Petrogenesis of the Piqiang mafic-ultramafic layered intrusion and associated Fe-Ti-V oxide deposit in Tarim Large Igneous Province,NW China

ABSTRACT

The Piqiang intrusion is one of the two important ma?c-ultrama?c layered intrusions that host giant Fe-Ti-V oxide deposits in the Permian Tarim Large Igneous Province, NW China. The intrusion mainly consists of gabbro, anorthosite and minor plagioclase-bearing clinopyroxenite in the marginal zone. Disseminated to massive Fe-Ti oxide ores occur as layers and lenses within the gabbro. SHRIMP zircon U-Pb results from both a gabbro from the Piqiang intrusion and a granite from the surrounding granitic dyke yield ages of ~270 Ma. Geochemically, the Piqiang silicate rocks are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), moderately depleted in high ?eld strength elements (HFSE), and have a limited range of Sr-Nd-Hf isotopic compositions. The similar mineralogy, mineral compositions, and trace element characteristics of the layered units suggest that all the rocks are co-magmatic. The parental magma is Fe-Ti-rich and is akin to the most primitive diabasic dyke which is associated with the Piqiang intrusion. Partial melting of the Tarim mantle plume with involvement of a subduction-metasomatized lithospheric mantle source best explains the geochemistry and petrogenesis of the parental magmas of the Piqiang intrusion. We propose that the lithospheric mantle source may have been metasomatized by subduction-related materials and the metasomatic enrichment of this source region which may be correlated with oceanic sediment recycling during southward subduction of the South Tianshan oceanic slab during the Early-Middle Paleozoic. Crystal settling and mechanical sorting is the predominant process responsible for the formation of the massive Fe-Ti oxide ores in the Piqiang intrusion. Central to ore formation is a combination of the protracted differentiation history of a Fe-Ti-enriched parental magma and the later addition of external H₂O from the country rocks to the slowly cooling magma chamber.     

Intercomparison of NO column measurements during MAP/GLOBUS 1985

Column measurements of nitric oxide were made using several techniques during the MAP/GLOBUS campaign in France in September 1985. The data sets are nearly co-located and simultaneous, therefore allowing a valid intercomparison of the various measurement methods. The range of altitudes sampled differs from instrument to instrument. This complicates the comparison because the data sets are to some extent complementary. The NO distributions apparently vary significantly from day to day, and possibly over shorter timescales. Changes in dynamics may be responsible for these variations. The results from the instruments which measure in the infrared and the ultraviolet are self-consistent, and show good agreement with photochemical predictions. On 19 September, when the intercomparison was made, the profile measured by the in-situ chemiluminescent instrument differed significantly from the predicted profile, and the measured columns were generally higher.     

First-Order Chemistry in the Surface-Flux Layer

We have discussed the behavior of a non-conserved scalar in the stationary, horizontally homogeneous, neutral surface-flux layer and, on the basis of conventional second-order closure, derived analytic expressions for flux and for mean concentration of a gas, subjected to a first-order removal process. The analytic flux solution showed a clear deviation from the constant flux, characterizing a conserved scalar in the surface-flux layer. It decreases with height and is reduced by an order of magnitude of the surface flux at a height equal to about the typical mean distance a molecule can travel before destruction. The predicted mean concentration profile, however, shows only a small deviation from the logarithmic behavior of a conserved scalar. The solution is consistent with assuming a flux-gradient relationship with a turbulent diffusivity corrected by the Damköhler ratio, the ratio of a characteristic turbulent time scale and the scalar mean lifetime. We show that if we use only first-order closure and neglect the effect of the Damköhler ratio on the turbulent diffusivity we obtain another analytic solution for the profiles of the flux and the mean concentration which, from an experimental point of view, is indistinguishable from the first analytic solution. We have discussed two cases where the model should apply, namely NO which, by night, is irreversibly destroyed by interaction with mainly O₃ and the radioactive ²²⁰Rn. Only in the last case was it possible to find data to shed light on the validity of our predictions. The agreement seemed such that a falsification of our model was impossible. It is shown how the model can be used to predict the surface flux of ²²⁰Rn from measured concentration profiles.     

Policy options to streamline the carbon market for agricultural nitrous oxide emissions

The majority of emissions of nitrous oxide – a potent greenhouse gas (GHG) – are from agricultural sources, particularly nitrogen fertilizer applications. A growing focus on these emission sources has led to the development in the United States of GHG offset protocols that could enable payment to farmers for reducing fertilizer use or implementing other nitrogen management strategies. Despite the development of several protocols, the current regional scope is narrow, adoption by farmers is low, and policy implementation of protocols has a significant time lag. Here we utilize existing research and policy structures to propose an ‘umbrella’ approach for nitrogen management GHG emissions protocols that has the potential to streamline the policy implementation and acceptance of such protocols. We suggest that the umbrella protocol could set forth standard definitions common across multiple protocol options, and then modules could be further developed as scientific evidence advances. Modules could be developed for specific crops, regions, and practices. We identify a policy process that could facilitate this development in concert with emerging scientific research and conclude by acknowledging potential benefits and limitations of the approach.

Key policy insights

• Agricultural greenhouse gas market options are growing, but are still underutilized

• Streamlining protocol development through an umbrella process could enable quicker development of protocols across new crops, regions, and practices

• Effective protocol development must not compromise best available science and should follow a rigorous pathway to ensure appropriate implementation

     

Trace gas measurements during aircraft flights in the tropopause region over Europe and North Africa

During aircraft flights in May 1981 from Munich (40°N) to north of the Spitsbergen Islands (82°N) and to Monrovia, Liberia (6°N), air samples were obtained in the altitude range of 8 to 11 km and during the ascents and descents near the airports. These samples have been analyzed for the trace gas mixing ratios of CH₄, CO and N₂O. The results of these analyses are presented and discussed.The results provide new evidence of tropospheric-stratospheric exchange events in the vicinity of the subpolar and subtropical tropopause foldings and possibly show a case of transport of CO-enriched air in the upper troposphere above the North Atlantic Ocean.     

农田生态系统温室气体排放研究进展

自1985年起,中国科学院大气物理研究所利用自行设计制造的自动观测仪器系统,历时十六年先后对我国四大类主要水稻产区的甲烷排放规律及其与土壤、气象条件和农业管理措施的关系进行了系统野外观测实验,并对稻田甲烷产生、转化和输送机理进行了理论研究,探讨了控制稻田甲烷排放的实用措施,建立了估算和预测稻田甲烷排放的数值模型.在甲烷排放的时空变化规律和转化率研究方面有一系列新的发现,在稻田甲烷产生率、排放率及其与环境条件的关系方面取得一系列新的成果,以充分证据改变了国际上关于全球和中国稻田甲烷排放总量的估算.在对稻田甲     

Studies of Nitrous Oxide Emission from Farmlands in North China

Measurements of nitrous oxide emission from agricultural lands were conducted. The results show that nitrous oxide fluxes on several soils are at the range of 2-60 μg . N / m2 h. Factors influencing the production rates of nitrous oxide from the soils, such as soil temperature, soil moisture and fertilization, are discussed. The calculated amount of nitrous oxide emission from China farmlands is 9.8 × 107 Kg . N per year, which accounts for about 10% of the total source strength in China areas.     

Laboratory study of the rates and products of the phototransformations of naphthalene adsorbed on samples of titanium dioxide,ferric oxide,muscovite, and fly ash

The photodegradation of naphthalene (NPH), chosen as a model of polynuclear aromatic pollutants, has been studied in the presence of a layer of four water-insoluble inorganic solids which can be found in the troposphere (TiO₂, Fe₂O₃, muscovite, and a fly ash sample). Direct photolysis of NPH is negligible at >340 nm. Dark adsorption of NPH on TiO₂ (mainly anatase, nonporous, 50 m² g^–1) at 293 K corresponds to a surface coverage ofca. 50% at equilibrium. Under these conditions (saturated surface), the stationary-state photocatalytic degradation reaches 0.4 molecule nm^–2 h^–1 (>340 nm, radiant fluxca. 22 mW cm^–2). Dioxygen is required and its partial pressure in air is such that the degradation is zero order in O₂. Water vapor markedly increases the rate. The other particulates have also an effect, less important than that of TiO₂, however quite noticeable with respect to surface area unit for the fly ash sample which contains 3.2% Fe₂O₃. Apart from 1,4-naphthoquinone, which is the main intermediate product in all cases, 2-naphthol, phthalide, phthaldialdehyde, phthalic acid, acetophenone, benzaldehyde, benzoic acid are also formed on dry TiO₂. Depending on their volatility, these compounds are transferred to the gas phase or remain principally adsorbed on the solid particles where they are further transformed. For instance, phthalic acid (or anhydride) and benzoic acid are generated from 1,4-naphthoquinone. Degradation mechanisms are briefly discussed.     

Kinetics of redox cycling of iron coupled with fulvic acid

The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10^–4 M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the > Fe^III-OH/Fe(II) wheel coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)₃(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.