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To date, the most complete paleolake‐level reconstructions for the late Pleistocene water bodies that once occupied the Dead Sea depression have been based on the combination of dating of lake sediments and terrestrial materials. However, despite these major accomplishments, there is still limited spatial control regarding the water levels, suggesting some degree of uncertainty concerning the magnitude and rate of lake‐level changes. Here, we re‐examine the late Pleistocene lake‐level changes in the Dead Sea during the transition from paleolake Lisan to the present‐day Dead Sea. We rely on systematic dating of fossil stromatolites including 84 radiocarbon and 15 U‐series ages, stable‐isotope measurements, paleobiology, high‐resolution topography, and numerical modeling to assess lake‐level changes. Our results indicate that the highstand of paleolake Lisan was of shorter duration and the transition between Lake Lisan and the Dead Sea occurred at least 5 Kyrs earlier than previously indicated. By refining the timeline and accuracy of lake‐level positions during the transition paleolake Lisan—Dead Sea, our study offers new insights into the regional and local paleo‐climatic conditions during the last glacial period in this region. Plain Language Summary: Index points, reflecting the unique position of the water levels in space and time, have been broadly used in marine realms to reconstruct past sea‐level changes. Here we study lake‐level variations using index points based on geomorphic and biological markers collected along the western and eastern coasts of the Dead Sea. Previous studies indicate that during the last glacial period (20–30 ka), the Dead Sea depression was filled by paleolake Lisan, which lasted 10 Kyrs. As it dried, dozens of paleo‐shorelines remained etched in the landscape. Lake level index points estimated from 99 radiometric ages in these paleo‐shorelines suggest that Lisan's highstand was shorter and the transition to the Dead Sea occurred 5 Kyrs earlier than previously thought. These novel results suggest an initial and wet period followed by drier conditions, altering the regional paleo‐climatic narrative during the last glacial period. Key Points: Lake paleo‐shorelines and fossil stromatolites are used to reconstruct lake‐level changes during the transition paleolake Lisan‐Dead SeaFossil stromatolites were dated using radiocarbon and U‐series applying temporal and vertical correctionsThe transition between paleolake Lisan and the Dead Sea occurred ∼5 Kyrs earlier than estimated by previous reconstructions [ABSTRACT FROM AUTHOR]

The Huatung Basin (HB), situated on the leading part of the Philippine Sea Plate, is directly involved in oblique subduction and mountain building in the Taiwan region. However, previous studies have reported a wide range of ages for the HB, from 30 to 130 Ma, making it difficult to properly constrain regional tectonics. We analyzed teleseismic waveforms recorded on Taiwan that traveled through the slab associated with the HB. By waveform matching, we have constrained the slab dimensions to approximately 400 km in length and 150 km in width, accompanied by an enhanced P-wave velocity of 6% within the slab core and an apparent dip angle of 55°. We used age-dependent subduction zone thermal models to estimate the thermal ages or the ages since the last thermal event of the HB. The best-fit thermal model indicates thermal ages ranging from 20 to 50 Ma, which is consistent with a suite of geophysical observations and the age inferred from geomagnetic anomaly data. However, our results differ considerably from the ages obtained through radiometric dating of rocks dredged from the seafloor. The discrepancy in age may be attributed to either thermal rejuvenation of the plate or dating of allochthonous samples dredged from the border of the basin. [ABSTRACT FROM AUTHOR]

The Easternmost Mediterranean is a transition region from the ocean to the continent where the spreading and collision zones of the lithospheric plates join. The methodology of paleomagnetic mapping of the transition zones is based on combining geological and geophysical techniques for continental and oceanic platforms: magnetic data interpretation, paleomagnetic reconstructions, results of magnetized rock radiometric dating, satellite data analysis, tectonic–structural reconstructions, biogeographical studies, and utilization of different geophysical survey results. The satellite-derived gravity map reflects practically all significant tectonic units in the region, which assists us in the supposed paleomagnetic mapping. The satellite-derived and aeromagnetic maps with the tectonic features and the map of Curie discontinuity of Israel indicate the complexity of this region. Advanced magnetic data analysis supported by paleomagnetic data attraction and other geological–geophysical methods allowed the revealing of the block of oceanic crust with the Kiama paleomagnetic zone relating to the Early Permian age. A narrow reversely magnetized Earth crust block was revealed in the Lower Galilee. Some examples of advanced magnetic anomaly analysis are presented for several areas where the magnetization vector inclination is other than the modern direction: the Sea of Galilee, Carmel, Rosh-Ha-Ayin, Malqishon, and Hebron. In Israeli land, for the combined paleomagnetic mapping, the well-studied using paleomagnetic and radiometric methods (as well as tectonic–structural) areas were selected: (1) Makhtesh Ramon, (2) the Sea of Galilee with the adjoining zones, (3) Carmel, (4) Hula, and (5) Hermon. It is shown that the regional analysis of paleomagnetic data distribution played an essential role in detecting the influence of the recently recognized counterclockwise rotating mantle structure on the near-surface layers. [ABSTRACT FROM AUTHOR]

Detachment faulting is one of the main styles of seafloor spreading at slow to intermediate mid-ocean ridges. However, we have limited insight into its role in back-arc basin formation. We surveyed a remnant back-arc spreading center in the Philippine Sea and determined the detailed features and formation processes of the Mado Megamullion (Mado MM) oceanic core complex (OCC). This was undertaken in the context of back-arc evolution, based on the shipborne bathymetry, magnetics, and gravity with radiometric age dating of the rock samples collected. The Mado MM OCC has a typical OCC morphology with prominent corrugations on the domed surface and positive gravity anomalies, suggesting that there has been an exposure of the lower crust and mantle materials by a detachment fault. The downdip side of the detachment continues to the relict axial rift valley, which has indicated that the Mado MM OCC was formed at the end of the back-arc basin opening. The spreading rate of the basin decreased once when the spreading direction changed after six million years of stable trench perpendicular spreading. The rate then further decreased immediately prior to the end of the spreading when the Mado MM OCC was formed. The existence of other OCC-like structures in the neighboring segment and the previously reported OCCs along the Parece Vela Rift have indicated that the melt-poor, tectonic-dominant spreading is a widespread phenomenon at the terminal phase of back-arc spreading. The decrease in spreading rate in the later stage is consistent with the previous numerical modeling because of the decrease in trench retreat. In the Izu–Bonin–Mariana arc trench system, the rotation of the spreading axis and the resultant axis segmentation have enhanced the lithosphere cooling and constrained mantle upwelling, which caused the tectonic-dominant spreading at the final phase of the basin evolution. [ABSTRACT FROM AUTHOR]

The easternmost Mediterranean is a distinct transition zone from the ocean to the continent located at the junction between the largest Earth's lithospheric segments: Eurasian and African. The methodology of paleomagnetic mapping of such transition zones is based on integrating the mapping techniques for both continental and oceanic platforms: paleomagnetic reconstructions, results of radiometric dating of magnetized rocks, tectonic-structural reconstructions, biogeography, and utilization of the results of various geophysical surveys. The geodynamic-paleomagnetic mapping makes it possible to reveal the multilevel structural heterogeneity and display complex elements of the geodynamics of different ages inherent in this transition zone. The region of northern Israel is the most complex area in the easternmost Mediterranean. For the combined paleomagnetic mapping, well-studied paleomagnetically and radiometrically areas were selected: (1) the Carmel area, (2) the Atlit area (internal part of the Carmel area), (3) the Sea of Galilee with the adjoining zones (primarily, the Kinnarot Valley), and (4) the area of the Hula Basin with adjacent areas of the Golan Plateau, Hermon Mt., and Galilea uplift. The constructed paleomagnetic profiles for the Carmel area (on the top of the accumulative surface of the Lower Cretaceous traps) and the Kinnarot Valley—Sea of Galilee—Hula Basin, evidently indicate the complex history of the paleogeodynamic evolution of the region. These studies demonstrate the effectiveness of paleomagnetic mapping integrated with paleomagnetic profiles crossing these geologically complex areas. [ABSTRACT FROM AUTHOR]

The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U-Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). The uranium distribution within fluorite is mapped using induced fission-track and synchrotron radiation X-ray fluorescence nano-imaging, showing that higher U content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr, implies that neither solid-state diffusion nor dissolution--recrystallization occurred. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of -23.6±0.4‰V-CDT. We propose that the U incorporation in the fluorite lattice results from the development of a redox front during bacterial sulfate reduction. Flog generation sampled and analyzed by laser ablation--inductively coupled plasma mass spectrometry (LA-ICP-MS) on four different crystals provides identical U-Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0±1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U-Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy. [ABSTRACT FROM AUTHOR]

Epidote -- here defined as minerals belonging to the epidote--clinozoisite solid solution -- is a low-µ (µ = 238U/204Pb) mineral occurring in a variety of geological environments and participating in many metamorphic reactions that is stable throughout a wide range of pressure-temperature conditions. Despite containing fair amounts of U, its use as a U-Pb geochronometer has been hindered by the commonly high contents of initial Pb, with isotopic compositions that cannot be assumed a priori.We present a U-Pb geochronology of hydrothermal-vein epidote spanning a wide range of Pb (3.9-190 µgg-1), Th (0.01-38 µgg-1), and U (2.6-530 µgg-1) contents and with µ values between 7 and 510 from the Albula area (eastern Swiss Alps), from the Grimsel area (central Swiss Alps), and from the Heyuan fault (Guangdong Province, China). The investigated epidote samples show appreciable fractions of initial Pb contents (f206 D 0:7-1.0) -- i.e., relative to radiogenic Pb -- that vary to different extents. A protocol has been developed for in situ U-Pb dating of epidote by spot-analysis laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with a magmatic allanite as the primary reference material. The suitability of the protocol and the reliability of the measured isotopic ratios have been ascertained by independent measurements of 238U/206Pb and 207Pb/206Pb ratios, respectively, with quadrupole and multicollector ICP-MS applied to epidote micro-separates digested and diluted in acids. For age calculation, we used the Tera--Wasserburg (207Pb/206Pb versus 238U/206Pb) diagram, which does not require corrections for initial Pb and provides the initial 207Pb/206Pb ratio. Petrographic and microstructural data indicate that the calculated ages date the crystallization of vein epidote from a hydrothermal fluid and that the U-Pb analyses of epidote returned reliable ages of otherwise undatable epidote-quartz veins. The Tera-Wasserburg approach has proven pivotal for in situ U-Pb system was not reset to younger ages by later events. Vein epidote from the Albula area formed in the Paleocene (62:7±3:0 Ma) and is related to Alpine greenschist-facies metamorphism. The Miocene (19:2±4:3 and 16:9±3:7 Ma) epidote veins from the Grimsel area formed during the Handegg deformation phase (22-17 Ma) of the Alpine evolution of the Aar Massif. Identical initial 207Pb/206Pb ratios reveal homogeneity in Pb isotopic compositions of the fluid across ca. 100 m. Vein epidote from the Heyuan fault is Cretaceous in age ( 107:2±8:9 Ma) and formed during the early movements of the fault. In situ U-Pb analyses of epidote returned reliable ages of otherwise undatable epidote--quartz veins. The Tera--Wasserburg approach has proven pivotal for in situ U-Pb dating of epidote, and the decisive aspect for low age uncertainties is the variability in intra-sample initial Pb fractions. [ABSTRACT FROM AUTHOR]

Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea (SCS). We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian continent. Results of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the east. The hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore–offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early Cenozoic. It was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene (33/34 Ma). The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 Ma. The plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene. [ABSTRACT FROM AUTHOR]

Complexly zoned microcrystals of uraninite were encountered in orthogneiss from the central Tauern Window in Austria (K1 gneiss, Felbertal scheelite mine) and analysed in-situ for U, Th and Pb with state-of-the-art FE-SEM/EDX techniques. A three times finer spatial resolution was achieved using an acceleration voltage of 8 kV, compared to the classic 15–20 kV set-up of U–Th–total Pb electron microprobe dating. The lower voltage allows a spheroid of material with a diameter of only 0.3 µm to be selectively analysed. Careful tests on three uraninite reference materials show that the low-voltage method yields sufficient precision and accuracy for U–Th–total Pb uraninite dating, with errors on individual spot ages in the order of 10–30 Ma. By means of this innovative analysis technique, small-scale age zoning patterns could be resolved and dated in the uraninite microcrystals from the orthogneiss. Based on microstructures observed in backscattered electron images we interpret that an older uraninite generation in the rock, with a late Permian formation age (~260 Ma), was recycled two times through a coupled dissolution–reprecipitation process at ~210 Ma and at ~30 Ma. The younger dissolution–reprecipitation phase at ~30 Ma coincides with the Alpine regional metamorphism (lower amphibolite facies). The two older ages (~210 Ma and ~260 Ma) have been previously recognized in rocks from the Tauern Window by uraninite dating, but it is the first time here that both are recorded in the same rock and even the same uraninite grain. The present study shows that recrystallized accessory uraninite can provide a sensitive geological "hard disk" where several discrete thermal events of an area are stored. In addition, our work attests that the mineral uraninite has an unexpected geochronological robustness, even on the microcrystal scale. [ABSTRACT FROM AUTHOR]

Uranium certified reference materials (CRM) issued by New Brunswick Laboratory were subjected to dating using four independent uranium-series radiochronometers. In all cases, there was acceptable agreement between the model ages calculated using the Pa-U, Th-U, Ac-U or Ra-U radiochronometers and either the certified Th-U model date (CRM 125-A and CRM U630), or the known purification date (CRM U050 and CRM U100). The agreement between the four independent radiochronometers establishes these uranium certified reference materials as ideal informal standards for validating dating techniques utilized in nuclear forensic investigations in the absence of standards with certified model ages for multiple radiochronometers. [ABSTRACT FROM AUTHOR]

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the Th/U ratio was calculated from the measured ratios of Th/Th and U/U and from calculated Th/U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The U interference on Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause. [ABSTRACT FROM AUTHOR]

Gigantopithecus was a giant ape once lived in Southeast Asia and China during the Pleistocene period. Longgupo and Jianshi Longgudong sites in West-Hubei and Three Gorges region in South China are the northernmost evidences of Gigantopithecus presence in the world up to date. To obtain the detailed chronology of these two sites, paleomagnetic and radiometric dating methods were attempted, including cosmogenic burial dating of the sediment. However, the efforts failed because of the scarce of quartz minerals in the sediment. Combined electron spin resonance and uranium series (ESR/U-series) method which could date the fossil teeth directly with the age range from Early to Late Pleistocene was also applied and the results obtained at Longgupo site already published. Here, we report the first radiometric dating results for teeth carried out from Jianshi Longgudong Western Branch cave which is renowned for the discovery of both Gigantopithecus fossils and undoubted stone artifacts. The main challenge of dating Jianshi Longgudong site is the reconstruction of external dose rate of the fossil samples where their provenance sections were not preserved. The mean radioelement concentrations in the sediments measured in the laboratory with different water content estimation were initially used to calculate the ESR/U-series ages. Our ESR/U-series dating of two mammalian fossil teeth from the lower layer 8 gives a weight mean age of 1512 ± 94 ka, while a mean age of 1044 ± 53 ka was obtained for two teeth from the upper layer 4. These ages support one of the previous paleomagnetic dating interpretation which propose that the hominin fossil layer in Jianshi site was not older than 1.78 Ma, i.e. that the upper boundary of the Olduvai subchron, and are in agreement with the faunal evidence which suggest that Jianshi site is younger than the adjacent Longgupo site dated also by combined ESR/U-series and paleomagnetic methods to 2.0-2.5 Ma. Further study of the site including the radiometric dating study of the fossil layers preserved in the Eastern Branch cave may help to achieve a definitive conclusion of the chronology of Gigantopithecus settlement in Jianshi Longgudong site. [ABSTRACT FROM AUTHOR]

Luminescence rock surface dating has an enormous potential in the radiometric dating of geo/archaeological features. There have been a rapid advances to improve the accuracy and precision of the technique [1,2]. These studies included the development of models to describe the penetration of light into rock surfaces, and the effect of subsequent burial [1,2,3]. Experiments have been undertaken to investigate the dependence on the model parameters controlling the bleaching/ accumulating of the luminescence signal in rock surfaces; these include light attenuation, effective dose rate and surface erosion rate [1,2,3,4]. Some attempts have also been made to connect the light attenuation coefficients to the rock lithology [2]. In this project, we investigate the luminescence signals from three different types of rock (sandstone, granite and basalt). We use a controlled bleaching experiment where rock samples are artificially irradiated (~3.25 kGy) to saturate the latent luminescence signals, before experiencing controlled light exposures. We determine the penetration of daylight into the surfaces of the 3 different lithologies, and analyze the luminescence depth profiles developed in these materials. Finally, our data are compared with those derived from archaeological buried rocks, and the implications of our work for dating are considered. [ABSTRACT FROM AUTHOR]

The compilation of stratigraphic, sedimentologic, paleontologic and geochronological data allows the proposal of a regional stratigraphic framework for the Late Permian to Lower Cretaceous succession of the Paraná Basin. Each unit is characterized in terms of sedimentological and stratigraphic characteristics, ages (fossils and radiometric dating) and regional correlation, allowing the construction of an integrated stratigraphic chart. The Permo-Mesozoic sedimentary succession is mostly characterized by fluvial and/or aeolian systems that can be subdivided into eight distinct depositional sequences limited by unconformities of tectonic origin. These sequences correspond to the following stratigraphic units: Rio do Rasto, Buena Vista, Sanga do Cabral, Santa-Maria-Caturrita, Piramboia, Guará, Pedreira and Serra Geral. The Paraná Basin sedimentary record is marked by a very complex tectono-stratigraphic evolution, characterized by sedimentary units accumulating in different depocenters and with a highly fragmented preservation, reflecting regional tectonic events of Gondwana. Despite the incomplete record, a general evolutionary scenario can be reconstructed where the paleoclimates and wind regimes of western Gondwana are inferred. The Middle to Late Permian is characterized by a progressive aridization, evidenced by the presence of distributive fluvial systems (Rio do Rasto Formation) overlain by extensive aeolian dune deposits (Buena Vista Formation). The Triassic Period (Sanga do Cabral, Santa Maria and Caturrita formations) is marked by an essentially fluvial sedimentation indicative of relatively wetter climate conditions, with a well-marked peak of humidity in the Carnian Age. The Jurassic Period is characterized by fluvio-aeolian systems of the Piramboia Formation, Guará Formation and Pedreira Sandstone, indicating a semi-arid setting. The Lower Cretaceous (Valanginian-Hauterivian) is characterized by the development of an extensive paleoerg (Botucatu Formation) denoting hyperarid climatic conditions, which later switches to wetter conditions during the volcanic events of the Serra Geral Group. Despite these climatic variations during the Permo-Mesozoic, the wind regime from Permian to Lower Cretaceous remained dominated by westerly winds in the mid-latitudes and monsoonal winds in the mid-to-low latitudes of Gondwana. • The Permo-Mesozoic sedimentary succession of the Paraná Basin can be subdivided into eight distinct depositional sequences. • The Paraná Basin can be considered as a successor basin. • Monsoonal wind pattern operating in low latitudes of Gondwana from Late Permian to Early Cretaceous. [ABSTRACT FROM AUTHOR]

The U-Pb geochronological data on detrital zircons from placers confined to Neoproterozoic quartzite-schist sequences, which are widespread in the Kokchetav massif of northern Kazakhstan, are discussed. Detrital zircons (332 grains in total) originate from the ore occurrences in the central, northern, and western parts of the massif. The concordant ages of detrital zircons from all the examined occurrences largely correspond to intervals of 1017-1528, 1628-1946, and 2653-2739 Ma. The obtained data imply that material of quartzite-schist sequences of the Kokchetav massif was provided by Mesoproterozoic, Paleoproterozoic, and Neoarchean rock complexes. The lower age limit determined for these sequences is approximately 1.06 Ga. The dates obtained for detrital zircons are most consistent with events that took place in Laurentia. They correspond to the formation and breakup of the Columbia/Nuna supercontinent (approximately 1650-1580 and 1450-1380 Ma ago, respectively) and formation of the Rodinia supercontinent in the period of 1300-900 Ma ago. [ABSTRACT FROM AUTHOR]

The U–Pb dating system has been widely used in geochronology because the system contains two independent parent/daughter pairs yielding three ages (i.e., 238U/206Pb, 235U/207Pb and 207Pb/206Pb ages) to internally check self-consistency. Among numerous U-bearing minerals, zircon has been recognized as the best mineral for U–Pb geochronology owing to its moderate U content, negligible initial unradiogenic Pb (or common Pb) and occurrence in a wide range of rock types. With the development of Secondary Ion Mass Spectrometry (SIMS) and in situ dating methods, the 238U/206Pb zircon age uncertainty could be achieved at an ∼1% level. However, the 207Pb/206Pb age uncertainty of Phanerozoic zircon is always very poor, when single-collector SIMS is used. The low level precision often hampers effective examination of concordance of young zircon between U–Pb and Pb/Pb ages, which is crucial to the data quality evaluation and chronological interpretations. In this study, we developed a hybrid “dynamic multi-collector U–Pb dating technique”. It takes advantage of both the static multi-collector mode and peak-hopping mono-collector mode. The technique is able to simultaneously measure with high-precision the 207Pb/206Pb ratio as in the static multi-collector mode without trade off in the analytical precision of the 238U/206Pb ratio of the conventional peak-hopping mono-collector mode. Four zircon reference materials (91500, M257, Temora and Plešovice) were measured to demonstrate that this new analytical protocol is able to achieve a higher precision for the 207Pb/206Pb age by a factor of two than the conventional mono-collector mode within the same working time. It is possible to simultaneously obtain the 207Pb/206Pb age and 238U/206Pb age with comparable quality to effectively evaluate the concordance of the U–Pb system for Phanerozoic samples. [ABSTRACT FROM AUTHOR]

The article reports on radioactive analysis of peridotite and pyroxenite xenoliths located in basalt rocks from northwest Spitzbergen and determination of melting process age. Topics discussed include various isotopic analysis including Nd-Sr, Re?Os and Rb?Sr were performed for the same, graphical depiction of the analysis and interpretations of analysis, reveal various stages of melting responsible for depletion of mantle rocks and deposition of magnesium oxides during Early Proterozoic.

The Three Gorges and Western Hubei area in the geographic central part of China was a potential migration corridor for early hominin and mammals linking South and North China during the Pleistocene period. Some key early hominin sites are known in this region where limestone cave and fissure sites are numerous but difficult to date as beyond the dating range of OSL and mass spectrometry U-series method. Here, we report radiometric dating study for such a hominin site, Meipu (Hubei Province), by coupled ESR and U-series dating of nine fossil teeth and cosmogenic 26Al/10Be burial dating of one quartz sediment. The burial age calculated by simple burial model (573 ± 266 ka) gives a minimum age constraint of the sediment. The fossil dating provided two main age groups at 541 ± 48 ka and 849 ± 39 ka, the older age group is in agreement with the U-series age (>630 ka) of the flowstone overlying the fossil layer and the paleomagnetic data which placed the Brunhes-Matuyama boundary in the fossil layer. The reason of this age difference is probably caused by the U-content discrepancy in the enamel of the dated fossil samples. This study exhibits the limitation of ESR/U-series fossil dating and the importance of using multiple dating approach when it is possible in order to identify the problematic ages. • A key hominin site in Three Gorges area at the corridor between South and North China was dated by radiometric methods. • Two radiometric dating methods were applied directly to the fossil layer of the Meipu hominin site. • The results of multiple dating approach were compared to constrain the age of an Early-Middle Pleistocene hominin site. [ABSTRACT FROM AUTHOR]

The author recalls his involvement in lead (Pb) dating since 1978. He states that his interest on Pb dating started when he met Frank Oldfield. He provides an overview of how they develop a radiometric assay by gamma spectrometry using hyper-pure germanium well-type detectors. He discusses his work in the 1990s concerning Pb and other fallout nucleotides.

Radiometric dating methods using 238U and 232Th decay chain isotopes have been developed and applied to volcanogenic massive sulfide (VMS) samples, most of which were collected from hydrothermal sites at volcanoes along the Kermadec and Mariana intraoceanic arcs. The activity ratios, 228Th/228Ra, 228Ra/226Ra (Bq.Bq-1), and 226Ra/Ba values (Bq.g-1), are used for dating VMS in the age ranges 0.3 to 12, 3 to 35, and 500 to 15,000 years, respectively. Black smoker chimneys 35 to 100 years old are dated using the activity ratio, 210Pb/226Ra, derived from 210Pb/[Pb] versus 226Ra/[Pb] isochron plots. Iron oxide crusts are dated using 210Pb in combination with either As or 10Be. The 228Ra/226Ra values for recent VMS mineralization from Brothers and East Diamante volcanoes are reasonably constant but greater than the theoretical ratios calculated from the Th and U contents of volcanic rock from the same area. The high initial 228Ra/226Ra values for VMS are most likely due to excess 228Ra (the daughter of 232Th) that is contained within sediment on the subducted plate. This implies that the residence time for Ba and Ra in the volcano would be less than ~35 years, considering the half-life of 228Ra (5.75 years). These Ra isotopes are used as a proxy for better understanding the transfer of Ba from magmas to the sea floor, via circulating fluids of the hydrothermal system. Radiometric dating shows VMS chimneys have been forming at Brothers volcano for at least 1,000 years. The supply of Ba and Ra to the chimneys and associated VMS deposits comes from magmas rich in these elements continuously emplaced via dike intrusion into a zone of hydrothermally altered rock. There, the dikes interact with evolved seawater to produce the metal-rich hydrothermal fluid discharging on the sea floor, forming the chimneys. [ABSTRACT FROM AUTHOR]

Abstract: The Sillai Patti carbonatite complex represents the second largest carbonatite body of the Peshawar Plain Alkaline Igneous Province of northern Pakistan. It is situated about 20 km west of Malakand, near Sillai Patti village. Here, the carbonatite occurs along a fault in the form of a sheet striking in the NNE–SSW direction and dipping towards south. The carbonatite body is about 12 km long and 2–20 m thick, predominantly intruded along the faulted contact of metasediments and granite gneiss but locally, within the metasediments. A fission-track age of 29.40 ± 1.47 Ma was obtained for the Sillai Patti carbonatite complex. Close resemblance of fission-track apatite age of this study with the fission-track as well as other high temperature radiometric ages from the same and the neighboring carbonatite complexes of the alkaline belt of northern Pakistan suggests emplacement of the Sillai Patti carbonatite complex at higher crustal level and subsequent extremely fast cooling to near ambient temperatures (<60 °C) required for the complete retention of fission tracks in apatite. The age data also point out that the fission-track age of 29.40 ± 1.47 Ma of this study is the age of intrusion of the carbonatitic magma of Sillai Patti carbonatite complex to shallow, near-surface level. Comparison of the uplift induced denudation rates of the region with the world data clearly reflects the presence of a post collisonal extensional environment in the region south of Main Mantle Thrust during Oligocene time. This strongly negates the idea of the earlier workers of emplacement of the carbonatite complexes of the Loe-Shilman and Sillai Patti areas along thrust faults during Oligocene. [Copyright &y& Elsevier]

Abstract: In forensic science, there is a strong interest in determining the post-mortem interval (PMI) of human skeletal remains up to 50 years after death. Currently, there are no reliable methods to resolve PMI, the determination of which relies almost exclusively on the experience of the investigating expert. Here we measured 90Sr and 210Pb (210Po) incorporated into bones through a biogenic process as indicators of the time elapsed since death. We hypothesised that the activity of radionuclides incorporated into trabecular bone will more accurately match the activity in the environment and the food chain at the time of death than the activity in cortical bone because of a higher remodelling rate. We found that determining 90Sr can yield reliable PMI estimates as long as a calibration curve exists for 90Sr covering the studied area and the last 50 years. We also found that adding the activity of 210Po, a proxy for naturally occurring 210Pb incorporated through ingestion, to the 90Sr dating increases the reliability of the PMI value. Our results also show that trabecular bone is subject to both 90Sr and 210Po diagenesis. Accordingly, we used a solubility profile method to determine the biogenic radionuclide only, and we are proposing a new method of bone decontamination to be used prior to 90Sr and 210Pb dating. [Copyright &y& Elsevier]

Abstract: We evaluate the 190Pt–186Os decay system, measured by laser ablation MC-ICPMS, as a useful geochronometric tool for direct dating of platinum-group minerals (PGM) in large mafic/ultra-mafic intrusions by analysing mineralised rocks from the geochronologically well constrained Bushveld Complex, S. Africa. Mixed PGM (laurite, cooperite, laurite–platarsite, sperrylite and Pt–Fe alloy) from the Merensky Reef yield a Pt–Os isochron age of 1995±50Ma (2σ, n=48, MSWD=1.16, initial 186Os/188Os=0.119819±0.000006). While this is 59Myr younger than the U–Pb zircon age for the Merensky Reef (Scoates and Friedman, 2008) it is consistent with recent Re–Os ages for the Platreef. Considering the younger age recorded by both Re–Os and Pt–Os systems, we propose that the Pt–Os isochron age records a late, low temperature hydrothermal event affecting PGM and sulphides in the Platreef and Merensky Reef. Pt-rich phases may also yield single grain 190Pt–186Os model ages since initial 186Os/188Os can be well constrained. A Pt–Os model age of 2024Ma±101Ma was calculated for a Merensky cooperite; a Pt–Fe alloy from the Onverwacht pipe and a Tweefontein Hill sperrylite give Pt–Os model ages of 2113±106Ma and 2042±102Ma, respectively. A Pt–Os isochron derived from all Bushveld units gives an age of 2012±47Ma (2σ, 186Os/188Osi =0.119818±0.000006) with an MSWD of 1.19, hence PGE mineralisation in different stratigraphic horizons of the complex cannot be distinguished temporally using the Pt–Os chronometer. Nonetheless, the potential for the Pt–Os system in dating events in PGE mineralised systems is evident and the agreement of single grain model ages in high Pt/Os phases with the Pt–Os and Re–Os isochron ages indicates their usefulness in the geochronology of these systems. [Copyright &y& Elsevier]

Abstract: The Taoxikeng tungsten deposit is located in the Jiangxi Province in the southern part of China, and is one of the largest wolframite quartz-vein type tungsten deposits in the country. The deposit is situated in Sinian (Neoproterozoic) to Permian strata at the contact with the buried Taoxikeng Granite. Sensitive High Mass Resolution Ion Microprobe (SHRIMP) zircon U–Pb analysis of the granite has yielded dates of 158.7±3.9 and 157.6±3.5Ma, which are interpreted as the emplacement age of the granite. Molybdenite separated from ore-bearing quartz-veins yields a Re–Os isochron age of 154.4±3.8Ma, and muscovite separated from greisen between the granite and country rocks yields 40Ar/39Ar plateau ages of 153.4±1.3 and 152.7±1.5Ma. These dates obtained from three independent geochronological techniques constrain the ore-forming age of the Taoxikeng deposit and link the ore genesis to that of the underlying granite. The Taoxikeng deposit is an example of a Jurassic regional-scale tungsten–tin ore-forming event between 160 and 150Ma in the Nanling region of the South China Block. The deposit''s strikingly low rhenium contents (4.9 to 13.0×10−3 μg/g) in molybdenite suggests that the ore was derived from a crustal source. This conclusion is consistent with previously published constraints from S, D and O stable isotopes, Sr–Nd systematics, and petrogenetic interpretations of spatially related granites. [Copyright &y& Elsevier]

Abstract: We describe an analytical methodology to quantify 238U–234U and 230Th using isotope-dilution systematics and inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) for geochronological purposes. This required characterization of the mass spectrometer detector performance over a large dynamic range, including a careful calibration between pulse and analogue ion-counting modes. Our methodology gives an analytical precision for 234U/238U and 230Th/238U of 4‰ and 7‰ (2 × standard error), respectively, and yields 230Th-ages with 4–5% uncertainty from 500 ng of 238U. We tested our methodology by analyzing carbonate samples (corals and speleothems) which were previously dated using MC-ICPMS; excellent agreement between both techniques was obtained. Our results indicate that ICP-QMS is suitable to obtain valuable meaningful geochronological data, but it is limited to dating samples older than 1 ka, and younger than 400 ka. Our methodology thus represents an attractive alternative to obtain geochonological data to select the most interesting samples prior to high-precision analysis. Moreover, such data would also valuable to build preliminary age-models, which can be further complemented with high-precision analyses. [Copyright &y& Elsevier]

Abstract: The Tianyu mafic–ultramafic intrusion is one of many important sulfide-bearing mafic–ultramafic intrusions in the eastern Tianshan terrane located in the southern margin of the Central Asian Orogenic Belt in north Xinjiang, NW China. The origin of sulfide mineralization in these intrusions, their relationship with Permian basalts and A-type granites, and the geodynamic setting of the bimodal magmatism in the region are controversial. In this paper we use zircon U–Pb age, Hf–Sr–Nd–Os isotope and lithophile–chalcophile trace element constraints from the Tianyu mafic–ultramafic intrusion to address these important issues. The U–Pb age of zircon from the Tianyu intrusion determined by SIMS is 280±2Ma. This confirms that the Tianyu intrusion is coeval with most sulfide-bearing mafic–ultramafic intrusions and some basalts and A-type granites in the Tianshan region. Similar to coeval basalts in the nearby Tuha basin, the Tianyu intrusive rocks are characterized by negative Nb anomaly and elevated εNd values varying between −1 and +4.6. The negative Nb anomaly in the Tianyu intrusion is not as pronounced as in the coeval A-type granites but the εNd values for these bimodal rocks are similar. The εHf values of zircon from the Tianyu intrusion are positive, varying between 3 and 8. These values suggest that the parental magma of the Tianyu intrusion was dominated by melt derived from a depleted source mantle. The γOs values of pyrrhotite from the Tianyu intrusion are high, ranging from 725 to 995, which can be modeled by selective assimilation of sulfide from the lower and upper crusts. Negative Pt anomaly is present in relatively sulfide-rich samples such as semi-massive and massive sulfide ores but not in sulfide-poor samples, which is more consistent with the effect of post-magmatic hydrothermal alteration than the original signature of the parental magma. The results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the Tianyu intrusion was depleted in all PGE, which is consistent with previous sulfide segregation at depth. Our data and modeling results support the model of decompression melting of upwelling asthenosphere due to slab break-off during a transition from oceanic subduction to arc–arc or arc–continent collision in the Permian. Decompression melting of the upwelling asthenosphere in the region produced mafic magma. Partial melting in the lower parts of a juvenile arc crust due to mafic magma underplating produced granitic melts. Mixing of the mafic magma with a small amount of granitic melts at depth followed by contamination with the upper crust at a higher level formed the parental magma of the Tianyu intrusion. PGE depletion in the parental magma of the Tianyu intrusion can be attributed to sulfide segregation associated to the first stage of crustal contamination at depth. We suggest that the formation of sulfide ores in the intrusion was related to the second stage of crustal contamination in the upper crust. [Copyright &y& Elsevier]

Abstract: The widespread occurrence of microbialites in the last deglacial reef frameworks (16–6KaBP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes. The present study is based on the sedimentological and chronological analysis (14C AMS dating) of drill cores obtained during the IODP Expedition #310 “Tahiti Sea Level” on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise. The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the “reefal microbialites” which developed a few hundred years after coralgal communities in shallow-water environments, whereas the “slope microbialites” grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities. The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (>50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~30%) and could not host a significant microbialite expansion. [Copyright &y& Elsevier]

Abstract: Accurate determination of the absolute ages of the oldest Solar System objects — chondrules and Ca–Al-rich inclusions (CAIs), requires knowledge of their 238U/235U ratios. This ratio was assumed to be invariant in all U–Pb dating of meteorites so far, but the recent discovery of U isotope variations in CAIs (Brennecka et al., 2010a) shows that this assumption is invalid. We present the first combined high-precision U and Pb isotopic data for a CAI, and U isotopic data for chondrules and whole rock fractions of the Allende meteorite. The Pb–Pb isochron age of the CAI SJ101 is 4567.18±0.50Ma, calculated using the measured 238U/235U=137.876±0.043 (2σ), reported relative to 238U/235U=137.837 of the CRM 145 standard. Our best current estimate of the average terrestrial value is: 238U/235U=137.821±0.014.The error in the age includes uncertainties in the Pb–Pb isochron intercept and in the 238U/235U ratio. Allende bulk rock and chondrules have 238U/235U=137.747±0.017 (2σ), distinctly lower than the CAI. The difference in the 238U/235U ratio of 0.129±0.046 (2σ) between the CAI and chondrules and bulk meteorite increases the 207Pb–206Pb age difference by ~1.4Ma, and eliminates apparent disagreement between the CAI–chondrule formation time interval determinations with the U–Pb and extinct nuclide (26Al–26Mg and 182Hf–182W) data. We discuss standardisation of 238U/235U measurements for U–Pb geochronology and cosmochronology, elemental and isotopic fractionation induced by intensive acid leaching, ages of CAIs in the context of 238U/235U variability, and possible causes of U isotopic variations in CAIs and meteorites. [Copyright &y& Elsevier]

The Mauer mandible, holotype of Homo heidelbergensis, was found in 1907 in fluvial sands deposited by the Neckar River 10 km southeast of Heidelberg, Germany. The fossil is an important key to understanding early human occupation of Europe north of the Alps. Given the associated mammal fauna and the geological context, the find layer has been placed in the early Middle Pleistocene, but confirmatory chronometric evidence has hitherto been missing. Here we show that two independent techniques, the combined electron spin resonance/U-series method used with mammal teeth and infrared radiofluorescence applied to sand grains, date the type-site of Homo heidelbergensis at Mauer to 60±40 ka. This result demonstrates that the mandible is the oldest hominin fossil reported to date from central and northern Europe and raises questions concerning the phyletic relationship of Homo heidelbergensis to more ancient populations documented from southern Europe and in Africa. We address the paleoanthropological significance of the Mauer jaw in light of this dating evidence. [ABSTRACT FROM AUTHOR]

Abstract: Detrital zircon dating from Neoproterozoic successions in the Sirwa inlier of the Anti-Atlas belt in Morocco confirms that the maximum depositional age of the main stratigraphic groups is significantly younger than has been previously proposed in lithostratigraphic correlations. This can probably be extended to the whole Anti-Atlas according to other recent data from the Saghro inlier. Although the relative stratigraphic position of the different units remains valid as published previously, a crucial implication of the new ages is that the sequences believed to be contemporaneous with oceanic crust and island arc formation during the rifting and break-up of the northern margin of the West African Craton (WAC), and believed to be involved in the first phases of the Pan-African orogeny, are actually late to post-orogenic. The age of the main deformation associated with the collision of the oceanic- and arc-derived terranes to the WAC, allegedly affecting the sediments of the Saghro Group, has been estimated at around 663–640Ma. However, the youngest zircon populations of sediments of the Saghro and Bou Salda Groups, obtained in this study, cluster around 620–610Ma, constraining the maximum age of deposition. This age of sedimentation is indistinguishable from the age of intrusive high-K calc-alkaline plutons of the Assarag Suite, suggesting a very rapid cycle of magmatism, relief formation, erosion and sedimentation in an active geodynamic scenario. Moreover, the proportion of the 610Ma detrital zircons becomes less with respect to the Paleoproterozoic zircons at higher stratigraphic levels, suggesting that the source of young zircons was progressively eroded and more extensive cratonic areas, that probably underlie the Neoproterozoic rocks, were exposed. We interpret these data in terms of the development of a ca. 610Ma magmatic arc, built upon WAC basement, and its progressive dismantling. This arc can be correlated with the voluminous late Neoproterozoic (ca. 640–570Ma) arc magmatism characteristic of the north Gondwana margin and the peri-Gondwanan terranes. The diamictite beds that appear in the Imghi Formation of the Saghro Group have been correlated with the Sturtian glacial period ca. 700Ma. However, zircons from one sample of these diamictites indicate that this correlation cannot be longer maintained, and instead they should be correlated with the Marinoan glacial period ca. 630–610Ma, with a widespread distribution of glaciogenic deposits in West Africa. In addition, around 375 U–Pb concordant analyses obtained from Paleoproterozoic zircons from six samples represent a statistically significant population of this area of the WAC basement, which can be a useful database for comparison with the detrital zircon populations of the peri-Gondwanan terranes of Europe and North America, as the WAC margins were one of the major sediment suppliers for these terranes. [Copyright &y& Elsevier]

Abstract: Simultaneous determinations of U–Pb dating and Hf isotopes on single zircon grains by excimer laser-ablation quadrupole and multiple-collector ICP-MS and petrologic and ore geochemical studies have been applied to the ore-bearing porphyry of the Jinduicheng porphyritic molybdenum deposit in East Qinling. Lithogeochemical data show that the porphyry is characteristic of high K2O, K-feldspar porphyritic calc-alkaline granitoids with 176Hf/177Hf=0.282020–0.282436 and ε Hf(t)=−23.7 to −8.9, which indicates its mixed origin involving a crustal and a mantle component. The weighted average U–Pb age from single zircon grains of the porphyry is 141.5±1.5Ma. This age coincides with the oldest molybdenite Re-Os model age as dated by others, suggesting that the period of mineralization was almost simultaneous with the porphyry emplacement, or slightly later. The porphyry intrusion and the molybdenum mineralization occurred during the transition from compression to extension in the Jurassic – Cretaceous periods. The corresponding tectonic setting was the intracontinental orogenic and extension stage after collision and orogenesis between the Southern China plate and the Northern China plate. The Jinduicheng porphyry and the deposit''s geochemical data indicate that the ore-forming material originated from a mixing of lower crust and upper mantle. When the molybdenum-enriched magma intruded into the upper crust along zones of structural weakness, ore-forming fluid generated by magma crystallization of the porphyry interacted with wall rock or mingled with meteoric water to form the deposit. [Copyright &y& Elsevier]

Abstract: Thermal indicators record exhumation of sedimentary units from depths in excess of 6km over most of the Outer Carpathian fold and thrust belt in Poland. Apatite fission track data, showing cooling ages ranging between 32.1±4.8 and 7.0±0.8 Ma, indicate that exhumation was partially coeval with shortening. However, new thermochronometric information obtained as part of this study allowed us to unravel a previously undetected, post-thrusting exhumation stage. The integration of new field data and structural analysis with low-T thermochronometry suggests that termination of thrusting – at ca. 11 Ma in the area of the present study – was followed by gravity disequilibria within the orogenic wedge. The related extension and denudation phenomena appear to have played a primary role in the recent (< 10 Ma) tectonic evolution of the Western Outer Carpathians, exerting a major control on exhumation processes in this key area of the Alpine–Carpathian mountain system. [Copyright &y& Elsevier]

The article offers information on the results of the dating of alkaline granitoids of the Ulug-Tanzek Massif deposit in Tuva, Russia through uranium-lead (U-Pb) method for zircon and Argon-Argon (Ar-Ar) method. A sample from polylithionite-bearing ribeckite granite was studied for Ar-Ar geochronological investigations, in which, results revealed that approximately 85% of Ar that has clearly formed reflected three-step plateau with an age of 296 plus-minus two million years (Ma). In U-Pb dating, a sample of muscovite quartz-albite-microline granite with a netlike texture was used, in which, the determined age of 301 plus-minus three Ma, is similar within the error limits of the age estimation for the first sample using Ar-Ar method.

Abstract: The fossils of Chaoxian hominin, widely accepted as representing archaic Homo sapiens in eastern China, were recovered from the middle or slightly higher levels of Layer 2 deposits of a collapsed cave at Yinshan, Anhui Province. Results of mass spectrometric U-series dating of intercalated speleothem calcites are presented. Based mainly on four broadly coeval calcite samples, the hominin fossils should be bracketed in the range of 310–360ka or somewhat older. These ages are much older than the previous estimate at 160–200ka based on the U-series dating of fossil teeth and bones, and may be cited as supporting evidence for an earlier H. erectus–archaic H. sapiens interface in China. [Copyright &y& Elsevier]

Abstract: We present the new 14C extraction line at ETH Zürich. This system is designed to extract in situ-produced cosmogenic 14C from terrestrial quartz samples, and to obtain pure CO2 gas for analysis with a gas ion source Accelerator Mass Spectrometry (AMS) system. Samples are degassed at 1550–1600°C without the use of a fluxing agent. Gas purification is achieved by a series of cryogenic traps and passage through hot Ag and Cu wool/mesh. Graphitization and, thus, sample dilution is not required. Tests to determine the CO2 recovery after gas extraction and cleaning yielded consistently good recovery rates of >99.8% (n =7). The 14C blank contribution from the all-metal tubing system is negligible. Our preliminary procedural blank estimate – deriving mostly from the hot extraction furnace – is <5×105 14C atoms. Extraction tests on two quartz samples by stepped-heating show a quantitative separation of atmospheric 14C at ≤500°C from the in situ component above 1200°C. Based on these data, we estimate to achieve a complete 14C extraction from a quartz sample. [Copyright &y& Elsevier]

The Miocene Stanislaus Group (Stanislaus, Calaveras, Tuolomne, Alpine and Mono counties, CA), composed of intercalated latite and quartz-latite (trachyandesite and trachyte/trachydacite) lavas and ignimbrites, provides an important marker for reconstructing the elevation history and tectonic development of the Sierra Nevada and Walker Lane. We present new 40Ar/39Ar geochronology and magnetostratigraphy indicating that the Stanislaus Group was emplaced in two pulses: (1) major outpouring of latite lavas at ca. 10.4 Ma and (2) ignimbrite eruptions alternating with lesser lava flow eruptions during ca. 9.4-9.8 Ma. These two events filled the ancestral Stanislaus River drainage in the region of the present Sierra Nevada crest, whereas the ignimbrite eruptions formed the Little Walker Caldera. Our new and previous results date these topographic changes and yield improvements to the Stanislaus Group stratigraphy. [ABSTRACT FROM AUTHOR]

Abstract: Instrumental and spectral characteristics germane to chemical dating of monazite have been tested using the Cameca SX-100 at Rensselaer Polytechnic Institute. Statistical analysis demonstrates that, for trace element analysis, equal counting time on peak and background is required for optimal statistical precision, thus rendering impractical the procedure of fitting the entire spectrum to obtain background values. Energy shifts require shifting the detector voltage window between peak and background positions, and it is concluded that the differential auto PHA mode works optimally for this. Analyses of Pb-free phosphates, silicates, and oxides are used to measure spectral interferences with the PbMα peak and background positions. Backgrounds were modeled using both linear and exponential fits. It was found that the difference in background counts using the two fits varies with each of the five spectrometers examined, and that the high-pressure (3bar) detectors show larger differences in exponential vs. linear peak-minus-background (P-B) values than the low-pressure (1bar) detectors. In addition, every spectrometer requires a unique correction for every major element in monazite. An analytical protocol is presented that incorporates these results. This protocol was applied to several monazite standards to determine inter-spectrometer variability, and spectrometer reproducibility from session to session. It was found that the difference in composition (and age) between spectrometers on identical spots exceeds the 2 sigma standard error of the mean of composition (or age) on either spectrometer. This means that (a) additional sources of error beyond the counting statistics exist between spectrometers; (b) the precision of microprobe ages cannot be continuously improved by additional counting; and (c) the minimum realistic precision is on the order of ±2–3% for monazites with around 1500–2000ppm total Pb, or an additional absolute uncertainty of 20–50ppm Pb. [Copyright &y& Elsevier]

Abstract: The ability to derive detailed thermal history information from apatite fission-track analysis is predicated on the reliability of track length measurements. However, insufficient attention has been given to whether and how these measurements should be standardized. In conjunction with a fission-track workshop we conducted an experiment in which 11 volunteers measured ~50 track lengths on one or two samples. One mount contained Durango apatite with unannealed induced tracks, and one contained apatite from a crystalline rock containing spontaneous tracks with a broad length distribution caused by partial resetting. Results for both mounts showed scatter indicative of differences in measurement technique among the individual analysts. The effects of this variability on thermal history inversion were tested using the HeFTy computer program to model the spontaneous track measurements. A cooling-only scenario and a reheating scenario more consistent with the sample''s geological history were posed. When a uniform initial length value from the literature was used, results among analysts were very inconsistent in both scenarios, although normalizing for track angle by projecting all lengths to a c-axis parallel crystallographic orientation improved some aspects of congruency. When the induced track measurement was used as the basis for thermal history inversion congruency among analysts, and agreement with inversions based on data previously collected, was significantly improved. Further improvement was obtained by using c-axis projection. Differences among inversions that persisted could be traced to differential sampling of long- and short-track populations among analysts. The results of this study, while demonstrating the robustness of apatite fission-track thermal history inversion, nevertheless point to the necessity for a standardized length calibration schema that accounts for analyst variation. [Copyright &y& Elsevier]

Abstract: Absolutely dated records of past sea-level change are extremely important for understanding the advance and retreat of the large ice sheets. When combined with other complementary climate archives and climate models, such records offer the potential to gain an improved understanding of Earth''s natural climate cycles, providing a firmer basis for assessing the role of anthropogenic effects, such as greenhouse gas emissions, in modifying climate. The U-series dating of fossil coral reefs has been widely utilized to provide absolutely dated records of past sea-level change and numerous observations now exist for the past 130,000 years spanning the last glacial cycle. Despite this, controversies still exist regarding the exact timing and character of sea-level events within this time interval, and extending the sea-level history further back in time on the basis of robust and independent age constraints for older fossil reefs remains very elusive. This is primarily due to a progressive loss in the resolution of the U-series chronometer as one goes further back in time, coupled to a lack of well-preserved, dateable coral in older fossil reefs. To overcome these limitations, the primary challenges are three-fold. First, new analytical protocols are required to improve the resolution of the U-series chronometer. Enhanced analytical precision must be coupled to accuracy through continued refinement of the U-series decay constant determinations and via the implementation of rigorous inter-laboratory calibration exercises. Second, efforts should continue to be focussed on gaining an improved understanding of the mechanisms controlling open-system exchange of the U-series isotopes in fossil reef systems. This will allow the number of ‘reliable’ U-series observations to be extended. Third, alternative dateable archives of past sea-level change must continue to be emphasized to further complement the coral reef database. These limitations are discussed in the context of current developments that further advance the application of U-series chronology to older fossil reef systems formed prior to the last glacial cycle. [Copyright &y& Elsevier]

We present 21Ne exposure ages of erosional glaciogenic rock surfaces on nunataks in northern Victoria Land, Antarctica: i) in the Prince Albert Mountains and ii) near Mesa Range. These nunataks are located directly at the margin of the polar plateau and therefore provide an immediate record of ice volume changes of the East Antarctic Ice Sheet, not biased by ice shelf grounding or narrow valley sections downstream the outlet glaciers. The sampling locations overlook the present ice surface by less than 200 m, but were last covered by ice 3.5 Ma BP (minimum age, not corrected for erosion). This strongly indicates that the ice sheet has not been substantially thicker than today since at least the early Pliocene, which supports the hypothesis of a stable East Antarctic Ice Sheet. First absolute ages are reported for the alpine topography above the erosive trimline that typically marks the upper limit of glacial activity in northern Victoria Land. Unexpectedly low nuclide concentrations suggest that erosion rates on the alpine topography are considerably higher due to the steep slopes than those affecting flat erosional surfaces carrying Antarctic tors. [ABSTRACT FROM AUTHOR]

Holocene changes in terrestrial provenance and processes of sediment transport and deposition are tracked along a fjord-to-shelf transect adjacent to Vestfirdir, Iceland, using the magnetic properties ofmarine sediments. Magnetic susceptibility (MS) profiles of 10 cores (gravity and piston) were obtained onboard using a Bartington MS loop. Remanent magnetizations were measured at 1-cm intervals from u-channel samples taken from six cores on a cryogenic magnetometer. Between six and nine alternating field demagnetization steps were used to isolate the characteristic magnetization directions. The chronologies of the cores used in this study were determined from AMS 14C dates on mollusks and foraminifera and constrained by the regional occurrence of the 10,200 ± 60 cal yr. BP Saksunarvatn tephra. Correlative fluctuations in magnetic concentration are noted between the fjord and shelf sites, though these fluctuations are partiallymasked by regional variations in carbonate content. The onset of Neoglaciation is interpreted by changes in magnetic properties including an increase in mass magnetic susceptibility that began approximately 3000 cal yr. BP. The maximum angular deviation and the median destructive field (generally <20 mT) suggest that the natural remanent magnetization is carried by a coarse ferrimagnetite mineralogy, likely magnetite or titano-magnetite. Reproducible paleomagnetic inclination values are observed in several records, including a nearly vertical inclination around 8000 cal yr. BP, suggesting that the magnetic pole may have been proximal to Iceland, followed by an interval of much shallower inclination (6000-7000 cal yr. BP). [ABSTRACT FROM AUTHOR]

The end of the Neoproterozoic is punctuated by glacial deposition, but the chronology of these deposits is hindered presently by the paucity of geochronological data. Here, we present new radiometric dating for the basal Sete Lagoas cap carbonate deposits that overlie glacial units in the São Francisco craton. Six samples from aragonite-pseudomorph crystal-rich facies, showing pristine textures and constant 87Sr/86Sr ratios around 0.7075, yielded a Pb–Pb isochron age of 740 ± 22 Ma, which is interpreted as the depositional age for these remarkably preserved rocks. This age can be used to infer a low-to-moderate palaeolatitude of 20–30° for carbonate (and glacial) deposition. In addition, as it overlaps the ages obtained for the oldest Neoproterozoic glacial successions, our result reinforces the idea of a long-standing ‘Sturtian’ interval, suggesting that this event represents either different discrete glaciations or a protracted event encompassing almost 80 Ma. [ABSTRACT FROM AUTHOR]

Large old landslides are common in the Three Gorges area. Baota landslide, a large rockslide, is one of the largest landslides in the Three Gorges area. In the landslide body there are two terraces to be recognized. The two terrace deposits is not a two-grade terrace, but mainly remnants left by an occurrence of Baota landslide. Optically stimulated luminescence (OSL) dating suggests that the age of the terrace deposits is 38–32 kyr BP. The OSL ages along with other Thermoluminescence (TL) and Radiocarbon (14C) ages support the conclusion that the Baota landslide was originally triggered by strong precipitation occurred in a warm climate period of 30,000–40,000 years BP. [ABSTRACT FROM AUTHOR]

This study presents the results of radiometric K-Ar measurements on separated amphiboles from the andesite of the Dubie complex dyke. The data obtained cover the period of (291.3 ± 6.4) Ma, which corresponds to Carboniferous-Permian transition. The age is contemporaneous to the rhyodacitic and basaltoid volcanism of the Krakow region. [ABSTRACT FROM AUTHOR]

The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic low grade metamorphic rocks. Biotite from five samples representing the homblende-biotite monzogranite, biotite monzogranite and biotite granodiorite has been dated using the K-Ar method for two size-fractions (0.25–0.35 and 0.35–0.5 mm). Finer fractions show more intense chloritization and therefore the results for them were rejected in further discussion. Coarser fractions with higher potassium content were accepted as yielding a maximum estimate approaching the true K-Ar biotite cooling ages. The results are clustered in two groups. The older age group (308.8±4.6 Ma and 305.5±4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4±1.7 Ma reported by Tumiak el al. (2005) and imply rapid cooling of the biotite granodiorite from magmatic temperatures down to the closure temperature of K-Ar isotopic system in biotite. The younger group is defined by 29 1.0±4.4 Ma and 298.7±5.2 Ma ages for the hornblende-biotite monzogranite and 294.2±4.3 Ma age for the biotite monzogranite. In the absence of precise U-Pb or Pb-Pb zircon data further geochronological studies are needed to decipher precisely the cooling history of the monzogranites. [ABSTRACT FROM AUTHOR]

The Lake Taihu drainage basin is an economically developed area with some of the highest population densities in China. The lake has deteriorated due to ecological destruction and eutrophication. Three short sediment cores from eastern, northeastern and southwestern Lake Taihu were collected. Total organic carbon (TOC), total nitrogen (TN), pigments, elements and particle size were analyzed for the purpose of understanding past trophic status and pollution levels. Sedimentation rates were based on 137Cs or 210Pb methods. Results indicated that sediment particle size became coarser since the 1920s, and the lake was contaminated by heavy metals, such as Cu and Zn, since the 1970s. A remarkable increase in eutrophication since the 1980s due to increased loading of untreated effluents from industry, agriculture and urbanization is reflected by total organic carbon, total nitrogen and pigments in the studied cores. However the onset times of eutrophication in different parts of Lake Taihu were not synchronous. [ABSTRACT FROM AUTHOR]

The difficulty in estimating growth rates and ages of tropical and warm-temperate tree species is well known. However, this information has many important environmental applications, including the proper management of native forests and calculating uptake and release of atmospheric carbon. We report the activities of Ra isotopes in the heartwood, sapwood and leaves of six tree species, and use the radial distribution of the 228Ra/226Ra activity ratio in the stem of the tree to estimate the rate of accretion of heartwood. A model is presented in which dissolved Ra in groundwater is taken up by tree roots, translocated to sapwood in a chemically mobile (ion-exchangeable) form, and rendered immobile as it is transferred to heartwood. Uptake of 232Th and 230Tb (the parents of 228Ra and 226Ra) is negligible. The rate of heartwood accretion is determined from the radioactive decay of 228Ra (half-life 5.8 years) relative to long-lived 226Ra (half-life 1600 years), and is relevant to growth periods of up to 50 years. By extrapolating the heartwood accretion rate to the entire tree ring record the method also appears to provide realistic estimates of tree age. Eight trees were studied (three of known age, 72, 66 and 35 years), including three Australian hardwood eucalypt species, two mangrove species, and a softwood pine (P. radiata). The method indicates that the rate of growth ring formation is species and climate dependent, varying from 0.7 rings yr-1 for a river red gum (E. camaldulensis) to around 3 rings yr-1 for a tropical mangrove (X. mekongensis). [ABSTRACT FROM AUTHOR]

The isochron dating method is a reliable radioactive dating method used to find the age of rocks. It is based on the measurement of the abundance of a radioactive parent isotope as well as the corresponding daughter isotope as a ratio to a reference isotope that is a non-radiogenic isotope of the daughter element. Its major advantage over the more basic dating method, such as the carbon-14 dating, is that this method does not require knowledge of the initial amount of daughter material; in fact this method allows you to determine its value. [ABSTRACT FROM AUTHOR]

Garnet in metapelites from the Wölz and Rappold Complexes of the Austroalpine basement east of the Tauern Window typically shows two distinct growth zones. A first garnet generation usually forms the cores of garnet porphyroblasts and is separated by a prominent microstructural and chemical discontinuity from a second garnet generation, which forms rims of variable width. Whereas the rims were formed during the Eo-Alpine metamorphic overprint, the garnet cores represent remnants of at least two pre-Eo-Alpine metamorphic events. The pressure and temperature estimates obtained from garnet isopleth thermobarometry applied to the first growth increments of the pre-Eo-Alpine garnet cores from the Wölz and Rappold Complexes cluster into two distinct domains: (i) in the Wölz Complex, incipient growth of the first-generation garnet occurred at 4 ± 0.5 kbar and 535 ± 20 °C, (ii) in the Rappold Complex, incipient growth of the oldest garnet cores took place at 5.3 ± 0.3 kbar and 525 ± 15 °C. The Eo-Alpine garnet generation started to grow at 6.5 ± 0.5 kbar and 540 ± 10 °C. According to radiometric dating, the low-pressure garnet from the Wölz complex was formed during a Permian metamorphic event. The first-generation garnet of the Rappold Complex is probably of Variscan age. [ABSTRACT FROM AUTHOR]

Radioisotopic dating of subaerial and submarine volcanic and plutonic rocks from the Aleutian Island Arc provides insight into the timing of arc formation in the middle Eocene. Twenty-eight 40Ar/39Ar ages constrain the duration of arc magmatism to the last 46 m.y. Basaltic lavas from the Finger Bay volcanics, the oldest exposed rocks in the arc, gave an isochron age of 37.4 ± 0.6 Ma, which is 12–17 m.y. younger than a widely cited age of 55–50 Ma. Three main pulses of arc-wide magmatism occurred at 38–29, 16–11, and 6–0 Ma, which coincide with periods of intense magmatism in other western Pacific island arcs. Using the geochronology and volumetric estimates of crust generated and eroded over the last 46 m.y., we calculate a time-averaged magma production rate for the entire arc that exceeds previous estimates by almost an order of magnitude. [ABSTRACT FROM AUTHOR]