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We present computational modeling outcomes for bilithologic (peridotite and pyroxenite) mantle melting in divergent environments, considering equilibrium and disequilibrium porous flow melting of 0–50 % pyroxenite in thermal equilibrium with peridotite, potential temperatures of 1300 and 1400 °C, upwelling rates from 1–50 cm yr−1, maximum porosities of 0.1–2.0 %, and four compositions that span pyroxenite melting behavior. Basalt-like pyroxenites (G2) uniquely produce low (226Ra/230Th) and (231Pa/235U) with high (230Th/238U), but quantities greater than ~10 % produce anomalously thick crust, restricting their global abundance. Silica-deficient pyroxenite (M7-16 and MIX1G) melts are more moderate, but require chemical re-equilibration during transport to resemble global basalts, while hybrid lithologies (KG1) produce melts similar to those of peridotites. Uranium-series disequilibria in partial melts can also be decoupled from trace elements by radioactive decay in two-dimensional regimes. The mantle must thus contain multiple types of pyroxenite on a global scale, with melts traveling by complex networks and experiencing heterogeneous extents of chemical re-equilibration.

In this article, we propose an approach to reconstruct the timing of human activity at Points Cave, an Upper Paleolithic rock art site located in the middle of the Ardèche River Gorge (Rhône valley, France), based on the dating and characterisation of a stalagmite containing soot. Points Cave ('Grotte aux Points' in French), also called the 'little sister of Chauvet Cave', is famous for its parietal art including a series of dots made of palm prints. A large number of stalagmites formed in the cave during the last 500 ka. However, quarrying of the cave floors during historic times led to the partial destruction of the sedimentary deposits, and many of the stalagmites were found lying on the floor. In particular, one of them (STM‐18‐04) showed the presence of at least four dark layers in cross‐section, which appeared as possible remnants of fire‐related activities in the cave. Despite being present at the same site, no other specific link between STM‐18‐04 and the rock art has been documented. This stalagmite, however, allows us to identify phases of human presence, located at the cave entrance. To do so, we performed a series of analyses to determine its period of growth and the nature of the dark layers that it contains. Scanning electron microscopy and Raman microspectroscopy confirmed that the dark layers include soot, and uranium‐series dating indicated that the fire events occurred, respectively, around 14,200–14,100 and 12,500 years ago, in agreement with the radiocarbon ages of charcoal specimens recovered from the excavation areas nearby. We thus highlighted phases of human activity at the site during the Upper Magdalenian and/or beginning of the Epipaleolithic. By comparing our results with the regional paleoclimatic record, the soot layers trapped in the stalagmite appear to be synchronous with two cold periods, likely the Older Dryas and the Younger Dryas. [ABSTRACT FROM AUTHOR]

Here we report (210Pb/226Ra), (226Ra/230Th), (230Th/238U) and (234U/238U) disequilibria for eleven lavas from the ABE vent site in the Lau Basin. Most ABE lavas have (210Pb/226Ra) > 1 and (226Ra/230Th) > 3. These results indicate that most of these lavas erupted within the past 100 years. Model ages calculated assuming initial (210Pb/226Pb) = 1.8–2.0 further constrain the timing of eruption, suggesting that more than half of the lavas erupted within the past 60 years. When combined with complementary data (side-scan sonar, lava flow morphology, tectonic mapping), this high-resolution record provides fundamental time constraints for interdisciplinary studies examining oceanic crustal construction and development of the hydrothermal system in the ABE vent field. Notably the youngest samples cluster around the active vent sites indicating that the ABE vent site’s location is a direct consequence of this concentrated young volcanism. This study is the first high resolution U-series study of a seafloor vent site and demonstrates the potential of using (210Pb/226Ra) for the determination of lava ages for young submarine lavas in spreading environments with active hydrothermal venting. As such these (210Pb/226Ra) measurements hold the promise for addressing in far greater detail the connections between spreading ridge eruptive and hydrothermal activity on the decadal to century time scales.

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The study of paleo shorelines, particularly of those formed during the late Quaternary, provides robust insights into past climate variability. Advances in surveying techniques and chronological methodologies have dramatically improved the inter-comparability of regional and basin-wide paleo shoreline surveys. However, these advances have been applied unevenly across the globe. This is especially true in southwestern Madagascar, where, in the 1960s and 1970s, emerged Pleistocene beach and reef facies were first described in detail and dated to Marine Isotope Stage (MIS) 5a using U–Th alpha activity counting by french geologist René Battistini. Now, 50 years on, no further analysis of the coastal sequence has been made. In this study, we present an updated late Pleistocene coastal evolution model for the southwestern Madagascar coast. Utilizing a combination of Structure-from-Motion/Multi-View Stereo techniques and differential Global Navigation Satellite System surveys, we have created five high-resolution 3D outcrop reconstructions that have, in turn, been chronologically constrained using 10 U-series ages from both in situ and reworked coral samples. Our data suggest that the emerged reef was deposited during MIS 5e (∼125 ka), then was covered by intertidal and beach sediment (including redeposited coral clasts of MIS 5e age), and finally capped off by thick eolianites. This sequence would suggest that the local sea level must have remained stable throughout MIS 5e in order to allow for the progradation of both the beach and reef environments.

Establishing chronologies of archaeological sites by using a single dating method may not always reliably constrain the age of a deposit or a fossil, as potential biases may naturally arise, particularly in complex sedimentary settings such as caves. In this study, we performed a multi-technique dating approach that targets different materials in two caves from the Cueva Mayor-Cueva del Silo karst system, Sierra de Atapuerca, Spain. Two new fossil teeth from lithostratigraphic unit LU4 (GE-I pit) at Galería de las Estatuas have been dated by combined U-series/ESR and Amino Acid Racemisation (AAR) methods. The former provides ages of 117 ± 13 and 87 ± 9 ka that agree with previous dating studies of this Neandertal site, confirming the assignment of level LU4 to Marine Isotope Stage (MIS) 5. In contrast, AAR analyses produce very scattered ages, pointing to significant post-burial chemical modifications in dentine. A first set of ages is presented for the Cata Litario pit at Sala de los Cíclopes, a palaeontological site formed exclusively of cave bear fossils belonging to the Middle Pleistocene species Ursus deningeri. We provide U-series/ESR and AAR ages for two bear teeth from lithostratigraphic unit LU5, and extended-range luminescence ages for the sediment deposits that host, and immediately underlie and overlie, the bear accumulation. Depositional ages of the sediment were obtained using single-grain thermally-transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains and post-infrared-infrared stimulated luminescence (pIR-IR) dating of K-feldspars. Several speleothems, both in situ and reworked fragments embedded in the different lithostratigraphic units, have additionally been dated by U-series to constrain the timing of the sequence formation. The results indicate that the sediment originally entered the cave between MIS-12 and MIS-10 (444 ± 28 ka to 367 ± 32 ka). Nevertheless, the AAR and U-series/ESR fossil ages, as well as some of the speleothem fragment ages from LUs 5 and 6 are significantly younger. Leaving aside methodologically questionable results for one of the bear tooth samples, the most reliable AAR and U-Series/ESR ages range from 287 ± 23 ka to 256 ± 24, while the speleothem fragments indicate several formation episodes between 444 ± 19 and 284 ± 8 ka. The apparent difference between the U-Series/ESR ages on the fossils and the luminescence ages on the host sediment are not likely to be wholly explained by uncertainties on uranium uptake modelling or gamma dose rate evaluation, and thus is most likely related to taphonomic processes or a complex site formation history. The presence of fossils and eroded speleothem clasts of younger age within these levels is consistent with either an event of prior erosion, transport and resedimentation of LUs 4, 5 and 6, and/or a complex post-depositional mixing history for the stratigraphic sequence at Cata Litario. This study highlights the importance of using different dating methods to reconstruct reliable chronological frameworks, and to understand the geological factors that can affect the dated materials. This includes the accumulation and taphonomic histories of fossils, post-depositional mixing or reworking processes affecting sediments during the residence time within the karst system. [ABSTRACT FROM AUTHOR]

The study of paleo shorelines, particularly of those formed during the late Quaternary, provides robust insights into past climate variability. Advances in surveying techniques and chronological methodologies have dramatically improved the inter-comparability of regional and basin-wide paleo shoreline surveys. However, these advances have been applied unevenly across the globe. This is especially true in southwestern Madagascar, where, in the 1960s and 1970s, emerged Pleistocene beach and reef facies were first described in detail and dated to Marine Isotope Stage (MIS) 5a using U-Th alpha activity counting by french geologist René Battistini. Now, 50 years on, no further analysis of the coastal sequence has been made. In this study, we present an updated late Pleistocene coastal evolution model for the southwestern Madagascar coast. Utilizing a combination of Structure-from-Motion/Multi-View Stereo techniques and differential Global Navigation Satellite System surveys, we have created five high-resolution 3D outcrop reconstructions that have, in turn, been chronologically constrained using 10 U-series ages from both in situ and reworked coral samples. Our data suggest that the emerged reef was deposited during MIS 5e (~125 ka), then was covered by intertidal and beach sediment (including redeposited coral clasts of MIS 5e age), and finally capped off by thick eolianites. This sequence would suggest that the local sea level must have remained stable throughout MIS 5e in order to allow for the progradation of both the beach and reef environments. [ABSTRACT FROM AUTHOR]

Meaningful analysis of uranium‐series isotopic disequilibria in basaltic lavas relies on the use of complex forward numerical models like dynamic melting (McKenzie, 1985, https://doi.org/10.1016/0012-821x(85)90001-9) and equilibrium porous flow (Spiegelman & Elliott, 1993, https://doi.org/10.1016/0012-821x(93)90155-3). Historically, such models have either been solved analytically for simplified scenarios, such as constant melting rate or constant solid/melt trace element partitioning throughout the melting process, or have relied on incremental or numerical calculators with limited power to solve problems and/or restricted availability. The most public numerical solution to reactive porous flow, UserCalc (Spiegelman, 2000, https://doi.org/10.1029/1999gc000030) was maintained on a private institutional server for nearly two decades, but that approach has been unsustainable in light of modern security concerns. Here, we present a more long‐lasting solution to the problems of availability, model sophistication and flexibility, and long‐term access in the form of a cloud‐hosted, publicly available Jupyter notebook. Similar to UserCalc, the new notebook calculates U‐series disequilibria during time‐dependent, equilibrium partial melting in a one‐dimensional porous flow regime where mass is conserved. In addition, we also provide a new disequilibrium transport model which has the same melt transport model as UserCalc, but approximates rate‐limited diffusive exchange of nuclides between solid and melt using linear kinetics. The degree of disequilibrium during transport is controlled by a Damköhler number, allowing the full spectrum of equilibration models from complete fractional melting (Da=0) to equilibrium transport (Da=∞). Access the full executable Jupyter notebook version of this manuscript here. Key Points: Cloud‐based Jupyter notebook presents an open source, reproducible tool for modeling U‐series in basaltsEquilibrium and pure disequilibrium porous flow U‐series models with 1D conservation of massScaled porous flow model introduces incomplete equilibrium scenario with reaction rate limitations [ABSTRACT FROM AUTHOR]

In this study, the correlation of the Balkayası travertine formations with the Salanda Fault Zone (SFZ) located within the Central Anatolian Volcanic Province (CAVP) was investigated. Additionally, source and paleoclimatic significance were researched with age dates for the travertine formations obtained with the U-series dating method, stable isotope data, and major oxide, trace, and rare earth element (REE) analyses. The ages of the travertines outcropping in the study area were determined to vary from 9 to 55 ka according to U-series age analysis data. In the stress analysis taking into account the trending's of Balkayası travertines deposited in SFZ, it was found that the main compression and extension directions in the region were NNW-SSE and ENE-WSW, respectively. The δ13CPDB values varied from 11.36 to 13.16 and δ18OPDB values were from − 10.41 to − 8.66. ∑REE were in the interval 1.08–22.97 ppm. Negative Eu and Ce anomalies were determined. Travertine formations outcropping in the region were classified according to morphology as fissure ridge, range front, and eroded sheet travertines. Age dates obtained from the travertines reveal they formed in MIS 3 (marine isotope layer) representing very cold (dry) periods and MIS2 and the initial period of MIS 1. The extensional direction is consistent with the Tuz Gölü Fault Zone (TGFZ), one of the important structures in the region. Linked to the age data from the travertine formations, the strike-slip transition on the SFZ is interpreted to have extended to the Late Pleistocene. In conclusion, according to stable isotope data and geochemical data, the Balkayası travertines have epigenic character; however, they were affected by the hypogenic environment, precipitated in fresh water, and were fed by high pH and hydrothermal waters. [ABSTRACT FROM AUTHOR]

Sarıhıdır travertines and associated manganese mineralization are located in an area known as the Central Anatolian Volcanic Province (CAVP). The topic of the study, the Sarıhıdır manganese mineralization, was deposited in association with fault zones in this tectonically-active region. Paragenesis of the mineralization includes pyrolusite, rhodochrosite and goethite with gangue minerals of calcite and quartz observed. Diagrams drawn using major oxide and trace elements like Fe–Mn–(Ni+Co+Cu)×10, Fe-Si×2-Mn, Co/Ni vs Cu+Co+Ni, Si/Al, Na/Mg, Fe/Ti vs. Al/(Al+Fe+Mn), Co+Ni/As+Cu+Mo+Pb+V+ Zn and FeO–MnO2–10× MgO show the mineralization found in the region is sourced in the hydrothermal field. The low total REE values and LREE>HREE ratio indicate the effect of hydrothermal solutions. Additionally, Ce, Eu and Ceanom anomalies indicate the source of the mineralization was hydrothermal with oxic-anoxic formation environment. The Y/Ho ratio is mean 30.1 which is lower compared to hydrothermal fluids. Mean values are δ13CPDB 12.24‰ and δ18OPDB 10.87‰ indicating deposition from fluids with a deep CO2 component. In conclusion, the Sarıhıdır mineralization and travertine were determined to have formed about 50–53 ka (Upper Pleistocene) based on U-series age data, as fault-controlled, hydrothermal-sourced mineralization.

Deglaciation ages for valley glaciers from the last glacial maximum are difficult to obtain with precision. The unequal or non-uniform loss of glacial ice cover (spatial heterogeneity) during glacial retreat results in exposure of considerable land surface area prior to complete deglaciation. New U-series dates from an 11cm long stalagmite in a shallow, high elevation (3242 m) cave in the southern San Juan Mountains of southwestern Colorado (USA), indicate that substantial, high-elevation glacial ice ablation occurred prior to 13.5 ka. The stalagmite dates compare well with other deglaciation studies in central and southern Colorado that show deglaciation occurred between ca. 13 ka to 15 ka. Low δ13C values from 13.5 ka speleothem growth bands, relative to the δ13C value of the host carbonate, suggest that alpine plant and soil cover was established at this location, aspect, and elevation prior to 13.5 ka. Calcite luminescence in the 13.5 ka growth bands indicates the presence of humic and fulvic acids released by the roots of living plants and decomposition of vegetative matter. The carbon isotope ratios, calcite luminescence, and U-series dates suggest that the southern San Juan Mountains, at this high elevation site and southern aspect were substantially ice-free prior to 13.5 ka.

Abstract The Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U‐230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of

The Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U‐230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of <10 kyr for major mineral phases in TBJ. This dichotomy is explained by a process of rhyolitic melt segregation from a crystal‐rich refractory residue that incorporates zircon, whereas a new generation of major mineral phases crystallized shortly before eruption. Ti‐in‐zircon temperatures and amphibole geothermobarometry suggest that rhyolitic melt was extracted from different storage zones of the magma reservoir as indicated by distinct but synchronous thermochemical zircon histories among the TB suite eruptions. Zircon from TBJ and TB2 suggests magma differentiation within deeper and hotter parts of the reservoir, whereas zircon from TB3 and TB4 instead hints at crystallization in comparatively shallower and cooler domains. The assembly of the voluminous TBJ magma reservoir was also likely enhanced by cannibalization of hydrothermally altered components as suggested by low‐δ18O values in zircon (+4.5 ± 0.3‰). Plain Language Summary: The collapse of a volcano edifice into its shallow magma chamber can produce one of the most dangerous single events in nature, known as a caldera‐forming eruption. The TBJ eruption in El Salvador is of this kind and occurred around 1,500 years ago, having a profound impact on Maya societies. Because of this, it is crucial to understand the inner workings of caldera‐forming eruptions to assess volcanic risks and their mitigation. Beneath Ilopango caldera, the micrometer‐sized radioisotopically datable mineral zircon grew within different storage levels of a silica‐rich magma reservoir suggesting continuous melt presence for up to ca. 80,000 years prior to eruption. The time information given by zircon contrasts with that extracted from other, more abundant minerals from the same rocks (<10,000 years). We explain this time difference between coexisting minerals by the ability of melt to carry along small zircon crystals, whereas coeval, larger, and more abundant minerals are left behind in the partially solidified portion of the magma reservoir. Once the segregated melt coalesced in a shallower and dominantly liquid magma chamber, major minerals resumed crystallization shortly before eruption. In addition, this new magma incorporated parts of older magmatic rocks from preceding volcanic cycles, thus generating even larger magma volumes. Key Points: U‐Th zircon ages for the last four explosive eruptions of Ilopango caldera reveal a long‐lived magma reservoir (>80 kyr)Contrasting residence times for major minerals and zircon suggest extraction of zircon along with evolved melt from crystal residueMelt extraction from vertically extensive, thermally zoned magma reservoir [ABSTRACT FROM AUTHOR]

Abstract Travertine deposits preserve an invaluable record of both ancient and modern fluid flow. The goal of this study is to reconstruct spatial and temporal patterns in travertine deposition associated with tectonic and climatic controls along the Lucero Uplift in New Mexico, USA. Uranium‐series ages of travertine deposits in the Lucero Uplift range from 0.94 ± 0.01 to 592 ± 110 ka, indicating that travertine formation has been episodically active since at least ∼600 ka. We find minimal evidence to attribute glacial and interglacial cycles to travertine formation in the Lucero Uplift. δ13C values in travertine deposits range from 2‰ to 9‰ (Vienna Pee Dee Belemnite), δ18O values range from 21‰ to 25‰ (Vienna Standard Mean Ocean Water). Positive correlation between travertine δ13C and δ18O values indicate travertine formation is closely associated with various degrees of CO2 degassing. 87Sr/86Sr values in travertine deposits range from 0.714 to 0.717 and (234U/238U)i values exhibit a remarkably wide range from 3.6 to 9.3, indicative of fluid‐rock interaction during deep crustal circulation in more radiogenic basement rocks. Reconstructed δ13C, δ18O, and (234U/238U)i values in the inferred deep fluid sources showed systematic variations with travertine formation ages, while 87Sr/86Sr values remain relatively constant. Based on dating of undeformed travertine deposits, which overlie tilted Santa Fe Group units, and high (234U/238U)i we infer that the Santa Fe fault has not produced a ground‐rupturing earthquake within the last 490 ± 52 to 592 ± 110 ka (2σ). Our study suggest that travertine formation is driven by fluid flow facilitated by tectonic and mantle structures.

Travertine deposits preserve an invaluable record of both ancient and modern fluid flow. The goal of this study is to reconstruct spatial and temporal patterns in travertine deposition associated with tectonic and climatic controls along the Lucero Uplift in New Mexico, USA. Uranium‐series ages of travertine deposits in the Lucero Uplift range from 0.94 ± 0.01 to 592 ± 110 ka, indicating that travertine formation has been episodically active since at least ∼600 ka. We find minimal evidence to attribute glacial and interglacial cycles to travertine formation in the Lucero Uplift. δ13C values in travertine deposits range from 2‰ to 9‰ (Vienna Pee Dee Belemnite), δ18O values range from 21‰ to 25‰ (Vienna Standard Mean Ocean Water). Positive correlation between travertine δ13C and δ18O values indicate travertine formation is closely associated with various degrees of CO2 degassing. 87Sr/86Sr values in travertine deposits range from 0.714 to 0.717 and (234U/238U)i values exhibit a remarkably wide range from 3.6 to 9.3, indicative of fluid‐rock interaction during deep crustal circulation in more radiogenic basement rocks. Reconstructed δ13C, δ18O, and (234U/238U)i values in the inferred deep fluid sources showed systematic variations with travertine formation ages, while 87Sr/86Sr values remain relatively constant. Based on dating of undeformed travertine deposits, which overlie tilted Santa Fe Group units, and high (234U/238U)i we infer that the Santa Fe fault has not produced a ground‐rupturing earthquake within the last 490 ± 52 to 592 ± 110 ka (2σ). Our study suggest that travertine formation is driven by fluid flow facilitated by tectonic and mantle structures. Key Points: Travertine deposits of the Lucero Uplift have been forming episodically since at least ∼600 ka through both glacial and interglacial periodsCarbon, oxygen, strontium, and uranium isotope data indicate mixing of deep and shallow crustal fluid sources involved in travertine formationTravertine formation is mainly driven by fluid flow influenced by regional tectonic (Rio Grande rift) and mantle (Jemez Upwelling) structures [ABSTRACT FROM AUTHOR]

Rock art dating has been one of the major challenges since its discovery and recognition. The methods have evolved through the last century, beginning with the study of superpositions and style until to the application of numeric methods since the 1990s. The aim of this paper is to evaluate and publish an up-to-date database of all of the numerical dates currently available for Iberian prehistoric rock art sites. For this purpose, the manuscript reviews all the methods applied so far to Iberian rock art discussing the limits, the sampling involved, and the problems affecting the results. After that, we present and discuss the most relevant results related to each cultural graphic tradition (Palaeolithic, Levantine, Schematic and Megalithic rock art) assessing their value and limitations. Finally, we reflect on the future of rock art dating: unfortunately most of the motifs are not dateble in numeric terms, meaning we still have to combine traditional with numerical methods; but also, we need to keep working on the problems affecting these methods to be able to create a more reliable chronological framework of use to address other issues such as group mobility, cultural networks, and reutilisation of symbolic elements, to name a few. [ABSTRACT FROM AUTHOR]

To investigate whether the source of the globally occurring garnet signature in mid‐ocean ridge basalt (MORB) is "true" (imparted by melting a garnet‐bearing source) or "apparent" (produced without the involvement of garnet), we present the basalt petrogenesis model Petrogen. Petrogen is built on Kinzler and Grove (1992a, https://doi.org/10.1029/91JB02841) and Behn and Grove (2015, https://doi.org/10.1002/2015JB011885) and calculates the major element, trace element, and isotopic compositions of primary lherzolite‐saturated mantle melts and their subsequent evolution to eruption. This model is experimentally calibrated for melting in the plagioclase, spinel, and garnet fields with and without small amounts of water. Petrogen predicts that garnet‐lherzolite melting requires small mantle porosity (ϕ = ∼0.1%) and enriched (NaK# > 0.1), hot (>1400–1450°C), and damp mantle (>350–700 ppm water) sources. When garnet‐lherzolite melting does occur, the fraction of melting that takes place in the garnet field is not sufficient to impart a recognizable true garnet signature in the major and trace element composition of pooled melts except at ultraslow‐spreading rates (half rate ≤ 0.5 cm/yr). Therefore, for ambiguous garnet trace element signatures in MORB to be "true" would require that they are near‐fractional garnet‐lherzolite melts or garnet‐pyroxenite melts diluted by mixing in random proportions. While we do not test the process of random mixing, we find that near‐fractional and pooled melts of variable major and trace element mantle peridotite compositions at different mantle potential temperatures can explain the range of garnet signatures in MORB. For spinel‐peridotite melting to support garnet signatures requires mantle porosities ϕ = ∼0.1%; however, plagioclase‐peridotite melting, under specific circumstances, can explain MORB garnet signatures with ϕ = ∼1%. Key Points: The major element composition of garnet peridotite melts provides critical evidence for identifying garnet signatures in MORBsGarnet signatures in MORBs are diverse and reflect melting of compositionally and thermally variable mantle without garnetShallow melting of plagioclase peridotite can explain MORB major and trace elements and U‐series isotopes with mantle porosity ϕ ≥ 1% [ABSTRACT FROM AUTHOR]

Sarıhıdır travertines and associated manganese mineralization are located in an area known as the Central Anatolian Volcanic Province (CAVP). The topic of the study, the Sarıhıdır manganese mineralization, was deposited in association with fault zones in this tectonically-active region. Paragenesis of the mineralization includes pyrolusite, rhodochrosite and goethite with gangue minerals of calcite and quartz observed. Diagrams drawn using major oxide and trace elements like Fe–Mn–(Ni+Co+Cu)×10, Fe-Si×2-Mn, Co/Ni vs Cu+Co+Ni, Si/Al, Na/Mg, Fe/Ti vs. Al/(Al+Fe+Mn), Co+Ni/As+Cu+Mo+Pb+V+ Zn and FeO–MnO2–10× MgO show the mineralization found in the region is sourced in the hydrothermal field. The low total REE values and LREE>HREE ratio indicate the effect of hydrothermal solutions. Additionally, Ce, Eu and Ceanom anomalies indicate the source of the mineralization was hydrothermal with oxic-anoxic formation environment. The Y/Ho ratio is mean 30.1 which is lower compared to hydrothermal fluids. Mean values are δ13CPDB 12.24‰ and δ18OPDB 10.87‰ indicating deposition from fluids with a deep CO2 component. In conclusion, the Sarıhıdır mineralization and travertine were determined to have formed about 50–53 ka (Upper Pleistocene) based on U-series age data, as fault-controlled, hydrothermal-sourced mineralization. [ABSTRACT FROM AUTHOR]

The chemical weathering rate of silicates is a key parameter of several geochemical processes; however, the long-term field measurement of these rates remains challenging. Currently, there are several methods for quantifying field weathering rates, but each presents it's own unique set of difficulties. In this study uranium-series nuclides were used to investigate long-term biotite weathering in a soil profile. For this purpose, pseudomorph grains of biotites (including weathering products) were hand-picked from four horizons of a soil profile and from underlying granitic saprolite from the experimental Breuil-Chenue site (France). Unexpected behaviors of U and Th nuclides were recorded from these samples. An unambiguous leaching of 232Th occurs during the weathering of biotite, while reduced U release relative to Th was observed, implying an efficient redistribution of U between the primary mineral and weathering products within the pseudomorphs. The measured U-series activity ratios reflect a regular and self-consistent pattern evolution. However, the "U-series-derived-weathered-stage" is not always coherent with the weathering features of major elements and/or with the location of the samples within the soil profile. For instance, biotite from the saprolite displays U-series activity ratios typical of significantly weathered samples, while major elements present rather limited signs of weathering. These results suggest an incongruent leaching of U and Th isotopes and suggest that U- and Th-series nuclides probe some water-mineral interactions that occur before macroscopic mineral tansformation. Using an open-system leaching model, coupled (234U/238U), (234U/230Th), and (226Ra/230Th) disequilibria measured from the samples allow us to calculate a weathering duration range of 6–52 ky for most weathered samples of this soil profile. The biotite weathering rate deduced from these data ranges from 7.8 × 10−17 mol·m−2·s−1 to 6.5 × 10−16 mol·m−2·s−1, which is consistent with the range of field rates previously reported. This rate was compared to the weathering rate of biotites induced by the substitution of vegetation occuring 35 years ago in a nearby soil profile, which was about 2–3 orders of magnitude higher than the long-term rate reported above. This feature is perfectly consistent with the decrease in the weathering rate with time that was previously widely documented but that still remains debated. Our results allude to a valuable use of U-series isotopes for mineral-weathering field rate determination and report a decrease in silicate weathering rates over long- (10,000s of years) and short-term (10s of years) weathering events recorded from the same site. The results show that short term laboratory experiments can be representative of field processes, and suggest that some forms of mineral weathering reactivation, similar to that observed during laboratory experiments, may naturally occur in soils in response to high frequency perturbation processes such as land cover change. [ABSTRACT FROM AUTHOR]

Volcanological studies coupled with detailed geochemistry can reveal important aspects regarding the melting and ascent processes of a magmatic body. The explosive part of the eruption giving rise to scoria and tephra deposits can hold a wealth of information which can complement chemical analyses of lava flows, however, it is often poorly exposed. A well-exposed scoria deposit and lava flow at the small eruptive center (SEC) San Jorge near Pucón in the Southern Volcanic Zone (SVZ), Chile, provides an opportunity to examine melting and storage processes in a primitive magma body almost in 'real time' through sampling up the stratigraphy of the deposit. This dataset comprises whole rock major and trace element chemistry, Sr–Nd and U-Th–Ra isotopes, in addition to mineral data through the eruption sequence. San Jorge whole rock compositions are unique in the area (MgO 10–12 wt%, SiO2 50–52 wt%, Cr 600–900 ppm) and the studied tephras extend to the highest uranium- and radium-excesses yet measured in the SVZ. The unusual composition of the volcanic material displays similarities to rocks from the arc-front stratovolcano Villarrica but is distinct from other stratovolcanoes in the area, which exhibit greater influence from sediment input to the source, crustal assimilation and prolonged storage. We model the San Jorge magmas as a mixture of melts originating from highly fluid-fluxed, depleted mantle and fractionated basalt from the same source, with increasing amounts of the latter component with progression of eruption. This suggests that San Jorge-like magmas were the main feeder of the longer lived system building Villarrica. Abrupt major element variations up-sequence additionally show a rapid switch to more fractionated compositions, indicating that storage and evolution through crystallization may have taken place once the initially wet melts 'dried out'. [ABSTRACT FROM AUTHOR]

Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Obtaining precise and accurate dates for late Quaternary terrestrial sequences containing Middle Stone Age or Middle Paleolithic archaeological materials (ca. 30–300 ka) can be challenging. Many such sequences lie beyond the limit of radiocarbon dating (∼50 ka) and lack volcanic ashes suitable for 40Ar/39Ar dating. We report a dating approach with about ten times the range of radiocarbon dating (∼500 ka) based on a novel protocol for 230Th/U dating of ostrich eggshell, a common component of African, Near Eastern and Asian archaeological sequences. Uranium in ostrich eggshell, typically at levels of tens to hundreds of ppb, is acquired after burial. However, accurate burial ages can be determined from measured 230Th/U ages when corrected for uranium uptake via diffusion. Using ostrich eggshells from a Pleistocene-Holocene east African site, we have: (1) characterized the spatial distribution of uranium and common thorium (232Th) concentrations in ostrich eggshell by laser ablation ICP-MS, (2) determined apparent 230Th/U ages on outer and inner layers of eggshells by solution ICP-MS analyses of selectively abraded eggshells, and (3) calculated 230Th/U burial ages using a simple model for diffusive uptake of uranium. We assess our method by comparing the 230Th/U burial ages (median uncertainty 2.3%, 1 SD) with radiocarbon dates on carbonate from the same eggshells. We find good agreement in seven out of nine eggshells, confirming the accuracy of their 230Th/U model ages. Eggshells that fail to yield reliable 230Th/U ages may be recognized by anomalous patterns of apparent 230Th/U ages, providing a reliability criterion innate to the 230Th/U data. Ostrich eggshells are resistant to diagenesis simplifying 230Th/U dating compared to bones and teeth. Eggshells of ostrich, emu, rhea and other living and extinct ratites found on six continents share similar structure and composition, suggesting our new approach to 230Th/U dating of eggshell may be applicable in diverse late Quaternary terrestrial settings. • We develop and test a new method for U-series dating of ostrich eggshells. • Modern and Pleistocene-Holocene archaeological ostrich eggshells were studied. • Optimal dating material was identified using laser ablation profiles of 238U and 232Th. • Most eggshells yielded accurate 230Th/U ages when corrected for prolonged U uptake. • Dating two fractions per eggshell aids identification of reliable 230Th/U ages. [ABSTRACT FROM AUTHOR]

Abstract The fossil evidence of hominins in China is crucial to understand the human evolution and dispersal in Eurasia. However, the dating of Chinese Early and Middle Pleistocene hominin record remains a serious problem. In this study, we applied coupled ESR/U-series dating method on Bailongdong hominin cave site in Hubei Province, central China, which is a key area to study early human migration between South and North China. The U-series analyses show that the fossil teeth samples from three horizons are close or beyond equilibrium, which indicate very early uptake or potential loss of uranium. Single saturation exponential fitting of 10 dose points irradiated up to 4 kGy was used for D E determination except one by double saturation exponential fitting with 16 dose points up to 63 kGy. Calculated by two uranium migration models, we obtain a weighted mean age of 509 ± 16 ka for five fossil teeth from layer 2. Combined with cosmogenic nuclides 26Al/10Be burial dating carried out on the cave deposits beneath the fossil layers in previous study, the multi-methods dating study places Bailongdong site at the early stage of Middle Pleistocene, and pinpoints the deposition of the fossil remains to the time of marine isotope stages 13. This is in agreement with the fauna composition and sedimentary characteristics which show a subtropical-tropical warm forest-grass environment. The multi-methods dating of Bailongdong site by both cosmogenic and coupled ESR/U-series methods is a good example for the future chronological studies of early human sites in China. Highlights • A Middle Pleistocene hominin site was dated by coupled ESR/U-series method. • Multi-methods dating study by ESR fossil dating and 26Al/10Be burial dating. • D E estimation by two fitting functions with different maximum doses was compared. [ABSTRACT FROM AUTHOR]

In this first detailed study of zircon from Ascension Island, South Atlantic, we take a novel approach combining trace element and O isotope compositional data with double-dating (disequilibrium 238U–230Th and (U–Th)/He) to decipher timescales and dynamics of magmatic processes. The Echo Canyon (EC) sequence comprises small-volume explosive-effusive eruptions of trachyte that tapped a compositionally zoned magma system. Associated volcanic hazards may be constrained from the age of volcanism, duration of magma storage, and magma source and plumbing system character. Zircon U–Th–Pb dating of lithic lava clasts has revealed recurrent evolved volcanism at 1.34 and 0.6 Ma, and 95 ka. The (U–Th)/He zircon cooling ages indicate that most of the EC explosive-effusive sequence erupted in a brief episode at ca. 95 ka. Additionally, uniform 238U–230Th zircon crystallisation ages suggest moderately protracted magma storage with melt present at depth for at most 103–104 years before eruption. The enriched character of zircon trace element compositions, relative to MORB, in the absence of a continental crustal signature in the oxygen isotope values (δ18O range 2.67–5.63‰), suggests the presence of an enriched component in the EC magma source. Furthermore, low δ18O zircon compositions imply assimilation of high temperature hydrothermally altered country rock by the source magma. The mineral assemblage in crystal-poor pumices indicates equilibrium storage conditions: zircon saturation and Ti-in-zircon crystallisation temperatures are consistent with alkali feldspar-melt temperatures. Significantly, zircon crystals were preserved both as macrocryst inclusions and in the groundmass of EC explosive and effusive deposits. These rocks preserve evidence of magma evolution by fractional crystallisation. This process led to pre-eruptive compositional stratification, which is evidenced in the range of whole-rock major and trace element compositions and zircon Zr/Hf values. Notably, zircon crystallisation and cooling ages derived from pumice, lava, and accidental lithic lava clasts in highly explosive pyroclastic deposits, have revealed episodes of evolved magmatism that would otherwise have gone undetected. In addition, the zircon trace element and isotope compositions, in combination with the range of crystallisation ages, evidence progressively deeper tapping of less evolved magma stored in discrete lenses. Thus, a combined zircon geochronological-geochemical approach can place constraints on the ca. 0.6 Ma recurrence of past explosive-effusive pulses of millennial to decamillennial duration and their enriched magma sources. This information is relevant for assessing hazards and informing monitoring and forecasting efforts to assist in managing associated risks for small ocean island volcanoes with particularly vulnerable populations and infrastructure. [Display omitted] • U–Th–Pb dating has identified recurrent felsic volcanism (1.34 Ma, 0.6 Ma, 95 ka) at Echo Canyon. • Eruption ages of the Echo Canyon explosive-effusive deposits converge at ca. 95 ka. • Pre-eruptive zircon crystallisation occurred over ca. 103–104 from ca. 111–98.5 ka. • Zircon trace element compositions indicate melt storage in discrete, zoned, lenses. • Deposits of the most explosive phases sample lithic clasts from previous eruptions. [ABSTRACT FROM AUTHOR]

U-series dating of corals is a crucial tool for generating absolute chronologies of Late Quaternary sea-level change and calibrating the radiocarbon timescale. Unfortunately, coralline aragonite is susceptible to post-depositional alteration of its primary geochemistry. One screening technique used to identify unaltered corals relies on the back-calculation of initial 234 U/ 238 U activity (δ 234 U i ) at the time of coral growth and implicitly assumes that seawater δ 234 U has remained constant during the Late Quaternary. Here, we test this assumption using the most comprehensive compilation to date of coral U-series measurements. Unlike previous compilations, this study normalizes U-series measurements to the same decay constants and corrects for offsets in interlaboratory calibrations, thus reducing systematic biases between reported δ 234 U values. Using this approach, we reassess (a) the value of modern seawater δ 234 U, and (b) the evolution of seawater δ 234 U over the last deglaciation. Modern coral δ 234 U values (145.0 ± 1.5‰) agree with previous measurements of seawater and modern corals only once the data have been normalized. Additionally, fossil corals in the surface ocean display δ 234 U i values that are ∼5–7‰ lower during the last glacial maximum regardless of site, taxon, or diagenetic setting. We conclude that physical weathering of U-bearing minerals exposed during ice sheet retreat drives the increase in δ 234 U observed in the oceans, a mechanism that is consistent with the interpretation of the seawater Pb-isotope signal over the same timescale. [ABSTRACT FROM AUTHOR]

We use the uranium-series (U-Th) dating method to investigate the accuracy of a relative chronology based on laminae correlation between a pair of coeval twin stalagmites and compare their stable isotope and trace element records based on the two chronologies. U-Th dating shows that a relative chronology based on laminae correlation can be inaccurate: a hiatus in one of the stalagmites was not recognised, as well as more subtle changes in growth rates. Use of the stratigraphic correlation alone resulted in significant differences in the timing of stable isotopes and trace element peaks, with implications for their interpretation. Our results reveal the importance of a robust and direct chronology with which to interpret proxy data. Poor relative chronologies can lead to a misinterpretation of palaeoclimate data. The study reveals potential implications for speleothem records where proxy data and samples for dating were not taken in close proximity to each other and/or were correlated via laminae over distances of more than a few centimetres. [ABSTRACT FROM AUTHOR]

Clay minerals hold some key information on time and rate of weathering processes that could be deciphered by U-series disequilibria. However a removal of organic matter is generally required prior to clay mineral chemical analyses, especially in soils. The impact of two protocols of organic matter removal on the U-series disequilibria in three different clay minerals was therefore investigated. Natural or commercial kaolinite, illite and montmorillonite were treated with hydrogen peroxide and by calcination. Both investigated treatments impact the U-series signature of clay minerals. Yet the extent of this impact strongly depends on the clay-type: while kaolinite remains almost insensitive to the treatments, illite shows some equivocal shifts since the activity ratios measured after calcination could describe more accurately the pure clay signal than initial activity ratios, and montmorillonite displays the larger reactivity. Overall, the H 2 O 2 treatment seems to induce more disturbance than the calcination process, mostly on U isotopes in illite and montmorillonite. Due to the oxidizing power of H 2 O 2 , the redox state of U held in the clays, i.e.: U(IV) or U(VI), strongly influences the extent of U leaching. In addition, a preferential leaching of 234 U relative to 238 U was observed in montmorillonite sample only, resulting to a U isotopic ratio fractionation. Conversely, during calcination, the most pronounced effect arises for Th isotopes. The congruent feature of Th loss, i.e.: Th loss ≈ mass loss, affecting the three clay minerals suggests a loss of Th through volatilization during this treatment. U or Ra are also affected, but to a lesser extent, by this volatilization. Overall, calcination causes a two- or three-fold reduced change of the ( 230 Th/ 234 U) and ( 234 U/ 238 U) activity ratios relative to H 2 O 2 treatment. The ( 226 Ra/ 230 Th) ratio was clearly the less sensitive to any treatment. It was only slightly affected in kaolinite after calcination, and the observed change suggests an improvement of the measured value due to a removal of a Th-bearing external matter. Albeit not perfect, calcination should therefore be preferred to H 2 O 2 treatment for organic matter removal before U-series analyses. [ABSTRACT FROM AUTHOR]

The Busidima Formation in the Afar region, Ethiopia, spans the Quaternary and records the cultural evolution of the genus Homo. Yet, the Middle Pleistocene to Holocene fluvial environments in which early humans lived are undersampled in eastern Africa. This paper examines the stratigraphy, geochronology and paleoenvironments of the newly designated Odele Member of the uppermost Busidima Formation (<152 thousand years ago (ka)), which has received little attention despite representing a critical period in the evolution of early Homo sapiens and its migration out of Africa. The Odele Member is 40–50 m thick and is dated using tephrochronology, radiometric, luminescence, and electron spin resonance techniques. The member spans 151 to 7 ka, defined at the base by the widespread Waidedo Vitric Tuff (WAVT, 151 ± 16 ka modeled age and 95.4% credible interval - C.I.). There are two prominent erosional unconformities in the Odele Member, a lower one after the WAVT deposition with a modeled 95.4% C.I. range of 124–97 ka; and an upper one involving widespread alluvial fan incision commencing between 21.7 and 12.9 ka. The uppermost Odele Member also contains black, organic-rich mats, redox features, reed casts, and freshwater gastropods marking wetter conditions during the terminal Pleistocene and Early Holocene. A black, fine-grained relict soil coeval with the Halalalee paleosol bounds the top of the Odele Member and has mollic and vertic properties, weathering since ∼12 ka. These incision events and prominent paleosol development near/at the top of the Busidima Formation document Middle to Late Pleistocene Awash River incision to its present-day course. Paleo-rainfall estimates suggest that the Early Holocene-age Halalalee paleosol weathered under a climate with mean annual rainfall 10–15% higher than today. A compilation of radiocarbon ages from aquatic gastropods, carbonized wood and charcoal from the upper Odele Member shows wetter and possibly more vegetated conditions during late marine isotope stage (MIS) 3 and the African Humid Period (AHP) that are tightly coupled with precession-driven summer insolation maxima. These key findings suggest that periods of incision, aggregation, and landscape stability in the Odele Member have an orbital precession pacing. The Odele Member revises upward the age of the Busidima Formation to 7 ka, showing that it spans into the Holocene and now includes Middle and Later Stone Age archaeological traditions. • The Odele Member documents final Busidima half-graben infilling. • Changes in fluvial style occur on a precessional rhythm. • Fluvial incision and paleo-wetland deposits are associated with interglacials. [ABSTRACT FROM AUTHOR]

Pedogenic carbonates (calcretes) have often been proposed as possible markers of the pedogenetic processes in soils under semi-arid climate. However, precise chronological constraints on their formation are required in order to investigate the climatic and paleo-environmental conditions that prevailed during and after their formation, and to improve our understanding of the physical and chemical conditions that promoted their development and preservation. Moreover, these authigenic calcium carbonate precipitates provide us with an interesting test of the U–Th radioactive disequilibrium dating method, the reliability of which has been demonstrated extensively in aragonitic corals and calcitic continental speleothems, but which remains much more questionable in highly porous, chemically and mineralogically complex media such as soil profiles. We report here 238 U– 234 U– 230 Th radioactive disequilibrium analyses measured by Thermo-Ionization Mass Spectrometry in calcretes from two sites in southwest India. Since calcretes are impure carbonates mixed with various amounts of parent rock and weathered minerals, all ages must be computed using the isochron technique, involving the extraction of several coeval subsamples from the same soil horizon and U–Th analyses after total dissolution (TSD) method, in order to correct for the detrital component. 232 Th is usually used as index of the detrital contamination, and the isochron age is derived from the isotopic composition ( 230 Th/ 238 U; 234 U/ 238 U) of the pure authigenic carbonate end-member of the mixing line. Our results show that each set of samples taken from decimetric blocks is characterized by a well-defined isochron line in a 3-D Osmond diagram ( 232 Th/ 238 U; 230 Th/ 238 U; 234 U/ 238 U). The regression lines obtained for most of the samples show probabilities of fit satisfying the mathematical assumptions of the isochron model (in most cases ≫ 0.05), and mean square weighted deviations (MSWD) values around 1. The compositions of the end-members are highly variable between the different isochrons, both for the carbonate phase, indicating various ages of cristallisation, and for the detrital phase, indicating various origins and compositions. Notably, our data demonstrate that the detrital component is in all cases out of secular equilibrium, by contrast with the standard paradigm of “dirty carbonate” dating, which is based on the assumption of average continental crust Th/U elemental ratio, and secular equilibrium values of the ( 230 Th/ 238 U) and ( 234 U/ 238 U) ratios. At the first site (Coimbatore), we obtain U–Th ages between 304 ± 38 ka and 44 ± 2.9 ka (2σ) from the base to the top of the profile. These suggest discontinuous precipitation of the different facies in good agreement with micromorphological observations. At the second study site (Gundlupet), the carbonate nodules sampled from two different profiles, yield consistent ages of 200 ka, which suggests that precipitation of nodular carbonate occurred across the entire pediment toposequence during a single event. Surprisingly, in mere contradiction with the standard model of impure carbonate dating, two puzzling samples display “vertical isochrons”, i.e., variable 232 Th/ 238 U without any variation of the 230 Th/ 238 U and 234 U/ 238 U ratios. Such patterns require extremely high 232 Th/ 238 U ratios, in an as yet unidentified detrital phase. Taken at face value, these results suggest that no clear correlation can be inferred between the precipitation of these pedogenic carbonates and major orbitally-driven climate variations recorded in other archives during the last glacial/interglacial cycles. [ABSTRACT FROM AUTHOR]

To understand the dynamics of solid mantle upwelling and melting in the Hawaiian plume, we present new major and trace element data, Nd, Sr, Hf, and Pb isotopic compositions, and 238 U– 230 Th– 226 Ra and 235 U– 231 Pa– 227 Ac activities for 13 Haleakala Crater nepheline normative basanites with ages ranging from ∼900 to 4100 yr B.P. These basanites of the Hana Volcanics exhibit an enrichment in incompatible trace elements and a more depleted isotopic signature than similarly aged Hawaiian shield lavas from Kilauea and Mauna Loa. Here we posit that as the Pacific lithosphere beneath the active shield volcanoes moves away from the center of the Hawaiian plume, increased incorporation of an intrinsic depleted component with relatively low 206 Pb/ 204 Pb produces the source of the basanites of the Hana Volcanics. Haleakala Crater basanites have average ( 230 Th/ 238 U) of 1.23 ( n = 13), average age-corrected ( 226 Ra/ 230 Th) of 1.25 ( n = 13), and average ( 231 Pa/ 235 U) of 1.67 ( n = 4), significantly higher than Kilauea and Mauna Loa tholeiites. U-series modeling shows that solid mantle upwelling velocity for Haleakala Crater basanites ranges from ∼0.7 to 1.0 cm/yr, compared to ∼10 to 20 cm/yr for tholeiites and ∼1 to 2 cm/yr for alkali basalts. These modeling results indicate that solid mantle upwelling rates and porosity of the melting zone are lower for Hana Volcanics basanites than for shield-stage tholeiites from Kilauea and Mauna Loa and alkali basalts from Hualalai. The melting rate, which is directly proportional to both the solid mantle upwelling rate and the degree of melting, is therefore greatest in the center of the Hawaiian plume and lower on its periphery. Our results indicate that solid mantle upwelling velocity is at least 10 times higher at the center of the plume than at its periphery under Haleakala. [ABSTRACT FROM AUTHOR]

Radiocarbon dating of marine samples requires a local marine reservoir correction, or ΔR value, for accurate age calibrations. For the Samoan Archipelago in the central Pacific, ΔR values have been proposed previously, but, unlike some Polynesian archipelagoes, ΔR values seem not to vary spatially and temporally. Here, we demonstrate such variability by reporting a ΔR of –101±72 ΔR for the Manu‘a Group—the eastern-most islands in the archipelago—for the colonization period. This value is based on accelerator mass spectrometry (AMS) 14C and uranium-thorium (U-Th) series dating of individual coral branches from pre-2300 cal BP archaeological contexts. This figure differs from the previously proposed modern ΔR of 28±26 yr derived from dated historic, pre-1950, shell samples from the western islands of Samoa. Consequently, we recommend using the ΔR of –101±72 yr for the 1st millennium BC in Manu‘a, and 28±26 yr for calibrating dates within the 2nd millennium AD in the western islands (Savai‘i to Tutuila). Until more data from across the archipelago and from throughout the entire culture-historical sequence document ΔR variability, we recommend that researchers use both of these ΔR values to evaluate how the dates of marine-derived samples compare with AMS dates on identified, short-lived wood charcoal. [ABSTRACT FROM AUTHOR]

Over the last decades, the U- and Th-series nuclides were successfully used to determine weathering rates in various environments. The objective of this study is to assess the potential impact of the vegetation change on the U- and Th-series signal recorded in forested soils. This study was carried out from the experimental forest site of Breuil-Chenue (Morvan, France) developed by the INRA-BEF team. The native forest of the site was partially clear-felled in 1976 and replaced by monospecific plantations stands (Oak and Douglas fir). U- and Th-series disequilibria were measured in 2011 in the podzolic soils developed under the native forest, and in the two replanted stands. Separation of primary minerals (biotite, muscovite and perthitic feldspar) and selective extractions of the Fe and Al oxides were performed to investigate the distribution of U and Th among these soil fractions. The selective extractions suggest that a significant part of U and Th is primarily held by Fe-bearing silicates. Our results suggest that the tree substitution seems to produce a large dissolution of these minerals under the Oaks, resulting to a release of U and Th. However, below 25 cm no impact of this release was observed on U-series disequilibria. A scenario allowing to reconcile the significant mobilization of U and the constancy of U-series disequilibria is proposed. Above 25 cm, additional pedogenic redistribution of U and Th isotopes occurs in all the profiles, inducing some discrepancies between U-series disequilibria. A clear correlation between the ( 230 Th/ 234 U) ratios and the proportions of amorphous and interlayer Al hydroxides has been highlighted. This correlation suggests a mobility of U and Th isotopes strongly associated to Al dynamics in these soils rather than Fe, despite the primary location of U in the Fe-bearing silicates and the overwhelming reported control of U VI by Fe-oxides in oxidized environments. These pedogenic processes make the shallowest horizons of podzolic soils unsuitable for U-series dating. In contrast, a soil production rate can be deduced from the deepest soil layers which do not show such effects on the U-series nuclides. The reproducible U-series disequilibria measured in four whole-profile replicates emphasize the robustness and the significance of the “long-lived” U-series disequilibria in deep soil layers relative to long-term weathering rates, independent of transient perturbations such as land cover changes. Finally, because Ra can strongly accumulates in plants, the ( 226 Ra/ 230 Th) ratios in the different soils were affected by the flux of 226 Ra released by litter degradation. The use of this ratio as a long-term chronometer should therefore be performed with caution in such contexts. No direct impact of the vegetation type on the ( 228 Ra/ 232 Th) ratios was identified, due to the short 228 Ra half-life. [ABSTRACT FROM AUTHOR]

Studies of uranium-series (U-series) disequilibria within and around ore deposits provide valuable information on the extent and timing of actinide mobility, via mineral-fluid interaction, over a range of spatial and temporal scales. Such information is useful in studies of analogs of high-level nuclear-waste repositories, as well as for mining and mineral extraction sites, locations of previous nuclear weapons testing, and legacy nuclear waste contamination. In this study we present isotope dilution mass spectrometry U-series measurements for fracture-fill materials (hematite, goethite, kaolinite, calcite, dolomite and quartz) from one such analog; the Nopal I uranium ore deposit situated at Peña Blanca in the Chihuahua region of northern Mexico. The ore deposit is located in fractured, unsaturated volcanic tuff and fracture-fill materials from surface fractures as well as fractures in a vertical drill core have been analyzed. High uranium concentrations in the fracture-fill materials (between 12 and 7700 ppm) indicate uranium mobility and transport from the deposit. Uranium concentrations generally decrease with horizontal distance away from the deposit but in this deposit there is no trend with depth below the surface. Isotopic activity ratios, 238 U– 234 U- 230 Th– 232 Th linear age trends, and U-Th-Pa model ages indicate an actinide mobility evolution that can be characterized as complex and varied. There is evidence of both open and closed system behavior for uranium, depending on both sample and time-scale. The 234 U/ 238 U activity ratios indicate U mobility from 1.2–0.2 Ma. In the last 0.2 Ma there is isotopic evidence for some U mobility but mostly U immobility. In almost all cases the Th‐Pa radionuclides studied here have been immobile for the past 200 ka. Radium appears to have been recently (0.1–8 ka) mobile due to ongoing fluid flow in the fractures. Overall, the mainly closed system behavior for U-Th-Pa over the past ~ 200 ka provides an indicator of the geochemical immobility of these actinides over time-scales relevant for potential nuclear waste repositories situated in fractured, unsaturated tuff. [ABSTRACT FROM AUTHOR]

To better understand how fluvial systems respond to late Quaternary climatic forcing OSL and U-series dating was applied to stratigraphically significant sedimentary units within a small (<6.5 km 2 ) alluvial fan system (the Sphakia fan) in southwest Crete. The resultant chronology (comprising 32 OSL and U-series ages) makes Sphakia fan one of the best dated systems in the Mediterranean and suggests that Cretan fans responded to climate in two ways. First, during the transitions between Marine Isotope Stage (MIS) 5a/4 and MIS 2/1 Sphakia fan was characterised by significant entrenchment and distal shift in the zone of deposition. It is proposed that the phases of entrenchment were driven by sea level induced base level fall during MIS 5a/4 and landscape stabilisation during the onset of the current interglacial (MIS 2/1). Second, with the exception of these two entrenchment episodes fan alluviation occurred across the entire last interglacial/glacial cycle in all climatic settings i.e. interglacials, interstadials and stadials. It is likely that the topographic setting of the catchment supplying sediment to Sphakia fan maintained high sediment transfer rates during most climatic settings enabling fan aggradation to occur except during major climatic driven transitions i.e. major sea level fall and postglacial vegetation development. [ABSTRACT FROM AUTHOR]

We address the question of whether melting of the mafic oceanic crust occurs beneath ordinary volcanic arcs using constraints from U-Series ( 238 U/ 232 Th, 230 Th/ 232 Th and 226 Ra/ 230 Th) measurements. Alteration of the top few hundred meters of the mafic crust leads to strong U enrichment. Via decay of 238 U to 230 Th, this results in elevated ( 230 Th/ 232 Th) (where brackets indicate activity ratios) over time-scales of ∼350 ka. This process leads to the high ( 230 Th/ 232 Th), between 2.6 and 11.0 in the mafic altered oceanic crust (AOC) sampled at ODP Sites 801 and 1149 near the Izu-Bonin-Mariana arc. Th activity ratios in the Izu arc lavas range from ( 230 Th/ 232 Th) = 1.2–2.0. These values are substantially higher than those in bulk sediment subducting at the Izu trench and also extend to higher values than in mid-ocean ridge basalts and the Mariana arc. We show that the range in Th isotope ratios in the Izu arc lavas is consistent with the presence of a slab melt from a mixed source consisting of AOC and subducted sediments with an AOC mass fraction of up to approximately 80 wt.% in the component added to the arc lava source. The oceanic plate subducting at the Izu arc is comparatively cold which therefore indicates that temperatures high enough for fluid-saturated melting of the AOC are commonly achieved beneath volcanic arcs. The high ratio of AOC/sediments of the slab melt component suggested for the Izu arc lavas requires preferential melting of the AOC. This can be achieved when fluid-saturated melting of the slab is triggered by fluids derived from underlying subducted serpentinites. Dehydration of serpentinites and migration of the fluid into the overlying crust causes melting to start within the AOC. The absence of a significant sediment melt component suggests there was insufficient water to flux both AOC and overlying sediments. [ABSTRACT FROM AUTHOR]

In situ U-series zircon dating has yielded unique insights into magmatic processes and the complexity of zircon crystallization. However, the approach requires some knowledge of the state of isotopic disequilibrium of the melt from which zircon crystallizes. Current practices for correcting initial 230 Th include use of an isochron array (defined by several coexisting zircons) or two-point isochrons based on a tie between each zircon and a common glass (or whole rock) measurement. However, magmas are complex and measured U/Th in zircons from a single extrusive can vary by up to a factor of seven, casting doubt on the assumption that a single glass composition is representative of the magma from which each zircon crystallized. We propose a correction scheme using the measured zircon 238 U/ 232 Th, a U/Th partition coefficient ratio between zircon and melt, and the observation that most magmas are within 15% (1σ) of the equiline. Using this correction scheme, we show that uncertainties can be underestimated by up to a factor of three and that published dates are potentially biased towards older ages. [ABSTRACT FROM AUTHOR]

The application of uranium-thorium dating methods to authigenic carbonates provides unique constraints on the temporal evolution of methane seeps at ocean margins. In this study, we report U-Th isotope measurements for carbonate breccias collected from within a hydrate-bearing pockmark located at the Niger Delta margin. These concretions were extracted from a carbonate-rich layer in the upper two meters of a sediment core (N2-KS-44; ~ 1200 m water depth), well above the present-day sulphate-methane transition zone (about 3 m depth) and the presence of gas hydrates in the sediment. The stratigraphy of core N2-KS-44 was established by tuning its downcore Al/Ti profile to a well-dated nearby reference core, and carbonate 230 Th/U ages were calculated using isochron methods. Our results indicate that a major event of aragonite precipitation occurred between about 13 and 2.5 ka at the studied location. Comparison of sediment accumulation rates at both core N2-KS-44 and the nearby reference site suggests that the initial stage of carbonate precipitation, between 13 and 10 ka, was associated with sediment winnowing, probably related to intense fluid seepage. In contrast, our data indicate that sedimentation rates rapidly increased within the pockmark after 7 ka. In agreement with the presence of carbonate breccias exhibiting U-Th ages older than their corresponding stratigraphic age, this observation would suggest that sediment reworking took place after that time, possibly caused by erosion of the surrounding sediment within the pockmark. We hypothesize that the period of carbonate formation between 13 and 2.5 ka was related to an upward migration of gas-hydrate reservoirs to the near seafloor environment. After this pulse of enhanced fluid flow, the diminution of methane fluxes at the base of the local gas-hydrate occurrence zone would have led to hydrate dissolution in sub-surface sediments and pockmark formation, thereby explaining the progressive increase in sedimentation rates, the absence of recent carbonate concretions and the deepening of the sulphate-methane transition zone at site N2-KS-44 inferred from pore water data. Overall, these results provide further constraints about the relationship between gas hydrate dynamics and the evolution of pockmarks at ocean margins through time. [ABSTRACT FROM AUTHOR]

Increasing evidence suggests that bifacial technology (Acheulian, Mode 2) arrived in Europe during the early Middle Pleistocene, i.e. significantly earlier than previously proposed. In northern France and Britain, much of the age attribution for these assemblages has been based on biostratigraphy and lithostratigraphy rather than absolute dates. This study presents a systematic application of electron spin resonance (ESR) dating of sedimentary quartz and ESR/U-series dating of fossil tooth enamel to key Acheulian sites of this area. Although the age estimates have large associated uncertainties, most of the derived dates are consistent with existing age estimates. The new chronologies and the problems associated with dating material of early Middle Pleistocene age are discussed. In Britain, the earliest archaeology (cores and flakes, Mode 1) is older than Marine Isotope Stage (MIS) 15, whereas localities containing Acheulian technologies span late MIS 15/MIS 13 through to MIS 9. A similar pattern is seen in northern France although age estimates from sites such as la Noira suggest the possible appearance of the Acheulian in central France as early as MIS 17. The dates presented here support the suggestion that the earliest Acheulian appeared in NW Europe during the early Middle Pleistocene, significantly after its appearance in the southern parts of the continent. [ABSTRACT FROM AUTHOR]

The last two decades have witnessed considerable advances in chronometric approaches to cave art, specifically with the application of new dating techniques (AMS 14 C, U-series, Thermoluminescence). In this paper we assess all the currently available chronological information (numerical dates, stylistic comparisons between portable and cave art, the immediate context of art and its relationship with archaeological strata and wider artistic styles) pertaining to cave art of the western Pyrenean and eastern Cantabrian regions, in order to summarize the evolution of art in this important area. The data allow only an imprecise definition of a broad chronological framework for the area of study: at present we cannot define precisely the origins of figurative cave art in the area; the earliest (Pre-Magdalenian) cycle is characterized by basic figures in which, frequently, only the outline is represented. By contrast, in the later (Magdalenian) cycle the figures are naturalistic and realistically composed. The critical analysis of available chronological information is necessary in order for us to advance towards the construction of more solid and less subjective frameworks for the development of art. [ABSTRACT FROM AUTHOR]

Two sulfuric acid speleogenesis (SAS) cave sites in northern Wyoming host speleogenetic byproducts that have been dated using the uranium-series method and thus provide the timing of the SAS events. Gypsum crusts that formed as byproducts of SAS in Lower Kane Cave, exposed by Bighorn River incision into the Little Sheep Mountain anticline, yield uranium-series dates of 20.5 ± 0.2 ka to 16.2 ± 0.2 ka that represent the timing of late stage speleogenesis of that cave. A calcite mammillary engulfed by elemental sulfur that formed during SAS of Shoshone Canyon Conduit Cave, exposed by Shoshone River incision of the homonymous canyon, yielded a uranium-series age of 174 ± 5 ka and represents late stage speleogenesis of that cave, although the process continued after the cave was elevated above the water table until at least 100 ± 5 ka. In addition to the timing of speleogenesis, the U-series results provide incision rates for these two canyons. The rate of canyon incision for the last 200 kyr by the Bighorn River in Little Sheep Mountain Canyon is measured as 190 ± 50 m/Ma, and for the Shoshone River in Shoshone Canyon as 400 ± 40 m/Ma. Using the Bighorn River incision rate, Upper Kane Cave located 33 m above Lower Kane Cave has a projected age of 170 ± 60 ka. We suggest that climatically driven hydrologic mechanisms rather than magmatic ones likely produced the pulses of SAS at these two cave sites. • Uranium-series dating of gypsum and calcite yield sulfuric acid speleogenesis timing. • Sulfuric acid speleogenesis in Lower Kane Cave took place ~20,000 years ago. • Incision rate of Bighorn River is measured using the age of Lower Kane Cave. • Upper Kane Cave age is estimated using the incision rate of the Bighorn River. • Shoshone Canyon Conduit Cave age is used to estimate Shoshone River incision rate. [ABSTRACT FROM AUTHOR]