A kinetic model of metamorphism: an application to siliceous dolomites     

Andreas?LüttgeEmail author  Edward?W.?Bolton  Danny?M.?Rye 《Contributions to Mineralogy and Petrology》2004,146(5):546-565

We use a kinetic model of a metamorphic system to study the effect of competing rates of reaction, fluid injection, and heating on the evolution of the reaction pathway in temperature/composition space at constant pressure. We show that for rocks in contact with mixed volatile (e.g., CO₂-H₂O) fluids the reaction path may be quite different from what is expected from equilibrium-based petrologic models. Equilibrium-based models, used to understand the development of rock systems undergoing mineral reactions during a metamorphic event, rely on the Gibbs phase rule and only consider stable phases. For constant pressure, the temperature-composition paths follow univariant curves and significant reactions may occur at invariant points. By contrast, the more general kinetic treatment is not constrained by equilibrium, although with the proper competing rates equilibrium is a possible endmember of the kinetic approach. The deviation from equilibrium depends on the competing rates of reaction, heating, and fluid injection. A key element required by the kinetic approach is the inclusion of metastable reactions in the formulation, whereas such reactions are irrelevant for equilibrium-based models. Metastable reactions are often involved in a complex interplay with common prograde stable metamorphic reactions. We present model results for the well-studied CaO-MgO-SiO₂-CO₂-H₂O (CMS) system to show how the system evolves under kinetic control. Our simulations and discussion focus on the behavior of the CMS system under a number of closed and open system conditions. Special attention is paid to closed system behavior in the vicinity of the (first) isobaric invariant point (with Dol, Qtz, Tlc, Cal, and Tr). Also, for open systems with massive fluid infiltration we consider heating rates varying from contact to regional metamorphic conditions. For some geologically reasonable rates of reactions, heating, and fluid injection, our results demonstrate that equilibrium conditions may be significantly overstepped in metamorphic systems. We used overall mineral reactions in this model with rates based on experimental results. Future models could rely on more fundamental dissolution and precipitation reactions. Such an extension would require additional kinetic rate data, as well as mineral solubilities in mixed volatile fluids.Editorial responsibility: J. Hoefs  相似文献   

Melt extraction pathways and stagnation depths beneath the Madeira and Desertas rift zones (NE Atlantic) inferred from barometric studies     

Stefanie?SchwarzEmail author  Andreas?Klügel  Cora?Wohlgemuth-Ueberwasser 《Contributions to Mineralogy and Petrology》2004,147(2):228-240

The Madeira and Desertas Islands (eastern North Atlantic) show well-developed rift zones which intersect near the eastern tip of Madeira (São Lourenço peninsula). We applied fluid inclusion barometry and clinopyroxene-melt thermobarometry to reconstruct levels of magma stagnation beneath the two adjacent rifts and to examine a possible genetic relationship during their evolution. Densities of CO₂-dominated fluid inclusions in basanitic to basaltic samples from São Lourenço yielded frequency maxima at pressures of 0.57–0.87 GPa (23–29 km depth) and 0.25–0.32 GPa (8–10 km), whereas basanites, basalts and xenoliths from the Desertas indicate 0.3–0.72 GPa (10–24 km) and 0.07–0.12 GPa (2–3 km). Clinopyroxene-melt thermobarometry applied to Ti-augite phenocryst rim and glass/groundmass compositions indicates pressures of 0.45–1.06 GPa (15–35 km; São Lourenço) and 0.53–0.89 GPa (17–28 km; Desertas Islands) which partly overlap with pressures indicated by fluid inclusions. We interpret our data to suggest a multi-stage magma ascent beneath the Madeira Archipelago: main fractionation occurs at multiple levels within the mantle (>15 km depth) and is followed by temporary stagnation within the crust prior to eruption. Depths of crustal magma stagnation beneath São Lourenço and the Desertas differ significantly, and there is no evidence for a common shallow magma reservoir feeding both rift arms. We discuss two models to explain the relations between the two adjacent rift systems: Madeira and the Desertas may represent either a two-armed rift system or two volcanic centres with separate magma supply systems. For petrological and volcanological reasons, we favour the second model and suggest that Madeira and the Desertas root in distinct regions of melt extraction. Magma focusing into the Desertas system off the hotspot axis may result from lithospheric bending caused by the load of the Madeira and Porto Santo shields, combined with regional variations in melt production due to an irregularly shaped plume.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: J. Hoefs  相似文献   

A late glacial Antarctic climate teleconnection and variable Holocene seasonality at Lake Pupuke, Auckland, New Zealand     

Thomas Stephens  Daniel Atkin  Paul Augustinus  Philip Shane  Andrew Lorrey  Alayne Street-Perrott  Andreas Nilsson  Ian Snowball 《Journal of Paleolimnology》2012,48(4):785-800

We present the first continuous paleolimnological reconstruction from the North Island of New Zealand (37°S) that spans the last 48.2?cal kyr. A tephra- and radiocarbon-based chronology was developed to infer the timing of marked paleolimnological changes in Lake Pupuke, Auckland, New Zealand, identified using sedimentology, magnetic susceptibility, grain size and geochemistry (carbon, nitrogen and sulphur concentrations and fluxes, carbon and nitrogen stable isotopes). Variable erosional influx, biomass and benthic REDOX conditions are linked to changing effective precipitation and seasonality within three inferred broad intervals of climatic change: (1) the Last Glacial Coldest Phase (LGCP) of reduced effective precipitation and cooler temperatures, from 28.8 to 18.0?cal kyr BP, (2) the Last Glacial Interglacial Transition (LGIT) of increasing effective precipitation and warmer conditions, from 18.0 to 10.2?cal?kyr?BP, and (3) a Holocene interval of high effective precipitation, beginning with a warm period of limited seasonality from 10.2?cal?kyr?BP and followed by increasing seasonality from 7.6?cal?kyr?BP. The LGCP and LGIT also contain millennial-scale climate events, including the coldest inferred glacial conditions during the LGCP from 27.8 to 26.0 and 22.0?C19.0?cal?kyr?BP, and a climate reversal in the LGIT associated with lower lake level, from 14.5 to 13.8?cal?kyr?BP, coeval with the Antarctic Cold Reversal. The onset of seasonal thermal stratification occurred at 5.7?cal?kyr?BP and was linked to natural eutrophication of Lake Pupuke, which produced enhanced organic sedimentation.  相似文献   

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (δ15N, δ13C) of Lake Pupuke     

Alexander M. Heyng  Christoph Mayr  Andreas Lücke  Bernd Striewski  Stefan Wasteg?rd  Holger Wissel 《Journal of Paleolimnology》2012,48(2):351-366

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165?cal.?year BP. The origin of organic matter was established using total-organic?Ccarbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (??¹³C_OM) and nitrogen (??¹⁵N) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. >7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165?years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600?cal.?year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the ??¹⁵N and ??¹³C values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600?cal.?year BP.  相似文献   

The climate tourism potential of Alpine destinations using the example of Sonnblick, Rauris and Salzburg     

Andreas Matzarakis  Martin H?mmerle  Elisabeth Koch  Ernest Rudel 《Theoretical and Applied Climatology》2012,110(4):645-658

The climate tourism potential of a region can be described by methods used in human biometeorology and applied climatology. Frequency analyses based on complex thermal bioclimatic indices (e.g. physiologically equivalent temperature) and diagrams of precipitation patterns based on thresholds offer new approaches of visualisation. An integral approach for tourism climatologic analyses is provided by the climate?Ctourism/transfer?Cinformation?Cscheme that also bases on frequency distributions of relevant factors and parameters which are important for a destination. The knowledge about the vertical variability of tourism climatologic factors is of high importance because of the several kinds of tourism activities affected by weather. The same holds for a quantification of extreme events like heat waves because of their possible effects on health and recreation over a year's course. The results show that the vertical gradient of bioclimatic and tourism-related parameters can be of value when developing strategies of adaption to climate change.  相似文献   

Reply to Comment of R. M. Eckman     

George Treviño  Edgar L Andreas 《Boundary-Layer Meteorology》2008,127(2):353-356

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Climate change effects on winter chill for tree crops with chilling requirements on the Arabian Peninsula     

Eike Luedeling  Jens Gebauer  Andreas Buerkert 《Climatic change》2009,96(1-2):219-237

Fruit production systems that rely on winter chill for breaking of dormancy might be vulnerable to climatic change. We investigated decreases in the number of winter chilling hours (0–7.2°C) in four mountain oases of Oman, a marginal area for the production of fruit trees with chilling requirements. Winter chill was calculated from long-term hourly temperature records. These were generated based on the correlation of hourly temperature measurements in the oases with daylength and daily minimum and maximum temperatures recorded at a nearby weather station. Winter chill was estimated for historic temperature records between 1983 and 2008, as well as for three sets of synthetic 100-year weather records, generated to represent historic conditions, and climatic changes likely to occur within the next 30 years (temperatures elevated by 1°C and 2°C). Our analysis detected a decrease in the numbers of chilling hours in high-elevation oases by an average of 1.2–9.5 h/year between 1983 and 2008, a period during which, according to the scenario analysis, winter chill was sufficient for most important species in most years in the highest oasis. In the two climate change scenarios, pomegranates, the most important tree crop, received insufficient chilling in 13% and 75% of years, respectively. While production of most traditional fruit trees is marginal today, with trees barely fulfilling their chilling requirements, such production might become impossible in the near future. Similar developments are likely to affect other fruit production regions around the world.  相似文献   

Keeping the Universe ionized: photoheating and the clumping factor of the high-redshift intergalactic medium     

Andreas H. Pawlik  Joop Schaye  Eveline van Scherpenzeel 《Monthly notices of the Royal Astronomical Society》2009,394(4):1812-1824

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Modelling the Spoon IRS diagnostic diagram     

Michael Rowan-Robinson  Andreas Efstathiou 《Monthly notices of the Royal Astronomical Society》2009,399(2):615-620

We explore whether our models for starbursts, quiescent star-forming galaxies and for active galactic nuclei (AGN) dust tori are able to model the full range of Spitzer Infrared Spectrograph (IRS) spectra measured with Spitzer . The diagnostic plot of 9.7 μm silicate optical depth versus 6.2 μm polycyclic aromatic hydrocarbon (PAH) equivalent width, introduced by Spoon and coworkers in 2007, gives a good indication of the age and optical depth of a starburst, and of the contribution of an AGN dust torus. However, there is aliasing between age and optical depth at later times in the evolution of a starburst, and between age and the presence of an AGN dust torus. Modelling the full IRS spectra and using broad-band 25–850 μm fluxes can help to resolve these aliases. The observed spectral energy distributions require starbursts of a range of ages with initial dust optical depth ranging from 50–200, optically thin dust emission ('cirrus') illuminated by a range of surface brightnesses of the interstellar radiation field, and AGN dust tori with a range of viewing angles.  相似文献   

Laboratory experiments on the weathering of iron meteorites and carbonaceous chondrites by iron‐oxidizing bacteria     

Aaron GRONSTAL  Victoria PEARSON  Andreas KAPPLER  Craig DOORIS  Mahesh ANAND  Franck POITRASSON  Terence P. KEE  Charles S. COCKELL 《Meteoritics & planetary science》2009,44(2):233-247

Abstract— Batch culture experiments were performed to investigate the weathering of meteoritic material by iron‐oxidizing bacteria. The aerobic, acidophilic iron oxidizer (A. ferrooxidans) was capable of oxidizing iron from both carbonaceous chondrites (Murchison and Cold Bokkeveld) and iron meteorites (York and Casas Grandes). Preliminary iron isotope results clearly show contrasted iron pathways during oxidation with and without bacteria suggesting that a biological role in meteorite weathering could be distinguished isotopically. Anaerobic iron‐oxidizers growing under pH‐neutral conditions oxidized iron from iron meteorites. These results show that rapid biologically‐mediated alteration of extraterrestrial materials can occur in both aerobic and anaerobic environments. These results also demonstrate that iron can act as a source of energy for microorganisms from both iron and carbonaceous chondrites in aerobic and anaerobic conditions with implications for life on the early Earth and the possible use of microorganisms to extract minerals from asteroidal material.  相似文献