Isotopic Studies Research Articles

Prehistoric Italian foodways: Meta-analysis of stable isotope data from the Neolithic to the Iron Age

Italian Later Prehistory was characterised by profound changes that impacted everyday life in many aspects. Whether or not and how such changes were reflected in the subsistence practices of ancient populations is an ongoing question in the archaeological debate. This question has been investigated using stable carbon and nitrogen isotope analysis for several decades. Here, we present a 6000-year-long review of isotopic studies in the Italian Peninsula from the Neolithic to the Iron Age. We reconstruct chronological variations in food practices by observing δ13C and δ15N trends for 776 humans, 382 animals, and 432 C3 plants from 111 archaeological sites. During the Neolithic, when farming is first introduced, a homogenous signal characterised by terrestrial protein consumption is visible. The Copper Age, instead, shows a more varied pattern, possibly representative of a more diversified use of the landscape, characteristic of those millennia. The new cultural paradigm that invested Europe during the Bronze Age is also reflected in food practices in Italy, with the introduction of millets - signalled by high δ13C values in the Northern regions - possibly representing a pivotal shift. Not much data is available for the Iron Age, as only two sites from Northern Italy, showing a diffused consumption of C4 plants, and one site from Southern Italy, with a diet centred around C3 plants, are available for this period. The analysis of this extensive set of data suggests that the “Secondary Products Revolution” probably meant a shift in subsistence practices, with secondary sources substituting meat rather than integrating it.

A Typology and Lead Isotope and Cultural Exchange Study on Bronze Knives from Shuangyuan Cemetery, Chengdu City, Southwest China

Background: Bronze knives, which have been excavated in large quantities and acquired hierarchical significance, are essential artifacts in Shu State in Southwest China. Building upon previous typological analyses of bronze knives, it is hypothesized that Shu culture may have imported foreign-style bronze knives. However, further demonstration of the provenance of metal materials, the typology of knives, and the cultural exchange necessitates a comprehensive examination through the lens of scientific analysis. The purpose of this study is to investigate the differences in the manufacturing processes and metal resources of Shu bronze knives with various cultural styles and whether bronze knives in the foreign styles were imported or locally imitated. Methods: In this study, the typology, portable X-ray fluorescence spectrometry and multi-collector inductively coupled plasma mass spectrometry were used to analyze twenty-four bronze knives unearthed from Shuangyuan cemetery, a cemetery of the Eastern Zhou Dynasty in Chengdu City, Sichuan Province, Southwest China. Results: The results of the study show that the knives of Shuangyuan Cemetery can be classified typologically into five types, encompassing both local and foreign styles. The predominant alloy composition of these knives is lead-tin bronze, characterized by a notably high tin content. Lead isotope ratios indicate that metal materials from the South China geochemical province and Yangtze geochemical province were mainly used to manufacture the bronze knives unearthed from the Shu state Conclusion: While the majority of foreign-style knives with ring-shaped heads were likely imported from neighboring regions like Chu state, distinctively styled type D and type E bronze knives appear to have been locally imitated by the Shu, showcasing a blend of external influences and indigenous innovation. The combination of typology and scientific analysis of the bronze knife may shed new light on the study of the Shu culture of the Eastern Zhou period.

Petrological, mineralogical, carbonate C-O and sulfide S isotope study of the Bayinqinggeli sandstone-hosted uranium deposit in the northern Ordos Basin

Petrological, mineralogical, carbonate C-O and sulfide S isotope study of the Bayinqinggeli sandstone-hosted uranium deposit in the northern Ordos Basin

Recommendations for stable isotope analysis of charred archaeological crop remains

Stable isotope analysis of plant remains recovered from archaeological sites is becoming more routine. There remains a lack of consensus, however, on how to appropriately select archaeological plant remains for isotopic analysis, how to account for differences in preservation and the effect of potential contamination, and how to interpret the measured isotope values in terms of the conditions in which the plants grew. In this paper, we outline the main issues to be considered when planning and conducting an isotopic study of archaeobotanical remains. These include: (1) setting out the research question(s) that will be answerable using available analytical approaches, (2) considering the archaeological context from which plant remains derive, (3) determining appropriate sample size through consideration of estimate precision, (4) establishing the conditions in which plant remains have been preserved and potential effects on their isotope values, and (5) accounting for possible contamination during deposition. With these issues in mind, we propose some recommendations for researchers to consider when planning and conducting an isotopic study of archaeobotanical remains.

Genesis of the Qingchayuan Flake Graphite Deposit in the Huangling Dome of Yangtze Block, South China

The Qingchayuan flake graphite deposit is located in the Huangling Dome, which represents a part of the Yangtze Block in South China. This deposit is a major and highly typical flake graphite deposit within this metallogenic region. The graphite ores are found within graphite-bearing mica schist and graphite-bearing biotite–plagioclase gneiss. The fixed carbon content varies from 3.52 to 13.78% with an average of 7.83%. The major element analysis shows that the main chemical components of the Qingchayuan flake graphite ore are SiO2, Al2O3, TFe2O3, and K2O. The carbon isotope study of the graphite ore indicates light carbon values ranging from −22.80 to −26.72‰, suggesting that it has a biogenic origin. In addition, the sulfur isotope values of the graphite samples range from −10.67 to −14.58‰, indicating the formation of the graphite deposit is related to biological processes. The presence of traces of migmatization around the graphite deposit indicates that the graphite has undergone ultra-high temperatures during the formation process. The origin of the Qingchayuan flake graphite deposit is explained by a two-stage genetic model, which involves material deposition and regional metamorphism (including migmatization). Firstly, after the deposition of carbonaceous material and its conversion into graphite by regional metamorphism, the graphite might have undergone recrystallization, resulting in the development of big flakes due to migmatization. This model is supported by previous studies and newly collected information.

Gestational Diabetes-like Fuels Impair Mitochondrial Function and Long-Chain Fatty Acid Uptake in Human Trophoblasts

In the parent, gestational diabetes mellitus (GDM) causes both hyperglycemia and hyperlipidemia. Despite excess lipid availability, infants exposed to GDM are at risk for essential long-chain polyunsaturated fatty acid (LCPUFA) deficiency. Isotope studies have confirmed less LCPUFA transfer from the parent to the fetus, but how diabetic fuels impact placental fatty acid (FA) uptake and lipid droplet partitioning is not well-understood. We evaluated the effects of high glucose conditions, high lipid conditions, and their combination on trophoblast growth, viability, mitochondrial bioenergetics, BODIPY-labeled fatty acid (FA) uptake, and lipid droplet dynamics. The addition of four carbons or one double bond to FA acyl chains dramatically affected the uptake in both BeWo and primary isolated cytotrophoblasts (CTBs). The uptake was further impacted by media exposure. The combination-exposed trophoblasts had more mitochondrial protein (p = 0.01), but impaired maximal and spare respiratory capacities (p < 0.001 and p < 0.0001), as well as lower viability (p = 0.004), due to apoptosis. The combination-exposed trophoblasts had unimpaired uptake of BODIPY C12 but had significantly less whole-cell and lipid droplet uptake of BODIPY C16, with an altered lipid droplet count, area, and subcellular localization, whereas these differences were not seen with individual high glucose or lipid exposure. These findings bring us closer to understanding how GDM perturbs active FA transport to increase the risk of adverse outcomes from placental and neonatal lipid accumulation alongside LCPUFA deficiency.

Evaluation of the source and mechanisms of groundwater recharge for the southern sections of the western Afar rift margin and associated rift floor

Study areaSouthern Sections of Western Afar rift margin and associated rift floor. Study focusThe purpose of this study is to identify the source and mechanisms of groundwater recharge based on geological, hydrochemical, and environmental isotope studies. New hydrogeological insightsThe investigation illustrate that the columnar jointed basalt was extended from the plateau to the rift margin. In addition, transverse structures trending NW-SE and NE-SW connect the plateau to the rift margin and the marginal grabens to the rift floor. The hydrochemical interpretations with EC and TDS shows that the groundwater from the plateau has evolved from Ca-dominated and slightly mineralized to Na-dominated and highly mineralized to the rift floor. Isotopically, the deep groundwater systems are depleted in the entire physiography in contrast to the shallow groundwater systems. Radon measurements are higher at the outlets of the marginal grabens and between the rift margin and the rift floor, suggesting groundwater feeds the river. A comprehensive analysis of the aforementioned results suggests that the deep circulating groundwater is recharged in the plateau and escarpment and chemically altered with increasing depth and along its preferential flow path into the rift floor. Therefore, the plateau area is the main source of recharge for the western Afar rift margin and associated rift floor, due to the presence of preferential pathways, mainly the columnar jointed basalts and cross-structures.

Water vapor stable isotope memory effects of common tubing materials

Abstract. Water molecules in vapor can exchange with gaseous water molecules sticking to surfaces of sampling tubing, and exchange rates are unique for each water isotopologue and tubing material. Therefore, water molecules on tubing walls take some time to reach isotopic equilibrium with a new vapor isotopic signal. This creates a memory effect that is observed as attenuation time for signal propagation in continuous stable water vapor isotope measurement systems. Tubing memory effects in δD and δ18O measurements can limit the ability to observe fast changes, and because δD and δ18O memory are not identical, this introduces transient deuterium excess (D-excess, defined as δD-8×δ18O) artifacts in time-varying observations. To our knowledge, a comprehensive performance comparison of commonly used tubing material water exchange properties in laser-based measurement systems has not been published. We compared how a large isotopic step change propagated through five commonly used tubing materials for water isotopic studies – perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), and copper – at two different temperatures and an airflow rate of 0.635 L min−1 through approximately 100 ft (30.5 m) of 1/4 in. (6.4 mm) outer diameter (o.d.) tubing. All commonly used tubing materials performed similarly to each other in terms of attenuation times, reaching δ18O-location-adjusted δD and δ18O 95 % completion in less than 45 s, with slight variations based on temperature. PFA does appear to perform slightly better than the other materials, although memory metric differences are small. A tubing material commonly used in the early 2000s but reported to have memory effects on δD, Dekabon, was also tested at ambient temperature and changing humidities. The Dekabon isotopic equilibrium was not reached until nearly an hour after source transition, much later than H2O mixing ratios equilibrated. Bev-A-Line XX (used in some soil O2 and CO2 gas studies) was also tested at ambient temperature, but it did not approach isotopic equilibrium until after nearly 6 h of testing. Therefore, we cannot recommend the use of Bev-A-Line XX or Dekabon in water vapor isotope applications. Source transition from heavy to light or from light to heavy affected isotopic transition speed only in experiments where H2O ppmv was changing. While a shorter tubing lengths and smaller inner diameters shorten the delay of signal propagation through the tubing, they did not greatly change the attenuation curves under these conditions for the current commonly used tubing materials tested. However, in Dekabon, attenuation curves were greatly extended with increased tubing length. Our results show that the commonly used plastic tubing materials tested were not inferior to copper in terms of isotopic memory under these conditions, and they are easier to work with and are less expensive than copper.

Hypogene Alteration of Base–Metal Mineralization at the Václav Vein (Březové Hory Deposit, Příbram, Czech Republic): The Result of Recurrent Infiltration of Oxidized Fluids

The Václav vein (Březové Hory deposit, Příbram ore area, Czech Republic) is a base–metal vein containing minor Cu-Zn-Pb-Ag-Sb sulfidic mineralization in a usually hematitized gangue. A detailed mineralogical study using an electron microprobe revealed a complicated multistage evolution of the vein. Early siderite and Fe-rich dolomite were strongly replaced by assemblages of hematite+rhodochrosite and hematite+kutnohorite/Mn-rich dolomite, respectively. In addition, siderite also experienced strong silicification. These changes were associated with the dissolution of associated sulfides (sphalerite, galena). The following portion of the vein contains low-Mn dolomite and calcite gangue with Zn-rich chlorite, wittichenite, tetrahedrite-group minerals, chalcopyrite, bornite, and djurleite, again showing common replacement textures in case of sulfides. The latest stage was characterized by the input of Ag and Hg, giving rise to Ag-Cu sulfides, native silver (partly Hg-rich), balkanite, and (meta)cinnabar. We explain the formation of hematite-bearing oxidized assemblages at the expense of pre-existing “normal” Příbram mineralization due to repeated episodic infiltration of oxygenated surface waters during the vein evolution. Episodic mixing of ore fluids with surface waters was suggested from previous stable isotope and fluid inclusion studies in the Příbram ore area. Our mineralogical study thus strengthens this genetic scenario, illustrates the dynamics of fluid movement during the evolution of a distinct ore vein structure, and shows that the low content of ore minerals cannot be necessarily a primary feature of a vein.

Isotopic study for evaluating complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction in a Mediterranean coastal karst environment

In this study groundwater provenance, circulation, and rock interaction processes have been assessed by cross processing the spatial distribution of chemical and isotopic signatures in freshwater with the hydrogeological features of the coastal karst carbonate aquifer of Murgia, located in the southeastern end of Italy, along the Adriatic Sea. Thanks to widespread groundwater quality monitoring (major, minor, and trace-element analyses) and multi-isotopic measures of O, H, Sr, and B, some assumptions about complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction have been drawn. Three sectors have been distinguished into the Adriatic side of the Murgia aquifer all fed by two main recharge areas located on the most elevated, inner side of the aquifer. Each sector is characterized by different groundwater circulation patterns, residence time, and hydrogeochemical features. The water samples collected into the western sector evidence a certain degree of water-rock interaction, which allows us to assume long groundwater flow paths and residence time. On the contrary, the eastern sector of Murgia has been proven to be characterized by short residence times and a possible direct freshwater contribution even in the downstream course due to the massive presence of karst forms. Herein, the isotopic analysis of the water samples does not provide evidence of water-rock interaction. Finally, in the third, central sector, water infiltrated at different locations mixes flowing through relatively long paths even though not sufficient to allow groundwater to gain the rock's isotopic signature.

Zircon Chronology and Hf Isotope Study of Sanyanlong-Galazi Granite in the Southern Songpan-Garze Orogenic Belt

Zircon Chronology and Hf Isotope Study of Sanyanlong-Galazi Granite in the Southern Songpan-Garze Orogenic Belt

ISOTOPE COMPOSITION OF Pb AND Nd OF THE LATE NEOPROTEROZOIC–EARLY PALEOZOIC GRANITOIDS IN EASTERN TUVA (Case study of the Kaa-Khem batholith)

We present the results of Nd and Pb isotope studies of late Neoproterozoic–early Paleozoic granitoids of the Kaa-Khem batholith, which formed in different geodynamic settings within the early Caledonian structures of Eastern Tuva (Altai–Sayan sialic area). Based on the obtained isotope data, we assess the role of different source materials in the formation of melts for these granitoids and compare these rocks with coeval granitoids from the Lake Zone of Mongolia. The plagiogranitoid associations of the island arc stage of the Kaa-Khem batholith formation (572–562 Ma) are characterized by mantle Nd isotope values. In contrast, the Pb isotope characteristics of these intrusive associations correspond to an upper-crust source formed predominantly by terrigenous sediments. The granitoid associations of the accretion–collision stage of the Kaa-Khem batholith formation (512–450 Ma) have a less radiogenic primary Pb isotope composition as compared with the island arc granitoids. Evidently, during the magma formation at this stage, the relative role of terrigenous material decreased, while the role of depleted mantle material increased. At the same time, the decrease in ɛNd values in the granitoids as compared with the depleted mantle indicates that, along with the upper-mantle component, the role of the lower-crust component increased. These Nd and Pb isotope characteristics of the accretionary granitoids of the Kaa-Khem batholith indicate a significant contribution of the lower-crust source to their formation. This source is the crystalline basement of the Tuva–Mongolian microcontinent. The Pb isotope characteristics of the accretion–collision granitoids of the Kaa-Khem batholith are shifted to the upper-crust compositions relative to those of the Lake Zone granitoids. The reason is that the latter formed predominantly through the transformation of early Caledonian island arc complexes, which were generated with a higher portion of mantle component.

The Role of Hydrocarbons in the Genesis of Mississippi-Valley-Type (MVT) Zn–Pb Deposits: Insights from In Situ Sulfur Isotopes of Sphalerite from the Southwestern Margin of the Yangtze Block, SW China

The coexistence of numerous Mississippi-Valley-type (MVT) Zn–Pb deposits and (paleo) oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. Xuequ–Shandouya middle MVT Zn–Pb deposits are mainly hosted in the Lower Cambrian Maidiping Member siliceous dolostone on the southwestern margin of the Yangtze Block, accompanied by large amount of bitumen in the orebodies. Therefore, this type of Zn–Pb deposit is a natural laboratory for studying the relationship between the mineralization and the accumulation of paleo-oil/gas reservoirs. The deposit is characterized by spheroidal and concentric banded sphalerite. In situ sulfur isotope studies are carried out to determine the sulfur sources, sulfate reduction mechanisms, and role of hydrocarbons in the zinc–lead mineralization process. According to the mineral paragenesis and relative temporal relationship, two mineralization stages (1 and 2) are identified. An in situ sulfur isotope analysis of spheroidal and concentric banded sphalerite particles from Stage 2 shows that there are the two following types of sulfur isotopes in the sphalerite: one with relatively invariable δ34S values in the core (+8.31 to +9.30‰), and the other with a gradual increase from the core margin (core) to the rim (+0.39 to +16.18‰). These two types reflect that they may have formed in different times, with first type forming in the early period of Stage 2, while the second type was formed in the late period of Stage 2. The sulfur isotopic data suggest the sulfur source of evaporated sulfate minerals and multiple formation mechanisms for reduced sulfur (H2S). In the early period of Stage 2 mineralization, the sulfate reduction mechanism is mainly a mixture of bacterial sulfate reduction (BSR) and/or thermochemical sulfate reduction (TSR), while a very small amount may come from the thermal decomposition of organic compounds (DOCs). In the late period of Stage 2, TSR is dominant, and the gradual increase in the δ34S value may be related to Rayleigh fractionation. The oil/gasreservoir not only acts as a reducing agent to provide the required hydrogen sulfide for zinc–lead mineralization through TSR or BSR, but also provides reduced sulfur for mineralization through the thermal decomposition of organic compounds directly.

A Comparative Study of Cave System Calcium Isotope Ratios: Implications for Quantitative Reconstruction of Paleorainfall From Speleothems

AbstractVariations in speleothem calcium isotope ratios (δ44Ca) are thought to be uniquely controlled by prior carbonate precipitation (PCP) above a drip site and, when calibrated with modern data, show promise as a semi‐quantitative proxy for paleorainfall. However, few monitoring studies have focused on δ44Ca in modern cave systems. We present a multi‐year comparative study of δ44Ca, carbon isotopes (δ13C), and trace elemental ratios from cave drip waters, modern calcite, and host rocks from two cave systems in California—White Moon Cave (WMC) and Lake Shasta Caverns (LSC). Drip water and calcite δ44Ca from both caves indicate PCP‐driven enrichment, and we used a simple Rayleigh fractionation model to quantify PCP variability over the monitoring period. Modern calcite trace element and δ44Ca data positively correlate at WMC, but not at LSC, indicating a shared PCP control on these proxies at WMC but not at LSC. At both WMC and LSC, we observe an inverse relationship between PCP and rainfall amounts, though this relationship is variable across individual drip sites. Our modeled data suggest that WMC experiences ∼20% more PCP than LSC, consistent with the fact that WMC receives less annual rainfall. This work supports speleothem δ44Ca as an independent constraint on PCP that can aid in the interpretation of other hydrologically sensitive proxies and provide quantitative estimates of paleorainfall. Additional, long‐term monitoring studies from a variety of climate settings will be key for understanding δ44Ca variability in cave systems more fully and better constraining the relationship between PCP and rainfall.

Anomalous tellurium enrichment associated with gold mineralization: A mineralogical and isotopic study of the Yongxin Te-Au deposit, northeast China

The Yongxin tellurium-gold (Te-Au) deposit, a large epithermal deposit in the Duobaoshan polymetallic metallogenic belt (DPMB) within eastern section of the Central Asian Orogenic Belt (CAOB), is mainly hosted by syenogranite and mylonite. However, the Te-Au occurrence, precipitation mechanism and genesis in this deposit remain elusive. In this study, pyrite, the primary host of Te-Au mineralization, was studied utilizing multiparametric techniques such as scanning electron microscope (SEM), electron probe microanalysis (EPMA), in-situ laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) and femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry (fs LA-MC-ICP-MS). The results show that there are three generations of pyrite termed here as Py1, Py2 and Py3. The coarse euhedral Py1 and fine vein Py2 contain negligible to low contents of Te and Au, whereas the anhedral aggregated Py3 with porosity and grain boundary (GB) shows the highest concentrations of Te and Au. Representative LA-ICP-MS profiles show that Te-Au occurs either as solid solution in the Py1 and Py2 or submicroscopic Au-Ag-Te-Bi inclusions, electrum and native gold in Py3. Thermodynamic data of telluride and sulfide show that the Te-Au was deposited under relatively oxidizing conditions with values of log f Te2 ranging from −15.2 to −11.2 and log f S2 from −16.7 to −12.1. at 200 °C. We infer that fluid mixing and fluid-rock interaction were the dominant mechanisms that triggered the precipitation of Te-Au in the Yongxin Te-Au deposit. Geochemical and geochronological data indicate that the likely source of Te is Te-rich oceanic sediments originating from the Western Pacific Plate. Pyrite and telluride from the gold deposits can be potential targets for Te exploration in the DPMB.

Molybdenum isotope behavior during subduction zone metamorphism

The molybdenum (Mo) isotope composition (defined as δ98Mo measured per mil relative to NIST-3134) of many modern arc systems and the upper continental crust is heavier than the mantle and most subducting slab lithologies. This observation has led to a model whereby fluids leaving the slab transfer isotopically heavy Mo preferentially to the mantle wedge, leaving the residual slab isotopically lighter. We explore this model via an Mo isotope study of the metasedimentary and mélange lithologies of the Catalina Schist in California. These rocks record subduction zone metamorphism over a wide range of high-pressure/low-to-medium temperature conditions.Mo isotope compositions of the metasedimentary rocks decrease with increasing metamorphic grade, from a δ98Momean of −0.04 ± 0.13 ‰ (1σ, n = 3) for the lawsonite albite facies to −0.38 ± 0.07 ‰ (1σ, n = 5) for the epidote–amphibolite facies. The highest grade [amphibolite facies] samples show a slight uptick in δ98Mo values, with a mean of −0.19± 0.14 ‰ (1σ, n = 4). When coupled with major and trace element variations, the changes in δ98Mo appear to reflect metamorphic effects rather than sedimentary source rock heterogeneity. The positive relationship between δ98Mo and [Mo] and negative relationship with Ce/Mo argue for progressive loss of Mo with isotope fractionation during increasing P-T conditions; the reversal of this trend, seen in the increase in δ98Mo between the epidote amphibolite and amphibolite facies may reflect a subsequent partial re-fertilization by fluids carrying isotopically heavy Mo. δ98Mo values in the mélange across all grades are highly variable, ranging from −1.75 to −0.19, consistent with large scale mobilization of Mo with isotope fractionation. A metasomatized amphibolite block and reaction rind show similar light isotope compositions and signs of Mo depletion and transport. Together these three whole-rock data sets demonstrate pervasive open system behavior and mobility of Mo in the Catalina Schist. LA-ICP-MS Mo measurement of minerals in the differing metasedimentary metamorphic grades indicates that Fe oxides and/or hydroxides, titanite, rutile, and epidote are important reservoirs of Mo but when comparing mineral Mo content and modal abundance to whole-rock Mo concentrations, several samples were found to have “missing Mo”, something that has been observed in other Mo inventory studies. We attribute this to sample heterogeneity between the thin section and whole-rock powder scales.

Geochemical and isotopic study of formations aquifers in a high mountain system: the Santander Massif (Colombia)

Geochemical and isotopic study of formations aquifers in a high mountain system: the Santander Massif (Colombia)

Petrogenesis of early Paleozoic syn-collisional granitoids and enclaves in Western Kunlun, Northwest China: Implications for the growth of continental crust

The Western Kunlun Orogenic Belt (WKOB), along the northwestern margin of the Qinghai–Xizang Plateau, was formed by the collision of Gondwana-derived terranes to the south and the Tarim Block to the north and was closely associated with closure of the Proto-Tethys Ocean during the late Neoproterozoic to early Paleozoic. We present a combined zircon UPb geochronology, whole-rock composition, and Sr–Nd–Hf isotopic study of syn-collisional granitoid plutons and mafic microgranular enclaves (MMEs) in the region. Zircon UPb dating yields ages of 443.8 ± 4.4, 451.9 ± 4.2, 462.9 ± 3.5, and 456 ± 4.2 Ma for the Tongayoupuagezi, Shanjie, and Pishigai plutons and MMEs from the Pishigai pluton, respectively. The granitoids are metaluminous to weakly peraluminous (A/CNK = 1.00–1.17) and belong to the high-K calc-alkaline series. They have (87Sr/86Sr)i ratios of 0.7058–0.7154, εNd(t) values of −8.78 to −0.93, and εHf(t) values of −19.72 to +6.87. The MMEs have variable SiO2 contents (45.7–60.2 wt%) and are more mafic than the host granitoids, but have similar Sr–Nd–Hf isotopic compositions to the host granitoids [(87Sr/86Sr)i = 0.7102–0.7110; εNd(t) = −6.57 to −3.56; εHf(t) = −7.17 to −1.81]. The MMEs are fragments of cumulates formed during the early stages of magma evolution. The granitoids were produced by the partial melting of a mélange source. The new data support the view that the Middle–Late Ordovician syn-collisional granitoids with MMEs distributed along the WKOB represent a magmatic response to terrane collision. This suggests that juvenile crustal growth in older orogenic systems, which occurs by arc addition, also involves some vertical addition during the final stage of orogenic collision. Our study suggests that mélange diaper melting is a key mechanism of crustal growth during the syn-collision stage in continental collision zones, associated with slab breakoff.

Relationships between high-K magmas and Cu–Au porphyry deposits in the Macquarie Arc, Australia

The Macquarie Arc is a long-lived volcanic arc terrane which began in the latest Cambrian and continued until the early Silurian. Early Silurian high-K suites associated with Cu–Au porphyry mineralization are typically considered shoshonitic; however, comparisons with well-studied examples of shoshonites in continental arcs and associated settings suggest few Macquarie Arc rocks would classify as shoshonitic. Notably, the Au-rich Cadia Intrusive Complex, which is marginally shoshonitic, and most high-K to ‘shoshonitic’ Macquarie Arc rocks are essentially high-K calc-alkaline, analogous to ‘primitive’ shoshonites generated within intraoceanic arc settings. Arc magmatism in the Macquarie Arc is consistently primitive and mantle derived prior to an increase in siliciclastic input and crustal thickening during the Silurian Benambran Orogeny, consistent with prior isotopic studies. Magma source regions can thus be interpreted as varying spatially and temporally due to variable enrichment from slab and mantle derived components, reflecting a maturing and potentially migrating arc system.

RADIOCARBON MORTAR DATING INTERCOMPARISON MODIS2—APPROACH FROM THE ZAGREB RADIOCARBON LABORATORY, CROATIA

ABSTRACT The Second International Mortar Dating Intercomparison Study (MODIS2) took place in 2020. Three mortar samples from different sites and chronologies were distributed among various research groups in form of bulk mortar and grain fraction smaller than 150 µm. This is the first time the Zagreb Radiocarbon Laboratory, with support of the Center of Applied Isotope Studies, University of Georgia, took part in the international mortar intercomparison. The initial approach of the Laboratory to mortar dating was to separate 32–63 µm grain fraction and collect three CO2 gas portions by sequential dissolution with acid. After checking the 14C date trends of the gas portions, which should be ascending with later fractions, the one for the first and shortest gas portion was reported as the age of the mortar. However, the first gas portion might not be true age of the mortar, since it still might contain some “dead” carbon. Therefore, data extrapolation from the first two initial CO2 portions was also conducted on the results, but not reported to the intercomparison. Though in general, all the intercomparison reported dates fit the expected historical ages, for one sample, the extrapolated result showed a better match to the historical data.