicting ages of 157–161 Ma (Early Upper Jurassic) and 137–144 Ma (Early Lower Cretaceous). Volcanic rocks in the ore field have even been proposed to include both ages. Our SHRIMP zircon U–Pb dating of the ignimbrite and tuff samples from the ore field, along with field observations and results from geochronological work on other volcanic and sub‐volcanic rocks in the region, shows that two populations of magmatic zircons, one autocrystic and the other xenocrystic, are present in the pyroclastic rocks. The autocrystic zircons have ages suggesting formation/eruption at approximately 140 Ma, whereas the xenocrystic zircons give ages of 155–159 Ma, indicating intrusion of granitic porphyries in the Early Upper Jurassic. Therefore, the pyroclastic rocks in the Lengshuikeng Ag–Pb–Zn ore field formed in the Early Lower Cretaceous. The youngest zircon U–Pb ages from pyroclastic rocks may not represent the formation/eruption ages of the host rock, depending most likely on the existence and/or abundance of juvenile or vitric pyroclasts in the rocks.

Numerical Analysis of the Anisotropy and Scale Effects on the Strength Characteristics of Defected Rockmass

Discontinuous defect in the rockmass is a key influential factor in controlling the strength behavior, and how to estimate the anisotropic strength and scale effect on the defected rockmass is the remaining challenging focus in engineering application. In the present study, intact tuff samples cored from the Xiabeishan tunnel engineering in situ are conducted by experiment tests (i.e., uniaxial compression test, triaxial compression test, and Brazilian tensile test) to obtain the corresponding mechanical parameters. Results from the numerical simulations using the particle flow code (PFC) by the flat‐jointed model (FJM) are performed to match the macroparameters from experimental results. It is observed that numerical results have good agreement with the macroscopic mechanical parameters of intact samples including UCS, BTS, triaxial compression strength, and corresponding deformation parameters. Finally, a series of uniaxial and confining compression tests are conducted by using a synthetic rockmass (SRM) method which is coupled with the discrete element method (DEM) and discrete fracture network (DFN). Then, the anisotropy and scale effects on the strength characteristics of the defected rockmass are investigated. The results show that defects have a vital effect on the failure mode and strength behavior of the rockmass in the research region. The strength parameters are changed with the specimen size. The REV size of the considered defected rockmass is regarded as 5 × 10 m, and this size is also influenced by the confinement level. The anisotropy of macroscopic strength parameters is found in the considered defected rockmass, whose stress‐strain curves and failure modes are also discussed.

Contribution to the Study of Paleoproterozoic Materials for the Improvement of Social Housing in the Kedougou Region: Case of Mako Andesitic Meta-Tuffs

The objective of this project is the valorization of Mako andesitic volcanic tuffs for use in social housing in the Kedougou region. To achieve these objectives, a geotechnical characterization of the tuff samples was carried out and the geopolymerization stabilization was adopted for the manufacture of bricks. These bricks stabilized by an alkaline activation offer compressive strengths that exceed the threshold value (2.9 MPa) set by the standard (NF P14-304). The best compressive strengths (12.14 MPa) and flexural tensile strengths (5.43 MPa) are obtained in the series of bricks made with 35% of the mass of a solution of caustic soda at 12 molars concentration with a curing temperature cooking of 185°C and an average absorbance of 13.21%.

Experimental Study on Freeze‐Thaw Cycle Duration of Saturated Tuff

The freeze‐thaw duration is one of the important factors affecting the change of rock properties. However, this factor has not formed a unified standard in the freeze‐thaw cycle test. This study uses saturated tuff samples taken from eastern Zhejiang, China, as research objects to explore the change law of the time required for the rock to reach a full freeze‐thaw cycle. Measured results show that the total duration of the freeze‐thaw cycle presents an increasing power function with the increase in the number of freeze‐thaw cycles. The freezing process is divided into three phases: initial freezing, water‐ice phase transition, and deep freezing. The melting process is also divided into three phases: initial melting, ice‐water phase transition, and deep melting. The time required for the ice‐water phase change stage of the melting process does not change with the increase in the number of freeze‐thaw cycles, while the other stages increase as a power function. The proportion of duration of each stage in the freezing process does not change with the increase in the number of cycles. By contrast, the duration proportion of the initial melting phase in the melting process decreases, and the deep melting phase increases. Experimental results of the freeze‐thaw cycles of tuff demonstrate that the freeze‐thaw duration of the freeze‐thaw cycles within 40 times can be set to 9 h. The freezing and melting processes are 6 and 3 h, respectively.

Tight tuff reservoir characteristics and its controlling factors: A comparative study of the Permian Tiaohu Formation and Carboniferous Haerjiawu Formation in the Santanghu Basin, NW China

Tight oil resources have been found in tight tuff reservoirs in many oil and gas bearing basins. The tight tuff reservoir developed in the Santanghu Basin (NW China) has provided an excellent opportunity for further research to enhance our cognition and understanding of tuff reservoir characteristics. This study focuses on the differences in the basic characteristics in petrologic features, reservoir space, and physical properties between the Tiaohu and Haerjiawu formations tuff reservoirs, then determines the formation mechanism causing these differences. (1) The tuff samples of the Tiaohu Formation mainly consist of vitric fragments, and quartz and albite are the major mineralogical components. However, the crystal fragment content is much higher in the Haerjiawu Formation tuff, and albite and anorthite are the major components. (2) Primary pores and the interparticle pores among authigenic minerals formed during alteration are the main pore types for both the Tiaohu Formation and Haerjiawu Formation tuffS. (3) The Tiaohu Formation tuff reservoir is characterized by high porosity (ranging from 10% to 25%) and relatively low permeability (on the order of 0.01–0.50 mD), while that of the Haerjiawu Formation is characterized by lower porosity (<10%) and lower permeability (mainly <0.1 mD). (4) Alteration and compaction processes contributed most to the pore formation in both the Tiaohu and Haerjiawu tuff reservoirs. Hence, the changes in total tuff reservoir porosity can be explained by the evaluation of compaction residual porosity and alteration porosity. The vitric fragments in the Tiaohu Formation originated from acidic or intermediate-acidic volcanic ashes, which are more liable to be altered than the basic volcanic ashes that formed the crystal fragments in the Haerjiawu Formation. Moreover, the Haerjiawu Formation tuff reservoir is buried hundreds of metres deeper than the Tiaohu Formation in general, and thus, experienced stronger diagenetic compaction, which indicates fewer residual pores for Haerjiawu Formation tuff samples. The nature of tuff and the deeper burial depth are the major reasons for the worse physical properties of the Haerjiawu Formation tuff reservoir.

High‐precision Dating and Geological Significance of Chang 7 Tuff Zircon of the Triassic Yanchang Formation, Ordos Basin in Central China

The Ordos Basin, as the second largest petroliferous basin of China, contains abundant oil and gas resources, oil shale, and sandstone‐type uranium mineral resources. Chang 7 shale is not only the major source rock of the Mesozoic petroliferous system of the Basin, but is also crucial in determining the space‐time distribution relationship of the shale section for the effective exploration and development of the Basin's oil and gas resources. To obtain a highly precise age of the shale development section, we collected tuff samples from the top and bottom profile of the Chang 7 Member, Yishi Village, Yaoqu Town, Tongchuan District, on the southern margin of the Ordos Basin and performed high‐precision chemical abrasion (CA)–isotope dilution (ID)–thermal ionization mass spectrometry (TIMS) zircon U‐Pb dating on the basis of extensive laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) zircon U‐Pb dating data. Our results show the precise ages of the top and bottom zircon in the Chang 7 shale to be 241.06±0.12 Ma and 241.558±0.093 Ma, respectively. We first obtained Chang 7 age data with Grade 0.1‐Ma precision and then determined the age of the shale development in the Chang 7 Member to be the early‐Middle Triassic Ladinian. This result is supported by paleontological evidence. The deposition duration of the Chang 7 shale is 0.5Ma with an average deposition rate of the shale section being 5.3 cm/ka. Our research results provide time scale and basic data for further investigation of the basin–mountain coupling relation of the shale section, the sedimentary environment and volcanic ash and organic‐matter‐rich shale development relation, and the organism break‐out and organic‐matter enrichment mechanism.

PREPARATION OF TUFF IN THE DUMPS OF BASALT QUARRIES FOR VIBRATION SCREENING

The article presents the current development of an integrated technology for the processing of tuff in the dumps of basalt pits to highlight the valuable metal fraction and silicate masses. In order to prepare tuff for processing, it is proposed to use the effect of moisture absorption and reduce the strength of tuff when moistened with water, since it has a porous structure and is relatively easy to absorb moisture. This operation, followed by vibratory screening in a small class of -2.5 + 2.0 mm, is promising for the selective extraction of tuff from dumps of basalt quarries, where, unlike other rocks, tuff is a water-absorbing mineral. The article presents the results of experimental studies and the development of mathematical models of the process of softening tuff with water. The objective of the research was to determine the degree of change in the strength of tuff under the influence of moisture and to establish the dependence of humidity and strength to predict the process of softening of tuff when wet. Experimental studies were carried out on various samples of tuffs of the Rafalovsky basalt quarry, while the exposure time of the sample in water was recorded, humidity, indenter indentation pressure on the press or contact load and compressive strength or contact stress during indenter penetration were determined. It was found that when moistening tuff during the day, humidity increases on average by 9%, strength decreases from 120.5 to 10.6 MPa and is 9.2% of the strength of the feedstock. Humidity of tuff in time increases according to the law of a quadratic parabola with a complex argument, the force of indentation of the indenter from moisture and wetting time changes according to the logarithmic law, strength from humidity and time - according to the law of the quadratic parabola. Also, the article proposes an algorithm for calculating humidity and strength characteristics during wetting during the day. It is advisable to use this technology of softening tuff with water as an ore preparation operation with the integrated technology of tuff processing.

Age and geological context of the Barby Formation, a key volcanic unit in the Mesoproterozoic Sinclair Supergroup of southern Namibia

Abstract Volcanic and sedimentary rocks of the Sinclair Supergroup occur in the Konkiep Terrane of Southern Namibia. Three volcanic and sedimentary cycles are recognised. In this work we describe and date volcanic rocks of the Barby Formation, a key unit in the Sinclair area. The coeval Spes Bona Syenite and the Tiras Granite Gneiss are also described and dated. The rock types in the Barby Formation are rhyolites, basaltic trachyandesites, trachybasalts and trachydacites as well as volcanoclastic rocks. The rocks are largely undeformed and partly altered by deuteric and contact metamorphic processes but not regionally metamorphosed. Our samples represent both the calc-alkaline and alkaline trends documented in previous work. U-Pb ion probe and laser ablation inductively coupled plasma (LA-ICP) multicollector mass spectrometer Lu-Hf microbeam analyses were made of zircon and baddeleyite grains from four samples. A felsic tuff sample from the base of the Barby Formation has a 207Pb/206Pb zircon age of 1214 ± 5 Ma (2σ). A rhomb porphyry sample from the top of an 8.5 km-thick stratigraphic section gives a 207Pb/206Pb baddeleyite age of 1217 ± 2 Ma. The Spes Bona Syenite which intrudes the top of the Barby Formation has a 207Pb/206Pb baddeleyite age of 1217 ± 3 Ma and an indistinguishable LA-ICP collision cell mass spectrometer Rb-Sr biotite isochron age of 1238 ± 20 Ma, showing that there was no &amp;gt;350°C regional metamorphic event. Multi-element diagrams for the calc-alkaline samples show a dominant signature of reworked crust which is superimposed on a possible subduction signature. However the alkaline samples contain clear subduction signatures which are not seen in the underlying 1.37 Ga Kumbis rhyolite. The Barby Formation samples and coeval Spes Bona Syenite have Lu-Hf crustal residence ages between 1682 and 1873 Ma, suggesting that both of these units formed from a mixture of juvenile mantle-derived and older crustal material. The Barby Formation is considered to have originated due to a subduction event which took place during the assembly of the Rodinia supercontinent. The duration of the Barby magmatic episode is constrained to a maximum 9 m.y. period between 1219 and 1210 Ma, and during this period the Konkiep Terrane was an active continental margin. The 1204 ± 9 Ma Tiras Granite Gneiss is slightly younger than the Barby Formation and intruded across the Lord Hills Shear Zone, which is the suture between the hardly metamorphosed Konkiep Terrane and the highly metamorphosed Grunau Terrane of the Namaqua-Natal Province. Its intrusion reflects the end of subduction-related volcanism, due to the collision of Namaqua terranes with the Konkiep Terrane.

In-situ oxidation effect on pore size distribution in investigating adsorption properties under various geochemical conditions

Redox affected pumice tuff was used to investigate the changes of pore properties due to oxidation and its possible consequences to adsorption of nuclides on it. Porosity and pore size distribution were analyzed by mercury injection technique and scanning electron microscopy. Batch experiment was carried out with 1 cm3 block shaped intact pumice tuff samples to determine adsorption coefficient, Kd at several pH, ionic strength and initial nuclide concentrations of stable cesium (133Cs). Pore area, surface area and specific surface area were determined from pore size distribution data before and after adsorption experiment and later compared between fresh and oxidized samples. The results showed that reduction of less than 0.33 μm size micro pores due to oxidation is mainly responsible for reducing surface areas, eventually reducing the sorption quantity. Influence of pore properties became negligible in redox affected pumice tuff indicating inverse relation of oxidation phenomena with adsorption coefficients values.