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Matthias Bernet - One of the best experts on this subject based on the ideXlab platform.
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A field-based estimate of the zircon fission-track Closure Temperature
Chemical Geology, 2009Co-Authors: Matthias BernetAbstract:International audiencefield-based estimate of the zircon fission-track Closure Temperature is proposed from 13 zircon fission-track cooling ages of the Gold Butte block, SE Nevada. Using previously published and new thermochronological data, the thermal history of the Gold Butte block is re-evaluated, resulting in a geothermal-gradient estimate of 20.3 °C/km and a slow cooling rate of 0.55 ± 0.02 °C/m.y. from the Late Jurassic to the early Miocene before onset of rapid Miocene cooling. The rapidly cooled part of the Gold Butte block provides a slip rate of 10.5 km/m.y. of the hanging wall that caused the Miocene exhumation of this crustal section. Assuming these thermal conditions are correct, the Closure Temperature of the zircon fission-track system is determined at 205 ± 18 °C, which is in good agreement with previous field-based estimates. Because of the variation in zircon fission-track annealing behavior with radiation damage, field studies are a suitable way to calibrate the Closure Temperature of the zircon fission-track system
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A field-based estimate of the zircon fission-track Closure Temperature
Chemical Geology, 2008Co-Authors: Matthias BernetAbstract:Abstract A field-based estimate of the zircon fission-track Closure Temperature is proposed from 13 zircon fission-track cooling ages of the Gold Butte block, SE Nevada. Using previously published and new thermochronological data, the thermal history of the Gold Butte block is re-evaluated, resulting in a geothermal-gradient estimate of 20.3 °C/km and a slow cooling rate of 0.55 ± 0.02 °C/m.y. from the Late Jurassic to the early Miocene before onset of rapid Miocene cooling. The rapidly cooled part of the Gold Butte block provides a slip rate of 10.5 km/m.y. of the hanging wall that caused the Miocene exhumation of this crustal section. Assuming these thermal conditions are correct, the Closure Temperature of the zircon fission-track system is determined at 205 ± 18 °C, which is in good agreement with previous field-based estimates. Because of the variation in zircon fission-track annealing behavior with radiation damage, field studies are a suitable way to calibrate the Closure Temperature of the zircon fission-track system.
Anthony J. Hurford - One of the best experts on this subject based on the ideXlab platform.
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thermochronometry and microstructures of quartz a comparison with experimental flow laws and predictions on the Temperature of the brittle plastic transition
Journal of Structural Geology, 1999Co-Authors: Bernhard Stockhert, Anthony J. Hurford, Manfred R Brix, Reiner Kleinschrodt, Richard WirthAbstract:Abstract A gradient in quartz microfabrics across a major strike-slip shear zone (with a minor vertical component), active during the Oligocene in the Eastern Alps (Alto Adige, Italy), is correlated with new zircon fission track thermochronometric data and available Rb–Sr biotite ages to constrain the depth/Temperature range of the recorded rheologic regimes. Distributed deformation in the semibrittle regime (i.e. beneath the brittle–ductile transition) is effective near the Closure Temperature for fission tracks in zircon (which we estimate as 280±30°C), with high-stress dislocation creep of quartz, microcracking, and pressure solution being active simultaneously. Steady state dislocation creep of quartz at moderate stress in the fully plastic regime is effective at Temperatures above the Closure Temperature for the Rb–Sr and K–Ar systems of biotite (ca. 310±30°C) and below that for the K–Ar system of white mica (ca. 350±50°C). For the inferred Temperatures and correlated flow stresses derived by paleopiezometry, the majority of available experimental flow laws for wet quartzite predict strain rates on the order of 10 −13 –10 −14 s −1 , consistent with the geological constraints. This finding supports the validity of the extrapolation of experimental flow laws to natural strain rates.
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Natural long-term annealing of the zircon fission-track system in Vienna Basin deep borehole samples: Constraints upon the partial annealing zone and Closure Temperature
Chemical Geology, 1996Co-Authors: Takahiro Tagami, Andrew Carter, Anthony J. HurfordAbstract:Abstract Fission-track (FT) analysis of zircon from Cretaceous and Tertiary sandstone samples in Vienna Basin boreholes has provided constraints for the thermal stability of the zircon FT system over a geological timescale. Confined track lengths and ages were measured for samples from depths of ∼ 1.5-7.5 km, the deepest with a present environmental Temperature of ∼ 200°C. Mean track lengths range from 10.3 to 10.8 μm, indistinguishable within error from the unannealed reference length of 10.7 ± 0.1 μm (± 1 standard error), thus showing no sign of systematic downhole reduction. Central zircon ages are consistently older than stratigraphic ages of parent rocks, with no single-grain ages significantly younger than their respective stratigraphic ages. Such FT age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition. Because the present geothermal regime as well as sample burial depths have been near-constant for at least the past 5 m.y. the lower Temperature limit of the zircon FT partial annealing zone is > 200°C for a heating duration of the order of 5–10 m.y. Such evidence from long-term natural annealing is compatible with a zircon FT partial annealing zone cf ∼ 200–350°C derived by the extrapolation of laboratory annealing results based on onfined track length measurements, but cannot alone discriminate between different annealing models. For the zircon FT Closure Temperature, a perhaps over-simplified concept, these results are consistent with the oft-quoted Temperature of ∼ 250°C for cooling rates of ∼ 10–100°C/m.y.
Yan Liang - One of the best experts on this subject based on the ideXlab platform.
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Effect of pressure on Closure Temperature of a trace element in cooling petrological systems
Contributions to Mineralogy and Petrology, 2017Co-Authors: Yan LiangAbstract:Closure Temperature is important to many diffusion-related problems involving cooling. The classic model of Dodson and its modifications for cooling petrological systems are formulated at constant pressure. Many petrologic processes involve changes in both Temperature and pressure. The effect of changing pressure on diffusional loss in cooling petrological systems has not been considered in Dodson’s model. During upwelling, the decompression rate is related to the cooling rate through the slope of the upwelling path. Simple analytical expressions for the average or mean Closure Temperature and Closure pressure in cooling-upwelling mono-mineralic and bi-mineralic systems are obtained by noting that both Temperature and pressure decrease as a function of time along the upwelling path. These pressure-adjusted equations are nearly identical to Closure Temperature equations for isobaric cases if one replaces the activation energy and pre-exponential factor for diffusion in the isobaric formulations by the path-dependent activation energy and pre-exponential factor. The latter also depend on the slope of the upwelling path. The competing effects between pressure and Temperature on diffusion during upwelling result in reductions in the effective activation enthalpy for diffusion and exchange enthalpy for partitioning, which in turn leads to systematic deviations in Closure Temperatures from cases of constant pressure. For systems with large activation volume for diffusion, it may be possible to deduce upwelling path and upwelling rate from Closure Temperatures and Closure pressures of selected elements. Examples of Closure Temperature and Closure pressure for REE diffusion in garnet and clinopyroxene and in garnet–clinopyroxene aggregates are presented and discussed in the context of the minor’s rule and the REE-in-garnet–clinopyroxene thermobarometer. Closure Temperatures for middle-to-heavy REE in garnet–clinopyroxene aggregates are controlled primarily by diffusion in clinopyroxene unless the modal abundance of garnet is very small or the effective grain size of clinopyroxene is considerably smaller than that of garnet.
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Closure Temperature in cooling bi-mineralic systems: I. Definition and with application to REE-in-two-pyroxene thermometer
Geochimica et Cosmochimica Acta, 2015Co-Authors: L. Yao, Yan LiangAbstract:Abstract Closure Temperature is an important concept to many diffusion related problems involving cooling. The basic idea and formulation were outlined in the seminal work of Dodson for cooling mono-mineralic systems. The Dodson’s equation has been widely used to calculate Closure Temperatures for igneous and metamorphic rocks that contain more than one mineral. The purpose of this study is to examine Closure Temperatures in cooling bi-mineralic systems and to investigate the physical meaning of Temperatures calculated using the REE-in-two-pyroxene thermometer. We conduct numerical simulations of diffusive redistribution of trace elements between two coexisting minerals under prescribed cooling using Temperature-dependent diffusion coefficients and mineral–mineral partition coefficients. Following Dodson’s treatment, the Closure Temperature in bi-mineralic systems can be defined by the evolution of either average trace element concentrations in the two minerals or their ratio. The latter defines an effective partition coefficient. Closure Temperatures calculated based on the two definitions are compared for a range of cooling rates, grain sizes, mineral proportions, and Temperature-dependent partition coefficients and diffusion coefficients. Temperatures defined by the effective partition coefficient are recommended. Application to diffusive redistribution of rare earth elements (REE) in orthopyroxene–clinopyroxene systems demonstrates that Closure Temperature differences among REE are small and hence their average value may be used as the Closure Temperature for the cooling two-pyroxene system. The average Closure Temperature of REE in the two-pyroxene system is essentially the same as the Temperature calculated using the REE-in-two-pyroxene thermometer and practically independent of pyroxene modal abundance in the system. Differences in Temperatures calculated using the REE- and major element-based two-pyroxene thermometers can be used to infer cooling rate of two-pyroxene bearing mafic and ultramafic rocks.
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A simple model for Closure Temperature of a trace element in cooling bi-mineralic systems
Geochimica et Cosmochimica Acta, 2015Co-Authors: Yan LiangAbstract:Abstract Closure Temperature is defined as the lower Temperature limit at which the element of interest effectively ceases diffusive exchange with its surrounding medium during cooling. Here we generalize the classic equation of Dodson (1973) for cooling mono-mineralic systems to cooling bi-mineralic aggregates by considering diffusive exchange of a trace element between the two minerals in a closed system. We present a simple analytical model that includes key parameters affecting the Closure Temperature of a trace element in cooling bi-mineralic systems: cooling rate, Temperature-dependent diffusion coefficients for the trace element in the two minerals, Temperature-dependent partition coefficient of the trace element between the two minerals, effective grain sizes of the two minerals, and volume proportions of the minerals in the system. We show that Closure Temperatures of a trace element in cooling bi-mineralic systems are bounded by the Closure Temperatures of the trace element in the two mono-mineralic systems and that our generalized model reduces to Dodson’s equation when one of the mineral serves as “an effective infinite” reservoir to the other mineral. Application to Closure Temperatures of REE in orthopyroxene and clinopyroxene bi-mineralic systems highlights the importance of REE diffusion and partitioning in the pyroxenes as well as clinopyroxene modal abundance and grain size in the systems. Closure Temperatures for REE in two-pyroxene bearing equigranular rocks are controlled primarily by diffusion in orthopyroxene unless the modal abundance of clinopyroxene is very small. This has important bearings on the interpretation of Temperatures derived from the REE-in-two-pyroxene thermometer.
John I. Garver - One of the best experts on this subject based on the ideXlab platform.
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A zero-damage model for fission-track annealing in zircon
American Mineralogist, 2004Co-Authors: Meinert Rahn, Geoffrey E. Batt, Mark T. Brandon, John I. GarverAbstract:A zircon fission track-annealing model is calculated on the basis of annealing experiments from the literature with induced tracks in α-decay event damage-free zircon samples. Empirically derived parallel and fanning equations for this “zero-damage” model yield an excellent fit to the data, with the fanning model providing slightly better statistical parameters. A comparison between annealing models with fanning iso-annealing lines but different α-decay event damage densities reveals that annealing Temperatures and Closure Temperatures for the estimated partial annealing zone are highest for the zero-damage model. Compilations of existing geologic constraints on the zircon partial-annealing zone on one hand and the zircon Closure Temperature on the other show that these constraints do not or only partly overlap with curves of proposed models for the zircon partial-annealing zone and Closure Temperature. This finding is consistent with the fact that the annealing behavior of zircon from long-duration Temperature evolutions is increasingly influenced by the accumulated α-decay event damage. Zircon samples of young age or low U content show a behavior closest to the predictions of the zero-damage model, and are in the predicted range of published models with low α-decay event damage density. For thermal events of more than 10 myr duration, however, constraints from field studies show marked differences from proposed partial-annealing zone boundaries of the zero- or low-damage models. The applicability of the zero-damage model is threefold. (1) It predicts correct Closure Temperatures in the case of very rapid cooling across the partial annealing zone where basically no α-decay event damage is accumulated. (2) It predicts an uppermost boundary for complete annealing of a mixture of zircon components of different age, as found in sedimentary samples, and in this case may be used as a thermometer. (3) It represents an important reference for the establishment of a more comprehensive model of zircon fission-track annealing that also includes the influence of α-decay event damage. For such a model, two different equations are discussed. However, additional detailed experimental and field data are needed for a more robust annealing model that includes the influence of α-decay event-damage annealing.
Dewen Zheng - One of the best experts on this subject based on the ideXlab platform.
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A Potential (U‐Th)/He Zircon Reference Material from Penglai Zircon Megacrysts
Geostandards and Geoanalytical Research, 2017Co-Authors: Youjuan Li, Huaiyu He, Jianzhang Pang, Yizhou Wang, Dewen Zheng, Ying Wang, Jingxing YuAbstract:In this study (U-Th)/He dating of the Penglai zircons, which occur as abundant megacrysts in Neogene alkaline basalts in northern Hainan Province, south-eastern China, was undertaken. A weighted mean age of 4.06 ± 0.35 Ma (2s) with a mean square weighted deviation (MSWD) of 1.79 was obtained from eighteen fragments of four zircon megacrysts using single-crystal laser fusion He determinations and the U-Th isotope dilution (ID) method. The (U-Th)/He ages are consistent, homogeneous and systematically slightly younger than the preferred 206Pb/238U age of 4.4 ± 0.1 Ma (95% confidence interval) determined by ID-TIMS and subsequently published U-Pb results. The U-Pb isotopic system in zircon has a high Closure Temperature of ~ 900 °C, and the preferred U-Pb age may record both the time since eruption and the zircon residence time in the magma chamber. In contrast, the Closure Temperature of the zircon (U-Th)/He system is ~ 190 °C and the zircon megacrysts were brought quickly to the surface by the host basaltic magma. Thus, the (U-Th)/He age represents the timing of the eruption. Based on the unlimited quantity, large grain size, mostly weak broad zoning, rapid cooling and homogenous (U-Th)/He ages, we consider the Penglai zircons suitable for use as a reference material in (U-Th)/He isotope geochronology.
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40 Ar/ 39 Ar analysis of supergene yavapaiite and preliminary investigation on Ar Closure Temperature
Science China Earth Sciences, 2012Co-Authors: Jing Yang, Dewen ZhengAbstract:Yavapaiite (KFe(SO4)2) is a new sulfate mineral with high potassium content, discovered in the oxidation zone of non-ferrous metal mining in the Tu-Ha Basin, Xinjiang Uygur Autonomous Region, northwestern China. Dating of this mineral by the K-Ar and 40Ar/39Ar method allows us to study the time and process of the region’s aridity, and further we can provide some insight into the influence of not only the Tibetan Plateau uplift but also formation and evolution of polar ice caps on climate of this region. However, as the Temperature of this region is up to 60°C in summer, it is still questionable whether this high Temperature causes the diffusive loss of 40Ar from yavapaiite in a long time, or whether the fine grain of the mineral can lead to diffusive loss of 40Ar from yavapaiite. These are important for interpreting the mineral age data. According to diffusion theory, we use 40Ar/39Ar step heating experiment to determine the apparent Ar diffusivity. Then we present a simple model of diffusive loss and radiogenic in-growth to evaluate the effect of extreme high ambient Temperature and the grain size upon the Ar age. The experimental results show that the diffusion parameters as follows: the activation energy E a is 71.30 kcal/mol and the frequency factor logD 0/a 2 is 13.71/s, the corresponding Closure Temperature T c is 294°C (assuming a cooling rate of 10°C/Ma), and the activation energy and Closure Temperature are very high. The simulation results show that the high ambient Temperature and the grain size have no effect on the Ar age after yavapaiite was precipitated. Furthermore, the reproducibility of the age attests to the suitability of supergene yavapaiite for K-Ar and 40Ar/39Ar dating.
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40 ar 39 ar analysis of supergene yavapaiite and preliminary investigation on ar Closure Temperature
Science China-earth Sciences, 2012Co-Authors: Jing Yang, Dewen ZhengAbstract:Yavapaiite (KFe(SO4)2) is a new sulfate mineral with high potassium content, discovered in the oxidation zone of non-ferrous metal mining in the Tu-Ha Basin, Xinjiang Uygur Autonomous Region, northwestern China. Dating of this mineral by the K-Ar and 40Ar/39Ar method allows us to study the time and process of the region’s aridity, and further we can provide some insight into the influence of not only the Tibetan Plateau uplift but also formation and evolution of polar ice caps on climate of this region. However, as the Temperature of this region is up to 60°C in summer, it is still questionable whether this high Temperature causes the diffusive loss of 40Ar from yavapaiite in a long time, or whether the fine grain of the mineral can lead to diffusive loss of 40Ar from yavapaiite. These are important for interpreting the mineral age data. According to diffusion theory, we use 40Ar/39Ar step heating experiment to determine the apparent Ar diffusivity. Then we present a simple model of diffusive loss and radiogenic in-growth to evaluate the effect of extreme high ambient Temperature and the grain size upon the Ar age. The experimental results show that the diffusion parameters as follows: the activation energy E a is 71.30 kcal/mol and the frequency factor logD 0/a 2 is 13.71/s, the corresponding Closure Temperature T c is 294°C (assuming a cooling rate of 10°C/Ma), and the activation energy and Closure Temperature are very high. The simulation results show that the high ambient Temperature and the grain size have no effect on the Ar age after yavapaiite was precipitated. Furthermore, the reproducibility of the age attests to the suitability of supergene yavapaiite for K-Ar and 40Ar/39Ar dating.