Geochronology and petrogenesis of the post-orogenic Cu–Ni sulfide-bearing mafic–ultramafic complexes in Jilin Province, NE China

Northeastern (NE) China is a well-documented example of a collisional zone characterized by widespread post-orogenic granites and mafic–ultramafic complexes. Based on a study of the Hongqiling and Piaohechuan Cu–Ni sulfide-bearing mafic–ultramafic complexes in central Jilin province, we present geological, petrological, geochemical and geochronological data which indicates their post-orogenic origin.The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Zircon U–Pb SHRIMP analyses on a leucogabbro of the Hongqiling complex yield a weighted mean ²⁰⁶Pb–²³⁸U age of 216±5 Ma. The Piaohechuan complex is composed of gabbro, pyroxenite and dolerite, exposed as dikes. A plagioclase-bearing pyroxenite has a U–Pb zircon weighted mean ²⁰⁶Pb–²³⁸U age of 217±3 Ma, identical to that of the Hongqiling complex. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than the regional metamorphism (240 Ma) and syn-orogenic granitic magmatism (246±4 Ma). This suggests that these mafic–ultramafic complexes are post-orogenic in origin. The age data also indicated a short period of lithospheric stabilization of about 30 Ma after cessation of orogenic activity.Geochemical investigation indicates that the primary mafic magma was a lithospheric mantle-derived basalt resulting from the upwelling of asthenosphere due to lithospheric delamination during post-orogenic processes. The magmatic source was contaminated by a small amount of crustal material, and subsequent crystal fractionation resulted in the Cu–Ni mineralization.The widespread occurrence of mafic–ultramafic complexes in the Xing'an–Mongolian Orogenic Belt of NE China and in the Altay–Tianshan–Junggar Orogenic Belt of Northern Xinjiang indicates that mafic intrusions are an important magmatic suite that evolved during post-orogenic processes. Portions of this mafic magma could have underplated the lower crust, and served as the heat source for associated late-stage granitic magmas.     

Whose carbon is burnable? Equity considerations in the allocation of a “right to extract”

Carbon emissions—and hence fossil fuel combustion—must decline rapidly if warming is to be held below 1.5 or 2 °C. Yet fossil fuels are so deeply entrenched in the broader economy that a rapid transition poses the challenge of significant transitional disruption. Fossil fuels must be phased out even as access to energy services for basic needs and for economic development expands, particularly in developing countries. Nations, communities, and workers that are economically dependent on fossil fuel extraction will need to find a new foundation for livelihoods and revenue. These challenges are surmountable. In principle, societies could undertake a decarbonization transition in which they anticipate the transitional disruption, and cooperate and contribute fairly to minimize and alleviate it. Indeed, if societies do not work to avoid that disruption, a decarbonization transition may not be possible at all. Too many people may conclude they will suffer undue hardship, and thus undermine the political consensus required to undertake an ambitious transition. The principles and framework laid out here are offered as a contribution to understanding the nature of the potential impacts of a transition, principles for equitably sharing the costs of avoiding them, and guidance for prioritizing which fossil resources can still be extracted.     

Report of the International Astronomical Union Division I Working Group on Precession and the Ecliptic

The IAU Working Group on Precession and the Equinox looked at several solutions for replacing the precession part of the IAU 2000A precession–nutation model, which is not consistent with dynamical theory. These comparisons show that the (Capitaine et al., Astron. Astrophys., 412, 2003a) precession theory, P03, is both consistent with dynamical theory and the solution most compatible with the IAU 2000A nutation model. Thus, the working group recommends the adoption of the P03 precession theory for use with the IAU 2000A nutation. The two greatest sources of uncertainty in the precession theory are the rate of change of the Earth’s dynamical flattening, ΔJ₂, and the precession rates (i.e. the constants of integration used in deriving the precession). The combined uncertainties limit the accuracy in the precession theory to approximately 2 mas cent⁻². Given that there are difficulties with the traditional angles used to parameterize the precession, z_A, ζ_A, and θ_A, the working group has decided that the choice of parameters should be left to the user. We provide a consistent set of parameters that may be used with either the traditional rotation matrix, or those rotation matrices described in (Capitaine et al., Astron. Astrophys., 412, 2003a) and (Fukushima Astron. J., 126, 2003). We recommend that the ecliptic pole be explicitly defined by the mean orbital angular momentum vector of the Earth–Moon barycenter in the Barycentric Celestial Reference System (BCRS), and explicitly state that this definition is being used to avoid confusion with previous definitions of the ecliptic. Finally, we recommend that the terms precession of the equator and precession of the ecliptic replace the terms lunisolar precession and planetary precession, respectively.     

Experimental hydrogen isotope studies,II. Fractionations in the systems epidote-NaCl-H2O,epidote-CaCl2-H2O and epidote-seawater,and the hydrogen isotope composition of natural epidotes

The hydrogen isotope fractionation factors between epidote and aqueous 1 M and 4 M NaCl, 1 M CaCl₂ solutions, and between epidote and seawater, have been measured over the temperature range 250–550°C over which the degree of dissociation of dissolved species varies significantly. Measured fractionations at 350°C are decreased by up to 12‰, 9‰ and 7‰ relative to pure water in seawater, 1 M CaCl₂ and 1 M NaCl respectively, while above 500°C fractionations are not measurably dependent on fluid composition. Water—solution fractionation factors are derived which are generally applicable to the correction of mineral—water hydrogen isotope fractionations for the composition of the fluid phase.The hydrogen isotope compositions of natural epidotes are interpreted in the light of experimental fractionation data for situations where temperature, δD (fluid), and, in some cases, fluid chemistry, are independently known. Epidotes from active geothermal systems have hydrogen isotope quench temperatures consistent with or close to measured well temperatures unless the measured temperature has declined substantially since epidote formation or there is uncertainty in the D/H ratio of the water associated with the epidote because of isotopic heterogeneity in the well waters. Hydrothermal and metamorphic epidotes show closure temperatures of 175–225°C and 200–250°C. There is no evidence that retrograde metamorphic fluids, if present, are isotopically different from prograde fluids.The water-solution fractionations indicate strong solute-solvent interactions between 250 and 450°C and imply that both dissociated and associated species contribute to the fractionation effects through modification of the orientations and structure of the water molecules. Solute-solvent interactions become negligible at temperatures around 550°C.     

Impact of dynamic feedbacks between sedimentation,sea-level rise,and biomass production on near-surface marsh stratigraphy and carbon accumulation

Salt marshes accrete both organic and inorganic sediments. Here we present analytical and numerical models of salt marsh sedimentation that, in addition to capturing inorganic processes, explicitly account for above- and belowground organic processes including root growth and decay of organic carbon. The analytical model is used to examine the bias introduced by organic processes into proxy records of sedimentation, namely ¹³⁷Cs and ²¹⁰Pb. We find that accretion rates estimated using ²¹⁰Pb will be less than accretion rates estimated using the ¹³⁷Cs peak in steadily accreting marshes if (1) carbon decay is significant and (2) data for ²¹⁰Pb extend below the ¹³⁷Cs peak. The numerical model expands upon the analytical model by including belowground processes such as compaction and root growth, and by explicitly tracking the evolution of aboveground biomass and its effect on sedimentation rates. Using the numerical model we explore how marsh stratigraphy responds to sediment supply and the rate of sea-level rise. It is calibrated and tested using an extensive data set of both marsh stratigraphy and measurements of vegetation dynamics in a Spartina alterniflora marsh in South Carolina, USA. We find that carbon accumulation in marshes is nonlinearly related to both the supply of inorganic sediment and the rate of sea-level rise; carbon accumulation increases with sea-level rise until sea-level rise reaches a critical rate that drowns the marsh vegetation and halts carbon accumulation. The model predicts that changes in carbon storage resulting from changing sediment supply or sea-level rise are strongly dependent on the background sediment supply: if inorganic sediment supply is reduced in an already sediment poor marsh the storage of organic carbon will increase to a far greater extent than in a sediment-rich marsh, provided that the rate of sea-level rise does not exceed a threshold. These results imply that altering sediment supply to estuaries (e.g., by damming upstream rivers or altering littoral sediment transport) could lead to significant changes in the carbon budgets of coastal salt marshes.     

Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.     

Forecasting Groundwater Temperature with Linear Regression Models Using Historical Data

Although temperature is an important determinant of many biogeochemical processes in groundwater, very few studies have attempted to forecast the response of groundwater temperature to future climate warming. Using a composite linear regression model based on the lagged relationship between historical groundwater and regional air temperature data, empirical forecasts were made of groundwater temperature in several aquifers in Switzerland up to the end of the current century. The model was fed with regional air temperature projections calculated for greenhouse‐gas emissions scenarios A2, A1B, and RCP3PD. Model evaluation revealed that the approach taken is adequate only when the data used to calibrate the models are sufficiently long and contain sufficient variability. These conditions were satisfied for three aquifers, all fed by riverbank infiltration. The forecasts suggest that with respect to the reference period 1980 to 2009, groundwater temperature in these aquifers will most likely increase by 1.1 to 3.8 K by the end of the current century, depending on the greenhouse‐gas emissions scenario employed.     

A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing

A potential zircon reference material (BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm³) from Sri Lanka was studied. Within‐grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g^?1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean ¹⁷⁶Hf/¹⁷⁷Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 10¹⁸ g^?1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA‐ICP‐MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW).     

长江中下游水阳江流域BZK0402孔多重地层划分及其冰后期海平面变化的沉积响应

[研究目的]开展水阳江流域标准孔BZK0402孔多重地层划分,探讨长江支流水阳江流域冰后期海平面变化的沉积响应以及古丹阳湖的成因和形成时代.[研究方法]以岩石地层为基础,在磁性地层和年代地层的双重约束下,对BZK0402孔进行多重地层划分.对比分析BZK0402孔和长江河谷、长江三角洲等邻区钻孔.[研究结果]BZK04...     

Analysis of stratigraphical sequences at Cocina Cave (Spain) using rare earth elements geochemistry

This study investigates the stratigraphical sequence of Cocina Cave (Spain) employing and testing for the first time the capability of rare earth elements as markers of human activities in caves. Located in Dos Aguas (Valencian Community, Spain), Cocina Cave is characterized by the presence of several Holocene archaeological deposits from the final Mesolithic to the present day and is a pivotal site for understanding the socio-ecological dynamics of the last hunter-gatherer inhabitants of the Iberian Peninsula and the transition to pastoral and agricultural economies in the Western Mediterranean. However, the identification of strata from particular time-periods in the cave is often difficult due to the homogeneity of layers, the poor archaeological record in some strata and the presence of severe disturbance phenomena. The methodological approach of this study consisted of cross-referencing rare earth elements and other chemical markers with the archaeological stratigraphical interpretation, in an attempt to not only support the identification of the anthropic contribution to the formation of Cocina Cave strata, but also to characterize and confirm different natural and occupational episodes, particularly those associated with hunter-gatherer, early agriculturalist, and shepherd activities. Sediments were collected from different excavation areas and analysed for major elements, trace elements, rare earth elements (REE), soil organic matter (SOM) amounts and pH. Multivariate statistics were employed to group samples according to their elemental profile, and these were then compared to the archaeological temporal interpretation. The obtained results showed that REE amount and fractionation geochemical processes were regulated by carbonates, phosphates and pH. The use of REE as markers was particularly useful as their concentrations and their calculated ratios and anomaly distributions were demonstrated to be highly consistent with the archaeological stratigraphical interpretation.