Large-scale Mechanical Redistribution of Orthopyroxene and Plagioclase in the Basement Sill, Ferrar Dolerites, McMurdo Dry Valleys, Antarctica: Petrological, Mineral-chemical and Field Evidence for Channelized Movement of Crystals and Melt     

Bedard  Jean H. J.; Marsh  Bruce D.; Hersum  Taber G.; Naslund  H. Richard; Mukasa  Samuel B. 《Journal of Petrology》2007,48(12):2289-2326

The Jurassic Ferrar dolerite sills of the McMurdo Dry Valleys,Antarctica represent the plumbing system for flood basalt eruptionsassociated with the breakup of Gondwana. Among the Ferrar sills,the 350–450 m thick cumulate-textured Basement Sill isdifferentiated into a Lower Marginal Zone (LMZ) gabbronorite,a thick Lower Zone (LZ) orthopyroxene–plagioclase orthocumulatepyroxenite, a strongly layered mela- to leuco-gabbronorite MiddleZone (MZ), a thick Upper Zone (UZ) gabbronorite with ferrogabbroicpods, and an Upper Marginal Zone (UMZ) gabbronorite. Texturesand mineral compositions in the LZ pyroxenite and MZ–UZgabbronorites are nearly identical, the main distinction beingthe greater relative proportion of plagioclase in the MZ–UZgabbronorites, and of pigeonite in the UZ. Most orthopyroxenein the LZ, MZ and UZ occurs as sub-euhedral, normally zonedprimocrysts, commonly with rounded plagioclase inclusions. Plagioclaseis usually sub-euhedral and normally zoned, but can containsodic cores interpreted to be xenocrystic. Orthopyroxene andfeldspar compositions thoughout the sill are generally fairlyuniform, and resemble the compositions of micro-phenocrystsin the chilled margins. We infer that the sill was filled bya c. 1250°C slurry of orthopyroxene + plagioclase phenocrystsor primocrysts that subsequently unmixed in response to buoyancyforces. The LZ websterite contains numerous anorthosite to gabbronoriteschlieren, veins and pipes (< 2 m diameter), which we interpretas fossil segregation channels. Textures and mineral compositionsin these felsic channels are very similar both to UZ and MZgabbronorites, and to the groundmass separating accumulatedorthopyroxene primocrysts in the LZ and MZ. We infer that plagioclase-charged,hydrous pore melt from the pyroxenite may have segregated, pooledand ascended through these conduits to feed growth of the UZgabbronorite. Detailed mapping shows that the pipes are separatedby about 15 m on average. Calculations suggest that this numberdensity of conduits could have drained the LZ cumulates of theirinterstitial melt + plagioclase in about 8 days. Sequences (eachc. 5–10 m thick) of layered leuco-gabbronorite in theMZ could represent intra-cumulate sills that formed from plagioclase-richslurries ascending in segregation channels. Fe–Ti-richpyroxenitic veins and pods (some pegmatitic) and an unusualcoarse-grained plagioclase facies occur at the contacts betweenmassive leuco-gabbronorite layers in the MZ. Discordant ferro-pegmatitepods and dykes occur throughout the UZ. We interpret these Fe-richpegmatoidal rocks as evolved residual melts expelled from thecompacting gabbronoritic cumulates of the MZ and UZ. KEY WORDS: Ferrar; cumulates; differentiation; Antarctica; layering  相似文献   

Modeling long-period noise in kinematic GPS applications     

Adrian A. Borsa  Jean-Bernard Minster  Bruce G. Bills  Helen A. Fricker 《Journal of Geodesy》2007,81(2):157-170

We develop and test an algorithm for modeling and removing elevation error in kinematic GPS trajectories in the context of a kinematic GPS survey of the salar de Uyuni, Bolivia. Noise in the kinematic trajectory ranges over 15 cm and is highly autocorrelated, resulting in significant contamination of the topographic signal. We solve for a noise model using crossover differences at trajectory intersections as constraints in a least-squares inversion. Validation of the model using multiple realizations of synthetic/simulated noise shows an average decrease in root-mean-square-error (RMSE) by a factor of four. Applying the model to data from the salar de Uyuni survey, we find that crossover differences drop by a factor of eight (from an RMSE of 5.6 to 0.7 cm), and previously obscured topographic features are revealed in a plan view of the corrected trajectory. We believe that this algorithm can be successfully adapted to other survey methods that employ kinematic GPS for positioning.  相似文献   

The relationship between total dissolved carbon dioxide and its stable carbon isotope ratio in aquatic sediments     

Bruce D LaZerte 《Geochimica et cosmochimica acta》1981,45(5):647-656

A model is constructed to predict the stable carbon isotope ratio of the total dissolved CO₂ in aquatic sediments and laboratory reactors. The major parameters of the model are the fractionation between CO₂ and CH₄ as well as the intra-molecular fractionation of acetate, the relative production of CH₄ from CO₂ reduction versus acetate fermentation, the net production ratio of CO₂ to CH₄ and the stable carbon isotope ratio of the source organic carbon. The model is fitted to published data and to date from the littoral sediments of Lake Memphremagog, Quebec, Canada. The inclusion of the intra-molecular fractionation factor of acetate in the model provides a good fit to the data; without this factor, the values of the other parameters necessary for a good fit appear unreasonable.  相似文献   

Unburned coal as a source of hydrocarbons in surface sediments     

Bruce W. Tripp  John W. Farrington  John M. Teal 《Marine pollution bulletin》1981,12(4):122-126

The isolation and quantification of the various sources of trace levels of hydrocarbons in environmental samples is a difficult analytical task. Based on the hydrocarbon concentrations found in non-polluted surface sediment and an estimate of the amounts of coal particles found in similar areas we conclude that unburned coal can be a significant source of sediment hydrocarbons in the coastal marine environment.  相似文献   

Electron paramagnetic resonance spectroscopy: A suggested approach to trace metal analysis in marine environments     

Bruce A. Burgess  N. Dennis Chasteen  Henri E. Gaudette 《Environmental Geology》1975,1(3):171-180

Electron paramagnetic resonance (EPR) spectroscopy analysis of marine samples from different environments appears to differentiate between adsorbed and structural Mn (II) and Fe (III) sites in the sediment. This suggests that EPR may provide a means of distinguishing different environmental influences on sediment. Acid extract solutions from sediment samples exhibit clearly defined EPR spectra due to Mn(II), Ti(III), Fe(III), and VO(IV), which are amenable to qualitative and quantitative analysis at concentrations below one part per million. Spectra of several shellfish vary considerably, both between species, and within a species, depending on sampling localities. Resonances from Mn(II), Mo(V), and Fe(III) can be obtained. Mn(II) is substituted for Ca(II) in the calcite structure of some shells. The low detection limits, small sample size, required and identification of oxidation states by EPR complement other analytical techniques and may prove useful in marine systems.  相似文献   

Model systems for anatexis of pelitic rocks     

Alan Bruce Thompson  Robert J. Tracy 《Contributions to Mineralogy and Petrology》1979,70(4):429-438

Subsolidus and melting reactions involving calcic plagioclase in pelitic assemblages in the K-Na-Ca model system occur at higher temperatures than their K-Na counterparts. For the most calcic plagioclase compositions observed in high-grade pelitic rocks (An₂₅-An₄₀) the equilibria are rarely extended by more than 30 ° C above those in KA1O₂-NaAlO₂-Al₂O₃-SiO₂-H₂O, although all discontinuities in facies inferred for the K-Na system are continuously displaced when they involve Ca-bearing plagioclase. The maximum pressure-temperature overlap between muscovite dehydration and initial melting reactions occurs in the pressure range of 4–6 kbar between about 640 ° and 720 ° C. This provides optimum conditions for anatectic melt generation in felsic rocks of the appropriate compositions progressively metamorphosed in kyanite-sillimanite facies series. Progressive regional metamorphism at pressures of 2–4 kbar, corresponding to andalusite-sillimanite facies series, shows little overlap between muscovite dehydration and initial melting reactions. Consequently anatectic melt generation in andalusite-sillimanite facies series would require the participation of biotite in dehydration-melting reactions. Felsic intrusive rock in andalusite-sillimanite terranes could have risen upward from their anatectic sites in high grade kyanite-sillimanite facies series at depth. Many andalusite-sillimanite facies series terranes culminating in migmatites could represent upward movement of kyanite-sillimanite facies series rocks to shallower depths with uplift rates faster than cooling rates.  相似文献   

Freshwater reserves of mid-atlantic coast barrier Islands     

Thomas H. Bolyard  George M. Hornberger  Robert Dolan  Bruce P. Hayden 《Environmental Geology》1979,3(1):1-11

A multiple regression model was constructed for the purpose of predicting barrier island hydrology from easily measureable island characteristics. The model was developed using data obtained from 17 sites on the Outer Banks of North Carolina. The accuracy of the model for predicting key hydrologic variables was evaluated by statistical and graphic procedures. In general, agreement between observed and predicted values of the hydrologic variables was very good, suggesting that the quantity of potable water at various island sites can be estimated without resorting to extensive field investigations. The model was then applied to Assateague Island, a barrier island located off the coasts of Maryland and Virginia. Results indicate that the original model developed for the Outer Banks may be applied to other barrier islands but that errors involved may necessitate corrections in detailed studies. Correction for bias in predictions for Assateague was shown to be possible with limited field data from surface resistivity surveys.  相似文献   

Quaternary Antarctic Bottom-Water history: Deep-sea benthonic foraminiferal evidence from the southeast Indian Ocean     

Bruce H. Corliss 《Quaternary Research》1979,12(2):271-289

Distinct assemblages of Recent deep-sea benthonic foraminifera from the southeast Indian Ocean have been shown to be associated with Antarctic Bottom Water (AABW) and Indian Bottom Water (IBW). The AABW assemblage is divided into two groups. One is dominated by Epistominella umbonifera and is associated with AABW having temperatures between ?0.2° and 0.4°C. The second group is dominated by Globocassidulina subglobosa and is associated with AABW having temperatures between 0.6° and 0.8°C. The IBW assemblage is marked by the strong dominance of Uvigerina spp. and Epistominella exigua. The faunal-water-mass relationships have been used to infer the history of bottom-water circulation over the last 500,000 yr in this region using faunal data from four Eltanin cores. One core was taken from the Southeast Indian Ridge in association with IBW, and three were taken from the flank of the ridge associated with AABW flowing within a western boundary contour current in the South Australian Basin. Little faunal variation exists in the core beneath IBW (E48-22), indicating that IBW was present on the Southeast Indian Ridge during the last 300,000 yr. A record of the intensity of AABW circulation during the last 500,000 yr is inferred from the benthonic foraminiferal data in the three cores located within the western boundary contour current. Marked oscillations in the relative proportions of AABW and IBW faunal assemblages are found in one core, E48-03. The faunal variations are inferred to have resulted from variation in intensity of AABW circulation between 500,000 and 195,000 yr B.P. In E48-03, the AABW assemblage was present most of the time between 500,000 and 195,000 yr B.P., with low intensity of AABW circulation occurring primarily during the equivalent of stages 8 and 7 (t = 305,000 to 195,000 yr B.P.). The intensity of AABW circulation varied, with a maximum occurring during the equivalent of stage 11 (t = 420,000 yr B.P.). Two additional cores, E45-27 and E45–74, show relatively constant intensity of AABW circulation from 195,000 yr B.P. to the present. The intensity of AABW circulation at the present appears to be intermediate between a maximum during the equivalent of stage 11 (t = 420,000 yr B.P.) and the minimum during the equivalent of stage 8 (t = 275,000 yr B.P.). AABW production has occurred during both glacial and interglacial episodes. Bottom-water productivity has been suggested to play an important role in glacial/interglacial oscillations during the late Quaternary (Weyl, 1968; Newell, 1974). In this study, the relationship between bottom-water circulation and climatic fluctuations appears to be more complex than had been previously suggested, since a simple relationship between Quaternary bottom-water circulation and paleoclimatic fluctuations is not shown.  相似文献   

The peterson limestone — early cretaceous lacustrine carbonate deposition in western wyoming and southeastern idaho     

Steven W. Glass  Bruce H. Wilkinson 《Sedimentary Geology》1980,27(2):143-160

The lacustrine Peterson Limestone of western Wyoming and southeastern Idaho comprises six lithofacies throughout its 20,000 km² aerial extent. These are: (1) calcareous sandstone and shale, (2) red nodular limestone, (3) pink sandy micrite, (4) biomicrite, (5) graded silty micrite, and (6) limestone conglomerate. The first two represent floodplain deposition and paleosols, whereas the remaining are shallow nearshore and deeper lacustrine sediments.This sequence was developed in a large fresh, hardwater lake surrounded by fluvial systems and associated flood plains in a warm temperate climate. Well-oxidized sandy terrigenous rocks, together with calcareous paleosol nodules, indicate that flood-plain deposition both preceded and was concurrent with lacustrine carbonate deposition. Micrite and biomicrite formed in deeper parts of the basin while sandy and silty carbonate accumulated in shallower lake-margin areas. Less-calcareous shale units which are interbedded with deeper-water carbonate were deposited either during rapid basin subsidence and deepening of the lake center or during periods of slower carbonate precipitation. Turbidity currents and subaqueous debris flows generated along steeper lake margins, resulted in the deposition of rhythmic layers of graded silty micrite and diamictic limestone conglomerate in the deepest part of the basin. The carbonate-rich sediments comprising these two lithofacies were originally deposited on shallow lake-margin benches and subsequently were transported downslope toward the lake center.Comparison with other carbonate-precipitating lacustrine systems indicates that this lake was not like modern playas. Although no known modern lacustrine system is precisely like Lake Peterson, the flora, fauna, composition, and distribution of facies within modern temperate-region lakes most closely resemble those of the Peterson Limestone.  相似文献   

Solute Changes During Aquifer Storage Recovery Testing in a Limestone/Clastic Aquifer   总被引：1，自引：0，他引：1  

June E. Mirecki  Bruce G. Campbell  Kevin J. Conlon  Matthew D. Petkewich 《Ground water》1998,36(3):394-403

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