Water and Iron effect on the P-T-x coordinates of the 410-km discontinuity in the Earth upper mantle

We performed multi-anvil experiments in the system MgO-SiO₂ ± H₂O at 13.0–13.7 GPa and 1,025–1,300°C and in the system MgO-FeO-SiO₂ ± H₂O, under reducing conditions, at 11.0–12.7 GPa and 1,200°C, to depict the effect of H₂O on the P-T-x coordinates of the 410-km discontinuity, i.e. the olivine–wadsleyite phase boundary. The charges were investigated with Electron Microprobe (EMP), Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Secondary Ion Mass Spectrometry (SIMS) and Electron Energy Loss Spectroscopy (EELS). We observe in the MgO-SiO₂-H₂O system at 1,200°C a 0.6 GPa shift of the phase boundary to lower pressure compared to dry conditions, due to the stronger water fractionation into wadsleyite (wad) rather than in olivine (ol). In the MgO-FeO-SiO₂-H₂O system, we reproduced the triple point, i.e. observed coexisting hydrous ol, wad and ringwoodite (ring). SIMS H quantifications provided partitioning coefficients for water: D_\textwad/ol^\textwater D_{\text{wad/ol}}^{\text{water}}  ~ 3.7(5) and D_\textring/ol^\textwater D_{\text{ring/ol}}^{\text{water}}  ~ 1.5(2) and D_{\textwad/ring}^\textwater D_{\text{wad/ring}}^{\text{water}}  ~ 2.5(5). For a bulk composition of x _Fe = 0.1, our data indicate only a slight difference in the width of the loop of the two phase field ol–wad under hydrous conditions compared to dry conditions, i.e. no broadening with respect to composition but a shift to lower pressures. For bulk compositions of x _Fe > 0.2, i.e. in regions where wad–ring and ol–ring coexist, we observe, however, an unexpected broadening of the loops with a shift to higher iron contents. In total, the stability field of hydrous wad expands in both directions, to lower and higher pressures. Fe³⁺ concentrations as determined by EELS are very low and are expected to play no role in the broadening of the loops.     

Mechanisms of Archean crust formation inferred from high-precision HFSE systematics in TTGs

It has been proposed that Archean tonalitic-trondhjemitic-granodioritic magmas (TTGs) formed by melting of mafic crust at high pressures. The residual mineralogy of the TTGs (either (garnet)-amphibolite or rutile-bearing eclogite) is believed to control the trace element budget of TTGs. In particular, ratios of high-field-strength elements (HFSE) can help to discriminate between the different residual lithologies. In order to place constraints on the source mineralogy of TTGs, we performed high-precision HFSE measurements by isotope dilution (Nb, Ta, Zr, Hf) together with Lu-Hf and Sm-Nd measurements on representative, ca. 3.85-2.8 Ga TTGs and related rock types from southern West Greenland, W-India and from the Superior Province. These measurements are complemented by major and trace element data for the TTGs. Texturally homogeneous early Archean (3.85-3.60 Ga old) and Mesoarchean (ca. 3.1-2.8 Ga old) TTGs have both low Ni (<11 ppm) and Cr contents (<20 ppm), indicating that there was little or no interaction with mantle peridotite during ascent. Ratios of Nb/Ta in juvenile Eoarchean TTGs range from ca. 7 to ca. 24, and in juvenile Mesoarchean TTGs from ca. 14 to ca. 27. Even higher Nb/Ta (14-42) were obtained for migmatitic TTGs and intra-crustal differentiates, most likely mirroring further fractionation of Nb from Ta as a consequence of partial melting, fluid infiltration and migmatisation. In the juvenile TTGs, positive correlations between Nb/Ta and Gd/Yb, La/Yb, Sr/Y, Zr/Sm and Zr/Nb are observed. These compositional arrays are best explained by melting of typical Isua tholeiites in both, the rutile-bearing eclogite stability field (>15 kbar, high Nb/Ta) and the garnet-amphibolite stability field (10-15 kbar, low Nb/Ta). With respect to the low end of Nb/Ta found for TTGs, there is currently some uncertainty between the available experimental datasets for amphibole. Independent of these uncertainties, the TTG compositions found here still require the presence of both endmember residues. A successful geological model for the TTGs therefore has to account for the co-occurrence of both low- and high-Nb/Ta TTGs within the same geologic terrane. An additional feature observed in the Eoarchean samples from Greenland is a systematic co-variation between Nb/Ta and initial εHf(t), which is best explained by a model where TTG-melting occured at progressively increasing pressures in a pile of tectonically thickened mafic crust. The elevated Nb/Ta in migmatitic TTGs and intra-crustal differentiates can shed further light on the role of intra-crustal differentiation processes in the global Nb/Ta cycle. Lower crustal melting processes at granulite facies conditions may generate high-Nb/Ta domains in the middle crust, whereas mid-crustal melting at amphibolite facies conditions may account for the low Nb/Ta generally observed in upper crustal rocks.     

Review of effects of radiation damage on the luminescence emission of minerals, and the example of He-irradiated CePO4

The accumulation of structural damage that is created in minerals upon corpuscular irradiation, has two apparently contrarious effects on their luminescence behaviour. First, irradiation may cause the generation of luminescent defect centres, which typically results in broad-band emissions. Such defect emissions are characteristic of low levels of radiation damage. Second, radiation damage depletes in general the luminescence of minerals, which is associated with broadenings and intensity losses of individual emission lines. Minerals that have suffered elevated levels of irradiation hence tend to be virtually non-luminescent. This review paper aims at giving an overview of the possible correlations of radiation damage and emission characteristics of minerals. After a brief, introductory summary of the damage-accumulation process and its causal corpuscular radiation, an array of examples is presented for how internal and/or external irradiation may change appreciably the emission of rock-forming and accessory minerals. As a detailed example for the complexity of changes of emissions upon damage accumulation, preliminary results of a case study of the photoluminescence (PL) of synthetic CePO₄ irradiated with 8.8 MeV He ions are presented. Irradiation-induced spectral changes include (i) the initial creation, and subsequent depletion, of a broad-band, defect-related PL emission of orange colour, and (ii) gradual broadenings and intensity losses of PL lines related to electronic transitions of rare-earth elements, eventually leading to gradual loss of their splitting into multiple Stark levels (shown for the ⁴F_3/2 → ⁴I_9/2 transition of Nd³⁺).     

Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos,Western Australia

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble‐based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum‐Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U‐series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Anthropogenic influence on the degradation of an urban lake - The Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil

The artificial reservoir Lagoa da Pampulha in central Brazil has been increasingly affected by sediment deposition and pollution from urban and industrial sources. This study investigates water chemistry and heavy metal concentrations and their fractionation in the lake sediment using ICP-OES, ICP-MS, and XRD analyses. Fractionation analysis was done by sequential extraction under inert gas as well as after oxidation. The lake exhibits a permanent stratification with an oxygen-free hypolimnion below 2 m depth. Nutrient concentrations are enriched for phosphorous components (SRP, PO₄). In the sediment it was not possible to detect oxygen. Carbon, sulfur, and most of the analyzed heavy metals are enriched in the top sediment layer with a pronounced downward decrease, indicating the presence of an anthropogenic influence. Statistical analysis, including correlations and a Principal Component Analysis (PCA) of depth-related total concentration data, helps to distinguish presumably anthropogenic heavy metals from geogenic components. Some samples with high element concentrations in the sediment also show elevated concentrations in their pore water. Analyses of element distribution between sediment and pore water suggest a strong bonding of heavy metals to the anoxic sediment. The trend towards elevated solubility in the pore water of oxidized samples is clear for most of the analyzed elements. Fractionation analysis reveals characteristic associations of selected elements to specific mineral bonding forms. In addition, it indicates that the behavior of heavy metals in the sediment is strongly influenced by organic substances. These substances provide buffering against oxidation, acidification, and metal release. The high nutrient loading causes reducing conditions in the lake sediment. These conditions trigger the accumulation of sediments rich in S²⁻, which stabilizes the fixation of heavy elements. In the future, care must be taken to reduce the supply of contaminants and to prevent the release of heavy metals from sediments dredged for remediation purposes.     

Climate change impacts on bedload transport in alpine drainage basins with hydropower exploitation

Sediment transport is known to have a significant impact on hydropower infrastructures and changes in sediment transport rates are important for sediment management measures and hydroelectricity production. In this study, we present how climate change may affect bedload transport in 66 high alpine catchments used by hydropower companies in the Valais, Switzerland. Future sediment yield is estimated with a runoff‐based sediment transport model for the two future 30 year time periods 2021–2050 and 2070–2099. The analysis is integrated into a modelling chain in which error‐corrected and downscaled climate scenarios generated in the framework of the ENSEMBLES project are coupled to the hydrological model PREVAH, glacier retreat and bedload transport. To calibrate the sediment transport model, we used the observed sediment volumes in water intakes and reservoirs if such data were available. The results obtained show on average a decrease of sediment yield due to the reduced runoff generation during summer, especially for the scenario period 2070–2099. A shift of the seasonal sediment transport regime with a current maximum during July and August to earlier months in the year is predicted. Projections of future sediment yield rely on the accuracy of the individual modeling chain elements. The different sources of uncertainty are discussed qualitatively. Copyright © 2015 John Wiley & Sons, Ltd.     

A conceptual framework for multi-regional climate change assessments for international market systems with long-term investments

A conceptual framework for climate change assessments of international market systems that involve long-term investments is proposed. The framework is a hybrid of dynamic and static modeling. Dynamic modeling is used for those system components for which temporally continuous modeling is possible, while fixed time slices are used for other system components where it can be assumed that underlying assumptions are held constant within the time slices but allowed to vary between slices. An important component of the framework is the assessment of the “metauncertainty” arising from the structural uncertainties of a linked sequence of climate, production, trade and decision-making models. The impetus for proposing the framework is the paucity of industry-wide assessments for market systems with multiple production regions and long-term capital investments that are vulnerable to climate variations and change, especially climate extremes. The proposed framework is pragmatic, eschewing the ideal for the tractable. Even so, numerous implementation challenges are expected, which are illustrated using an example industry. The conceptual framework is offered as a starting point for further discussions of strategies and approaches for climate change impact, vulnerability and adaptation assessments for international market systems.     

李希霍芬对中国地质和地球科学的贡献

斐迪南·冯·李希霍芬出生于1833年。少年时的教育和生活环境使他对地质学产生了兴趣。当他还是小孩子的时候,就随父母游历了家乡的许多地方,并且利用暑假到阿尔卑斯去旅行。在柏林学习地质学的时候,就显示出他宽厚的知识基础,他很快就意识到对他而言,未来工作的目标就是成为一个科学家。1859年,为了获得财政支持进行欧洲以外地区的研究,李希霍芬申请参加了普鲁士政府向东亚派遣的一支探险队,开始了他最初对中国地质的研究。1862年当探险队的成员开始返回柏林,他独自到了上海开始他自己在中国的研究工作。只是由于太平天国起义,他的计划没能立即实现。1868年新年前夕,他和他的朋友对全球地质勘探的状况做了一个回顾,认为中国无论在科学上,还是在应用上都是最有研究价值的国家之一。于是他选择了中国作为他进行地质研究的对象。在参考大量文献的基础上,他制定了详细的研究方向和工作方法。李希霍芬希望建立一个系统的中国地质学的基础。他认为野外工作是第一位的。除了对可开采的矿床进行了估计,他还特别注意了中国煤炭沉积的储量和产量。在1868到1872年期间,他在中国先后进行了7次旅行。他是第一位对中国地质从基础上进行研究的外国地质学家。旅行的资金有一部分是来自加利福尼亚银行和上海商业会馆。他提交了一份地区经济信息的报告,这个报告包括了中国的交通、贸易路线,煤矿的形成、品位和储量、可采性以及在世界市场上的竞争力等。他重要的科学文献是关于经济、运输和人口地理学。从他的著作《中国》我们可以看出,他对于“丝绸之路”的命名是在汉学家、古典文献学家以及地图学家共同合作研究之前。在综合大量的文献后,他在地图上详细地标注了“丝绸之路”,并且讨论了汉朝及其以后历史时期内中国境内主要的贸易路线。由于丝绸一直都是重要的贸易商品,因此他把这条贸易路线称之为“丝绸之路”。对于社会、经济问题与地质问题的综合认识,使他同时又成为一个地理学家。李希霍芬和德国的地图工作者一起开创了一种新的地形的描绘方法,并且修正了当时的中国地图,使中国地图有了更为详尽的内容。对比当时在中国出版的地图,他们绘制的地图在很多方面是全新的,如他们采用图解法(graphicpresentationsofmontains)来代表山脉和其他的地形形态特征。在地质学领域,他绘制了中国地质图,及《中国地图集》中的地形图,连同后来出版的4卷《中国》书稿中大量的横断面和地层剖面,奠定了中国乃至东亚的地质学基础。但是他从来没有把制图作为他旅行的一个主要目的。对他来说,制图只是作为来证实他的野外观察的一个方法,以尽可能正确地体现出地貌的基本特征。李希霍芬到中国旅行的最主要的目的是研究中国地质。他是第一个把中国地质按着现代组成物的分布、序列,发展成为一个系统。可以认为,他是把中国地质学发展成为一门科学的创始人。古生物学和地层学的知识使他很快就认识到了中国地质结构的原理。他的综合知识使他可以在地图上系统地标绘出他所观察到的现象。他的主要成果集中体现在《中国地图集》中的27张地质图,《中国》书稿中另外14张地质图以及大量的剖面图。另外矿产资源也是他研究的主要的内容。他不仅研究了煤炭资源,同时也经常记录贵金属矿产资源。他是最早注意到中国黄土具有风成特征的地质学家。他在研究黄土剖面时,注意到大部分没有层理的沉积物都保存有大量的陆生软体动物的壳。由此,他得出与前人相反的结论,认为黄土不是湖相沉积物,而是风成沉积物。并以北美大草原所见到的草将粉尘固定的过程作为他风成假设的证据。他认为黄土沉积是草原环境下形成的,当时的植被是草原。并且认识到粉尘来源于西部和北部的中亚的沙漠地区。他只是没能将冰期、间冰期的粉尘沉积加以区分。他研究的另一个科学领域是地貌学。在地貌学中他是最先描述一些地表变化过程的先驱者之一。正如他一直意识到的自然与人类活动的相互关系一样,他同样将地球生态系统看作是地质结构、地貌过程、与气候有关的生态环境和人类活动所组成的一个复合体。他是最早萌生地球系统的科学思想的科学家。李希霍芬对中国的研究起初并没有得到人们的重视。直到他的《中国》出版以后,他对中国地质学和地理学的影响才明显起来:他的著作和地图很快就传入中国,在学术界被广泛地阅读和讨论;他的书是地质学和地理学专业的基础教材。不仅在中国,在世界范围内,他的发现也得到了认可,并获得了很高的评价。19世纪末,世界上没有哪个科学家像他那样了解中国和东亚。他也从一个地质学家成为一个跨越多个学科的大科学家,他的影响在他的那个时代体现在科学领域的很多学科之中。李希霍芬在中国现在仍然有很高的赞誉。他的方法学的研究以及他的《探险家指南》,对于年轻的地质科学工作者,仍然具有指导意义。他的地球系统科学的思想对当前土地退化、生态不平衡等环境问题的解决仍然起着指导性作用。     

How to Include Ignorance into Hydrocarbon-Resource Assessments? A Case Study Applied to the Presence of Source Rock at the Argentine Deep Water Margin

The underexplored deep Argentine continental margin may be a prospective area for hydrocarbon resources. This study quantifies the degree of certainty about a fundamental part in a petroleum system, the presence of source rocks. Probability theory and, in particular, Bayesian networks provide powerful assessment tools based on incomplete knowledge. However, they should not be applied uncritically in cases where necessary assumptions like independence are not fulfilled or prior probabilities are not known. We discuss the difference between a low probability and the ignorance of a hypothesis, and apply an alternative method to the assessment of source rock presence. The results of this probabilistic argumentation system coincide with the intuitive judgement, stating that there is a quantifiable evidence for a source rock, but no evidence against it.