Fractionation vs. magma mixing in the Wangrah Suite A-type granites, Lachlan Fold Belt, Australia: Experimental constraints

The Wangrah Suite granites (Lachlan Fold Belt, Australia) reflect different stages of differentiation in the magmatic history of an A-type plutonic suite. In this study we use experimentally determined phase equilibria of four natural A-type granitic compositions of the Wangrah Suite to constrain phases and phase compositions involved in fractionation processes. Each composition represents a distinct granite intrusion in the Wangrah Suite. The intrusions are the Danswell Creek (DCG), Wangrah (WG), Eastwood (EG) and Dunskeig Granite (DG), ordered from “most mafic” to “most felsic” by increasing SiO₂ and decreasing FeO_total.

Experimental investigation show that the initial water content in melts from DCG is between 2–3 wt. % H₂O. If the DCG is viewed as the parental magma for the Wangrah Suite, then (1) fractionation of magnetite, orthopyroxene and plagioclase ( 20 wt. %) of the DCG composition, leads to compositions similar to that of the EG; (2) further fractionation of plagioclase, quartz, K-feldspar and biotite ( 40 wt. %) from the EG composition, leads to the DG composition. These fractionation steps can occur nearly isobarically and are confirmed by bulk rock Ba, Sr, Rb and Zr concentrations.

In contrast, the generation of the most abundant WG composition cannot be explained by fractional crystallisation from the DCG at isobaric conditions because of the high K₂O content of this granite. Magma Mixing could be the process to explain the chemical distinctiveness of the Wangrah Granite from all the other granites of the Wangrah Suite.     

Particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump: A synthesis of global sediment trap programs since 1983

Particulate organic carbon (POC) is vertically transported to the oceanic interior by aggregates and their ballasts, mainly CaCO₃ and biogenic opal, with a smaller role for lithogenic aerosols through the mesopelagic zone. Diel migrating zooplankton communities effect vertical transport and remineralization of POC in the upper layers of the ocean. Below 1.5 km, the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport. We normalized the fluxes of POC, CaCO₃, and biogenic opal from data published on samples collected at 134 globally distributed, bottom-tethered, time-series sediment trap (TS-trap) stations to annual mole fluxes at the mesopelagic/bathypelagic boundary (m/b) at 2 km and defined them as F_m/bC_org, F_m/bC_inorg, and F_m/bSi_bio. Using this global data set, we investigated (1) the geographic contrasts of POC export at m/b and (2) the supply rate of ∑CO₂ to the world mesopelagic water column. F_m/bC_org varies from 25 (Pacific Warm Pool) to 605 (divergent Arabian Sea) mmolC m⁻² yr⁻¹; F_m/bC_inorg varies from >8 (high latitude Polar Oceans) or 15 (Pacific Warm Pool) to 459 (divergent Arabian Sea) mmolC m⁻² yr⁻¹; and F_m/bSi_bio, the most spatially/temporally variable flux, ranges from 6 (North Atlantic Drift) to 1118 (Pacific Subarctic Gyre) mmolSi m⁻² yr⁻¹. The oceanic region exhibiting the highest POC flux over a significantly large region is the area of the North Pacific Boreal Gyres where the average F_m/bC_org = 213, F_m/bC_inorg = 126, and F_m/bSi_bio = 578 mmol m⁻² yr⁻¹. F_m/bC_org and F_m/bC_inorg are particularly high in large upwelling margins, including the divergent Arabian Sea and off Cape Verde. One of the data sets showing the lowest flux over a significant region/basin is F_m/bC_org = 39, F_m/bC_inorg = 69, and F_m/bSi_bio = 22 mmol m⁻² yr⁻¹ in the North Pacific subtropical/tropical gyres; Pan-Atlantic average fluxes are similar except F_m/bSi_bio fluxes are even lower. Where C_org/C_inorg and Si_bio/C_inorg are <1 defines the “Carbonate Ocean”, and where these ratios are ?1 defines the “Silica Ocean”. The Carbonate Ocean occupies about 80% of the present world pelagic ocean between the two major oceanographic fronts, the North Pacific Polar Front and the Antarctic Polar Front, and the Silica Ocean is found on the polar sides of these fronts. The total global annual fluxes of F_m/bC_org, F_m/bC_inorg, and F_m/bSi_bio at m/b calculated by parameterizations of the export flux data from 134 stations are surprisingly similar; 36.2, 33.8, and 34.6 teramol yr⁻¹ (120, 112, and 114 mmol m⁻² yr⁻¹), respectively, resulting in a near uniform binary ratio between the above three elements of about one. The global ternary % ratios estimated from 152 TS-trap samples of the three elements are 35:32:33. From our global F_m/bC_org and a published model estimate of the global export production, we estimate the regeneration rate of CO₂ through the mesopelagic zone by the biological pump is 441 teramolC yr⁻¹. Based on our global F_m/bC_inorg and recently estimated global primary production of PIC, 36-86 teramolC yr⁻¹ of PIC is assumed to be dissolved within the upper 2 km of the water column.     

The self-organizing map,a new approach to apprehend the Madden–Julian Oscillation influence on the intraseasonal variability of rainfall in the southern African region

The Madden–Julian Oscillation (MJO) is the major mode of intraseasonal variability (30–60 days) in the tropics, having large rainfall impacts globally, and possibly on southern Africa. However, the latter impact is not well understood and needs to be further explored. The life cycle of the MJO, known to be asymmetric, has been nevertheless analyzed usually through methods constrained by both linearity and orthogonality, such as empirical orthogonal function analysis. Here we explore a non-linear classification method, the self-organizing map (SOM), a type of artificial neural network used to produce a low-dimensional representation of high-dimensional datasets, to capture more accurately the life cycle of the MJO and its global impacts. The classification is applied on intraseasonal anomalies of outgoing longwave radiation within the tropical region over the 1980–2009 period. Using the SOM to describe the MJO is a new approach, complimentary to the usual real-time multivariate MJO index. It efficiently captures this propagative phenomenon and its seasonality, and is shown to provide additional temporal and spatial information on MJO activity. For each node, the subtropical convection is analyzed, with a particular focus on the southern Africa region. Results show that the convection activity over the central tropical Indian Ocean is a key factor influencing the intraseasonal convective activity over the southern African region. Enhanced (suppressed) convection over the central Indian Ocean tends to suppress (enhance) convection over the southern African region with a 10-day lag by modulating the moisture transport.     

关于“含水中基性大陆下地壳部分熔融能形成C型埃达克岩吗？”的回复

焦永玲等对笔者发表在《高校地质学报》2012年第18 卷第1 期的“含水大陆下地壳的部分熔融：大别山C型埃达克 岩成因探讨”一文提出质疑。针对他们的问题,笔者进行了回复,并提出：（1）大别山C 型埃达克岩的源岩可能是基性的 （SiO2 含量50% 左右）,但是比较准确的成分估计还需要进一步研究;（2）变质含水基性岩（角闪岩）在1.0~1.2 GPa 压力下（相当于35~40 km）可以形成含石榴石20% 以上的残余体;（3）中钾的角闪岩（K2O 含量1% 左右）部分熔融可以形成高钾钙碱性长英质熔体（K2O 含量3.5%~5%）。     

The chemistry of magmatic gases from Erta'Ale,Ethiopia

The chemical composition of the gases emitted from a hornito close to the active lava lake of Erta'Ale, Ethiopia, as derived from chemical analyses on 18 samples collected on 23 January 1974, was found to be (in mol-%): H₂O: 79.4, CO₂: 10.4, total S: 7.36, HCl: 0.42, H₂: 1.49, N₂: 0.18, Ar: 0.001, CO: 0.46, and COS: 0.009. Thermodynamic considerations, based on the equilibria CO₂ + H₂ ? CO + H₂O and CO₂ + 3H₂ + SO₂ ? COS + 3H₂O show that the analytical values represent the equilibrium composition of a gas mixture at the measured temperature of around 1130°C under close to the surface pressure conditions. Comparison of the Erta'Ale gas emissions with those from other volcanoes suggests a close similarity in their chemical composition. This similarity is considered to be due to common processes governing the release of gaseous species from a magma.     

Comparative high-resolution chemostratigraphy of the Bonarelli Level from the reference Bottaccione section (Umbria-Marche Apennines) and from an equivalent section in NW Sicily: Consistent and contrasting responses to the OAE2

The Bonarelli Level (BL) from the upper Cenomanian portion of the reference Bottaccione section (central Italy) is characterized by the presence of black shales containing high TOC concentrations (up to 17%) and amounts of CaCO₃ near to zero. In the absence of carbonate and, consequently, of relative carbon- and oxygen-isotopic data, the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean during the OAE2. Based on several geochemical proxies (Rb, V, Ni, Cr, Si, Ba), the BL is interpreted as a high-productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle. The enrichment factors of peculiar trace metals (Zn, Cd, Pb, Sb, Mo, U) provide further insight about the H₂S activity at the seafloor during the organic-rich sediment deposition and permitted us to evaluate the use of Ba as palaeoproductivity tracer in conditions of high rate of sulphate reduction.By comparing geochemical records from the reference Bottaccione section (central Italy) with those previously obtained for the coeval Calabianca section (northwestern Sicily), different degrees of oceanic anoxia were delineated and ascribed to different abundance and type (degradable or refractory) of organic matter, which are limiting factors in the bacterial sulphate reduction reactions and in subsequent euxinic conditions at seafloor in the Tethys realm. Based on a ciclostratigraphic approach, consistent fluctuations at 100 ky scale in the chemostratigraphic signals from the two sections are inferred to be expression of a strong orbital-climatic forcing driving changes in the oceanic environment during the BL deposition.     

Brood patch temperature during provocation of common eiders in Ny-Ålesund, Svalbard

In this short note we describe the behaviour and body changes of three incubating female common eiders ( Somateria mollissima ) during provocation made by humans approaching the nest. The study site was near the settlement of Ny-Ålesund, Svalbard. Temperture transmitters were implanted subcutaneously at the brood patch and data recorded using a VHF receiver. We found that the female experiment exhibited a passive defence response ("freezing"), accompanied by a significant drop in brood patch temperature (0.6 °C) during provocation; this temperature drop lasted for 5 minutes. These accord with other studies of the physiological changes which the passive defence response in birds and other animals.     

The role of economic sectoral structure as a policy mechanism towards more resilient peripheral regions: the case of South Africa

The role of economic sectoral structure in regional growth and development is widely acknowledged. However, there has been scarce reflection on its role as a policy instrument, particularly for peripheral regions. In reaction, this paper investigates the role of economic sectoral structure as a policy instrument towards more resilient peripheral regions. Through a multiple country policy analysis, the paper determines to what degree economic sectoral structure is reflected in regional development policies of 18 countries with predominantly rural characteristics and lagging regions. Moreover, the role of economic sectoral structure towards more resilient regions is quantified and measured for a specific peripheral region case in South Africa as developing country exhibiting poor economic resilience. The paper highlights related variety as a key ingredient for a region to reach a state of dynamic stability between adaptation and adaptability towards enhanced long-term resilience capacity of the peripheral region. The research concludes that policy focus should support the maintenance of the sectors and industries of comparative advantage on the regional scale, but strongly focus on sectoral comparative advantage within the national scale (if present) to establish a more robust region. This will establish and strengthen the identified peripheral growth centres as centres of national competitiveness and specialisation. Primary policy actions as emanated from the literature and the multiple country policy analysis will promote more efficient sectoral composition as key towards more resilient peripheral regions. It is acknowledged that these policy actions must be informed by a detailed regional economic analysis for different peripheral regions to determine inherent and latent economic potential and link with interdependent industries. This paper will highlight that regional policy should become more explicit by exploiting the role of economic and natural resources as growth engines for the peripheral regional economy in a more effective way through a multi-centred territorial structure.

     

Accumulation and transport behaviour of 241americium, 60cobalt and 134cesium by eggs of the spotted dogfish Scyliorhinus canicula

An experimental study examined the 96-h net influx from seawater of the anthropogenic radionuclides (241)Am, (60)Co and (134)Cs through the egg-case of the spotted dogfish Scyliorhinus canicula. Net influx directly through the wall of the egg-case was greatest for (134)Cs, then (241)Am and lastly (60)Co. Within the egg-case wall itself the measured concentration factors (CFs) and their gradients in the external, median and internal layers showed that for both (241)Am and (60)Co they were >10(3) in the external layer and declined by an order of magnitude in the interior layer. In contrast (134)Cs had a CF of only about three in the external layer which declined by a factor of 2 towards the two more internal layers of the egg-case. The egg-case apertures, that open within the prehatching stage of embryological development, significantly (P<0.05) increased the net influx of (241)Am and (60)Co to the interior of the egg-case, although their water concentrations were still lower than those in the labelled seawater bath. In contrast, the aperture did not increase the net influx of (134)Cs whose water concentrations equilibrated with those in seawater. Together these results indicate that the egg-case wall is very permeable to (134)Cs, representing little barrier to its movement, and hence consistent with the lack of importance of the aperture in determining its internal water concentrations in the egg-case. In contrast, (241)Am and (60)Co show much higher rates of accumulation by the egg-case, consistent with the measured reduced permeability of its wall, and therefore giving greater prominence to its aperture in the net transfer of these two radionuclides to the egg case's interior. The presence of the embryo within its egg-case did not significantly (P>0.05) affect the rates of influx of radioisotopes, with the exception of an interactive effect for (60)Co with the egg-case aperture (P<0.05). The CF of only (241)Am in the embryo itself relative to the external seawater concentration was significantly (P<0.05) enhanced by the presence of the aperture.