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131.
KAr and ages have been determined for altered submarine tholeiitic and boninite (high-Mg andesite) lavas from the Dabi Volcanics, Cape Vogel Peninsula, Papua New Guinea. whole rock total fusion and plateau ages identify a Late Paleocene age for the tholeiitic lavas (58.9 ± 1.1 Ma) and also for the boninitic lavas (58.8 ± 0.8 Ma). Apparent KAr ages for the same samples range from 27.2 ± 0.7 to 63.9 ± 4.5 Ma, and young KAr ages for glassy boninites are probably due to variable radiogenic 40Ar (40Ar1) loss. These new ages effectively reconcile previously ambiguous age data for the Dabi Volcanics and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast PNG during the Late Paleocene.Smectites, developed as alteration products after glass in oceanic lavas commonly do not retain 39Ar during or subsequent to irradiation, but in some cases may contain 40Ar1. In the absence of other factors modifying K and Ar contents, samples which have not lost 40Ar1 from smectite and suffer 39Ar loss only, are interpreted to have been altered immediately subsequent to the crystallization of the lava; whereas samples which have lost 40Ar1 as well as 39Ar may be the result of either recent alteration, or of continuous 40Ar1 loss since the time of crystallization. 相似文献
132.
Ian Jackson 《Earth and Planetary Science Letters》1983,62(1):91-103
The physical properties(?, K, K′) of the adiabatically decompressed lower mantle are interpreted in terms of an (Mg,Fe)SiO3 perovskite + magnesiowüstite mineralogy. The approach employed in this paper involves the removal of the relatively better characterised magnesiowüstite component from the two-phase mixture in order to highlight the physical properties required of the perovskite phase for consistency between the seismological data and any proposed compositional model. It is concluded that a wide tradeoff (emphasized by Davies [1]) between composition, temperature and the physical properties (especially thermal expansion) of the perovskite phase accommodates most recently proposed compositional models including Ringwood's [2] pyrolite and the more silicic models of Burdick and Anderson [3], Anderson [4], Sawamoto [5], Butler and Anderson [6], Liu [7,8] and Watt and Ahrens [9]. 相似文献
133.
Chironomid remains from Big Lake, British Columbia were analysed and paleosalinities were estimated using a pre-existing transfer function and several developed using new regression methods. A two component partial-least-squares model (PLS-2) had the highest coefficient of determination (R2
(Jackknifed) = 0.75) and lowest root-mean-squared error-of-prediction (RMSEP). As compared to the pre-existing model, it was also less sensitive to the influence of rare taxa. Nevertheless, the marginally larger R2
(Jackknifed) and lower RMSEP do not clearly identify a single best model. The models were applied to Big, Mahoney and Kilpoola lakes, revealing the sensitivity of paleosalinity inferences to model selection. A synopsis of chironomid-based paleosalinities in British Columbia and their correspondence with other paleoclimatic data are presented and discussed. 相似文献
134.
A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli's theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli's theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump. 相似文献
135.
Ian Knowles Michael Teubner Aimin Yan Paul Rasser Jong Wook Lee 《Hydrogeology Journal》2007,15(6):1107-1118
A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate
a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga
Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined
significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater
recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter
values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good
estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved
groundwater resource management.
Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478. 相似文献
136.
Prior to oxygen isotope analysis of biogenic silica by fluorination techniques, sediments must be cleaned of all organic compounds.
Despite the expanding volume of research utilising oxygen isotope ratios in biogenic silica in palaeoclimatology, very little
is known about the effects of different standard preparation methods for the removal of organic matter on the isotope values.
Here we compare a number of methods for the removal of organic matter in order to assess their effectiveness and influence
on subsequent isotope measurements. Not all the methods described here effectively removed organic matter, the best treatments
were H2O2 and ignition in air at 550°C. Ignition in air at 950°C, and heating in vacuum at 250 and 450°C results in marked alteration
of isotope values, whereas use of hydrogen peroxide (H2O2), nitric acid (HNO3) and plasma ashing have little or no effect, within the bounds of analytical error. Ignition in air at 550°C was the most
effective technique, and induced no alteration of δ18Osilica, but practical constraints may limit the application of this method routinely. Our findings indicate that considerable caution
is required when preparing sediment for isotope analysis of biogenic silica. 相似文献
137.
138.
Ian Robson 《Astronomy& Geophysics》2007,48(4):4.30-4.30
IYA2009 will be a great opportunity for all of us working in astronomy (and space) to make an impact; certainly locally and nationally and, we hope, globally. So what is going on and how can you participate? Ian Robson has the answers. 相似文献
139.
Mike Hapgood and Ian Crawford assess the relevance of the BNSC UKSEWG Report for the Royal Astronomical Society. 相似文献
140.
Costas Dounas Ian Davies George Triantafyllou Panayota Koulouri George Petihakis Christos Arvanitidis George Sourlatzis Anastasios Eleftheriou 《Continental Shelf Research》2007
Disturbance of the seabed resulting from bottom trawling affects ecosystem processes, such as the rate and magnitude of nutrient regeneration. The potential responses of the plankton community arising from such effects can be modelled, provided that reliable data on the effects on nutrient fluxes are available. In a north Cretan outer continental shelf and upper slope fishing ground (Heraklion Bay, Crete, Eastern Mediterranean) we applied a new field instrument which can simulate the passage of trawl groundropes across the sea floor and made direct seasonal measurements of the rate of dissolved and particulate nutrient releases resulting from seabed disturbance. These observational data were then integrated in a 3D ecosystem model. Results revealed that bottom trawling may trigger off considerable productivity pulses, in addition to pulses from the natural seasonal cycle. 相似文献