Isotope Data Research Articles

Rb–Sr Pyrite Dating and S–Pb Isotopes in the Fang’an Gold Deposit, Wuhe Area, Eastern Anhui Province

The Fang’an gold deposit in the Wuhe area, Anhui Province, is located in the area adjacent to the Bengbu Uplift and Wuhe Platform Depression in the southeastern part of North China. This study aimed to determine the deposit’s mineralization age and the source of its metallogenic materials and mineralization processes through investigations into its geological characteristics, Rb–Sr isotopes, and S–Pb isotopes. The orebodies of the Fang’an gold deposit in the Neoarchean Xigudui Formation primarily exhibit a vein-type structure. The ore-forming process can be divided into four stages: (i) the quartz stage (Py1); (ii) the quartz–pyrite stage (Py2); (iii) the polymetallic sulfide stage (Py3); and (iv) the carbonate stage. Of these, the main mineralization stage is also the main period in which gold mineralization occurs. In situ sulfur isotope results of pyrite (Py1 to Py3) in the first three mineralization stages, suggesting a contribution of sulfur from crust–mantle magmatic fluids. The δ34S values for Py2 (average 5.51‰) are higher than Py1 (average 4.45‰) and showed that the magmatic fluids mixed with meteoric waters. The δ34S values for Py3 (average 5.18‰) are lower than Py2 (average 5.51‰), revealing that it related fluid immiscibility. The lead isotopic compositions of sulfides within the ores possessed 206Pb/204Pb ratios ranging from 16.759 to 16.93, 207Pb/204Pb ratios ranging from 15.311 to 15.402, and 208Pb/204Pb ratios ranging from 37.158 to 37.548. These lead data were plotted close to the Xigudui Formation, relatively distant from the Mesozoic granites, indicating that the Xigudui Formation was the source of lead for the Late Mesozoic ores of the deposit. Taken together, due to the degassing of mantle-derived magma in the shallow parts of the crust, it can be determined that the sources of ore-forming sulfur and lead were crust–mantle magmatic activities in the Wuhe area. Rb–Sr dating of pyrite from Fang’an gold deposit reveals that the mineralization occurred at 126.89 ± 0.58 Ma. Considering the previous research into the dating of magmatic rocks in the Wuhe area, we propose that the genesis of the Fang’an gold deposit is closely associated with magmatic activities in the area at around 130 Ma.

Tracing anthropogenic mercury in soils from Fe–Hg mining/smelting area: Isotopic and speciation insights

Mercury (Hg) stable isotope ratios supplemented by Hg solid speciation data were determined in soils in a former Fe–Hg mining/smelting area (Jedová hora, Czech Republic, Central Europe). The dominant Hg phase in the studied soils was found to be cinnabar (HgS). A secondary form of soil Hg(II) was represented by Hg weakly and strongly bound to mineral (micro)particles, as revealed by thermo-desorption analysis. These Hg species probably play a key role in local soil Hg processes and biogeochemical cycling. The Hg isotopic data generally showed small differences between HgS (−1.1 to −0.8‰; δ202Hg) and the soil samples (−1.4 to −0.9‰; δ202Hg), as well as limited isotopic variability within the two studied soil profiles. On the other hand, the detected negative δ202Hg shift (∼0.4‰) in organic horizons compared to mineral soils in the highly contaminated profile suggests the presence of secondary post-depositional Hg processes, such as sorption or redox changes. For the less contaminated profile, the observed Hg isotopic variation (∼0.3‰; δ202Hg) in the subsurface mineral soil compared to both overlying and underlying horizons is likely due to cyclic redox reactions associated with Hg isotopic fractionation. We assume that the adsorption of Hg(II) to secondary Fe(III)/Mn(III,IV)-oxides could be of major importance in such cases.

Oligocene melting of subducted mélange and its mantle dynamics in northeast Asia

Melting of subducted mélange can potentially transport mass from the slab-mantle interface to the mantle wedge in subduction zones. The mélange diapir model was primarily proposed from the results of laboratory experiments and thermodynamic modeling. However, the melting mechanisms of mélange diapirs in subduction zones remain unclear. To further constrain the mantle dynamics of a mélange diapir, we studied Oligocene alkaline intermediate rocks on the northeast Asian continental margin. We report whole-rock geochemical and Sr-Nd-Pb-Mg-Zn isotope data and show that these rocks formed by partial melting of mélange. We conclude that a diapir was the mechanism for Oligocene melting of the mélange. We also identified younger rocks formed by melting of mélange in the eastern part of northeast Asia, implying an eastward shift in such magmatism since the Oligocene. Our results and the tectonic setting indicate that melting of mélange diapirs occurred preferentially during tectonic transitions, such as the formation of a back-arc basin triggered by trench-perpendicular mantle flow. The low-viscosity mantle with an incompressible stress field triggered melting of the mélange diapirs. Interactions occurred between the mélange diapirs and carbonated peridotites, constraining the depth of mélange-mantle interactions to the asthenosphere, which is deeper than the depth inferred in previous studies.

Philippine Sea plate and surrounding magmatism reveal the Antarctic-Zealandia, Pacific, and Indian mantle domain boundaries

Delineation of geochemically distinct domains in Earth’s mantle is essential for understanding large-scale mantle convective flow and dynamics. Previous studies identify possible long-lived (>60 million-year) mantle isotopic domains (i.e. Antarctic-Zealandia, Pacific and Indian) near the Philippine Sea and western Pacific. Here we compile published basalt geochemistry of the Philippine Sea and surroundings and add new Mo isotopic and water content data for Gagua Ridge lavas, northwestern Philippine Sea, to distinguish slab-derived components during subduction. The water content, trace element, and Mo-Sr-Nd isotope compositions of Gagua Ridge arc lavas suggest that slab fluids and sediment melts are responsible for element recycling to the arc. The Philippine Sea basalts show both Indian and Zealandia-Antarctic Pb isotopic signatures; restoration of the basalt locations within a plate reconstruction shows the far-travelled Philippine Sea traversed these mantle domains. We establish the Indian mantle domain eastern boundary at ~120°E under SE Asia and the Indian Ocean. The Antarctic-Zealandia mantle domain lies south of ~10°N within the SW Pacific and has mostly remained in oceanic realms since ~400 Ma with only limited continental material input.

Ultrapotassic plutons as a source of uranium of vein-type U-deposits (Moldanubian Zone, Bohemian Massif): insights from SIMS uraninite U–Pb dating and trace element geochemistry

AbstractThe Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

Robust sulfur and oxygen isotope evidence for a highly anoxic paleoenvironment in Late Devonian seawater: Insights from marine anhydrites in the Zaige Formation, South China

A global-scale mass extinction event occurred in the Late Devonian, and its triggering mechanisms have remained a subject of controversy. The key to resolving this controversy lies in elucidating paleoenvironmental characteristics and their coupling relationship with the mass extinction. Marine evaporites serve as sensitive indicators that can be used for reconstructing the geochemical history of ancient oceans. In this study, we present a dual sulfur and oxygen isotopic dataset of marine anhydrites in the Lunatian gypsum deposit (Yunnan, China), and investigate its paleoenvironmental significance within the framework of the Late Devonian mass extinction. These anhydrites originate in arid and hot continental margin seas near convergent plate boundaries, forming as a result of the dehydration of marine gypsums during burial processes. Anhydrites exhibit a conspicuous positive anomaly in δ34S values (23.6–25.1‰, averaging 24.3‰), primarily attributed to bacteria-mediated sulfate reduction. The δ18O values of the Lunatian anhydrites (12.2–15.2‰, averaging 14.0‰) indicate a slightly higher oxygen isotope composition for Late Devonian seawater (8.7–11.7‰, averaging 10.5‰) compared to those of contemporary seawater (9.5–10.1‰). Such an oxygen isotopic characteristic for the Lunatian anhydrites is intricately associated with the chemical processes that occur during the diffusion of sulfides into the upper seawater. The anhydrite-forming evaporating system has a noticeable brine layering where the surface seawater is less dense than the deeper brine, and bacterial processes gradually increase δ34S in the deep brine. When the deep brine and surface seawater rapidly mix, it leads to a significant positive shift in the sulfur isotope composition of the resulting evaporites. Our sulfur and oxygen isotope data from Lunatian anhydrites validate the existence of an exceedingly anoxic marine environment during the Late Devonian, potentially serving as a pivotal factor in the mass extinction event.

High-Precision Measurements of 44Ca/40Ca Using Multiple-Collector Inductively Coupled Plasma Mass Spectrometry without Collision-Cell Technology.

Herein, we present a new method for determining the Ca isotopic composition of geological samples. To eliminate matrix elements from Ca, a column chromatography method was developed using a N,N,N'N' tetraoctyl-1,5-diglycolamide (TODGA) resin. The Ca isotopic compositions were measured by a multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) without collision cell equipment, especially that direct measurement to 44Ca/40Ca can be achieved. To mitigate the interference from 40Ar during 40Ca measurement, the cold plasma technique was used to suppress the Ar+ generation, resulting in a background Ar+ intensity of <300 mV, in contrast to the conventional hot plasma conditions, which typically yield thousands of volts for Ar+ intensities. Given the potential for a concentration mismatch between the sample and bracketed standard solutions to cause an intensive shift in measured Ca isotopic compositions, a correction for the [Ca] match is needed. To avoid matrix effects arising from residue matrix elements, it is crucial to limit the concentrations below 1% of Ca for most matrix elements (including Al, Mg, K, Na, and Sr) and below 1‰ for Fe. Notably, the tolerance of residue Sr is effectively improved compared to measurements with CC-MC-ICP-MS and traditional Hot-plasma-SSB-MC-ICP-MS methods with the conventional hot plasma technique, thereby lowering the complexity of column chemistry. The measured δ44/40Ca, δ44/42Ca, and ε40Ca values for eight reference materials agree well with previously reported values within analytical uncertainties. This method demonstrates long-term precision is better than 0.10‰ (two standard deviations) for both δ values (i.e., δ44/40Ca and δ44/42Ca). We anticipate that the proposed method will benefit the growth of the Ca isotope data set and foster an increase in the application of Ca isotope in Earth science studies.

Shifting groundwater fluxes in bedrock fractures: Evidence from stream water radon and water isotopes

Geologic features (e.g., fractures and alluvial fans) can play an important role in the locations and volumes of groundwater discharge and degree of groundwater-surface water (GW-SW) interactions. However, the role of these features in controlling GW-SW dynamics and streamflow generation processes are not well constrained. GW-SW interactions and streamflow generation processes are further complicated by variability in precipitation inputs from summer and fall monsoon rains, as well as declines in snowpack and changing melt dynamics driven by warming temperatures. Using high spatial and temporal resolution radon and water stable isotope sampling and a 1D groundwater flux model, we evaluated how groundwater contributions and GW-SW interactions varied along a stream reach impacted by fractures (fractured-zone) and downstream of the fractured hillslope (non-fractured zone) in Coal Creek, a Colorado River headwater stream affected by summer monsoons. During early summer, groundwater contributions from the fractured zone were high, but declined throughout the summer. Groundwater contributions from the non-fractured zone were constant throughout the summer and became proportionally more important later in the summer. We hypothesize that groundwater in the non-fractured zone is dominantly sourced from a high-storage alluvial fan at the base of a tributary that is connected to Coal Creek throughout the summer and provides consistent groundwater influx. Water isotope data revealed that Coal Creek responds quickly to incoming precipitation early in the summer, and summer precipitation becomes more important for streamflow generation later in the summer. We quantified the change in catchment dynamic storage and found it negatively related to stream water isotope values, and positively related to modeled groundwater discharge and the ratio of fractured zone to non-fractured zone groundwater. We interpret these relationships as declining hydrologic connectivity throughout the summer leading to late summer streamflow supported predominantly by shallow flow paths, with variable response to drying from geologic features based on their storage. As groundwater becomes more important for sustaining summer flows, quantifying local geologic controls on groundwater inputs and their response to variable moisture conditions may become critical for accurate predictions of streamflow.

An updated chronostratigraphic framework for the Cenozoic sediments of southeast margin of the Tibetan Plateau: Implications for regional tectonics

As one of the most important accommodation zones during the India-Asia collision, the southeast margin of the Tibetan Plateau (SEMTP) is characterized by many large-scale strike-slip faults, a regional low-relief relict that has been deeply incised by several continental scale rivers that originate from central Tibet, and numerous plant and vertebrate fossil biotas residing in Cenozoic sedimentary basins. Therefore, the SEMTP not only provides a meaningful constraint on the geodynamic evolution of the Tibetan Plateau, but also serves as an exemplar to understand the various interactions among surface uplift, drainage network reorganization, climate change, and biodiversity. Precise dating of Cenozoic sediments in the basins of the SEMTP is crucial for understanding these processes. Previously, the geochronologic framework of Cenozoic sediments in the SEMTP largely relied on fossils and regional stratigraphic correlations, which often involved circular reasoning and large uncertainties. In the past two decades, high-resolution magnetostratigraphy, detrital zircon geochronology, and isotopic dating of interbedded tephra layers have been carried out on SEMTP Cenozoic sedimentary basins in Yunnan and eastern Xizang provinces, SW China. Using these new data, we build a revised chronostratigraphic framework for Cenozoic sediments in SEMTP, and use this updated temporal framework to contextualize regional tectonics and climate change. The new chronostratigraphic framework shows that (1) many of the “Neogene” sedimentary basins based on plant fossils and regional lithostratigraphic correlation in the SEMTP were actually formed in the late Eocene and early Oligocene; (2) most of the Paleogene sedimentary successions in the SEMTP ended at the late Eocene-early Oligocene and were unconformably overlaid by Middle-Late Miocene sediments. Oligocene-Early Miocene sediments are often regionally absent. Sedimentary structures within the basin successions show that Paleogene basins were generally formed in compressional settings while the Late Miocene basins were mostly developed in extensional settings. The new chronostratigraphic framework, together with analyses of sedimentary basin structures, suggests that the SEMTP began to experience crustal shortening early in the India-Asia collision (∼50 Ma), producing Paleogene sedimentary basins and giving rise to the subsequent widespread surface uplift and regional erosion in the Oligocene-Middle Miocene. Tectonic inversion from compression to extension since the Middle Miocene precludes significant uplift of the SEMTP after this time, which may be related to geodynamic changes in the evolution of the Tibetan Plateau.

Analysis of sediment provenance using geochemical and isotopic data for a post-LGM sediment core from the western Great Rann of Kachchh, India: Implications for climate control on source regions

This study addresses the nature and causes of post-Last Glacial Maxima (LGM) sedimentation in the Western Great Rann of Kachchh, Gujarat, India. Specifically, we report geochemical and isotopic data (87Sr/86Sr and 143Nd/144Nd) for a 46.5 m sediment core from the Nara River bed. These data indicate that up to the beginning of the Holocene, sedimentation mostly comprised contributions from monsoon-dominated rivers of Western Himalaya. Later in the early Holocene, a shift towards Indus-derived sediments occurred, with a minor reversal at ∼7 ka, attributed to the rejuvenation of the Ghaggar-Hakra channel. A renewed contribution from the Indus River routed through the Nara River and through the Kori Creek (mouth of the Nara River) occurred during the mid- to late Holocene. Persistent availability of freshwater during the mid- to late Holocene helped sustain early Iron Age and medieval cultures in the region. However, significant decline in the hydrological system anchored in the shifting Indus River through the Nara channel after the medieval period, likely caused the gradual collapse of these cultures. Our study is important as it demonstrates that, if the sediment source is from regions of contrasting climatic domains (for example, monsoon-dominated western Himalaya rivers and the westerlies-dominated Indus River), temporal changes in precipitation intensities exert a first order control in modulating the sediment provenances.

Geochemistry of metabasite in Mariana forearc serpentinite mudflows documents interactions between serpentinizing fluid and subducted seamount basalts

Understanding the chemical composition of materials within the subducting slab is crucial for studying slab dehydration and melting mechanisms. Previous research has primarily focused on examining sediments and altered basalts collected near the seafloor, which has overlooked the chemical changes occurring within the forearc subduction channel. The Mariana forearc serpentinite mud volcanoes offer a unique opportunity to investigate metabasite xenoliths, providing valuable insights into the compositional changes of subducting slab materials at forearc depths. In this study, we present Pb-Nd-Hf isotopic data for blueschist-facies mafic clasts obtained from the Asùt Tesoru serpentinite seamount in the Mariana forearc. These data are combined with existing Sr isotope and trace element data to address the aforementioned issues. The mafic clasts display NdHf isotopic signatures reminiscent of the HIMU- and EM1-type basalts discovered in the Magellan seamounts. However, their SrPb isotopes display mixed signatures, indicating the influence of sediments and altered mid-ocean ridge basalts. These findings underscore the importance of serpentinizing fluids resulting from the interaction between sediment pore water and forearc mantle peridotite in altering the SrPb elemental and isotopic compositions of subducted slab materials. This process is achieved through interactions between slab materials and serpentinizing fluids within the subduction channel. It is important to emphasize that the blueschist-facies mafic clasts themselves do not directly serve as source materials for arc volcanism. However, their SrPb isotopes can undergo further modifications through exchanges with unaltered seamount basalts facilitated by serpentinizing fluids within the deep subduction channel, which extends from depths of 30 to 100 km. In this scenario, the mafic clasts with modified isotopic signatures could potentially contribute as source materials for arc volcanism.

Procedures from samples to sulfur isotopic data: A review.

Sulfur isotopes have been widely used to solve some key scientific questions, especially in the last two decades with advanced instruments and analytical schemes. Different sulfur speciation and multiple isotopes analyzed in laboratories worldwide and in situ microanalysis have also been reported in many articles. However, methods of sampling to measurements are multifarious, and occasionally some inaccuracies are present in published papers. Vague methods may mislead newcomers to the field, puzzle readers, or lead to incorrect data-based correlations. We have reviewed multiple methods on sulfur isotopic analyses from the perspectives of sampling, laboratory work, and instrumental analysis in order to help reduce operational inhomogeneity and ensure the fidelity of sulfur isotopic data. We do not deem our proposed solutions as the ultimate standard methods but as a lead-in to the overall introduction and summary of the current methods used. It has been shown that external contamination and transformation of different sulfur species should be avoided during the sampling, pretreatment, storage, and chemical treatment processes. Conversion rates and sulfur isotopic fractionations during sulfur extraction, purification, and conversion processes must be verified by researchers using standard or known samples. The unification of absence of isotopic fractionation is needed during all steps, and long-term monitoring of standard samples is recommended. This review compiles more details on different methods in sampling, laboratory operation, and measurement of sulfur isotopes, which is beneficial for researchers' better practice in laboratories. Microanalyses and molecular studies are the frontier techniques that compare the bulk sample with the elemental analysis/continuous flow-gas source stable isotope ratio mass spectrometry method, but the latter is widely used. The development of sulfur isotopic measurements will lead to the innovation in scientific issues with sulfur proxies.

Magnesium isotope behavior during titanomagnetite fractionation in basaltic lavas

Knowledge of the behavior of magnesium (Mg) isotopes during magmatic differentiation is a prerequisite for applying Mg isotopes as a tracer of crustal recycling and mantle heterogeneity. Crystal fractionation of mafic silicate minerals leads to limited Mg isotope fractionation; hence, Mg isotopic variations in basalts largely result from contributions of subducted crustal materials into their mantle sources. However, recent studies have revealed that the segregation of iron oxides, such as chromite during early-stage basaltic differentiation and titanomagnetite and ilmenite during late-stage differentiation, can potentially modify Mg isotopic compositions of mantle-derived lavas. Titanomagnetite is much more commonly observed in terrestrial basaltic lavas than chromite and ilmenite, and can also form during early-stage basaltic differentiation. To constrain the effects of titanomagnetite crystallization on Mg isotopic systematics of basaltic magma, we report Mg isotopic data for a suite of well-characterized alkaline basaltic lavas (MgO wt% = 4.99 to 6.52) from Gerba Guracha, western Ethiopian Plateau, which have undergone extensive titanomagnetite fractionation. Their δ26Mg values range from −0.29‰ to −0.17‰ and do not correlate with indicators of titanomagnetite fractionation such as TiO2 and V. These observations suggest that the segregation of titanomagnetite produced limited Mg isotope fractionation, possibly because of its composition-dependent, highly variable Δ26MgTi-Mgt−melt (Δ26MgTi-Mgt−melt = δ26MgTi-Mgt − δ26Mgmelt) values. Considering that most iron oxides occur as complex solid solutions that are controlled by the oxygen fugacity of magmas, the effects of oxide segregation on Mg isotopic systematics of basalts require further evaluation.

Spatio-temporal variations of lacustrine groundwater discharge and related nutrient fluxes in a typical lake in front of hillocks

Lacustrine groundwater discharge (LGD) as a hidden hydrologic process has been widely found to affect water and nutrient balance in various lakes, but a comprehensive research on both spatial and temporal variations of LGD and associated nutrient fluxes was poorly conducted. Herein, this study elucidated their spatio-temporal variations and underlying factors of a typical lake in front of hillocks with spatially variable topography and hydrogeology, and intense seasonal groundwater-lake exchange, within central Yangtze River basin. The 222Rn mass balance model was used in conjunction with hydrochemistry, water isotope, and nutrient data. The results showed that the overall LGD rate and related N/P fluxes were clearly higher in the wet season than in the dry season, for which the stronger evaporation relative to precipitation, more groundwater recharge from agricultural irrigation or aquacultural pond infiltration, and more N/P input from anthropogenic or aquacultural activities could be responsible. In the wet season, the area with more recharge from irrigating water or fish pond water infiltration and associated extensive agricultural or aquacultural activities, had the significantly highest LGD rate and related N/P fluxes. In the dry season, the area with the deepest water depth and largest topographic slope, exhibited the significantly highest LGD rate and slightly higher LGD-related N/P fluxes due to relatively low groundwater N/P concentrations. This study enriched the understanding on LGD and related nutrient fluxes in the perspective of both spatial and temporal variations, taking a new type of lakes (i.e., lakes in the transitional zone of hills and plains in temperate climate) as a typical case.

Species and origin determinations of an ivory chess set: An application of the ivory workflow implemented by California’s Wildlife Forensic Laboratory

Despite the prevalence of elephant poaching and ivory trafficking, domestic and international ivory markets around the world are slowly closing due to increased education and enforcement efforts. This includes California’s ivory market in 2016 after the passage of Assembly Bill 96 (AB 96), which prohibits the purchase, sale, offer for sale, possession, or importation with intent to sell, of ivory from elephant, mammoth, and mastodon along with other non-proboscidean species. To assist with enforcement efforts, the California Department of Fish and Wildlife’s Wildlife Forensic Laboratory (CDFW-WFL) has created and implemented a scientific workflow to taxonomically identify, geographically assign, and age California’s seized ivory. Here we discuss the application of this scientific workflow to a 32-piece ivory chess set, which was purchased in 1969 and donated to and examined by the WFL in 2021. Genetic data revealed 11 unique haplotypes and 19 unique genotypes, suggesting a diverse set of African elephants from numerous locations in Africa were used to assemble the chess set. Stable isotope data corroborated these findings and radiocarbon dating suggested the ivory used to carve these chess pieces grew approximately 6 years prior to the chess set being purchased. Our results indicate that the use of a variety of scientific techniques provides a wide scope of information; furthermore, taxonomically identifying, geographically assigning, and aging the ivory chess set demonstrates to law enforcement officers how our ivory workflow can assist them in coordinating efforts locally, nationally, and internationally to help stop the illegal importation of ivory into California.

Allanite U–Pb dating places new constraints on the high‐pressure to high‐temperature evolution of the deep Himalayan crust

AbstractDuring continental collision, crustal rocks are buried, deformed, transformed and exhumed. The rates, timescales and tectonic implications of these processes are constrained through the sequence and conditions of metamorphic reactions in major and accessory phases. Petrographic, isotopic and elemental data from metabasite samples in NW Bhutan, eastern Himalaya, suggest initial equilibration under high‐pressure (plagioclase‐absent and rutile‐present) conditions, followed by decompression to lower pressure conditions at high‐temperatures that stabilized plagioclase, orthopyroxene and ilmenite. Field observations and chemical indicators suggest equilibration under the lower pressure conditions is likely linked to the infiltration of melt from the host metasedimentary rocks. The metabasites preserve two metamorphic growth stages of chemically‐and petrographically distinct allanite that temporally overlap two stages of zircon growth. Allanite cores and zircon mantles grew at c. 19 ± 2 and 17–15.5 Ma respectively, linked texturally and chemically to the high‐pressure evolution. Symplectitic rims on embayed allanite cores, wholly symplectized Aln–Ilm and Aln–Cpx grains, and high U zircon rims grew at c. 15.5–14.5 Ma, linked chemically to the presence of melt and lower pressure, high‐temperature conditions. A single garnet Lu–Hf date is interpreted as geologically meaningless, with the bulk rock composition modified by melt infiltration after garnet formation. The open system evolution of these rocks precludes precise determination of the reactive bulk composition during metamorphic evolution and thus absolute conditions, especially during the early high‐pressure evolution. Despite these limitations, we show that combined geochemical and petrographic datasets are still able to provide insights into the rates and timescales of deep orogenic processes. The data suggest a younger and shallower evolution for the NW Bhutan metabasites compared to similar rocks in the central and eastern Himalayas.

Explosive volcanic activity in Central-Southern Italy during Middle Pleistocene: A tale from tephra layers of the Acerno basin

The cored succession of the Acerno basin, a tectonic palaeolake located in the southern Apennines (Italy), represents a key point of the Italian tephrostratigraphic network for the Quaternary. Trace element and isotope (87Sr/86Sr and 143Nd/144Nd) data have been acquired on bulk rock, glassy groundmass and separated minerals (feldspar and pyroxene phenocrysts) from twenty-one tephra layers, dated between ∼570 and 470 ka, embedded in the lacustrine sediments of the basin. The already available major element compositions have been here combined with the newly acquired data. The whole dataset provides a full geochemical characterization of the tephra that strengthens and improves previous attempts to identify their volcanic sources and potential correlatives. In this context, several previously proposed correlations among distal archives have been here confuted. The geochemical fingerprints highlight that the volcanic record preserved in the Acerno lacustrine succession can be attributed to the explosive activity of the Roccamonfina, Colli Albani, Sabatini, Pontian islands (Latium region, Central Italy) and the Neapolitan Volcanic Area (Campania region, South Italy), providing new insights to enhance the current knowledge on the Middle Pleistocene volcanic record in Italy. Moreover, tephra attributions suggest still unknown eruptive activity of such volcanoes during the Quaternary. From this perspective, our study testifies how difficult it is to precisely correlate different geological archives even in a very short time interval. Such a difficulty arises from a large number of volcanic events concentrated in a relatively short time span, with products of similar chemical composition, and from the incomplete characterization of the successions in proximal outcrops. A thorough reconstruction of the eruptive history of these volcanic complexes requires a wider and denser study of distal archives, alongside further investigations in proximal areas.

Facies architecture, geochemistry and petrogenesis of Middle Triassic volcaniclastic deposits of Mt. Ivanščica (NW Croatia): evidence of bimodal volcanism in the Alpine-Dinaridic transitional zone

During the Middle Triassic, intensive volcanic activity took place along the eastern margin of Pangea, including the Greater Adria promontory, due to the Neotethyan oceanization. This resulted in the formation of various volcanic and volcaniclastic rock types. The region of NW Croatia, acting as a transition zone between the Southern Alps and the Dinarides, showcases the outcrops of these rocks. The present study investigates the facies of volcaniclastic rocks, the distribution of those facies, formation processes, as well as the genesis of the primary magma to gain a better understanding of the complex geodynamics of this region during the Middle Triassic. Six profiles across the Vudelja quarry front were surveyed using drone imaging and samples were collected for detailed petrographic and geochemical analyses. Two groups of volcaniclastic rocks were identified—mafic and intermediate/felsic. The former is represented by (I) autoclastic effusive facies and (II) resedimented autoclastic facies, while the latter is represented by (III) secondary pyroclastic facies. Mafic volcaniclastics were generated through basaltic effusions in marine environments, fragmentation in contact with seawater, mixing with shallow marine carbonate clasts, and subsequent redeposition in deeper marine areas. The secondary pyroclastic facies (III) consists of a regionally distributed felsic Pietra Verde tuff whose deposits may be related to pyroclastic density currents and syn-eruptive resedimentation by turbidite-like currents. Geochemical data indicate that parental magmas responsible for generating the mafic volcaniclastics had a calc-alkaline composition and originated in ensialic and mature arc settings of an active continental margin. The observed chemical composition is likely inherited from older, arc-related lithologies, associated with the subduction of the Paleotethys Ocean. Parental magmas are thought to have formed during continental rifting of the passive Middle Triassic margins of the Greater Adria through (i) partial melting of the heterogeneous lithospheric mantle, which had been metasomatized during an earlier Hercynian subduction, and (ii) subordinate processes related to the melting of the upper continental crust and subsequent fractionation. Ar/Ar dating on plagioclase separates yielded an age of 244.5 ± 2.8 Ma for mafic volcaniclastics. This aligns well with biostratigraphic ages of felsic tuffs which crop out on a broader regional scale of the Dinarides, the Southern Alps, and the Transdanubian Range. The overlapping ages obtained from radiometric dating of mafic volcaniclastics and biostratigraphic ages of the felsic Pietra Verde tuffs strongly suggest that the Greater Adria region experienced concurrent bimodal volcanism during the Middle Triassic.

Human-cattle interactions in PPNB and Early/Middle Bronze Age Cyprus: integrating zooarchaeological and stable isotope data

Human-cattle interactions in PPNB and Early/Middle Bronze Age Cyprus: integrating zooarchaeological and stable isotope data

Spatiotemporal Variation of the Cretaceous‐Eocene Arc Magmatism in Lhasa‐Tengchong Terrane

AbstractIt was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip.