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To better understand the origin of the Andean iron oxide-apatite (IOA) deposits, we conducted a study on the geology and magnetite geochemistry of the Mariela IOA deposit in the Peruvian Iron Belt, central Andes. The Mariela deposit is hosted by gabbroic and dioritic intrusions. The major high-grade massive ores are primarily composed of magnetite and contain variable amounts of apatite and actinolite. Based on textural and geochemical characteristics, three different types of magnetite are recognized: Type I magnetite occurs in the massive magnetite ore, subclassified as inclusion-rich (I-a), inclusion-free (I-b), and mosaic (I-c); Type II magnetite is associated with abundant actinolite and titanite; and Type III magnetite is disseminated in altered host rocks. However, the magnetite geochemistry data for the Mariela deposit plot shows different genetic areas in [Ti + V] vs. [Al + Mn], Ti vs. V, and Fe vs. V/Ti discrimination diagrams, indicating a paradox of magmatic and hydrothermal origins. Our interpretation is as follows: Type I-a magnetite had an initial magmatic or high-temperature magmatic-hydrothermal origin, with slight modifications during transportation and subsequent hydrothermal precipitation (Types I-b and I-c). Type II magnetite is formed from hydrothermal fluid due to the presence of abundant actinolite. Disseminated magnetite (Type III) and veinlet-type magnetite formed after fluid replacement of the host rock. We stress that elemental discrimination diagrams should be combined with field studies and textural observations to provide a reasonable geological interpretation. A clear cooling trend is evident among the three subtypes of Type I magnetite (I-a, I-b, and I-c), as well as Type II and Type III magnetite, with average formative temperatures of 737 °C, 707 °C, 666 °C, 566 °C, and 493 °C, respectively. The microanalytical data on magnetite presented here support the magmatic-hydrothermal flotation model to explain the origin of IOA deposits in the Coastal Cordillera of Southern Peru.

As the global population ages and the proportion of individuals afflicted with musculoskeletal disease spirals upward, there is an increasing interest in understanding and preventing bone‐related diseases. Bone diseases, such as osteoporosis and osteoarthritis, are known to be influenced by a variety of factors including age, gender, nutrition, and genetics, but are also inherently linked to the human body's ability to produce biominerals of suitable quality. Because the crystal lattice structure and mineralogy of bone hydroxyapatite is surprisingly analogous to geological hydroxyapatite, trace element levels and exposure have long been proposed to influence the structure of biominerals as they do geological minerals (e.g., strontium substitution changes the crystal lattice of bone minerals, while toxic lead disrupt bone cellular processes leading to bone disease). Here, we explore the distribution of trace elements in human bones to evaluate the distribution of these elements with respect to bone type (cortical vs. trabecular) and bone disease (osteoarthritis vs. osteoporosis). We find higher concentrations of many metabolically active transition metals, as well as lead, in cortical bone compared to trabecular bone. When compared to patients who have osteoarthritis, and thus presumably normal bone minerals, osteoporosis patients have higher concentrations of scandium and chromium (Cr) in trabecular bone, and Cr and lead in cortical bone. Lower concentrations of barium and titanium are associated with osteoporotic trabecular bone. This survey is an exploratory cross‐sectional geochemical examination of several trace element concentrations previously understudied in human bone minerals. Plain Language Summary Bone‐related diseases, like osteoporosis, are a growing concern as the global population ages. There are many factors which can influence bone health, including age, sex, and genetics, but ultimately osteoporosis is a disease of bone mass and bone strength. Bone minerals are like minerals found in nature, which contain trace element impurities. When these impurities occur in bones, they affect bone strength, with some trace elements increasing bone strength, and others decreasing it. The amount and kind of trace elements found in bone can be affected by environmental exposures or from the body's own processes which may be different between healthy and diseased individuals. This study compares the concentrations of 16 trace elements in bones from people with osteoporosis, a disease where bones themselves are diseased, and osteoarthritis, as disease of joint cartilage that is not expected to impact the trace element chemistry of bone minerals. We find that bones from osteoporosis patients have higher concentrations of some elements, including toxic lead, but lower concentrations of other elements. The location of these element deficiencies or excesses in the bones may suggest if their concentrations are more likely to be a cause of osteoporosis or a symptom of it. Key Points Concentrations of metabolically regulated trace elements differ between cortical and trabecular bone Data is consistent with metabolically regulated trace elements recording differential bone remodeling in osteoporotic fracture patients Lead (Pb) concentrations recorded in long‐term bodily stores (cortical bone minerals) are elevated in osteoporotic fracture patients

The Late Cretaceous Pandan Formation in Cebu Island is one of the oldest sedimentary units in the Central Philippines. The inconsistencies in geological descriptions and interpretation of the depositional environment of the Pandan Formation complicated efforts to determine the origin and tectonic history of the basement of Cebu Island. This study therefore looks into the petrological and geochemical characteristics of the Pandan Formation and their implications for the tectonic development of the Philippine Arc during the late Mesozoic. Petrographic analyses indicate significant contribution from mafic sources with additional inputs from felsic rocks, siliciclastics and metamorphic sources. Enrichment of detrital quartz from felsic volcanic and plutonic rocks, as well as from siliciclastic and metamorphic sources, has shifted the SiO2 composition of the Pandan clastics from a mafic to a more intermediate source. Whole‐rock geochemical analyses revealed low SiO2/Al2O3 = 4.21, low K2O/Na2O = 1.16, low Th/Sc = 0.13, low Th/U = 2.78, high La/Th = 4.51, significantly low REEs = ca 76.45 ppm and low LaN/YbN = 4.28. A slight negative chondrite‐normalized Eu/Eu* (0.91) anomaly and significantly high PAAS‐normalized positive Eu/Eu* (1.39) values are consistent with derivation from a young undissected magmatic arc terrane. Tectonic discrimination diagrams suggest formation in an oceanic island arc to active margin/collision zone modelled to be located at the oceanic leading edge of Australia. Rapid uplift and erosion of the magmatic arc and older allochthonous blocks gave way to the rapid deposition of the Pandan Formation in the Late Cretaceous at the subequatorial region. The Pandan Formation provides vital information on the Late Cretaceous evolution of Cebu Island in the Central Philippines. Collision of the proto‐Philippine arc with the East Philippine‐Daito arc modelled to be located at the oceanic leading edge of the Australian plate led to rapid uplift and erosion of the magmatic arc and continental derived sediments which gave way to deposition of the Pandan Formation in the Late Cretaceous at the subequatorial region.

Oceanic island basalts are the products of mantle plume melting and their chemistry provides insights into the Earth's deep interior. We report a statistical and machine learning study of 8 radiogenic isotopes and 19 incompatible trace element ratios in basalts from 27 oceanic island volcanic chains associated with mantle plumes compiled from the GEOROC and EARTHCHEM‐PetDB databases. Machine‐learning hierarchical analysis and agglomerative clustering results based on t‐distributed stochastic neighbor embedding (t‐SNE) reveal distinct clusters of isotopic compositions corresponding to canonical ones of HIMU, EM I, EM II, PREMA. and DM as well as a LOND cluster, which however do not reflect the existence of discrete components. The HIMU clan is restricted to only a couple of plumes and is characterized by low K/U, Pb/Ce, Ba/Nb and strong REE fractionation. EM I has higher K/U, Ce/Rb, Ba/Nb and lower U/Pb, Rb/Ba, Rb/Sr than EM II reflecting a difference in prevalent recycled components. Stepwise multiple regression reveals that fractionations of incompatible element ratios can be explained by variations in partial melting controlled by lithospheric thickness and plume buoyancy flux; the latter indicates that buoyancy flux primarily reflects plume temperature. 3He/4He also correlates with plume buoyancy flux, suggesting that the hottest plumes carry the least radiogenic He. The hottest plumes may be those rising from the core‐mantle boundary. This, and the absence of evidence of a primordial mantle reservoir suggest that unradiogenic He may be derived from the core. Plain Language Summary Oceanic island basalts are the products of mantle plumes and are commonly divided among several compositional “clans” based on radiogenic isotope ratios. We show that unsupervised machine learning clustering algorithms recognizes these “clans.” We then used the clustering results to identify and explore the differences in trace element compositions between these clans. The differences likely reflect differences in the prevalence of various subducted components, including oceanic crust, marine sediment, and lower continental crust incorporated into mantle plumes, respectively, dominating the HIMU, EM II, and EM I clans. We then show that much of the fractionation of trace element ratios occurring during partial melting can be explained primarily by variations in mantle plume buoyancy flux, a proxy for plume temperature, and secondarily by lithospheric thickness, which limits the height of the melting region. The latter is most important for element ratios that are fractionated by garnet. Key Points Machine learning analysis of radiogenic isotope and trace element ratios of oceanic island basalts revealed distinct compositional clusters Trace element fractionation varies with plume buoyancy (a proxy for temperature) and lithospheric thickness The association of high 3He/4He with the hottest plumes suggests that this He was derived from the core or a dense layer atop it

The Velay anatectic dome in the Variscan French Massif Central exposes a low-pressure–high-temperature metamorphic sequence, which represents an ideal natural laboratory for documenting the behavior of rare-metals and fluxing elements during crustal melting. We investigated the silicate and bulk-rock geochemistry of sub- to suprasolidus metapelites and orthogneisses, as well as related granites, and performed forward thermodynamically constrained geochemical modeling to quantify the respective effects of melting pressure, temperature, H 2 O activity, and protolith composition on the Li and F contents of granitic melts. We find that biotite compositions are good proxies of melt compositional evolutions during prograde melting. The crystallization of peritectic cordierite at low pressure (< 5 kbar) and “water-fluxed” melting both inhibit the Li enrichment of anatectic melts. Metapelite-derived melts consistently show modest Li–F contents, and a decoupling is observed as melts with the highest Li concentrations (~ 200–400 ppm) are produced below 750 °C, whereas F-richest melts (~ 0.2–0.4 wt%) are produced above 750 °C near the biotite-out isograd. Peraluminous orthogneiss anatexis can generate a melt that is concomitantly enriched in both F (~ 0.3–1 wt%) and Li (~ 600–1350 ppm) at relatively low temperature (< 750 °C), which can evolve toward rare-metal granite compositions (~ 10,000 ppm Li; ~ 2 wt% F) after 80–90 wt% of fractional crystallization. Melting of felsic meta-igneous rocks followed by magmatic differentiation is thus a viable mechanism to form Li-F-rich rare-metal granites and pegmatites, providing a direct link between protracted crust recycling and rare-metal magmatism in late-orogenic settings.

The recently discovered Fåvne vent field, located at 3,040 m depth on the slow‐spreading Mohns mid‐ocean ridge between Greenland and Norway, is a high‐temperature (≥250°C) vent field that is characterized by Fe oxyhydroxide‐rich and S‐poor chimneys and mounds. The vent field is located on both the hanging wall and footwall of a normal fault with a ∼1.5 km throw that forms the western edge of the ∼20 km wide ridge axial valley. Data collected during exploration of the site using a remotely operated vehicle as well as mineralogical and geochemical analyses of rock samples and sediments are used to characterize the geological setting of the vent field and composition of the hydrothermal deposits. The chimney walls are highly porous and lack defined chalcopyrite lined conduits, typical of high‐temperature chimneys. Overall, abundant Fe oxyhydroxide precipitation at high‐temperature vents at Fåvne reflects an excess of Fe over reduced S in the fluid, leading to precipitation of Fe oxide and oxyhydroxide minerals at high to moderate temperature vents (>100°C), and as microbially mediated and abiotic precipitation of Fe oxyhydroxide minerals at low‐temperature diffuse vents (<100°C). The mounds and chimneys exhibit low base metal and reduced S concentrations relative to globally averaged seafloor deposits and suggest subseafloor mixing of hydrothermal fluid with seawater, causing metal sulfide precipitation. Cobalt enrichment at Fåvne may reflect a subsurface influence of an ultramafic substrate on circulating fluids, although ultramafic rocks are absent on the seafloor and no other elements typical of ultramafic deposits are present. Plain Language Summary Seafloor hydrothermal deposits are mineral deposits formed from seawater penetrating the oceanic crust and becoming enriched in metals by leaching the surrounding rocks as the temperature rises close to a heat source. Once heated, the fluid rises back to the seafloor where it comes into contact with cold seawater and the metals precipitate, forming chimneys and mounds. The minerals and metal concentrations record temperatures of formation and environments, and can help us understand the processes associated with plate tectonics and the formation of ore deposits. Using underwater vehicles, we collected rocks and sediments from the Fåvne vent field and measured the temperature of the chimneys, mounds, and surrounding seafloor to understand how these deposits form on the seafloor. The Fåvne vent field differs from other vent fields because it is enriched in iron‐rich‐minerals and depleted in sulfur‐rich‐minerals. The dominance of iron‐rich minerals and the abundance of fractures in the seafloor at the vent field suggest that the hydrothermal fluid is cooled by seawater percolating along the fractures, accumulating these metals in the subsurface instead of at the seafloor. This process is important for understanding the current land‐based mineral deposits being mined today and for the exploration of seafloor mineral deposits. Key Points The Fåvne vent field consists of chimneys and mounds composed of Fe oxyhydroxide minerals with minor sulfide minerals Venting of hot fluids with temperatures up to 267°C is dominantly diffuse, sustaining significant microbial communities Low base metal concentrations of the Fåvne deposits suggest subsurface seawater mixing and mineral precipitation

Large Igneous Provinces (LIPs) are unusual volcanic events in which massive amounts of melt (∼106 km3) erupt in relatively short time periods (<106 years). Most LIP magmas have undergone extensive fractional crystallization and crustal contamination, but the crustal magmatic plumbing systems and the processes triggering eruptions are poorly understood. We present new major and trace element and radiogenic isotope data for 43 individual lava flows from a continuous 1,200 m thick stratigraphic profile through the upper, most voluminous part of the Deccan LIP (Bushe to Mahabaleshwar Formations). Eruption rates for this section are constrained by published paleomagnetic directions and absolute U‐Pb ages for zircons from weathered flow tops exposed in the profile. We find four magmatic sequences each lasting ∼104–∼105 years during which major and trace element compositions change systematically, followed by an abrupt change in geochemistry at the start of a new sequence. Within each sequence, the MgO content and proportion of crustal contamination decrease progressively, indicating a continuous replenishment of the associated magma reservoirs with less contaminated but more evolved melts. These geochemical signatures are best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoir located in different crustal levels. Plain Language Summary Volcanism occurs predominantly at plate boundaries, either at mid‐ocean ridges or subduction zones, where most mantle melts are produced. However, the Earth's history is punctuated by volcanic events which are not related to plate boundary processes and during which large amounts of melt erupt (∼106 km3) in relatively short periods of time (<106 years). These Large Igneous Provinces (LIPs) are associated with the activity of mantle plumes and eruption rates during their main stages are significantly higher than those of today's largest magmatic systems. However, since no LIP is currently active, the architecture of the associated plumbing systems is relatively unknown. In order to understand the magmatic processes during the emplacement of a LIP, we generated geochemical data from a continuous stratigraphic profile covering the most voluminous stage of the ∼66 Ma Deccan LIP. By combining these new data with published paleomagnetic directions and absolute U‐Pb ages for zircons, we found four eruption sequences each lasting ∼104–∼105 years. During these sequences, geochemical compositions change systematically, which is best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoirs located at different crustal levels. Key Points Four recharge‐crystallization‐eruption sequences fed the most voluminous Deccan lava Magmatic plumbing system with interconnected small‐ to medium‐sized magma reservoirs Complex emplacement history including multiple stages of ascent, mixing, and storage

Rare earth elements (REEs) and trace elements, due to their relative stability during sedimentary processes, are effective geochemical proxies for sediment provenance. In the Dongdaohaizi Depression of the eastern Junggar Basin, the provenance of the Middle Jurassic Sangonghe Formation remains contentious. In this study, representative sandstone samples were systematically collected from all three members of the Sangonghe Formation in both the Dongdaohaizi Depression and its western margin. Through comprehensive petrographic and geochemical analyses, we obtained the following results. The Sangonghe Formation is primarily composed of feldspathic lithic sandstones, lithic sandstones, and minor lithic–feldspathic sandstones. The heavy mineral assemblage includes zircon, garnet, chromite, and rutile, suggesting source rocks of intermediate to acidic igneous, metamorphic, and mafic lithologies. The total REE contents range from 101.84 to 192.68 μg/g, with an average of 161.80 μg/g. The ∑LREE/∑HREE ratios vary from 6.59 to 13.25 (average 10.96), and the average δEu values are close to 1. The δCe value ranges from 1.09 to 1.13 (average 1.11). Trace element discrimination diagrams, including La-Th-Sc, Th-Co-Zr/10, Th-Sc-Zr/10, and La/Y-Sc/Cr ternary plots, indicate that most samples fall within the continental island arc domain, with a few plotting in the passive continental margin field. Comparison with potential surrounding source regions reveals dual provenances: an eastern source from the Kalamaili Mountains and a western source from the Zhayier Mountains. During the Early Jurassic, these two orogenic belts acted as distinct sediment sources. The Zhayier Mountains provided stronger input, with fluvial and tidal processes transporting sediments into the basin, establishing the primary subsidence center in the west of the depression. By the Middle Jurassic, continued thrusting of surrounding fold belts caused a migration of the lake center and the main depocenter to the western edge of the Dongdaohaizi Depression, while the former depocenter gradually diminished. Furthermore, sustained erosion and denudation of the Mosowan Uplift during the Early–Middle Jurassic reduced its function as a structural barrier, thereby promoting increased mixing between eastern and western sediment sources. The study not only refines existing paleogeographic models of the Junggar Basin, but also demonstrates the utility of REE–trace geochemistry in deciphering complex provenance systems in tectonically active basins.

Several examples of zircon grains from high- to ultrahigh-pressure (UHP) and ultrahigh-temperature (UHT) metapelites exhibit a characteristic, yet atypical, core–rim interface domain < 5-μm wide observed in cathodoluminescence (CL) imaging. The interface domain is located immediately against the magmatic core and is comprised of an irregular, 0–2-μm wide, CL-dark domain that is rimmed by a complex, 0–5-μm wide, CL-bright domain with cuspate margins. The outer margin of the interface domain is rimmed by intermediate-CL zircon with low contrast zoning. To characterize the nature of the interface domain and to identify mechanisms of trace element mobility in metamorphosed zircon, we analyzed several specimens prepared from zircon from the Rhodope Metamorphic Complex (eastern Greece) and the Goshen Dome (western Massachusetts, USA) via atom probe tomography (APT). The data reveal three types of geochemical anomalies, each with a unique morphology. (1) Toroidal clusters with high concentrations of Pb (+ Y, Al) are found exclusively within the core of the Rhodope grain. These clusters are interpreted as decorated dislocation loops that formed during metamorphism and annealing of radiation damage to the lattice. Geochronological and geochemical data support this interpretation. (2) Complex, cross-cutting planar and linear features with anomalous concentrations of Y + P + Yb or U are spatially restricted to the core–rim interface domain; these features do not correlate with inherited geochemical variation (oscillatory zoning) or deformation-induced microstructures. Instead, the planar features likely formed in response to an interface-coupled dissolution–reprecipitation reaction that propagated into the crystal during metamorphism. The observed cross-cutting relationships are the product of either multiple events or complexity of the process that originally formed the domains. (3) Ellipsoidal features with high concentrations of Y + P + Yb (+ Al) are found exclusively within the high-Y + P + Yb planar features. These features are interpreted as the product of spinodal decomposition that occurred during exhumation as the zircon passed the solvus where local equilibria favored nm-scale exsolution to minimize the Gibbs free energy. The presence of multiple types of geochemical features in these examples indicates that trace element mobility in zircon is driven by multiple processes over the course of orogenesis. Given that these atypical domains are apparently restricted to zircon metamorphosed at UHT and (U)HP conditions, their presence may represent a marker of metamorphism at very high-grade conditions.

Exhumed serpentinites are fragments of ancient oceanic lithosphere or mantle wedge that record deep fluid‐rock interactions and metasomatic processes. While common in suture zones after closure of ocean basins, in non‐collisional orogens their origin and tectonic significance are not fully understood. We study serpentinite samples from five river basins in a segment of the non‐collisional Andean orogen in Ecuador (Cordillera Real). All samples are fully serpentinized with antigorite as the main polymorph, while spinel is the only relic phase. Watershed delineation analysis and in‐situ B isotope data suggest four serpentinite sources, linked to mantle wedge (δ11B = ∼−10.6 to −0.03‰) and obducted ophiolite (δ11B = −2.51 to +5.73‰) bodies, likely associated with Triassic, Jurassic‐Early Cretaceous, and potentially Late Cretaceous‐Paleocene high‐pressure (HP)–low‐temperature metamorphic sequences. Whole‐rock trace element data and in‐situ B isotopes favor serpentinization by a crust‐derived metamorphic fluid. Thermodynamic modeling in two samples suggests serpentinization at ∼550–500°C and pressures from 2.5 to 2.2 GPa and 1.0–0.6 GPa for two localities. Both samples record a subsequent overprint at ∼1.5–0.5 GPa and 680–660°C. In the Andes, regional phases of slab rollback have been reported since the mid‐Paleozoic to Late Cretaceous. This tectonic scenario favors the extrusion of HP rocks into the forearc and the opening of back‐arc basins. Subsequent compressional phases trigger short‐lived subduction in the back‐arc that culminates with ophiolite obduction and associated metamorphic rock exhumation. Thus, we propose that serpentinites in non‐collisional orogens are sourced from extruded slivers of mantle wedge in the forearc or obducted ophiolite sequences associated with regional back‐arc basins. Plain Language Summary Serpentinites are metamorphic rock products of fluid‐mediated alteration of the mantle. They occur in the ocean floor and the core of mountain belts resulting from continental collisions after the closure of ancient oceanic basins. However, their origin in non‐collisional mountain belts, such as the Andes, remains unclear. To address this conundrum, we studied serpentinite boulders from five river basins in the Ecuadorian northern Cordillera Real. We found that rocks are composed of the high‐temperature serpentine mineral, while spinel is the only original mineral preserved. River basin analysis and boron stable isotopes indicate four potential sources for the studied rocks, juxtaposed to rocks ranging in age from ∼240 to 55 million. Bulk‐rock chemistry and boron isotopes suggest that the serpentinization was triggered by crustal fluids at depths between 80 and 30 km in a subduction zone environment. Through time, the Andes have been characterized by extensional and compressional tectonic phases. These tectonic scenarios enhance the extraction of rocks at deep sections of the Earth along major faults. We propose that Andean serpentinites are fragments of the Earth's mantle sourced from ancient subduction zones and back‐arc basins. Key Points Serpentinites associated with HP–LT rocks are common in the Andes, but their origin and tectonic significance are not fully understood Our results in Cordillera Real serpentinites suggest four sources derived from the mantle wedge and obducted ophiolites Serpentinites in non‐collisional orogens are exhumed during slab rollback and back‐arc basin closure phases