Fractionated Rare Earth Element Patterns Research Articles

Late Paleozoic Tectonic Evolution of the Northern Great Xing’an Range, Northeast China: Constraints from Carboniferous Magmatic Rocks in the Wunuer Area

Northeast China composes the main part of the Central Asian Orogenic Belt. Traditionally, Northeast China has been considered a collage of several microcontinental blocks. However, the tectonic evolution of these blocks remains uncertain. Igneous rocks can be used to infer the magmatic histories of the blocks and thus help reconstruct their evolution. In this study, we present new zircon U–Pb and whole-rock geochemical data for Carboniferous igneous rocks from the Wunuer area, northern Great Xing’an Range, Northeast China, to constrain the Carboniferous amalgamation of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs. On the basis of zircon U–Pb dating results, we identify two main stages of magmatism, i.e., early Carboniferous (332–329 Ma) and late Carboniferous (312–310 Ma). The early Carboniferous igneous rocks include diorites and granodiorites, with the former being classified as calc-alkaline to tholeiitic and the latter as tholeiitic. Both rock types are enriched in Th and U and depleted in Nb and Ti. The rocks display slightly fractionated rare earth element (REE) patterns, with an enrichment in light REEs and a depletion in heavy (H)REEs. The geochemical characteristics of the early Carboniferous rocks indicate that they formed in a subduction-related continental-arc setting. The late Carboniferous igneous rocks include monzogranites and syenogranites, both of which are classified as high-K calc-alkaline rocks and show enrichment in Th, U, and Rb and depletion in Nb and Ti. The rocks display strongly fractionated REE patterns, with an enrichment in light REEs and a depletion in HREEs. The geochemical characteristics of the late Carboniferous rocks indicate that they formed in a syn-collisional tectonic setting. Combining the new geochronological and geochemical results and inferred tectonic settings with regional magmatic data, we propose a new three-stage model to interpret the late Paleozoic tectonic evolution of the united Xing’an–Erguna and Songnen–Zhangguangcai Range massifs of Northeast China: (1) early Carboniferous (360–340 Ma) subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and formation of the Wunuer oceanic basin in the Yakeshi area; (2) early to late Carboniferous (340–310 Ma) sustained subduction of the Paleo-Asian oceanic plate beneath the united Xing’an–Erguna Massif and initiation of subduction of the Wunuer oceanic basin; and (3) late Carboniferous–early Permian (310–275 Ma) syn-collisional to post-collisional tectonic transition between the united Xing’an–Erguna Massif and the Songnen–Zhangguangcai Range Massif.

Critical metal geochemistry in groundwaters influenced by dredged material

This study investigated critical metal (CM) geochemistry including rare earth elements (REEs), Co, Ni, and Mn in groundwaters below and surrounding two dredged material placement facilities (DMPFs). Metal concentrations are elevated at both sites, spanning several orders of magnitude. The highest CM concentrations measured exceed many environments considered as aqueous resources (Co and Ni > 1 mg L−1, REEs > 3 mg L−1). Correlations between sulfur and iron, major cations, and CMs indicate that oxidation of sulfides present in the DM releases metals both directly from sulfide minerals and indirectly through acid dissolution of and/or desorption from additional minerals. REE fractionation patterns indicate that their mobility in the groundwaters may be influenced by interactions with silicate, carbonate, and phosphate minerals. Significant positive Gd and Eu anomalies were observed, which may be attributed to increased mobility of Eu2+ and anthropogenic Gd. Nanogeochemical analysis of filtered samples revealed several REE-bearing nanoparticulate (diameter < 100 nm) species, some of which co-occurred with aluminum, suggesting an (oxy)hydroxide or a clay mineral component. Further characterization of soluble and nano scale geochemical speciation is needed to fully assess the viability of CM recovery from DM-associated groundwater. CM recovery from DM-associated waters can provide a beneficial use, both offsetting costs associated with disposal, and supplementing domestic CM resources.

Geochronological and geochemical constraints on the petrogenesis of alkali granites from the Makrohar Granulite Belt: Evidence for Mesoproterozoic extensional regime in the eastern Central Indian Shield

The Chotanagpur Gneissic Complex (CGC) is characterized by the Makrohar Granulite Belt (MGB) at its north‐western margin parallel to Son‐Narmada lineaments. The MGB exhibits a typical association of mantle‐derived mafic tholeiitic and alkaline rocks along with the felsic units. The zircon U–Pb data on the intrusive granite gneiss from this association define a crystallization age of 1,498 ± 38 Ma, representing a widespread Mesoproterozoic within‐plate magmatic event in CGC synchronous with the breakup of the Columbia Supercontinent. These granite gneisses have an alkaline affinity and are metaluminous in character. They exhibit many of the geochemical characteristics of anorogenic (A‐type) magmas, including enrichment of incompatible trace elements, like Zr, Hf, Nb, Y, Ga, and rare earth elements (REE), but low in Ba and Sr as well as high FeOt/(FeOt + MgO) (~0.98) values and Ga/Al (~3.92) ratios. They show less fractionated REE patterns, characterized by relatively enriched LREE and flat HREE with negative Eu anomaly, and have high Zr‐saturation temperatures (~955°C). Considering their field characteristics and all the geochemical and isotopic features, we conclude that they were derived from melting the lower crust metasomatized by mantle‐derived alkali‐rich fluids due to asthenospheric upwelling.

Geochemistry and new zircon U–Pb geochronology of Mesoproterozoic Punugodu granite pluton, SE India: implications for anorogenic magmatism along the western margin of Nellore Schist Belt, India

AbstractWe report a new zircon U–Pb age of 1257 ± 6 Ma for the Punugodu granite (PG) pluton in the Eastern Dharwar Craton (EDC), Southern India. The Mesoproterozoic PG is alkali feldspar hypersolvus granite emplaced at shallow crustal level, as evident from the presence of rhyodacite xenoliths and hornfelsic texture developed in the metavolcanic country rocks of the Neoarchaean Nellore Schist Belt (NSB). Geochemically, the PG is metaluminous, ferroan and alkali-calcic, and is characterized by high SiO2 and Na2O + K2O, Ga/Al ratios &gt;2.6, high-field-strength elements and rare earth element (REE) contents with low CaO, MgO and Sr, indicating its similarity to anorogenic, alkali (A-type) granite. The highly fractionated REE patterns with negative europium anomalies of PG reflect its evolved nature and feldspar fractionation. Mafic (MME) to hybrid (HME) microgranular enclaves represent distinct batches of mantle-derived magmas that interacted, mingled and undercooled within the partly crystalline PG host magma. Felsic microgranular enclaves (FME) having similar mineralogical and geochemical characteristics to the host PG most likely represent fragments of marginal rock facies of the PG pluton. The PG appears to be formed from an oceanic island basalt (OIB)-like source in an anorogenic, within-plate setting. The emplacement of PG (c. 1257 Ma) in the vicinity of Mesoproterozoic Kanigiri Ophiolite (c. 1334 Ma) shows an age gap of nearly 77 Ma, which probably suggests PG emplacement in an extensional environment along a terrain boundary at the western margin of the Neoarchaean NSB in the EDC.

Rare earth element geochemistry in soils along arid and semiarid grasslands in northern China

BackgroundRare earth elements (REE) are a group of trace elements that behave geochemically coherently. REE fractionation patterns normalized to reference materials provide a powerful tool for documenting pedogenesis. In-soil processes are particularly difficult to illustrate with respect to contemporary and past climate conditions. In this study, we characterize the rare earth element (REE) contents in bulk soils and respective geochemical fractions (e.g., exchangeable, carbonate-bound, reducible, and oxidizable fractions) and to decipher the relationships between REE geochemistry components and climatic factors across a large-scale northern China transect (NCT).ResultsAcross the NCT, bulk REE concentrations ranged from 55.2 to 241.1 μg g−1 with a main portion in the residual fraction (49–79%), followed by oxidizable fraction (2–40%), reducible fraction (3–22%), carbonate-bound fraction (0.1–16%), and negligible exchangeable fraction. The REE contents of geochemical components (carbonate-bound, reducible, and oxidizable) in topsoils correlated to climate factors (mean annual precipitation, mean annual temperature, potential evaporation, and aridity index (AI)). The normalized abundances to the upper continental crust (UCC) composition show that the middle REE was generally enriched than the light REE and heavy REE in topsoils along the transect. The overall UCC-normalized bulk REE patterns in topsoils and subsoils were similar, characterized by weak negative Ce anomalies and positive Eu anomalies.ConclusionsOur data in topsoils and depth profiles collectively suggest that cycling of REE was primarily regulated by abiotic processes in area with AI < 0.2, while the biological effect on REE circulation in soil played a more effective role in area with AI > 0.3. The similar UCC normalized patterns in topsoils suggest that the REE was originated from a common source with limited influences from other sources (e.g., atmospheric dusts and anthropogenic contributions). Our results to some extent provide evidence for climatic influence REE distribution patterns both in topsoils and subsoils across the continental-scale transect. Our investigation gives insights into future studies on vertical REE mobility and its associated biogeochemical pathways.

From subduction initiation to hot subduction: Life of a Neoarchean subduction zone from the Dengfeng Greenstone Belt, North China Craton

Abstract We report a spatially and temporally linked arc magmatic association of 2.55–2.50 Ga mid-ocean ridge basalt (MORB)-affinity gabbros, arc-affinity basalts, high-Mg basalts/basaltic andesites (HMBA), Nb-enriched basalts (NEB), and a tonalite-trondhjemite-granodiorite (TTG)-like granodiorite from the Dengfeng greenstone belt (DFGB), North China Craton. These are identical to arc magmatic rock suites from hot subduction in the present plate mosaic, and resemble suites formed during subduction initiation. Laser ablation–inductively coupled plasma–mass spectrometry zircon U-Pb dating indicates that gabbros and granodiorites intruded at ca. 2.55 Ga and the HMBAs formed at ca. 2.50 Ga, indicating a long duration of subduction zone magmatic activity of at least 50 m.y. in the DFGB. The gabbros are characterized by flat light-rare earth element (LREE) patterns without negative Nb and Zr anomalies, showing a MORB-like geochemical affinity. Combined with previously reported normal-MORB-type basalts, we suggest that they may represent magmatic products during intraoceanic subduction initiation where their mantle source was slightly metasomatized by subduction-derived fluids during the initiation stage. The arc-affinity basalts are characterized by slightly enriched LREE patterns with negative Nb and Zr anomalies. The HMBAs have higher contents of MgO, Ni, and Cr and display more fractionated rare earth element (REE) patterns and large negative Nb and Zr anomalies than the arc-affinity basalts. The NEBs are characterized by high absolute contents of Nb (9.9–14 ppm) and high ratios of Nb/Laprimitive mantle (pm) (0.40–0.46) and Nb/Thpm (0.44–0.54), and moderately fractionated REE and minor negative Nb anomalies with no Zr anomalies. One granodiorite sample is characterized by a highly fractionated REE pattern and negative Nb and Zr anomalies. Geochemical modeling suggests that the association of the normal arc-affinity basalt (NAB)-HMBA-NEB can be interpreted to be generated by hybridization of mantle wedge peridotites by slab-derived TTG-like melts. Positive values of whole-rock εNd (t) and zircon εHf (t) of the 2.55–2.50 Ga magmatic associations are consistent with a long-term depleted mantle source for the mafic assemblage. The 2.55–2.50 Ga magmatic association from MORB-affinity gabbros and basalts to arc-affinity NAB-HMBA-NEB may record a continuous Neoarchean geodynamic process from intraoceanic subduction initiation to mature arc magmatism. The NAB-HMBA-NEB association with regional sanukitoids and high-Al TTGs indicates that hot subduction may have played an important role in the production of arc-related magmatism during the Archean.

Effects of topography and soil properties on the distribution and fractionation of REEs in topsoil: A case study in Sichuan Basin, China

In order to investigate how topographic factors and soil physicochemical properties influenced the distribution and fractionation of rare earth elements (REEs) in soil, Jiangjin district of Sichuan Basin, an area with mountainous topography, was selected as a study area. The concentration of REEs, pH and organic matter (OM) and major elements in 156 topsoil samples were measured and analyzed. The topographic factors considered were elevation, slope, and topographic wetness index (TWI), which were extracted by using the digital elevation model (DEM). The median concentration of total REEs in topsoil of the study area was 147 mg/kg, lower than the Chinese soil background value (164 mg/kg). The concentration of LREEs and HREEs, and the ratio of LREEs/HREEs and LaN/YbN indicated that the distribution and fractionation patterns of REEs in topsoil were LREEs-enriched. Significant Eu negative anomalies and weak Ce negative anomalies were observed in topsoil according to the median values of δEu (0.57) and δCe (0.89). The coefficient of weathering and eluviation (BA), an important factor affecting the distribution and fractionation of REEs, was substantially correlated with δEu (r = 0.344, p < 0.01), δCe (r = −0.252, p < 0.01), ∑REEs (r = 0.135, p < 0.01), and LREEs/HREEs (r = −0.281, p < 0.01) in topsoil. Soil pH and OM had some influence on the distribution and fractionation of REEs. Under the geographical environment of the study area, Ce was positive anomaly with the elevation and slope increasing. The enrichment of LREEs was more significant than HREEs as elevation increased. The findings revealed that topographical attributes and soil physicochemical properties integratedly influenced the distribution and fractionation of REEs in topsoil.

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.

Two contrasting Neoarchean metavolcanic rock suites in eastern Hebei and their geodynamic implications for the northern North China Craton

The late Archean was a crucial transition period for global geodynamics. Metavolcanic rocks, as one of the predominant components of Archean cratons, are key to deciphering the geodynamic regimes of early Earth crust-mantle interactions. Neoarchean supracrustal rocks in the central K-rich granitoid belt of the eastern Hebei-western Liaoning Province, northern North China Craton, may be subdivided into a lower metavolcanic sequence and an upper metavolcanic-sedimentary sequence by an angular unconformity.The lower sequence metavolcanic rocks consist primarily of 2558–2536 Ma amphibolite to granulite facies metamorphosed basaltic-andesitic rocks and high- and low-MgO dacitic rocks. The basaltic-andesitic samples display calc-alkaline affinity, high MgO contents, low (Nb/La)N and moderate (Hf/Sm)N values and were most likely derived from partial melting of mantle materials metasomatized by subducted slab- and sediment-derived melts and fluids. The high-MgO dacitic samples are characterized by strongly fractionated rare earth element (REE) patterns and relatively high MgO contents, which resemble typical high-SiO2 adakites. The magmatic precursors originated from subducted oceanic slabs and sediments. The samples with low-MgO dacite compositions have the highest SiO2 and lowest MgO contents, and the magmatic precursors were generated by partial melting of metamorphosed high-K mafic rocks and sedimentary rocks in the lower crustal level.The upper sequence metavolcanic rocks chiefly comprise greenschist to amphibolite facies metamorphosed tholeiites, tholeiitic to transitional basalts, calc-alkaline basalts, andesites, and dacites with magmatic crystallization ages of 2522–2511 Ma. The tholeiite samples are characterized by left-declined REE patterns and high (Nb/La)N and chondrite-like (Hf/Sm)N values resembling typical N-MORBs and were formed by partial melting of a depleted mantle source. The tholeiitic to transitional basalt samples resemble back-arc basin basalts and display weakly right-declined REE patterns, mildly negative Nb and Ti anomalies, and low (Nb/La)N and chondrite-like (Hf/Sm)N values. Their magmatic precursors were derived from partial melting of a slightly fluid- and melt-metasomatized depleted mantle source. The calc-alkaline basalt and andesite samples exhibit fractionated REE patterns and apparent Nb, Ta, and Ti depletions and originated from a strongly fluid- and melt-metasomatized depleted mantle source. The dacite samples show the highest SiO2 and lowest MgO contents in the upper sequence metavolcanic rocks and were derived from partial melting of lower crustal metasedimentary rocks. Systematic petrological, geochemical, and petrogenetic studies indicate that a mature continental arc setting and a back-arc basin setting may account for the formation of the lower and upper sequence metavolcanic rocks, respectively. Three stages of deformation can be identified in the K-rich granitoid belt, including 2525–2505 Ma extensional deformation in a back-arc basin setting (D1), ca. 2500 Ma top-to-the-NEE-SSE thrusting in a collisional orogenic setting (D2) and 2500–1800 Ma nearly N-S-oriented strike-slip shearing (D3), with D2 deformation accompanied by the synchronous occurrence of paired high-pressure and high-temperature medium-pressure granulite facies metamorphism. Integrating the petrogenesis, spatiotemporal relationships, deformational and metamorphic features of the Archean lithological assemblages, we consider that the late Neoarchean K-rich granitoid belt was formed in an active continental margin setting with a southeastward subduction polarity and experienced multi-stage trench retreats and a subsequent collision between the arc and continent.

Paleoproterozoic metaluminous syenites synchronous with the c. 2.21 Ga mafic dyke swarms from the Eastern Dharwar Craton, India: implications for alkaline magmatism associated with the breakup of supercraton Superia

Abstract The Eastern Dharwar Craton (EDC) hosts numerous Late Neoarchean to Paleoproterozoic syenites whose genesis remains unclear. Here we present a petrological and geochemical study on the syenites from Peddavaduguru, Danduvaripalle and Vannedoddi, towards the western margin of the Paleo-Mesoproterozoic Cuddapah Basin in the EDC. These syenite bodies constitute a part of the Paleoproterozoic (2210 ± 110 Ma) Dancherla alkaline complex and are contemporaneous with a mafic dyke swarm emplacement in the EDC. The Danduvaripalle and Vannedoddi syenites display geochemical affinities to adakites. The Peddavaduguru syenite shows a negative Eu anomaly and relatively gentle chondrite-normalized rare earth element (REE) pattern, suggesting an origin by a different process. The ɛ Nd values range between 0.5 and 0.8 for the Peddavaduguru syenite, − 5.2 and − 4.2 for the Danduvaripalle syenite, and − 6.0 and − 1.0 for the Vannedoddi syenite. In tectonic discrimination diagrams, the Peddavaduguru syenite shows affinities to within-plate granitoids similar to syenites from the Deccan large igneous province whereas the others show geochemical similarities to arc-related alkaline rocks and volcanic arc granitoids. The adakitic syenites show deficiency of MgO, Ni, Cr and Sc, highly fractionated REE patterns and negative Nb–Ta–Ti anomalies along with low Nb/U and high Th/U ratios. These geochemical traits are compatible with their origin by the partial melting of a mafic crustal source that subsequently underwent fractionation of amphibole and garnet responsible to impart an adakitic character. We suggest that the crustal source of these syenites underwent partial melting by heat from the rising plume during the Paleoproterozoic extension of the Superia supercraton. The non-adakitic Peddavaduguru syenite, on the other hand, is suggested to have originated from direct fractionation of mafic magma.

Petrogenesis of Cretaceous granitoids in the Bengbu–Wuhe area, southeastern North China Craton: Implications for gold mineralization

Sinistral slip along the Tancheng–Lujiang Fault Zone (TLFZ) during the Mesozoic resulted in an offset of approximately 400 km between the Dabie and Sulu orogens. The Bengbu–Wuhe gold belt (BWGB) represents an extension of the Zhaoyuan–Yexian gold belt to the west of the TLFZ. Early Cretaceous intrusions are widely distributed throughout the BWGB. Gold deposits in the BWGB are commonly associated with intermediate acid dykes that are roughly contemporaneous with mineralization, and some orebodies are hosted in granitoids. This paper investigates granitoids within the BWGB to constrain their petrogenesis, tectonic setting, and metallogenic significance using systematic whole-rock elemental geochemistry, apatite geochemistry, zircon U–Pb dating, zircon Lu–Hf isotopes, and whole-rock Sr, Nd, and Pb isotopes. The timing of Au mineralization (134–113 Ma) in the area is consistent with the age of intrusive adakite-like rocks (130–115 Ma) and normal calc-alkaline granitoids (114–109 Ma). The adakite-like samples are characterized by pronounced enrichment in light rare earth elements (REE), depletion in heavy REE ((La/Yb)N = 30.5–66.2), an absence of Eu anomalies, high Sr contents and Sr/Y ratios, low Y and Yb contents, and fractionated REE patterns ((Dy/Yb)N = 1.22–1.69). They have relatively low Mg# values (38–42) and variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7083–0.7111; εNd(t) = −22.2 to −14.9; 206Pb/204Pb(t) = 17.219–18.010; zircon εHf(t) = −21.0 to −12.3). These features indicate that the parental magmas of the adakites were derived from partial melting of thickened lower crust of the South China Plate and/or the North China Craton. The normal calc-alkaline granitoids have low Sr/Y (6.0–40.5), La/YbN (6.8–24.7), and Dy/YbN (0.90–1.28) ratios, exhibit negative Eu anomalies, and have variable Sr–Nd–Pb–Hf isotopic compositions (87Sr/86Sr(t) = 0.7082–0.7085; εNd(t) = −22.7 to −17.7; 206Pb/204Pb(t) = 16.686–16.713; zircon εHf(t) = −24.9 to −19.0), indicating they were derived from the middle to lower crust of the North China Craton. Compared with the normal calc-alkaline granitoids, the adakite-like rocks have higher zircon Ce4+/Ce3+, higher apatite SO3 and lower apatite MnO contents, lower and more variable zircon crystallization temperatures, and higher apatite molar OH/F and Cl/F ratios, indicating that the adakitic magmas were more enriched in volatiles and more highly oxidized. Taken together, field observations and geochemical data suggest that the adakite-like rocks related to the subducted South China Block are the ore-causative rocks.

Rare earth element cycling and reaction path modeling across the chemocline of the Pettaquamscutt River estuary, Rhode Island

Rare earth elements (REEs) were measured in the water column of the highly stratified and euxinic Upper Basin of the Pettaquamscutt River estuary (Rhode Island) to investigate their cycling and evolution across the chemocline. The euxinic bottom waters of the estuary exhibit total dissolved sulfide (i.e., ΣS-II) concentrations up to 4 mmol kg−1, which exceeds values of the Black Sea by nearly 10-fold and makes this system ideal for study of redox-sensitive elements. The REE concentrations decrease with depth in the oxic surface waters, before substantially increasing across the chemocline, corresponding to redox cycling of manganese (Mn) and iron (Fe). For example, the mean ± 1σ neodymium (Nd) concentration in the oxic surface waters is 511 ± 184 pmol kg−1, but increases by approximately 5-fold across the chemocline reaching 2476 pmol kg−1 at 7.4 m depth. Concurrently, Mn and Fe concentrations increase by 5- and 11-fold, respectively, within the chemocline relative to their oxic surface water values. The pore water within the Upper Basin sediments exhibits REE concentrations that are on average 130-fold greater than their values in the overlying waters, driving an upward diffusive REE flux into the euxinic bottom waters. An outstanding feature of the REEs in this study is the preservation of negative cerium (Ce) anomalies across the chemocline into the highly euxinic bottom waters. Likewise, our reaction path model shows that the mass balance of the local water sources is the major driver of the REE compositions of the water column. Primarily, the negative Ce anomaly in the euxinic bottom waters highlights the influence of the Ce depleted sediment pore water on the REE composition and fractionation patterns of the euxinic bottom waters. This study underscores the importance of local sources and indicates that negative Ce anomalies can persist in highly euxinic waters that evolve from Ce depleted sources, further demonstrating that negative Ce anomalies are not necessarily a good proxy of the redox conditions of aqueous environments.

Late Neoarchean volcanic rocks in the southern Liaoning Terrane and their tectonic implications for the formation of the eastern North China Craton

The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane (SLT) of the eastern North China Craton (NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt (Group#1), basaltic andesite (Group#2), dacite (Group#3) and rhyodacite (Group#4). LA-ICP-MS zircon U–Th–Pb dating reveals that they formed at ~2.53–2.51 ​Ga. Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element (REE) patterns with low (La/Yb)N ratios and a narrow range of (Hf/Sm)N ratios, and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids. Compared to Group#1 samples, Group#2 samples display strongly fractionated REE patterns with higher (La/Yb)N ratios and more scattered (Hf/Sm)N ratios, indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids. Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns, which resemble typical high-Si adakites, and the magmatic precursors were derived from partial melting of a subducted oceanic slab. Group#4 samples have the highest SiO2 and the lowest MgO and transition trace element contents, and were derived from partial melting of basaltic rocks at lower crust levels. Integrating these tholeiitic to calc-alkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses, the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin. Furthermore, the affinities in lithological assemblages, metamorphism and tectonic regime among SLT, eastern Hebei to western Liaoning Terrane (EH–WLT), northern Liaoning to southern Jilin Terrane (NL–SJT), Anshan-Benxi continental nucleus (ABN) and Yishui complex (YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.

Petrogenesis of the Cretaceous granitoids in Zhejiang, northeast South China Block and their implications for episodic retreat and roll-back of the Paleo-Pacific Plate

Abstract Two Cretaceous granitoid belts (i.e., the northwest and southeast belts) have been identified in Zhejiang, northeast South China Block. In this study, seven granitoid plutons from both the two belts were collected for zircon U-Pb dating, whole-rock geochemistry, Sr-Nd isotope, and zircon Hf isotope analyses. Chronologically, the Longyou (132 Ma), Sucun (136 Ma), Shanghekou (131 Ma), and Huangshitan (ca. 126 Ma) plutons from the northwest belt display older magma crystallization age than those of the Xiaoxiong (100 Ma), Zhujiajian (108 Ma), and Qingbang island (108 Ma) plutons from the southeast belt. The Sucun quartz monzonite and the Longyou, Shanghekou, Zhujiajian, and Qingbang island granites therein are fractionated I-type granites (i.e., partial melting of meta-igneous rocks) with relatively moderate-low Zr saturation temperature (723–823 °C) and pronouncedly evolved Nd and Hf isotopic compositions (εNd(t) = –8.17 to –5.67 and εHf(t) = –15.07 to –5.67), indicating that they are derivatives of ancient crustal melt-dominated magmas. The Huangshitan granite shows A-type granitic (i.e., granites that are alkaline and anhydrous and from anorogenic setting) features with high Ga/Al (3.47–5.58), rare earth element (REE) content (271–402 ppm), and Zr saturation temperature (781–889 °C). It holds less enriched Nd and Hf isotopic compositions (εNd(t) = –4.13 to –3.60 and εHf(t) = –5.90 to –2.16) and is attributed to partial melting of mature crustal materials with minor basaltic magma incorporation. The Xiaoxiong (quartz) syenitic porphyry is characterized by moderate SiO2 content (60.68–69.92 wt%), high alkali (9.03–11.66 wt%) and REE contents with fractionated REE pattern [(La/Yb)N = 13.8–26.1]. Its relatively depleted Nd and Hf isotopic compositions (εNd(t) = –3.67 to –3.42 and εHf(t) = –5.76 to –2.25) imply that it could be a derivative of basaltic magma from K-rich metasomatized mantle. Available geochronological data indicate that there were two episodic magmatic pulses at ca. 140–120 Ma and ca. 110–85 Ma associated with the Paleo-Pacific Plate underthrusting beneath the northeast South China Block. Here we put forward an episodic slab retreat and roll-back model to account for generation of these magmatic rocks. Firstly, the subducting Paleo-Pacific slab roll-back initiated at ca. 140 Ma and reached climax at ca. 130–120 Ma, which led to formation of the Longyou, Sucun, and Shanghekou I-type granites and the Huangshitan A-type granite, respectively. Subsequently, a flat slab subduction stage occurred with eastward trench retreat, causing a period of magmatic quiescence from ca. 120 to 110 Ma. The following second slab roll-back started at ca. 110 Ma and reached climax at ca. 100 Ma, giving rise to the earlier Zhujiajian and Qingbang island I-type granites and the later Xiaoxiong (quartz) syenitic porphyry.

Accumulation patterns and species-specific characteristics of yttrium and rare earth elements (YREEs) in biological matrices from Maluan Bay, China: Implications for biomonitoring

The critical usage of rare earth elements (REEs) in a variety of industrial applications has increased their release to the environment as emerging contaminants, while little is known about the fate and transport of REEs in coastal aquatic biota. In the present study, seven common species were collected and the concentrations of 15 naturally occurring REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) were determined. Significant differences in total REEs concentrations were found among species even in the same taxa or phylum, suggesting that REEs bioaccumulation patterns appeared to be species- and element-dependent even in the same taxa or phylum, but with limited potential for bio-magnification based on the nitrogen isotope signatures (δ15N). Except for occasional anomalies for redox-sensitive elements of Ce and Eu, the abundance patterns of REEs normalized to chondrite revealed similar REE distribution trends, indicating a common source of REEs in all samples. Additionally, the abundances of light REEs (from La to Eu) were much higher than those of heavy REEs (from Gd to Lu and Y), demonstrating the fractionation between the light and heavy REEs. Furthermore, REEs concentrations in molluscs were notably higher than other species, implying their potential as bio-indicators of REEs due to the habitat and specific feeding behavior. Overall, this is not only the first study to focus on distribution levels, accumulation characteristics, geochemical and fractionation patterns of REEs in coastal species from identical area, but quantifying and tracing REE behavior will contribute to better evaluating the possible environmental impacts of REEs enrichment for future biomonitoring research.

Behavior of rare earth elements in an aquifer perturbed by CO2 injection: Environmental implications

Three cubic-meters of CO2-saturated water was injected into a subsurface fractured aquifer in a post-mined area, using a push-pull test protocol. Groundwater samples were collected before and after CO2-injection to quantify geochemical changes. CO2-injection initially reduced the pH of water from 7.3 to 5.7, led to the enrichment of major ions (Ca2+, Mg2+, and alkalinity), and dissolved trace metals (including Fe, Mn, As, and Zn) in the groundwater. Rare earth elements (REE) and yttrium concentrations were also measured in these samples before and after CO2 perturbation, to evaluate their behavior. An enrichment of total Y plus REE (REY) occurred. REY fractionation was observed with higher heavy REE (HREE) enrichment compared to light REE (LREE), and significant variations in La/Yb and Y/Ho ratios were observed following CO2 perturbation. Enrichment by a factor of three was observed for Y, Lu, and Tm, and by nearly one order of magnitude for Dy and Yb. A geochemical model was used to evaluate the amount of REE aqueous ions complexed throughout the experiment. Modeling of the results showed that speciation of dissolved REE with carbonate, along with desorption from iron oxyhydroxide surface were the main factors controlling REE behavior. This study increases an understanding of dissolved REE behavior in the environment, and the potential use for applying iron oxides for REE recovery from mine drainages. Furthermore, the description of REE fractionation patterns may assist in surveying CO2 geological storage sites, surveying underground waste disposal sites, and for understanding the formation of ore deposits and fluid inclusions in geological formations.

Thickness and geothermal gradient of Neoarchean continental crust: Inference from the southeastern North China Craton

The thickness and geothermal gradient of Archean continental crust are critical factors for understanding the geodynamic processes in Earth's early continental crust. Archean tonalite-trondhjemite-granodiorite (TTG) gneisses provide one of the potential indicators of paleo-crustal thickness and geothermal gradient because crust-derived TTG melts are generally thought to originate from partial melting of mafic rocks at the crustal root. In the Western Shandong Province (WSP) of the North China Craton (NCC), two episodes of Neoarchean TTG magmatism are recognized at ~2.70 Ga and ~2.55 Ga which were sourced from partial melting of juvenile crustal components. The ~2.70 Ga TTG gneisses show highly fractionated rare earth element (REE) patterns (average (La/Yb)N = 39), whereas the ~2.55 Ga TTG gneisses have relatively less fractionated REE patterns (average (La/Yb)N = 18). Petrogenetic evaluation suggest that the magmatic precursors of the TTG gneisses of both episodes originated from partial melting of juvenile crustal materials at different crustal depths with residual mineral phases of Grt, Cpx, Amp, Pl and Ilm. Together with the garnet proportion in the residue, the P–T pseudosections of equilibrium mineral assemblages, and the temperature calculated from Titanium-in-zircon thermometer, we estimate the Neoarchean crustal thicknesses as 44–51 km with geothermal gradients of 17 to 20 °C/km for the ~2.70 Ga TTG gneisses whereas the ~2.55 Ga TTG gneisses show lesser crustal thicknesses of 35–43 km with geothermal gradients of 19 to 26 °C/km, with an approximately 10 km difference in crustal thickness. Our estimates on the thicknesses and geothermal gradients of the Neoarchean crust are similar to those (~41 km, ~20 °C/km) of the modern average continental crust, indicating that a modern-style plate tectonic regime may have played an important role in the formation and evolution of the Neoarchean continental crust in the NCC.

Petrology and geochemistry of the Yoro-Yangben Pan-African granitoid intrusion in the archaean Adamawa-Yade crust (Sw-Bafia, Cameroon)

Abstract: South of Bafia (Cameroon), the Pan-African Yoro-Yangben massif is emplaced in the Adamawa-Yade block, an archaean-paleoprotrozoic micro-continent that detached from the Congo craton during the early Neoproterozoic. This emplacement within a micro-continent raises the problematic of its (i) origin either by the melting of a subducted slab and the mantle wedge, or by the melting of the base of a thick crust or both, and (ii) bearing on the evolution of the Pan-African orogeny in Cameroon. Granodiorites, quartz monzonites, quartz diorites and adamellites occur as massive bodies crosscut by dykes of gabbros and granites. The texture varies progressively from granular bands at the core of the massif to foliated texture towards the border. Mineralogical composition is constant in all the rock types (Am+Bt+Pl+Kfs+Qtz+Op+Sph+Zrn+Ap), except the adamellites which are amphibole-free. Chemically, these potassic rocks are either magnesian and metaluminous, or ferroan and peraluminous. Quartz diorites, granodiorites and granites are High-K calc-alkaline whereas quartz monzonites, adamellites and gabbros are shoshonitic. Most incompatible elements (e.g. Nb, Zr) show an erratic variation with increasing silica contents. Granites rare earth elements (REE) patterns are highly fractionated with a positive Eu anomaly (Eu/Eu* = 2.50–2.04) compared to less fractionated REE patterns of adamellites, quartz monzonites, and granodiorites. The negative anomalies in U, Nb, Ta and Ti shown by gabbros, quartz diorites, quartz monzonites and granodiorites spider diagrams as Th, K, Pb, Zr and Hf positive anomalies for the adamellites and granites patterns are consistent with magmas derived from a subduction setting. The low 87Sr/86Sr(600) initial ratio (0.697–0.706) and eNdi values (−0.82706- 1.03707) of the rocks plot in the mantle array. However, a wide variation of the 87Sr/86Sr ratio values with constant eNdi suggests an enrichment in radiogenic 87Sr likely from an old crust displaying high Rb/Sr ratio. The variations of the La/Yb, Y/Nb and Zr/Nb ratios preclude the fractional crystallization process. Moreover, these characteristics, combined with the erratic (Zr, Nb) suggest particular magmatic sources and complex fusion processes to the Yoro-Yangben heterogeneous granitoids. The lower range of Ba/Nb values (130–135) and the occurrence of shoshonitic magmas likely point to the melting of an oceanic slab; while the higher range (225–230) indicates a blend of melts from oceanic slab and the associated sediments. Granite compositions are similar to melting liquids of metagreywackes. La/Sm and Sm/Yb ratios in gabbros, quartz monzonites and quartz diorite indicate an origin by a batch melting of phlogopite-amphibole-garnet lherzolite, whereas granodiorites and adamellites parent magmas may have originated from a batch melting of a metasomatized spinel lherzolite. Whole rock Sm-Nd and Rb-Sr results yield a unique age of 600 Ma, assigned to the collision time between the West-African and the Congo cratons. Thus, the Yoro-Yangben intrusion is part of the numerous Pan-African granitoids in Cameroon, South of Chad and East of Nigeria.

Discrimination of rare earth element geochemistry and co-occurrence in sediment from Poyang Lake, the largest freshwater lake in China

Geochemical distribution of trace elements in sediments could reflect the impact of anthropogenic activities on environmental changes in aquatic ecosystems. In this study, rare earth elements (REEs) were used as geochemical tracers to study the environmental processes in a complex and dynamic aquatic environment. Both surface and core sediment samples were collected from Poyang Lake, the largest freshwater lake located in the middle-low region of the Yangtze River. Sediment samples were analyzed for their respective REE spatial distributions, fractionation, and co-occurrence patterns. The inner relationships and geochemistry characters of REEs were assessed by geostatistics and co-occurrence network analysis. Results indicated that total REE concentrations in the sediments from Poyang Lake ranged from 145.1 to 351.1 μg g−1, with an average concentration of 254.0 μg g−1. Light rare earth element (LREE, La - Sm) enrichment was evident in all sediment samples, indicating the effects of river-lake interactions and the contributions from terrestrial inputs. The negative Ce and Eu anomalies were found in most sediment samples, indicating the differentiation between Ce, Eu, and other REEs in the processes of sediment transportation and deposition. Collectively, the identification of the major contamination sources of REEs in sediment, analyzed by the patterns of the co-occurrence networks and REE fractionation, revealed that the REEs in sediments from Poyang Lake originated both natural and anthropogenic sources and were disturbed by the impact of anthropogenic activities.

Petrogenesis of the two phases of intrusive rocks at Chodarchay, NW Iran: using trace and rare earth elements

The Chodarchay area is located 50 km east of the city of Zanjan, within the Tarom-Hashtjin subzone, in the Western Alborz structural zone of NW Iran. Igneous rocks in the area include intrusive granitic (phases I and II), and volcanic rocks. Geochemical characteristics of the granitic rocks were determined using their trace and rare earth element (REE) compositions. The phase I intrusive rocks at Chodarchay include quartz monzonite and quartz syenite, while the phase II mainly consists of granite and alkali granite. These intrusive rocks have SiO2 contents ranging between 60.11 and 69.14 wt%, high K2O + Na2O (8.20 to 10.21 wt%) and K2O/Na2O ratios of 1.24 to 2.56. Petrological and geochemical studies indicate that the granitoids have high-K to shoshonitic affinity, they are metaluminous to mildly peraluminous and characterize as I-type granitoids. The investigated granitoids (phases I and II) have fractionated REE patterns characterized by enrichment in light REEs and varying degrees of depletion in heavy REEs. Large-ion lithophile element (LILE) enrichment, high-field strength element (HFSE) depletion, and distinct positive Pb anomaly in the primitive mantle-normalized trace element patterns of the rocks imply subduction-related arc magmatic signatures. It is suggested that the granites formed in a volcanic arc to post-collision setting from a garnet spinel lherzolite source.