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1.
Gas maturity and alteration systematics across the Western Canada Sedimentary Basin from four mud gas isotope depth profiles 总被引：1，自引：0，他引：1
Carbon isotope and molecular compositions of Mississippian to Upper Cretaceous mud gases have been examined from four depth profiles across the Western Canada Sedimentary Basin (WCSB). The profiles range from the shallow oil sands in the east (R0 = 0.25) to the very mature sediments in the overthrust zone to the west (R0 = 2.5). In the undisturbed WCSB, δ13C1–δ13C2 and δ13C2–δ13C3 cross-plots show three maturity and alteration trends: (1) pre-Cretaceous gas sourced from type II kerogen; (2) Cretaceous Colorado Group gas; and (3) Lower Cretaceous Mannville Group biodegraded gas. A fourth set of distinctly different maturity trends is recognized for Lower Cretaceous gas sourced from type III kerogen in the disturbed belt of the WCSB. Displacement of these latter maturity trends to high δ13C2 values suggests that the sampled gas was trapped after earlier formed gas escaped, probably as a result of overthrusting. Unusually 13C-enriched gas (δ13C1 = −34‰, δ13C2 = −13‰, and δ13C3 = 0‰), from the Gething Formation in the disturbed belt, is the result of late stage gas cracking in a closed system. In general, gas maturity is consistent with the maturity of the host sediments in the WCSB, suggesting that migration and mixing of gases was not pervasive on a broad regional and stratigraphic scale. The ‘Deep Basin’ portion of the WCSB is an exception. Here extensive cross-formational homogenization of gases has occurred, in addition to updip migration along the most permeable stratigraphic units. 相似文献
2.
Hege Fonneland-Jorgensen Harald Furnes Karlis Muehlenbachs Yildirim Dilek 《Island Arc》2005,14(4):517-541
Abstract The Solund‐Stavfjord ophiolite complex (SSOC) in western Norway represents a remnant of the Late Ordovician oceanic lithosphere, which developed in an intermediate‐ to fast‐spreading Caledonian back‐arc basin. The internal architecture and magmatic features of its crustal component suggest that the SSOC has a complex, multistage sea floor spreading history in a supra‐subduction zone environment. The youngest crustal section associated with the propagating rift tectonics consists of a relatively complete ophiolite pseudostratigraphy, including basaltic volcanic rocks, a transition zone between the sheeted dyke complex and the extrusive sequence, sheeted dykes, and high‐level isotropic gabbros. Large‐scale variations in major and trace element distributions indicate significant remobilization far beyond that which would result from magmatic processes, as a result of the hydrothermal alteration of crustal rocks. Whereas K2O is strongly enriched in volcanic rocks of the extrusive sequence, Cu and Zn show the largest enrichment in the dyke complex near the dyke–volcanic transition zone or within this transition zone. The δ18O values of the whole‐rock samples show a general depletion structurally downwards in the ophiolite, with the largest and smallest variations observed in volcanic rocks and the transition zone, respectively. δ18O values of epidote–quartz mineral pairs indicate 260–290°C for volcanic rocks, 420°C for the transition zone, 280–345°C for the sheeted dyke complex and 290–475°C for the gabbros. The 87Sr/86Sr isotope ratios show the widest range and highest values in the extrusive rocks (0.70316–0.70495), and generally the lowest values and the narrowest range in the sheeted dyke complex (0.70338–0.70377). The minimum water/rock ratios calculated show the largest variations in volcanic rocks and gabbros (approximately 0–14), and generally the lowest values and range in the sheeted dyke complex (approximately 1–3). The δD values of epidote (?1 to ?12‰), together with the δ18O calculated for Ordovician seawater, are similar to those of present‐day seawater. Volcanic rocks experienced both cold and warm water circulation, resulting in the observed K2O‐enrichment and the largest scatter in the δ18O values. As a result of metal leaching in the hot reaction zone above a magma chamber, Zn is strongly depleted in the gabbros but enriched in the sheeted dyke complex because of precipitation from upwelling of discharged hydrothermal fluids. The present study demonstrates that the near intact effect of ocean floor hydrothermal activity is preserved in the upper part of the SSOC crust, despite the influence of regional lower greenschist facies metamorphism. 相似文献
3.
During the Quaternary glacial episodes, when sea level was considerably lower, Asia and North America were linked by large extensions of circumarctic land (Beringia), which remained unglaciated. This land mass served not only as a biogeographical bridge for plants, animals, and humans, but also supported a biome very different from present tundra or boreal coniferous forests, which was dominated by steppes and a rich mammalian megafauna. Carbon stable isotope ratios of Beringian late Pleistocene mummified remains of bison, equids, mammoth, caribou, musk-ox, moose, woolly rhino, and other undetermined species, found preserved in permafrost, indicate that these megaherbivores fed exclusively on C3 plants, and that C4 grasses were not differentially ingested by bison, as previously suggested. Paleoclimatic constraints probably prevented the formation of a warm-season (C4) guild during the later part of the growing season in the steppes of Beringia during the last glaciation. 相似文献
4.
This study explores the potential of integrating state-of-the-art physically based hydrogeological modeling into slope stability simulations to identify the hydrogeological triggers of landslides. Hydrogeological models considering detailed morphological, lithological, and climatic factors were elaborated. Groundwater modeling reveals locations with elevated pore water pressures in the subsurface and allows the quantification of temporal dynamics of the pore water pressures. Results of the hydrogeological modeling were subsequently applied as boundary conditions for the slope stability simulations. The numerical models illustrate that the hydrogeological impacts affecting hillslope stability are strongly controlled by local groundwater flow conditions and their conceptualization approach in the hydrogeological model. Groundwater flow itself is heavily influenced by the inherent geological conditions and the dynamics of climatic forcing. Therefore, both detailed investigation of the landslide’s hydrogeology and appropriate conceptualization and scaling of hydrogeological settings in a numerical model are essential to avoid an underestimation of the landslide risk. The study demonstrates the large potential in combining state-of-the-art computational hydrology with slope stability modeling in real-world cases. 相似文献
5.
Rennie B. Kaunda Ronald B. Chase Alan E. Kehew Karlis Kaugars James P. Selegean 《Environmental Earth Sciences》2010,60(7):1545-1558
A back propagation artificial neural network approach is applied to three common challenges in engineering geology: (1) characterization
of subsurface geometry/position of the slip (or failure surface) of active landslides, (2) assessment of slope displacements
based on ground water elevation and climate, and (3) assessment of groundwater elevations based on climate data. Series of
neural network models are trained, validated, and applied to a landslide study along Lake Michigan and cases from the literature.
The subsurface characterization results are also compared to a limit equilibrium circular failure surface search with specific
adopted boundary conditions. It is determined that the neural network models predict slip surfaces better than the limit equilibrium
slip surface search using the most conservative criteria. Displacements and groundwater elevations are also predicted fairly
well, in real time. The models’ ability to predict displacements and groundwater elevations provides a foundational framework
for building future warning systems with additional inputs. 相似文献
6.
Steven Creighton Thomas Stachel Hayley McLean Karlis Muehlenbachs Antonio Simonetti Dave Eichenberg Robert Luth 《Contributions to Mineralogy and Petrology》2008,155(5):541-554
Twenty-five diamonds recovered from 21 diamondiferous peridotitic micro-xenoliths from the A154 South and North kimberlite
pipes at Diavik (Slave Craton) match the general peridotitic diamond production at this mine with respect to colour, carbon
isotopic composition, and nitrogen concentrations and aggregation states. Based on garnet compositions, the majority of the
diamondiferous microxenoliths is lherzolitic (G9) in paragenesis, in stark contrast to a predominantly harzburgitic (G10)
inclusion paragenesis for the general diamond production. For garnet inclusions in diamonds from A154 South, the lherzolitic
paragenesis, compared to the harzburgitic paragenesis, is distinctly lower in Cr content. For microxenolith garnets, however,
Cr contents for garnets of both the parageneses are similar and match those of the harzburgitic inclusion garnets. Assuming
that the microxenolith diamonds reflect a sample of the general diamond population, the abundant Cr-rich lherzolitic garnets
formed via metasomatic overprinting of original harzburgitic diamond sources subsequent to diamond formation, conversion of
original harzburgitic diamond sources occurred in the course of metasomatic overprint re-fertilization. Metasomatic overprinting
after diamond formation is supported by the finding of a highly magnesian olivine inclusion (Fo95) in a microxenolith diamond that clearly formed in a much more depleted environment than indicated by the composition of
its microxenolith host. Chondrite normalized REE patterns of microxenolith garnets are predominantly sinusoidal, similar to
observations for inclusion garnets. Sinusoidal REEN patterns are interpreted to indicate a relatively mild metasomatic overprint through a highly fractionated (very high LREE/HREE)
fluid. The predominance of such patterns may explain why the proposed metasomatic conversion of harzburgite to lherzolite
appears to have had no destructive effect on diamond content.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
18O-Enrichment of silicic magmas caused by crystal fractionation at the Galapagos Spreading Center 总被引：1，自引：1，他引：0
An extremely differentiated suite of unaltered volcanic rocks dredged from the Galapagos Spreading Center ranges in
18O from 5.7 to 7.1 At 95°W, low K-tholeiites, FeTi-basalts, andesites and rhyodacites were recovered. Their lithologic and major element geochemical variation can be accounted for by crystal fractionation of plagioclase, pyroxenes, olivine and titanomagnetite in the same proportions and amounts needed to model the
18O variation by simple Rayleigh fractionation. More complicated behaviour was observed in a FeTi-basalt suite from 85°W. This study shows that 90% fractionation only enriches the residual melt by about 1.2 in 18O. It also implies that the magma chambers along parts of the Galapagos Spreading Center were static and isolated such that extreme differentiation could occur. 相似文献
8.
Proterozoic low-sulfidation epithermal Au-Ag mineralization in the Mallery Lake area, Nunavut, Canada 总被引：2，自引：0，他引：2
William Turner Jeremy Richards Bruce Nesbitt Karlis Muehlenbachs John Biczok 《Mineralium Deposita》2001,36(5):442-457
The Mallery Lake area contains pristine examples of ancient precious metal-bearing low-sulfidation epithermal deposits. The deposits are hosted by rhyolitic flows of the Early Proterozoic Pitz Formation, but are themselves apparently of Middle Proterozoic age. Gold mineralization occurs in stockwork quartz veins that cut the rhyolites, and highest gold grades (up to 24 g/t over 30 cm) occur in the Chalcedonic Stockwork Zone. Quartz veining occurs in two main types: barren A veins, characterized by fine- to coarse-grained comb quartz, with fluorite, calcite, and/or adularia; and mineralized B veins, characterized by banded chalcedonic silica and fine-grained quartz, locally intergrown with fine-grained gold or electrum. A third type of quartz vein (C), which crosscuts B veins at one locality, is characterized by microcrystalline quartz intergrown with fine-grained hematite and rare electrum. Fluid inclusions in the veins occur in two distinct assemblages. Assemblage 1 inclusions represent a moderate temperature (Th=150 to 220 °C), low salinity (~1 eq. wt% NaCl, with trace CO2), locally boiling fluid; this fluid type is found in both A and B veins and is thought to have been responsible for Au-Ag transport and deposition. Assemblage 2 inclusions represent a lower temperature (Th=90 to 150 °C), high salinity calcic brine (23 to 31 wt% CaCl2-NaCl), which occurs as primary inclusions only in the barren A veins. Assemblage 1 and 2 inclusions occur in alternating quartz growth bands in the A-type veins, where they appear to represent alternating fluxes of dilute fluid and local saline groundwater. No workable primary fluid inclusions were observed in the C veins. The A-vein quartz yields '18O values from 8.3 to 14.5 (average=10.9ǃ.7 [1C], n=30), whereas '18O values for B-vein quartz range from 11.2 to 14.0 (average=13.0ǂ.9, n=12). Calculated '18OH2O values for the dilute mineralizing fluid from B veins range from -2.6 to 0.2 (average=-0.8ǂ.9, n=12) and are consistent with a dominantly meteoric origin. No values could be calculated for the brine, however, because all A-vein quartz samples contain mixed fluid inclusion populations. However, the fact that A-vein quartz samples extend to lower '18O values than the B veins suggests that the brine had a lighter isotopic signature relative to the dilute fluid. Hydrogen isotopic ratios of fluid inclusion waters extracted from eleven quartz samples of both vein types range from 'DFI=-56 to -134, but show no particular correlation with vein type. In most respects, the mineralogical and fluid characteristics of the Mallery Lake system are comparable to those of Phanerozoic low-sulfidation deposits, and although the presence of high salinity brines is unusual in such deposits, it is not unknown (e.g., Creede, Colorado). In addition, one of the few other examples of well-preserved, Precambrian, low-sulfidation epithermal deposits, from the Central Pilbara tectonic zone, Australia, contains a similarly bimodal fluid assemblage. The significance of these saline brines is not clear, but from this study we infer that they were not directly involved with Au-Ag transport or deposition. 相似文献
9.
Hubert Staudigel Karlis Muehlenbachs Stephen H. Richardson Stanley R. Hart 《Contributions to Mineralogy and Petrology》1981,77(2):150-157
18O and87Sr/86Sr isotopic data from smectites, calcites, and whole rocks, together with published isotopic age determinations, alkali element concentration data and petrographic observations suggest a sequential model of ocean floor alteration. The early stage lasts about 3 m.y. and is characterized by palagonite and smectite formation, and solutions with a large basaltic component, increasing with temperature which varies from 15° to 80° C at DSDP site 418A. Most carbonates are depositedafter this stage from solutions with a negligible basaltic Sr component and temperatures of 15° to 40° C. Water of seawater Sr and O isotopic composition is shown to percolate to at least 500 m into the basaltic basement. No evidence was found for continuing exchange of strontium or oxygen after 3 m.y.Lamont-Doherty Geological Observatory Contribution number 3199 相似文献
10.
T.A. Abrajano N.C. Sturchio B.M. Kennedy G.L. Lyon K. Muehlenbachs J.K. Bohlke 《Applied Geochemistry》1990,5(5-6)
Methane-hydrogen gas seeps with mantle-like C and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the Zambales ophiolite, Philippines. New measurements of noble gas and 14C isotope abundances, rock/mixed-volatile equilibrium calculations, and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration. The gas seeps are produced in rock-dominated zones of serpentinization, and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization. 相似文献