Petrogenesis of low-δ<Superscript>18</Superscript>O quartz porphyry dykes,Koegel Fontein complex,South Africa

This paper investigates the origin of low-δ¹⁸O quartz porphyry dykes associated with the 144–133 Ma Koegel Fontein Igneous Complex, which was intruded during the initial phase of breakup of Africa and South America. The 25-km diameter Rietpoort Granite is the largest and youngest phase of activity, and is roofed by a 10-km diameter pendant of gneiss. Quartz porphyry (QP) dykes, up to 15 m in width, strike NW–SE across the complex. The QP dykes that intruded outside the granite have similar quartz phenocryst δ¹⁸O values (average 8.0‰, ± 0.7, n?=?33) to the granite (average 8.3?±?1.0, n?=?7). The QP dykes that intruded the roof pendant have quartz phenocrysts with more variable δ¹⁸O values (average 1.6‰, ± 2.1, n?=?55). In some cases quartz phenocrysts have δ¹⁸O values as low as ? 2.5‰. The variation in δ¹⁸O value within the quartz crystal population of individual dykes is small relative to the overall range, and core and rim material from individual quartz phenocrysts in three samples are identical within error. There is no evidence that quartz phenocryst δ¹⁸O values have been affected by fluid–rock interaction. Based on a ?_quartz?magma value of 0.6‰, magma δ¹⁸O values must have been as low as ? 3.1‰. Samples collected along the length of the two main QP dykes that traverse the roof pendant have quartz phenocryst δ¹⁸O values that range from +?1.1 to +?4.6‰, and ? 2.3 to +?5.6‰, respectively. These δ¹⁸O values correlate negatively (r = ? 0.96) with initial ⁸⁷Sr/⁸⁶Sr, which can be explained by the event that lowered δ¹⁸O values of the source being older than the dykes. We suggest that the QP dykes were fed by magma produced by partial melting of gneiss, which had been variably altered at high temperature by ¹⁸O-depleted meteoric water during global glaciation at ~?550 Ma. The early melts had variable δ¹⁸O value but as melt pockets interconnected during melting, the δ¹⁸O values approached that of average gneiss. Variable quartz phenocryst δ¹⁸O values in the same dyke can be explained by vertical emplacement, at variable rates of ascent along the dyke. The lateral variation in quartz, and hence magma δ¹⁸O value at a particular point along a single dyke would depend on the rate of ascent of magma at that point along the dyke, and the ‘age’ of the particular magma batch.     

Composition of barian mica in multiphase solid inclusions from orogenic garnet peridotites as evidence of mantle metasomatism in a subduction zone setting

Multiphase solid inclusions in minerals formed at ultra-high-pressure (UHP) provide evidence for the presence of fluids during deep subduction. This study focuses on barian mica, which is a common phase in multiphase solid inclusions enclosed in garnet from mantle-derived UHP garnet peridotites in the Saxothuringian basement of the northern Bohemian Massif. The documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source. Barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite KMg₃(Si₃Al)O₁₀(OH)₂, kinoshitalite BaMg₃(Al₂Si₂)O₁₀(OH)₂ and ferrokinoshitalite BaFe₃(Al₂Si₂)O₁₀(OH)₂. In addition to Ba (0.24–0.67 apfu), mica is significantly enriched in Mg (X_Mg ~ 0.85 to 0.95), Cr (0.03–0.43 apfu) and Cl (0.04–0.34 apfu). The substitution vector involving Ba in the I-site which describes the observed chemical variability can be expressed as BaFe^IVAlClK_?1Mg_?1Si_?1(OH)_?1. A minor amount of Cr and ^VIAl enters octahedral sites following a substitution vector ^VI(Cr,Al)₂□^VI(Mg,Fe)_?3 towards chromphyllite and muscovite. As demonstrated by variable Ba and Cl contents positively correlating with Fe, barian mica composition is partly controlled by its crystal structure. Textural evidence shows that barian mica, together with other minerals in multiphase solid inclusions, crystallized from fluids trapped during garnet growth. The unusual chemical composition of mica reflects the mixing of two distinct sources: (1) an internal source, i.e. the host peridotite and its garnet, providing Mg, Fe, Al, Cr, and (2) an external source, represented by crustal-derived subduction-zone fluids supplying Ba, K and Cl. At UHP–UHT conditions recorded by the associated diamond-bearing metasediments (c. 1100 °C and 4.5 GPa) located above the second critical point in the pelitic system, the produced subduction-zone fluids transporting the elements into the overlying mantle wedge had a solute-rich composition with properties of a hydrous melt. The occurrence of barian mica with a specific chemistry in barium-poor mantle rocks demonstrates the importance of its thorough chemical characterization.     

Apatite-hosted melt inclusions from the Panzhihua gabbroic-layered intrusion associated with a giant Fe–Ti oxide deposit in SW China: insights for magma unmixing within a crystal mush

The ～?2-km-thick Panzhihua gabbroic-layered intrusion in SW China is unusual because it hosts a giant Fe–Ti oxide deposit in its lower zone. The deposit consists of laterally extensive net-textured and massive Fe–Ti oxide ore layers, the thickest of which is ～?60 m. To examine the magmatic processes that resulted in the Fe enrichment of parental high-Ti basaltic magma and the formation of thick, Fe–Ti oxide ore layers, we carried out a detailed study of melt inclusions in apatite from a ～?500-m-thick profile of apatite-bearing leucogabbro in the middle zone of the intrusion. The apatite-hosted melt inclusions are light to dark brown in color and appear as polygonal, rounded, oval and negative crystal shapes, which range from ～?5 to ～?50 µm in width and from ～?5 to ～?100 µm in length. They have highly variable compositions and show a large and continuous range of SiO₂ and FeO_t with contrasting end-members; one end-member being Fe-rich and Si-poor (40.2 wt% FeO_t and 17.7 wt% SiO₂) and the other being Si-rich and Fe-poor (74.0 wt% SiO₂ and 1.20 wt% FeO_t). This range in composition may be attributed to entrapment of the melt inclusions over a range of temperature and may reflect the presence of µm-scale and immiscible Fe-rich and Si-rich components in different proportions. Simulating results for the motion of Si-rich droplets within a crystal mush indicate that Si-rich droplets would be separated from Fe-rich melt and migrate upward due to density differences in the interstitial liquid when the magma unmixed. Migration of the Si-rich, immiscible liquid component from the interstitial liquid caused the remaining Fe-rich melt in the lower part to react with plagioclase primocrysts (An_59–60), as evidenced by fine-grained lamellar intergrowth of An-rich plagioclase (An_79–84)?+?clinopyroxene in the oxide gabbro of the lower zone. Therefore, magma unmixing within a crystal mush, combined with gravitationally driven loss of the Si-rich component, resulted in the formation of Fe-rich, melagabbro and major Fe–Ti oxide ores in the lower part and Si-rich, leucogabbro in the upper part of the intrusion.     

Carbon costs and benefits of France’s biomass energy production targets

Background

Concern about climate change has motivated France to reduce its reliance on fossil fuel by setting targets for increased biomass-based renewable energy production. This study quantifies the carbon costs and benefits for the French forestry sector in meeting these targets. A forest growth and harvest simulator was developed for French forests using recent forest inventory data, and the wood-use chain was reconstructed from national wood product statistics. We then projected wood production, bioenergy production, and carbon balance for three realistic intensification scenarios and a business-as-usual scenario. These intensification scenarios targeted either overstocked, harvest-delayed or currently actively managed stands.

Results

All three intensification strategies produced 11.6–12.4 million tonnes of oil equivalent per year of wood-based energy by 2026, which corresponds to the target assigned to French wood-energy to meet the EU 2020 renewable energy target. Sustaining this level past 2026 will be challenging, let alone further increasing it. Although energy production targets can be reached, the management intensification required will degrade the near-term carbon balance of the forestry sector, compared to continuing present-day management. Even for the best-performing intensification strategy, i.e., reducing the harvest diameter of actively managed stands, the carbon benefits would only become apparent after 2040. The carbon balance of a strategy putting abandoned forests back into production would only break even by 2055; the carbon balance from increasing thinning in managed but untended stands would not break even within the studied time periods, i.e. 2015–2045 and 2046–2100. Owing to the temporal dynamics in the components of the carbon balance, i.e., the biomass stock in the forest, the carbon stock in wood products, and substitution benefits, the merit order of the examined strategies varies over time.

Conclusions

No single solution was found to improve the carbon balance of the forestry sector by 2040 in a way that also met energy targets. We therefore searched for the intensification scenario that produces energy at the lowest carbon cost. Reducing rotation time of actively managed stands is slightly more efficient than targeting harvest-delayed stands, but in both cases, each unit of energy produced has a carbon cost that only turns into a benefit between 2060 and 2080.

     

‘Filament’ marker beds in the Karababa-A Member (Turonian) of the Arabian platform,SE Turkey: Palaeo-environmental significance,stratigraphy and correlation potential

A ‘filament’ event bed/level corresponds to the occurrence of thin elongate calcitic, shells, or plates of pelagic, bivalve or crinoidal, origin, within pelagic, laminated and organic-matter rich limestones. These organic-rich limestones had been generally deposited under hypoxic/anoxic conditions in an outer-ramp environment. These thin elongate, bivalve shells, or crinoidal plates, are found broken in small pieces, disintegrated, or simply preserved parallel to bedding as almost complete specimens. Such ‘filament’ beds were spotted in SE Turkey in deposits, namely the Karababa-A Member, around the Cenomanian-Turonian boundary (C/TB) and above. On a global scale, these filament event beds illustrate sea-level rise related to eustacy and/or climatic change. The abundance of filaments close to the C/TB is a biological marker of high organic productivity resulting from a climatic change to warmer conditions. The prevailing higher sea-level conditions were then favourable to the accumulation and preservation of organic-rich facies, characteristic of the Oceanic Anoxic Event 2 (OAE2). Using both biostratigraphic and carbon isotopic data, those deposits were dated from the latest Cenomanian-Turonian age. ‘Filament’ event beds were recorded in the same order, except for some small differences. A good number of these bio-events are global. Consequently, on a global scale, they are susceptible to constrain the C/TB, especially the base of the Turonian stage, with a significant degree of confidence.     

The investigation of flood risk perception as a quantitative analysis from socio-demographic perspective

The priority of flood management planning is physical victimization and focuses on taking structural measures. Although this approach is an accurate approach, more information is needed in implementing efficient precautionary and planning decisions. It is an indisputable fact that the existence of nothing that is not sustainable in nature cannot continue. Hence, it is necessary to implement a planning decision suitable for the structure of the population living in the region so that the continuity of the policies to be carried out against natural hazards of hydrometeorological origin such as a flood is ensured. How the socio-demographic structures affect the flood risk perception of 245 people living in the city center of Bayburt is examined in this study. It is the first research conducted for the province of Bayburt for this perspective. The participants were asked to fill a questionnaire containing 24 items and consisting of 2 sections. T test and one-way ANOVA (one-way analysis of variance) statistical methods were used to ascertain the difference between the responses of the participants to the questionnaire, based on their demographic structure. As the result of the study, significant differences were observed between the expressions depicting flood risk perception and the participant's age, income levels and educational background. In addition, it has been noted that there is a positive relationship between education and income levels and flood risk perception.

     

Long- and short-term volcanic hazard assessment of El Chichón Volcano (Mexico) through Bayesian inference

Natural Hazards - The 1982 eruption of El Chichón volcano constitutes the worst volcanic disaster in Mexico producing more than 2000 fatalities, thousands of displaced people and severe...     

Age and origin of groundwater resources in the Ararat Valley,Armenia: a baseline study applying hydrogeochemistry and environmental tracers

Within the Ararat Valley (Armenia), a continuously growing water demand (for irrigation and fish farming) and a simultaneous decline in groundwater recharge (due to climate change) result in increasing stress on the local groundwater resources. This detrimental development is reflected by groundwater-level drops and an associated reduction of the area with artesian conditions in the valley centre. This situation calls for increasing efforts aimed at more sustainable water resources management. The aim of this baseline study was the collection of data that allows for study on the origin and age distribution of the Ararat Valley groundwater based on environmental tracers, namely stable (δ²H, δ¹⁸O) and radioactive (³⁵S, ³H) isotopes, as well as physical-chemical indicators. The results show that the Ararat Valley receives modern recharge, despite its (semi-)arid climate. While subannual groundwater residence times could be disproved (³⁵S), the detected ³H pattern suggests groundwater ages of several decades, with the oldest waters being recharged around 60 years ago. The differing groundwater ages are reflected by varying scatter of stable isotope and hydrochemical signatures. The presence of young groundwater (i.e., younger that the 1970s), some containing nitrate, indicates groundwater vulnerability and underscores the importance of increased efforts to achieve sustainable management of this natural resource. Since stable isotope signatures indicate the recharge areas to be located in the mountains surrounding the valley, these efforts must not be limited to the central part of the valley where most of the abstraction wells are located.

     

Combined effects of pumped-storage operation and climate change on thermal structure and water quality

Climatic Change - The assessment of ecological impacts of pumped-storage (PS) hydropower plants on the two connected water bodies is usually based on present climatic conditions. However,...     

An integrated approach to assess the ecological and chemical status of lakes with HOD/AHOD: a case study of two lakes

The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal strati?cation,and anaerobic conditions arise. The determination of hypolimnetic oxygen demand(HOD) and areal hypolimnetic oxygen demand(AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes dif fering by size and af fected by dif ferent anthropogenic sources, are investigated in this respect. At?rst, bathymetric studies were conducted to determine the depth, surface area, and volume relationships.Then, based on monitoring studies conducted in 2013 and 2014, the thermal strati?cation dynamics and layer properties were established using the relative thermal resistance to mixing(RTRM) index based on temperature and density pro?les. Following this, the oxygen depletion rates were determined by oxygen and temperature pro?ling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic in?uences, were found to be 0.848 and 0.569 g O 2/(m·d), respectively.The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O 2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes.