Partial Melting of Spinel Lherzolite in the System CaO-MgO-Al2O3-SiO2 {+/-} K2O at 1{middle dot}1 GPa     

LIU  XI; O'NEILL  HUGH ST. C. 《Journal of Petrology》2004,45(7):1339-1368

The compositions of multiply saturated partial melts are valuablefor the thermodynamic information that they contain, but aredifficult to determine experimentally because they exist onlyover a narrow temperature range at a given pressure. Here wetry a new approach for determining the composition of the partialmelt in equilibrium with olivine, orthopyroxene, clinopyroxeneand spinel (Ol + Opx + Cpx + Sp + Melt) in the system CaO–MgO–Al₂O₃–SiO₂(CMAS) at 1·1 GPa: various amounts of K₂O are added tothe system, and the resulting melt compositions and temperatureare extrapolated to zero K₂O. The ‘sandwich’ experimentalmethod was used to minimize problems caused by quench modification,and Opx and Cpx were previously synthesized at conditions nearthose of the melting experiments to ensure they had appropriatecompositions. Results were then checked by reversal crystallizationexperiments. The results are in good agreement with previouswork, and establish the anhydrous solidus in CMAS to be at 1320± 10°C at 1·1 GPa. The effect of K₂O is todepress the solidus by 5·8°C/wt %, while the meltcomposition becomes increasingly enriched in SiO₂, being quartz-normativeabove 4 wt % K₂O. Compared with Na₂O, K₂O has a stronger effectin depressing the solidus and modifying melt compositions. Theisobaric invariant point in the system CMAS–K₂O at whichOl + Opx + Cpx + Sp + Melt is joined by sanidine (San) is at1240 ± 10°C. During the course of the study severalother isobaric invariant points were identified and their crystaland melt compositions determined in unreversed experiments:Opx + Cpx + Sp + An + Melt in the system CMAS at 1315 ±10°C; in CMAS–K₂O, Opx + Cpx + Sp + An + San + Meltat 1230 ± 10°C and Opx + Sp + An + San + Sapph +Melt at 1230 ± 10°C, where An is anorthite and Sapphis sapphirine. Coexisting San plus An in three experiments helpdefine the An–San solvus at 1230–1250°C. KEY WORDS: feldspar solvus; igneous sapphirine; mantle solidus; partial melting; systems CMAS and CMAS–K₂O  相似文献   

Helium loss from Martian meteorites mainly induced by shock metamorphism: Evidence from new data and a literature compilation     

S. P. SCHWENZER  J. FRITZ  D. STÖFFLER  M. TRIELOFF  M. AMINI  A. GRESHAKE  S. HERRMANN  K. HERWIG  K. P. JOCHUM  R. K. MOHAPATRA  B. STOLL  U. OTT 《Meteoritics & planetary science》2008,43(11):1841-1859

Abstract— Noble gas data from Martian meteorites have provided key constraints about their origin and evolution, and their parent body. These meteorites have witnessed varying shock metamorphic overprinting (at least 5 to 14 GPa for the nakhlites and up to 45–55 GPa (e.g., the lherzolitic shergottite Allan Hills [ALH] A77005), solar heating, cosmic‐ray exposure, and weathering both on Mars and Earth. Influences on the helium budgets of Martian meteorites were evaluated by using a new data set and literature data. Concentrations of ³He, ⁴He, U, and Th are measured and shock pressures for same sample aliquots of 13 Martian meteorites were determined to asses a possible relationship between shock pressure and helium concentration. Partitioning of ⁴He into cosmogenic and radiogenic components was performed using the lowest ⁴He/³He ratio we measured on mineral separates (⁴He/³He = 4.1, pyroxene of ALHA77005). Our study revealed significant losses of radiogenic ⁴He. Systematics of cosmogenic ³He and neon led to the conclusion that solar radiation heating during transfer from Mars to Earth and terrestrial weathering can be ruled out as major causes of the observed losses of radiogenic helium in bulk meteorites. For bulk rock we observed a correlation of shock pressure and radiogenic ⁴He loss, ranging between ?20% for Chassigny and other moderately shocked Martian meteorites up to total loss for meteorites shocked above 40 GPa. A steep increase of loss occurs around 30 GPa, the pressure at which plagioclase transforms to maskelynite. This correlation suggests significant ⁴He loss induced by shock metamorphism. Noble gas loss in rocks is seen as diffusion due to (1) the temperature increase during shock loading (shock temperature) and (2) the remaining waste heat after adiabatic unloading (post shock temperature). Modeling of ⁴He diffusion in the main U, Th carrier phase apatite showed that post‐shock temperatures of ?300 °C are necessary to explain observed losses. This temperature corresponds to the post‐shock temperature calculated for bulk rocks shocked at about 40 GPa. From our investigation, data survey, and modeling, we conclude that the shock event during launch of the meteorites is the principal cause for ⁴He loss.  相似文献   

Desorption-diffusion model and lost gas quantity estimation of coalbed methane from coal core under drilling fluid medium   总被引：1，自引：0，他引：1  

Geoff WANG 《中国科学:地球科学(英文版)》2010,(4)

The differences of coalbed methane(CBM) desorption-diffusion from coal drilling-core under various drilling fluid medium are not considered in the present calculating methods of lost CBM quantity,which leads possibly to the inaccuracy of CBM quantity in coal seam.Here we took the desorption of CBM from coal core under drilling fluid medium as a pressure-swing process,and based on the Langmuir equation and Fick-first law,established the desorption-diffusion model and numerical modeling method of lost gas(inc...  相似文献   

Mesozoic sedimentation rates in the Western Canada Basin as indicators of the time and place of tectonic activity     

V. E. Chamberlain  R. ST J. Lambert  W. S. McKerrow 《Basin Research》1989,2(3):189-202

Abstract The Mesozoic stratigraphy of the westernmost part of the Western Canada Basin is used to estimate sedimentation and relative crustal subsidence rates in the region between 49^oN and 60^oN, immediately to the east of the disturbed belt. Average rates of subsidence varied from zero to 120 m/Myr, with prominent maxima occurring three times during the Mesozoic. The first occurred during the Tithonian, when rates rose to 100 m/Myr; the second during the Albian to early Santonian, when rates rose to 120 m/Myr in the north and to 70 m/Myr in the south, with subsidence occurring earlier in the north than in the south. The third period of rapid subsidence occurred during the Campanian and Maastrichtian, with rates rising to 120 m/Myr in the southern part of the basin. During non-peak periods, average rates of subsidence ranged from 3.5 m/Myr to 35 m/Myr in the Triassic, from zero to 20 m/Myr in the Jurassic and from zero to 30 m/Myr in the Cretaceous.
Tectonic loading of the lithosphere is considered to be the most probable cause for all three of these periods of rapid subsidence. The three separate episodes are correlated with the separate arrivals of accreted terranes; the first in north-east Oregon and central west Idaho during the Late Jurassic, the second in the central Yukon during the late Early Cretaceous and the third in south-east British Columbia during the Late Cretaceous.  相似文献   

The Effects of Small Amounts of H2O, CO2 and Na2O on the Partial Melting of Spinel Lherzolite in the System CaO-MgO-Al2O3-SiO2 {+/-} H2O {+/-} CO2 {+/-} Na2O at 1{middle dot}1 GPa     

LIU  XI; O'NEILL  HUGH ST. C.; BERRY  ANDREW J. 《Journal of Petrology》2006,47(2):409-434

The effects of small amounts of H₂O (<4 wt % in the melt)on the multiply saturated partial melting of spinel lherzolitein the system CaO–MgO–Al₂O₃–SiO₂ ±Na₂O ± CO₂ have been determined at 1·1 GPa inthe piston-cylinder apparatus. Electron microprobe analysisand Fourier transform infrared spectroscopy were used to analysethe experimental products. The effects of H₂O are to decreasethe melting temperature by 45°C per wt % H₂O in the melt,to increase the Al₂O₃ of the melts, decrease MgO and CaO, andleave SiO₂ approximately constant, with melts changing fromolivine- to quartz-normative. The effects of CO₂ are insignificantat zero H₂O, but become noticeable as H₂O increases, tendingto counteract the H₂O. The interaction between H₂O and CO₂ causesthe solubility of CO₂ at vapour saturation to increase withincreasing H₂O, for small amounts of H₂O. Neglect of the influenceof CO₂ in some previous studies on the hydrous partial meltingof natural peridotite may explain apparent inconsistencies betweenthe results. The effect of small amounts of H₂O on multiplysaturated melt compositions at 1·1 GPa is similar tothat of K₂O, i.e. increasing H₂O or K₂O leads to quartz-normativecompositions, but increasing Na₂O produces an almost oppositetrend, towards nepheline-normative compositions. KEY WORDS: H₂O; CO₂; FTIR; hydrous partial melting; mantle melting; spinel lherzolite; system CaO–MgO–Al₂O₃–SiO₂ ± H₂O ± CO₂ ± Na₂O  相似文献   

Riverine influence determines nearshore heterogeneity of nutrient (C,N, P) content and stoichiometry in the KwaZulu-Natal Bight,South Africa     

UM Scharler  MJ Ayers  AM de Lecea  M Pretorius  ST Fennessy  JA Huggett 《African Journal of Marine Science》2016,38(1):S193-S203

Riverine influences on nearshore oceanic habitats often have detrimental consequences leading to algal blooms and hypoxia. In oligo- to mesotrophic systems, however, nutrient delivery via rivers may stimulate production and even be a vital source of nutrients, as may nutrient supplements from upwelling. We investigated the nutrient content (C, N, P) and stoichiometry of sediment, and several pelagic, benthopelagic and benthic species in the KwaZulu-Natal (KZN) Bight, a narrow shelf area on the south-east coast of South Africa, bordering the Agulhas Current. Three suggested nutrient sources to the bight are the Thukela River in the central region of the bight, upwelling in the northern part and a semi-permanent eddy (Durban Eddy) in the southern part. Elemental content of the various groups studied showed significantly higher values for most groups at the site near the Thukela River. C:P and N:P were highest in the southern part of the bight, and lowest near the Thukela Mouth or at Richards Bay in the north, indicating the latter were the P-richer sites. Sediment organic matter showed lowest elemental content, as expected, and zooplankton stoichiometry was highest compared to all other biotic groups. Environmental heterogeneity played a greater role in organismal C, N and P content and stoichiometry compared to phylogeny, with the exception of the differences in C:P and N:P of zooplankton. From this bight-wide study, the higher elemental content and lower ratios at the Thukela Mouth site supported previous findings of the importance of coastal nutrient sources to the bight ecosystem. Reductions in river flow for water use in the catchment areas may therefore have negative consequences for the productivity of the entire ecosystem.  相似文献   

Subtropical demersal fish communities on soft sediments in the KwaZulu-Natal Bight,South Africa     

ST Fennessy 《African Journal of Marine Science》2016,38(1):S169-S180

  相似文献   

Probabilistic GIS-based method for delineation of urban flooding risk hotspots   总被引：3，自引：1，他引：2  

Fatemeh Jalayer  Raffaele De Risi  Francesco De Paola  Maurizio Giugni  Gaetano Manfredi  Paolo Gasparini  Maria Elena Topa  Nebyou Yonas  Kumelachew Yeshitela  Alemu Nebebe  Gina Cavan  Sarah Lindley  Andreas Printz  Florian Renner 《Natural Hazards》2014,73(2):975-1001

Identifying urban flooding risk hotspots is one of the first steps in an integrated methodology for urban flood risk assessment and mitigation. This work employs three GIS-based frameworks for identifying urban flooding risk hotspots for residential buildings and urban corridors. This is done by overlaying a map of potentially flood-prone areas [estimated through the topographic wetness index (TWI)], a map of residential areas and urban corridors [extracted from a city-wide assessment of urban morphology types (UMT)], and a geo-spatial census dataset. A maximum likelihood method (MLE) is employed for estimating the threshold used for identifying the flood-prone areas (the TWI threshold) based on the inundation profiles calculated for various return periods within a given spatial window. Furthermore, Bayesian parameter estimation is employed in order to estimate the TWI threshold based on inundation profiles calculated for more than one spatial window. For different statistics of the TWI threshold (e.g. MLE estimate, 16th percentile, 50th percentile), the map of the potentially flood-prone areas is overlaid with the map of urban morphology units, identified as residential and urban corridors, in order to delineate the urban hotspots for both UMT. Moreover, information related to population density is integrated by overlaying geo-spatial census datasets in order to estimate the number of people affected by flooding. Differences in exposure characteristics have been assessed for a range of different residential types. As a demonstration, urban flooding risk hotspots are delineated for different percentiles of the TWI value for the city of Addis Ababa, Ethiopia.  相似文献