Light Enrichment Research Articles

Tracking geochemical signatures of rare earth and trace elements in spring waters and outcropping rocks from the hidden geothermal system of Acoculco, Puebla (Mexico)

A geochemical mapping of rare earth (REE) and other trace elements in water and rock samples of the hidden geothermal system of the Acoculco caldera was carried out. REE and other trace elements were measured at low concentrations in waters (ΣREE <50 μg/L) and rocks (ΣREE <773 μg/g), and used, for the first time, to understand the water-rock interaction processes of this geothermal system. A bimodal frequency distribution of pH was found among acidic waters (pH <3.5) that emerge from cold springs located inside the caldera, and slightly-acid to hot alkaline spring waters (pH 5 to 9.2) from outside the caldera. The geochemical modelling of REE showed that minerals containing Al3+, Fe, and F− were the main phases that control their concentrations in acidic waters. Different degrees of REE complexation in waters located inside the Acoculco caldera (Alcaparrosa and Los Azufres) clearly showed new signatures of geothermal activity. LnSO4+ complexes and free ions of Ln3+ were identified as major species of the acidic waters of Alcaparrosa, whereas in less acidic waters of Los Azufres, LnF2+ show an increase in their complexation percentages. The REE chondrite-normalized patterns observed in acid waters display a depletion from light-REE (LREE) to heavy-REE (HREE), and an inverse correlation between high REE concentrations and acid pH's. The REE concentration in felsic and intermediate rocks shows “gull-wing” chondrite-normalized patterns characterised by an enrichment of LREE, a negative anomaly of Eu, and depletion of HREE with a flat tendency. The present study of water-rock interaction contributed to the identification of new geochemical signatures of major and trace elements that provide new evidences of deep formation temperatures between 200 °C and 300 °C, becoming in an effective tool for finding out convincing anomalies in hidden geothermal systems.

>1.8 Ga cold subduction of lithospheric mantle: Evidences from the Fengzhen olivine-bearing garnet pyroxenite xenoliths in Trans-North China Orogen

Whether modern-style subduction exists in Paleoproterozoic has been hotly debated because of the scarcity of robust petrological evidence. Here, we present a comprehensive study of olivine-bearing garnet pyroxenite xenoliths hosted in the Paleoproterozoic Fengzhen carbonatite. The carbonatite is located in the conjugate area between the Paleoproterozoic Trans-North China Orogen (TNCO) and the Khondalite Belt in North China Craton (NCC) with a dated age of 1810 ± 3 Ma. Petrographically, four-stages of evolution have been identified in the studied olivine-bearing garnet pyroxenite: 1) the formation of the protolith spinel websterite (S1), 2) the prograde metamorphism of spinel-lherzolite facies to garnet-lherzolite facies (M1), 3) retrograde metamorphism to Ariegite subfacies (M2) with formation of symplectite-I, and 4) Seiland subfacies (M3) forming symplectite-II. The clinopyroxene in the xenoliths display high Mg# (Mg2+/(Mg2++Fe2+)*100 = 89–94), strongly depleted HREE (heavy REE) and HFSE (high field strength elements; e.g., Nb, Zr, Ti) and enriched LREE (light REE) and LILE (large ion lithophile elements; e.g., Th and U). Similarly, the whole-rock chemistry exhibits high Mg# (85–88) and high Al2O3 + CaO (20.2–21.9 wt%) with enrichment in LREE and LILE (Th, U) and depletion in HREE and HFSE (e.g., Nb, Ta, Zr, Hf, Ti). The geochemical signatures imply that they might originate from the refractory mantle wedge in subduction zone and have been metasomatized by crust-derived melts. Major mineral thermobarometry yields the peak PT conditions of 26–33 kbar and 890–962 °C corresponding to a cold subduction geothermal gradient (307 ± 35 °C/GPa) with a depth up to 110 km for olivine-bearing garnet pyroxenites, which is also consistent with the results by zirconium-in-rutile and REE thermobarometers. This studies suggest that that the modern-style subduction of the lithospheric mantle was initiated at least since 1.8 Ga.

Geochemical characteristics of rare earth elements (REEs) in soils developed on different parent materials, in the Baoshan area, Yunnan Province, SW China

The geochemistry of rare earth elements (REEs) was studied in rock samples from host formations, ore samples from two mineral deposits (the Hetaoping Cu-Pb-Zn mine: HTP and the Heiyanao Fe-Cu-Pb-Zn mine: HYA) and the overlying or nearby soils to better understand REE concentrations, distributions and behaviour during weathering from different parent materials at the regional scale, Baoshan area, Yunnan Province, SW China. The mudstone and sandstone formations have the highest total REE (ΣREE) contents. Chondrite-normalized diagrams for rocks and ores show significant light REEs (LREEs) enrichments and Eu depletion (except for ores in HYA). Cerium displays an obvious negative anomaly in carbonate rocks (Є-3-R, C-R, D-R, T-1-R and T-2-R). Soils overlying carbonate rock formations (T-1-S, C-S and Є-3-S) have the highest ΣREE contents, while soils overlying basalts have the lowest ΣREE contents. Soils show enrichments in LREEs with negative Eu anomalies and slight Ce anomalies in the studied soils. Soils with high ∑LREE/∑heavy REE (HREE) values may result from the preferential absorption of LREEs by organic matter. Negative Eu anomalies in soils occur for parent materials in the study area lacking feldspar, especially soils developed from carbonates. Compared to the parent materials, most soils show REE enrichment because alkali metals are removed and REEs are concentrated by low mobility in surficial processes and positive Ce anomalies because of weathering dissolution of other trivalent REEs with ionic radii similar to that of Ca 2+ . Supplementary material: Additional data (Tables S1 and S2) and sample locations (Fig. S1) are available at https://doi.org/10.6084/m9.figshare.c.5303140

A-type granite in the Boein-Miandasht Complex: Evidence for a Late Jurassic extensional regime in the Sanandaj-Sirjan Zone, western Iran

The Boein-Miandasht Complex (BMC) in the central part of the Sanandaj-Sirjan Zone, western Iran, is composed of metamorphic rocks, and gabbro, gabbro-diorite, and granite intrusions, in which co-magmatic mingling structures are commonly found. Zircon U-Pb ages demonstrate that crystallization of the granitic rocks occurred during the Late Jurassic (158 ± 5 Ma to 156 ± 4 Ma). Whole-rock granite geochemistry indicates low abundances of MgO (0.43–1.16 wt%), CaO (0.92–2.34 wt%), P2O5 (0.12–0.20 wt%) and Sr (72.2–254 ppm), high contents of SiO2 (66.9–72.0 wt%), alkalis (Na2O + K2O = 8.04–8.94 wt%), Rb (153–213 ppm), high field-strength elements (HFSE), rare earth elements (REE), and high FeOt/MgO ratios. The rocks are calc-alkalic to alkali-calcic and metaluminous to slightly peraluminous, typical characteristics of ferroan A-type granites. Chondrite-normalized REE diagrams display slight enrichment of light REE, flat HREE patterns and significant negative Eu anomalies. The primitive mantle-normalized multi-element variation diagrams show negative Eu, Nb, Sr, P and Ti anomalies. Both REE and other incompatible elements are consistent with A-type granite affinities for these rocks. The thinning of the continental crust and injection of hot mafic magmas within the crust were probably responsible for the partial melting of the lower crust to produce A-type granitic magmas in the region. This process is consistent with an extensional tectonic regime in the central part of the Sanandaj-Sirjan Zone during the Late Jurassic.

Emplacement ages and petrogenesis of intermediate‐acid intrusive rocks in the Lajishan region of the Central Qilian Belt, China: Constraints from zircon U–Pb ages, Hf isotopes, and whole‐rock geochemistry

As a major tectonic unit along the southwestern rim of the Central Qilian Belt, the Lajishan region plays an important role in the amalgamation of continental plates in the Qilian Orogenic Belt. In this study, zircon laser ablation inductively coupled plasma mass spectrometry for U–Pb dating and Hf isotope analysis, as well as geochemical analysis of intermediate‐acid intrusive rocks from the Lajishan area were conducted. Results show that formation ages of the intermediate‐acid intrusive rocks are 438–452 Ma. Whole‐rock geochemistry results show that the diorite and monzodiorite are metaluminous, low‐ to medium‐K series, and characterized by obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments. The εHf(t) values of zircons from monodiorite range from +2.71 to +10.59 and the two‐stage model ages range from 751 to 1,253 Ma. A large transversal span of εHf(t) values suggests that the source of depleted mantle was mixed with a small amount of older crustal material. The diorite and monzodiorite show a covariant relationship between εHf(t) values and Th/U ratios, which imply the existence of source heterogeneity. The diorites and monzodiorites were most likely produced in an arc setting. The granites are low K in composition and metaluminous to weakly peraluminous. In view of obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments, parent magmas of the granites are suggested to have formed with the participation of crustal source materials. The εHf(t) values of zircons from granite range from +5.82 to +8.90, and the two‐stage model ages range from 861 to 1,057 Ma, indicating that magmas of the granites were mainly derived from partial melting of depleted mantle or juvenile thickened lower crust. The granites were most likely produced in an arc setting and share a similar source with the diorite and monzodiorite. Correlation between major oxides and SiO2 show that during the formation of the three kinds of rocks, crystallization and differentiation both played important roles. Combined with published data from the Central Qilian Belt and its vicinity, our results conclude that the northward subduction of oceanic crust contributed to the formation of an Early Palaeozoic subduction–accretion system in the Lajishan region. This model reveals a tectonic–magmatic thermal event and provides important insights into the tectonic evolution process in the Qilian region, as well as the Central Orogenic Belt during the Early Palaeozoic.

New insights into the petrogenesis of the Puerto Vallarta Batholith, Mexico: Evidence from petrology, zircon petrochronology, and phase equilibrium modeling

At subduction zones, continental magmatic arcs are produced by differentiation processes. The Puerto Vallarta Batholith, at the Mexican Pacific margin, is the final product of the subduction of oceanic Farallon plate beneath the North American plate during the Cretaceous. Although this Cordilleran Batholith has been subject to different studies, its petrogenetic evolution remains unclear. To better constrain the magmatic processes that gave origin to the granitic rocks of the Puerto Vallarta Batholith, we combined detailed fieldwork, zircon petrochronology, and conventional thermobarometry coupled with phase equilibrium modeling. We present the crystallization and emplacement evolution, and its relationship to magmatic processes of the Puerto Vallarta Batholith. In the granitic rocks, we observed calc-alkaline and metaluminous signatures, as well as enrichment in light-rare earth elements (LREE) relative to the heavy-rare earth elements (HREE). The early crystallization stages of the Puerto Vallarta Batholith started at ~729–776 °C and ~3.5–5.3 kbar, with the last melt portion crystallized at ~675–685 °C. Fieldwork observations and Zr saturation thermometry reveal mixing of melts during the last crystallization stages. Geochemical signatures of zircons from granitic rocks suggest crystallization after minor plagioclase fractionation with likely assimilation of crustal components. Our results from geochemical whole-rock data further indicate partial melting of a heterogenous source in the mantle wedge and the differentiation of those primary melts as the principal processes that gave origin to the Puerto Vallarta Batholith. We show that the magmatic processes that originated the granitic rocks of this Cordilleran Batholith occurred in the middle crust during the Late Cretaceous. Our results provide new evidence to better constrain the origin of this magmatic system.

First petrologic data for Vitória Seamount, Vitória-Trindade Ridge, South Atlantic: a contribution to the Trindade mantle plume evolution

The Vitória Seamount (VTS), distant ~300 km from the Brazilian coastline at latitude 20°S, is the second closest offshore volcanic complex of the Vitória-Trindade Ridge (VTR) which corresponds to a ca. 1200 km long ridge of seamounts and islands composed of SiO2-undersaturated magmatic rocks commonly considered to be the volcanic track of the Trindade mantle plume in the South American Plate. Based on the first sample dredged from Vitória Seamount, new petrographic and electron microprobe analyses from its rock show an alkaline basalt with pseudotrachytic texture consisting of bytownite and salite phenocrysts, labradorite microliths, anhedral titanomagnetite, and a yellowish green pseudomorphic phase composed of MgO–Al2O3–SiO2–FeO. The fine-grained groundmass is mainly composed of strongly oriented lath-shaped labradorite microliths, opaque minerals, and vesicles filled by a yellowish green pseudomorphic phase. Whole-rock analyses of the Vitória Seamount rock reveal its SiO2 undersaturation (SiO2ca. 40 wt.%; normative nepheline = 13.8), enrichment in Cr, Co, Ni, V and Sc, along with depletion in Zr, La and Nd contents compared to the other seamounts of the VTR. VTS show a strong enrichment in light-REE (La/SmNca. 2.68) compared to heavy-REE (La/YbN = 20.79). Major and trace element evidence indicate that the melting of an enriched mantle source to generate the Vitória Seamount magma occurred dominantly in the garnet stability field. Trace element composition of VTS is consistent with ≤ 3% partial melting of the mantle source. Neodymium and Sr isotopic data suggest that the mantle source of the Vitória Seamount had been variably metasomatized by melts derived from enriched mantle component, which may have developed approximately 600 Ma, reconciling with the Brasiliano Orogeny, according to Nd age model. Modeling of the Nd–Sr isotope systematics points out that the primary melt was formed from an asthenospheric mantle (DMM – Depleted MORB [Mid-Ocean Ridge Basalts] Mantle) that underwent mixing with a continentally derived material (represented by EMI [Enriched Mantle I] component). This process can be explained by the mixing of melts from these mantle components during magma genesis.

Early Permian continental arc magmatism in the Zhaojinggou area of the northern North China Craton: Implications for crust-mantle interactions during southward Paleo-Asian plate subduction

Early Permian magmatism in the Zhaojinggou area of Inner Mongolia, northern China produced intrusive gabbroic diorite and granites including biotite granite, K-feldspar granite and fine-grained granite. We present zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf isotopic compositions of these rocks to resolve complex crust–mantle processes beneath the northern margin of the North China Craton (NCC). Zircon U–Pb dating reveals that the rocks were emplaced in the Early Permian, with gabbroic diorite (291.1 ± 1.8 Ma) forming ~10 Myr earlier than the granites (biotite granite, 280.0 ± 1.6 Ma; K-feldspar granite, 279.7 ± 2.1 Ma; fine-grained granite, 282.2 ± 2.9 Ma). Geochemical data indicate that the rocks have calc-alkaline to high-K calc-alkaline and metaluminous to peraluminous affinities, with enrichment in light rare-earth elements (LREE) and large-ion lithophile elements (LILE), and depletion in high-field-strength elements (HFSE), typical of continental arc magmatic rocks. The gabbroic diorite is characterized by low–moderate Mg# values (38–59, mean 50), moderate average Cr (45.0 ppm) and Ni (36.5 ppm) contents, and moderately enriched Sr–Nd–Hf isotopic compositions with (87Sr/86Sr)i values of 0.704719–0.705497; εNd(t) values from −7.8 to −7.0; and εHf(t) values from −11.2 to −6.7. These features, combined with highly variable Rb/Y, Ba/La, Th/Yb, Th/Ce and Th/Sm ratios and Ba contents, indicate that the gabbroic diorite was derived from subduction-related enriched sub-continental lithospheric mantle (SCLM), previously metasomatized by slab fluids and ~5% sediment melts. Weakly negative to strongly positive Eu anomalies among gabbroic diorite samples indicate no residual plagioclase accumulation or fractionation during magma evolution. The granites have similar ages and enriched isotopic features (87Sr/86Sri = 0.703611–0.707427; εNd(t) = −11.4 to −9.2; εHf(t) = −12.8 to −7.2) with old Nd and Hf model ages of 1980–1801 Ma and 1730–2088 Ma, respectively, indicating that they originated through partial melting of ancient mafic lower crust. Both biotite granite and K-feldspar granite exhibit weakly negative to highly positive Eu anomalies and relatively low Zr saturation temperatures of 618–648 °C. In contrast, the fine-grained granite has negative Eu anomalies and relatively high Zr saturation temperatures (692–709 °C). These features imply that the magma source of the fine-grained granite (with plagioclase accumulation) was deeper than that of the biotite granite and K-feldspar granites (without plagioclase accumulation). Different mantle and crustal sources involved in the generation of continental arc magmatism in the Zhaojinggou area have implications for extensive and complex crust–mantle interactions beneath the northern margin of the NCC related to southward subduction of the Paleo-Asian oceanic crust during the Early Permian.

Rare earth and trace elements in deep-sea sponges of the North Atlantic

The available data on trace elements (TE) of deep-sea organisms is scarce and nonexistent for rare earth elements (REE). Hence, this study characterizes REE and TE in five porifera genera (Jaspis, Geodia, Hamacantha, Leiodermatium, Poliopogon) collected in deep-sea areas (between 481 and 2656 m) of the North Atlantic. Aluminium was the most common TE while lead was the less abundant. These sponges showed an increased accumulation of TE compared with other probably influenced by volcanic activity. Poliopogon amadou sampled at the deepest location presented the highest concentration of all REE. All studied species exhibited a Light REE enrichment in comparison to Heavy REE and showed a negative Ce anomaly with a less conspicuous Eu depletion. Besides the establishment of a baseline for future comparisons, this study provides the first record of REE in a sessile deep-sea marine invertebrate group.

Geochemical characterization of monazite sands based on rare earth elements, thorium and uranium from a natural high background radiation area in Tamil Nadu, India

The Kanyakumari coastal area in the southernmost part of Tamil Nadu, India is a well-known natural high background radiation area due to the abundance of monazite in beach placer deposits. In the present study, the concentrations of major oxides, rare earth elements (REEs), Th and U were measured to understand geochemical characteristics of these monazite sands. Based on the ambient dose rate, 23 locations covering an area of about 60 km along the coast were selected for sample collection. The concentrations of U and Th ranged from 1.1 to 737.8 μg g−1 and 25.2–12250.6 μg g−1, respectively. The Th/U ratio ranged from 2.2 to 61.6, which clearly indicated that Th was the dominant contributing radionuclide to the enhanced natural radioactivity in this coastal region. The chondrite-normalized REEs pattern of the placer deposits showed enrichment in light REEs and depletion in heavy REEs with a negative Eu anomaly that indicated the monazite sands were derived from granite, charnockite, and granitoid rocks from the Nagercoil and the Trivandrum Blocks of the Southern Granulite Terrain.

Geochemistry, mineralogy and thermal analyses of Cretaceous coals from the Benue Trough basin Nigeria: Reconnaissance assessments

Selected coal samples from the Benue Trough Basin (Nigeria) were analysed by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), Fourier transform-infrared spectroscopy (FT-IR), and all the techniques used. The main minerals detected are clays (e.g., kaolinite and illite), quartz, feldspar, hematite and magnetite with traces of calcite, siderite, dolomite, orthoclase and graphite. The authigenic and detrital origins of the clay minerals detected were confirmed by FT-IR analysis. The XPS spectra identified elements similar to the mineral phases observed in the XRD spectra. The contents of Al2O3, CaO, Fe2O3, K2O, Na2O and P2O5 were below the values reported for US and Chinese coals. The elemental indexes (e.g. Al2O3/TiO2, Co/Th vs. La/Sc, Cr/Th vs. Sc/Th) showed that the influence of intermediate-mafic materials derived from source-region sediments is negligible. The Ni/Co ratio showed that the coal forming marsh experienced comparatively mild redox conditions. The ratios of V/(V + Ni), Co/Ni, and Mo/Ni revealed marginal or non-existent marine effects. Trace metals ratios such as V/Ni, Sr/Ba, Rb/Sr, Sr/Cu and V/Zn showed evidence of a large degree of freshwater environment mainly in a humid climate. Maceral composition reflects fluctuations of dry and wet conditions in the forest swamp in a humid environment with an entry of marginal marine system and good plant tissue preservation. The rare earth elements (REE) in the coal samples studied are characterized by light-REE enrichment. Thermal decomposition resulted in the range of residual mass (RM = 33.67%–61.28%) and mass losses (ML = 38.72% - 66.33%), which attributed to the drying, devolatilization, and coke formation. Thermal reactivity followed the sample order A-5 > A-1 > A-6, which indicates A-5 is more thermally reactive. The results indicate that the coal samples could be exploited for electric power generation.

Geochemical Characteristics of Quartzite in Parts of Paleoproterozoic Dhanjori Group, Singhbhum Craton, Eastern India: Implications for Provenance and Paleoweathering

Abstract Singhbhum craton preserves the records of sedimentation, magmatism, and tectono-thermal events from Mesoarchaean to Neoproterozoic. The Dhanjori Group (DG), located on the northeast margin of the Singhbhum craton, comprises of a variety of rocks including quartz pebble conglomerate, quartzite, schist, interlayered with mafic to intermediate and rarely acidic lava flows, tuff and agglomerate. Petrography and geochemical characteristics of the Dhanjori quartzite have been undertaken to interpret paleoweathering and provenance characteristics. Studied quartzites are made up of abundant quartz, feldspar, mica, and lithic fragments. With the help of geochemical data, the studied quartzites are classified as quartz-arenites and sub-arkoses. In addition to the A-CN-K plot, various chemical indices such as the chemical index of weathering (CIW), chemical index of alteration (CIA), and plagioclase index of alteration (PIA) indicate moderate to intense chemical weathering of the provenance under semi-humid climatic conditions. Rare earth element (REE) chondrite normalized patterns of the studied samples illustrate enriched light rare earth elements (LREEs) (LaN/SmN = 3.11 – 6.19), depleted heavy rare earth elements (HREEs) (GdN/YbN = 0.35 – 3.12) and negative Eu anomaly (Eu/Eu* = 0.55 - 0.87, ~ 0.68). Such patterns are similar to that of the upper continental crust (UCC). In the discrimination function diagram, studied samples of the Dhanjori Group fall in quartzose sedimentary field. In addition, La/Sc vs. Th/Co and La-Th-Sc diagrams, various ratios like Th/Sc (~0.61), La/Sc (~4.42), Th/Co (~0.03), La/Co (~0.11), and Cr/Th (~141.62) imply a mixed provenance for the studied samples. Hence, it has been inferred that the meta-sediments and orthoamphibolites of the older metamorphic group, Singhbhum granitoid complex, as well as associated Archaean metavolcanic suites, would have acted as the probable source rocks for the studied Dhanjori quartzites.

Occurrence and Contamination of Rare Earth Elements in Urban Mangroves of Shenzhen, South China

Mangroves acted as sinks of terrestrial pollutants, but the occurrence and contamination of rare earth elements (REEs) in urban mangroves lacked systematic evaluation. In rapidly developing Shenzhen, China, four typical urban mangroves were selected to determine the REEs in urban mangroves, including Baguang mangrove (BGM) and Futian mangrove (FTM) featured with ecological preserve and central business district, respectively; Xixiang mangrove (XXM) and Shajing mangrove (SJM) both featured with industry district. The mean concentrations of total REEs (TREEs) in sediment (0–25 cm depth, μg g−1) were SJM (465.28) &gt; FTM (411.25) &gt; XXM (342.76) &gt; BGM (118.63), with Ce to be the dominant REEs element. The depositions of REEs in urban mangroves were significantly affected by sediment sulfur accumulation and fine sediment, including silt and clay fractions. The main fractionation pattern of REEs in urban mangroves was the enrichment of light REEs (LREEs) and loss of heavy REEs (HREEs). Geo−accumulation index, modified degree of contamination, pollution load index, and potential ecological risk index showed the moderately contaminated level of REEs in FTM, followed by SJM, and XXM, with uncontaminated level in BGM. This study provided important information on REEs in urban mangroves for pollution prevention and remediation in the future.

Tracing fault‐related fluids using in situ trace elements: A case study in Upper Cambrian dolostone in Gucheng area, Tarim Basin, NW China

The Gucheng area, located in the east of the Tarim Basin, is one of the important gas exploration targets, and the Upper Cambrian dolostone is the main pay layer. The dolostone is considered to be altered by hydrothermal fluids, but the hydrothermal altering degrees are still unclear. In this study we report the petrography and in situ trace elemental data, and try to discuss the hydrothermal fluids and their impact on the Upper Cambrian dolostones. Based on the petrography and CL properties, five types of dolomites are identified. MD1 and MD2 are the matrix dolomites. The crystal size of MD1 range from approximately 30 to 100 μm, while the MD2 is larger than 200 μm. Cement dolomite (CD) occurring only in vugs and fractures is subdivided into three types depending on the CL properties. CD‐zone1 is the core of CD with dull CL colours. CD‐zone2 comprises a bright red CL colour zone and a dull CL colour zone, and CD‐zone3 is the rim of CD dolomite with bright red CL colours. MD2 and CD‐zone1 show light rare earth elements (LREE) depletion, middle rare earth elements (MREE) enrichment and negative Eu anomalies. The REEY patterns of CD‐zone3 dolomite are marked by LREE enrichment and positive Eu anomalies. CD‐zone2 is the transitional mineral phase that shows slightly LREE depletion and negative Eu anomalies. The REEY patterns of CD‐zone1 suggest that CD‐zone1 is likely formed by local redistribution of older dolomites in a closed system. The REEY patterns of CD‐zone3 may indicate a magmatic associated hydrothermal fluid. Based on the petrography and in situ trace elemental data, the Permian magmatic fluid, which is recorded in CD‐zone2 and CD‐zone3 dolomites, may be only limited within fractures, while unlikely significantly altered the matrix dolomite in the Upper Cambrian.

In situ LA-ICPMS U[sbnd]Pb dating and geochemical characterization of fault-zone calcite in the central Tarim Basin, northwest China: Implications for fluid circulation and fault reactivation

Direct evidence for fault reactivation is crucial for understanding long-term fault behavior and reconstruction of fluid circulation and hydrocarbon migration and accumulation during active tectonics. However, absolute dating of fault reactivations and fluid circulation is still challenging due to dissolution and recrystallization of fault zone materials and obliteration of previous events by the latest deformation/hydrothermal event. The lower Ordovician limestone strata at 3.8 km depth in the Central Uplift of the Tarim Basin, northwest China experienced multi-stage regional tectonic activities that developed a series of NW–SE striking reverse faults and NE–SW oriented strike-slip faults. In this study, we performed in situ laser-ablation ICP-MS UPb dating and trace element characterization of calcites collected from borehole cores within one of the main fault zones in the Central Uplift of the Tarim Basin. A new in-house calcite standard AHX-1A (209.8 ± 1.3 Ma), collected from the Tarim Basin, calibrated against well-calibrated WC-1 and ASH-15 calcite standards, is used for mass-bias correction. We obtained in situ UPb ages of 9 calcite samples from two wells within a Paleozoic fault zone in the Tarim Basin. They are 456 ± 11 Ma, 454.7 ± 7.2 Ma, 450.4 ± 6.2 Ma, 435.2 ± 9.7 Ma, 328.0 ± 9.2 Ma and 307.6 ± 7.1 Ma from well TZ2, and 371 ± 18 Ma, 390.6 ± 6.0 Ma and 395 ± 14 Ma from well TZ4 (all reported uncertainties are 2σ). Combined with petrographic evidence, these results define at least six generations of secondary calcite precipitations in the fault zone, that occurred during 456 ± 11 to 450.4 ± 6.2 Ma (weighted mean 452.8 ± 4.3 Ma), 435.2 ± 9.7 Ma, 395 ± 14 to 390.6 ± 6.0 Ma (weighted mean 391.3 ± 5.5 Ma), 371 ± 18 Ma, 328.0 ± 9.2 Ma and 307.6 ± 7.1 Ma. Chondrite-normalized rare earth element (REE) + yttrium (Y) patterns of these calcite samples show prominent positive Gd and Y anomalies, lack of negative Ce anomaly, and enrichment in light REE but depletion in heavy REE, similar to the shallow marine platform host-rock limestone. The results suggest multi-stage fluid circulation under shallow burial, low temperature, and non-oxidizing environments along the fault zone, with the secondary calcite precipitating from a similar fluid source that originated from dissolution of host-rock carbonate or early-stage diagenesis. The detail petrographical and mineralogical analysis of this study, combined with the new interpretation of high-resolution seismic data, constrains two main episodes of faulting and related uplift during 456–435 Ma and 395–371 Ma, as well as a younger faulting episode with weaker intensity during 328–308 Ma. This study demonstrates that the central fault zone of the Tarim Basin experienced ~150 Ma of episodical reactivation during the Paleozoic, which has important implications for hydrocarbon exploration.

Geochemical, mineralogy, and Sr–Nd–Pb isotopic compositions of the gold-related lamprophyre in the Bengbu–Wuhe Area, southeastern North China Craton: Implications for gold mineralization

Besides granite porphyries, many mafic dikes also have a close temporal and spatial relationship with orebodies in the BWGB. However, compared with the granite porphyries, no detailed attempt has been made to determine the petrogenesis of these mafic dikes or to elucidate their relationships with the gold mineralization. Here, we present comprehensive bulk-rock geochemical data; pyrite, apatite, and amphibole compositions; Sr-Nd-Pb isotopes, and U-Pb zircon data for the lamprophyres to provide constrains on their petrogenesis, magmatic properties, geodynamic setting, and metallogenic implications. We obtained zircon U-Pb ages, which reveal that the lamprophyres were emplaced ~ 130 Ma. The lamprophyres are characterized by pronounced light rare earth element (LREE) enrichment, heavy rare earth element (HREE) depletions ((La/Yb)N > 10). They also have low SiO2 (<51 wt%) and high MgO (>4.1 wt%) contents; low Rb/Sr (0.01–0.04), Th/La (0.1–0.12), and Lu/Yb (0.13–0.16) ratios; high Ba/Rb ratios (>18), low Sr-Nd values (87Sr/86Sr(t) = 0.7060–0.7076; εNd(t) = –8.8 to –12.5); and a wide range of radiogenic Pb isotopic ratios (206Pb/204Pb(t) = 16.37–17.35), indicating an enriched mantle source metasomatized by the upper crust of the subducted South China Block (SCB). Their low apatite MnO contents and high apatite SO3 contents, high apatite molar OH/F ratios, and high amphibole Mg* and VIAl* values suggest that the mafic magmas were more highly oxidized and hydrated. Taken together, the lithospheric mantle source was initially metasomatized by the SCB and was further hydrated by the subducted Paleo-Pacific Plate, resulting in a mafic melt with a high H2O content and oxygen fugacity value, which are favorable conditions for gold transportation.

An Intra-Oceanic Subduction System Influenced by Ridge Subduction in the Diyanmiao Subduction Accretionary Complex of the Xar Moron Area, Eastern Margin of the Central Asian Orogenic Belt

This study focuses on the geology, geochemistry, Sr-Nd isotopes and their tectonic settings of three types of basalts in Diyanmiao ophiolite in the Xar Moron area located on the eastern margin of the Central Asian Orogenic Belt. Type I basalts are oceanic tholeiites with a depleted light rare earth element (LREE) pattern, which are similar to the typical N-mid-oceanic ridge basalt (MORB) and suggests that they were formed at a mid-oceanic ridge. The initial 87Sr/86Sr ratios of Type I basalts range from 0.703 966 to 0.705 276 and the eNd(t) values are from 16.49 to 17.15, indicating that they were derived from a depleted mantle source. Type II basalts belong to the medium-potassium calc-akaline series and have the geochemical characteristics of Nb-enriched basalt (NEB) with high Nb content (14.5 ppm) and strong enrichment in LREEs, implying that they were created by the partial melting of mantle wedge peridotite that previously metasomatized by slab melts. Type III basalts are high-Al basalt (HAB) with high-Al contents (Al2O3=16.75 wt.%–18.00 wt.%), distinct Nb depletion and high Th/Yb ratios. Thus they were likely generated in a normal island-arc setting. Therefore, the association of MORB, NEB, and HAB in the study area may be due to the subduction of a mid-oceanic ridge, and the Diyanmiao ophiolite is proposed to be formed in the forearc setting of a mid-oceanic ridge subduction system.

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, “V”-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples, the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

Rare earth elements in Uranium ore for nuclear forensic application

The contents of the Lanthanides, which are Rare Earth Elements (REE), that show consistent patterns under changing geochemical conditions in uranium ore have been studied. The objective is to determine the nuclear forensic parameters inherent to the various uranium ore samples collected from parts of northern Nigeria using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analytical technique for the purpose of baseline data generation and nuclear forensic application. The REE fingerprint obtained in this study suggests that the uranium is of uraninite/pitchblende granitic (vein-type) origin. The REE concentrations varied from 0.011 ± 0.000 ppm to 2.337 ± 0.082 ppm for Riruwai, 0.001 ± 0.000 ppm to 0.035 ± 0.002 ppm for Mika-I, 0.002 ± 0.000 ppm to 0.357 ± 0.007 ppm for Mika-II and 0.001 ± 0.001 ppm to 0.159 ± 0.005 ppm for Michika. A positive correlation between the REEs showed symmetrical chemical properties as well as their overall presence in the samples. The normalised REE/Cl-Chondrites pattern show Light Rare Earth Elements(LREE) enrichment, Heavy Rare Earth Elements (HREE) fractionation with a negative Europium (Eu) anomaly. The ΣLREE/ΣHREE ratio presented varied values for the samples while a negative value of 143Nd/144Nd ratio (0.512638) in the Chondritic Uniform Reservoir (CHUR) ε Nd(-0.64285) suggested LREE uniformity and radiogenic origin.

Late Permian–Early Triassic mafic dikes in the southwestern margin of the South China block: Evidence for Paleo-Pacific subduction

The link of the widespread Late Permian–Triassic magmatism in the southwestern corner of the South China block to a subduction zone or the Emeishan mantle plume is debated. We have carried out an integrated geochronological-petrological-geochemical study of four mafic dikes in the Gulinjing–Nanxi area of this region to shed new light on the issue. Zircon grains from the Gulinjing–Nanxi mafic dikes yield UPb ages from 254 ± 2 to 250 ± 2 Ma, indicating that they are coeval with abundant felsic intrusive-extrusive rocks in the region, but are 6–7 myr younger than the nearby Emeishan flood basalts and associated mafic-ultramafic intrusions. The Gulinjing–Nanxi mafic dikes are characterized by light rare-earth element enrichments and pronounced negative NbTa anomalies, similar to typical arc basalts worldwide, plus enriched Sr-Nd-Hf isotope compositions (initial 87Sr/86Sr from 0.7088 to 0.7103, εNd(t) from −6.6 to −4.6, and zircon εHf(t) from −3.7 to −0.3). The isotopes and incompatible trace element ratios indicate that the parental magmas for the Gulinjing–Nanxi mafic dikes are consistent with contaminated arc mafic magmas, but not contaminated Emeishan flood basalts in the region. This, together with a significant age difference between the mafic dikes and the Emeishan flood basalts and associated mafic-ultramafic intrusions in the nearby areas, support the interpretation that the Gulinjing–Nanxi mafic dikes are unlikely to be parts of the Emeishan mantle plume. Based on regional igneous association and the distribution of known paleo subduction zones in the surrounding regions, we conclude that the Gulinjing–Nanxi mafic dikes are linked to Paleo-Pacific subduction to the south, and not Paleo-Tethys subduction to the west.