Amygdaloidal Basalt Research Articles

Petrology and Geochemistry of Intrusive Rocks in the Tanjung Area, South Sulawesi, Indonesia: Implications for Magma Origin, Source Materials, and Geodynamic Setting

The origin of magma, source materials, and geodynamic setting of plutonic and volcanic rocks was elucidated by studying the characteristics of the rocks in the Tanjung area, South Sulawesi, Indonesia. The composition of plutonic rocks is dominated by granodiorite, granite, monzonite, and quartz monzonite, whereas volcanic rocks consist of porphyry basalt, amygdaloidal basalt, trachyte, and trachy-andesite. The main minerals in the rocks are quartz, K-feldspar plagioclase feldspars, Hornblende, biotite, pyroxene, and some opaque minerals. Plots of plutonic rock samples with calc-alkaline affinity indicated a typical I-type granitic rock. Meanwhile, plots of volcanic rock samples with calc-alkaline to shoshonitic affinity indicated S- and I-type basaltic rocks. Harker diagrams suggested that the rocks underwent crystallisation fractionation during magma evolution. Plutonic and Volcanic rocks showed enrichment of LILE and LREE and negative Eu anomalies, which resemble continental crust affinity. It is a product of partial melting in the upper continental crust. The geochemical characteristics demonstrate the relationship between the subduction environment and a continental arc.

OIB-type mafic–ultramafic rocks in South Guangxi, South China: A record of interaction between Paleo-Tethys subduction and Emeishan large Igneous Province

Late Permian ultramafic–mafic igneous rocks in the Pingxiang area, Guangxi, South China include wehrlite, gabbro, diabase, and amygdaloidal basalt. Geochemical characteristics document interaction between the Emeishan Large Igneous Province (ELIP) and the mantle wedge related to subduction of the Paleo–Tethys. Gabbro and basalt show chondrite–normalized rare earth elements (REEs) and primitive mantle–normalized trace element patterns that parallel ocean island basalts (OIB) and mafic intrusions from the ELIP. Melts in equilibrium with clinopyroxenes, in both wehrlite and gabbro, have REEs and trace element compositions similar to OIB and high–Ti mafic rock of the ELIP. The clinopyroxenes also show a rift–related compositional trend and cover those from the ELIP rocks. These compositional features, along with their moderate initial 87Sr/86Sr and εNd(t) values (−0.8 to +3), are consistent with derivation from an enriched mantle plume source. This is the first time that ultramafic–mafic rocks are reported beyond the established extent of the ELIP and could represent an offshoot from the main mantle plume or indicate that the ELIP plume was considerably bigger than current proposals but has been significantly denuded by subsequent erosion. In addition, the Pingxiang rock units display slightly enriched εNd(t) values and slight negative Nb, Ta, and Zr relative to OIB rocks, indicating an enriched component in the mantle source. Formation of the ELIP spatially and temporally overlapped with subduction of the Paleo–Tethys ocean and interaction between the plume and mantle wedge accounts for the compositional diversity of the ELIP. Such interaction is probably common along the southwestern–southern margin of the Yangtze Block.

Crushed amygdaloidal basalt rock and its effects on tomato production

Abstract
 Sustainable agriculture plays an important role in agricultural productivity, in which it seeks to reduce dependence on conventional synthetic fertilizers (imported from Europe) and promote the use of alternative, low-cost and environmentally friendly sources. An experiment was carried out in the municipality of Santa Maria, Rio Grande do Sul, Brazil, with the objective of evaluating the efficiency and agronomic viability of using a mineral product (amygdaloid basalt powder) as an agricultural input on tomato productivity Solanum lycopersicum. The experimental design used was randomized blocks with six treatments and four replications, at doses 0 (treatment 1 - control), 1.0 ton ha-1 of rock dust (treatment 2), 2.5-ton ha-1 of rock dust (treatment 3), 3.5-ton ha-1 of rock dust (treatment 4), 4.5-ton ha-1 of rock dust (treatment 5), and recommended fertilization for tomato 5-20-20 NPK (treatment 6 - standard). The treatments were applied in December 2018 and the transplant took place in February 2019. According to the conditions under which the experiment was submitted and analyzing the results obtained, it can be inferred that the application of 1-ton ha-1 of amygdaloidal basalt in the soil increased parameters such as root length, stem diameter, green and dry mass of shoots and roots, number of flowers/plants, number of fruits/plant and productivity in tomato Solanum lycopersicum. It is a viable, sustainable, and low-cost strategy that contributes to the achievement of the Sustainable Development Goal (SDG 2) and can be replicated in Brazil and worldwide.

Middle Permian basic and acidic volcanism in the Istanbul zone (NW Turkey): evidence for post-variscan extensional magmatism

ABSTRACT The Istanbul Zone (NW Turkey) forms the eastward extension of Avalonia and was subjected to deformation, uplift and erosion for a time period of 40–50 Ma following the collision with the Sakarya Zone during Early to Late Carboniferous. This paper deals with the petrology and age of the volumetrically minor basic and acidic volcanism at the lowermost horizons of Middle Permian continental red beds, which are overlain by Lower Triassic marine sedimentary rocks in the Kocaeli Peninsula. The volcanic activity is represented mainly by amygdaloidal basalt, rhyolite and minor trachydacite. The amygdaloidal basalt was derived from near-primary middle-K calc-alkaline mantle melts with negligible crystal fractionation. On the other hand, the rhyolite and trachydacite compositionally resemble A2-type rhyolites and underwent low-pressure crystal fractionation as indicated by the presence of a significant Eu anomaly. Initial ɛNd values of amygdaloidal basalt range from 0.0 to 1.5 and those of rhyolite-trachydacite are between −0.4 and −3.4. Amygdaloidal basalt and rhyolite-trachydacite are not directly related to each other by crystal fractionation. Amygdaloidal basalt probably represents the product of the near-primary mantle melts from low-degree melting of a spinel peridotitic source, and the rhyolite-trachydacite originated from highly-fractionated products of basic magmas that are slightly more alkaline than amygdaloidal basalt. However, basic and intermediate products of alkaline basic magmas are unknown in this region to date. U-Pb dating of zircons from a rhyolite sample yielded an igneous crystallization age of 261 ± 3 Ma (2σ), suggesting that the date of deposition of the continental red beds goes back to the latest Middle Permian. Based on the transgressive nature of the Permian-Triassic sequence that starts from the Middle Permian continental red beds and grades into Lower Triassic marine deposits, we suggest that the volcanism likely occurred in an extensional setting. This extension was concurrent with the northward subduction of the Palaeo-Tethys beneath the Sakarya and Istanbul zones after the Variscan orogeny. Therefore, the latest Middle to Late Permian volcanism might have occurred during the initial stage of a back-arc extensional setting

Domainal Investigation of a Quartz-Fluorite Composite Using Spectroscopic Techniques

The analysis of geological samples that have several chemically diffused zones which formed under certain physico-chemical condition is difficult to achieve. The quantitative estimations of the minerals in such samples are tedious. The present work demonstrates the application of LIBS for qualitative and quantitative analyses of a quartz-fluorite composite which was procured from an amygdaloidal basalt from Deccan Traps, India. The presence of weak emission lines of F in the spectral range of 200–900 nm makes it challenging to quantify the fluorine. This study has addressed a promising alternative to quantify the fluorine using electronic bands of CaF molecules observed in the Laser-induced Breakdown Spectroscopy (LIBS) spectrum. In addition to this spectroscopic technique, the authors also have used Photoacoustic Spectroscopy (PAS) and UV-VIS spectroscopy technique to obtain molecular information from the geological sample. Principal Component Analysis (PCA) was applied to a truncated spectral region of the CaF molecule, and it showed 99% variance. Further, the obtained results with these spectroscopic techniques were compared with the results that were obtained from X-ray diffraction and Electron Probe Micro Analyzer, and they show good agreement. Thus, the LIBS technique can be promising for in situ profile section (varies from few microns to centimeters size) studies without the sample’s destruction using the point detection capability of LIBS.

Crushed amygdaloidal basalt rock and its effects on tomato production

Abstract
 Sustainable agriculture plays an important role in agricultural productivity, in which it seeks to reduce dependence on conventional synthetic fertilizers (imported from Europe) and promote the use of alternative, low-cost and environmentally friendly sources. An experiment was carried out in the municipality of Santa Maria, Rio Grande do Sul, Brazil, with the objective of evaluating the efficiency and agronomic viability of using a mineral product (amygdaloid basalt powder) as an agricultural input on tomato productivity Solanum lycopersicum. The experimental design used was randomized blocks with six treatments and four replications, at doses 0 (treatment 1 - control), 1.0 ton ha-1 of rock dust (treatment 2), 2.5-ton ha-1 of rock dust (treatment 3), 3.5-ton ha-1 of rock dust (treatment 4), 4.5-ton ha-1 of rock dust (treatment 5), and recommended fertilization for tomato 5-20-20 NPK (treatment 6 - standard). The treatments were applied in December 2018 and the transplant took place in February 2019. According to the conditions under which the experiment was submitted and analyzing the results obtained, it can be inferred that the application of 1-ton ha-1 of amygdaloidal basalt in the soil increased parameters such as root length, stem diameter, green and dry mass of shoots and roots, number of flowers/plants, number of fruits/plant and productivity in tomato Solanum lycopersicum. It is a viable, sustainable, and low-cost strategy that contributes to the achievement of the Sustainable Development Goal (SDG 2) and can be replicated in Brazil and worldwide.

The Evolution of Paleo-Porosity in Basalts: Reversing Pore-Filling Mechanisms Using X-Ray Computed Tomography

Often carrying a high-volume fraction of vesicles, basaltic rocks can be an important reservoir horizon in petroleum systems, and are considered an excellent candidate for CO2 storage by in situ mineral trapping. The frequency of amygdaloidal basalts in many sequences highlights the prevalence of mineralisation, but when the vesicle network has been filled, the basalts can act as impermeable seals and traps. Characterising the spatial and temporal evolution of the porosity and permeability is critical to understanding the petro-physical properties and CO2 storage potential of basalts. We exploit X-ray computed tomography (XCT) to investigate the precipitation history of an amygdaloidal basalt containing a pore-connecting micro fracture network now partially filled by calcite as an analogue for CO2 mineral trapping in a vesicular basalt. The fracture network likely represents a preferential pathway for CO2-rich fluids during mineralisation. We investigate and quantify the evolution of basalt porosity and permeability during pore-filling calcite precipitation by applying novel numerical erosion techniques to “back-strip” the calcite from the amygdales and fracture networks. We provide a semi-quantitative technique for defining reservoir potential and quality through time and understanding sub-surface flow and storage. We found that permeability evolution is dependent on the precipitation mechanism and rates, as well as on the presence of micro fracture networks, and that once the precipitation is sufficient to close off all pores, permeability reaches values that are controlled by the micro fracture network. These results prompt further studies to determine CO2 mineral trapping mechanisms in amygdaloidal basalts as analogues for CO2 injections in basalt formations.

Effect of natural defects on the fracture behaviors and failure mechanism of basalt through mesotesting and FDEM modeling

As an important geological medium for engineering construction in Southwest China, basalt typically contains natural defects, such as hidden joints and amygdales, which significantly affect its mechanical properties. In this work, the fracture behaviors of basalt with different defects were studied in terms of its strength, deformation and failure characteristics, and crack evolution laws using a comprehensive mesotesting scheme and finite-discrete element method (FDEM) modeling, revealing the failure mechanism of basalt. The results showed that: (1) Intact specimens exhibiting high strength and smooth stress–strain curves burst instantly when loaded to the peak strength, and the corresponding acoustic emission events are abnormally concentrated, indicating a fragmentation failure mode. (2) The strength of fractured samples decreases significantly, the stress–strain curve is bimodal or multimodal, and the acoustic emission events are very active during the entire failure process, which is closely related to the local damage generated during each significant stress drop, with tension dominant, shear dominant, or tension–shear composite failure modes. (3) For amygdaloidal basalt samples with a serrated stress–strain curve, each small-scale stress drop is accompanied by the initiation, propagation, and coalescence of microcracks, resulting in relatively scattered acoustic emission events, indicating a splitting failure mode. (4) Because of the small particle size, dense arrangement, good uniformity, and high strength at the grain scale, intact basalt exhibits a relatively uniform stress field easily induced under loading, leading to an extremely high strength, fragmentation failure mode, and significant brittleness. However, a heterogeneous stress field near the original defects, such as hidden joints or amygdales, is prominent, and it significantly affects the fracture paths, which is the main reason for the strong randomness of the mechanical properties, evident strength reduction, and significant change in the failure modes. The research results can provide reference for revealing the occurrence mechanism, guiding warning systems, and formulating control methods for high-stress disasters in hard brittle rocks.

Origin of the Cretaceous olistostromes in the Oman mountains (Sultanate of Oman): Evidence from clay minerals

Mid- to Late Cretaceous olistostrome generation ensued sequentially, linked to progressive southwest-directed thrusting of the Semail Ophiolite towards and over Arabia – at first in the northeastern part of the oceanic Hawasina Basin (Umar Sub-Basin) and then in its southwestern part (Hamrat Duru-Sub-Basin). Thrusting steepened slopes, causing seismic tremors, which destabilized slope sediments and triggering olistostrome formation. Ophiolite thrusting over Arabia created the Aruma Foreland Basin. Olistostrome formation in the foredeep ensued last and on the flank of the uplifting forebulge.As olistoliths, Olistostrome 1 contains radiolarian limestone, plain micrite, allodapic limestone, basalt, amygdaloidal basalt, radiolarian chert and coarse, massive limestone with crystalline texture (Oman Exotics). These olistoliths “float” in shale, containing illite/muscovite, vermiculite and kaolinite. Olistostrome 1 formed in the Umar Sub-Basin.Olistostrome 2 is associated with the Late Albian to Coniacian Nayid Formation of the Hamrat Duru Sub-Basin. It is characterized by olistoliths of graded limestones (calc-turbidites) with angular shelfal limestone lithoclasts. The olistoliths are embedded in shale with unidentifiable clay minerals. Olistostrome 2 formed in the Hamrat Duru Sub-Basin, postdating Olistostrome 1.Olistostrome 3 is associated with the Upper Cretaceous Aruma Foreland Basin and characterized by olistoliths, like lithoclastic packstone (calcarenite), dolomitic limestone, and sandstone with carbonate lithoclasts. The matrix of the olistoliths is a pyrophyllite- and kaolinite-bearing shale. Olistostrome 3 formed in the foredeep as the youngest olistostrome.The different clay mineralogy of Olistostrome 1 and Olistostrome 3, reflects their different basinal origin. Shale samples taken from conventional sediments (no olistostromes) of the syn-tectonic and post-tectonic Aruma units show some resemblance in their clay mineralogy as they contain detritus from the Oman Mountains. Olistolith types of both Hawasina olistostromes differ significantly.The reviewed and novel data may serve as a guideline for future olistostrome studies in the Oman Mountains and may be particularly helpful in identifying the basinal origin of olistostromes in case of fault-bounded olistostromes, unexposed olistostrome contacts and inconclusive olistoliths. Evaluating matrix shales of olistostromes leads to important decision criteria, such as color, oxygenation state and clay mineralogy, to determine the paleogeographic basin position.

Effects of amygdale heterogeneity and sample size on the mechanical properties of basalt

Due to the complex diagenesis process, basalt usually contains defects in the form of amygdales formed by diagenetic bubbles, which affect its mechanical properties. In this study, a synthetic rock mass method (SRM) based on the combination of discrete fracture network (DFN) and finite-discrete element method (FDEM) is applied to characterizing the amygdaloidal basalt, and to systematically exploring the effects of the development characteristics of amygdales and sample sizes on the mechanical properties of basalt. The results show that with increasing amygdale content, the elastic modulus (E) increases linearly, while the uniaxial compressive strength (UCS) shows an exponential or logarithmic decay. When the orientation of amygdales is between 0° and 90°, basalt shows a relatively pronounced strength and stiffness anisotropy. Based on the analysis of the geometric and mechanical properties, the representative element volume (REV) size of amygdaloidal basalt blocks is determined to be 200 mm, and the mechanical properties obtained on this scale can be regarded as the properties of the equivalent continuum. The results of this research are of value to the understanding of the mechanical properties of amygdaloidal basalt, so as to guide the formulation of engineering design schemes more accurately.

Fracture variability in basalts and its effect on river erosion: a case study in the Paraná Volcanic Province

The variation in the structural characteristics (cooling joints and tectonic fractures) of basaltic flows implies potential variability in the intensity of erosion by plucking. The erosive behavior of the rivers that sculpt these areas depends on their interaction with the diverse fracture systems. In view of this, we analyzed the effect of fracture variability in basalts on erosion in a bedrock river reach located in the Continental Volcanic Province of the Paraná Basin, southern Brazil. The 120-m-long reach is influenced somewhat by a possible fault that crosses it near one end. The fracture density and fracture direction were evaluated through field photogrammetry in seven sample areas distributed along the reach. The fracture direction and main erosion axes were also surveyed by remote piloted aircraft (RPA) aerial imaging. Tectonic fractures were identified in the field; they do not always appear in the survey of the sample areas but are evident in the RPA survey. The main erosion axes coincide with the principal fracture directions (tectonic fractures), which are disposed obliquely to the channel flow direction, making an average angle of 50°. The more abundant and multidirectional cooling joints act to control the plucking process and not to determine the erosion direction. The fracture density decreases with increasing distance from the fault crossing zone (from 9.62 to 3.73 m/m²), although the lower value is influenced by the presence of an amygdaloidal basalt zone. The higher fracture density favors more intense plucking.

Experimental Investigation and Numerical Modeling of Coupled Elastoplastic Damage and Permeability of Saturated Hard Rock

The mechanical behavior and permeability evolution of saturated hard rock are significantly important to the stability and safety of super-high arch dams. A series of triaxial compression tests were conducted on amygdaloidal basalt under different pore pressures. Based on the experimental results, a micromechanical-based elastoplastic damage model is proposed for such saturated hard rock. The hydromechanical coupling is formulated using the thermodynamic framework for saturated media. Damage is induced by the growth of microcracks and the plastic deformation is related to the frictional sliding between rough crack surfaces. The thermodynamic forces associated with damage and plasticity are deduced with a special thermodynamic potential for saturated hard rocks. New plastic and damage criteria are proposed to describe the evolutions of the internal variables. The permeability evolution is estimated by the volumetric averaging of the local permeability in microcracks. The developed models were calibrated and validated by a series of triaxial compression tests on saturated hard rocks. The main mechanical behaviors and permeability evolution properties of saturated hard rock are well captured by the proposed model.

Study on the Effect of Amygdales on Mechanical Characteristics of Basalt Using the Combined Finite‐Discrete Element Method

Amygdaloidal basalt, as a heterogeneous rock, is widely exposed at Baihetan hydropower station, China. The geometric effect of amygdales needs further studies and quantifying the shape, orientation, and statistical distribution of amygdales plays an important role in the laboratory and numerical experiments. Therefore, digital image processing (DIP) was first utilized to build a heterogeneous model (HM) to calibrate against the laboratory test results. Then, the heterogeneous models (HMs) with prescribed geometric features were generated by the inverse Monte‐Carlo (IMC) algorithm. The uniaxial compression experiments based on HMs were conducted to study the mechanism of the crack initiation and propagation in the amygdaloidal basalt. The tensile fractures were mainly occurred in the matrix, and the shear fractures were mainly occurred in the amygdales. With the increase in the elliptic coefficient of amygdales, the uniaxial compressive strength (UCS) showed a linear growth trend. With the increase in the orientation of amygdales, the UCS exhibited a “V‐shaped” distribution characteristic. This paper provides a numerical method for studying the mechanical properties of rocks with flaws.

Evaluation of Deformation and Permeability Behavior of Amygdaloidal Basalt under a Triaxial Cyclic Loading Creep Test

Amygdaloidal basalt is a typical rock mass in the dam foundation of the Baihetan hydropower project in southwest China. With rising and drawdown of the reservoir water level, the permeability and creep deformation characteristics of the amygdaloidal basalt are much complicated in the long-term cyclic loading processes. A cyclic loading-unloading creep test on the amygdaloidal basalt was performed to evaluate its deformation and permeability behavior. The results showed that Poisson’s ratio and elastic modulus of the rock specimen varied significantly under different loading processes with a relatively large irreversible deformation. The permeability and strain rates of rock changed in two phases under lower deviatoric stresses, while there are three typical stages of strain growth with the final stress level of 121.8 MPa. For axial stress of 128 MPa, the creep deformation and creep rate in the axial direction are smaller than these in the lateral direction. Before the sample failure, the lateral deformation accelerates earlier than the axial deformation. The results also suggested that the permeability of the rock specimens decreases considerably during each loading process and then tends to be constant with time. No apparent change in steady permeability is observed with variation of stress. For 128 MPa axial stress, the permeability first decreases, then tends to be in a stable value, and at last increases during the sample failure.

Experimental investigation of the mechanical properties of basalt in the Baihetan hydropower station region in China

The Baihetan hydropower station is mainly situated in the basalt formations of Mount Emei (Sichuan Province, China). During the excavation process, basalt has shown some special mechanical characteristics. In this study, the deformation and failure characteristics of basalt are investigated via laboratory tests (uniaxial and triaxial compression tests on blocky basalt samples) and field deformation tests (rigid bearing plates applied in situ to columnar jointed basalt). The information gathered is then analyzed to reveal the mechanisms responsible for the failure of basalt. Results show that (1) the stress–strain curves of cryptocrystalline basalt are essentially linear in the pre-peak region and the stress drops rapidly in the post-peak region. The failure mode of the rock changes from being fragmentation-dominated under low–medium confining pressure to fragmentation–shear composite failure under high confining pressure. (2) In the post-peak region, amygdaloidal basalt exhibits brittle mechanical behavior under low confining pressure and ductile behavior under high confining pressure. In terms of failure mode, the basalt transforms from splitting failure under low confining pressure to shear failure under medium–high confining pressure. (3) The deformation moduli measured during field tests with rigid bearing plates are spread over a large range and are influenced by various factors (including column nature, lumpiness, loading direction, unloading-induced relaxation, and stress state). (4) The deformation moduli of the rock masses of Classes II, III1, and III2 successively decrease and exhibit significant anisotropy.

Influence of amygdale on crack evolution and failure behavior of basalt

Amygdaloidal basalt is one of the two major types of surrounding rocks that are widely exposed in the super large-scale underground powerhouse caverns of Baihetan Hydropower Station, China. Excavation of the caverns induced a series of mechanical responses, including cracking and fracture relaxation. This study comprehensively explored the deformation and failure characteristics and the fracture evolution process of the amygdaloidal basalt using conventional MTS triaxial laboratory testing equipment and continuous–discontinuous modeling (FDEM) with the aim of clarifying its failure mechanism. The research results indicate that: (1) amygdales significantly changed the deformation and failure characteristics of basalt. Whereas the post-peak mechanical behavior of cryptocrystalline basalt was brittle, that of amygdaloidal basalt was brittle under low confining stresses and ductile under high confining stresses. Meanwhile, whereas the failure mode of cryptocrystalline basalt was fragmentation failure, that of amygdaloidal basalt was splitting failure at low confining stresses and shear failure at high confining stresses. (2) An FDEM model considering the heterogeneity of the rock mesostructure was established based on the statistical laws of the amygdales in real samples, and this confirmed the stress–strain curve characteristics, failure modes, and characteristic strengths measured in laboratory tests. (3) A complicated inhomogeneous stress field formed readily around amygdales and had a significant effect on the fracture path. (4) With an increase in confining stresses, the degree of tensile stress concentration at the upper and lower tips of amygdales decreased and the lateral displacement became restricted. Consequently, the total number of micro-cracks and the ratio of tensile cracks to shear cracks decreased, the crack initiation mode changed from tensional cracking to shear cracking at the tips of the amygdale, and the distribution of crack orientations transitioned from an approximately vertical direction to preferential concentration along fracture planes. The research results form a solid foundation for the accurate understanding of the mechanical response and fracture mechanism of the rock surrounding underground powerhouse caverns at Baihetan hydropower station, and also provide a reference for the prediction of the mechanical properties of rock with flaws and the stability control of engineering rockmasses.

Archaeal Communities in Deep Terrestrial Subsurface Underneath the Deccan Traps, India

Archaeal community structure and potential functions within the deep, aphotic, oligotrophic, hot, igneous provinces of ∼65 Myr old basalt and its Archean granitic basement was explored through archaeal 16S rRNA gene amplicon sequencing from extracted environmental DNA of rocks. Rock core samples from three distinct horizons, basaltic (BS), transition (weathered granites) (TZ) and granitic (GR) showed limited organic carbon (4–48 mg/kg) and varied concentrations (<1.0–5000 mg/kg) of sulfate, nitrate, nitrite, iron and metal oxides. Quantitative PCR estimated the presence of nearly 103–104 archaeal cells per gram of rock. Archaeal communities within BS and GR horizons were distinct. The absence of any common OTU across the samples indicated restricted dispersal of archaeal cells. Younger, relatively organic carbon- and Fe2O3-rich BS rocks harbor Euryarchaeota, along with varied proportions of Thaumarchaeota and Crenarchaeota. Extreme acid loving, thermotolerant sulfur respiring Thermoplasmataceae, heterotrophic, ferrous-/H-sulfide oxidizing Ferroplasmaceae and Halobacteriaceae were more abundant and closely interrelated within BS rocks. Samples from the GR horizon represent a unique composition with higher proportions of Thaumarchaeota and uneven distribution of Euryarchaeota and Bathyarchaeota affiliated to Methanomicrobia, SAGMCG-1, FHMa11 terrestrial group, AK59 and unclassified taxa. Acetoclastic methanogenic Methanomicrobia, autotrophic SAGMCG-1 and MCG of Thaumarcheaota could be identified as the signature groups within the organic carbon lean GR horizon. Sulfur-oxidizing Sulfolobaceae was relatively more abundant in sulfate-rich amygdaloidal basalt and migmatitic gneiss samples. Methane-oxidizing ANME-3 populations were found to be ubiquitous, but their abundance varied greatly between the analyzed samples. Changes in diversity pattern among the BS and GR horizons highlighted the significance of local rock geochemistry, particularly the availability of organic carbon, Fe2O3 and other nutrients as well as physical constraints (temperature and pressure) in a niche-specific colonization of extremophilic archaeal communities. The study provided the first deep sequencing-based illustration of an intricate association between diverse extremophilic groups (acidophile-halophile-methanogenic), capable of sulfur/iron/methane metabolism and thus shed new light on their potential role in biogeochemical cycles and energy flow in deep biosphere hosted by hot, oligotrophic igneous crust.

Effect of the mineralogical composition on the petrophysical behavior of the amygdaloidal and vesicular basalt of Wadi Wizr, Eastern Desert, Egypt

This paper gives an account of the petrophysical characteristics and the petrographical descriptions of Tertiary vesicular and amygdaloidal olivine basalt flows from Wadi Wizr in the central Eastern Desert of Egypt. The petrographical studies indicated that the studied vesicular basalts are rich in calcic-plagioclase, augite and olivine in addition to numerous amounts of fine opaque minerals and vesicles filled with carbonate and quartz amygdales. The degree of oxidation and alteration of magnetite and ilmenite are discussed in detail. Petrophysically, the studied samples can be grouped into two main groups; the first group includes amygdaloidal basalts and the second group consists of vesicular basalts. The vesicular group (the permeable one) is characterized by fair to very good porosity (∅), good permeability (k), very low true formation resistivity factor (F) and contain micro to ultra micropores. On the other hand, the amygdaloidal basalt group (impermeable group) is characterized by very low storage capacity properties, fair porosity, negligible permeability, medium to high true formation resistivity factor and ultra micropores. The mercury injection capillary pressure technique (MICP) indicates that the pore throats of the studied vesicular samples have a binomial distribution (rank IV), while that of the amygdaloidal samples have a trinomial distribution (rank V). It has been found in this study that the petrophysical behavior of basalts is dependent on the degree of oxidation and alteration; and in particular on the rate of cooling and oxidation of the opaque minerals which caused filling in the primarily produced vesicles by low temperature secondary minerals.

Estimation of the number of specimens required for acquiring reliable rock mechanical parameters in laboratory uniaxial compression tests

The inhomogeneous variability of natural rock always leads to the uncertainty of the parameters gained from the compressive testing data of a limited number of specimens. In this technical note, a systematic comparison for two presented classical approaches, i.e. the Yamaguchi's “decision of the sample number approach (DSNA)” and the “confidence interval approach (CIA)”, is firstly made to identify the cause of discrepancy in the number of required specimens evaluated with different methods. Based on the advantages of both methods, the confidence interval dynamic process approach (CIDPA) is proposed to dynamically determine the number of required specimens during the test process. This presented technical method can effectively avoid the waste of rock specimens while ensuring the accuracy of parameters under a given confidence level. In addition, all of the methods mainly used for the uniaxial comprehensive strength with the Gaussian distribution are extended to obtain a reliable elastic modulus that usually obeys lognormal distribution. Finally, uniaxial compression tests of oblique porphyritic basalt (OP-basalt) and amygdaloidal basalt (Am-basalt) are analyzed to verify the contrast between the results obtained with different approaches and the rationality of CIDPA.

Evidence of the deformation of dykes from the Central Deccan Volcanic Province, Aurangabad, Maharashtra, India

Abstract The Deccan Volcanic Province (DVP) covers an area of more than 500 000 km 2 . There are three major dyke swarms in this province, viz. the Narmada-Tapi, the Western Coast and the Pune-Nasik. In addition, the Nandurbar-Dhule and Pachmari dykes have also been studied. However, the Central Deccan Volcanic Province (CDVP), including parts of Aurangabad (Maharashtra, India), has received less attention than the SW, northern and NE parts of the Deccan Trap. We report on deformed/offset dykes in and around Aurangabad, in the CDVP. These dykes intrude the stratified host basaltic lava flows composed of weathered porphyritic and amygdaloidal basalt. This rheological contrast locally affected the emplacement of dykes, producing offset, the formation of sills, the curvature of dyke walls and finger-like intrusions. The offset of dykes is presumably caused by variations in local stress. The dyke swarm from the CDVP is reported for the first time. The range in the length and width of the dykes is 2.4–26.2 and 1–27 m, respectively. The dykes trend NE, which matches that of the Narmada-Tapi dyke swarm. The present study indicates that the feeder dyke(s) may have fed the basaltic lava flows of the Aurangabad region. The bent pipe vesicles indicate that the lava flowed towards the SE.