Isotope Data Research Articles

Re−Os Isotope and PGE Abundance Systematics of Coast Range Ophiolite Peridotites and Chromitite, California: Insights into Fore-Arc Magmatic Processes

Abstract We report platinum-group element (PGE) and Re concentrations, and Re−Os isotopic data for peridotites and podiform chromitite from the mid-Jurassic Coast Range ophiolite (CRO), California. Our aim is to provide insights into the formation and evolution of the CRO in a fore-arc tectonic setting. The CRO peridotites are divided into two groups: abyssal and supra-subduction zone (SSZ). They have Ir-group PGE concentrations similar to estimates for the primitive mantle and nearly chondritic relative abundances [(Os/Ir)N ≈ 1.1]. Abyssal-type peridotites have slightly subchondritic Pd-group PGE (PPGE)−Re abundances and flat chondrite-normalized patterns, whereas the SSZ-type ones are depleted overall with highly fractionated PPGE−Re patterns. The CRO peridotites have 187Os/188Os values of 0.1188 to 0.1315 (γOs = −8.3 to 1.4) and 187Re/188Os ranging from 0.022 to 0.413. The oxygen fugacity based on the V/Yb ratios of the CRO peridotites is equivalent to the fayalite−magnetite−quartz buffer. The abyssal-type peridotites are residues after ≤5% melting of the primitive upper mantle and represent a remnant of oceanic lithosphere trapped in an SSZ setting but before it was re-melted or modified by subduction processes. The abyssal-type peridotites yield an aluminachron model age of ~1.5 Ga, implying that the CRO mantle had experienced episode(s) of melt extraction before the CRO crust was formed. The SSZ-type peridotites are refractory residues after ~5% to 15% melting. Extraction of fore-arc basalts generated mainly by decompression melting resulted in the SSZ-type peridotites. The chromitite has 187Os/188Os value of 0.1250 (γOs = −3.5) and PGE−Re patterns complementary to that of boninite, indicating a genetic link to fore-arc magmatism.

Home on the range: A multi-isotope investigation of ungulate resource partitioning at Ashfall Fossil Beds, Nebraska, USA

During the Miocene (ca. 23.0–5.3 Ma), North America's Great Plains were a broad mosaic of savanna-woodlands inhabited by a diverse ungulate fauna. We investigated resource partitioning among ungulates at Ashfall Fossil Beds State Historical Park (henceforth “Ashfall”) in north-central Nebraska to establish how taxa shared the landscape. This mid-Miocene (11.86 ± 0.13 Ma) site preserves a watering-hole filled with volcanic ash that entombed hundreds of skeletons of medium- and large-bodied ungulates. We analyzed carbon (δ13C), oxygen (δ18O), and strontium (87Sr/86Sr) isotopes in enamel from seven species: the rhinoceros Teleoceras major (n = 13); three horses (Cormohipparion occidentale, Pliohippus pernix, and Pseudhipparion gratum; n = 3 each); two camels (Procamelus grandis and Protolabis heterodontus; n = 1 each); and one small ruminant artiodactyl (Longirostromeryx wellsi; n = 3). Carbon isotope data indicate that all seven ungulates foraged in open habitats dominated by C3 plants (enamel δ13CVPDB range from −9.6‰ to −6.9‰) with little to no evidence of C4 plant consumption. The overall range in δ18OVPDB values is ca. 6‰ (−7.6‰ to −1.3‰), while the range for 87Sr/86Sr is narrow (0.70864–0.70898). Horses have significantly higher δ18O and 87Sr/86Sr than T. major, which we suggest indicates horses foraged in relatively dry habitats, while T. major inhabited wet habitats with different strontium sources. Both camels isotopically resemble horses, and Longirostromeryx wellsi has intermediate 87Sr/86Sr and wide-ranging δ18O values. Plotting Teleoceras and co-occurring ungulates in a model that tests for semi-aquatic behavior using δ18O suggests that T. major from Ashfall was semi-aquatic; ecology and behavior may have varied among Teleoceras species living in different places at different times. This study exemplifies how 87Sr/86Sr data complement δ13C and δ18O analyses when reconstructing ancient environments; they can provide nuanced ecological information even in landscapes with homogeneous bedrock.

Arc building and maturation of the Lombok Island, East Sunda Arc

Intra-oceanic subduction zones are major sites of crust–mantle material exchange and crustal growth; however, the processes responsible for the magmatic evolution and transformation of nascent arcs into mature oceanic arcs with thicker crust are debated. We present mineral chemistry, zircon UPb age and Hf isotopic data, and whole-rock chemical and Sr–Nd–Hf–Pb isotopic data for Cenozoic volcanic rocks on Lombok in the East Sunda Arc, Indonesia, to investigate their petrogenesis and arc maturation. SIMS zircon UPb analyses of lavas from southern Lombok yield an early Oligocene age of ∼30 Ma. The lavas can be divided into three groups based on their ages and geochemical characteristics: group I (late Eocene) and II (∼30 Ma) lavas from southern Lombok, and group III lavas (∼3–0 Ma) from northern Lombok. The lavas are characterized by a progressive enrichment in K2O and incompatible element contents, and NdHf isotopic compositions with time. Group I lavas are tholeiitic basalts with low K2O contents (0.15–0.17 wt%) and Indian-MORB like rare earth element (REE) patterns and NdHf isotopic compositions (εNd = +7.4; εHf = +14.5), enrichment in large-ion lithophile elements (e.g., Rb, U, and K), and typical forearc basalt (FAB) geochemical characteristics. Group II lavas are low-K basaltic andesites to dacites that yield flat chondrite-normalized REE patterns [(La/Sm)N = 0.9–1.4], uniform initial 87Sr/86Sr ratios (0.7038–0.7042), and positive εNd(t) (+5.9 to +6.8) and εHf(t) (+13.9 to +14.4) values. Group III lavas are typically medium- to high-K calc-alkaline basalt to andesite and are enriched in light REEs [(La/Sm)N = 1.6–3.3] with uniform initial 87Sr/86Sr ratios (0.7038–0.7042) and slightly low εNd(t) (+3.9 to +5.4) and εHf(t) (+10.5 to +12.5) values. Progressive enrichment in incompatible element contents and NdHf isotopic compositions over time, from FAB to high-K calc-alkaline lavas, reflect the maturation of the East Sunda Arc. Sr–Nd–Pb–Hf isotopic mixing models, along with trace element ratios (e.g., Ba/Th, La/Yb, Th/Yb), suggest that increasing amounts of sediments were incorporated into the mantle sources of the magmas from group I (∼0%) to group II (<0.5%) and group III (0.5%–1.0%) lavas. Partial melting models show that the formation of group I and II lavas can be reproduced by high-degree (∼10%) partial melting of spinel peridotite, whereas the group III lavas were formed by low-degree (∼5%) partial melting of spinel peridotite. We propose that the evolution of Lombok arc magmas was controlled mainly by the fluxes of subducted slab material, along with decreasing degrees of partial melting as a result of crustal thickening over time.

Barium-Mg isotopes in high Ba-Sr granites record a melt-metasomatized mantle source and crustal growth

High Ba-Sr granites are geochemically distinct from the more familiar I-, S- and A-types (of igneous, sedimentary or anorogenic/anhydrous/alkaline parentage), in particular by their lack of depletion in Ba and Sr relative to other large-ion lithophile elements (LILE). These differences are sufficient enough to indicate different petrogenetic processes which are still the subject of considerable debate. High Ba-Sr plutons from the classic Caledonian type location in NW Scotland show a range of elemental and isotopic enrichment, ideal for novel petrogenetic investigations such as the application of “non-traditional” stable isotope systems. Two directly comparable plutons have been analysed for Ba and Mg isotopes, from either end of the range of enrichment. Barium isotopes (δ138/134Ba values of −0.05 to +0.23 ‰ in the relatively “depleted” Strontian pluton and −0.19 to +0.03 ‰ in the enriched Rogart comparator) overlap normal mantle values but extend to lighter compositions, consistent with addition of up to 5 % pelagic sediment that has incorporated variable amounts of biogenic barite. Magnesium isotopes (δ26Mg values of −0.30 to −0.25 ‰ versus −0.42 to −0.23 ‰ in Strontian and Rogart, respectively) lie largely within the normal mantle range, with two light outliers possibly indicative of carbonate involvement but for which fractional crystallization cannot be excluded. Associated relationships between fluid-mobile and melt-mobile elements suggest that sediment melting transfers the crustal isotope signature to a dominantly mantle source, itself variable between isotopically depleted mantle wedge and previously enriched lithospheric mantle. The combined Ba, Mg, O, Sr, and Nd isotope and elemental data are all consistent with a small percentage of pelagic sediment in a mantle source for high Ba-Sr granites, and this is sufficient to disguise these essentially mantle-derived rocks as reworked continental crust. First-order estimates suggest that some 10 % of granites worldwide may have high Ba-Sr character, although the proportion of these that represent largely juvenile origin is currently unknown. Nevertheless, as compositional equivalents of Archean sanukitoids, they may represent unrecognized mantle contributions to crustal growth over some 3 billion years of Earth history.

A comparative study of different radiometric dating techniques applied to Quaternary volcanic rocks from Jeju Island, South Korea

A comparative study of different radiometric dating techniques applied to Quaternary volcanic rocks from Jeju Island, South Korea

Zircon and cassiterite geochronology of Sn-polymetallic pegmatite from the Xianghualing ore field, South China: Implications for multi-stage magmatic-hydrothermal events

The Nanling metallogenic belt (South China) is one of the largest W-Sn polymetallic provinces in the world. The ore bodies are mainly hosted in Triassic-Jurassic granitoids which formed during a complex history of magmatic evolution. Among them, the Laiziling pluton, which forms the northern part of the Xianghualing district, is an example of Sn-polymetallic deposits that underwent multiple Mesozoic episodes. In this study, the first in-situ U-Pb age dating of zircon and cassiterite minerals, trace element, and Lu-Hf isotopic data are reported for Laiziling NYF-type pegmatites. Four types of pegmatites are identified: stock-like pegmatite, vein-type pegmatite, peripheral vein-type pegmatite, and cap/sill-like pegmatite. Zircon LA-ICP-MS U-Pb geochronology of pegmatites yields an age of ~150 Ma, which is consistent with the age of the associated mineralized granitic pluton. Results of cassiterite age dating indicate that the W-Sn mineralization took place at ca. 150 Ma coeval with pegmatite emplacement. Combined with structure and trace element composition, two young ages (i.e., ~130 and 90 Ma) can be identified from pegmatite veins, suggesting that the studied zircon crystals experienced two distinct periods of magmatic-hydrothermal evolution during the Cretaceous (related to Late Yanshanian magmatism). In addition, some zircon grains are obviously enriched in LREE, which is associated with hydrothermal metasomatism. Compared to the narrow range of magmatic zircons, a wide range of inherited zircons (Proterozoic to Paleozoic) are observed in the studied Late Jurassic pegmatite (Pg1 and Pg2b), suggesting that they were incorporated from pre-existing basement rocks during magma ascent and/or emplacement. Furthermore, U-Pb data for 14 disseminated cassiterite grains yield a 206Pb/238U age of 221.5 ± 4.2 Ma, documenting evidence of cassiterite inheritance during melt ascension from country rocks or representing the initial stage of Sn enrichment. The εHf values of magmatic zircons show negative εHf values from −4.4 to −16.6 and their crustal model ages (TDM2) vary between 1328 Ma to 2200 Ma, suggesting the parent magma of the Laiziling pegmatites were derived from partial melting of older crustal components (Proterozoic basement in the Cathaysian Block of South China) and the mixing of mantle materials. This study proposes that multi-stage magmatic-hydrothermal events may have occurred not only in the Xianghualing area but also in the whole Nanling Range, and provides fresh insights into the formation processes of rare metal-bearing pegmatites in South China.

Mandibular bone mass density in a medieval population and its relationship with stable isotopes δ13C and δ15N.

The aim of this study was to compare the level of bone mass in digital orthopantomograms in two populations (medieval and current) using two radiomorphometric indexes, and to correlate the mandibular bone mass value, in the medieval mandible population, with stable isotope data δ13C and δ15N. An observational, cross-sectional, and analytical study on mandibles from two diachronic groups, 15 mandibles from the medieval settlement of La Torrecilla (Granada, Spain) and 15 mandibles from current patients at the Faculty of Dentistry of the University of Granada (Spain), matched by age and sex was conducted. The bone mass density was determined using the Mandibular Cortical Width Index (MCW) and the Mandibular Panoramic Index (PMI) in digital panoramic radiographs. In the medieval group, the values of bone mass density were correlated with those of two stable isotopes (δ13C and δ15N). The mean value of MCW in mm in the medieval group was 3.96 ± 0.60 (mean ± standard deviation) and in the current group was 4.02 ± 1.01. The PMI was 0.33 ± 0.06 and 0.35 ± 0.08 in the medieval and current groups respectively, with similar results in both groups (p = 0.820 and p = 0.575). A negative correlation was found between both morphometric indices and the δ15N isotope (rs = 0.56, p = 0.030 and rs = 0.61, p = 0.016, respectively). The bone mass density in mandibles belonging to the two compared populations, determined by two quantitative radiomorphometric indices, is similar. Within the medieval population, there is an inverse correlation between the δ15N value and bone mass density.

Pan-tropical daily L-band microwave land surface emissivity retrieval from GNSS-R observations

ABSTRACT The uncertainties in microwave land surface emissivity (MLSE) measurements have long limited the use of spaceborne microwave radiometer data. As an emerging observation method, Global Navigation Satellite System Reflectometry (GNSS-R) has demonstrated great potential in several land and ocean applications. In this study, a method for obtaining daily MLSE dataset in the pan-tropical region from Cyclone GNSS (CYGNSS) observations is presented and evaluated. The CYGNSS observations are first aggregated into the Equal-Area-Scalable-Earth (EASE) 2.0 36 km grid by a combined weight function of distance, time, and signal-to-noise ratio variance. Then, the method employs a pixel-by-pixel regression algorithm to conduct the daily MLSE retrieval using reference emissivity derived from the Soil Moisture Active Passive (SMAP) brightness temperature. The CYGNSS MLSE shows good agreement with SMAP MLSE, delivering an overall root-mean-square error (RMSE) of 0.022 and 0.017 for horizontal and vertical polarization, respectively, during the training set spanning the whole year of 2018. Furthermore, on the test set from January 2019 to May 2019, the RMSE values amounted to 0.030 and 0.023 for horizontal and vertical polarization, respectively. Temperature records from the International Soil Moisture Network are employed to calculate the emissivity and for in-situ validation, which yield an RMSE of 0.034 and 0.026 for the two polarizations, respectively. The proposed algorithm provides an encouraging approach to obtain accurate daily MLSE dataset for microwave remote sensing. Compared to the SMAP MLSE, the CYGNSS MLSE has a remarkable improvement of 86% in temporal resolution, greatly complementing the existing microwave emissivity datasets.

Radiometric and petrographic characterization of El-Yatima granite: Evaluating radiological risks and mineralogical features

The current investigation aims to assess the potential of El-Yatima granitic pluton as a decorative stone by examining its natural radioactivity and mineralogical elements. Specifically, the study aims to determine the concentrations of radionuclides 40K, 232Th, and 226Ra, perform petrographic analyses, and evaluate the associated radiological risks to determine the safety and usability of the granite in construction and decoration, as well as to assess the potential of these granitic rocks as a safe and effective decorative stone for various applications. It has a 12 km2 surface area of 812 m above sea level. It is situated in the Eastern Central Desert. Its hypidiomorphic texture, medium-to-coarse grain size, and predominant composition of K-feldspars, quartz, and plagioclase are observed, along with minute amounts of muscovite and biotite. By employing NaI (Tl) gamma-ray spectroscopy, the natural radionuclide concentrations of 40K, 232Th, and 226Ra in El-Yatima granitic rocks were ascertained. Additionally, radiological concerns were identified for the materials that were examined. The average concentrations of radionuclides 40K, 232Th, and 226Ra are 178 Bqkg−1, 44 Bqkg−1, and 41 Bqkg−1, respectively. The following are the computed values: 117 Bqkg−1, 0.43, 0.32, 53 nGyh−1, average radium equivalent (Raeq), hazard indices (Hin and Hex) and dose rate (D), respectively. When compared to levels typically indicated, it was discovered that its values were within the worldwide standard. The study's findings could be a starting point for radiometric data for upcoming surveillance and epidemiological research.

Dogs under urbanization: Isotopic insight from the Bronze Age Central Plains of China (ca. 2000–1000 BCE)

Although dogs played multifaceted roles during the early stages of urbanization in China’s Central Plains, research remains limited concerning the management of dogs, the dynamics of human–dog relationships, and dogs’ entanglements with the political economy, ritual, and daily life. Here, we compare stable carbon and nitrogen isotope data from 95 dogs and associated human skeletons from 15 Late Neolithic – Bronze Age sites. Results show two distinct dietary patterns in dogs. Early sites (Xinzhai-Erlitou period, 1900–1520 BCE) show more variability in dog diets, indicative of looser approaches to dog management. Later sites (Late Shang-Western Zhou periods, 1320–770 BCE) show a widespread, homogeneous diet among dogs characterized by higher consumption of C4 millet (greater than in humans’ diets), suggesting the possibility of the emergence of specialized, broadly shared dog management practices linked to increased ritual use of dogs. This study also underscores the complexity of management practices, which would have been influenced by site-specific conditions, including environment and available resources, the site’s position in hierarchical settlement networks, and the varying roles of the dogs. Importantly, this study demonstrates that the comparison of isotopic data from broad temporal and spatial contexts can shed light on animal management practices in early urban economic systems and political economies.

Geochemistry and fluid inclusion study of the Jbel Tirremi fluorite-baryte deposit, Morocco: New insights into the genetic model in relation to Mesozoic tectonics

The highly fractured Jurassic carbonates at Jbel Tirremi in northeastern Morocco host fluorite-baryte deposit. The mineralization occurs both as stratabound in marl-limestone contact and as fault-hosted veins (N-S- and NNW-SSE). The mineral paragenesis consists of two fluorite and baryte generations and calcite with subordinate amounts of quartz, dolomite, traces of sulfides (chalcopyrite, pyrite, galena), and oxidized minerals. Fluid inclusion data reveal that hot moderately saline fluids derived from the Paleozoic basement mixed with Triassic brines and cooler, meteoric waters. The REY inventory, C-O-S-Pb-Sr-Nd isotope, and crush-leach data point to the Paleozoic basement as the primary source of metals with a contribution from the Triassic red beds. The refined ore genetic model developed in this study from our new geological and geochemical data includes the downward movement of Triassic-Jurassic evaporated seawaters along normal faults, followed by the leaching of metals from Paleozoic and Triassic rocks, and the subsequent upward flow of these metalliferous fluids. During the Late Cretaceous-Paleocene basin inversion, the deep-seated ore-forming fluids migrated upward, which eventually mixed with Triassic brines and cooler meteoric waters. This fluid mixing caused the precipitation of multiple generations of fluorite and baryte.

Maintaining the Ramesside Empire: Isotopic Evidence for Elite Migration to Upper Nubia under Pharaonic Rule

Abstract Pharaonic Egypt ruled Upper Nubia (now northern Sudan) from around 1450 to 1070 BCE: previous research has demonstrated how co-opted local elites and descendants of earlier immigrants held senior administrative positions following the initial conquest. Strontium isotope data from 39 individuals buried at the colonial centre of Amara West, combined with archaeological and epigraphic evidence, enable us to demonstrate that elites continued to arrive from outside Nubia in the last 150 years of pharaonic rule, settling amongst long-standing communities. Migration to the occupied territory clearly remained a key component of the colonial project, at a time when indigenous Nubian material culture and practice had become more visible within the pharaonic towns. This pattern of immigration seems to have ceased following the pharaonic state losing control of the region.

Magnesium isotope fractionation during magmatic differentiation in the lower continental crust

The Mg isotopic compositions display a significant disparity between the lower continental crust and the mantle. However, due to the limited availability of representative samples from the lower crust, our understanding remains incomplete regarding whether Mg isotope fractionation occurred during its formation and its potential influence on the observed isotopic differences. This study addresses this gap by presenting Mg isotopic data for juvenile lower crustal mafic xenoliths from Daoxian, Southeast China, providing new insights into this poorly understood process. The xenoliths, classified as websterites and two-pyroxene granulites, equilibrated at 818–912 °C and 10.6–15.4 kbar. They exhibit high Mg# (77–85), Cr (154–1451 ppm), and Ni (143–312 ppm), as well as trace element patterns resembling those of island arcs and evolved Sr–Nd–Pb isotopic compositions (87Sr/86Sri = 0.7046–0.7071; εNd(t) = −2.44 to +4.62; 206Pb/204Pbi = 18.26–19.03), indicating their derivation primarily from an enriched mantle source. Despite this, these xenoliths display a diverse range of Mg isotopic compositions. Websterite xenoliths exhibit mantle-like δ26Mg values (−0.27‰ to −0.29‰), indicating no influence from hybridized mantle source or pyroxene fractional crystallization/accumulation on their Mg isotopes. In contrast, granulite xenoliths show lower and variable δ26Mg values (−0.26‰ to −0.49‰), which positively correlate with Mg#, Cr, and V, but negatively correlate with Na2O + K2O, indicating that magmatic processes likely influenced Mg isotope fractionation in these samples. Petrological features, coupled with correlations between MgO and CaO/Al2O3, Cr, Co, and Ni, indicate that fractional crystallization and/or accumulation of olivine, spinel, clinopyroxene, orthopyroxene, and plagioclase played crucial roles in the formation of the granulite protoliths. Furthermore, the segregation of spinel during magmatic differentiation could have enriched residual melts in light Mg isotopes inherited by the cumulate Cpx + Opx + Pl (i.e., the granulite protoliths). Overall, the weighted average δ26Mg value of the lower crust in South China is estimated to be −0.34 ± 0.04‰. This finding, together with previous studies on granulite xenoliths in North China and Australia, strongly indicates heterogeneous Mg isotopic compositions in the lower continental crust relative to the mantle.

Hydrogeologic and hydrochemical inputs to emerging wetlands on the shores of the receding Salton Sea, California

AbstractThe Salton Sea has experienced significant recession over the past two decades due to changes in the diversion of Colorado River water to the Salton Trough for agricultural irrigation. As a result, wetlands have emerged in some exposed playa areas along the Salton Sea, primarily in regions with extensive agricultural return flows and agricultural drainage. One notable wetland system, known as the Bombay Beach Wetlands, has formed on the north shore of the Salton Sea, in an area devoid of agriculture. In many other areas with limited or no agriculture, wetlands have failed to develop, leaving exposed playa surfaces as the Salton Sea recedes. These dry playa surfaces pose a significant threat to the health of local residents due to the presence of toxins contained in windblown dust associated with playa deposits. In this study, stable water isotope data, combined with other hydrological information, led to identification of two potential water sources for the Bombay Beach Wetlands. The first possibility proposes that thermal artesian waters alone contribute to the wetlands' water source, while the second hypothesis involves a combination of drainage from Salton Sea bank storage water mixing with the thermal artesian water. The thermal artesian water discharges into drainage channels that flow towards the Bombay Beach Wetlands, initially devoid of possible groundwater baseflow until reaching the wetlands. Studies were subsequently done along the full reach of the drainage channels receiving thermal artesian water. Dissolved solids content, P and N nutrients, arsenic, and stable water isotopes were tested synoptically along the drainage channels. Channel investigations led to the development of a novel model of salinization, which is linked to channel discharge, channel morphometrics, and channel incision.

Iron isotope constraints on the genesis of giant Beiya Au-base metal deposits, Yunnan, Southwest China

The Beiya Au-base metal deposit in southwest China is characterised by a huge amount of iron associated with gold mineralization. The formation of the Beiya deposit is generally thought to be related to Tertiary potassic intrusion, as porphyry- and skarn-type mineralization are the two most important types of mineralization in the region. However, the lack of direct evidence to constrain the source of iron and gold as well as other metals makes it difficult to accurately conceptualise the ore genesis model. In this study, we report high-precision (0.03 ‰; 2sd) Fe isotope data on Fe-bearing minerals including magnetite, pyrite and chalcopyrite, and major igneous rocks exposed in the area, including monzogranite porphyry (MGP), mafic microgranular enclave (MME), lamprophyre and basalt. Magnetites have a wide range of δ Fe from 0.15 to 0.64 ‰, reflecting substantial isotopic fractionation at different mineralization stages. MMEs have heaviest Fe isotopic composition (0.35 ‰ to 0.88 ‰) compared to MGPs (0.19 ‰ to 0.48 ‰), lamprophyre (∼0.2 ‰) and basalt (∼0.0 ‰). A negative correlation between δ56Fe and TFe2O3 is found for both MPGs and MMEs, which indicates the leaching of iron by hydrothermal fluids mobilizes light Fe and leaves behind isotopically heavy Fe in the remaining source rock. Fe isotopic compositions of MPG and MME overlap with those of magnetite, both of which are proposed to be the source of Fe in magnetite. The basalt has δ56Fe value of 0 ± 0.03 ‰, similar to those of global basalts, suggesting a negligible contribution to the formation of iron ores. Therefore, we propose that magmas parental to the MGP and MME may be the main source of iron to form the Beiya deposit; post-magmatism hydrothermal activities play a key role in leaching the metals out and transporting them to the mineralization area.

ISOSCAPES AND PALEOISOTHERMS OF THE HOLOCENE MEAN JANUARY AIR TEMPERATURE IN THE NORTHWESTERN SIBERIA (BASED ON STABLE OXYGEN ISOTOPE COMPOSITION OF ICE WEDGES)

Holocene ice wedges at 16 sites in the Northwestern Siberia were studied, the age of ice wedges was determined, and stable isotope data ( 18O and 2Н values) for all studied ice wedges have been summarized. The δ2H-δ18O ratio and the dexc values for ice wedge ice indicate good preservation of the isotope signal of winter precipitation in ice, which allows to use the obtained δ18O values for paleotemperature reconstructions. The isoscapes (lines of equal 18O values) created for the Holocene ice wedges and modern ice veinlets are generally submeridional; the 18O values decrease from west to east of the study area. Taking into account a new Holocene tripartite division scheme it was shown that the mean January air temperature (TmJ) in the Northwestern Siberia ranged approximately from -21 to -30°С during Greenlandian and the first half of the Northgrippian stage of the Holocene (11,4 to 6 cal ka BP) and approximately from -24 to -27°С from the end of the Northgrippian - to the Meghalayan stage of the Holocene (5,2 to 0,9 cal ka BP). The Holocene isotherms are close to the modern sub-meridional position and show an eastward decrease in TmJ values. Winter climatic conditions in the Northwestern Siberia were generally stable during the Holocene, meanwhile TmJ was on average 1-2°C lower than modern ones.

Lutetian–Bartonian (Middle Eocene) micropalaeontology, biostratigraphy and palaeoecology of the Mengen Coal Basin, Northwest Türkiye (Turkey)

This study focuses on the upper Lutetian–lower Bartonian Tokmaklar Formation in the Mengen Basin of Northwest Türkiye (Turkey), examining various aspects such as biostratigraphy, palaeoecology, and isotope data (δ18O and δ13C), providing insights into the geological history and environmental conditions during this interval. Moreover, the study incorporates coal petrography on four samples to explore a potential correlation between the coalification process and the preservation of palynomorphs. The formation is informally divided into two distinct categories: a coal-bearing sequence positioned at the base of the formation and a coal-free sequence above it. However due to dense vegetation and soil cover in the area, the availability of suitable outcrops for measured sections and obtaining samples is severely limited. Therefore, we relied on drilling data from Turkish Coal Enterprises (TCE) for the purpose of coal exploration, as well as two partial sections (Ender and Çorak) from underground mining. Microapalaeontological evidences involving benthic foraminiferans, ostracods, and palynomorphs, along with isotope data (δ18O and δ13C), suggest that the Tokmaklar Formation was deposited as a result of a local transgressive process during the late Lutetian–early Bartonian. Furthermore, palynological data, particularly the existence of mangroves such as Nypa, lepidocaryoid palm and Acrostichum aureum, coupled with quantitative palaeoclimate analysis, the negative δ18O values, and the lower δ13C values indicate a warm, probably tropical climate under high rainfall.

Evolution of Devonian and Carboniferous pre-Andean arc magmatism in the Frontal Cordillera (27°-35°S), Argentina: Insights from U–Pb zircon and isotopic studies

We propose a conceptual model for the magmatic system that gave rise to the Devonian and Carboniferous subduction-related magmatism in the Frontal Cordillera of Argentina, (representing the pre-Andean margin of SW Gondwana), integrating previous geochronological studies with new geochronological data from granitoids and subvolcanic dikes, which include reported petrological, geochemical, and isotopic data. This conceptual magmatic system postulates an extended magmatic activity, similar to that reported in a previous study for the Devonian foreland magmatism located in the present-day Sierras Pampeanas of Argentina. The geochronological data play a central role in the model, and lead us to postulate the presence of a deep mush reservoir, where a prolonged magmatic activity, permitted the extended crystallization of Devonian (ca. 400 ± 3 and 414 ± 3 Ma) and Carboniferous antecrysts (334 ± 2 Ma, 341 ± 2, and 348 ± 2, where the age of 348 Ma maybe considered as derived from the source, i.e. xenocrysts). Migration of the parental magma from the mush reservoir zone occurred near the time of emplacement and culminated in the formation of an ephemeral magma chamber located in shallow levels, where Devonian and Carboniferous zircon autocrysts crystallized (382 ± 5 Ma and 325 ± 2 Ma, respectively). Age spectra reported within individual sample, favors the idea of a massive migration of magma when conditions were favorable (e.g., thermally matured crust). Notably, the Carboniferous geochronological data is strongly consistent with previous geochronological data recently reported for the granitic rocks of the Tabaquito batholith. Although this model supports a protracted magmatic system for the Devonian and Carboniferous subduction-related magmatism, previous and new isotopic data reveal a significant difference in the petrogenetic processes. While the Carboniferous arc magmatism shows significant juvenile material contribution, this is not the case for the Devonian magmatic arc, where isotopic data suggest an older continental lithosphere as the dominant source. These different sources are attributed to two contrasting geodynamic settings, with advancing and retreating oceanic slabs, respectively.

Geochronology, geochemistry, and isotope signatures of porphyries from the dabate Mo—Cu deposit, Western Tianshan, China: Implications for petrogenesis and geodynamic setting

The Dabate deposit in the West Tianshan Orogenic Belt is a large porphyry Mo-Cu deposit with obvious zoning feature. The Dabate pluton is closely related to mineralization associated with the rhyolite and granite porphyries. Copper (Cu) mineralization occurs on the margin of the rhyolite porphyry, and molybdenum (Mo) mineralization occurs in the interior of the rhyolite porphyry. Petrology, zircon U-Pb isotopic data, whole-rock geochemistry, and Sr-Nb-Hf-Pb isotopic data of the rhyolite and granite porphyries in the Dabate Mo-Cu mining zone and to discuss the properties, sources, evolution, and tectonic environment of the magma. Zircon U-Pb age dating shows that the rhyolite porphyry and granite porphyry were formed in 300.1 ± 1.3 Ma and 290.4 ± 5.2 Ma, respectively, and they are geochemically similar. Both are characterized by negative Eu anomalies (δEu = 0.09–0.15 and 0.10–0.11, respectively) and are slightly rich in light rare earth elements (LREE) but depleted in high-field-strength elements (HFSE), which indicates that they are both A2 type granites that underwent high differentiation. The Sr isotope (ISr) values for the rhyolite and granite porphyries range from 0.70564 to 0.70658 and 0.70833–0.70954, respectively. The Nd isotopic composition [εNd(t)] values for both are negative but close to zero (−0.25 to −0.46 and −0.65 to −1.10, respectively), and the two-stage depleted mantle Nd model ages (TDM2(Nd)) are 1.07–1.10 Ga and 1.11–1.14 Ga, respectively. Zircon εHf(t) values are 7.29–11.97 and 6.26–11.08 for rhyolite porphyry and granite porphyry, respectively, and the two-stage Hf model ages (TDM2(Hf)) are 550–848 Ma and 605–916 Ma, respectively. The initial Pb isotope ratios for the rhyolite and granite porphyry are close at (206Pb/204Pb)i = 18.26–18.65, (207Pb/204Pb)i = 15.54–15.64, and (208Pb/204Pb)i = 38.19–38.57. These results indicate that the two porphyries have a mixed source, likely originating from the partial melting of mantle blended with some recently formed lower crust material. The geochronology, geochemistry, and Sr-Nd-Hf-Pb isotope data of existing intrusions in the West Tianshan imply that the Late Carboniferous to Early Permian Dabate area was underplated in a post-collisional extensional setting, and A2-type granite intrusions with related Mo-Cu mineralization were formed.

A Contiguous Taltson‐Thelon Margin Revisited

AbstractThe amalgamation of Laurentia was initiated along the western margin of the Rae craton. However, the tectonic setting that generated magmatic rocks along this margin has long been debated, with the Thelon tectonic zone in the north having formed in an arc setting, and the Taltson magmatic zone in the south variably attributed to either continental arc or intracratonic magmatism. The magmatic rocks of the Great Slave Lake shear zone (GSLsz) lie between these two tectonic belts and, thus, may be critical to the interpretation of the evolution of the western Rae margin. To understand the origin of the rocks in the GSLsz, we have applied U‐Pb geochronology, trace‐element geochemistry, and O and Hf isotope analyses to zircons from a suite of samples that transect the La Loche River fault (LRf)—a major structure that bisects the GSLsz. Samples collected to the north of the LRf are Neoarchean in age, have mantle‐like δ18O (4.7–5.8‰) and chondritic to juvenile εHf values (0–4.5), whereas those to the south are exclusively Paleoproterozoic in age and have more elevated δ18O (6.3–7‰) and much more evolved εHf values (−12 to −6); these results indicate that the LRf marks a crustal‐scale suture between the Slave craton and the Taltson magmatic zone. Our isotopic data, together with other regional constraints from the area, are most consistent with the Taltson magmatic zone having formed in a continental arc setting emplaced into ca. 2.3 Ga juvenile basement crust.