Granite Samples Research Articles

Implications for identification of principal stress directions from acoustic emission characteristics of granite under biaxial compression experiments

The rock fracture characteristics and principal stress directions are crucial for prevention of geological disasters. In this study, we carried out biaxial compression tests on cubic granite samples of 100 mm in side length with different intermediate principal stress gradients in combination with acoustic emission (AE) technique. Results show that the fracture characteristics of granite samples change from ‘sudden and aggregated’ to ‘continuous and dispersed’ with the increase of the intermediate principal stress. The effect of increasing intermediate principal stress on AE amplitude is not significant, but it increases the proportions of high-frequency AE signals and shear cracks, which in turn increases the possibility of unstable rock failure. The difference of stress in different directions causes the anisotropy of rock fracture and thus leads to the obvious anisotropic characteristics of wave velocity variations. The anisotropy of wave velocity variations with stress difference is probable to identify the principal stress directions. The AE characteristics and the anisotropy of wave velocity variations of granite under two-dimensional stress are not only beneficial complements for rock fracture characteristic and principal stress direction identification, but also can provide a new analysis method for stability monitoring in practical rock engineering.

Preparatory Slip in Laboratory Faults: Effects of Roughness and Load Point Velocity

AbstractAseismic slip may occur during a long preparatory phase preceding earthquakes, and what controls it remains poorly understood. In this study, we explored the role of load point velocity and surface roughness on slow slip during the preparatory stage prior to stick‐slip events. To that end, we conducted displacement‐rate controlled friction experiments by imposing varying load point velocities on sawcut granite samples with different surface roughness at a confining pressure of 35 MPa. We measured the average slip along the fault with the recorded far‐field displacements and strain changes, while acoustic emission sensors and local strain gages were used to capture local slip variations. We found that the average amount of aseismic slip during the preparatory stage increases with roughness, whereas precursory slip duration decreases with increased load point velocity. These results reveal a complex slip pattern on rough faults which leads to dynamic ruptures at high load point velocities.

Igneous Records of Mongolia–Okhotsk Ocean Subduction: Evidence from Granitoids in the Greater Khingan Mountains

Large-scale Mesozoic granitoids are exposed in the Greater Khingan Mountains. Their relationship with the Mongolia–Okhotsk and the Paleo-Pacific Ocean is still under discussion and a matter of debate. In this study, field observations were made and a total of 18 granitoids exposed in the vicinity of the Heihe–Baishilazi area in the northern part of the Greater Khingan Mountains were sampled for petrological, geochronological, and geochemical research. In addition, to complement this study, 90 granitic samples from the Xinghua, Dajinshan, Yili, Chabaqi, and Sankuanggou areas in the Greater Khingan Mountains were compiled in order to reveal rock assemblages, magma sources, and then inquire into the tectonic background. Zircon LA–ICP–MS U–Pb dating indicates that two samples from the Heihe area were formed in the Early Jurassic period (194.2 ± 1.4 Ma and 183.1 ± 1.3 Ma), and the εHf(t) values and TDM2 of the zircons were mainly +5.8 to +10.7 and 528 Ma to 834 Ma, respectively, with a large variation range. The intrusive rocks from the Greater Khingan Mountains (108 in total) belonging to the T1T2G1G2 assemblage contained tonalites (T1), trondhjemites (T2), granodiorites (G1), and granites (G2). These granitoids are presented as subalkaline series in a plot of total alkali versus SiO2 (TAS diagram), medium-K calc-alkaline and high-K calc-alkaline series on SiO2 versus K2O diagram, with metaluminous to peraluminous characteristics on an A/CNK versus A/NK diagram. These are shown as a MA (magnesium andesite) series and LMA (lower (or non) magnesium andesite) series on a SiO2 versus MgO diagram, which can be further divided into the higher-pressure TTG subtype of the MA (corresponding to high-SiO2 adakite (HSA)) series and the lower-pressure TTG subtype of LMA (corresponding to typical calc-alkaline suprasubduction zone rocks). In addition, granitoids were enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), corroborating a suprasubduction zone environment. Regional correlations as well as geochemical characteristics indicate that the rocks from the Greater Khingan Mountains formed in a subduction zone environment during the Early Jurassic; primary magma had presumably originated from the melting of young and hot oceanic crust under eclogite to amphibolite facies conditions. According to the spatial variation in rock assemblages (T1T2G1 to G1G2 and G2), we speculate that the northeastern Heihe, Baishilazi, and Xinghua areas as well as the westward Dajinshan area were adjacent to the ocean and formed an outer subduction zone, whereas the southwestward Sankuanggou, Yili, and Chabaqi areas were adjacent to the continent, forming an inner subduction zone. The distribution sites of the inner and outer subduction zones indicate southward and southwestward ocean subduction. Therefore, we propose a direct connection with southward subduction of the Mongolia–Okhotsk Ocean.

The last Neoproterozoic rift magmatism on the western margin of Yangtze block, South China: New insights of Marinoan onset from low-δ18O magmatic events

The geological record preserves evidence of “Snowball Earth” glaciations during the Cryogenian Period, the Sturtian onset at ca. 720 Ma and the Marinoan onset at ca. 650 Ma. Compared to the Sturtian, the trigger for the Marinoan is still unclear due to the absence of large igneous provinces (LIPs). This study first discovered low-δ18O Luoluobuzi (LLBZ) granite which emplaced on the eve of the Marinoan at the Yangtze Block in South China. The granite with U-Pb age of 651.2 ± 2.1 Ma and has εHf (t) values between + 6.8 to + 13.3, and low-δ18O values between + 2.74 to + 5.34 ‰. Granite samples show Ba, Nb, Ta, Sr, Eu, and Ti depletion and enrichment in Rb, U, Th, and Pb, modeling calculations to suggest they originated from partial melting of nearby Neoproterozoic mafic rocks and formed in a continental rift. We systematically compiled data and found an interglacial period between the Sturtian-Marinoan glaciations is absent of magmatic activities. Extensional magmatic activity similar to the LLBZ granite started at ca. 651 Ma, which within errorsoverlapped the onset of the Marinoan. Such temporal ruling also existed in other worldwide rift-related magmatic activities. After combining chemical index of alteration (CIA) and palaeomagnetic results, we found the last episode of Rodinia breakup played an important role in the onset of the Marinoan.

Continental crust delamination in a retreating subduction zone: A case study in the southern Alxa (Inner Mongolia, China), Central Asian Orogenic Belt

Carboniferous-Permian igneous rocks in the southern Alxa (Inner Mongolia, China) of the southern Central Asian Orogenic Belt exhibit an oceanward migration trend, which provides an ideal area to reconstruct the process of crust-mantle material exchange within a retreating subduction zone. This study presents new geochronological and geochemical data for the Shouji plutons from the southern Alxa to address crust-mantle material exchange process. All these diorite, granodiorite, and K-feldspar granite samples from the Shouji batholith exhibit Early Permian zircon U-Pb ages (ca. 282−270 Ma). These diorite and granodiorite are characterized by high Sr contents as well as low Y, and Yb concentrations, coupled with distinctively high Sr/Y values. They exhibit fertile Nd-Hf isotopic compositions with negative whole-rock εNd(t) values, and zircon εHf(t) values, similar to those of continental crust-related adakites, which might originate from partial melting of lower crust, and followed by melt-mantle interactions. These K-feldspar granite samples display peraluminous and high-K calc-alkaline compositions, and negative zircon εHf(t) and whole-rock εNd(t) values, and originated from partial melting of Paleoproterozoic igneous rocks, with additions of mantle-derived melts in their sources, in low-temperature, low-pressure conditions. Previously published zircon U-Pb age data show that numerous mafic igneous rocks were mostly generated during the Early Permian, marking the onset of mafic volcanism in the southern Alxa. Moreover, compiled detrital zircon U-Pb age data for Late Carboniferous−Permian sedimentary succession imply a regional topographic uplift during the Early Permian. Both of these two lines of evidence suggest an Early Permian lower crustal delamination in the southern Alxa. These Shouji adakitic plutons were most likely to be generated during the lower crustal delamination. Furthermore, Sr-Nd isotope data of Carboniferous-Permian igneous rocks show that the continental crust was recycled back into the mantle during Early Permian within the southern Alxa by means of subduction erosion and lower crustal delamination.

On the fracture and energy characteristics of granite containing circular cavity under variable frequency-amplitude fatigue loads

The cavities left after engineering construction obviously affect the stability of underground rock mass. Extensive studies have been devoted to investigate the mechanical behaviors of cavity-contained rock under static or impact stress paths, however, the damage process and energy dissipation characteristics were not well understood. The presented studies aim to reveal the volumetric deformation and energy dissipation characteristics of granite samples with different cavity orientations under unconventional cyclic loading conditions. The applied stress path is characterized with variable frequency-amplitude sinusoidal loads. Testing results show that the intersection between the maximum principal stress and cavity orientation affects the strength, deformation, energy, and failure modes. Crack damage evolution and hole collapse were revealed using strain rate and energy rate. It is found that the dissipated energy rate gives an early instability warning than the volumetric strain rate.A series of CT images of the failed rock give new insights into the mesoscopic mechanism of hole spalling and crack coalescence. A transition from tensile failure to shear failure was found as the cavity orientation increases with respect to the principal stress.

Ultrahigh-Pressure Mineral Inclusions in a Crustal Granite: Evidence for a Novel Transcrustal Transport Mechanism

Spherical crystals in minerals from prismatine-bearing rock from Waldheim, including ultrahigh-pressure (UHP) minerals such as stishovite and coesite, were previously described in uncommon crustal environments. To determine if this was an outlier phenomenon, we searched for equivalent inclusions in other rocks, which we indeed discovered in a Variscan tin-bearing granite sensu stricto from the Erzgebirge/Germany. The identification of more examples of this phenomenon implies a novel, very rapid transcrustal transport mechanism, which, however, is not unique. We demonstrate the unusual occurrence of UHP minerals (moissanite, diamond, lonsdaleite, stishovite, coesite, kumdykolite, and cristobalite-II) in topaz the investigated granitic samples, which reflects the direct interaction of mantle and crust via supercritical fluids or extremely volatile-rich melts. Mostly, the UHP minerals we recognized occur as tiny inclusions in moissanite. The trapping by this mineral prevents a fast reaction in an exogenous environment.

Petrogenesis of the Ore-Related Intrusions of the Aikengdelesite Mo (–Cu) and Halongxiuma Mo Deposits: Implication for Geodynamic Evolution and Mineralization in the East Kunlun Orogen, Northwest China

The East Kunlun Orogenic Belt (EKOB) is the most important Triassic polymetallic metallogenic belt in China. A study about the petrogenesis of the ore-related intrusions is of great significance to the geodynamic evolution of orogenic belts. In this study, analysis of U–Pb zircon dating, whole-rock major and trace element compositions, and zircon Hf isotopes for the granitoids hosting the Aikengdelesite Mo (–Cu) and Halongxiuma Mo deposits in the EKOB are studied to determine their chronology and petrogenesis. Zircon date results show that the Aikengdelesite granite porphyry and the Halongxiuma granodiorite porphyry formed at 244.2 ± 1.7 Ma and 230.0 ± 1.0 Ma respectively. All samples of the Aikengdelesite granite porphyry and the Halongxiuma granodiorite porphyry which have high SiO2 and K2O contents, and low MgO and Cr, belong to the high-K calc-alkaline series. The Aikengdelesite granite porphyry samples show I-type geochemical affinities, whereas the Halongxiuma granodiorite porphyry samples are A-type granitoids. They all show negative zircon εHf(t) values (−7.4 to −3.3 and −3.7 to −2.5). We suggest that the Aikengdelesite granite porphyry may have been derived from the lower continental crust. While the Halongxiuma granodiorite porphyry could have formed by partial melting of basic lower crustal materials. By combining the results of this study with previous data, two magmatic and mineralization peak periods (278–237 Ma and 230–210 Ma) were observed in the Paleo-Tethys of the EKOB. Porphyry–skarn deposits occurring in the first episode were formed in the setting of an active continental margin related to the Paleo-Tethys Ocean plate subduction (e.g., Aikengdelesite porphyry deposit), while deposits occurring in the second episode were formed in a post-collisional setting (e.g., Halongxiuma porphyry deposit).

Evaluation of the radiation shielding properties of ornamental rocks produced in Brazil: A Monte Carlo approach

In this work, the Monte Carlo MCNPX (2.7.0) code was used to evaluate the radioprotective properties of ten ornamental granitic samples produced in Brazil. For each sample of granite, the mass attenuation coefficient (µ/ρ) and half-value layer (HVL) were evaluated using the photon energy emitted by the following radioisotopes: 241Am (59,5 keV), 133Ba (356 keV), 137Cs (662 keV), 60Co (1250 keV), and 22Na (1274 keV). The MCNPX results showed agreement with the values obtained by using the XCOM database, as well as with theoretical and experimental results, available on the literature. The computational model built in this work can be used by the scientific community interested in parameters involving new materials for gamma radiation shielding, which has been used in different areas of the nuclear sciences.

In-situ flow visualization with Geo-Positron-Emission-Tomography in a granite fracture from Soultz-sous-Forêts, France

We investigate the fluid flow field in a fractured granite core sample. Sequential imaging with Positron-Emission-Tomography (PET) allows direct reconstruction of flow streamlines, thus providing a unique insight into the fluid dynamics of complex fractured crystalline materials. Pulse migration experiments using the positron-emitting radionuclide 18F− as tracer were conducted on a fractured granitic drill core, originating from a depth of 1958 m of the Enhanced Geothermal System (EGS) reference site at Soultz-sous-Forêts, France. The flow field was analyzed as a function of in- and outlet positions across the fracture, as well as applied flow rates. Different flow path characteristics were identified. Both the fracture aperture variation and the topography of the fracture surface affect the flow field with consequences on flow channeling and preferential flow paths. Furthermore, pulse migration experiments were also numerically simulated with a 2.5D model using COMSOL Multiphysics®.While the higher flow rate experiments show wider and higher dispersion of the flow path, lower velocity results in more localized flow and channeling behavior. This type of study thus yields enhanced experimental insights into the hydrodynamics of fracture flow and its relation to the rough structure of a single fracture, compared to input-output experiments. It can help to validate model simulations and experimentally determine hydrodynamic parameters needed for reactive transport modeling that are otherwise estimated with a high degree of uncertainty.

Determination of Se and Te by hydride generation-inductively coupled plasma mass spectrometry after mixed-acid digestion of tungsten ores

Se and Te in tungsten ores are important parameters for exploring the metallogenetic process of tungsten ores; however, due to their high refractory, low abundance, extreme volatilization, as well as the complex matrix interference during analysis, it is a challenge to accurately determining their concentrations in tungsten ores. This study presents a method of combining hydride generation device with inductively coupled plasma mass spectrometry (HG-ICP-MS) to determine the contents of Se and Te in tungsten ores. As a pre-processing step, tungsten ores were dissolved in the mixture of HF + HNO3 + HClO4 and microwaved for digestion. The analytical results show that the main matrix components (K, Na, Ca, Mg, Fe, Mn and Pb) in tungsten ores have no interference, and the interference of W, Cu, Zn and Bi can be eliminate by adding an appropriate amount of Fe3+. The method was used to test 6 samples with different tungsten concentrations. Compared with the results of hydride generation atomic fluorescence spectrometry (HG-AFS) method, the mean values of HG-ICP-MS method showed a good consistency and the relative mean deviations of Se and Te contents were in the range of −5.2%­ to 6.2% and − 3.8%­ to 3.4%, respectively. The values of Se, Te and Te/Se ratio determined from various geological samples (30 soil and sediment samples, 30 granite samples, 25 poly-metallic sulfide ore samples and 29 tungsten ore samples) highlight their potential prospecting in the metallogenetic process of tungsten ores.

Early Palaeozoic intracontinental orogeny in South China Block: Insights from migmatites and potassic mafic rocks in southern Guangdong

ABSTRACT The early Palaeozoic orogen in South China is considered as one of the typical examples of intraplate orogens in the world. However, the nature of the orogen, for example, the onset time and the timing of tectonic transition from syn-orogenic compression to post-orogenic extension, are still controversial. Here, we present new zircon U–Pb age and Hf isotope data, and whole-rock geochemical and Sr–Nd isotopic data for migmatites and potassic mafic rocks in southern Guangdong, from the Cathaysia Block, South China. Migmatites consist of metatexite and diatexite, including various amounts of palaeosome, melanosome, and leucosome. Leucosomes from metatexite and diatexite/migmatite granite samples yield consistent U–Pb ages of 451.5 ± 2.0 Ma to 458 ± 16 Ma, respectively. Zircon U–Pb dating from two potassic plutons yield consistent crystallization ages of 451–446 Ma. Our new results of field investigation, mineralogy and microstructures, geochronology, and geochemical compositions demonstrate that the protoliths of migmatites are metasedimentary rocks, while metatexites and diatexites are the products of variable degrees of partial melting of the protolith. The potassic rocks have SiO2 contents ranging from 52.5 to 60.2 wt.%, high K2O/Na2O ratios (0.7–1.3), with MgO contents of 3.0–6.2 wt.% and Mg number of 42–57. They have enriched Sr–Nd–Hf isotopic compositions with (87Sr/86Sr)i ratios of 0.7085–0.7151, ɛNd(t) values of −9.9 to −6.2, and εHf (t) values of −10.5 to −5.3, indicating that they were generated from an enriched mantle source modified by ancient oceanic subducted sediments. Regional crustal anatexis occurred at about 451 Ma, and the timescale from crustal anatexis to melt homogenization and accumulation spans over an interval of ~15 Myr. The association of migmatites and the potassic rocks may form in post-orogenic extension setting. Thus, we suggest that the tectonic transition from syn-orogenic compression to post-orogenic extension occurred by the Late Ordovician (ca. 451–446 Ma) for the early Palaeozoic orogen in South China.

Granite thermal reservoirs in Lingshui area of Hainan Island and their significance to geothermal resources, China

Hainan Island located at the southernmost tip of the continental crust of the South China Plate, has high terrestrial heat-flow values, widely-distributed hot springs, and rich geothermal resources. Intensified researches on the origin and potentials of geothermal resources can promote Hainan Island's development into a clean energy island. To determine the geological conditions for the formation of geothermal resources in southern Hainan Island, we collected core samples of granites from the Baocheng batholith in southern Hainan Island and conducted systematic analysis in respect of petrology, geochronology, geochemistry, and petrophysical property. The results of this study are as follows. The Baocheng batholith in the southern Hainan Island has a crystallization age of 98.42 ± 0.56 Ma, making it the product of magmatism in the early stage of the Late Cretaceous. It mainly consists of high-K calc-alkaline granites, which were intruded by intermediate-to-mafic veins. The Baocheng batholith has a high radioactive heat generation rate of 2.712–6.843 μW/m3, with an average of 3.846 μW/m3, a radioactive heat-flow value of 30.768 mW/m2 and a heat-flow contribution rate of 38.95%–43.95%. As shown by the results of their thermophysical property analysis, the granites have high thermal conductivity and can serve as high-quality geothermal reservoirs. In combination with previous geological and geophysical data, the geothermal model of the Lingshui area was established in this study. The deep structure indicates the presence of high-conductivity and low-resistivity layers in the basement of the Baocheng batholith. It can be inferred thereby that asthenospheric upwelling may occur and that there exist two magma vents at depth in the batholith. Therefore, magmatic heat at depth and granites with high radioactive heat generation rate serve as the main heat sources in the Lingshui area.

Experimental Investigation of Mechanical and Fracture Behavior of Parallel Double Flawed Granite Material under Impact with Digital Image Correlation

During the excavation of underground projects, the rock masses left as the bearing support system are also subjected to dynamic loads from the excavation activities ahead. These rock masses have been damaged and fractured during the initial exposure (dynamic loads) and are subjected to static loads in the subsequent process as the support system. In this study, granite rock samples and specimens with different angles were produced, preloaded with different confining pressure, and under a combination of dynamic and static loading tests using a modified dynamic and static loading system: split Hopkinson pressure bar (SHPB). The peak strain and dynamic modulus of elasticity are weakened by the inclination angle in a similar way to the strength, with the specimens showing an evolutionary pattern from tensile strain to shear damage. The change in the inclination angle of flaws would weaken the dynamic and combined strengths, and a larger inclination flaw results in a significant decrease in its strength. Fractal analysis revealed that the fractural dimension was closely related to the fissure angle and showed a good linear correlation with the strain rate. This study will provide an important security assurance for deep mining.

Impact dynamic characteristics and constitutive model of granite damaged by cyclic loading

To study the influence of damage degree on dynamic characteristics of damaged rock mass, the samples with different damage degrees were obtained by cyclic loading test and then the impact failure test was carried out by a 100-mm diameter split Hopkinson pressure bar (SHPB) device. In addition, the Zhu-Wang-Tang (ZWT) constitutive model was improved to establish the dynamic constitutive model of damaged granite. Results show that when the cyclic upper limit stress (CULS) reached 60% of the compressive strength of rock mass, the Felicity effect was significant and the Kaiser effect basically disappeared. Furthermore, there was obvious compressive strengthening effect of damaged rock mass under impact load, with the increase of the CULS in the early stage, the dynamic compressive strength of granite samples showed an overall decreasing trend. The damage degree had a significant effect on the propagation and energy absorption ability of rock mass, thus affecting its failure characteristics. Eventually, the proposed constitutive model was fitted with the experimental data, which showed that the model could accurately describe the dynamic mechanical properties of damaged granite under impact load.

Early Paleoproterozoic tectonic evolution of the Yinshan Block in the North China Craton: Constraints from the geochronology and geochemistry of basic to felsic magmatic rocks in the Guyang area

The earliest Paleoproterozoic magmatic rocks have recorded the transition from the Neoarchean cratonization of the NCC to its post-Archean tectonic evolution, which will provide insight into the onset of the modern-style subduction. This study focuses on the early Paleoproterozoic granodiorite, monzonitic diorite, alkali feldspar granite and gabbro in the Guyang area to decipher the early Paleoproterozoic tectonic evolution of the Yinshan Block. Zircon U–Pb dating indicates that these rocks were emplaced at ca 2.46 – 2.41 Ga. The ∼ 2.46 Ga granodiorite samples have high Sr contents, low Y and Yb contents with high Sr/Y ratios, similar to the characteristics of adakitic rocks. Based on their high Mg# values, Na2O/K2O ratios, Cr, Co and Ni concentrations, and positive εNd(t) values, we propose that the granodiorite was likely produced by partial melting of subducting oceanic slab. The contemporary monzonitic diorite samples are characterized by high Nb concentration, which are similar to those of Nb-enriched basalt/andesite. The monzonitic diorite samples are characterized by LREE-enriched patterns with negative Eu anomalies and have negative εNd(t) values (-0.4 – −1.4), which suggest that they were derived from partial melting of fertile mantle peridotite metasomatized by adakitic melts. The ∼ 2.44 Ga alkali feldspar granite samples have negative εNd(t) values (-4.0 – −1.9) and show geochemical characteristics of A-type granites, indicating an extension background. The distinct geochemical characteristics of ca. 2.46 – 2.44 Ga Guyang adakatic granodiorite, Nb-enriched monzonic diorite and A-type alkali feldspar granite suggest that a slab window was opened in the southern margin of the Yinshan Block. The gabbros were emplaced at ∼ 2.41 Ga revealed by U-Pb dating. The enriched LREEs and relatively flat HREEs patterns with negative Nb-Ta anomalies of gabbros indicate a subducting tectonic setting. Their high Ba/Th and low Nb/Y ratios imply that the mantle source was metasomatized by slab-derived fluids. This special rock association not only constrains the tectonic evolution in the southern margin of the Yinshan Block, but also indicates modern-style subduction operated already in the early Paleoproterozoic.

Radiological and environmental hazards of granitic rocks in Wadi Faliq El Sahl and El Waar area, North Eastern Desert, Egypt

Chronologically, the main exposures in the study area include; tonalite, granodiorite, adamellite, Hammamat Sediments, monzogranite, syenogranite, rapakivi syenogranite, alkali feldspar granite and dykes. This work aims to determine the suitability of the granitic rocks for using as ornamental stones through detecting their radiological and ecological impacts. The studied samples were measured radiometrically by using Na-I detector for determination of 226Ra, 232Th and 40K concentrations. External hazard indices (Hex) in some samples are more than unity, also, the (Raeq) are higher than the exemption limits (370 Bq.kg−1) exceeds the upper limit of exposure. The hierarchical cluster analysis (HCA) was applied to investigate the correlation between the radionuclides and the corresponding radiological hazard variables. Based on the statistical analysis, 232Th and 226Ra mainly contribute to the radioactive risk of the studied rocks. Regarding ecological indices, 42.1% of younger granite samples have Pollution load index values greater than 1, indicating deterioration, while the majority of older granite samples are lower than 1 suggesting perfection samples. Where, some sample from the older granitoids and younger granites have many radiological and ecological parameters greater than the recommended international limits, so, these samples should not be used in construction for safety reasons.

Estimation of stresses in a massive granite using laser ultra-sonic testing and stress memory effect

This paper addresses in-situ stress-estimation methods based on the Kaiser effect. The physical and mechanical properties of granite, diorite, and granodiorite samples selected at different depth intervals of the core obtained from a wellbore were examined. The ultimate uniaxial compressive strength, modulus of elasticity, and Poisson’s ratio of the rock samples were determined using presses and strain gauges. Also, local longitudinal and shear wave velocities were measured using a high-accuracy laser-ultrasonic system with a view to assessing the structure of the samples. Based on the resulting elastic wave velocity maps, samples with no obvious discontinuities were chosen. These undisturbed samples were subjected to uniaxial compression and their acoustic emission was simultaneously measured. In-situ stresses were estimated from the results of the interpretation of acoustic emission measurements. The experimental in-situ stresses were compared with the results of a numerical simulation. The ratio of the estimated in-situ stresses to the calculated ones is within the range from 0.81 to 1.11. This means that the laser ultrasonic and acoustic emission methods make it possible to effectively estimate in-situ stresses in a rock mass and assess the degree of rock mass damage.

Insights into the evolution of the southeastern Dom Feliciano Belt and its connection to the Pan-African Orogeny based on new U-Pb and Lu-Hf zircon data

The Neoproterozoic supracrustal units of the Dom Feliciano Belt in southern Brazil and eastern Uruguay provide a record of the tectonic evolution of the Brasiliano/Pan-African cycle in terms of sedimentation, deformation, and metamorphism during the western Gondwana supercontinent assembly. From the northern Punta del Este Terrane (Jaguarão Domain) and neighboring Herval Complex were acquired new LA-ICPMS U-Pb and Lu-Hf zircon data from significant samples of metasedimentary rocks and intrusive granites. The central units of the domain are the Arroio Telho and Arroio Grande metasedimentary complexes, which have detrital zircon data ranging in age from 3.2 to 0.7 Ga, with prominent age peaks at 2.2–1.7 Ga, 1.5–1.0 Ga, and 1.0–0.7 Ga. The Herval Complex samples revealed a similar provenance of detrital zircon ages, with two main intervals of 1.5–1.1 Ga and 1.0–0.7 Ga, and also minor Paleoproterozoic (2.0–1.7 Ga) and Archean (2.8–2.4 Ga) ages. The maximum depositional age of the supracrustal complexes is constrained to age populations between 700 and 650 Ma. The mylonitic intrusive peraluminous granites yielded crystallization ages of ca. ∼570 Ma. The Neoproterozoic metamorphic zircon overgrowths range from 680 to 570 Ma. The Lu-Hf data from the meso- to Paleoproterozoic zircons have εHf(t) values ranging from −10 to +10, with the dominance of slightly positive results, and Hf(t) model ages from Paleoproterozoic to Archean. The εHf(t) values in Neoproterozoic zircons are dominantly negative (−15 to +5) with meso- to Paleoproterozoic Hf(t) model ages. These results demonstrate that sedimentary deposition ceased and underwent metamorphism during the development of the Cryogenian/Ediacaran arc-related magmatism of the Dom Feliciano belt. Given the scarcity of Mesoproterozoic rocks in the Mantiqueira Province and nearby cratonic areas, the obtained data suggest that these detrital populations originated in southwestern African rocks. The Congo/Kalahari cratons (Africa) are the most likely source area for Paleoproterozoic and Archean detrital zircons. The geological context and isotopic results of the investigated supracrustal complexes point to a prior extensional tectonic setting during the Tonian (∼800 Ma), with regional deformation and metamorphism linked with the Dom Feliciano Belt accretionary and collisional stages (660–570 Ma).

Processing of micro-CT images of granodiorite rock samples using convolutional neural networks (CNN), Part II: Semantic segmentation using a 2.5D CNN

X-ray computed tomography (XCT) is routinely used in geosciences for the purpose of rock characterisation. High-quality micro-CT images are successfully used for fracture characterisation, as well as analysis of grains and pores. In contrast, the use of XCT for mineral identification is uncommon and often ineffective. Implementation of micro-CT imaging techniques for mineral identification is affected by the accuracy and precision of the image segmentation results. Conventional segmentation methods such as thresholding, watershed, and active contouring are user-biased and do not provide the robust distinction between various heavy accessory minerals in granite rocks. Heavy ore minerals such as pyrite, chalcopyrite, molybdenite, and ilmenite are readily recognised in grey-scale micro-CT images because of their high attenuation coefficient, but further differentiation between these minerals using only traditional segmentation methods is challenging. Conversely, deep convolutional neural networks (CNNs) are fully self-trained, and they have demonstrated accurate semantic segmentation results for rock images. However, the application of CNN semantic segmentation for igneous rocks is not well documented. In this research, the U-Net 2.5D CNN was deployed to train the neural network on a combination of high-resolution micro-CT and mineral liberation analysis (MLA) images to identify different accessory mineral regions of interest (ROIs). The image segmentation results were assessed using MLA and SEM data, and the accuracy of segmentation was found to be greater than 97%. The methodology developed in this study can be extended to map the mineralogy of granite samples unseen by the CNN to further validate the robustness of the approach.