Paleozoic Granites Research Articles

South Tibetan Detachment System (STDS), NW Himalaya: A possible Cambro–Ordovician tectonic terrane boundary, and its Cenozoic remobilization

The South Tibetan Detachment System is an important extensional fault zone, separating the Greater Himalayan Sequence from the overlying Tethyan Himalayan Sequence, and is well exposed in the upper reaches of the Dhauliganga valley, NW Himalaya. This fault system is characterized by the occurrence of an extensive Cambro–Ordovician granite belt between Sutlej and Dhauliganga valleys, although only a few small granitoids intrude the high-grade mylonite gneiss of the Greater Himalayan Sequence in its immediate footwall. These bodies yielded U-Pb zircon crystallization ages between 498.92 ± 5.5 Ma and 486.54 ± 2.3 Ma. This work postulates that the South Tibetan Detachment System evolved as a major proto-tectonic marginal extensional terrane boundary during the Cambro–Ordovician Kurgiakh/Bhimphedian Orogeny, when it was the conduit for emplacement of the Cambro–Ordovician granite belt. Denudation of the Neoproterozoic Greater Himalayan Sequence and the Paleozoic granites on its footwall provided approximately ∼ 10 km thick sediments into the Tethyan Basin due to this fault system as a master growth fault. Reactivation of this fault system controlled further melting and emplacement of the Higher Himalayan Leucogranite belt during the Cenozoic. Zircon growth is observed in two distinct modes: pulsative from the Late Eocene to Early Oligocene, with peaks at 33.99 ± 1.07 Ma, 30.53 ± 0.32 Ma and 25.03 ± 0.54 Ma; and in the continuous mode from 23.68 ± 0.94 Ma to 13.30 ± 0.30 Ma, in the Miocene, for nearly 10.0 myr. These datasets reveal some of the oldest pulsative movements in the Late Eocene–Early Oligocene during crustal thickening, thrusting and associated metamorphism, followed by continuous extension during the Miocene. Data from the South Tibetan Detachment System are distinct in character, and do not support either its eastwards younging or diachronous movements along the Dhauliganga valley.

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.

LA-ICP-MS zircon U–Pb ages, geochemistry, and genesis of Paleozoic granites from Biezhentao Mountain, Western Tianshan, Xinjiang

The geologic history of the Western Tianshan region is important for understanding the evolution of the Central Asian Orogenic Belt and accretionary orogenesis. Paleozoic and Mesozoic igneous rocks are present along the northern margin of the Yili Block; however, studies of Paleozoic subduction and collisional events have been relatively limited. Published geochronologies of Middle Devonian magmatic rocks in this region are also lacking. Therefore, this study analyzed the zircon U–Pb ages and major and trace elemental compositions of three granite types collected from Biezhentao Mountain (Wenquan County, Western Tianshan). The medium-grained diorite (384.1 ± 3.6 Ma) and diorite–porphyrite (382 ± 3.2 Ma) are silica-rich, weakly peraluminous, alkali-rich, enriched in large-ion lithophile elements, depleted in high field strength elements, and belong to the calc–alkaline series, with A-type granite characteristics. The monzogranite (423.3 ± 9.4 Ma) exhibits A-type granite characteristics and belongs to the peraluminous calc–alkaline series. The findings suggest that the granitoids recorded two stages of tectonomagmatism during the Middle Devonian–Late Silurian. The Middle Devonian medium-grained diorite and diorite–porphyrite formed in a back-arc extensional setting, whereas the Late Silurian monzogranite formed in an active continental margin setting during the subduction of the North Tianshan Ocean. These results provide insights into the tectonic and magmatic processes that occurred during the evolution of the Western Tianshan region and the formation and evolution of the Central Asian Orogenic Belt.

Geochemistry and Zircon U–Pb Geochronology of the Wugongshan Granites in the Northwestern Jiangxi Area, China: Implications for the Paleozoic Tectonic Development of South China

The properties of the Caledonian orogeny along the transition belt of the Yangtze and Cathaysia blocks have received much attention in recent years. The widespread Early Paleozoic granites provide critical geological clues for unraveling the tectonic evolution and geodynamic processes of the South China Continent (SCC). Here we present new zircon U–Pb chronology, whole-rock major and trace elements, in situ Hf isotopes for Paleozoic granites, i.e., the Wugongshan granites in the northwest Jiangxi province, and aim to explore the magmatism and properties of the Caledonian orogeny involved in their formation. Our new data show that the Wugongshan granites were emplaced during the Early Silurian Period (442–438 Ma). The Paleozoic Wugongshan granites belong to S-type muscovite-bearing peraluminous granites (MPG) and show a single origin. The Wugongshan granites exhibit negative εHf(t) values (−11.56 to −6.19) and TDM2 model ages of 2148–1809 Ma, indicating their derivation from an ancient crustal source, through partial melting of ancient crustal material. The Wugongshan granitic magmatism is probably being generated in an extensional environment related to an intracontinental orogeny setting. It is inferred that the Paleozoic tectonic–magmatic event in the Wugongshan area was associated with the oceanic–continental convergence of the Paleo-Tethys Ocean. The Wugongshan granites highlight the intracontinental magmatism in the Early Paleozoic orogeny in the SCC.

Early Paleozoic granitic magmatism and mineralization in the Debao Sn-Cu deposit, South China: Constraints from zircon and cassiterite U-Pb geochronology and whole-rock geochemistry

Numerous W-Sn deposits are developed in South China. While the majority of these deposits are related to the Yanshanian granites, a few of them are associated with the Early Paleozoic granites, and their geological significance is poorly understood. The Debao deposit is a typical skarn Sn-Cu polymetallic deposit that is spatially related to the Early Paleozoic Qinjia granites. Zircon U-Pb dating of three lithofacies (coarse-grained biotite granite, medium-grained porphyritic biotite granite and fine-grained porphyritic biotite granite) of the Qinjia granites yielded emplacement ages of 437.8 ± 3.0 Ma, 440.2 ± 2.0 Ma and 441.0 ± 3.0 Ma, respectively, consistent with cassiterite U-Pb ages of skarn ore (439.6 ± 2.7 Ma), indicating a close genetic relationship between the granitic magmatism and Sn mineralization. Biotite from the Qinjia granites belong to the ferro-biotite series with relatively high F contents (up to 0.70 wt. %). The Biotite compositions plot near the Ni-NiO (NNO) buffer on a Fe3+-Fe2+-Mg2+ diagram, suggesting formation under relatively low oxygen fugacity. The Qinjia granites are characterized by highly silicious (70.37–72.88 wt. %), high alkali (Na2O + K2O = 6.98–8.88 wt. %) and metaluminous to strongly peraluminous with the A/CNK ratios of 0.92–1.21, belonging to the I-S transform-type granites. They are enriched in U, Th, Zr, Nd and Hf, and depleted in Ba, Sr, Nb, Ta and Ti. They display right-declining chondrite-normalized REE patterns with significant negative Eu anomalies (EuN/Eu* = 0.33–0.66), and have low Nb/Ta and K/Rb ratios, indicating that the Qinjia granites experienced a high degree of fractional crystallization. The zircon εHf(t) values (−2.7 to +1.4), together with TDMC of 1.59 to 1.33 Ga, indicate that the granites formed via partial melting of Mesoproterozoic crustal with minor addition of mantle materials. The reduced (fO2 near NNO and Ce4+/Ce3+ ratios of zircon < 100), fractionated and volatile-rich magma facilitated the enrichment of Sn in the residual melt and hydrothermal fluids. Combined with previous studies on the Early Paleozoic magmatic rocks and tectonic activities in South China, we suggest that the Qinjia granites and associated Sn-Cu mineralization were likely formed in the post-collisional extensional environment during the Wuyi-Yunkai orogeny.

TARAGAI PERIDOTITE MASSIF AS AN EXPLOSIVE PIPE IN THE WESTERN BUREYA TERRANE (SOUTHERN RUSSIAN FAR EAST)

Taragai peridotite massif is interpreted as an explosive ultramafic pipe emplaced through the Neoproterozoic carbonate skarnoids and Early Paleozoic granites of the western Bureya terrane. Peridotites at the surface are represented by strongly eroded bowl-shaped structure filled with disintegrated explosive material containing abundant peridotite boulders and host rock xenoliths. Explosive character of the Taragai massif is further emphasized by the occurrence of magnetite, iron-carbonate-silicate (with magnetite) and Cu-Ag-Au microspherules characteristic of explosive eruptions. Formation of the Taragai ultramafic pipe is related to the assimilation of mantle wedge or lithospheric mantle material over the stagnant Izanagi slab by the ultra-hot and reduced upwelling fluid flow within the transform-type continental margin tectonic setting.

The Kaolin and Bentonite Deposit of Tamame De Sayago (Zamora, Spain): Mineralogy, Geochemistry, and Genesis

A geological, mineralogical, and geochemical characterization of the Tamame de Sayago (Zamora, Spain) deposit was carried out with the aim of knowing the conditions that facilitated the genesis in the same deposit of kaolinite and smectites. The alteration processes affecting a Variscan granite were deduced throughout the study of a very wide group of representative samples by X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analyses of major, minor, and trace elements, as well as δ18O, δ34S stable isotope and K/Ar dating analyses. In addition, 2D and 2.5D graphs of the kaolinite and smectite isoconcentrations were obtained from core data. According to the color and texture, two different clayey rock types were identified and named as homogeneous alteration zones (ZAHO) and heterogeneous alteration zones (ZAHE). The ZAHO are regoliths in which the granite texture is preserved, and the feldspars are almost completely kaolinized. In the ZAHE, the original texture of the granitic rock is lost, and the main clay mineral is smectite. The mineralogical composition is similar, with kaolinite, smectite, mica, quartz, scarce feldspar, and occasionally natroalunite and APS (aluminum-phosphate-sulphate); however, the mineral concentration varies considerably because ZAHO are rich in kaolin areas whereas ZAHE are bentonitic areas. Both rock types contain numerous veins and nodules. The weathering of the Paleozoic granite alongside the absence of sedimentation during the Mesozoic led to the formation of kaolinite that is preserved in ZAHO materials. Nonetheless, during the Cretaceous–Tertiary transit, the conditions of tectonic stability varied. Late Variscan faults reactivated which allowed the percolation of Mg- and Ca-rich hydrothermal fluids through the already kaolinized granite, increasing the alteration of the primary silicates and leading to the formation of smectites in ZAHE materials. The amount of smectites is greater closer to the faults. The stable isotopes indicate the meteoric nature of the low-temperature hydrothermal fluids. The K/Ar data obtained from the natroalunite of veins indicate that those hydrothermal fluids circulated in different pulses from 66.4 ± 1.7 to 58.8 ± 1.5 Ma, as a minimum. Those ages are coincident with the first formation stages of the Duero Basin.

Hydrogeological conditions and hydrogeochemistry of the Kamenskoye hydro-radon occurrence, Novosibirsk, Russia

Hydrogeological and hydrogeochemical conditions, the concentrations of major and some minor ions and 222Rn were determined in the Kamenskoye hydro-radon occurrence in the Southern part of West Siberia. Two different aquifer systems were revealed in the hydrogeological section: the Quaternary sediments with pore waters and the Upper Paleozoic granites including the waters of regional fracturing zone and fracture-vein waters. They are located in a common mixing area and are affected by flooding and anthropogenic pollution. Mineral radon fracture-vein waters in granites, not affected by anthropogenic impact, have been revealed in two boreholes. These waters are cool, fresh (TDS 613.4 to 689.9 mg/L) and Si4+ content within a range from 10.3 to 13.6 mg/L. The pH of these waters is neutral to weakly alkaline (6.9–7.8), the gases dissolved in the waters are oxygen and nitrogen. The determined activity of 222Rn varies within the range from 1101 to 1570 Bq/L; 238U concentration varies between 5.6·10−3–6.5·10−3 mg/L, while 226Ra ranges from 2.7·10−9 to 1.8·10−8 mg/L. The relative fractions of cations (Mg2+, Ca2+, Na+, Sr2+, Ba2+) decrease with an increase in TDS value due to the formation of poorly soluble carbonate and sulphate compounds. The forms of Fe(II) are represented by Fe2+, FeHCO3+, FeCO30, and Fe(III) migrates in the forms of hydroxo complexes Fe(OH)2+ and neutral species Fe(OH)30. Manganese migrates mainly as a cation, while other forms (MnHCO3+, MnCO30) are less abundant, and MnSO40, MnCl+, MnOH+ are minor. The chemical forms of nickel and copper migration are free cations, as well as hydrocarbonate and carbonate complexes. Copper, as well as beryllium, also migrate as hydroxo complexes. The forms in which chemical elements migrate and their migration coefficients provide evidence that the equilibrium minerals become more complicated when passing from surface waters (greenalite, siderite, and ferrihydrite and greenalite) to the fracture-vein waters in the Upper Paleozoic granites saturated with dolomite, calcite, talc, magnesite and rhodochrosite.

Гидротермально изменённые породы – индикаторы зон разгрузки углеводородов Красноленинского свода (Западная Сибирь)

Our own research data as well as numerous publications of recent years on modern problems of oil potential in the West Siberian oil and gas province were used in this study. Based on the Palyanovskaya, Talinskaya and adjacent areas of the Krasnoleninsky arch, the issues of deposits structure and confinement to certain regional levels of the section, the problems of unconventional reservoirs formation in the zones of tectonic deformations and hydrothermal-metasomatic changes in pre-Jurassic basement rocks (Paleozoic granites), as well as problems of highly permeable “supercollector” (the lower horizons of the Jurassiccomplex – Sherkalinskaya formation) and an almost impermeable reservoir with difficult to recover huge hydrocarbon reserves (its upper horizons – Bazhenov formation) are discussed. The oil deposits distribution in the Jurassic part of the section was shown to comply with the fluid migration model with the participation of deep hydrocarbon fluid. New types of unconventional reservoirs have been identified in the basement granites and in the unloading zones in the Jurassic deposits of the sedimentary cover.

Petrogenesis and tectonic implications of the early Paleozoic granites in the Lincang granitic batholith, southwestern China: Constraints from geochronology, geochemistry and Hf isotopes

This study presents the recently discovered Wulao Shan Ordovician granite within the Lincang granitic batholith, discusses its geochemical affinity, genesis, and tectonic significance, and interprets the proto-Tethys orogenic model in southwest Yunnan. LA-ICP-MS zircon U-Pb analyses indicate a crystalline age of 473.0 ± 2.9 Ma for the Wulaoshan gneissic granite. Geochemical analyses show that the Wulaoshan granite exhibits relatively high SiO2 concentrations (73.4–77.3 wt.%), strong peraluminous properties (ASI > 1.1), strongly Eu-negative anomalies, light and heavy rare earth fractionation, and relative Ba, Nb, Ta, Sr, P, and Ti depletion. SiO2 and P2O5 exhibit a strong negative correlation, whereas Rb and Y-Th with a positive correlation. The magmatic zircons have negative εHf(t) values of -5.47∼2.74. Petrographic observations and whole-rock geochemical and isotopic analyses imply no aluminum-rich minerals such as cordierite, indicating that the Wulaoshan granite is a highly fractionated, high-temperature I-type granite, which may have formed via partial melting of the magnesian-iron igneous crust. Additionally, K-feldspar, plagioclase, and biotite within the granite samples may have undergone intense fractional crystallization. The Wulao Shan gneissic granite is an arc granite associated with subduction, indicating that the Lincang Block underwent proto-Tethys subduction. This finding provides evidence for proto-Tethys subduction down to the Lincang-Simao block and further supports the bidirectional subduction model of the proto-Tethys.

Paleozoic Tectonic Switch in the North Qinling Orogenic Belt: Constraints from the Paleozoic Granites from the Northern Qinling Migmatite Terrane

AbstractThe variations in source rocks and melting conditions of granites can provide essential clues for the crustal magmatic response in orogenic process. Based on geochronology, whole‐rock and mineral chemistry, this paper reveals two different granites in the Northern Qinling migmatite complex, which reveal obvious differences in source region and melting condition. The older granodiorite (402 ± 0.8 Ma) displays typical Na‐rich adakite affinity, i.e., high Na2O/K2O (2.04 to 2.64) and Sr/Y (96 to 117) ratios, they have relative evolved isotopic compositions (εNd(t) = –0.52 to –0.04; zircon εHf(t) = –0.06 to +7.78). The younger leucogranite (371 ± 2 Ma) displays higher SiO2 (72.32 to 73.45 wt%), lower (TFeO + MgO + CaO + TiO2) contents (&lt;2 wt%) and depleted Sr‐Nd‐Hf isotopic compositions (i.e., εNd(t) = +2.6 to +3.0; zircon εHf(t) = +5.94 to +14.12), as well as high 10000 × Ga/Al and TFeO/MgO ratios, indicating that they represent highly fractionated I‐type granites that derived from melting of juvenile crust. The variations in source rocks and melting condition of the two granites indicating a tectonic switch from compression to extension in 400 to 370 Ma, this switch is later than that in the eastern section of the North Qinling, indicating a scissor collision process between the South Qinling and North China Craton (NCC) in Devonian era.

Redefinition of the Petersburg batholith and implications for crustal inheritance in the Dinwiddie terrane, Virginia, USA

Field relations as well as geochemical and petrologic studies of meta-igneous rocks assigned to the Pennsylvanian–Permian Petersburg batholith identify at least two distinct rock types: foliated metagranitoid gneiss and massive to porphyritic granite. Foliated metagranitoid gneiss of mostly granodioritic composition is geochemically distinct from associated massive and porphyritic granitic rocks. These gneissic rocks yield radiometric ages from ca. 425 Ma to ca. 403 Ma and document that many of the rocks assigned to the late Paleozoic Petersburg batholith are 100 m.y. older than the youngest portions of the composite batholith and are part of an earlier infrastructural terrane. Two samples of massive equigranular granite southwest of Petersburg, Virginia, yield ages of ca. 321 Ma and ca. 317 Ma, which are 15–20 m.y. older than ca. 300 Ma ages for porphyritic granite, massive granite, and monzodiorite near Richmond, Virginia. Geologic mapping shows that the Early Pennsylvanian granite southwest of Petersburg is separated from Late Pennsylvanian to early Permian granite near Richmond by a map-scale septum of Silurian–Devonian foliated metagranitoid gneiss, referred to herein as the informal Pocoshock Creek gneiss. Laser ablation–inductively coupled plasma–mass spectrometry data from one sample of a quartz-muscovite felsic schist xenolith show a peak age mode of ca. 529 Ma that we interpret to be the maximum depositional age. Inherited zircons from foliated metagranitoid gneiss and massive equigranular granite range from ca. 631 Ma to ca. 376 Ma, but many are Cambrian. Neoproterozoic–Cambrian quartz-muscovite felsic schist and amphibolite, Silurian–Devonian Pocoshock Creek gneiss, and Pennsylvanian–Permian granite comprise a fault-bounded terrane referred to herein as the Dinwiddie terrane. Ages of inherited cores in zircon from igneous rocks and limited detrital zircon geochronology suggest the terrane is of peri-Gondwanan affinity. U/Pb ages of healed fractures in zircon grains from foliated metagranitoid gneiss indicate low-grade deformation of the gneiss at ca. 378–376 Ma, while ca. 320–280 Ma rims on many grains record intrusion of late Paleozoic granite. The temperature-time-deformation history of the Dinwiddie terrane is distinct from the adjacent Goochland and Roanoke Rapids terranes. Orogen-scale dextral transpression likely translated the Dinwiddie terrane southward during the Alleghanian orogeny, at which time they were intruded by Pennsylvanian to Permian granite.

On Some Accessory Minerals in Upper Paleozoic Granites of the Khrami Crystalline Massif

The Khrami crystalline massif is exposed within the Black Sea – Central Transcaucasian terrane (Georgia). The massif is built up of Preсambrian gneiss-migmatite complex, the packet of Middle Paleozoic (?) metasandstones and protrusions of mantle serpentinites; Paleozoic gabbroids; Middle-Upper Paleozoic granitoids and rocks of volcanogenic-sedimentary complexes and Upper Paleozoic quartz-porphyry - granite-porphyry formations. A number of scientists have studied the granitoids of the Khrami crystalline massif, but detailed investigations on some minerals using modern analytical facilities have not been conducted yet. The Late Variscan granitoids of the Khrami massif are represented by biotite-hornblende-allanite-, biotite-microcline- and biotite-garnet-bearing granites and aliaskites. We have studied in detail the accessory minerals - garnet and allanite in the Late Variscan granites of the massif. Their microprobe analysis has been performed. According to the microprobe analysis of the studied garnets, the centre of the crystal is homogeneous, while the peripheral part is zonal. The amount of FeO decreases slightly from the centre to the periphery, while the amount of CaO and MgO significantly decreases; a well-expressed increase in MnO content is recorded. The variation in almandine content is insignificant. The amount of pyrope and grossular drops sharply from the centre to the periphery while the number of spessartine increases. The amount of Al2O3 in all varieties of granitoids is similar. In our opinion, the garnet formation occurred in two stages: during the crystallization process of granitic magma and its subsequent post-magmatic stage. The core of the garnet was formed in the magmatic stage, but its periphery - was in the cooling stage of granitic magma. According to the results of the microprobe study of allanite, the same - two stages of their formation have been conducted: during the crystallization process of granitic magma and in its next post-magmatic stage. The genesis of allanite in the biotite-hornblende-allanite-bearing granites of the massif is due to the concentration of REE in the granitic magma and the introduction of calcium by hydrothermal solutions. These allanites belong to the cerium variety with high content of Ce2O3, La2O3 and Nd2O3.

Mesozoic-Cenozoic Exhumation History of the Bogda Range, Eastern Tianshan: Insights from Apatite Fission Track Thermochronology

The Bogda Range (hereafter referred to as the Bogda) is located in the Eastern Tianshan. Interpreting its tectono-thermal history is critical to understanding the intra-continental evolution of the Tianshan. In this study, we report new apatite fission track data from the late Paleozoic–Mesozoic sedimentary rocks in the northern Bogda and the Late Paleozoic granites in the southern Bogda to investigate the exhumation history of the Bogda. Apatite fission track ages dominantly range from the Jurassic to earliest Cenozoic (~143–61 Ma), except for one siliciclastic sample from the Early Permian strata with an older age of ~251 Ma. Thermal history modeling, together with detrital apatite fission track age peaks, reveal that the Bogda underwent three episodes of cooling during the Late Triassic, the Late Cretaceous, and the Late Miocene. The Late Triassic rapid cooling may represent the initial building of the Bogda, which is probably related to the final closure of the Paleo-Asian Ocean. During the Late Cretaceous, the Bogda may have experienced a moderate exhumation, which was possibly triggered by the extensive tectonic extension in the central–eastern Asian regime during the Cretaceous. The Late Miocene rapid cooling may be a response to the rapid uplift of the whole Tianshan, due to the far-field effect of the continuous India–Eurasia collision since the beginning of the Cenozoic.

Provenance of the Mesozoic Succession of Franz Josef Land (North‐Eastern Barents Sea): Paleogeographic and Tectonic Implications for the High Arctic

AbstractStudy of the Mesozoic succession of Franz Josef Land (FJL) has shed new insights on the stratigraphy and geological history of the neighboring portion of the Arctic. Based on the composition of pebbles and cobbles from Lower Jurassic conglomerates, we suggest that the pre‐Mesozoic stratigraphy of the NE Barents Sea comprises Cambrian metasandstones intruded by Late Paleozoic granites and overlain by Carboniferous–Permian sedimentary deposits. U‐Pb and ZHe ages of detrital zircons from Uppermost Triassic–Lower Cretaceous strata of FJL reveal Precambrian to Early Mesozoic grains. The most abundant Late Paleozoic detrital zircon population suggests the existence of the same in age magmatic events in the provenance area. ZHe ages show Late Triassic (ca. 225 Ma) exhumation of the provenance area. Moreover, the youngest grains of detrital zircons are Middle‐Late Triassic in age pointing that significant uplift of provenance coincides with magmatic activity. Based on these data, we suggest that the provenance area for Triassic–Lower Cretaceous strata of FJL was characterized by a similar geological composition, as well as magmatic and tectonic history, to the Taimyr fold‐and‐thrust belt and Kara terrane. A comparison of detrital zircon data from coeval strata elsewhere in the Arctic realm suggests that this eastern provenance area was actively sourcing sediments right across the Barents Sea Basin, and possibly as far as the Sverdrup basin, during the Latest Triassic–Jurassic. The period of Late Triassic uplift represented a significant tectonic event across the north‐eastern Barents Sea, and likely initiated an increase in sediment supply and a reorganization of pre‐existing sediment transport pathways.

Post-collisional reworking of subducted continental crust: Insights from late Paleozoic granites in the North Qaidam orogen, northeastern Tibet

Post-collisional granites are widely distributed in continental collision orogenic belts, and deciphering their petrogenesis has great bearings for understanding the deep crustal compositional and tectono-thermal evolution of collisional orogens. Here we carried out a combined study of whole-rock major-trace elements and Sr–Nd–Hf isotopes, and zircon UPb ages and LuHf isotopes for late Paleozoic granites from the North Qaidam orogen, northeastern Tibet. The results indicate that they were derived from partial melting of subducted continental crust at high thermal gradients due to post-collisional rifting orogeny. Zircon UPb dating of the granites yields weighted mean 206Pb/238U ages between 377 ± 3 Ma and 384 ± 5 Ma, which postdate the ultrahigh-pressure (UHP) metamorphic ages (ca. 438–420 Ma) of deeply subducted continental crust in the North Qaidam orogen. Therefore, they are products of post-collisional magmatism. Most relict zircons in the granites have concordant Neoproterozoic (793–972 Ma) and early Paleozoic (405–442 Ma) UPb ages, generally consistent with the protolith and metamorphic ages of the UHP metaigneous rocks in the orogen, respectively. The granites are commonly calc-alkaline to high-K calc-alkaline with total alkali contents of 6.89–8.56 wt%, and weakly to moderately peraluminous with A/CNK values of 1.00–1.18 [A/CNK = Al2O3/(CaO + Na2O + K2O), in molar]. They exhibit arc-like trace element distribution patterns and enriched Sr–Nd–Hf isotope compositions with whole-rock (87Sr/86Sr)i ratios of 0.7074–0.7104, ɛNd(t) values of −9.0 to −4.4 and ɛHf(t) values of −4.2 to +2.9, and syn-magmatic zircon ɛHf(t) values of −7.6 to +7.7 (except one analysis of −15.0). These granites mostly have comparable SrNd isotope compositions to the UHP orthogneiss and continental eclogite in this collisional orogen, indicating their derivation from the subducted continental crust. Using the average compositions of the orthogneiss and continental eclogite in the orogen as the starting materials, phase equilibrium modelling results suggest that the whole-rock major elements of the post-collisional granites can be explained by the mixed melts mainly derived from these two lithologies, which were partially melted at high thermobaric ratios of 1156–1867 °C/GPa associated with different water contents (1–5 wt% for continental eclogite, 1–3 wt% for orthogneiss). Therefore, this study provides integrated geochemical constraints on the source rocks of the post-collisional granites and physicochemical conditions for their genesis.

Hydrogeochemistry and stable isotopes in radon-rich thermal waters of Belokurikha (Altai, Russia).

The first integrated isotope and chemistry results have been obtained for radon-rich thermal waters from the Belokurikha field which are used at a large spa resort in Altai, Russia. The waters reside in an unconfined aquifer composed of Quaternary soft sediments and in a confined (artesian) aquifer of monolithic to weathered Upper Paleozoic granites. The waters belong to three geochemical groups: low-radon nitrogen-silicic interstitial waters in weathered Paleozoic granites; groundwaters of REE-enriched and background compositions; surface waters of the Belokurikha River. The interstitial waters in granites have HCO3-SO4 Na and SO4-HCO3 Na major-ion chemistry, total salinity from 198 to 257 mg/L, pH = 8.6-9.6, silica contents of 19.8 to 24.6 mg/L, and 222Rn activity from 160 to 360 Bq/L (290 Bq/L on average). Judging by their oxygen and hydrogen (deuterium) isotope compositions (-17.5 to -14.2 ‰ and -126.9 to -102.7 ‰, respectively), the Belokurikha aquifers recharge with infiltrating meteoric water, especially the winter precipitation. The carbon isotope composition of dissolved inorganic carbon (-9.7 to -25.6 ‰ δ13СDIC) corresponds to biogenic origin. Comparison of radon-rich mineral waters from different areas of southern Siberia shows that the change from oxidized to reduced environments leads to 232Th/238U increase from 4.20∙10-5-7.39∙10-2 to 0.0022-26, respectively, with an intermediate range of 2.63∙10-5-0.20 in transitional conditions.

Sources and Forms of Metals Accumulation in Coal-Bearing Deposits of the Southern Primorye: Validation of the “Granite-Water” Model

The work deals with the role of Paleozoic granites as possible sources of metals in coals. The process of dissolution and transfer of metals in the system “granite-water” was modeled. It is shown that the scale of accumulation of ore matter in water depends on the duration of interaction between water and rock. As a result of physical and chemical modeling, the probable set of migration forms of components and their transformations were calculated. The results of modeling indicate in favor of the assumption that the studied leucocratic granites of the pre-Cenozoic basement could be a source of metals concentrated in the coals of the Rakovka depression.

Changes in the melt structure and enrichment of rare metals W-Sn-Nb-Ta in granitic magma: An example from the Xiaru Early Paleozoic granites

藏南喜马拉雅造山带新生代高硅淡色花岗岩富集稀有金属元素(Nb、Ta、W、Sn、Be、Li等), 成矿潜力大, 是未来矿产勘探的重要靶区。除了新生代花岗岩, 早古生代花岗岩分布广泛, 具有和新生代花岗岩相似的地球化学特征, 是否也具有成矿潜力, 是有待深入研究的一个重要课题。夏如穹窿主体由早古生代花岗片麻岩以及侵入其中的新生代淡色花岗岩和伟晶岩组成, 这些花岗岩具有与新生代高硅淡色花岗岩相似的地球化学特征, 在Sn-W和Nb-Ta系统关系上, 可以分成两组: 一组富集W和Sn(W=5×10^-6~42×10^-6, Sn=12×10^-6~35×10^-6), 另一组富集Nb和Ta(Nb=23×10^-6~108×10^-6, 个别高达217×10^-6, Ta=8×10^-6~38×10^-6, 个别高达143×10^-6)。与富集W-Sn的花岗片麻岩相比, 富集Nb-Ta的花岗片麻岩具有: (1)较高的Na₂O, 为富Na花岗岩, (2)较低的K₂O、FeO^T、TiO₂、P₂O₅、Sr、Zr; (3)略微富集MREE, 亏损LREE和HREE, 显著的负Eu异常; (4)较高的Nb、Ta, 但较低的W、Sn。元素的系统关系表明, 这两类花岗片麻岩都是较原始岩浆经历了不同程度斜长石、锆石、云母等矿物分离结晶作用的产物, 富集Nb-Ta的花岗片麻岩分异程度最高。夏如早古生代两类花岗岩的Nb/Ta比值都小于5, 但富集W-Sn花岗岩中Zr/Hf&gt;20, 富集Nb-Ta花岗岩中Zr/Hf &lt; 20。随着花岗质岩浆的分异逐步增强, 当Zr/Hf=20时, 熔体结构发生实质性变化, 花岗质熔体从富钾质变成富钠质, 从富集W-Sn变成富集Nb-Ta。本研究表明, 在喜马拉雅造山带, 不仅新生代花岗岩, 而且古生代花岗岩都富集稀有金属元素, 熔体结构的改变是控制花岗岩富集稀有金属的主要因素。

The Early Paleozoic granites in the Mohe region of northern Great Xing'an Range: Response to post-collision extension of the Erguna-Xing'an blocks

本文报道了大兴安岭北段漠河地区早古生代二长花岗岩的岩相学、锆石U-Pb年龄、Hf同位素组成以及全岩主-微量元素地球化学数据，以揭示古亚洲洋构造域早古生代期间的构造-岩浆演化过程。漠河地区花岗岩中锆石发育典型的岩浆振荡生长环带和高Th/U比值，表明为岩浆成因锆石，其LA-ICP-MS U-Pb同位素测试结果显示漠河地区花岗岩形成于482~456Ma，代表奥陶纪-志留纪岩浆活动的产物。花岗岩主体为二长花岗岩，主要矿物组成为石英、斜长石和碱性长石，及少量黑云母。全岩主-微量元素地球化学分析结果显示，花岗岩具有高SiO₂、Al₂O₃和全碱（Na₂O+K₂O）含量，低MgO、Mg^#、Cr和Ni含量，并显示高钾钙碱性的属性；结合花岗岩准铝质特征，表明其属于高钾钙碱性I型花岗岩。此外，花岗岩样品富集大离子亲石元素（Rb、Ba、K、Sr等）和轻稀土元素，亏损高场强元素（Nb、Ta、P、Ti等）和重稀土元素，显示明显Eu负异常，与地壳组分的地球化学特征较为相似。花岗岩的锆石<i>ε</i>_Hf（<i>t</i>）值大多为正值，结合它们相应的Hf同位素二阶段模式年龄（1487~1106Ma），表明花岗岩的岩浆源区以中-新元古代期间新增生的年轻地壳组分为主，并且存在少量古老地壳物质的贡献。结合部分花岗岩样品重稀土元素亏损的特征，表明漠河地区早古生代花岗岩可能起源于石榴石角闪岩相和角闪岩相地壳物质的部分熔融作用，岩浆演化后期的分离结晶作用对岩浆成分的变化影响并不显著。结合额尔古纳地块广泛发育的同时期造山后岩石组合（A型花岗岩，双峰式岩石组合和碱性侵入体），本文认为漠河地区早古生代花岗岩是地幔物质底侵导致下地壳物质重熔的产物，与额尔古纳地块和兴安地块碰撞后的伸展环境下地幔物质上涌密切相关。