Compositionally zoned Cl-rich amphiboles from North Dabie Shan, China: monitor of high-pressure metamorphic fluid/rock interaction processes

Amphiboles containing up to 4.2 wt.% Cl are found in felsic granulites from Yanzihe within the North Dabie area of the Dabie–Sulu ultrahigh- and high-pressure metamorphic belt in eastern China. Most amphibole grains show considerable zonations with Cl contents ranging from 0 to 4.2 wt.%. Based on their textural features, amphiboles can be divided into four generations: (1) amphibole occurring as inclusions in orthopyroxene (Am-in) with Cl contents around 3.5 wt.%; (2) amphibole forming cores of grains in the matrix (AM-I) with Cl contents between 3.0 and 4.2 wt.%; (3) amphibole with Cl contents of 0.2 to 2.5 wt.% (Am-II) occurring as hydrothermally altered parts of the original amphibole; (4) Cl-free amphibole (Am-III) usually developed at the outermost rim of the grain. Major and rare earth elements show significant variations for Am-I, Am-II and Am-III.

Different generations of amphiboles are related to different metamorphic stages of the granulite in Yanzihe, and provide a monitor for fluid/rock interactions and P–T evolution during the high-pressure metamorphism of Dabie Shan. Pressure and temperature estimates suggest that Am-in was formed during prograde metamorphism of 10 kbar and 700–800 °C; Am-I was formed under peak metamorphic conditions (20 kbar, 800–960 °C), whereas Am-II and Am-III were formed during retrograde metamorphic stages (560–770 °C and 5–7 kbar, and 520–670 °C and <5 kbar, respectively). In contrast to most previous studies, in which the earliest amphiboles to form are typically Cl-poor and later amphiboles become progressively Cl-rich, we show that the earliest amphiboles in the investigated rock are Cl-rich and later formed amphiboles are Cl-poor. The present study also demonstrates that the fluid system of the granulites in North Dabie Shan did not evolve in a simple way: while it behaved as a closed system during prograde and peak metamorphism, after the metamorphic peak it probably acted as an open system in which new fluids were introduced. The varying magnitude of Cl contents in amphiboles stresses the very local fluid control during metamorphism.     

Intercalibration of Mg Isotope Delta Scales and Realisation of SI Traceability for Mg Isotope Amount Ratios and Isotope Delta Values

The continuous improvement of analytical procedures using multi‐collector technologies in ICP‐mass spectrometry has led to an increased demand for isotope standards with improved homogeneity and reduced measurement uncertainty. For magnesium, this has led to a variety of available standards with different quality levels ranging from artefact standards to isotope reference materials certified for absolute isotope ratios. This required an intercalibration of all standards and reference materials, which we present in this interlaboratory comparison study. The materials Cambridge1, DSM3, ERM‐AE143, ERM‐AE144, ERM‐AE145, IRMM‐009 and NIST SRM 980 were cross‐calibrated with expanded measurement uncertainties (95% confidence level) of less than 0.030‰ for the δ^25/24Mg values and less than 0.037‰ for the δ^26/24Mg values. Thus, comparability of all magnesium isotope delta (δ) measurements based on these standards and reference materials is established. Further, ERM‐AE143 anchors all magnesium δ‐scales to absolute isotope ratios and therefore establishes SI traceability, here traceability to the SI base unit mole. This applies especially to the DSM3 scale, which is proposed to be maintained. With ERM‐AE144 and ERM‐AE145, which are product and educt of a sublimation–condensation process, for the first time a set of isotope reference materials is available with a published value for the apparent triple isotope fractionation exponent θ_app, the fractionation relationship ln α(^25/24Mg)/ln α(^26/24Mg).     

Magmatic and metamorphic evolution of metagabbros in the Münchberg Massif,N.E. Bavaria

The central gneiss complex of the Münchberg Massif consists of the Liegendserie at the base and the Hangendserie at the top. Metagabbros are found in the Liegendserie; eclogites occur in the Hangendserie. New isotope data revive the discussion whether a genetic relationship exists between metagabbros and eclogites in the Münchberg Massif. It is possible to relate the two types of rocks to the same protoliths by variable degrees of crustal contamination and magmatic accumulation. Therefore, a common magmatic origin may be assumed. Both the metagabbros and the eclogites were affected by amphibolite-facies metamorphism. The amphibolitization of the metagabbros was a prograde metamorphic event. Increasing temperature is indicated by inverse zonation of recrystallized plagioclase and increasing Mg/Fe ratios in garnet from core to rim. Geothermobarometry yields a temperature of 600°C and a pressure of about 11 kbar for the peak of metamorphism. In contrast, the eclogites underwent a first high-pressure stage at a minimum pressure of 14 kbar and a temperature estimated at 600°C and were subsequently overprinted under amphibolite-facies conditions at 10 kbar/700°C. A common magmatic origin of metagabbros (Liegendserie) and eclogites (Hangendserie) of the Münchberg Massif can no longer be discarded. However, the converging P-T-t paths reflect a different geodynamic evolution of the Liegendserie and the Hangendserie after magmatism and before amphibolite-facies metamorphism.     

Uncertainty representations of mean sea-level change: a telephone game?

Climatic Change - For the long-term management of coastal flood risks, investment and policy strategies need to be developed in light of the full range of uncertainties associated with mean...     

The H2O and CO2 adsorption properties of phyllosilicate-poor palagonitic dust and smectites under martian environmental conditions

The recent detection of up to ∼10 wt% water-equivalent H heterogeneously distributed in the upper meter of the equatorial regions of the martian surface and the presence of the 3-μm hydrations feature across the entire planet raises the question whether martian surficial dust can account for this water-equivalent H. We have investigated the H₂O and CO₂ adsorption properties of palagonitic dust (<5 μm size fraction of phyllosilicate-poor palagonitic tephra HWMK919) as a martian dust analog and two smectites under simulated martian equatorial surface conditions. Our results show that the palagonitic dust, which contains hydrated and hydroxylated volcanic glass of basaltic composition, accommodates significantly more H₂O under comparable humidity and temperature conditions than do the smectites nontronite and montmorillonite.     

Structural control of low-sulfidation epithermal gold mineralization in the Rosario–Bunawan district, East Mindanao Ridge, Philippines

The Rosario–Bunawan district is situated about 200 km north of Davao City, the capital of the Mindanao Island, Southern Philippines. Gold is produced from the Co-O mine, containing about 2,034,000 t of ore at 10.9 g/t Au, and in numerous small-scale operations by local miners. Epithermal gold mineralization in the Rosario–Bunawan district and the Co-O mine is confined to narrow (0.2–4 m) low-sulfidation quartz–chalcedony–calcite veins in volcanic and volcaniclastic wall rocks. Three major vein orientations are distinguished: (1) the NNW–SSE-trending set with a sinistral strike-slip sense of deformation (Philippine Fault trend); (2) the ENE–WSW-trending dextral strike-slip set (Palawan trend) and associated veins in the Riedel geometry; and (3) the WNW–ESE-trending conjugate set (Co-O trend). Three structural stages are defined: (1) extensional shear or shear veins formed in the Co-O, the Philippine Fault, and Palawan trends during regional NW–SE compression and near vertical vein opening (D₁); (2) reactivation of veins in the Philippine Fault, veins associated with the Palawan, and, to a lesser extent, the Co-O trends during E–W compression and near horizontal N–S-oriented vein opening (D₂). New D₂ extensional shear or shear veins formed in the Philippine Fault, and structures associated with the Palawan and associated Riedel trends; (3) the D₃-stage block faulting subsequently displaced all of the auriferous veins. The auriferous Rosario–Bunawan district is situated between two splays of the Philippine Fault, which acted as a lateral ramp system during the oblique convergence of the Philippine Sea plate and the Eurasian plate. The oblique convergence resulted in a change from a compressional (D₁) to a transpressional (D₂) regime, which was a prerequisite for the two-stage vein opening and hydrothermal mineralization, leading to an economic gold enrichment. D₁ compressional tectonics may have caused an elevated geothermal gradient in shallow crustal levels, forming the heat source for the fluid plumbing system, which is at variance to typical epithermal deposits formed in extensional zones. D₂ thrusting of a limestone nappe together with syn-tectonic diorite intrusions may have further increased the geothermal gradient, maintaining the fluid plumbing system. The limestone nappe may, at the same time, have represented an aquitard forcing the hydrothermal fluids into the volcanic and volcaniclastic wall rocks, which is regarded as critical for the two-stage gold mineralization in the Rosario–Bunawan district.     

Neoendemic ground beetles and private tree haplotypes: two independent proxies attest a moderate last glacial maximum summer temperature depression of 3–4 °C for the southern Tibetan Plateau

Previous findings regarding the Last Glacial Maximum LGM summer temperature depression (maxΔT in July) on the Tibetan Plateau varied over a large range (between 0 and 9 °C). Geologic proxies usually provided higher values than palynological data. Because of this wide temperature range, it was hitherto impossible to reconstruct the glacial environment of the Tibetan Plateau. Here, we present for the first time data indicating that local neoendemics of modern species groups are promising proxies for assessing the LGM temperature depression in Tibet. We used biogeographical and phylogenetic data from small, wingless edaphous ground beetles of the genus Trechus, and from private juniper tree haplotypes. The derived values of the maxΔT in July ranged between 3 and 4 °C. Our data support previous findings that were based on palynological data. At the same time, our data are spatially more specific as they are not bound to specific archives. Our study shows that the use of modern endemics enables a detailed mapping of local LGM conditions in High Asia. A prerequisite for this is an extensive biogeographical and phylogenetic exploration of the area and the inclusion of additional endemic taxa and evolutionary lines.     

Identification of the natural product 2,3,4,5-tetrabromo-1-methylpyrrole in Pacific biota, passive samplers and seagrass from Queensland, Australia

Halogenated natural products (HNPs) are frequently detected in marine organisms. High HNP concentrations have previously been found in marine mammals from the Great Barrier Reef, Australia, including in the blubber of herbivorous dugongs (Dugong dugon). To identify the source of HNPs we initially focused on the analysis of Australian seagrass (Halophila ovalis) which serves as the principal food source for dugongs. GC/MS analysis of the seagrass indicated the presence of several organobromine compounds. One compound was identified as 2,3,4,5-tetrabromo-1-methylpyrrole (TBMP) by synthesis. Subsequent analysis of semipermeable membrane devices demonstrated that the photo-sensitive TBMP is widespread in the Great Barrier Reef (Queensland, Australia). The detection of larger TBMP concentrations in fish fillets from Chile and traces in mussels from New Zealand indicated that this potential HNP may be distributed throughout the Southern Pacific Ocean.     

Recommendations on methods for the detection and control of biological pollution in marine coastal waters

Adverse effects of invasive alien species (IAS), or biological pollution, is an increasing problem in marine coastal waters, which remains high on the environmental management agenda. All maritime countries need to assess the size of this problem and consider effective mechanisms to prevent introductions, and if necessary and where possible to monitor, contain, control or eradicate the introduced impacting organisms. Despite this, and in contrast to more enclosed water bodies, the openness of marine systems indicates that once species are in an area then eradication is usually impossible. Most institutions in countries are aware of the problem and have sufficient governance in place for management. However, there is still a general lack of commitment and concerted action plans are needed to address this problem. This paper provides recommendations resulting from an international workshop based upon a large amount of experience relating to the assessment and control of biopollution.     

The effects of adaptation and mitigation on coastal flood impacts during the 21st century. An application of the DIVA and IMAGE models

This paper studies the effects of mitigation and adaptation on coastal flood impacts. We focus on a scenario that stabilizes concentrations at 450 ppm-CO₂-eq leading to 42 cm of global mean sea-level rise in 1995–2100 (GMSLR) and an unmitigated one leading to 63 cm of GMSLR. We also consider sensitivity scenarios reflecting increased tropical cyclone activity and a GMSLR of 126 cm. The only adaptation considered is upgrading and maintaining dikes. Under the unmitigated scenario and without adaptation, the number of people flooded reaches 168 million per year in 2100. Mitigation reduces this number by factor 1.4, adaptation by factor 461 and both options together by factor 540. The global annual flood cost (including dike upgrade cost, maintenance cost and residual damage cost) reaches US$ 210 billion per year in 2100 under the unmitigated scenario without adaptation. Mitigation reduces this number by factor 1.3, adaptation by factor 5.2 and both options together by factor 7.8. When assuming adaptation, the global annual flood cost relative to GDP falls throughout the century from about 0.06 % to 0.01–0.03 % under all scenarios including the sensitivity ones. From this perspective, adaptation to coastal flood impacts is meaningful to be widely applied irrespective of the level of mitigation. From the perspective of a some less-wealthy and small island countries, however, annual flood cost can amount to several percent of national GDP and mitigation can lower these costs significantly. We conclude that adaptation and mitigation are complimentary policies in coastal areas.