Granite Research Articles

Geothermal extraction performance in fractured granite from Gonghe Basin, Qinghai province, China: Long-term injection and production experiment

The efficient exploitation of geothermal energy through enhanced geothermal systems (EGS) has been a relevant topic for hot dry rock (HDR) geothermal resources. When cryogenic fluid is injected into a thermal reservoir, improving heat exchange efficiency is key to achieving the optimal exploitation of HDR. In this paper, granite outcrops from Gonghe Basin were used as the testing sample. The natural fractures in the granite samples were relatively well developed. To simulate long-term injection and production from multi-wells in situ, physical experiments were performed in a newly-developed, in-house large-scale true triaxial experimental system. Geothermal extraction performance of an HDR was simulated for long-term injection and production operations. Simultaneously, the mode of one-injection and multiple-production wells was represented. In the paper, the effects of the production-injection well spacing, the number of production wells and the injection rate on the production temperature and flow rate are discussed. The results show that, during long-term injection and production, there are two stages of production temperature variation, namely stabilization and attenuation. When the number of the production wells is increased, the heat extraction efficiency is accelerated. Moreover, competitive diversion of fluid among fractures occurred due to different conductivities. Furthermore, under different production modes, the production flow rate contributed differently to the heat extraction. Finally, the effect of the production-injection wells spacing on the heat exchange performance was analyzed; this is mainly reflected in the change of the effective heat exchange area between the rock and the injected fluid. The results emphasize the importance of designing an appropriate production mode and optimizing the injection-production parameters to ensure efficient HDR exploitation.

Neoarchean magmatism and Rhyacian reworking in the northeast of the Amapá Block, southeastern Guiana Shield, Brazil: Geochemistry, U–Pb geochronology, and Hf–Nd isotopes

This study investigates the age, geochemical nature, sources, and Rhyacian reworking of the Neoarchean magmatism at the northeastern portion of the Amapá Block, southeastern Guiana Shield (northeast Amazonian Craton). This block consists of a large Archean continental landmass strongly reworked during the Transamazonian orogeny (2.26–1.95 Ga). We provide the very first geochemical results for Archean basement units of the Amapá Block, which are the Mesoarchean Tumucumaque and Neoarchean Guianense complexes, and Neoarchean Mungubas Granite. The first two exhibited geochemical affinity with enriched TTG-type and hybrid granitoids, respectively, while the Mungubas Granite showed affinity with biotite granites. Such affinity with C-type granitoids indicates that the genesis of these units involves partial melting of crustal sources. LA-MC-ICP-MS zircon U–Pb and Lu–Hf, and whole-rock Sm–Nd data were obtained for the Neoarchean Mungubas Granite and Guianense Complex. In both units, zircon U–Pb dating provided a distribution of dates that span ∼50 Ma forming two groups with distinct mean 207Pb/206Pb ages of ∼2.70 Ga and ∼2.65 Ga, respectively. The older age is considered as the crystallization/emplacement age of the Mungubas Granite and the Guianense orthogneiss protolith, while the younger one is ascribed to concealed Pb loss. The recognition of Mesoarchean inherited zircon core and xenocryst with ages of 2.84 Ga and 2.99 Ga suggest that these units reworked older basement rocks from the Amapá Block. Subchondritic ԐHf(2.70 Ga) of zircon and ԐNd(2.70 Ga) of whole-rock, along with their respective Hf-TDMC (3.6–3.2 Ga) and Nd–TDM (3.6 Ga) model ages, for both units, reflect the substantial crustal reworking of predominant Paleoarchean sources during the Neoarchean in the northeastern Amapá Block. In addition, U–Pb dating on titanite crystals from the Guianense orthogneiss yielded an unprecedented ∼2.05 Ga age, arguing that a Late Rhyacian metamorphic event affected the Archean orthogneisses. This 2.05 Ga event coincides with the emplacement of Rhyacian granitoids in the area, as well as with the 2.06–2.04 Ga late orogenic HT granulite facies and amphibolite facies metamorphic events identified, respectively, at the northern border and in the central-southern portion of the Amapá Block.

Application of Multi-Near-Surface Geophysical Surveys for Geothermal Spring: A Case Study in Kon Tum Province, Vietnam

The occurrence of geothermal spring not only enhances human health, but also plays a crucial role in generating community’s revenue that boosts up the standard living of locals. An endeavor has been made to delineate the prospective areas of geothermal spring in Kon Tum province, Vietnam by the utilization of joint-geophysical techniques. The blended mode as mentioned is opted for its superiority in providing the rapidassesments of temperature in shallow temperature survey, comprehensive understanding the subsurface structure in electrical resistivity tomography in copporating with the validation in well log interpretation. The results found that the overlapping region of high temperature (35°C) region and low resistivity (200 Ωm) is observed in the east in the vicinity of Dlak Bla river, and it probably broadens to the west of the study area. The outcome of geophysical approaches strongly concur with the well log interpretation, revealing the presence of water-bearing zone encountered in fractured granite. The results also corroborated the existence of concealing fault F5 as a branch of the NE-SW fault F2 which is favorable for creating a route to form the geothermal spring. The output of this research could be considered as an intentive consultation for Kon Tum’s planners and makers on expanding the investigation and exploitation.

Nd isotope systematics of Late Paleozoic granitoids from the Western Transbaikalia (Russia): Petrological consequences and plume model testing

Late Paleozoic granites of the Angara-Vitim batholith (AVB) occupy an area of 200,000 km2 in Western Transbaikalia (the eastern part of the Central Asian fold belt). Batholith granitoids form a sheet-like body with an average thickness of 7–10 km and a volume of about 1 million km3. The granitoid massifs that make up the batholith are composed of high-potassium calc-alkaline and subalkaline quartz monzonites, quartz syenites, amphibole-biotite granodiorites, and biotite granites of autochthonous and allochthonous facies. An extremely high heterogeneity of the batholith isotopic structure was established, which basically corresponds to the parameters of uneven-aged crustal metaterrigenous protoliths. There are significant variations in εNd(Т) and accordingly T(DM-2) in granitoids of different complexes. It is assumed that the isotopic heterogeneity of AVB was formed due to the melting of a limited protoliths number that are maximally contrasting in isotopic and lithological composition: the Paleoproterozoic continental crust with εNd(Т) ≈ -20 ÷ -22 and T(DM-2) = 2.9–2.5 Ga and Neoproterozoic mafic granulites of increased potassium alkalinity, enriched in the juvenile component (εNd(Т) ≈ -3.0; T(DM-2) = 1.2–1.3 Ga). The latter were the main magmas source of postbatholitic alkali granites. Melts from these contrasting protoliths were only in some cases complementary to the salic melts sources. The main mechanism that determined the isotopic composition of AVB granitoids was the mixing of isotopically contrasting magmas in different proportions. Mingling dikes, mafic inclusions in granitoids, and synplutonic mafic intrusions in the AVB indicate an additional mixing component. It was mafic magma from an enriched mantle reactivated in the Late Paleozoic under the mantle plume influence on the heated plastic crust of a young (Hercynian) orogen.

Insights from Dikes for Multistage Granitic Magmatism in the Huayangchuan Uranium Polymetallic Deposit, Qinling Orogen

The Huayangchuan U-polymetallic deposit in the Qinling Orogen is a newly verified carbonatite-hosted deposit on the southern margin of the North China Craton (NCC) in Central China. Granitic magmatism is extensively developed in the Huayangchuan deposit area and is lacking analysis on the reasons for these situations; however, its ages, petrogenesis, and relationship with uranium mineralization are not well constrained. Zircon U–Pb ages for the hornblende-bearing granite porphyry and medium-fine-grained biotite granites in close proximity to carbonatite rocks are 229.8 ± 1.1 and 135.3 ± 0.6 Ma, respectively. High-K calc-alkaline series and weakly peraluminous Triassic hornblende-bearing granite porphyry are slightly enriched in light rare earth elements (LREE) with flat heavy rare earth element (HREE) patterns, enriched in Ba and Sr, and depleted in Nb, Ta, P, and Ti, i.e., geochemical characteristics similar to those of adakite-like rocks. The Early Cretaceous medium-fine-grained biotite granites are characterized by LREE enrichment and flat HREE patterns, which belong to high-K calc-alkaline series, and metaluminous belong to weakly peraluminous I-type granite, with U and large ion lithophile element (LILE) enrichment and high field strength element depletion. The high initial 87Sr/86Sr ratios and enriched Nd (εNd(t) = −10.7 to −9.5 and −19.9 to −18.9, respectively) and Hf (εHf(t) = −21.8 to −13.0 and −30.5 to −19.0, respectively) isotopes revealed that both granitic rocks from the Huayangchuan deposit mainly originated from lower crustal materials, generated by partial melting of the ancient basement materials of the Taihua Group. Triassic hornblende-bearing granite porphyry is significantly different from the mantle origin of the contemporaneous U-mineralization carbonatite. In combination with tectonic evolution, we argue that the Qinling Orogenic Belt was affected by the subduction of the North Mianlian Ocean during the Late Triassic. The ongoing northward subduction of the Yangtze Craton resulted in crustal thickening, forming large-scale Indosinian carbonatites, U-polymetallic mineralization, and contemporaneous intermediate-acid magmatism. Additionally, due to the tectonic system transformation caused by Paleo-Pacific Plate subduction, intracontinental lithosphere extension and lithospheric thinning occurred along the southern NCC margin in the Early Cretaceous. Intense magma underplating of the post-orogeny created a large number of magmatic rocks. The tremendous heat could have provided a thermal source and dynamic mechanism for the Yanshanian large-scale U-polymetallic mineralization events.

Mapping hydrothermal alterations and associated lineaments within Kaiama, north-central Nigeria, using Landsat 8 Operational Land Imager Data and Digital Elevation Model

This research focuses on the geological investigation of Kaiama region, which is characterized by a diverse range of rock formations, including mylonites, porphyritic granites, gneiss, schist, phyllites, and pink granites. The study employs remote sensing techniques, utilizing Landsat 8 OLI data and Digital Elevation Models, to systematically map the spatial distribution of hydrothermal alterations and tectonic structures associated with mineralization in the Kaiama area. Various image processing methods such as Color Composites, Band Rationing, and Principal Component Analysis (PCA) were employed to extract valuable information from the collected datasets. Utilizing Sabins band ratios (4/2, 6/7, and 6/5), we categorized alterations associated with iron oxides, clay minerals, and ferrous minerals. PCA was applied to refine the identification of alteration zones, using two distinct sets of images: H-image (comprising bands 2, 4, 5, and 7) and F-image (comprising bands 2, 5, 6, and 7), which represented iron-oxide and hydroxyl mineral deposits, respectively. The synthesis of H, F, and H+F images in RGB format provided an optimal representation of the spatial distribution of hydrothermal alterations, exhibiting a strong positive correlation with known mining regions for gold, copper, wolframite, and tantalite within the study area. Furthermore, a comprehensive analysis of regional lineaments revealed a consistent NNE-SSW to NE-SW correlation, suggesting a predominant control on mineralization trends. This study advocates for adopting remote sensing techniques, specifically Landsat 8 data and DEM, as an effective approach for mapping hydrothermal alterations and identifying key structural controls associated with mineralization.

Monte Carlo Methods to Simulate the Propagation of the Created Atomic/ Nuclear Particles from Underground Piezoelectric Rocks through the Fractures Before the Earthquakes

Until now, many studies have been performed on particle radiations before or during earthquakes (EQs). Neutron, gamma, electron, proton, and ultra-low frequency (ULF) photons are among the particles, detected during EQs. In our previous study, with the help of piezoelectricity relationships and the elastic energy formula, the Monte Carlo N‐Particle eXtended (MCNPX) simulation code was applied to find the amount of created atomic/nuclear particles, the dominant interactions; and the energy of the particles for various sizes of quartz and granite blocks. In this study, using the MCNPX simulation code, we have estimated the flux of the particles (created from under-stressed granitic rocks) at different distances from the EQ hypocenter inside the fractures, filled with air, water, and CO2. It was found that inside a water-filled fracture, the particles do not show the flux far from the EQ hypocenter. However, inside the gases like air and CO2 with the normal condition density, different types of particles can have a flux far from the source (more than a kilometer) and they might reach themselves to the surface in the case that the EQ hypocenter is very shallow (0­-5 km). However, for deep EQs, it seems that the most detected nuclear particles on the surface should pass via the vacuum-filled fractures and reach the surface. Moreover, it was concluded that the higher the density of the fracture’s filling fluid, the less distance that the particles can have a flux.

Effect of rock properties on wear and cutting performance of multi blade circular saw with iron based multi-layer diamond segments

This study is an attempt for comprehensive, combining experimental data with advanced analytical techniques and machine learning for a thorough understanding of the factors influencing the wear and cutting performance of multi-blade diamond disc cutters on granite blocks. A series of sawing experiments were performed to evaluate the wear and cutting performance of multi blade diamond disc cutters with varying diameters in the processing of large-sized granite blocks. The multi-layer diamond segments comprising the Iron (Fe) based metal matrix were brazed on the sawing blades. The segment’s wear was studied through micrographs and data obtained from the Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray (EDS). Granite rock samples of nine varieties were tested in the laboratory to determine the quantitative rock parameters. The contribution of individual rock parameters and their combined effects on wear and cutting performance of multi blade saw were correlated using statistical machine learning methods. Moreover, predictive models were developed to estimate the wear and cutting rate based on the most significant rock properties. The point load strength index, uniaxial compressive strength, and deformability, Cerchar abrasivity index, and Cerchar hardness index were found to be the significant variables affecting the sawing performance.

Coevolving edge rounding and shape of glacial erratics: the case of Shap granite, UK

Abstract. The size distributions and the shapes of detrital rock clasts can shed light on the environmental history of the clast assemblages and the processes responsible for clast comminution. For example, mechanical fracture due to the stresses imposed on a basal rock surface by a body of flowing glacial ice releases initial “parent” shapes of large blocks of rock from an outcrop, which then are modified by the mechanics of abrasion and fracture during subglacial transport. The latter processes produce subsequent generations of shapes, possibly distinct in form from the parent blocks. A complete understanding of both the processes responsible for block shape changes and the trends in shape adjustment with time and distance away from the source outcrop is lacking. Field data on edge rounding and shape changes of Shap granite blocks (dispersed by Devensian ice eastwards from the outcrop) are used herein to explore the systematic changes in block form with distance from the outcrop. The degree of edge rounding for individual blocks increases in a punctuated fashion with the distance from the outcrop as blocks fracture repeatedly to introduce new fresh unrounded edges. In contrast, block shape is conservative, with parent blocks fracturing to produce self-similar “child” shapes with distance. Measured block shapes evolve in accord with two well-known models for block fracture mechanics – (1) stochastic and (2) silver ratio models – towards one or the other of these two attractor states. Progressive reduction in block size, in accord with fracture mechanics, reflects the fact that most blocks were transported at the sole of the ice mass and were subject to the compressive and tensile forces of the ice acting on the stoss surfaces of blocks lying against a bedrock or till surface. The interpretations might apply to a range of homogeneous hard rock lithologies.

Whole-rock geochemical and zircon U-Pb-Hf isotopic compositions of the Yunlougang and Wucun granitic plutons in the Hetai area of South China: Implications for petrogenesis and geodynamic setting

In the Nanling tectono-magmatic belt of South China, the geodynamic settings and tectonic style of Indosinian and Yanshanian magmatism remain debatable. Hereby, an integrated study of zircon U-Pb ages and Lu-Hf isotopes as well as whole-rock elemental and Sr-Nd isotopic compositions was carried out on the Yunlougang (Late Permian) and the Wucun (Late Jurassic) granitic plutons in the Hetai area, located to southwest of the Nanling region. Zircon U-Pb dating yielded emplacement ages of 255 Ma for the Yunlougang biotite monzogranite, 240 Ma for the Yunlougang granodiorite as dyke crosscutting the former, and 155 Ma for the Wucun two-mica granite. The biotite monzogranite and the two-mica granite are strongly peraluminous S-type granites (A/CNK ratios of 1.06–1.21) with a relatively low zircon saturation temperature (631–741 °C). The high initial 87Sr/86Sr ratios (0.71733 to 0.73383) and low εNd(t) values (−14.6 to −8.69) suggest a crustal protolith. However, the Wucun biotite granite is highly fractionated I-type one (most samples are metaluminous with A/CNK < 1.1) with a relatively high zircon saturation temperature (762–770 °C). Additionally, they exhibit less radiogenic 87Sr/86Sri ratios (0.70724–0.70786) and higher εNd(t) values (−5.34 to −4.94) as well as zircon εHf(t) values of −5.67 to −2.44, suggesting an origin of a crustal source with extra input from mantle. Based on the tectonic history of South China, we infer that the Yunlougang granite occurred in a compressive setting and might be produced by partial melting of a thickened ancient crust during the collision between the South China and the Indochina blocks, while the Wucun complex granites generated in an extensional environment that was influenced by the paleo-Pacific tectonic regime. Combined with previous studies, a NE-oriented I-type granite belt probably existed along the juncture belt of the Yangtze and Cathaysia blocks, which was respond to the foundering rather than rollback of the paleo-Pacific plate that led to the rapid change of the temperature of granite precursor and the involvement of mantle components into the Hetai region.

Geology and Geochemical Characterization of Basement Rocks Around Burumburum Area North Central Basement Complex Nigeria

The geology and the geochemical characterization of rocks around Burumburum area north central basement complex of Nigeria was studied. Twelve (12) rocks samples were prepared for petrographic studies through a standard procedure while thirty (30) whole rocks samples were analyzed using X-ray Fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry(ICP-MS). The result of the field investigation revealed that the study area is underlain by migmatites, gneisses, biotite microgranites, fine grained biotite granites, medium grained biotite granites, porphyritic biotite-hornblende granites, granodiorites, syenites, diorites, dolerites, quartzite, pegmatites and aplites. The geochemical characterizations of the granites, granodiorites, syenites based on Na&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O/K&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O versus SiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; showed acidic compositions while diorites and dolerites are intermediate to basic compositions. The granites, granodiorites, syenites, diorites and dolerites are generally peraluminous (ASI&amp;gt;1.1) to metaluminous (ASI≤1). The granitic rocks, diorites, dolerites and syenites plotted mainly in shoshonite series while the granodiorites occur in High-K calc-alkaline fields. The granitic rocks, syenites, diorite and dolerites based on A/CNK versus SiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; are of I-type while granodiorites are of S-type. The multi-elements discrimination trends for granites, granodiorites, syenites, diorites and dolerites revealed relative enrichment in Large Ion Lithophile Elements (LILE: Ba, La, Rb, and Th and depletion in High Field Strength Elements (HFSE: Nb, P, Ti and Sr) which indicates crustal contamination of magma. The enrichment in the light rare earth element (LREE) relative to heavy rare earth element (HREE) for granodiorites, fine grained biotite granites, medium grained biotite granites (except medium grained biotite granites S12 and S14 with positive Eu), porphyritic biotite-hornblende granites and syenites with negative Eu anomaly suggest moderate to high degree of fractionation. The enrichment in light rare earth element (LREE) for diorites and dolerites relative to moderate to flat HREE with weak negative Eu anomaly indicates low degree of fractionation. The Y+Nb vs Rb, Y vs Nb, Ta + Yb vs Rb and Yb vs Ta tectonic discrimination diagram revealed that granites and syenites plotted mainly within volcanic arc granite, syn-collisional granite and in the within plate granites fields, the granodiorites clearly plotted in the within the plate granites field. The tectonic ternary molecular proportions MgO – FeOt – Al&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3 &amp;lt;/sub&amp;gt;revealed that dolerites and diorites plotted mainly in the spreading center island field.

Effect of multiple-compaction on laterite soil: geotechnical and geo-statistical analysis

Multiple-compaction demonstrates cyclic loading on laterite soils used in highway construction and its effects on engineering properties. The method determines the mechanical stability of derived soils from porphyritic granite, granite gneiss, and charnockite. Fifty-one soil samples were obtained from the horizons of the laterite soil profiles. Four sets of dynamic compactions were carried out on each sample. Index engineering properties such as specific gravity, Atterberg limits, and particle size distribution were investigated before and after multiple-compaction. The changes in engineering properties and moisture-density characteristics were investigated using the granulometric modulus and hardness index. Through multiple-compaction, larger grains in soils derived from granite gneiss and porphyritic granite disintegrated into smaller particles. The fine grains break down more easily than the large grains of quartz bound by clayey materials in charnockite-derived soils. Interestingly, the maximum dry density and optimum moisture content remain consistent in porphyritic and granite gneiss-derived soils after multiple compactions. Based on the densification and behaviour of the derived soils under multiple compaction in highway construction, porphyritic granite and granite gneiss-derived soils are more suitable as engineering materials than charnockite-derived soils.

Integrating geological, hydrogeological and geophysical data to identify groundwater resources in granitic basement areas (Guéra Massif, Chad)

In Chad, hard-rock aquifers are the main source of drinking water for the population located on basement areas. In these basement aquifers, and in particular those of the Guéra region, water drilling failure rates remain high despite research on one- and two-dimensional electrical resistivity techniques and lineaments as a means to improve access to the resource, mainly because these techniques are only used on an observational and structural basis to locate fractures. This study combines electrical resistivity tomography (ERT) with geology, hydrogeology and geomorphology, in order to characterise the structure and geometry of the aquifer system, assess borehole productivity and determine the factors controlling it. After validating the large dataset and its representativeness, 315 high- and low-yield wells, of which 41 have complete geophysical datasets, were selected. This large dataset allows a multi-parameter approach to (1) better characterise each facies according to its electrical resistivity and (2) clearly identify the main formations constituting the local conceptual hydrogeological model. The most suitable areas for productive boreholes are characterised by the presence of an overburden of <20 m depth, well-developed weathered and fractured horizons of granites and biotite granites (preferably) containing little or no clay, and a nearby drainage network. The most substantial flow rates are found in the first 30 m of the fissured horizon, below the base of the alterites. The experience gained from the present study will guide future analysis of ERT sections in order to reduce the probability of drilling dry wells.

FIELD GEOLOGY AND PETROGRAPHY AROUND NABARDO-TORO ENVIRONS, NORTH EASTERN, NIGERIA

Background: The mapping exercise within the study ar ea on a scale of 1:25,000 was carried out to study the rocks, determine their distribution, composition, structures and assess the economic potential of the area. Objectives: The geology mapping aim to identify and understand the various geological structures present in the area to gain insights into the tectonic history and deformation processes that have shaped the area and to identify the minerals present in the rock, to understand the rock formation, composition and potential geologic processes involved. Method: Method of mapping involved road, footpath, rivers and stream traverses. Representative rock samples were collected for petrographic studies and geochemical analysis to establish the geology of the study area. Result: The study area which is part of Sheet 148, Toro SE is entirely typical of the Nigerian Basement Complex and is underlain by the following rock units: Migmatitic Gneiss, Granite gneiss, mica schist and porphyritic granite. The Migmatitic Gneiss constitutes the largest group of the rock units covering more than 45% of the mapped area and trending mainly NW/SE with few exceptions in an almost N/S to NE/SW direction. It is pertinent to know that almost E-W structures were also observed which forms relics of the older structure believed to have been affected by the eburnean (possibly) orogenic event. The granite gneiss shares boundary mainly with the migmatitic gneiss showing a weak foliation of light and dark materials. The mica schist is exposed at the western end, highly weathered with a general trend of NW/SE. The porphyritic granite intruded both the migmatite and granite gneiss occurring prominently as hilly and bouldery outcrops. However, flat lying low lying was also observed in some other localities. With respect to field observation and petrographical study the lithologies encountered were grouped into nine (9) categories- homogeneous, inhomogeneous, stromatic, banded orthogneiss, nebulitic, apo granite, pegmatite, intermediate and schist.Conclusion: Field evidence suggests that the study area has undergone an episode of metamorphism and deformations as depicted by the structural features like preferred orientation of the mineralogical and lithological units. It was also observed from the field measurements, that the main structural trend within the study area is from NNE/SSW.

Late Triassic to Early Jurassic anatectic magmatism in the Chiapas Massif Complex, southern Mexico: New evidence for the onset and mode of crustal extension in western equatorial Pangea

During the Triassic, continental breakup started in western equatorial Pangea, while active continental margins developed along North and South America’s Pacific borders. Besides many uncertainties about how peri-Gondwanan terrains of Mexico evolved during and after Pangea’s amalgamation, the apparent absence of Late Triassic magmatism has been an enigmatic feature of Mexico’s geology. Here, we present the first documented occurrences of Late Triassic igneous rocks and a coeval high-grade metamorphic event in southern Mexico, as well as evidence for subsequent Early Jurassic ductile deformation and magmatism. Samples come from the Chiapas Massif Complex (CMC), a crystalline basement of the southern Maya Block. Field evidence suggests that garnet-bearing leucogranitic stocks intruded a former structural boundary between different Precambrian-Paleozoic basement units. High-precision Sm-Nd garnet-whole-rock ages (ID-TIMS partial dissolution techniques) and U-Pb geochronology on zircon rims (LA-ICPMS) revealed Norian igneous crystallization ages for the leucogranites (∼221–213 Ma). Isotope and geochemical data indicate that these granites originated from crustal reworking by anatexis. A garnet-bearing leucosome from a migmatite yielded a slightly younger Sm-Nd age (∼204 Ma), indicating cooling soon after the peak conditions of the anatectic event. Additionally, monazite from a mylonitized leucogranite yielded an Early Jurassic U-Pb age (∼179 Ma), indicating ductile deformation. Nearly coeval zircon ages from an undeformed pink granite and a nearby volcaniclastic sequence (∼184–189 Ma) further imply contrasting erosion levels during the Early Jurassic. The new data support models for regional stretching of eastern and southern Mexico, where crustal extension during the gravitational collapse of a collisional orogen in paleo-northern Mexico led to continental rifting and the breakup of Pangea. In the CMC, crustal extension is reflected by Norian anatectic crustal melts and migmatites, as well as Early Jurassic plutonic and extrusive magmatism that are localized in certain fault-bounded blocks with different erosion levels compared to adjacent blocks.

Aptian Li-F Granites of the Northern Verkhoyansk–Kolyma Orogenic Belt, Eastern Russia: Composition, Genesis, and Ore Potential

This paper reports the results from an investigation on the geochemistry and petrogenesis of the Aptian Li-F granites from the Omchikandya, Burgali, and Arga Ynnakh Khaya ore fields in the northern Verkhoyansk–Kolyma orogenic belt in eastern Russia. Li-F microcline–albite granites intrude the Late Jurassic to Early Cretaceous syn-collisional granitoids. According to their geochemical composition, they are close to A-type granites and can be subdivided into low-P and high-P varieties, differing in their geochemistry and genesis. The low-P microcline–albite granites (Omchikandya massif) intrude syn-collisional biotite granites. It is assumed that the formation of their parent melt occurred at deep levels in the same magma chamber that produced biotite granites. The high-P granites (Verkhne–Burgali ethmolith and Kester harpolith) are supposed to have been derived from melts originated from a high-grade metamorphosed lower crustal protolith under the influence of deep-seated fluid flows related to diapirs of alkaline-ultrabasic or alkaline-basic composition. It is supposed that their formation was related to post-collisional extension during the early stages of the evolution of the Aptian–Late Cretaceous Indigirka belt of crust extension. All studied Li-F granites are enriched with rare metals and have associated Li deposits with accompanying Sn, W, Ta, and Nb mineralization. In the low-P Li-F Omchikandya massif, mineralization tends to occur within greisenized granites and greisens in their apical parts. In the high-P granite massifs, mineralization is found throughout their volume, and, therefore, the Verkhne–Burgali ethmolith and Kester harpolith can be considered as large ore bodies. There is a direct dependence of the content and reserves of Li2O on the content of P2O5. Minimum Li2O reserves are established in low-P Li-F microcline–albite granites of the Polyarnoe deposit of the Omchikandya ore field, whereas in the high-P granites of the Verkhne–Burgali and Kester deposits, the Li2O reserves are significantly higher.

The shape function method of nonlinear thermal stress of granite fracture tips in a high-temperature environment

Exposed rock masses in tunnel portals are susceptible to thermal deterioration in southern China, where temperatures are relatively high. The thermal stress field of rock masses is affected by fracture shape and distribution as fractures near the surface are channels for solar radiation energy to be converted into rock thermal energy. In this study, a function expression is developed for triangular heat sources of fractured rock masses in a tunnel portal in a high-temperature environment. By the function expression, the temperature field and thermal stress field are calculated, and the influence of fracture shape parameters and multi-fracture interaction is analyzed. The results are as follows: (1) the temperature field and thermal stress field of exposed rocks are redistributed by fractures. The internal temperature of the fractured rocks is higher than that of non-fractured rocks, and thermal stress near the fracture tip increases. (2) For triangular fractures of the same length, thermal stress increases as the apex angle increases. (3) When the spacing between parallel fractures or coplanar fractures is close, the superposition effect of thermal stress becomes significant. (4) In a high-temperature environment, temperature field and thermal stress field of a fractured rock are both nonlinear as temperature and thermal stress around fractures increase significantly. The results provide effective reference for stability evaluation of fractured rock masses in tunnel portals and offer theoretical foundation for thermal diseases analysis and protection measures of tunnel engineering in high-temperature environments of southern China.

Nyatygran intrusive suite, Bureya massif: Petrography, geochemistry, and age

The proposed review and analytical article provides updated information on the geology, petrography, mineralogy, and chemical composition of rocks of the Precambrian Nyatygran intrusive suite. The article provides a geochemical interpretation of the chemical and trace element compositions and presents the most actual data on the uranium-lead isotopic age of the rocks. The igneous formations of the Nyatygran gabbro-granodiorite-granite complex make up small intrusive massifs of gabbroids and granitoids, located near the ore-bearing Mel’gin trough, in the basins of the Verkhny Mel’gin, Chepkan, and Bureya rivers and their tributaries. In the gabbroids, the main rock-forming minerals are labradorite, andesine, bluish-green hornblende, and biotite. The gneissic granitoids are dominated by cataclastic quartz and feldspars (andesine, oligoclase, microcline) and contain abundant micas (biotite, sericite). The subalkaline leucogranites are dominated by oligoclase, quartz, orthoclase, and microcline; they also contain significant amounts of biotite and aegirine and rare amphibole (hornblende). The gabbro and gabbrodiorites of normal and elevated alkalinity are assigned to the high-aluminous high-magnesian rocks. The gabbroids represent I-type igneous rocks. The gneissic granitoids of normal and elevated alkalinity are predominantly high-aluminous, more ferroan than magnesian rocks, and are represented by S- and I-type granitoids. The determined isotopic ages of the Nyatygran suite formations are confined to the three main ranges: 933 ± 12–916,3 ± 7,2 Ma (1st magmatic phase: gabbro, gabbrodiorites, amphibole-biotite granites), 909,0 ± 6,6–907,3 ± 5,5 Ma (2nd phase: granodiorites and granites), and 806,8 ± 6,6–789 ± 4,0 Ma (3rd phase: biotite granites and granite-porphyry dikes). The Nyatygran suite age is established as Neoproterozoic and corresponds to the early Neoproterozoic, or Tonian (1000–720 Ma), according to the International Chronostratigraphic Scale, 2018. On the 3rd generation 1:1 000 000-scale State geological maps of the Russian Federation, it is presented as Early Proterozoic.

Fracture surface morphology effect on radial seepage flow in a horizontal single granite fracture

Fracture surface morphology effect on radial seepage flow in a horizontal single granite fracture

Evaluation of sintered bauxite proppant for binary enhanced geothermal systems

Solid granular proppant particles are widely used in oil and gas development to sustain permeability through fractures after hydraulic stimulation. Similar proppants are of interest for geothermal applications where the goal of sustaining permeability is the same, but the harsh geothermal environment risks rapid proppant degradation that will reduce fracture permeability. Here, we present proppant conductivity experiments using saw cut granite, tensile fractured granite, and aluminum control specimens packed with sintered bauxite ceramic proppants at concentrations of 0.0, 0.1, and 1.0 kg/m2. Simulated geothermal conditions included temperatures up to 130 °C and normal closure stresses up to 60 MPa. Compared to unpropped specimens, peak fracture conductivity enhancement was up to 6 orders of magnitude. At simulated geothermal conditions, proppants were able to sustain fracture conductivity over 60 h, but chemical dissolution and decreasing permeability over time were evident. Irreversible conductivity reductions with crushing and embedment of proppants during loading stages were also observed. Overall, sintered bauxite proppant remains a promising option for low-temperature binary-cycle enhanced geothermal systems.