Chlorite Schist Research Articles

Lithological Impact on Radon Levels: A Study of Indoor and Soil Gas Radon in the Centre Region of Cameroon

AbstractThe objectives of the current study are to carry out soil gas radon (Rn) measurements, to evaluate the total inhalation effective dose, to determine risk levels over the lithological formations of the study area. The behavior investigation of Rn activity concentration distributions in dwellings and soils, and soil Rn mapping were also conducted. Soil gas Rn measurements were made at 102 sampling points by Markus 10 instrument. This data was combined with previously reported results from 140 indoor Rn RADTRAK dosimeters to determine the total inhalation effective dose and to conduct a statistical analysis. Overall, the Rn activity concentrations in soil and dwellings range from 4 to 66 kBq m−3 and from 15 to 140 Bq m−3, with averages of 31 ± 15 kBq m−3 and 41 ± 24 Bq m−3 respectively. The corresponding total inhalation effective dose ranges from 0.35 to 3.53 mSv y−1, with a mean value of 1.37 ± 0.58 mSv y−1. For soil gas Rn, the chlorite schist lithology showed the highest average concentration level. Which could be justified by the possible presence, within chlorite minerals, highly emitting zones of alpha particles, leading to the formation of radioactive halos. Normal and high‐risk level of Rn were found for about 82% and 11% of the total area surveyed respectively. These findings highlight the need for preventive measure against Rn exposure in homes within the investigated areas. This study contributes valuable insights into Rn distribution patterns and risk assessment, offering a basis for targeted interventions in the region.

Characterization of a Metamorphosed Volcanic Stratigraphy and VMS Alteration Halos Using Rock Chip Petrography and Lithogeochemistry: A Case Study from King North, Yilgarn Craton, Western Australia

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe2O3) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets.

Mineral chemistry and P–T conditions of the winchite-bearing metabasic rocks in the NE edge of the Menderes Massif (Western Türkiye)

The Menderes massif is a large metamorphic crystalline complex located in western Turkey. The massif consists of late Neoproterozoic basement (core) rocks and Palaeozoic - Cenozoic cover units that have undergone by high- and low-grade polyphase metamorphisms. Palaeozoic to Mesozoic cover units cropped out in the NE edge of the massif (east of Sivaslı) are overlaid tectonically by upper Cretaceous meta-ophiolitic rocks. The meta-ophiolitic unit comprises blocks mainly of metabasalt, metagabbro, metadiorite and metaultramafite within an intensively sheared serpentinite matrix. It also includes blocks of epidote-actinolite-schist and tremolite-actinolite-schist, which originated from basic rocks, as well as chlorite schist blocks, which originated from ultramafic rocks. Sodic-calcic amphiboles recorded in the samples of metabasalt block taken from the marble-metabasalt block boundary, at the tectonic contact where the meta-ophiolitic rocks overlap the underlying marble sequence. Sodic-calcic amphiboles were classified into winchite and ferri-winchite with relatively homogeneous TSi (7.35–8.01 a.p.f.u.), and XMg (0.69–0.80) values. P-T conditions were estimated to be around 300–400 °C and 5–6 kb based on the mineral chemical analyses of the sodic-calcic amphiboles. According to these values, the NE edge of the Menderes Massif must have undergone metamorphism under a medium-pressure (MP) greenschist facies.

Bakestones in Northern Norway: An Archaeological Witness to Medieval Foodways and Maritime Trade

BAKESTONES ARE A 11TH-CENTURY EARLY MEDIEVAL INNOVATION associated with flatbread production that reflect a distinctive Norwegian food culture spanning some 600 years. Large scale manufacture of chlorite schist bakestones at Ølve-Hatlestrand, western Norway, was linked to further distribution in Norway from the port of Bergen. Bakestones were an important item of maritime trade transported to northern Norway in exchange for stockfish (dried cod) and are most commonly found in coastal fishing villages and settlement mound sites. An attribute-based analysis of bakestones from northern Norway in the Arctic University Museum of Norway archaeological collection, the first comprehensive study outside of medieval towns, explores the role of bakestones for Norse/Norwegian maritime settlement and as a valued trade commodity, as demonstrated by reuse of bakestone fragments. In addition to documenting spatial and temporal bakestone distribution, geochemical (XRF) characterisation and a preliminary analysis of organic residues were also undertaken. Although bakestones are primarily associated with Norwegian settlement, their role in contexts with a combination of indigenous Sámi and Norse/Norwegian elements is also evaluated.

Sulphide petrology and ore genesis of the stratabound Sheep Creek sediment-hosted Zn–Pb–Ag–Sn prospect, and U–Pb zircon constraints on the timing of magmatism in the northern Alaska Range

The Sheep Creek prospect is a stratabound Zn–Pb–Ag–Sn massive sulfide occurrence in the Bonnifield mining district, northern Alaska Range. The prospect is within a quartz–sericite–graphite–chlorite schist unit associated with Devonian carbonaceous and siliceous metasedimentary rocks. Volcanogenic massive sulfide (VMS) deposits in the district are hosted in felsic metavolcanic rocks (362 ± 2 Ma) associated with siliciclastic and carbonaceous sedimentary rocks that overlie the stratigraphic sequence hosting the Sheep Creek prospect. Felsic metaigneous rocks in underlying units are 372 ± 4 to 366 ± 4 Ma. Sheep Creek is atypical of the other sulfide deposits in the district in (1) having Sn grades up to 1.2%; (2) being contained in fine-grained, quartz-rich rocks and quartz–pebble conglomerate that likely originated as chert and chert-clast sediment, respectively; and (3) showing minimal evidence of volcanic components in the host rocks. Comparison of immobile trace-element proportions for graphitic and siliceous rocks from the Sheep Creek area with those for argillite associated with the Bonnifield VMS deposits indicates a continental volcanic-arc provenance for the former and a within-plate and passive margin provenance for the latter. In contrast to previously published interpretations, our data analysis supports a clastic-dominated (CD) rather than a VMS affinity for the Sheep Creek prospect. In our model, Zn–Pb–Ag–Sn mineralization formed by syngenetic or early diagenetic processes on or beneath the seafloor, possibly in the shallow-water environment of an outer continental shelf setting. Potential analogues are the Paleozoic CD deposits in the Canadian Selwyn Basin outboard of the Laurentian continental margin.

A rational construction method and deformation control system of tunnelling in extremely soft and fractured chlorite schist medium

The large deformation disaster is a major engineering problem that has not been sufficiently addressed in tunnelling in soft rock mass. Previous investigations essentially focused on large deformation control methods or measures for soft rock masses, with little attention to extremely soft and fractured rock masses. As a result, we here conduct a comparative field test of the cross diaphragm (CRD) method and the three-bench annular excavation method with reserved core soil. The case study site is the Lianchengshan Tunnel of the Baoji-Hanzhong Highway in Shaanxi Province and we could establish an appropriate construction methodology for the chlorite schist stratum. Following that, the mechanism of large deformation of extremely soft and fractured surrounding rocks is revealed, and the compatibility of the main methods of controlling large deformation in very soft and fractured layers is discussed. Thereafter, a suitable large deformation control approach and support system for extremely soft and fractured rock strata is proposed. Based on engineering practice, we also elaborate on the cooperative bearing principle of each component of the support system in detail. Our findings indicate that the CRD method has no outstanding effect on the deformation control of the Lianchengshan Tunnel. The three-bench annular excavation method with reserved core soil outperforms the CRD method in controlling the settlement of the tunnel arch, reducing the construction risk, and ensuring the construction progress. In general, it works better than the CRD method and should be preferred in tunnel construction. Considering the “soft” and “fractured” geological features of chlorite schist in the Lianchengshan Tunnel, a multi-layered and staged support system is developed with strengthening support as the core and stress release, as well as section optimization as the assistance. Under the support system, the tunnel deformation is effectively controlled. Compared to the single-layered primary support scheme via the same constructional approach, the maximum values of settlement and convergence of the measured section are reduced by 51 % and 56 %, respectively. The achieved results reveal that the overall stiffness of the single-layered primary support consisting of HW200 × 200 steel rib is about 3 times that of I22b steel rib, and the overall stiffness of the double-layered primary support consisting of HW200 × 200 steel rib is about 2.7 times that of a single layer. The results of this study not only contribute to the control concept and method of large deformation, but also provide a novel pathway and a substantial reference to solve the problem of control of large deformations of tunnels in extremely soft and fractured strata.

Scandio-winchite, ideally ☐(NaCa)(Mg4Sc)(Si8O22)(OH)2: The first Sc-dominant amphibole-supergroup mineral from Jordanów Śląski, Lower Silesia, southwestern Poland

Abstract Scandio-winchite, the first natural Sc-dominant amphibole-supergroup mineral, has been discovered in a granitic pegmatite that crops out in close association with rodingite-like calc-silicate rocks and metasomatized granitic bodies in a serpentinite quarry at a Jordanów Śląski village near Sobótka, ~30 km south of Wrocław, Lower Silesia, SW Poland. It occurs as an isolated subhedral crystal, with the size of ~20 × 8 μm in planar section, and as three polycrystalline aggregates, up to 50 μm across, composed of needle-shaped crystals dominated by {110}. It is present within chlorite aggregates that supposedly represent remnants of partly recrystallized xenoliths of the blackwall chlorite schists and is in quartz-feldspar portions of the pegmatite adjoining such xenolithic assemblages. Owing to the scarcity of the material and the exceptionally small size of the crystals, the color, streak, and optical properties could not be measured. By analogy with other amphiboles, scandio-winchite has a vitreous luster, brittle tenacity, and a Mohs hardness of ~5½. The mineral shows an uneven fracture and {110} perfect cleavage, with an angle of ~56° between cleavage planes. The density calculated from the empirical formula and refined unit-cell parameters is 3.026 g/cm3. The holotype crystal is composed of (in wt%): 55.88 SiO2, 0.11 TiO2, 0.53 Al2O3, 9.22 Sc2O3, 0.44 MnO, 8.89 FeO, 12.77 MgO, 5.71 CaO, 4.12 Na2O, 0.17 K2O, and 2.09 H2Ocalc(+); total 99.93. The composition normalized on the basis of 22 O2– + 2 (OH)– ions corresponds to the empirical formula A(☐0.966K0.031Na0.003)Σ1B(Na1.132 Ca0.868)Σ2C(Mg2.704Fe1.0552+Mn0.053Sc1.140Al0.023Ti0.012)Σ4.987T(Si7.935Al0.065)Σ8.000O22(OH)2, simplified formula (☐,K)(Na,Ca)2[(Mg,Fe)4Sc](Si8O22)(OH)2, and the ideal formula ☐(NaCa)(Mg4Sc)(Si8O22)(OH)2. The crystal structure was refined in the monoclinic system, space-group symmetry C2/m, with R1 index of 6.57%. Its unit-cell parameters are: a = 9.864(2) Å, b = 18.163(3) Å, c = 5.3053(16) Å, β = 104.41(3)°, V = 920.6(4) Å3; Z = 2, and the a:b:c ratio is 0.5431:1:0.2921. The crystal-structure refinement indicates almost exclusively Si-occupied T sites, the M4 sites occupied by nearly equal amounts of Na and Ca, M1 and M3 sites by divalent Mg + Fe cations, and M2 filled in equal proportions by divalent cations and Sc. These results, along with the dominant vacancy at the A site, univocally indicate that the mineral corresponds to a M2Sc-analog of winchite. Scandio-winchite is most likely a secondary phase of metasomatic origin related to the evolution of the country rocks and partial alteration of the blackwall chlorite schists xenolith induced by the pegmatitic melt and associated fluids.

Exotic Electronic Properties of 2D Nanosheets Isolated from Liquid Phase Exfoliated Phyllosilicate Minerals.

Spectrally inactive, electrically insulating, and chemically inert are adjectives broadly used to describe phyllosilicate minerals like mica and chlorite. Here, the above is disproved by demonstrating aqueous suspensions of liquid exfoliated nanosheets from five bulk mica types and chlorite schist. Nanosheet quality is confirmed via transmission electron and X-ray photoelectron spectroscopies, as well as electron diffraction. Through Raman spectroscopy, a previously unreported size- and layer-dependent spectral fingerprint is observed. When analyzing the high-yield suspensions (≈1mgmL-1 ) through UV-vis spectroscopy, all phyllosilicates present bandgap (Eg ) narrowing from ≈7eV in the bulk to ≈4eV for monolayers. Unusually, the bandgap is inversely proportional to the areal size (A) of the nanosheets, measured via atomic force microscopy. Due to an unrecorded quantum confinement effect, nanosheet electronic properties scale toward semiconducting behavior (bandgap ≈3eV) as nanosheet area increases. Furthermore, modeling X-ray diffraction spectra shows that the root cause of the initial bandgap narrowing is lattice relaxation. Finally, with their broad range of isomorphically substituted ions, phyllosilicate nanosheets show remarkable catalytic properties for hydrogen production.

Surface flaking mechanism of stone components of ancient building complex in Wudang Mountain, China

Surface flaking, a deterioration pattern widely existing in stone components of the ancient building complex in Wudang Mountain, has significantly compromised its historical value. However, a comprehensive investigation into the mechanisms underlying surface flaking of stone components in this region has not been conducted thus far. This study aims to address this gap by employing a range of techniques, such as X-ray diffraction and scanning electron microscopy, to explore the factors contributing to the observed surface flaking. Petrographic analysis revealed that chlorite schists is widely used in ancient buildings as a natural building material, containing clinochlore, actinolite, albite, muscovite, quartz, and various clay minerals. Comparative analyses of mineral composition and microstructure of the samples exhibiting varying degrees of deterioration suggested that the water–rock interaction played a crucial role in surface flaking. It is proposed that this interaction potentially altered the physicochemical and structural characteristics of the stones through the hydration swelling effect of clay minerals (illite, clinochlore, and vermiculite) and dissolution effect of soluble minerals (muscovite, albite, and zeolite). Consequently, an increase in secondary porosity and a weakening of cohesiveness occurred, leading to a reduction in the overall strength of the stone and eventual flaking along the schistosity plane. Furthermore, this deterioration mechanism was validated by comparing strength and deformation of samples under different dry and wet conditions. The findings of this study will not only guide the comprehensive conservation of the ancient building complex in Wudang Mountain but also provide theoretical and methodological support for the preservation of substantialstone cultural relics located in the high-humidity climate zone of southern China.

Investigation of anisotropic strength criteria for layered rock mass

Layered rock mass is a type of engineering rock mass with sound mechanical anisotropy, which is generally unfavorable to the stability of underground works. To investigate the strength anisotropy of layered rock, the Mohr-Coulomb and Hoek-Brown criteria are introduced to establish the two transverse isotropic strength criteria based on Jaeger's single weak plane theory and maximum axial strain theory, and parameter determination methods. Furthermore, the sensitivity of strength parameters (K1, K2, and K3) that are used to characterize the anisotropy strength of non-sliding failure involved in the strength criteria and confining pressure are investigated. The results demonstrate that strength parameters K1 and K2 affect the strength of layered rock samples at all bedding angles except for the bedding angle of 90° and the angle range that can cause the shear sliding failure along the bedding plane. The strength of samples at any bedding angle decreases with increasing K1, whereas the opposite is for K2. Except for bedding angles of 0° and 90° and the bedding angle range that can cause the shear sliding along the bedding plane, K3 has an impact on the strength of rock samples with other bedding angles that the specimens' strength increases with increase of K3. In addition, the strength of the rock sample increases as confining pressure rises. Furthermore, the uniaxial and triaxial tests of chlorite schist samples were carried out to verify and evaluate the strength criteria proposed in the paper. It shows that the predicted strength is in good agreement with the experimental results. To test the applicability of the strength criterion, the strength data of several types of rock in the literature are compared. Finally, a comparison is made between the fitting effects of the two strength criteria and other available criteria for layered rocks.

Genesis of the Longwanggou iron deposit in the Yudongzi Complex, South China: Implications for the redox state of seawater at the onset of the Great oxidation Event

Banded iron formations (BIFs) deposited during the onset of the Great Oxidation Event (GOE) are crucial to understanding fundamental changes in the redox conditions of Earth’s surface environments, however, they are poorly understood in South China. Here, we investigate the petrographic, geochronological, and geochemical characteristics of a set of continuous magnetite quartzite samples from a drill core through the Longwanggou iron deposit in the Yudongzi Complex, South China. These magnetite quartzite samples exhibit diagnostic features of BIFs — 1) they comprise alternating magnetite and quartz layers at the centimeter–millimeter scales, 2) they are dominantly composed of SiO2 + Fe2O3T (87.8–95.8 wt%, average = 91.4 wt%), and 3) they are characterized by shale-normalized rare earth elements plus yttrium patterns similar to seawater. The maximum depositional age of the Longwanggou BIF (i.e., magnetite quartzite) is constrained to ca. 2.49 Ga based on U–Pb dating of detrital zircon grains from chlorite schist that is intercalated with the BIF. The metamorphic complex of the Yudongzi Complex that hosts the BIF was intruded by ca. 2.5–2.45 Ga granitoid gneisses, indicating that the BIF must be older than 2.45 Gyr. Accordingly, the depositional age of the Longwanggou BIF is constrained to ca. 2.49–2.45 Ga, coincident with the onset of the GOE. The positive Eu anomalies (1.3–4.2; average = 2.2) that occur throughout BIF samples suggest a continuous flux of submarine, high-temperature hydrothermal fluids to the ocean at the Archean–Proterozoic boundary. Based on elemental mass balance, the proportion of submarine, high-temperature hydrothermal fluids that contributed to the deposition of the BIF was less than 0.1%. Unlike BIFs deposited during the GOE, the Longwanggou BIF samples lack negative Ce anomalies, suggesting that the water column in which the BIF was deposited was at least locally anoxic during the onset of the GOE. Identification of the Longwanggou BIF provides new constraints for the Precambrian evolution of South China and lays the foundation for further study of the environmental changes at the Archean–Proterozoic boundary.

Study on strength characteristics and permeability of chlorite schist during triaxial compression permeability

Study on strength characteristics and permeability of chlorite schist during triaxial compression permeability

Nitrogen fractionation in mica metapelite under hot subduction conditions: Implications for nitrogen ingassing to the mantle

Nitrogen partitioning between its main hosts is investigated using partly devolatilized natural quartz–muscovite–chlorite schist (mica schist), with NH4+-rich muscovite, under conditions corresponding to hot subduction: 3.0–7.8 GPa, 750–1090 °C, and oxygen fugacity (fO2) about the NNO (Ni-NiO) buffer. At these conditions, mica schist transforms into an eclogitic assemblage, while muscovite (C2/c) recrystallizes successively into two high-pressure white mica phases. The resulting phases are phengite (P3112) and a phase intermediate between the dioctahedral and trioctahedral mica series (C2/m). During dehydration and decarbonation reactions at run P-T conditions mica schist releases an H2O-CO2 fluid containing 0.3–14 rel.% N2 and < 0.1–3.7 rel.% NH3. The contents of NH4+ determined by Fourier transform infrared spectroscopy (FTIR) decrease from 1600 to 2000 ppm in primary muscovite to ∼1500 ppm in phengitic muscovite at 6.3 GPa and 1000 °С and to 610–990 ppm in the intermediate between the dioctahedral and trioctahedral mica phase at 7.8 GPa and 1070-1090 °C. Ammonium in the analyzed metapelite shows incompatible behavior (DNH4Mica−Fluid=0.05–0.15) at ≥ 5.5 GPa and temperatures and fO2 common to hot oxidizing slabs, which is expected to cause its efficient outgassing from subducting metasediments depleted in volatiles. Nitrogen partitioning under hot subduction conditions at sub-arc depths is generally controlled by devolatilization of measediments, phase transitions in N-bearing micas, and changes of fluid composition near the second critical point.

The El Cortijo Formation: Ocean Plate Stratigraphy in the Tandilia Belt Paleoproterozoic basement (Argentina). Insights into subduction-accretion processes in the southern sector of the Río de la Plata Craton

An Ocean Plate Stratigraphy (OPS) sequence is a record of the oceanic crust geological evolution which allows the identification of paleo-oceans preserved in suture zones of orogenic belts. In the Paleoproterozoic basement of the Tandilia Belt (Argentina), Río de la Plata Craton, the El Cortijo Formation (ECF) crops out in a large suture zone with an E-W orientation and vertical to subvertical inclination. It includes a low-grade metavolcano-sedimentary sequence constituted by metacherts, metabasites, metacarbonate, metawacke, and phyllite. In order to provide genetic interpretations of the ECF, based on the OPS model, petrographic, geochemical, and geochronological studies of some of these rocks were performed. Mineral assemblages identified in metabasites, metawacke, and phyllite indicate a transition from prehnite-pumpellyite to greenschist facies conditions. Metabasites, classified as metavolcanite of intermediate to basic composition, chlorite schist and tremolite-actinolite schist, are interbedded between metacherts and metacarbonate bands. Geochemical analyses revealed particular chemical fingerprints which indicate that the protoliths of these metabasites would have been part of a volcanic arc rock association consistent with adakites, Nb-enriched basalts, high-Mg andesites, and “normal” tholeiitic to calc-alkaline basalts and andesites. The metawacke and the phyllite seem to derive from wackes and semi-pelites, respectively, whose main source is consistent with igneous-metamorphic rocks of acidic to intermediate composition linked to a continental arc system. The first LA-ICP-MS U–Pb data obtained for detrital zircons of the phyllite from the ECF yielded a weighted average age of 2138 ± 9 Ma and a youngest individual 207Pb/206Pb spot age of 2047 ± 22 Ma, which locates the maximum sedimentation age in the early Orosirian, during the maximum tectono-magmatic activity of the Tandilia Belt. According to Lu–Hf data, phyllite zircons derived from crustal sources and yielded Archean Hf model ages. Moreover, εHf(t) data of this rock exhibit a more subchondritic signal than the corresponding for some plutons of the Tandilia Belt, which could be indicating that zircons were not derived from plutons but are instead representative of the host rocks of such plutons. In this sense, the information indicates that the top of the sequence, constituted by the metawacke and the phyllite, represents the arrival of the oceanic plate to the trench zone. The study of the ECF has revealed conclusive evidence to postulate that the whole unit corresponds to the upper part of an OPS sequence of convergent type linked to intra-oceanic arc and continental fore-arc trench tectonic environments. The presence of this oceanic sequence, now preserved in a subduction-accretion complex, allows the Tandilia Belt to be classified as a Paleoproterozoic Pacific-type orogenic belt.

Analysis of Rheological Factors of Soft Rock Tunnel Based on Constitutive Model of Rock Parameters Attenuation with Equivalent Effect

Rock mass deformation is a time related process, especially for soft rock. Its deformation usually has a certain timeliness. Moreover, the deformation of surrounding rock is typically asymmetric. Therefore, it is of great significance to reasonably describe the time-dependent mechanical properties and behaviors of rock mass for practical engineering, especially when the actual engineering is a symmetric structure. Taking the chlorite schist section at the west end of the diversion tunnel of Jinping II Hydropower Station as the research object and introducing the characteristic that creep parameters attenuate with equal effect change into Burgers constitutive model used for numerical calculation, an improved Burgers model is proposed. Then, according to the actual situation of the project, the improved three-parameter H-K model, which is suitable for this study, is proposed by using the fractional calculus method. The effects of different factors on the rheological properties of soft rock tunnels are discussed. The results show that When K is equal to 1, creep is positively correlated with burial depth; When the burial depth H is 1500 m, the creep deformation is positively correlated with the horizontal geostress; The farther away from the working face, the greater the instantaneous elastic deformation release and the later creep displacement; After the tunnel excavation is stopped, the earlier the support is, the smaller the later creep deformation is; After excavation and support of the upper bench, the longer the stagnation time is, the more unfavorable the rheological deformation of the tunnel is.

DECCAN VOLCANIC OF MALWA, STRATIGRAPHY AND CORRELATION OF BASALTIC LAVA FLOWS USING MEGACRYST BEARING HORIZON AS TOOL, PARTS OF WESTERN M.P. INDIA

A review of earlier studies of the Deccan Trap occurrences of parts of Ratlam, Mandsaur, Jhabua, Dhar, Khargone, Indore, Ujjain and Shajapur districts of Madhya Pradesh, India was carried out of the area falling between latitudes 220 0000 to 2400000N and longitudes 7400000 to 7600000 in Survey of India Quadrangle sheet Nos. 46I, 46J, 46M and 46N.The main objectives of the study were to synthesize the data on the Deccan Trap basaltic lava flows , their types ,their diagnostic characteristics with special emphasis on delineating and identifying the various megacryst horizons , their levels with specific elevation above m.s.l. to build up the litho-stratigraphy for regional correlation. Broadly the area exhibits the Proterozoic Aravalli Supergroup, the Cretaceous, Bagh and Lameta Groups and the Deccan basaltic lava flows with intruded dykes and sills. The Aravalli Supergroup is represented by the Udaipur, Lunavada and Champaner Groups. The Udaipur Group consists mainly of hornblende gneiss, marble and calc-silicate, carbonaceous phyllites and chlorite schist. The Lunavada Group comprises dolomitic limestone (Phosphate bearing), quartzite, muscovite quartzite, quartz muscovite schist, feldspathised quartzite, gneissic feldspathic rock and biotitic gneiss. The Champaner Group is represented by dolomite, phyllite, slates and basic intrusives. The Aravalli Super group of rocks is also intruded by serpentinite, pyroxinite, granite and basic rocks. The Aravalli Supergroup of rocks is unconformably overlain by Cretaceous marine sedimentary deposits of Bagh Group. It includes Lower arenaceous and Upper calcareous units and occurs as discontinuous outcrops. These are almost horizontally to sub horizontally disposed. The Bagh Group is represented by three units / Formations i.e. Nimar sandstone overlain by nodular limestone and subsequently by coralline limestone. The Lameta Group of rocks is noticed in the area east and South East of Bagh exposures, overlying the Nimar sandstones. These rocks predominantly consist of limestone, gritty sandstone and conglomerate and generally exhibit hummocky topography and sometimes display solution channels. These are mostly horizontally to sub-horizontally disposed with an average thickness of 5- 6 m. The Deccan Trap has occupied a very long stretch of area which consists of a sequence of 121 basaltic lava flows with a cumulative thickness of about 610 m. These flows represent a sequence of cyclic lava eruptions with fine to medium grained a aphyric to sparsely / moderately / highly / mega porphyritic lava. About two third of the total flows exhibit Aa characters and the rest are compound and simple Pahoehoe. Some of these flows consist of megacryst units containing feldspar laths varying in size round two to five cm. These megacryst horizons have been identified at different elevations in Quadrangles 46I, J, M, N and on the basis of these horizons, various flows have been grouped into to six Formations which have specific nomenclatures and stratigraphic status. These formations are in the order of antiquity 1) Mandleshwar formation, 2) Choral formation,3) Dhar formations 4) Indore Formation 5) Bargonda Formation and 6) Singarchori Formation. Full sequence is exposed only in quadrangle 46N whereas the Quadrangles 46I, J, M do not exhibit Bargonda and Singarchori Formations. An attempt has been made to correlate the various Formations in degree sheets 46 I, J, M, N with the surroundings Geological Quadrangles. The Megacryst bearing lava- flows act as marker horizons for this purpose. A large number of dykes and dyke swamps of basaltic as well as doleritic compositions have been marked around the Narmada River. The intensity of the dykes is more in the oldest Mandleshwar Formations and it gradually decreases in increasing order of antiquity towards the younger Bargonda and Singarchori Formations. The general trend of these dykes varies from East North East – West South West to E-W running sub parallel to the Narmada lineament, besides a few dykes also cut across this lineament trend and oriented along NNW-SSE to N-S direction. The Length of these dykes varies from about 200 m to 20 Km with width varying from a few meters to as much as 200 m. The possibility exists that these dykes may have been actually feeders through which periodic eruptions of tholiitic basaltic lava took place resulting in formation of such a thick pile of lava flows. Besides as many as seven Intertrapean fossiliferous sedimentary horizons have been recognized within the basal part of the flows. These demonstrate episodic nature of volcanic activity, long periods of quiescence and resilience. The overall study of various lava flow s and their interrelations their relative dispositions thinning /swelling and pinching nature. Their relative elevations, occurrence of marker megacryst units, change in lava characters, overall gradient of lava flows and their relation to preexisting topography and slope elements reveals that the sources of lava eruptions of Older Formations are situated somewhere in the west and south west whereas those of Younger Formations are located in the Eastern part of Mhow of the area studied.

Tectonic setting and mineralisation potential of the Cowley Ophiolite Complex, north Queensland

Northeast Queensland contains multiple slices of mafic–ultramafic units, strung out along regional faults that mark major tectonic boundaries. One such complex is the Cowley Ophiolite Complex, which is situated along the Russell-Mulgrave Fault. The Cowley Ophiolite Complex is a differentiated mafic–ultramafic complex composed of gabbro, chlorite schist, anthophyllite schist and serpentinite. We interpret that the alteration assemblages observed throughout the Cowley Ophiolite Complex reflect an amphibolite facies metasomatic overprint within a supra-subduction zone setting. This interpretation is consistent with geochemical discrimination of the gabbro, and chromite grains from the anthophyllite schist. The Cowley Ophiolite Complex records a higher metamorphic grade than the surrounding Hodgkinson Formation, and we interpret this to reflect the allochthonous structural setting of the complex, positioned along an ancient subduction margin. This subduction margin is represented today by the Russell-Mulgrave Fault. Metasomatism and emplacement of the complex probably pre-dated deposition of the Mossman Orogen’s active margin successions. Our interpretation of an active subduction complex, which pre-dated the formation of the Mossman Orogen, suggests that the Russell-Mulgrave Fault is a Paleozoic, continental suture zone. The Cowley Ophiolite Complex presents little indication of economic mineralisation; however, much of the complex remains unexplored. KEY POINTS The Cowley Ophiolite Complex is a differentiated, mafic–ultramafic complex formed within a supra-subduction zone setting. Emplacement of the Cowley Ophiolite Complex, along the Russell-Mulgrave Fault, pre-dated the formation of the Hodgkinson Province. The Russell-Mulgrave Fault represents an ancient subduction margin, and is interpreted as a Paleozoic, continental suture zone.

Long-term stress monitoring and in-service durability evaluation of a large-span tunnel in squeezing rock

The long-term safety and in-service durability of tunnels in squeezing rock are the focus of tunnel management and maintenance. Previous studies mainly focused on the disaster-causing mechanism, prediction method, and control technology of large deformation during the construction of squeezing rock tunnels. So far, only few studies have concentrated on the long-term safety of in-service highway/railway tunnels in squeezing rock tunnels, resulting in unclear long-term mechanical response of tunnel structure and lack of data support for safety evaluation and durability prediction. Therefore, we conducted long-term, real-time, and continuous monitoring on the structural stress of the Lianchengshan Tunnel, which suffered severe large deformation during the construction, and performed a regression analysis on the structural stress by constructing four typical stress-time mathematical models. Subsequently, we evaluated the long-term safety and in-service durability of the tunnel structure based on a stress prediction. The results of our study show that the structural stress of the tunnel is not stabilized during the operation period but fluctuates periodically with an annual cycle. Moreover, the structural stress peak presents an increasing trend with the service life. The rheology of the surrounding rock composed of chlorite schists in Lianchengshan Tunnel is dominated by steady creep and decay creep. Despite a risk of local cracking or damage of concrete before the design service life due to excessive stress at individual positions of the secondary lining, such as the inverted arch, the safety factors of the secondary lining in the early stage (within 30 years) are higher than the threshold of 2.0. This indicates that the early safety of the tunnel structure can achieve the service requirements. The results of our study provide a reference for the long-term safety evaluation and in-service durability prediction of squeezing rock tunnels with high geo-stress.

Tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean in central Jilin (NE China): Constraints from the early Mesozoic high-Mg andesites

The Jilin–Yanji Suture is situated at the convergent margin between the North China Craton and Jiamusi-Khanka Massif, playing as a key hinge to link up the tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean. However, many parameters of this suture, e.g. the timing of its emplacement, tectonic setting and precise location remain controversial. For addressing these issues, we focused on the high-Mg andesites within the Seluohe Group which is a typical subduction-related volcanic association along the Jilin–Yanji Suture. Seven chlorite schist and six andesite samples were collected for petrological, geochemical and geochronological analyses. The geochemical results indicate the protoliths of chlorite schists and the andesite samples are high-Mg andesites, and their magma source was produced by the metasomatized mantle wedge by subducted slab-derived fluids in a continental island arc setting. Eight high-Mg andesites give the crystallization ages of 249 ± 3 Ma–246 ± 4 Ma, with a weighted mean age of 247 ± 1 Ma (MSWD = 0.27) yielded by 69 youngest zircons, indicative of an Early Triassic age. Based on our new results and the field investigation, we propose that the Seluohe Group is a set of Early Triassic volcanic-sedimentary association with continental island arc affinity related to the south-westward subduction of the Heilongjiang Ocean, rather than a Mesoproterozoic sequence or Late Permian accretionary complex as previously considered. Integrated with previous studies on the regional tectonic evolution, we suggest the Jilin-Yanji Suture belongs to the southern extension of the Jilin-Heilongjiang high-pressure metamorphic belt, which records the final collision between the Jiamusi-Khanka Massif and North China Craton during the Triassic caused by the subduction of the Paleo-Pacific Ocean, and the Late Permian-Late Triassic is a key period of tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean in the eastern edge of Eurasia.

Formation of serpentinite-hosted talc in a continental crust setting: Petrographic, mineralogical, geochemical, and O, H and Cl isotope study of the Gilów deposit, Góry Sowie Massif (SW Poland)

The Gilów deposit is located in the Góry Sowie Massif of the Central Sudetes (NE Bohemian Massif, SW Poland). Talcose rocks are associated with serpentinite bodies hosted by country migmatitic paragneiss, in an area where paragneiss also hosts amphibolitized eclogite bodies and granitic pegmatite veins. The talcose rocks and wall rocks were subjected to petrographic examination, electron microprobe study of minerals (including monazite Th-U-total Pb chemical dating), bulk rock chemical examination, as well as stable O, H and Cl isotope analysis. The talcose rocks can be used as a carving material and in ceramics, although the presence of tremolite and anthophyllite, and high Cr and Ni contents, preclude application in pharmacy and cosmetics. High Cr (2121.0–2148.4 ppm), Ni (1079–1561 ppm) and Co (57.4–84.8 ppm) contents, low ΣREE (2.13–13.81 ppm), as well as isotopic composition of O and H, classify the talcose rocks as a serpentinite-hosted type of deposit. Location in the strongly folded metamorphic unit, in the intimate vicinity of several faults and mylonitic zones, implies classification along the thrust-bound and fold-related metamorphogenic deposits. The talcose rocks are separated from serpentinites by the metasomatic chlorite schist, which contains two generations of monazite yielding two, different Th-U-total Pb dates. Older (389.8 ± 11.4 Ma) probably dates serpentinites juxtaposition with country paragneiss and chlorite formation. Younger (365.0 ± 18.2 Ma) likely dates amphiboles and talc formation, as overlaps the ages of amphibolite facies, country paragneiss migmatitization and intrusions of granitic pegmatites, and the talcose rocks contain talc-tremolite-anthophyllite assemblage indicative of the low-pressure mid-amphibolite facies. High MgO (24.27–27.21 wt%), Fe2O3 (5.06–5.12 wt%), Cr, Ni and Co contents are inherited from serpentinites. On the other hand, SiO2 (57.30–60.46 wt%), CaO (0.86–4.39 wt%), Al2O3 (1.38–3.04 wt%), TiO2 (0.02–0.04 wt%) and F (197–337 ppm) contents in the talcose rocks are higher than in host-serpentinites, likely due to a metasomatic introduction by fluids derived from migmatitic paragneisses or intruding pegmatites. Introduction of these elements is evidenced by a negative δ37Cl and elevated δ18O of the talcose rocks relative to host-serpentinites that are typical effects of interaction with a felsic crustal material. Interaction with paragneiss- and pegmatite-derived fluids is further evidenced by REE and trace elements patterns of the talcose rocks. The LREE/HREE enrichment, negative Sr and Ti anomalies, and positive Nb-La and Zr-Hf-Sm slopes, of the talcose rocks patterns, are similar as in paragneiss and pegmatite. Serpentinite bodies transformation into the talcose rocks was gradual and associated with increase of δ18O, and decrease of a Cl content, δD and δ37Cl. Pseudomorphic serpentinite, similar to abyssal serpentinites in terms of an isotopic composition (δ18O = +5.7‰, δD = −64‰, δ37Cl = +2.0‰), recrystallized into non-pseudomorphic serpentinite (δ18O = +7.1‰, δD = −48‰, δ37Cl = −0.1‰), which, in turn, was replaced by the talcose rock (δ18O = +8.3‰ to +8.7‰, δD = −52‰ to −48‰, δ37Cl = −2.6‰ to −0.1‰). Moreover, paragneiss- and pegmatite-derived fluids might have interacted with eclogite bodies during amphibolite facies-retrogression. Amphibolitized eclogite has Cl-rich amphibole rims, and negative δ37Cl (−0.5‰) consistent with a Cl-rich crustal fluid.