Geochemistry of Palaeoproterozoic volcanic rocks of the Iricoumé Group,Pitinga Mining District,Amazonian craton,Brazil

The Iricoumé Group includes 1.88 Ga volcanic units of the Iricoumé–Mapuera volcano-plutonic association, part of the Uatumã magmatic series in the Guyana shield portion of the Amazonian craton. In the Pitinga Mining District, these rocks consist dominantly of felsic trachyte to rhyolite, associated with voluminous ignimbrite and minor ash-fall tuffs and surge deposits. Mafic rocks are present as basaltic clasts within volcanic breccias, and mostly as mafic microgranular enclaves in the associated Mapuera plutonic rocks. The felsic rocks have high contents of SiO₂, FeO_t, K₂O, Rb, and alkalis; low TiO₂, CaO, Sr, Ba, Nb, Ta, and Eu; and show metaluminous to weakly peraluminous bulk-rock compositions. They exhibit alkaline geochemical features, expressed by Na₂O?+?K₂O averages of 8.8 wt.%, FeO_t/(FeO_t?+?MgO) ≥ 0.8, and high Ga/Al ratios, compatible with A-type magmas. The studied samples plot in the field of within-plate or post-collisional rocks in a (Nb?+?Y) versus Rb diagram. Nb/Y ratios indicate that they are comparable to A2-type rocks which, allied with their high LREE/Nb ratios, suggest that they were produced from mantle sources modified by previous subduction in a post-collisional setting. Two compositional populations of Ca-amphibole, a Mg-rich (actinolite to Mg-hornblende) and a Fe-rich one (Fe-edenite to Fe-pargasite, Fe-hornblende and Fe-actinolite), characterize the Iricoumé Group volcanics. The Fe-rich amphiboles crystallized under lower fO₂ and higher pressure conditions compared with the Mg-rich amphiboles, indicating different levels of crystallization or re-equilibration during ascent of the magmas. Zircons from rhyolites show trace-element compositions typical of magmatic crystals with high Th/U ratios, and REE patterns compatible with zircon-melt partition coefficients for silicic magma compositions. Their relatively lower zircon/rock partition coefficients are due to early apatite crystallization. Fractional crystallization mainly of plagioclase-hornblende and biotite-alkali feldspar with minor amounts of apatite explains the geochemical trends observed in the felsic Iricoumé volcanic rocks.     

Preservation of organic matter in the STONE 6 artificial meteorite experiment

The exposure of a carbonaceous siltstone sample to atmospheric entry, as part of the STONE 6 artificial meteorite experiment, has allowed a controlled investigation of the effect of heat shock during atmospheric entry on organic matter in carbonaceous meteorites and, potentially, sedimentary martian meteorites containing carbonaceous biomolecules. Thermal alteration is evident in an increase in structural order of the carbon (i.e. degree of graphitisation), preferential loss of thermally unstable compounds and substantial loss of extractable organic matter. There is a gradient of increasing alteration towards the outer, exposed margin of the rock, and also an increase in hydrocarbons that suggests outward migration following thermally-induced generation. The carbon has not been completely graphitised, and sufficient biomarker compounds survive to prove the biological origin of the organic matter. The experiment implies that meteorites of appropriate size could preserve evidence of biological activity on their parent body.     

Nitrile gas chemistry in Titan’s atmosphere

This work presents the first study of the gaseous products resulting from the partial dissociation of methane and nitrogen in the PAMPRE experimental setup simulating Titan’s atmospheric chemistry.Using cryogenic trapping, the gaseous products generated from the chemical reactions occurring in the reactor have been trapped. Analyses of these products by gas chromatography coupled to mass spectrometry have allowed the detection and identification of more than 30 reaction products. Most of them are identified as nitrile species, accompanied by aliphatic hydrocarbons and a few aromatics compounds. The observed species are in agreement with the data from the recent Cassini-Huygens mission as well as from other laboratory setups capable of dissociating nitrogen and methane. This work emphasizes the probable importance of nitrogen-bearing compounds in the chemistry taking place in Titan’s atmosphere.Furthermore, a quantification of mono-nitriles with saturated alkyl chains has been performed relatively to hydrogen cyanide and shows a power law dependence in their concentration. This dependence is consistent with the Cassini-INMS data and Titan’s photochemical models.An empirical relationship has been extracted from our experimental data: [C_xH_2x−1N] = 100x⁻⁵, where x is the number of carbon atoms in the nitrile molecule. This relationship can be directly used in order to foretell the concentration of heavier nitriles induced by chemistry in Titan’s atmosphere.     

亥废料处置概念库近场热-水-应力耦合模型及数值分析

特别考虑了缓冲层中温度梯度水分扩散、水蒸汽扩散对水连续性及能量守恒的影响，进一步完善了所建立的分析饱和-非饱和介质中热-水-应力耦合现象的控制方程，并针对试验资料，使用所开发的有限元程序对一个核废料处置概念库近场的热-水-应力耦合过程进行了数值模拟，考察了缓冲层及岩体中若干点的温度、饱和度、孔隙水压力及主应力的变化、分布情况，并将部分结果与国外类似软件的计算数据作了对比，结果显示，在定性和定量上二者的规律有某种一致性，从而得出了一定的认识。     

Multi-scale analysis of disturbance regimes in the northern Chihuahuan Desert

Remote sensing facilitates cross-scale validation, enables analysis of processes and patterns in time and space, and is thus viable for the conduct of earth system science. Multi-scale analyses of natural vegetation patterns and processes in the northern Chihuahuan Desert show that natural vegetation is capable of recovering from short-term, high intensity disturbances such as an atomic bomb blast. In contrast, mesquite dunelands persist on other sites grazed before the blast, showing the Chihuahuan is less resilient to long-term low intensity disturbances. A geographic information system (GIS) was used to register historical Landsat Multi-Spectral Scanner (MSS) data acquired over Trinity National Historic Site (TNHS), New Mexico, and the vicinity. Aerial and ground photography provide supporting detail, at finer scales, regarding the distribution and pattern of natural vegetation at TNHS Ground Zero and adjacent weapons impact targets. Aside from initial mechanical or thermal damage to vegetation from the first atomic test over a half century ago, analyses of vegetation at satellite and airphoto scales show no apparent persistent blast effects around TNHS.     

喀斯特地区梯级水库建造对水化学分布的影响

为深入了解河流梯级筑坝对喀斯特地区河流水化学分布的影响,于2017年1、4、7和10月别对乌江干流洪家渡水库(多年调节)、乌江渡水库(季调节)和索风营水库(日调节) 3个具有不同滞留时间的水库进行水样采集,分析入库水、坝前剖面水和下泄水的水化学特征,探讨河流梯级筑坝对水化学分布及风化速率估算的影响.研究结果表明:3个水库深层水比表层水HCO3-浓度分别高12.9%、5.5%和8.0%,Ca²⁺浓度分别高15.9%、2.4%和8.5%.河流梯级筑坝一定程度上改变了水体水化学组成,从而影响碳酸盐岩风化速率估算.整体上,洪家渡水库、索风营水库和乌江渡水库的全年风化速率变化范围分别为:-1.7%～15.4%、-5.6%～1.1%和-0.3%～3.4%.河流筑坝作用对风化速率估算及主量离子浓度的影响:HCO₃^-与Ca²⁺浓度分布均为:洪家水库>乌江渡水库>索风营水库,这与水体滞留时间长短规律一致,表明水体滞留时间影响着水化学的组成分布.同时水体离子浓度表现出明显的季节性差异,丰水期各水库变化率明显...     

奠基海洋化学研究,助推海洋科学发展——中国科学院海洋研究所海洋化学研究70年

本文系统总结了中国科学院海洋研究所建所70年来,海洋化学研究的发展历程和主要科学贡献,在此基础上,提出了海洋化学的发展愿景。建国初期的中科院海洋研究所是我国海洋化学研究的主要奠基者和引领者,70年来一直是我国化学海洋学、海洋生物资源化学利用以及海洋腐蚀与防护等领域的中坚力量,为中国海洋化学的发展做出了不可替代的重大贡献。1950—1990年,系统获得了渤黄东海重要化学要素的分布特征,发现了黄东海溶解氧存在最大值系冬季保持而来;构建了大型海藻经济组分提取的系统化方案,奠定了世界最大规模海藻化学工业的基础;系统开拓了我国海洋腐蚀与防护领域的研究。1990—2020年,中科院海洋研究所的海洋化学研究全面与国际接轨,系统研究了中国近海化学要素特别是微痕量无机/有机组分的分布迁移转化特征及机制,提出了海洋生物地球化学研究的系统思路;研制成功褐藻多糖硫酸酯治疗肾衰新海洋药物,发现大量具有生物活性的海洋活性物质,在应用海洋化学领域也有重要进展。