Geochemical Signatures Research Articles

A machine learning-based approach using clinopyroxene data to improve accuracy and efficiency in predicting tectonic settings: Implications for Rodinia supercontinent breakup triggered by mantle plume events

Abstract Basalts are ubiquitous mafic rocks found within diverse tectonic settings on Earth. Despite concerted efforts to distinguish tectonic settings through the chemical compositions of basalt, some features of these rocks related to tectonic processes can be obscured by weathering and erosion over geological time, making the discrimination results ambiguous. In this study, we utilized major and trace element data of clinopyroxene in basalts from five distinct tectonic settings: continental within-plate basalts (WPB), island arc basalts (IAB), ocean island basalts (OIB), oceanic floor basalts (OFB), and continental flood basalts (CFB). Employing three machine learning techniques—Multi-layer Perceptron (MLP), Support Vector Machine (SVM), and Random Forest (RF)—we aim to discriminate tectonic settings and magma affinities. Sparse Multinomial Regression (SMR) approach is used to quantitatively discern geochemical signatures that are distinctive of each tectonic setting. The outcomes reveal the efficacy of SVM, which attains an accuracy of 92.1% (major element-based) and 95.2% (major and trace elements-based) for tectonic discrimination. Furthermore, SVM achieves an accuracy of 92.9% (major elements-based) and 95.7% (major and trace elements-based) for magma affinity discrimination. Our study shows that the integration of electron microprobe data from clinopyroxene with machine learning techniques provides an effective approach to distinguish various tectonic settings and magma affinities. The classifier models have been applied to investigate the Neoproterozoic geodynamics of the Jiangnan Orogen. The models show the two pulses of mantle plume events (∼830 Ma and ∼785 Ma) triggering break-up of the Rodinia supercontinent.

Early Devonian Slab Melting of the Proto-Tethys Ocean: Insights from Adakitic Granitoids in the Jiayuguan Area, Hexi Corridor (NW China)

Abstract The tectonics of the Proto-Tethys Ocean during the Early Devonian are still heavily debated in the North Qilian orogen. In order to further constrain this issue, we explore geology, chronology, geochemistry, and isotopes of three newly discovered Early Devonian adakitic granitoids of the Jiayuguan complex in the North Qilian orogen, NW China. The granitoids exhibit typical adakitic geochemical signatures with high SiO2 (>56%), Na, Al, and Sr contents, depleted in Yb and Y, and high Sr/Y (82–277) and (La/Yb)N (7.65–15.16) values. Additionally, their high Mg# (62–68) and εHf(t) (+6.5–+11.9) values indicate partial melting of slab genesis. However, they have comparatively low εNd(t) (−2.3–+0.13). Their incompatible Hf and Nd isotopes could be caused by contamination between the source magma and continental crust during the emplacement processes. The three adakitic granitoids yield zircon U–Pb ages of 415–403 Ma, implying that the northern Qilian Ocean was subducting until the Early Devonian (403 Ma) and that young/hot/ridge subduction formed the Jiayuguan adakitic granitoids. Combined with regional data, we propose that the Proto-Tethys Ocean was subducting until 403 Ma in the Qilian area.

Zircon U-Pb geochronology and Sr-Nd-Pb-Hf-O isotope signatures of Middle Eocene high-K plutons from the Eastern Pontides Orogenic Belt, NE Turkey: implications for parental magma sources and magmatic processes

ABSTRACT The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a well-preserved continental magmatic arc in the Alpine-Himalayan Orogenic Belt and contains many Eocene I-type high-K plutons. Employing LA-ICP-MS U-Pb zircon geochronology, the crystallization ages of the investigated Yaylalıköy and Taşbaşı plutons were established to be Lutetian (Middle Eocene), ranging from 47 Ma to 46 Ma. These plutons exhibit a compositional spectrum ranging from diorite to granodiorite, characterized by I-type, metaluminous, and high-K geochemical signatures. Notably, they are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), displaying pronounced negative Eu anomalies (EuN/Eu* = 0.58–0.96). Isotopic signatures reveal homogeneous and moderately low initial 87 Sr/86 Sr(i) ratios (0.704643–0.705034) and positive εNd(i) values (0.24 to 1.67) for the investigated plutons. These isotopic signatures are consistent with mantle origin, as evidenced by their position within the mantle array on isotope ratio diagrams. Lead isotope compositions exhibit limited variations, with initial ratios of 206 Pb/204 Pb(i) (18.55–18.64), 207 Pb/204 Pb(i) (15.61–15.64), and 208 Pb/204 Pb(i) (38.46–38.75). Zircon εHf(i) values are positive (2.32–6.20), plotting between the depleted mantle and chondritic evolution lines. Additionally, these rocks display low zircon δ18 O values (+4.54 to + 6.53‰), comparable to mantle composition. The petrographic characteristics of the investigated plutons suggest that fractional crystallization with minimal assimilation and/or magma mixing played a dominant role during their solidification. The integration of geochemical and isotopic data, alongside regional geological constraints, advocates for enriched lithospheric mantle as the source for the parental magmas of the studied plutons. These magmas subsequently underwent differentiation within a deep-seated magma chamber, followed by emplacement into the crust.

Proteomic characterization of a foraminiferal test’s organic matrix

Foraminifera are unicellular protists capable of precipitating calcite tests, which fossilize and preserve geochemical signatures of past environmental conditions dating back to the Cambrian period. The biomineralization mechanisms responsible for the mineral structures, which are key to interpreting palaeoceanographic signals, are poorly understood. Here, we present an extensive analysis of the test-bound proteins. Using liquid chromatography-tandem mass spectrometry, we identify 373 test-bound proteins in the large benthic foraminifer Amphistegina lobifera, the majority of which are highly acidic and rich in negatively charged residues. We detect proteins involved in vesicle formation and active Ca2+ trafficking, but in contrast, do not find similar proteins involved in Mg2+ transport. Considering findings from this study and previous ones, we propose a dual ion transport model involving seawater vacuolization, followed by the active release of Ca2+ from the initial vacuoles and subsequent uptake into newly formed Ca-rich vesicles that consequently enrich the calcification fluid. We further speculate that Mg2+ passively leaks through the membrane from the remaining Mg-rich vesicles, into the calcifying fluid, at much lower concentrations than in seawater. This hypothesis could not only explain the low Mg/Ca ratio in foraminiferal tests compared to inorganic calcite, but could possibly also account for its elevated sensitivity to temperature compared with inorganically precipitated CaCO3.

2.08 Ga andesitic gneisses in the southwestern Yangtze Block: Unveiling new insights into its geological evolution

The early geological history of the Yangtze Block has been difficult to unravel due to limited exposure of Archean to Paleoproterozoic rocks. Through detailed geological investigations and mapping in the southwestern (SW) Yangtze Block, this study identified Paleoproterozoic andesitic and granitic gneisses, as well as associated sedimentary rocks, within the Xinanchang (XAC) Complex. Zircon U-Pb dating yields a concordant age of 2078 ± 11 Ma for the andesitic gneiss, and a weighted mean 207Pb/206Pb age of 1835 ± 12 Ma for the granitic gneiss. The zircon grains from these gneisses exhibit oscillatory zoning and Th/U ratios of 0.40–0.94, corroborating their magmatic origins. Additionally, U-Pb age spectra of concordant zircon grains from the XAC strata range from 1.80 to 2.69 Ga. Together with the intrusive relationship between the 1.84 Ga granitic gneiss and the strata, this implies a depositional age of ca. 1.84 Ga for the XAC strata. The andesitic gneiss exhibits enrichment in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), but shows depletion in Nb, Ta, and Ti. These geochemical signatures are consistent with those of contemporaneous andesitic magmatic rocks in the northern Yangtze Block, suggesting that they were derived from subduction-related sources. In contrast, the granitic gneiss in the XAC Complex shows A-type granite affinities, similar to contemporaneous granitoids widely found across the Yangtze Block. This indicates that these granitoids were formed in a post-orogenic extensional tectonic setting. The northern and SW Yangtze blocks both show records of a transition from subduction to post-orogenic extensional environments between 2.10 Ga and 1.85 Ga, suggesting that the proto-Yangtze Block likely aggregated before 2.10 Ga.

Characterizing variability in geochemistry and mineralogy of western US dust sources

Dust events originate from multiple sources in arid and semi-arid regions, making it difficult to quantify source contributions. Dust geochemical/mineralogical composition, if the sources are sufficiently distinct, can be used to quantify the contributions from different sources. To test the viability of using geochemical and mineralogical measurements to separate dust-emitting sites, we used dust samples collected between 2018 and 2020 from ten National Wind Erosion Research Network (NWERN) sites that are representative of western United States (US) dust sources. Dust composition varied seasonally at many of the sites, but within-site variability was smaller than across-site variability, indicating that the geochemical signatures are robust over time. It was not possible to separate all the sites using commonly applied principal component analysis (PCA) and cluster analysis because of overlap in dust geochemistry. However, a linear discriminant analysis (LDA) successfully separated all sites based on their geochemistry, suggesting that LDA may prove useful for separating dust sources that cannot be separated using PCA or other methods. Further, an LDA based on mineralogical data separated most sites using only a limited number of mineral phases that were readily explained by the local geologic setting. Taken together, the geochemical and mineralogical measurements generated distinct signatures of dust emissions across NWERN sites. If expanded to include a broader range of sites across the western US, a library of geochemical and mineralogical data may serve as a basis to track and quantify dust contributions from these sources.

Final subduction-closure process of the Paleo-Asian Ocean in the middle segments of the southern Central Asian Orogenic Belt: Constraints from Permian volcanic rocks and late Triassic mafic dike swarms

The final subduction-closure process of the Paleo-Asian Ocean (PAO) in the middle segments of the southern Central Asian Orogenic Belt (CAOB) is widely debated. Linear arc-related pyroclastic sedimentary rocks and subsequent mafic-alkaline intrusive rocks parallel to the orogenic belt provide valuable constraints on ocean closure. Linearly distributed volcanic samples from the northern margin of the Alxa Block have zircon UPb ages ranging from 272 to 271 Ma, displaying arc geochemical signatures and large ranges of variation (−14.4 to +6.4) of zircon Hf isotopic composition. The Honggueryulin mafic dikes in the Nuoergong–Langshan Belt (NLB) with zircon and apatite UPb dating of 232–231 Ma show a clear geochemical imprint of subduction components with enrichment of light rare earth elements and large-ion lithophile elements (e.g., K, Rb, and Ba) and depletion of high-field-strength elements (e.g., Nb, Ta). The whole-rock major and trace elements and Sr–Nd–Hf isotopic compositions suggest that the Late Triassic mafic dikes mainly originated from a lithospheric mantle that had been metasomatized by subduction-related fluids. Coupled with published data, our geochronological and geochemical data support an east–west-trending Late Triassic alkaline–mafic intrusive rock belt distributed along the northern margin of the Alxa Block–North China Craton, which was formed in a post-orogenic intraplate extensional setting. These pyroclastic sediments and mafic dikes in the NLB document the tectonic transition from the Permian subduction to the Late Triassic post-orogenic extension. Therefore, the final closure of the PAO in the middle segments of the southern CAOB is constrained to between the Early and Middle Triassic.

Detachment of the Subducting Slab in Ancient Subduction Zones Discerned Using Machine Learning

AbstractIdentification of complex geochemical signatures of basalts from various tectonic settings using trace elements contents is still challenging due to uncertainties in existing classification diagrams and machine‐learning attempts. To address this, we trained a machine‐learning model using a random forest classifier on trace element concentrations of a global basalt‐dataset, categorized by types of tectonic plate boundary—destructive or constructive—at which they formed. Achieving an accuracy exceeding 98%, the model efficiently extracts the distinctive characteristics from each basalt type. When applied to the Bangong‐Nujiang suture zone in central Tibet, the model reveals that the basalts exhibited features of both boundary types prior to 108–107 Ma before transitioning to solely destructive characteristics. This transition is likely to be caused by the detachment of a descending oceanic slab, aligning with existing geological evidence. This case study highlights the promising potential of machine learning models, trained on simplified basalt types, in more accurately tracing lithospheric evolution.

The timing of the Middle Triassic magmatism in the Dolomites area (Southern Alps, Italy): U[sbnd]Pb geochronology of zircon and titanite hosted in plutonic rocks and phonolite dykes

The Middle Triassic magmatic event in the Southern Alps (Italy) is characterised by the emplacement and eruption of multiple magma batches with different geochemical affinities in a short time span. In this work, we present the first geochemical and geochronological data on highly differentiated alkaline dykes (phonolites) exposed in and near the Middle Triassic Predazzo magmatic complex (Southern Alps, Italy) and a first complete geochronological survey of the Predazzo pluton. The phonolites, cutting the Middle Triassic volcanic sequences, are sodalite- and aegirine-bearing and have titanite, apatite and magnetite as accessory phases. Their trace element concentration reflects a geochemical signature similar to the orogenic-like signature typical of the Middle Triassic magmatic rocks of the Predazzo complex. New in situ UPb dating on titanite from the phonolite dykes and UPb dating on zircon separates from all the magmatic units of the Predazzo pluton show that the phonolite dykes were emplaced between 233.8 ± 3.1 Ma and 238.1 ± 4.5 Ma, i.e., overlapping to and postdating the emplacement and crystallisation of plutonic rocks, which yield ages ranging from 237.97 ± 0.15 Ma to 238.31 ± 0.13 Ma. The ages obtained for the diverse suites of the pluton are in good agreement with previous dating and show that silica-saturated to -undersaturated rocks were placed within the same context in a short time span. Thermometry and hygrometry on titanite, clinopyroxene and K-feldspar revealed that phonolites represent volatile- and REE-rich (H2O = 8 ± 0.6 wt%) highly differentiated alkaline melts intruding at relatively low T (752–868 °C), which easily caused the spatially related CuW mineralisation. Comparisons with sub-volcanic rocks exposed in the Central (Edolo) and Western Alps (Finero mafic complex) indicate that the phonolites still preserve the orogenic signature of the Middle Triassic event in the Southalpine, that characterise all magmas emplaced before the opening of the Alpine Tethys in the Late Triassic. These new geochronological constraints on the Predazzo pluton and phonolite dykes enable us to outline the complete sequence of magmatic events associated with the emplacement of the Predazzo volcano-plutonic complex during Mid-Triassic and to speculate about the genesis of CuW mineralisation.

Gaussian process regression as a powerful tool for analysing time series in environmental geochemistry

Monitoring programs require more advanced data management for the registered time series. Classical temporal series decomposition cannot fulfil current needs regarding adequate data representation, optimization of the spatial-temporal sampling resolution and predictive power. In the manuscript at hand, we will demonstrate that Gaussian process regression (GPR) models are a vital machine-learning tool to interpret temporal series, improving understanding of geochemical cycles, providing input data for geochemical models and acting as a guide for future decisions in environmental monitoring. Firstly, we explore the impacts of sampling frequency in the GPR performance for temporal series with variable lengths and sampled frequencies of water discharges. On a second approach, we present the strengths and weaknesses between classical decomposition of temporal series and GPR results for a case study: a 14-year record of water discharge, suspended particulate matter and antimony concentrations in the Garonne River. Our results suggest that (i) even short temporal series with low sampling resolution can be accurately characterized by GPR when presenting well defined seasonal patterns, and (ii) GPR provides more detailed and robust support than classical statistics to identify processes responsible for multi-scale geochemical signals. This work provides a reference for researchers, engineers, and stakeholders for more reliable monitoring, understanding, and managing aquatic ecosystems.

Unraveling the genetic type and metallogenetic mechanism of the oldest uranium deposit associated with granitoid, South China: A comprehensive analysis of whole-rock geochemistry, and elemental and U-Pb isotopic signatures of uranium minerals

The Daliang deposit in the Motianling area of South China is unique for its synchronous uranium mineralization with regional metamorphism. To elucidate its genetic mechanism, whole-rock geochemistry from the Daliang deposit was undertaken, along with analyses of the chemical and isotopic signatures of minerals. The Motianling granitoids exhibit strongly peraluminous S-type affinities with low Th/U ratios, representing a uranium source for mineralization. Altered mineralogical and geochemical signatures of altered and ore samples indicate a multi-stage history after granitic emplacement: (1) Late magmatic-hydrothermal alteration characterized by greisenization, K-feldspathization, and propylitization; and (2) brittle-ductile deformation with uranium mineralization. Notably, ore-stage alteration mineral contains chlorite + quartz + sericite, which is consistent with the mineral assemblage of low-greenschist facies metamorphism. EMPA and LA-ICPMS dating on pitchblende yielded ages of 378 and 380 Ma, coinciding with the timing of regional ductile deformation. The pitchblende exhibits weak fractionation between LREEs and HREEs and negative Eu anomalies, mirroring characteristics observed in syn-metamorphic uranium deposits. Therefore, we suggest that uranium mineralization within the Daliang was related to crustal metamorphism, and the Daliang deposit belongs to syn-metamorphic deposit. Fluids likely have been liberated from the acidic brines-bearing Sibao Group that underwent low-greenschist facies metamorphism. Paleozoic intracontinental orogeny in South China resulted in brittle-ductile deformation in the Motianling pluton. These zones provided favorable pathways for the migration of ore-forming fluids and subsequent uranium mineralization. Late Devonian retro-metamorphism facilitated the percolation of oxidizing metamorphic fluids into the Motianling granitoids, circulating along the pre-existing brittle-ductile zones. This study presents the first evidence for syn-metamorphic uranium deposits within the granite of South China. This finding suggests potentially distinct mineralization mechanisms compared to traditional granite-related uranium deposits in the region, warranting further investigation.

Tectonic implications of a rare metamorphic event in eastern China during the Earth's ‘middle age’

The Mesoproterozoic Era has long been considered a relatively stable, silent and even ‘boring' period in Earth history, during which the lithosphere was tectonically inactive. However, an increasing amount of evidence suggests that metamorphism and magmatism were much more widespread and intense than previously thought, implying that this period was dynamic. Here, we report metamorphism at c. 1.4 Ga along the southeastern margin of the North China Craton in eastern China. We conducted analyses using a TESCAN Integrated Mineral Analyser (TIMA) combined with electron microprobe analysis (EMPA) and zircon sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry U–Pb dating on garnet amphibolites and their country rocks. The detailed mineral composition of a representative garnet amphibolite sample was identified and determined by TIMA. Phase equilibria modelling using pseudo-sections combined with the EMPA data indicated the peak metamorphism stage (M 2 ) of the garnet amphibolites at a P – T condition of 10.6–11.2 kbar and 820°C. The SHRIMP zircon U–Pb analysis yielded an age of 1366 ± 17 Ma for the garnet amphibolites, which is slightly younger than that of the country rock schist (1376 ± 22 Ma). Integrating the metamorphic event with geochemical signatures, magmatic records and sedimentation patterns in analogous geological settings on other continents, our findings collectively demonstrate a protracted and pervasive orogenic process along the periphery of the Columbia supercontinent.

Generation of Cu-Au skarn mineralization by mafic magma recharge: Insights from the Bozymchak deposit in the Chatkal-Kurama region, Kyrgyzstan, West Tianshan

Large numbers of igneous intrusions are emplaced in the magmatic arcs above subduction zones, but only a small fraction of them are mineralized with Cu ± Au ± Mo. Despite significant advances in recognizing the importance of magma source, volatile content, and redox condition in controlling mineralization, the magmatic processes required to form a mineral deposit are still poorly understood. Here, we demonstrate that mafic recharge to the magma chamber is critical for Cu-Au mineralization, as exemplified by the Bozymchak Cu-Au skarn deposit in the Chatkal-Kurama arc of Kyrgyzstan, West Tianshan. The Bozymchak intrusion associated with the mineralization comprises monzonite porphyry and granodiorite porphyry. A sensitive high-resolution ion microprobe zircon U-Pb age of 305 ± 2 Ma was obtained for the monzonite porphyry, which is consistent with the U-Pb age of zircon from the granodiorite porphyry (304 Ma) and an Re-Os age for the molybdenite (305 Ma). These ages indicate that both the monzonite porphyry and granodiorite porphyry were coeval with mineralization. The monzonite porphyry exhibits high-K calc-alkaline (K2O = 3.36−3.50 wt%), metaluminous and magnesian-rich characteristics, enrichment in large ion lithophile elements (LILEs; e.g., Cs, Th, Ba, K, and Pb), and negative anomalies in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti). These geochemical signatures, combined with the Sr-Nd-Hf isotopic signatures [ISr(avg) = 0.7059, εNd(t) = −3.5 to −2.8, εHf(t) = −3.8 to +1.4], suggest that the magma was the product of partial melting of a metasomatized mantle wedge and was subjected to subsequent assimilation and fractional crystallization (AFC). The development of disequilibrium textures in both the monzonite porphyry and the granodiorite porphyry, such as acicular apatite, reverse zoning of plagioclase, and coexisting high-Al and low-Al amphiboles, indicates that the magma evolved in an open crustal magma chamber with mafic magma recharge. The magmas were moderately oxidized (∼ΔFMQ +1.0; FMQ is the fayalite-magnetite-quartz oxygen buffer) and water-rich, with 5.9 wt% and 6.5 wt% H2O in the granodiorite porphyry and monzonite porphyry, respectively. The repeated influx of hot mafic magma batches prolonged the existence of the magma chamber and promoted the maturation of the arc magma. In addition to introducing more Cu and Au, the replenishment of mafic magma in the chamber also introduced additional H2O and Cl, as shown by the presence of high-Al amphiboles and the elevated oxygen fugacity, which further promoted Cu-Au mineralization.

Early Cretaceous to Eocene magmatic evolution of Livingston Island, South Shetland Archipelago: Geochronological and isotope geochemical constraints from intrusive suites

The magmatic products exposed across Livingston Island comprise a part of the South Shetland magmatic arc built on an active continental margin. The main magmatic phases of Livingston Island include the Early to Late Cretaceous plutonic and volcanic rock associations, the Eocene plutons, and some sporadically distributed intrusions of Paleocene to Eocene dykes. The intrusions were emplaced into the strongly deformed turbiditic sedimentary rocks of the Miers Bluff Formation. 40Ar39Ar and zircon UPb geochronologic data presented here define four distinct episodes of intrusive activity represented by the emplacement of the Hesperides (125 Ma), the Cerro Mirador (104–97 Ma), the Siddons Point (80 Ma) and the Barnard Point suites (42 Ma), in addition to some dyke intrusions with emplacement ages of 105 to 40 Ma. The intrusions are represented by mafic to intermediate compositions characterized by middle potassic, calc-alkaline affinities, with only a few samples from the Eocene activity exhibiting tholeiitic character. Trace element, Sr-Nd-Pb isotope and zircon Hf isotope variations indicate magma generation in a subduction setting with extensive involvement of continental crust-derived melts for the Early to Late Cretaceous activity. The effects of crustal input on melt chemistry appear to have diminished in time, especially from the Paleocene onwards, leading to magma generation with typical oceanic island arc geochemical signatures. This change in melt chemistry is likely partly related to the roll-back induced overriding plate extension which resulted in a time-integrated increase in the rate of melt movement and a decrease in the residence time in crustal levels. Slab steepening caused by the systematic decrease in plate convergence rate led to an enhanced involvement of isotopically depleted mantle component, producing a heterogeneous source with variable subduction signature.

Diagenetic impacts on calcium isotopes and Mg/Ca ratios of Globigerinoides ruber shells in the eastern Mediterranean

The presence of Mg-rich calcite in foraminifera shells has impeded traditional calcite-based paleothermometry in the eastern Mediterranean, complicating our understanding of the region's past climate. This study analysed the calcium isotopic composition ( δ 44/40 Ca) in the shells of the planktonic foraminifera species Globigerinoides ruber (white), collected from 12 core top sediment samples spanning the Aegean and Levantine Seas in the eastern Mediterranean. The shells exhibited varying degrees of early diagenetic Mg-rich authigenic calcite coatings, which complicates traditional calcite-based paleothermometry in the region. Our findings demonstrate a significant correlation between the δ 44/40 Ca data and the Mg/Ca ratios of the shells and suggest that the inorganic calcite overgrowth originates from seawater. Moreover, the calcium isotopic composition increases with the amount of calcite overgrowth. This relationship allowed us to quantify the maximum potential inorganic endmember. The highest amount of post-depositional calcite precipitation was observed in the warm, shallow basins of the South Aegean Sea. The diagenetic alteration of the primary biogenic δ 44/40 Ca geochemical signal is linked to the quantity of secondary calcite present. By combining Ca isotope and Mg/Ca measurements on isolated foraminifera tests, we provide novel insights into the early diagenetic history of carbonate-bound geochemical proxies.

Late Cretaceous ecosystem dynamics in the southern incipient Arctic Ocean: A micropaleontological and geochemical perspective

Micropaleontological and geochemical analyses in samples from the Coniacian-Maastrichtian-aged Smoking Hills and Mason River formations in the Anderson Basin of the northern mainland coast of Arctic Canada provide a refined picture of the environmental conditions occurring in the incipient southern Arctic Ocean at the end of the Cretaceous. These units were deposited within a 22 myr time span in an outer shelf setting characterized by relatively stable tectonic conditions and low sedimentation rates. The Coniacian-middle Campanian Smoking Hills Formation was deposited during times of marine transgression and water column stratification. Surface waters were highly productive and dominated by dinoflagellates, red algae, green algae and likely diatoms and silicoflagellates. Bottom waters were predominantly anoxic-euxinic, but the presence of benthic foraminifera and variations of geochemical signatures in some intervals indicate episodic ventilation. The deposition of the Smoking Hills Formation is temporally consistent with the Oceanic Anoxic Event 3 (OAE3), but the duration of these anoxic conditions is much longer in the Anderson Basin. During the middle Campanian, relative sea level reached a highstand, fostering the expansion of planktic siliceous microorganisms, including diatoms, silicoflagellates and radiolarians. During the late Campanian to at least the Maastrichtian, sediments of the Mason River Formation were deposited during a regressive sedimentation phase characterized by high productivity fueled by river run-off and the proliferation of diatoms, red and green algae. Despite high productivity, bottom waters were oxygenated. This study highlights the importance of data integration to reconstruct the environmental conditions of the past as many, if not all, of the proxies utilized to this end are subjected to preservational and diagenetic bias.

Morphology, epidermal features and δ13C signature of Lopingian (late Permian) conifers

Conifers, the most successful group of Permian gymnosperms, dominate the famous Bletterbach (Dolomites, NE-Italy) plant fossil assemblage, a highly diverse and well-documented late Permian (Lopingian) flora. An integrated analysis of morphology, cuticles and isotope geochemistry was carried out on approximately 50 conifer shoots across five genera (Ortiseia, Majonica, Dolomitia, Pseudovoltzia and Quadrocladus) and eight species, including three (Pseudovoltzia sjerpii, Quadrocladus solmsii, Quadrocladus cf. orobiformis) described for the first time from Bletterbach. Taxon-specific carbon isotope analyses reveal intra-specific and/or intra-generic variability, identifying a unique geochemical composition for Majonica alpina, which may reflect a possible species-specific geochemical signature or adaptation to particular environmental conditions. The isotopic differences observed between leaves and axes indicate the preservation of distinct isotopic ratios in photosynthetic versus heterotrophic tissues, underscoring the importance of sampling multiple plant parts to accurately capture individual and taxonomic isotopic variability. The study of stable isotopes of organic carbon on well-preserved plant remains is enhanced the paleoenvironmental reconstruction of the Bletterbach flora.

The Borborema province (NE Brazil) Neoproterozoic magmatic arcs: A review of geochemical and isotopic data of granitic rocks

The Borborema Province in NE Brazil is assumed to have been formed by Cryogenian-Ediacaran convergent events during the assembly of western Gondwana. Among the many geological markers of such episodes, the granitic record is widespread, representing the best testimony of the Brasiliano-Pan African Orogeny that took place between 800 and 500 Ma. Several granitic batholiths and stocks are interpreted as root remnants of arc edifices that grew during the consumption of large tracts of oceanic crust, such as the Goiás-Pharusian and Transordestino-Central África realms. Most of them share geochemical signatures that are typical for subduction-related magmas, such as enrichment in large-ion lithophile elements, aligned with depletion in high-field strength elements, including negative anomalies in Nb, Ta, P, and Ti, as well as systematic plots consistent with convergent-related settings in classical tectonic discrimination diagrams. The older record is represented by the Lagoa Caiçara unit (ca. 880-800 Ma) of the Santa Quitéria magmatic arc of the Northern Subprovince, interpreted as relics of an intra-oceanic setting, responsible for lithospheric growth in the region. A subsequent magmatic episode is marked by the injection ca. 650-620 Ma cordilleran and peraluminous magmas that formed a large set of batholiths and stocks in the Santa Quitéria and Conceição (Transversal Subprovince) magmatic arcs, as well those related to the Pernambuco-Alagoas Terrane and Sergipano Belt in the Southern Subprovince. Rocks crystallized in this age interval share similarities with those of the calc-alkalic and alkali-calcic series, interpreted to have been emplaced in the continental crust via upper mantle melting and subsequent crustal contamination. Finally, rocks aged between ca. 620-550 Ma are widespread and represent high-K, meta-to peraluminous and alkali-calcic precursor magmas, that also share geochemical similarities with S-type granites (crustal anatexis), being interpreted as syn-collisional with respect to the final assembly of Gondwana. The final framework of the Borborema Province is marked by extrusion tectonics that is materialized by the complex network of shear zones deforming the previous formed granites and injecting of non-subduction related melts. Although there is a lack of consensus regarding the assembly of the province during the Neoproterozoic, we suggest that accretionary-collisional events played a major role, as testified by the geochemical-isotopic signature of the arc-related granites, in addition to a number of structural, geophysical, and geological mapping data published in the recent years.

Jurassic magmatism in the Garzón region of the Colombian Andes: insights from whole-rock geochemistry and zircon isotope analysis of granites and subvolcanic rocks

ABSTRACT New whole-rock geochemical and zircon U – Pb dating and Lu – Hf isotope data are presented for the Garzón granites and related subvolcanic rocks, which formed during widespread Jurassic arc magmatism in the Colombian Andes. This magmatism resulted from the subduction of a proto-Pacific plate under the NW South American margin. Our data indicate that the granitic and related rocks of the Algeciras, Altamira, and Sombrerillo Plutonic Massifs in the Garzón region have crystallization ages ranging from 179 to 169 Ma. These rocks are characterized as high-K alkali-calcic or calc-alkaline, magnesian, with 0.66 ≤ Fe# ≤ 0.94, and metaluminous to slightly peraluminous, with 0.67 ≤ ASI ≤ 1.01, exhibiting geochemical signatures. The trace element patterns normalized to MORB reveal pronounced negative anomalies for Nb, P, and Ti, alongside positive anomalies for Pb, Rb, Sr, Y, Zr, and Ba. The REE patterns display strong LREE fractionation over HREEs, with moderate to absent negative Eu anomalies in mafic to intermediate rocks (0.5 ≤ Eu/Eu* ≤ 1.0) and greater significance in felsic rocks (Eu/Eu* up to 0.6). Most granitic rocks display negative εHf(t)-in-zircon values (−7.7 to −1.2), indicating substantial contributions from ancient continental crust. In contrast, the subvolcanic rocks have a mix of positive and negative εHf(t) values (from −7.9 to + 11.5), reflecting significant input from both juvenile mantle and ancient crustal sources (221 Ma ≤ TDM ≤1516 Ma). After 167 Ma, the magmatic activity diminished and ceased in the Garzón region, while it continued to the west in the Central Cordillera until ca. 129–110 Ma, with a gradual increase in contributions from the mantle, as indicated by systematic zircon Hf isotopes, arguably due to changes in the subduction regimes.

Carbon, iron and sulfur records of lacustrine paleo-environments during the middle Eocene in eastern China

It is widely recognized that anoxic conditions facilitate the preservation of organic carbon in marine sediments. However, the specific geological factors that lead to the development of such conditions in paleo-lakes are less well understood. Owing to their smaller size, paleolakes could experience more frequent and stronger changes in geochemical conditions than oceans. Such changes, such as volcanism, hydrothermal fluids, or ocean transgressions, can also strongly affect the lacustrine organic carbon burial thereby complicating sediment diagenesis record. Here, we used total organic carbon content (TOC), organic carbon isotope (δ13Corg), iron speciation, and pyrite sulfur isotope (δ34Spy) data to establish relationships between organic carbon preservation and anoxic conditions in fine-grained sediments from the middle Eocene lacustrine depositional environments from the Shahejie Formation of the Jiyang Depression, Bohai Bay Basin, eastern China. The results reveal TOC between 1 % and 10 %, highly-reactive iron to total iron ratios >0.38, and most TOC to total sulfur ratios exceeding 2. These data indicate that the organic-rich shales of the Shahejie Formation were formed as a result of high primary productivity during the warm and humid middle Eocene period, coupled with the efficient preservation of organic matter in anoxic bottom waters. Negative δ13Corg and δ34Spy excursions recorded in the Shahejie Formation indicate water column conditions to have been influenced by transient volcanic eruptions. Positive δ13Corg and negative δ34Spy excursions may have been caused by hydrothermal fluids input whereas δ34Spy values approaching 20 ‰ suggest frequent marine transgressions. In particular, despite potential inputs of S into the paleolake by volcanism, hydrothermal fluids, or marine transgressions, bacterial sulfate reduction efficiently depleted the sulfate pool to have created ferruginous geochemistry water conditions for the effective preservation of organic carbon in sediments. Our results establish a direct link between lacustrine shale geochemical signatures and geological phenomena that impact its sedimentation.