Search

[Display omitted] • VMS-hosted felsic volcanic rocks and marine limestones were formed contemporarily. • Chemostratigraphy of limestones and zircon U-Pb dating reveal their early Cambrian age. • VMS-hosted volcanic rocks were produced by high degree partial melting of juvenile lower crust. • VMS-hosted rocks were formed in the back-arc setting where the marine transgression occurred. The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO 2 and Na 2 O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking. Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O (SMOW) values from 17.1 to 23.8 ‰ and δ13C (PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings. [ABSTRACT FROM AUTHOR]

[Display omitted] • TTG magmatism derived from both depleted mantle and crustal reworked components. • I-type granitic intrusions show evidence of TTG reworking. • Mafic and ultramafic volcanic rocks are derived from depleted mantle. The southeastern Superior Province contains Meso- to Neoarchean (2952–2677 Ma) tonalite-trondhjemite-granodiorite (TTG) suites, volcanic (2773–2703 Ma) and sedimentary (<2724 Ma) supracrustal sequences, and granitoid intrusions (2708–2598 Ma). The region is a key crustal cross-section for understanding the growth, evolution, and stabilization of Archean cratons. Whole-rock geochemistry and Nd isotopic analyses have been performed on TTG suites, volcanic assemblages and granitoid plutons of the La Grande, Nemiscau and Opatica subprovinces. These analyses, combined with existing structural and U-Pb geochronological data, have been used to investigate the extend of the basement within the three subprovinces, their interaction, and the degree of crustal reworking in the southeastern Superior Province. Nd isotope data and zircon inheritance indicate that the TTG suites were generated from: (i) an old crustal domain with Nd model ages at 3.5–3.2 Ga that may represent the southern extension of the Langelier Complex, (ii) a ca. 3.0 Ga domain with isotopically juvenile signatures, and (iii) the reworking of < 3.0 Ga Nd model age TTG suites from the Opatica subprovince. The Nd juvenile signatures of the mafic to ultramafic volcanism at ca. 2773–2756 and ca. 2723–2703 Ma suggest continuous or multiple mantle plume events beneath the southeastern Superior Province, whereas interlayered felsic volcanic rocks were formed from anatectic melting at high pressure. Subsequent magmatism was related to sanukitoid suites (2704–2693 Ma) emplacement that record mantle-TTG melt interactions. Based on a common tectonometamorphic evolution of the three subprovinces from ca. 2756 Ma, previous studies argued that the Mesoarchean TTG suites exposed in the La Grande and Opatica subprovinces represent a single crustal block. The sedimentary belts of the area were deposited in sagduction-type basins formed at ca. 2724–2706 Ma and, within less than 15–20 myr, were buried and metamorphosed up to granulite facies at 2697–2685 Ma during dip-slip-dominated D 2. The burial and the following exhumation of these rocks from ca. 2677 Ma may be attributed to the delamination of lower crustal residues, favoring interaction between mantle and TTG melts, and the formation of sanukitoids and anatectic S-type granites. Nd signatures of the 2646–2598 Ma I-type granitic intrusions indicate extensively reworking of TTGs due to crustal thickening during the D 3 -D 4 events. Our study suggests that the Archean tectonic regime recorded in the southeastern Superior Province is the result of mantle plume tectonics. We conclude that the La Grande-Opatica boundary does not represent a major suture zone but rather but rather a fossil boundary within an older extensively reworked crustal block over which the metasedimentary rocks of the Nemiscau and La Grande subprovinces were deposited. [ABSTRACT FROM AUTHOR]

To improve our understanding and guide future studies and applications, we review the biogeochemistry of the rare earth elements (REE). The REEs, which form a chemically uniform group due to their nearly identical physicochemical properties, include the lanthanide series elements plus scandium (Sc) and yttrium (Y). These elements, in conjunction with the neodymium isotopes, are powerful tools for understanding key oceanic, terrestrial, biological and even anthropogenic processes. Furthermore, their unique properties render them essential for various technological processes and products. Here, we delve into the characteristics of REE biogeochemistry and discuss normalization procedures and REE anomalies. We also examine the aqueous speciation of REEs, contributing to a better understanding of their behavior in aquatic settings, including the role of neodymium isotopes. We then focus on their environmental distribution, fractionation, and controlling processes in different environmental systems across the land‐ocean continuum. In addition, we analyze sinks, sources, and the mobility of REEs, providing insights into their behavior in these environments. We further investigate the sources of anthropogenic REEs and their bioavailability, bioaccumulation, and transfer along food webs. We also explore the potential effects of climate change on the cycling, mobility and bioavailability of REEs, underlining the importance of current research in this evolving field. In summary, we provide a comprehensive review of REE behavior in the environment, from their properties and roles to their distribution and anthropogenic impacts, offering valuable insights and pinpointing key knowledge gaps. Key Points: Rare earth elements (REE) are powerful tracers of both natural and anthropogenic processes within terrestrial and ocean environmentsREE are controlled by absorption, adsorption/desorption, co‐precipitation, remineralization, and particle dissolutionREE are technology‐critical metals with broad applications in the future low‐carbon global economy [ABSTRACT FROM AUTHOR]

Dating of igneous rocks from paleo-island arc complexes of orogenic belts makes it possible to determine the precise timing of subduction processes that occurred during the formation of the orogen. Within the central (East Transbaikal) part of the Mongol–Okhotsk orogenic belt, the Kamenka island-arc terrane is an example of such a complex. Its intrusive part is included into the Bereya complex, represented by a gabbro-diorite-tonalite-plagiogranite series of rocks demonstrating subduction geochemical characteristics. The dating of zircons from acidic rocks of this complex by the U–Pb classical method showed that they were formed in a narrow time interval of 203 ± 1–205 ± 1 Ma, which corresponds to the Norian–Rhaetian boundary of the Late Triassic. Taking into account the previously obtained age of the diorites (254 ± 5 Ma), the timing of formation of the entire series of the intrusive rocks is about 50 Ma, thus indicating the probable subduction along the northern (in modern coordinates) margin of the Mongol–Okhotsk Paleocean under the Siberian paleocontinent in the Late Permian – Late Triassic. The diorites of the first phase have positive values of εND(254 Ma) = 3.2–3.6 (TNd(DM) = 879–994 Ma), and the plagiogranites have ɛND(205 Ma) = 2.3–3.5 (TNd(DM) = 859–1028 Ma), which points to the relationship between these rocks and the substance of the depleted mantle source and is consistent with the Sm–Nd isotope characteristics of the juvenile crust of the Central Asian orogenic belt. [ABSTRACT FROM AUTHOR]

Phosphorites of the Georgina Basin (northern Australia) are an established economic source of phosphate and have recently been recognized to be a potential source of rare earth elements (REE). Previous bulk‐rock geochemistry work focused on the eastern margin of the basin revealed that phosphorites from the southern region have significantly higher (up to 0.5%) REE contents than equivalent prospects further to the north. In this study, we examine the origin of REE enrichment in the Georgina Basin phosphorites using an integrated geochemical, petrographic, mineralogical, and isotopic (Sm‐Nd and Sr) approach. The trace element geochemistry of primary phosphate minerals is consistent with a seawater origin for the REEs in phosphorites, with minimal input from the underlying basement rocks. Variations in total REE concentrations are controlled largely by the seawater composition, depositional environment, and the texture of the phosphorite (grainstone vs. mudstone phosphorite). Grainstone phosphorite yields on average higher concentrations of REEs compared to the mudstone phosphorite, likely due to the higher surface‐to‐mass ratio of the grainstone phosphorite resulting in the uptake of higher concentrations of REEs during coastal reworking. The formation of the low‐REE northern and central deposits took place during early transgression in oxidized, shallow supratidal to subtidal platformal environments. During the subsequent main transgressive event, fault‐controlled topography in the southern domain allowed phosphogenesis along basement highs to be facilitated along a redox boundary, where more saline and REE‐rich deep anoxic bottom waters, along with Fe‐cycling and bacterial mediation played a major role in the enrichment of REEs in the southern phosphorites. Key Points: The origin of rare earth element (REE) enrichment in phosphorites of the Georgina Basin in northern Australia, was determined using an integrated geochemical, mineralogical, and isotopic approachThe enrichment of REEs in phosphorites is controlled by the texture and the depositional environment at the time of phosphorite formationVarying levels of REE enrichment occurred at different stages of marine transgression [ABSTRACT FROM AUTHOR]

The origin of the recently discovered Flatreef remains debated due to the pronounced interaction of the magmatic rocks with sedimentary floor rocks, resulting in a complex intrusive stratigraphy. In this study, we report new Nd isotopic compositions of Flatreef lithologies intersected by borehole UMT-393 on the farm Macalacaskop in order to improve our understanding of the magmatic history of the deposit and to further test the putative correlation between the Flatreef/Platreef and the Upper Critical Zone of the remainder of the Bushveld Complex. The initial epsilon Nd (εNdi) values for the Flatreef range between −5.2 and −7.6, overlapping with εNdi values of the Upper Critical Zone from the eastern (ranging between − 4.8 and − 8.5) and the Upper Critical Zone and Main Zone from the western limb (−6.3 and −7.6, and −6.3 and −7.4 respectively) of the Bushveld Complex. The Flatreef εNdi values also overlap with those of the Platreef; however, due to the varying footwall lithologies of the Platreef along strike, Platreef rocks display a wider variation in isotopic composition. Our findings support the correlation of the Flatreef with the Upper Critical Zone — Main Zone transition interval in the remainder of the Bushveld Complex, which includes the Merensky and Bastard reefs. Due to significant overlap between the εNdi values of the Flatreef and local potential contaminants occurring at the base of the Northern Limb, we propose that the Sr–Nd isotopic composition of the magmas that gave rise to the Flatreef are most likely attributable to the interaction of mantle-derived magma with upper and lower crustal rocks of the Kaapvaal Craton within a sub-Bushveld staging chamber, with possible syn- to post-emplacement modification as a result of interaction with dolomitic footwall rocks. [ABSTRACT FROM AUTHOR]

Abstract Phosphorites of the Georgina Basin (northern Australia) are an established economic source of phosphate and have recently been recognized to be a potential source of rare earth elements (REE). Previous bulk‐rock geochemistry work focused on the eastern margin of the basin revealed that phosphorites from the southern region have significantly higher (up to 0.5%) REE contents than equivalent prospects further to the north. In this study, we examine the origin of REE enrichment in the Georgina Basin phosphorites using an integrated geochemical, petrographic, mineralogical, and isotopic (Sm‐Nd and Sr) approach. The trace element geochemistry of primary phosphate minerals is consistent with a seawater origin for the REEs in phosphorites, with minimal input from the underlying basement rocks. Variations in total REE concentrations are controlled largely by the seawater composition, depositional environment, and the texture of the phosphorite (grainstone vs. mudstone phosphorite). Grainstone phosphorite yields on average higher concentrations of REEs compared to the mudstone phosphorite, likely due to the higher surface‐to‐mass ratio of the grainstone phosphorite resulting in the uptake of higher concentrations of REEs during coastal reworking. The formation of the low‐REE northern and central deposits took place during early transgression in oxidized, shallow supratidal to subtidal platformal environments. During the subsequent main transgressive event, fault‐controlled topography in the southern domain allowed phosphogenesis along basement highs to be facilitated along a redox boundary, where more saline and REE‐rich deep anoxic bottom waters, along with Fe‐cycling and bacterial mediation played a major role in the enrichment of REEs in the southern phosphorites.

Silicate weathering has long been considered to maintain the Earth's climate stability, yet how the weathering responds to the late Cenozoic cooling remains unclear, partly because of the complicated factors which obscure the weathering records. Large rivers in East Asia integrate continental weathering history, but how the source-to-sink system evolution affected the weathering signals need to be clarified. We compile proxy data of Nd isotopes, zircon ages and Chemical Index of Alteration (CIA) in East Asian margin and source terranes, along with new proxy data from core CSDP-2 in the shelf region, to understand the large river evolution and assess their influence on weathering proxy records. The median εNd values of East Asian marginal sediments increased from −18.8 in pre-3.6 Ma period to −11.3 since the 1.0 Ma, corresponding to the isotopic signatures in North China Craton and Northeastern (NE) Tibetan Plateau/Loess Plateau terranes, respectively. The zircon ages further confirmed the provenance shift, hinting that the modern-like Huanghe (Yellow River) system has been fully integrated during early Pleistocene, no later than ∼1.0 Ma. This integration facilitated the sediment transportation from plateaus into the continental margin. Consequently, the CIA records in marginal regions show a more significant decrease than other Asian regions, within the context of Plio-Pleistocene cooling. Our study found that the upland expansion of large river system and global cooling jointly controlled the decline in the weathering intensity records, highlighting the importance to understand the evolution of source-to-sink system before interpreting the weathering signals from the continental margin sediments. • Detrital Nd isotopes and zircon ages are compiled to constrain the sediment sources in East Asian margin. • The sediment provenance shifted from proximal lowlands to uplands, links to the Huanghe integration. • Large river expansion in East Asia amplified the decline in weathering intensity proxy records since the Pliocene. [ABSTRACT FROM AUTHOR]

The near closure of the Panama Seaway during the late Miocene resulted in the modification of deep-ocean currents and the formation of modern oceanic circulation. However, it is unclear how this closure impacted the north Pacific western-boundary deep circulation since the late Miocene. Here, we combine Nd isotope records in the north Pacific and a newly developed water-mass proxy (amorphous Fe hydroxide content, AFHs) from the western Pacific to investigate deep-current evolution since the late Miocene. These proxies consistently indicate a significant deep water-mass change in the north Pacific at ∼5 Ma, reflecting shoaling of the Panama seaway that curtailed intermediate and deep-water exchange between the East Equator Pacific and Atlantic. Although intensification of Antarctic bottom water since ∼3.4 Ma (Northern Hemisphere Glaciation) has been widely documented, a decrease in western-boundary currents has occurred since ∼3 Ma. We suggest that this phenomenon is likely due to the increased mixing of south-ward and north-ward deep western-boundary currents in the north Pacific. This water mass mixing may have a significant impact on the western Pacific biogeochemical cycling. • Records of amorphous Fe hydroxide from a Fe-Mn nodule elucidate western Pacific deep-current evolution since the late Miocene. • Nd isotope records indicate east-west mixing of deep-waters in the north Pacific before the closure of the Panama seaway. • Nd isotope and amorphous Fe hydroxide results suggest enhanced south-north mixing of deep western-boundary currents in the north Pacific since ∼3 Ma. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three volcanic events during Ediacaran – Cambrian are found in the Tannuola terrane. • The volcanic rocks record the transition from an oceanic subduction to a collision setting. • The volcanic rocks from the Tannuola terrane have high positive (+5.6 to +8.5) εNd(t) values. • Deep geodynamics is mainly controlled by the various configuration of the subducted slab. Magmatism associated with oceanic subduction plays a dominant role in crustal growth during the Earth's evolution. The Tannuola terrane, situated in the northern Central Asian Orogenic Belt (CAOB), is a key area to understanding oceanic subduction and initial collision processes in the northern CAOB. In order to investigate the switch from subduction to collision settings, detailed field mapping, zircon SHRIMP U-Pb geochronological and whole-rock geochemical studies of volcanogenic-sedimentary rocks from the Tannuola terrane were carried out. Zircon U-Pb ages indicate multi-stage volcanism lasted at least 30 Ma from ∼540 to ∼510 Ma, that can be divided into three events: the late Ediacaran (before ∼540 Ma), the early Cambrian (∼520 Ma) and the middle Cambrian (∼510 Ma). These ages are interpreted to the initial, main and final stages of oceanic subduction during the late Proterozoic – early Paleozoic. During the late Ediacaran, tholeiitic basalts with high ε Nd(t) values (from +7.4 to +8.5) were emplaced. Likely forming by the 10 %–30 % partial melting of spinel – garnet mantle source during slab subduction. During the early Cambrian, transitional from tholeiitic to calc-alkaline basaltic rocks with ε Nd(t) value (+5.6) and coeval intermediate–felsic volcanic rocks with similar ε Nd(t) values (+5.9 and +6.5) formed. The early Cambrian basaltic rocks are interpreted to be derived by 10 %–30 % partial melting of a depleted mantle source metasomatized by slab-derived fluids released from the subducting oceanic slab. The middle Cambrian calc-alkaline basaltic rocks with ε Nd(t) value of +6.2 might be emplaced as a result of low (5 %–10 %) degree partial melting of a metasomatized mantle followed by fractional crystallization of clinopyroxene and plagioclase. Associated intermediate-felsic volcanic rocks with ε Nd(t) values from +6.0 to +6.8 were formed through fractionation of the juvenile Neoproterozoic sources. The middle Cambrian volcanism is interpreted to be triggered by the slab break-off during the transition to a collisional setting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Apatite REE + Y variations are determined primarily by elemental partitioning. • Mineral fractionation can cause apatite Sr, Pb, Th, and U variations. • Apatite Nd isotopes have the potential to serve as geological indicators. Compositional variations of apatite are mainly determined by parameters such as partition coefficients and the composition of parental magma. However, the relative importance of these parameters in relation to apatite geochemistry in different lithologies of magmatic rocks is not well constrained. In this study, six Mesozoic (219–154 Ma) mafic–felsic intrusions from the eastern North China Craton, were selected for detailed apatite microanalyses (trace elements and Nd isotopes). Apatite from the studied intrusions has uniform textures in the cathodoluminescence image. They exhibit high abundances of rare earth elements (REE) and are characterized by light REE enriched patterns, indicative of a magmatic origin. Alongside compiled apatite data, these findings suggest that compositional variations of REE + Y in apatite from mafic to felsic magmatic rocks are controlled primarily by elemental partitioning between apatite and melts. The competitive crystallization of other accessory minerals prior to apatite can be responsible for compositional variations of Sr, Pb, Th, and U. New Nd isotope data for apatite are discussed and compared with whole-rock Nd and zircon Hf isotope data for the same sample. The Nd isotopic compositions between the whole-rock and apatite are identical. The integrated dataset provides an alternative interpretation for the isotopic decoupling between apatite Nd and zircon Hf isotope systems. In conclusion, apatite REE concentrations and Nd isotopes have the potential to serve as geological indicators. [ABSTRACT FROM AUTHOR]