•Thermal history of the Baogutu porphyry Cu deposit is constrained by multi-methods.•Zircon/apatite (U–Th)/He dating reveal a five-episode cooling history of the deposit.•The far-field effect of ...Qiangtang–Eurasia and Lhasa–Qiangtang collision is recorded.
Understanding postmineralization tectonic movements in porphyry deposits, is critical to interpreting the complete thermal-tectonic history. This study reports new zircon U–Pb ages, hydrothermal biotite 39Ar/40Ar age, and zircon and apatite (U–Th)/He ages from the Baogutu porphyry copper deposit, which, in conjunction with pre-existing geochronology and thermochronology and inverse modeling simulations, constrain the thermal-tectonic history of the deposit. Zircon LA-ICP-MS U–Pb concordia ages indicate a Late Carboniferous age of 320.1±2.2Ma for the diorite complex and 309.8±2.2Ma for the mineralized granodiorite porphyry. Hydrothermal biotite selected from a quartz–biotite–chalcopyrite vein yields a plateau age of 311.0±1.8Ma which agrees with the age of the granodiorite porphyry and a previously reported molybdenite Re–Os age, and suggests that hydrothermal fluid circulated about 310m.y. ago. Diorite and granodiorite porphyry yield weighted mean zircon (U–Th)/He ages of 200.6±5.7Ma and 241.1±8.1Ma, respectively, with ages ranging from 221.0Ma to 174.3Ma and 225.9 to 261.6Ma. Weighted mean diorite and granodiorite porphyry apatite (U–Th)/He ages of 87.4±2.3Ma and 120.0±4.2Ma were obtained with ages ranging from 68.9Ma to 100.8Ma, and from 91.0Ma to 152.0Ma, respectively. The wide range of zircon (U–Th)/He ages may be due to the combined effects of U and Th zonation and radiation damage, and radiation damage effect may also account for the wide range of apatite (U–Th)/He ages. The combined effects of depth and cooling due to meteoric water circulation contribute to an older (U–Th)/He age for the granodiorite porphyry, relative to the diorite. A five-episode cooling rate history for the diorite can be deduced by inverse model simulation: fast cooling—moderate fast cooling—relatively slow cooling—fast cooling again—very slow cooling. The thermal and tectonic history of the wall rock indicates that it suffered significant far-field effects from the Qiangtang–Eurasia and Lhasa–Qiangtang collision, however, no visible thermal effect from the India–Asia collision is observed.
Detrital studies that utilize zircon U–Pb geochronology and fission-track (FT) thermochronometry are subject to a range of potential sources of bias that should be properly evaluated and minimized. ...Some of them are common to any single-grain mineral analysis (e.g., variable bedrock mineral fertility, hydraulic sorting during transport, selective grain loss during sample processing), whereas others are intrinsic to zircon, and are related to radiation damage and age discordance. In this article, we quantify the impact of intrinsic bias on detrital studies thanks to the analysis of modern detritus shed from the European Alps, and illustrate the general implications on geological interpretations.
We show that detrital zircon U–Pb age distributions based on statistically robust datasets are highly reproducible and representative of the parent bedrock ages in the catchment. Arbitrary or selective removal of discordant grain ages can be minimized by using the Kolmogorov–Smirnov test to identify an appropriate cutoff level. Loss of metamict (α-damaged) zircon has a minor impact on data representativeness, and is mainly controlled by regional metamorphism rather than by mechanical abrasion during river transport. Zircon FT grain-age distributions were found to have poor reproducibility, although age spectra are consistent with bedrock data. However, unlike the U–Pb datasets, U-rich zircon grains (>1000ppm) are systematically missed, and undatable grains may exceed 50%. We identify two major sources of distribution bias specific to zircon FT datasets: (i) sediment sources dominated by U-rich zircon grains are markedly underrepresented in the detrital record, because such grains often have uncountable high densities of fission tracks (“U concentration bias”); (ii) sediment sources that shed zircon grains with high levels of α-damage are underrepresented, because these grains are lost during chemical etching for FT revelation (“etching bias”). In the case of multimethod dating on the same grains (e.g., FT and U–Pb double dating), bias affecting detrital zircon FT dating propagates to the entire dataset. These effects may not impact on exhumation-rate studies that utilize the youngest grain ages (i.e., lag-time approach). However, they represent a limiting factor for conventional provenance studies, and generally preclude application of zircon FT dating to sediment budget calculations.
•Metamict zircon is selectively destroyed during metamorphism of source rocks.•River transport is not effective in promoting rounding of zircon grains.•The K–S test can be used to set the cutoff level for discordant U–Pb ages.•U concentration and etching bias are specific to zircon fission-track datasets.•Zircon grains undatable by fission-track analysis exceed 50% of a dataset.
Denisova Cave in the Siberian Altai (Russia) is a key site for understanding the complex relationships between hominin groups that inhabited Eurasia in the Middle and Late Pleistocene epoch. DNA ...sequenced from human remains found at this site has revealed the presence of a hitherto unknown hominin group, the Denisovans
, and high-coverage genomes from both Neanderthal and Denisovan fossils provide evidence for admixture between these two populations
. Determining the age of these fossils is important if we are to understand the nature of hominin interaction, and aspects of their cultural and subsistence adaptations. Here we present 50 radiocarbon determinations from the late Middle and Upper Palaeolithic layers of the site. We also report three direct dates for hominin fragments and obtain a mitochondrial DNA sequence for one of them. We apply a Bayesian age modelling approach that combines chronometric (radiocarbon, uranium series and optical ages), stratigraphic and genetic data to calculate probabilistically the age of the human fossils at the site. Our modelled estimate for the age of the oldest Denisovan fossil suggests that this group was present at the site as early as 195,000 years ago (at 95.4% probability). All Neanderthal fossils-as well as Denisova 11, the daughter of a Neanderthal and a Denisovan
-date to between 80,000 and 140,000 years ago. The youngest Denisovan dates to 52,000-76,000 years ago. Direct radiocarbon dating of Upper Palaeolithic tooth pendants and bone points yielded the earliest evidence for the production of these artefacts in northern Eurasia, between 43,000 and 49,000 calibrated years before present (taken as AD 1950). On the basis of current archaeological evidence, it may be assumed that these artefacts are associated with the Denisovan population. It is not currently possible to determine whether anatomically modern humans were involved in their production, as modern-human fossil and genetic evidence of such antiquity has not yet been identified in the Altai region.
Estimates of age and growth of yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna remain problematic because validation of growth zone deposition (opaque and translucent) has not been ...properly evaluated. Otolith growth structure (zone clarity) can be poorly defined for tropical tunas, but the use of bomb radiocarbon dating has validated age estimates to 16-18 years for yellowfin and bigeye tuna. Use of the radiocarbon decline period--defined by regional coral and otoliths--provided valid ages through ontogeny. Yellowfin tuna aged 2-18 years (n = 34,1029-1810 mm FL) and bigeye tuna aged 3-17 years (n = 12, 1280-1750 mm FL) led to birth years that were coincident with the bomb radiocarbon decline. The results indicate there was no age reading bias for yellowfin tuna and that age estimates of previous studies were likely underestimated for both species.
Lens crystallines are special proteins in the eye lens. Because the epithelial basement membrane (lens capsule) completely encloses the lens, desquamation of aging cells is impossible, and due to the ...complete absence of blood vessels or transport of metabolites in this area, there is no subsequent remodelling of these fibers, nor removal of degraded lens fibers. Human tissue ultimately derives its (14)C content from the atmospheric carbon dioxide. The (14)C content of the lens proteins thus reflects the atmospheric content of (14)C when the lens crystallines were formed. Precise radiocarbon dating is made possible by comparing the (14)C content of the lens crystallines to the so-called bomb pulse, i.e. a plot of the atmospheric (14)C content since the Second World War, when there was a significant increase due to nuclear-bomb testing. Since the change in concentration is significant even on a yearly basis this allows very accurate dating.
Our results allow us to conclude that the crystalline formation in the lens nucleus almost entirely takes place around the time of birth, with a very small, and decreasing, continuous formation throughout life. The close relationship may be further expressed as a mathematical model, which takes into account the timing of the crystalline formation.
Such a life-long permanence of human tissue has hitherto only been described for dental enamel. In confront to dental enamel it must be held in mind that the eye lens is a soft structure, subjected to almost continuous deformation, due to lens accommodation, yet its most important constituent, the lens crystalline, is never subject to turnover or remodelling once formed. The determination of the (14)C content of various tissues may be used to assess turnover rates and degree of substitution (for example for brain cell DNA). Potential targets may be nervous tissues in terms of senile or pre-senile degradation, as well as other highly specialised structures of the eyes. The precision with which the year of birth may be calculated points to forensic uses of this technique.
"One of the best books written about interracial relationships to date. . . . Childs offers a sophisticated and insightful analysis of the social and ideological context of black-white interracial ...relationships."-Heather Dalmage, author Tripping on the Color Line
"A pioneering project that thoroughly analyzes interracial marriage in contemporary America."-Eduardo Bonilla-Silva, author of Racism without Racists: Color-Blind Racism and the Persistence of Racial Inequality in the United States
Is love color-blind, or at least becoming increasingly so? Today's popular rhetoric and evidence of more interracial couples than ever might suggest that it is. But is it the idea of racially mixed relationships that we are growing to accept or is it the reality? What is the actual experience of individuals in these partnerships as they navigate their way through public spheres and intermingle in small, close-knit communities?
In Navigating Interracial Borders, Erica Chito Childs explores the social worlds of black-white interracial couples and examines the ways that collective attitudes shape private relationships. Drawing on personal accounts, in-depth interviews, focus group responses, and cultural analysis of media sources, she provides compelling evidence that sizable opposition still exists toward black-white unions. Disapproval is merely being expressed in more subtle, color-blind terms.
Childs reveals that frequently the same individuals who attest in surveys that they approve of interracial dating will also list various reasons why they and their families wouldn't, shouldn't, and couldn't marry someone of another race. Even college students, who are heralded as racially tolerant and open-minded, do not view interracial couples as acceptable when those partnerships move beyond the point of casual dating. Popular films, Internet images, and pornography also continue to reinforce the idea that sexual relations between blacks and whites are deviant.
Well-researched, candidly written, and enriched with personal narratives, Navigating Interracial Borders offers important new insights into the still fraught racial hierarchies of contemporary society in the United States.
The Xitian tungsten–tin (W–Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W–Sn deposits in the Nanling W–Sn ...metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230–215 Ma) and Yanshanian (Late Jurassic–Early Cretaceous, 165–141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U–Pb analysis yielded two ages of 225.6±1.3 Ma and 151.8±1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 149.7±0.9 Ma, in excellent agreement with a weighted mean age of 150.3±0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded 40Ar/39Ar plateau ages of 149.5±1.5 Ma and 149.4±1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U–Pb age of 151.8±1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W–Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W–Sn ore-forming event (160–150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W–Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere.
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•U–Pb, Re–Os and Ar–Ar dating are systematically used to constrain the magmatism and W–Sn mineralization in the Xitian W–Sn deposit.•All published ages from various styles of W–Sn deposits in the Nanling region at 160–150 Ma are collected.•Jurassic magmatism and mineralization are linked to back–arc lithospheric extension in the Nanling region, possibly triggered by a flat–slab subduction of Paleo–Pacific plate.•High Re contents in molybdenite suggest that the ore–forming components were from mixed mantle and crustal sources.
The study of bedrock fault scarps is a useful approach to identify paleo-earthquakes and acquire the faulting history in bedrock areas where traditional trench techniques are not applicable. Here, we ...report a study on the Luoyunshan piedmont fault (LYSPF), southwestern Shanxi Rift, China. Although several studies have analyzed the LYSPF, its faulting behavior is still under debate. For example, the tectonic geomorphology fails to determine the frequency of past slips and the elapsed time. To address these problems, we investigated two bedrock fault surfaces, Luoyuncun (northern segment) and Weicun (southern segment) using quantitative morphology analyses together with multiple Quaternary dating techniques. Quantitative morphology analysis shows that both bedrock fault surfaces have the characteristics of vertical segmentation. This kind of segmentation indicates that the fault surfaces are exhumed intermittently, likely owing to periodic faulting earthquakes. Therefore, earthquake events can be identified as morphological segments, and the corresponding co-seismic displacement can be determined by the height of these segments. According to the results from the quantitative morphology and dating techniques, four seismic events, with a co-seismic vertical displacement of 0.9 m, 0.82 m, 1.64 to 2.38 m and 2.30 to 2.54 m, on the northern segment occurred during the late Pleistocene, whereas, two seismic events, with a co-seismic vertical displacement of ~1.33 m and 1 to 1.08 m are identified on the southern segment occurred during the Holocene. Combined with the results of knickpoint series and trench techniques of the LYSPF, eight paleo-earthquake events were identified since 45 ka, with an average recurrence interval of 5.8 kyr. The more complete paleo-earthquake sequence also showed the possibility that the variation of the slip rate along the LYSPF depends on the segment, and that the displacement produced by the Linfen M 7½ earthquake of 649 CE has been recorded at the WC fault surface.
•A paleo-earthquake history of the Luoyunshan piedmont fault (45 ka–present) was constructed.•Four seismic events were identified on the northern segment --, and two seismic events were identified on the southern segment -.•The fault can produce earthquakes with magnitude greater than 7.5, and the vertical displacement of the latest event was 1 to 1.08 m.•The vertical slip rate of LYSPF was estimated to be 0.09 to 0.13 mm/a on the northern segment, and 0.23 to 0.53 mm/a on the southern segment.
The potential abuse of dating applications (apps), including during the current lockdowns due to COVID-19, has resulted in a growing community of research to learn to what extent the impacts of these ...apps have on the individual's psychological and physiological being, as well as the presumed security of their sensitive information. In this paper, we seek to review the existing literature that encompasses the issues surrounding dating apps. Specifically, we focus on crimes that can occur from the use of dating apps, potential mitigation strategies, the physiological and psychological effects on not only the general population, but also minority groups, and lastly, an assessment on the associated cybersecurity risks and potential digital artifacts of interest in criminal investigations. Although research on dating apps will continue to struggle with the ever-changing technological landscape, it is important to examine best practices and mitigation strategies that dating app developers can utilize to create safer platforms. Finally, we conclude this paper with a number of potential research opportunities.
The dating of organic findings is a fundamental task for many scientific fields. Radiocarbon dating is currently the most commonly used method. For wood, dendrochronology is another state‐of‐the‐art ...method. Both methods suffer from systematic restrictions, leading to samples that have not yet been able to be dated. Molecular changes over time are reported for many materials under different preservation conditions. Many of them are intrinsically monotonous. These monotonous molecular decay (MD) patterns can be understood as clocks that start at the time when a given molecule was formed. Factors that influence these clocks include input material composition and preservation conditions. Different wood species, degrees of pyrolysis, and pretreatments lead to different prediction models. Preservation conditions might change the speed of a given clock and lead to different prediction models. Currently published models for predicting the age of wood, paper, and parchment depend on infrared spectroscopy. In contrast to radiocarbon dating, dating via MD does not comprise a single methodology. Some clocks may deliver less precise results than the others. Ultimately, developing a completely different, new dating strategy‐such as MD dating–will help to bring to light a treasure trove of information hidden in the darkness of organic findings.
This review focuses on molecular changes over time. Having been discussed since the 1960s, the variety of
molecular clocks includes the change in amino acids in the primary structure of a protein over time. Molecular decay (MD) has a mainly monotonous function, a prerequisite to serving as such a clock. In addition, such clocks need a defined starting point and a defined decay function. In contrast to the decay of alpha and beta emitters, MD is influenced by several environmental factors indicated by preservation conditions. The MD method has the potential to be used for different organic materials and different scientific fields.
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