Granitoid Rocks Research Articles

A multi-scale methods comparison to provide granitoid rocks thermal conductivity

Granitoid rocks are frequently used in modern construction and restoration, hence the importance of knowing their petrophysical properties. These rocks find several applications in various types of surfaces, from flooring to walls, coupled to radiant devices for indoor air conditioning or as geological target in hot dry rock geothermal systems. In order to support the thermophysical characterization, the thermal conductivity of seven granitoid rocks belonging to five different lithologies (granodiorite, tonalite, granite, gabbro, and syenite) has been analysed, as main property which must to be assessed, by comparison between traditional measurement methods and a new analytical approach. In detail, the thermal conductivity was measured directly on the bulk rock samples, evaluated by applying Quantitative Phase Analysis starting from the Digital Imaging Analysis (DIA) and Rietveld refinement associating thermal parameters to each phase, and analysed by thermal modelling. Thermal simulation obtained by the 2D modelling highlights on the dependence of the thermo-physical properties of considered rocks from the minerals content, according to the abundance of quartz, as well as to the mineral’s grain size and the geometrical grain distribution. This procedure provides a reliable estimation of the rock’s thermal behaviour considering concurrently different mineralogical and textural parameters. The comparison between different approaches to thermal conductivity evaluation of granitoids allowed to consider the validity of the predictive approach, based on thermal modelling.The methodologies here developed and compared considering the thermal properties of granitic rocks can be extended and optimized for other types of rocks.

Comprehensive assessment of groundwater quality using heavy metal pollution indices and geospatial technique: a case study from Wanaparthy watershed of upper Krishna River basin, Telangana, India

The present study is to characterize groundwater quality using heavy metal pollution indices and geospatial variations. A total of 58 samples from hand pump/submersible bore wells were collected from the Wanaparthy watershed of the upper Krishna River basin according to the grid size (5×6 km2). The trace elements’ concentration in groundwater samples are found in the order of Zn (38.67%) > B (32.67%) > Ba (13.59%) > As (8.49%) > Hg (3.71%) > Cr (1.28%) > Ni (0.52%) > Cd (0.47%). Among these trace elements, arsenic (22.4%) and mercury (5.1%) were found above the permissible limits of WHO drinking water guideline values. A positive correlation between TH versus EC/TDS indicates the presence of trace elements due to chemical reaction (rock–water interaction). Arsenic correlation with EC/TDS/TH indicates artificial intervention. Drainage network analysis enumerates high concentration of parameters at near or joining to upper order of drainage system, which might be due to input of runoff water (interaction of variable rocks composition) and later stage infiltration to subsurface and reached to an aquifer. Heavy metal pollution index (HPI) showed 86.2% of samples are in the category of low class, whereas 12.07% of samples fall within medium class. According to metal index (MI) classification, 12.07% samples are in very pure, 24.14% samples are pure, while the remaining 63.79% samples are in the slightly to strongly affect category. This study suggested the main source of trace elements in groundwater might be from the dominant granitoid rocks because the area is mostly devoid of industrialization.

Petrogenesis of Tertiary granitoid rocks from east of the Bidhand fault, Urumieh-Dokhtar Magmatic Arc, Iran: Implication for an active continental margin setting

Tertiary granitoid rocks including diorite, quartz diorite, quartz monzodiorite, monzonite, and quartz monzonite occur in southeast of Qom and to the east of Bidhand fault in the central Urumieh-Dokhtar Magmatic Arc (UDMA). Zircon U–Pb dating reveals an age of ca. 17 Ma for the crystallization of Kerogan quartz diorite. The study samples show sub-alkaline to transitional, metaluminous, and I-type affinity with low to middle SiO2 (53.9–63.9 wt%). Micro granitoid enclaves (MGEs) are widespread in these rocks, exhibiting diorite to monzodiorite composition (SiO2 = 56.75–58.4 wt%). MGEs and host rocks are slightly enriched in LREEs and LILEs, and depleted in HFSE including Nb, Ta and Ti as expected in granitoids formed in an active continental margin setting. The granitoid rocks display initial Sr isotopic compositions of 0.7047–0.7062, positive εNd(t) of 3.2–6.6, and 206Pb/204Pb (18.6431–18.8499), 207Pb/204Pb (15.6322–15. 6902), and 208Pb/204Pb ratios (38.5585–38.9325), and positive zircon εHf(t) values of 6.7–8.7. MGEs also display identical Sr-Nd isotopic compositions (87Sr/86Sri = 0.70537–0.70576; εNd(t) = 2.3–5.3) to the host rocks. The isotopic characteristics in combination with the geochemical signatures indicate that the granitoid rocks and MGEs most likely originated by interaction between mantle-derived mafic and basaltic lower crust-derived melts. Major and trace element modeling reveals that the mafic lower crust is composed of less ~40% partial melting of garnet-free amphibolite. Petrographic and geochemical characterization together with bulk rock Nd-Sr isotopic data suggest that host rocks and associated enclaves derived from the same parent by interaction between basaltic lower crust (~10%) and lithospheric mantle (~90%) during their generation that subduction related compositions have also been involved in their petrogenesis. This magma has experienced high fractional crystallization but minor crustal contamination during magma ascent to the upper crustal level. Petrographical, geochemical, and Sr-Nd-Pb isotopic similarities between granitoid and MGEs imply that MGEs are cognate late cumulates, formed by pressure quenching mechanism during the late stage of magma evolution in crustal magma chamber. The Tertiary magmatism in the study area originated in an arc-related setting induced by slab roll-back of northward Neo-Tethyan oceanic lithosphere subduction beneath central Iranian micro continent and resulted in lithospheric extensional regime and subsequently asthenosphere upwelling. The heat induced by the upwelling of the asthenosphere likely led to melting of upper mantle and the mafic crustal material during Early Miocene as the final magmatism phase in the central part of the UDMA before collision.

Distribution of light (LHREE) and heavy rare earth elements (HREE) in Kelantan granitoids rock

Peninsular Malaysia is being distributed into three parallel belts (Western, Central and Eastern). Kelantan is one of the states in Peninsular Malaysia and consider as a unique territory to have all three belts (Western, Central and Eastern). Each belts divided into several formations which are Western Belt (Main Range Granite), Central Belt (Jeli Granite, Kemahang Granite, Noring Granite, Kenerong Leucogranite, Berangkat Tonalite and Senting Granite) and Eastern Belt (Boundary Range Granite). Rare Earth Elements (REEs) are usually concentrated related to the alkaline – peralkaline, carbonalite igneous rocks, as well as sedimentary rocks. Granitoid and some intrusive volcanic rocks are widely exposed in Malaysia, as well as Kelantan state. REEs are relatively abundant in the Earth crust, however these elements are rarely concentrated in the mineable ore deposit. There are a lot of research about granitoids, but very limited studies about the distribution of the REE. The objective of this study is to investigate the distribution of REEs in different type of granitoid rocks in Kelantan. For this purpose, 15 samples were selected and analysed using Inductive Coupled Plasma Mass Spectrometry (ICP-MS). Result shows that, distribution of light REEs in all samples up to 78% and heavy REE up to 22% with total value 5350.69 ppm and 1491.27 ppm respectively. Surprisingly, Jeli Granite formation (LT15) is high potential of REE among the samples tested with total REE 3164.93 ppm and Kemahang Granite (JD18) is least potential with total REE 31.95 ppm. The granitoid distribution can be found widely in Kelantan with special characteristic and detailed study about mineral composition will help identifying the REE potential as well as generate more relatable study about genesis and nature of rocks in Malaysia.

Comparison of hydraulic conductivity of rock matrix and fractured blocks of granitic rocks

Field measurements of hydraulic properties of the rock matrix and in low permeability hard rocks generally require highly accurate and sensitive technical equipment and special methods of measurement. Hydraulic conductivity of intact rocks is mostly measured in the laboratory conditions; field measurements are less common. The Czech geological survey developed equipment, which allows measurements of very low consumption of water during WPT (water pressure tests). This device enables to implement the same testing methodology for all sections of the borehole and subsequently compare the obtained results from low-permeability as well as more permeable sections. Hydraulic conductivity of eight different granitoids was studied in the Bohemian Massif in the Czech Republic. Mean values of hydraulic conductivity of fractured rock are on the order of 10-8 to 10-7 m·s-1, while hydraulic conductivity of rock matrix was most frequently on the order of 10–11 to10-12 m·s-1. The difference of values measured in laboratory and field is caused by scale effect. The significance of scale effect in rock matrix is determined mainly by the connectivity of a network of microfissures. Length and aperture of microfissures govern mainly the connectivity of fissure net in rock matrix. Coarse-grained granitoids have greater length and aperture of microfissures, higher connectivity and hydraulic conductivity, and the scale effect is less significant. The fracture network appearance and hydraulic conductivity of rock matrix is similar and characteristic for different types of granitoid rocks.

Mineralogical and textural influence on physico-mechanical properties of selected granitoids from Besham Syntaxis, Northern Pakistan

The Dubair-Shang granitoids are the major intrusive bodies in Besham group and are exposed along the Karakoram Highway in Besham and lower Kohistan districts. A variety of these granitoid rocks have been investigated in terms of their petrographic features and physico-mechanical properties. The studied rocks are classified into four different textural varieties including Dubair mylonitized (DM), Dubair coarse grained (DCG), Shang coarse grained (SCG) and Shang foliated (SF) granitoids based on field observations and petrographic features. Petrographically quartz, potash feldspar, plagioclase and biotite are the essential minerals present in all varieties in varying amount. Beside these hornblende, chlorite, epidote, ore mineral(s) and sphene are also present in the accessory amount. As a part of the present investigation some of the mechanical and physical properties including uniaxial compressive strength (UCS), uniaxial tensile strength (UTS), specific gravity, water absorption, total porosity, and Los Angeles abrasion were also determined. The combined approach of petrographic features with the physico-mechanical investigation revealed that the textural characteristics and mineralogy have a significant influence on the physico-mechanical properties of the studied rocks. It is determined that modal percentage of minerals, degree of alteration, recrystallization, grain size and shape, types of grain boundary contacts have significant effect on characteristics of these granitoids. Based on strength tests studied rocks fall in category of moderately strong to strong. The values of specific gravity, porosity, water absorption and Los Angeles are within the range permissible for their use as constructional materials except SF. Based on physico-mechanical properties and petrographic examination Dubair-Shang granitoids could be used as aggregate for the construction of road, railway tracks, embankment, and canals. Theses rocks could also be used as sills, lentils, and roofing but should not be used for load bearing masonry like bridges, tunnels, buildings, dams etc.

Deep weathering in the semi-arid Coastal Cordillera, Chile

The weathering front is the boundary beneath Earth’s surface where pristine rock is converted into weathered rock. It is the base of the “critical zone”, in which the lithosphere, biosphere, and atmosphere interact. Typically, this front is located no more than 20 m deep in granitoid rock in humid climate zones. Its depth and the degree of rock weathering are commonly linked to oxygen transport and fluid flow. By drilling into fractured igneous rock in the semi-arid climate zone of the Coastal Cordillera in Chile we found multiple weathering fronts of which the deepest is 76 m beneath the surface. Rock is weathered to varying degrees, contains core stones, and strongly altered zones featuring intensive iron oxidation and high porosity. Geophysical borehole measurements and chemical weathering indicators reveal more intense weathering where fracturing is extensive, and porosity is higher than in bedrock. Only the top 10 m feature a continuous weathering gradient towards the surface. We suggest that tectonic preconditioning by fracturing provided transport pathways for oxygen to greater depths, inducing porosity by oxidation. Porosity was preserved throughout the weathering process, as secondary minerals were barely formed due to the low fluid flow.

Geochronology and geochemistry of the Xiaoqinling Taihua Complex in the southern Trans-North China Orogen: Implications for magmatism during the early Paleoproterozoic global tectono-magmatic shutdown

The Taihua Complex in the Xiaoqinling area of the southern Trans-North China Orogen (TNCO) records extensive magmatism during the early Paleoproterozoic. This contrasts with the tectono-magmatic quiescence recorded globally at this time. Based on zircon U−Pb geochronological and whole-rock geochemical data, the 2.36–2.30 Ga granitic gneisses in the Taihua Complex can be subdivided into three groups. Group-1 gneisses (2.36–2.33 Ga), mainly in the Dumutai area, are high-K2O granitoid rocks, which record the earliest magmatism. These rocks have fractionated rare earth elements (REE) patterns, marked negative Eu−Sr anomalies, and variable whole-rock εNd(t) (−1.67 to +2.41) and εHf(t) values (−0.89 to +3.41), and were likely derived by partial melting of a mixture of pre-existing tonalite–trondhjemite–granodiorite (TTG) and K-rich rocks with residual plagioclase in the source at high-temperature and low-pressure conditions. Group-2 gneisses (2.33–2.31 Ga), mainly in the Jialu and Xitongyu areas, are granitoid rocks that formed after the Group-1 gneisses. These rocks have less fractionated REE patterns, low La/Yb and Sr/Y ratios, and slightly positive to negative whole-rock εNd(t) (−3.91 to +2.00) and εHf(t) values (−7.99 to +0.87), which resulted from high-degree partial melting of ancient crust in an extensional setting. Group-3 gneisses (~2.30 Ga) are TTG rocks from the Bayuan area, which represent the youngest magmatism. These rocks have high La/Yb and Sr/Y ratios, high MgO, Cr, and Ni contents, and negative whole-rock εNd(t) (−1.71 to −1.67) and εHf(t) values (−0.57 to −0.10), which indicate derivation by partial melting of delaminated lower crust and interaction with mantle materials. Samples from all groups have variable zircon εHf(t7/6) (−6.38 to +7.70) and δ18O values (3.97‰ − 6.79‰), indicative of a heterogeneous magmatic source. Most zircons have slightly positive to negative εHf(t7/6) values, indicating significant reworking of ancient crustal materials and limited crustal growth during this period. The age, geochemistry, and petrogenesis of the studied granitoid rocks record orogenic collapse and a transition from post-collisional extension to crustal delamination in the early Paleoproterozoic. This followed late Archean subduction–collision–accretion processes in the southern NCC.

Geochemistry, origin and anatexis temperature of monzogranite formation in Mount Khalaj (Mashhad, Iran)

Geochemistry, origin and anatexis temperature of monzogranite formation in Mount Khalaj (Mashhad, Iran)

Porphyry Cu-Au prospectivity modelling using semi-supervised learning algorithm in Dehsalm district, eastern Iran

Porphyry Cu-Au prospectivity modelling using semi-supervised learning algorithm in Dehsalm district, eastern Iran

Monazite EPMA-CHIME dating of Sangmelima granulite and granitoid rocks in the Ntem Complex, Cameroon: Implications for Archean tectono-thermal evolution of NW Congo craton

Electron microprobe (EPMA) monazite Th–U – Pb ages have been determined from a suite of granulite and granitoids rocks of the Sangmelima granite-greenstone Belt (SGB) of the Ntem Complex in Cameroon or NW Congo Craton. The monazite-bearing rocks include charnockitic gneiss, migmatitic tonalite-trondhjemite-granodiorite (TTG) gneisses, granodiorite, monzogranite and a late pegmatite intrusion. The monazites of Sangmelima can be classified as monazite-Ce. Based on published ages and EPMA Th–U – Pb monazite age data from the SGB, the geodynamic evolution of the NW Congo Craton was refined through its tectonometamorphic and magmatic events. The major charnockitic and TTG magmatism event in Ntem Complex occurred between ~2950 and 2850 Ma. This Mesoarchean crystalline basement underwent two major ductile tectonothermal events M1 – D1 and M2 – D2. (1) The onset of M1 – D1 corresponds to the migmatization of TTG at 2843 Ma coeval with the emplacement of syn-kinematic granite dykes (monzogranites) at 2840–2825 Ma. The S1 regional penetrative foliation (D1) was progressively generated during the M1 metamorphic event, which led to the formation of associated hypersthene-garnet-bearing granulitic mineral assemblage that peaked at ~2830 Ma. (2) The M2 – D2 event between 2760 and 2740 Ma corresponds to the folding of S1 regional foliation by F2 folds and development of C2 shear zones synchronous with the anatexis event that generated the high-K granitoids at 2750 Ma. Late Neoarchean granitic pegmatite/aplite dikes and/or veins emplaced during the brittle deformation D3 and protracted cooling of the Ntem Complex between ~2700 and 2550 Ma. Our new EPMA monazite U–Th – Pb ages from the SGB highlight similar magmatic and tectonothermal events of the adjacent northern Gabonese domain and the Chaillu Massif in Gabon part of the NW Congo craton (ca. 3.0–2.5 Ga).

Mineral chemistry and ages of the Eocene Gapdan granitoid pluton and related dykes (Sistan suture zone, eastern Iran): multi-stage emplacement of a zoned pluton during progressive deformation and exhumation

• The Eocence Gapdan pluton in the Sistan suture zone is syn -tectonic and calc-alkaline. • Mineral chemistry and thermo-barometry reveal a multistage evolution. • Biotite granite crystallized first at 44.3 Ma and 4–5.4 km depth. • It was exhumed to 2.5 km, where it was intruded by granodiorite at 42.2 Ma. • Crosscutting diorite dykes contain amphibole antecrysts crystallized at 23 km depth. Mineral compositions provide key information on the petrogenesis and tectonic settings of granitoid rocks. These relationships are addressed in the present paper, which is focused on the Eocene Gapdan pluton, near Zahedan in eastern Iran. The pluton is part of a granitoid suite intruded into Late Cretaceous to Middle Eocene flysch of the Sistan suture zone. It is zoned, consisting of granodiorite in the center and biotite granite at the margin, and is cross-cut by late diorite dykes. The country rocks are low to medium grade biotite schists with subordinate amphibolite. Biotite is the only ferromagnesian mineral in the Gapdan granitoids, consistent with calc-alkaline and I-type affinities, and with formation in an arc-related tectonic setting. Thermo-barometry and geochronology, combined with lithological observations, establish the following sequence of events: (i) melting of mantle related to subduction of the Sistan oceanic slab and closure of the oceanic basin, generation of basaltic magma, and finally crustal melting and hybridization with crustal melts during ascent. (ii) At 44.31 ± 0.21 Ma the resulting granitic magma crystallized at 4–5.4 ± 1 km depth; biotite and feldspar thermometers indicate crystallization temperatures of ~ 850˚C and ~ 730˚C, respectively. (iii) This stage was tectonically controlled and the pluton was exhumed to shallower crustal levels of ~ 2.5 km, imparting a mylonitic fabric on the granite. (iv) At 42.15 ± 0.55 Ma granodiorite was emplaced in the center of the pluton at a depth of ~ 2.5 km. Crystallization depths are supported by the pressure estimates from Al-in-hornblende in rocks of the contact aureole. (v) Cross-cutting diorite dykes were emplaced at ~ 2.5 km, but they contain phenocrysts of magnesio-hastingsite that had crystallized at 894 ± 55 °C and ~ 23 km depth during ascent of the magma, followed by kaersutite crystallization at temperature decreasing to 744 ± 15 °C at ~ 12 km depth.

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The Demeni-Mocidade domain (DMD) comprises a large area of granitoid rocks, located on the border between the states of Roraima and Amazonas, Brazil, within the inner part of the Ventuari-Tapajos Province of the Amazonian Craton, where large amounts of granitoid rocks, formed between 2.0-1.8 Ga, are predominant. This study examines six granite samples collected from the Mocidade and Demeni mountains, which are related in time to the Uatuma Silicic Large Igneous Province (SLIP), which, in turn, covers several tectonostratigraphic domains whose evolution is associated with an intercontinental setting, allowing a common association with I- and A-type granitoid rocks formed within the same 1.88 to 1.87 Ga time interval. These rocks are monzogranites and correspond petrographically to holocrystalline anisotropic lithotypes with fine to medium grain sizes. Their textural relationships, including some lithotypes containing phenocrysts with oscillatory zoning and resorbed rims, indicatethat crystallization occurred at subvolcanic or hypabyssal depths. Moreover, the association between plutonic and subvolcanic rocks in the same suite shows variations in the crustal development of the magmatic chambers. The granitoids of the DMD share a common geochemical signature with those of the Agua Branca Suite, which occurs within the Uatuma and Trombetas-Erepecuru domains of the Guiana Shield, suggesting that their crystallization occurred in similar magmatic chambers. Six U-Pb zircon ages show that most zircon crystals are concordant and the few ones which are discordant are well aligned along Discordia straight lines descending to zero. The calculated Concordia ages, covering the 1884 to 1877 Ma interval, agree within experimental error, indicating a probably similar crystallizationage. Such apparent age values, close to 1900 Ma for the DMD, made it possible for the domain of the Uatuma SLIP to spread to the West, and the area of the Ventuari-Tapajos Province could extend towards the Amazonas State of Venezuela. Finally, the coexistence between I- and A-type granitoids in the DMD, with ages within the range 1.88-1.87 Ga, stimulates a discussion, and there are three possibilities: (1) The calc-alkaline magmatism can be associated with late (post-collisional) processes related to subduction. (2) The granitoid rocks are formed in an intracontinental setting under more stable (post-orogenic) tectonic conditions. (3) The granitoid rocks are predominantly formed by A-type and alkaline magmatism in intraplate settings.

Siderian to Rhyacian evolution of the Juiz de Fora Complex: Arc fingerprints and correlations within the Minas-Bahia Orogen and the Western Central Africa Belt

The Juiz de Fora Complex (JFC) is one of the basement units of the Occidental Terrane, Central Ribeira belt, in the Neoproterozoic framework of Western Gondwana, regarded as part of the reworked border of the São Francisco Paleocontinent. The JFC comprises Paleoproterozoic granitoid rocks with TTG, calc-alkaline, sanukitoid, and tholeiite-type geochemical compositions. They exhibit complex deformational fabrics associated with two episodes of granulite-facies metamorphism, occuring in the early Orosirian and the Ediacaran. The new U-Pb (SHRIMP) isotopic ages and Lu-Hf (LA-MC-ICPMS) data combined with available lithogeochemical, whole-rock Sm-Nd and Rb-Sr isotopic data constrain the tectonic evolution of the JFC to a Siderian-Rhyacian evolved arc system. Five samples were selected for U-Pb geochronology and Lu-Hf analysis on zircon grains: a low-K tholeiite, one TTG, two sanukitoids, and a mafic tholeiite. Combined whole-rock Sm-Nd, Rb-Sr isotopes, and zircon Lu-Hf isotopic data suggest the following evolution: an initial moderately juvenile (2445 Ma) low-K tholeiitic magmatism (εNd(t) of − 0.1; εHf(t) from − 8 to + 3), followed by a moderately juvenile to evolved (2200–2182 Ma) coeval TTG-sanukitoid pulse (εNd(t) from − 0.6 to − 4.8; εHf(t) from − 11.7 to + 2.5), and eventually by a moderately juvenile (2130 Ma) tholeiitic magmatism (εNd(t) = − 0.05). The integrated information provides preliminary petrogenetic insights for these magmatic episodes, such as interaction between mantle sources and supracrustal subducted material, melting of the oceanic slab, and crustal assimilation. A ca. 2035 Ma collisional granulite event recorded in metamorphic rims and neoformed zircon grains in leucosomes, possibly marks the amalgamation of the JFC onto the Mantiqueira Complex. Geochronological and isotopic correlations with coeval terranes of the Minas-Bahia Orogen in the Brazilian and African counterparts are addressed for tectonic implications at a broader scale.

Regional variations of sulfur isotope compositions for metallic deposits in South Korea

AbstractSouthern Korean peninsula comprises five major geotectonic provinces, throughout which various metallic deposits are distributed. We reviewed sulfur isotope data (n = 1,574) of sulfide minerals collected from previous works for 177 metallic deposits in the provinces to interpret the sulfur isotope characteristics of each province, comprising different wall rocks and geologic settings. The averaged δ34S values of each metallic deposit associated with Precambrian metamorphic rocks and Jurassic granitoids in the Gyeonggi massif and Yeongnam massif range from −7.1 to +10.3‰ (av. +4.5‰) and from −3.6 to +7.8‰ (av. +3.5‰), respectively. The Taebaeksan basin produced the highest δ34S value among the five, −0.4 to +13.2‰ (av. +6.1‰). This was influenced by sulfate sulfur derived from marine carbonate host rock. The Okcheon metamorphic belt, comprising metasedimentary and metavolcanics rocks, shows an isotope range from +1.9 to +8.3‰ (av. +5.7‰). The sulfur isotope distribution of the Gyeongsang basin with a range from −1.2 to +11.7‰ (av. +5.2‰) can be divided into two zones: higher δ34S values from the inner zone related to the volcanic rocks and magnetite‐series Cretaceous granitoids, and lower δ34S values from the outer zone related to the organic‐rich sedimentary rocks. Sulfur isotope variations of metallic deposits in each geotectonic province were mainly influenced by igneous sulfur and inherent wall rock sulfur sources, 32S‐enriched sedimentary sulfur (e.g., Precambrian metasedimentary rocks and biogenic sulfur‐rich sedimentary rocks), and 34S‐enriched seawater sulfur (e.g., carbonates and acid to intermediate volcanic rocks). These wall rocks also contributed to the changes in δ34S values for granitoid rocks and metallic deposits by time, ore genetic type, and ore species in South Korea.

The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma

Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.

The effect of low-temperature annealing on discordance of U\u2013Pb zircon ages

Discordant U–Pb data of zircon are commonly attributed to Pb loss from domains with variable degree of radiation damage that resulted from α-decay of U and Th, which often complicates the correct age interpretation of the sample. Here we present U–Pb zircon data from 23 samples of ca. 1.7–1.9 Ga granitoid rocks in and around the Siljan impact structure in central Sweden. Our results show that zircon from rocks within the structure that form an uplifted central plateau lost significantly less radiogenic Pb compared to zircon grains in rocks outside the plateau. We hypothesize that zircon in rocks within the central plateau remained crystalline through continuous annealing of crystal structure damages induced from decay of U and Th until uplifted to the surface by the impact event ca. 380 Ma ago. In contrast, zircon grains distal to the impact have accumulated radiation damage at shallow and cool conditions since at least 1.26 Ga, making them vulnerable to fluid-induced Pb-loss. Our data are consistent with studies on alpha recoil and fission tracks, showing that annealing in zircon occurs at temperatures as low as 200–250 °C. Zircon grains from these samples are texturally simple, i.e., neither xenocrysts nor metamorphic overgrowths have been observed. Therefore, the lower intercepts obtained from regression of variably discordant zircon data are more likely recording the age of fluid-assisted Pb-loss from radiation-damaged zircon at shallow levels rather than linked to regional magmatic or tectonic events.

Sediment provenance and tidal current-driven recycling of Yellow River detritus in the Bohai Sea, China

A detailed sediment-provenance study is presented on the modern Bohai Sea, China, the innermost gulf of the Yellow Sea, using framework petrography, heavy-mineral and grain-size analyses. A series of subaqueous river deltas, characteristic of multisource, is distinguished along the coastal zone. First-cycle fluviodeltaic sediments are attributed principally to three large source areas: the Loess Plateau, the Yanshan highlands, and the Horqin sandland. Coastal sands along eastern Liaodong Bay are produced by weathering and physical erosion of near-source Mesozoic granitoid rocks during Quaternary lowstands. Apart from subaqueous deltas and coastal sands, sediment provenance is only attributed to two end-member mixing with various proportions between recycled Holocene Yellow River sediments and ancient fluvial sediments of the Liaohe river system, even though detrital sources are multiple along the coast. Relative contributions are quantified on a ternary diagram of heavy-mineral compositions, using the proportion of relative distances between a given mixed area and the two end-member deltas. The eastern Bohai flood-tidal delta, characterized by abundant garnet and ilmenite, is regarded as a large repository of ancient Liaohe sediments, which had been intermittently accumulated during Quaternary lowstands and reworked during multiple transgressions. As a secondary sediment source detached from the present-day Liaohe River delta, it is remobilized and involved in the modern sedimentation. A complete tidal current-dominated depositional pattern is proposed throughout the Bohai Sea to explain sediment accumulation and recycling. We suggest that dominant ebb tidal currents, prevailing in the southern Bohai Strait, are a primary driver carrying fine-grained Yellow River sediments eastward to the Yellow Sea. In contrast, the recycling of Yellow River sediments is driven by flood tidal currents, prevailing in the northern Bohai Strait. The internal recycling process in the Bohai Sea builds the sand sheet and its terminal lobe, i.e., the eastern Bohai mud belt, whereas the external recycling process that involves the depocenters of Yellow River sediments in the outside North Yellow Sea builds the sand ridges and its terminal lobe, i.e., the quartz-rich area. This study improves our understanding on the Yellow River dispersal system. It also provides a typical example that demonstrates how ancient alluvial sediments accumulated during eustatic lowstands are reactivated and join the modern sedimentation processes.

ОСОБЕННОСТИ ПОВЕДЕНИЯ ХИМИЧЕСКИХ ЭЛЕМЕНТОВ В СИСТЕМЕ ВОДА–ПОРОДА РАЙОНА РАЗРАБАТЫВАЕМОГО КАРЬЕРА БУТОВОГО КАМНЯ В ПИТКЯРАНТСКОМ РУДНОМ РАЙОНЕ (КАРЕЛИЯ)

Актуальность. Изучение особенностей перераспределения химических элементов в системе вода–порода в районах, где ведется активная разработка месторождений полезных ископаемых, актуально ввиду потенциального влияния этих процессов на экологическую обстановку и изменение геохимических условий природной среды. В частности, это важно для выбранного района, который входит в площадь водосбора крупнейшего природного резервуара пресной воды в Европе – Ладожского озера. Целью представленного исследования является изучение выноса химических элементов водой из гранитоидных пород, вскрытых карьером, и их дальнейшего поведения в природных водах и донных отложениях района. Объектом исследования являются природные воды и донные отложения района разрабатываемого карьера бутового камня (Питкярантский рудный район, республика Карелия). Авторы проследили изменения химического состава природных вод и связанных с ними донных отложений по мере движения воды от ее сброса из карьера до впадения в речную сеть. Методы. Анализ химического состава природных вод и донных отложений проведен стандартными методами: потенциометрия, титриметрия, ICP-AES, ICP-MS. Исследования минералов в составе пород карьера бутового камня проведено при помощи LA-ICP-MS, химический состав горных пород изучен методами XRF, ICP-MS и ICP-AES. Физико-химическое моделирование форм нахождения в природных водах и осаждения минералов проведено в программном комплексе HydroGeo. Верификация модели проведена на основе анализа химического состава донных отложений. Результаты. В изученных водных объектах в отдельных точках отмечены превышения ПДК Fe, Mn, Cu, Zn, Mo, V. При удалении от карьера бутового камня снижается величина общей минерализации природных вод и содержание макрокомпонетов, а также Sr, U, V, Mo, Zn, Cd. Концентрация железа, наоборот, увеличивается ввиду роста содержания органического вещества в воде. В донных отложениях пик концентрации многих элементов (Fe, Mn, Co, Cu, Zn, Cs, Ce, La, Y) наблюдается в точке сброса воды из карьера. Максимальное содержание U отмечается чуть ниже по потоку изучаемых вод, что согласуется с данными по составу донных отложений и моделирования, которые указывают на возможность выпадения уранинита из водного раствора в водоеме, сформировавшемся при сбросе воды из карьера бутового камня и истоке ручья, берущего начало в этом водоеме. Роль органического вещества в изученных водах высока для процесса накопления железа в воде за счет образования устойчивого гидроксо-фульватного комплекса железа, а также для редкоземельных элементов за счет образования комплекса с гуминовой кислотой. Анализ распространенности, форм нахождения и осаждения химических элементов позволили заключить, что эксплуатация карьера бутового камня вносит существенный вклад в перераспределение химических элементов в изучаемом районе.

Radiogenic heat production of crystalline rocks in the Gonghe Basin Complex (northeastern Qinghai–Tibet plateau, China)

The Gonghe Basin Complex is a pull-apart basin located in the Northeastern Qinghai–Tibet plateau (Qinghai, China) displaying several geothermal features, such as high geothermal gradients and hot springs. The adjacent mountain ranges and the basement are comprised of granitoid rocks, which, at sufficient depth and temperature, are suitable for deep enhanced geothermal systems. Nonetheless, the origin of the heat source mechanisms is not conclusively determined so far. The presented study provides insights of the radiogenic heat productions of the Gonghe Basin Complex and its surroundings. In total, 30 newly sampled Triassic, Silurian, Ordovician, and Devonian intrusive rocks were extracted from outcrops in the surroundings and within the Gonghe Basin Complex, of which one sample was retrieved from exploration well DR2 at c. 1800 m. Samples were analyzed by thin section analysis and a petrographic description is provided. To geochemically characterize the samples, X-ray fluorescence measurements were performed, and radiogenic heat productions were subsequently calculated. Additionally, analysis of 341 intrusive, 105 extrusive, 155 sedimentary, and 76 metamorphic rocks of the Qinling–Qilianshan–Kunlunshan were taken from the literature and compared to the data sampled in the Gonghe Basin Complex. As evidenced in the presented research, the radiogenic heat production values measured in the Gonghe Basin Complex are within the highest calculated for the Qinling-Qilianshan-Kunlunshan. However, radiogenic heat production rates in the Gonghe Basin Complex range from 5 µW m−3 in two-mica granites and syenogranites. Nonetheless, average heat productions analyzed do not evidence large intrusions of HHP (high heat producing) granitoids as a source of the geothermal features in the Gonghe Basin Complex.