U-Pb zircon geochronology of late Neoproterozoic–Early Cambrian granitoids in Iran: Implications for paleogeography, magmatism, and exhumation history of Iranian basement     

Jamshid Hassanzadeh  Daniel F. Stockli  Brian K. Horton  Gary J. Axen  Lisa D. Stockli  Marty Grove  Axel K. Schmitt  J. Douglas Walker 《Tectonophysics》2008,451(1-4):71-96

Eurasia has largely grown to its present enormous size through episodic addition of crustal blocks by recurring birth and demise of oceans such as Paleotethys and Neotethys. Excluding the Kopet Dagh Mountains in the northeast, crystalline basement rocks of various dimensions are exposed in all continental tectonic zones of Iran. These rocks have traditionally been viewed as continental fragments with Gondwanan affinity and summarily been assigned Precambrian or younger ages, despite the fact that evidence from isotopic dating has largely been lacking. This study presents new ion microprobe and thermal-ionization zircon U-Pb geochronological data from granitoids and orthogneisses from several locations in central Iran and the Sanandaj–Sirjan structural zones to determine crystallization ages and investigate the origin and continental affinity of these various crustal fragments. The resulting U-Pb crystallization ages for the granites and orthogneisses range from late Neoproterozoic to Early Cambrian, matching the mostly juvenile Arabian–Nubian shield and Peri-Gondwanan terranes constructed after the main phase of Pan-African orogenesis. TIMS analyses of zircons with inherited cores from western Iran suggest that the Neoproterozoic crust of Iran might not be entirely juvenile, pointing to the potential presence of inherited older Proterozoic components as is common in the eastern Arabian shield. More importantly, the new zircon U-Pb crystallization ages unequivocally demonstrate that crystalline basement underlying the Sanandaj–Sirjan zone, central Iran, and the Alborz Mountains is composed of continental fragments with Gondwanan affiliation, characterized by wide spread late Neoproterozoic subduction-related magmatism. The exposure of these late Neoproterozoic–Early Cambrian basement rocks in the Iranian regions north of the Zagros is structurally controlled and linked to both large-scale crustal extension and exhumation during Mesozoic and Tertiary time as well as Tertiary collisional tectonics associated with the closure of Neotethys.  相似文献   

Effect of iron and carbonation on the diffusion of iodine and rhenium in waste encasement concrete and soil fill material under hydraulically unsaturated conditions     

Dawn M. Wellman  Kent E. Parker  Laura Powers  Greg A. Whyatt  Libby N. Clayton  Shas V. Mattigod  Marcus I. Wood 《Applied Geochemistry》2008,23(8):2256-2271

Assessing long-term performance of Category 3 cement wasteforms and accurate prediction for radionuclide encasement requires knowledge of the radionuclide–cement interactions and mechanisms of retention (i.e. sorption or precipitation). A set of sediment-concrete half-cell diffusion experiments was conducted under unsaturated conditions (4% and 7% by weight moisture content) using carbonated and non-carbonated concrete–soil half cells. Results indicate the behavior of Re and I release was comparable within a given half-cell test. Diffusivity in soil is a function of moisture content; a 3% increase in moisture content affords a one to two order of magnitude increase in diffusivity. Release of I and Re was 1–3 orders of magnitude less from non-carbonated, relative to carbonated, concrete monoliths. Inclusion of Fe in non-carbonate monoliths resulted in the lowest concrete diffusivity values for both I and Re. This suggests that in the presence of Fe, I and Re are converted to reduced species, which are less soluble and better retained within the concrete monolith. The release of I and Re was greatest from Fe-bearing, carbonated concrete monoliths, suggesting carbonation negates the effect of Fe on the retention of I and Re within concrete monoliths. This is likely due to enhanced formation of microcracks in the presence of Fe, which provide preferential paths for contaminant migration. Although the release of I and Re were greatest from carbonated concrete monoliths containing Fe, the migration of I and Re within a given half cell is dependent on the moisture content, soil diffusivity, and diffusing species.  相似文献   

INTERSTATE POPULATION MIGRATION PROCESS AND STRUCTURE IN THE UNITED STATES, 1935 TO 1970*     

Christopher Clayton 《The Professional geographer》1977,29(2):177-181

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A multidimensional scaling approach to enforce reproduction of transition probabilities in truncated plurigaussian simulation   总被引：2，自引：1，他引：1  

Jared L. Deutsch  Clayton V. Deutsch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):707-716

Truncated plurigaussian (TPG) simulation is a flexible method for simulating rock types in deposits with complicated ordering structures. The truncation of a multivariate Gaussian distribution controls the proportions and ordering of rock types in the simulation while the variogram for each Gaussian variable controls rock type continuity. The determination of a truncation procedure for complicated geological environments is not trivial. A method for determining the truncation and fitting variograms applicable to any number of rock types and multivariate Gaussian distribution is developed here to address this problem. Multidimensional scaling is applied to place dissimilar categories far apart and similar categories close together. The multivariate space is then mapped using a Voronoi decomposition and rotated to optimize variogram reproduction. A case study simulating geologic layers at a large mineral deposit demonstrates the potential of this method and compares the results with sequential indicator simulation (SIS). Input proportion and transition probability reproduction with TPG is demonstrated to be better than SIS. Variogram reproduction is comparable for both techniques.  相似文献   

Bioturbation by gophers and marmots and its effects on conifer germination          下载免费PDF全文

Clayton J. Whitesides  David R. Butler 《地球表面变化过程与地形》2016,41(15):2269-2281

Although climate has been shown to have a considerable influence on alpine forest dynamics, many fine‐scale processes contribute to observable forest patterns. Disturbances created by burrowing mammals may provide conifer seedlings with refuge in previously inhospitable environments and may result in conifer invasion that is not directly associated with climate change. In Olympic National Park, Washington, USA, Olympic marmot (Marmota olympus) populations have declined. Abandoned marmot burrows, which may provide ideal sites for conifer establishment, now dot the alpine landscape. Similarly, in Glacier National Park, Montana, USA, pocket gophers (Thomomys talpoides) have disturbed large areas of alpine meadows at treeline. Field and laboratory analysis of gopher eskers and spoil mounds of abandoned marmot burrows illustrated that such sites are less compacted than soils in adjacent, undisturbed locations. Additionally, disturbed soils contained higher amounts of phosphorus and lower amounts of potassium and organic matter. Soils disturbed by gophers were cooler at the surface and warmer at depth than undisturbed soils, whereas marmot‐disturbed soils were warmer at the surface and cooler at depth. Experimental seed germination of subalpine fir (Abies lasiocarpa) was higher on mammal‐disturbed soils, and this was statistically significant for marmot‐disturbed soils. These findings suggest that fossorial mammal disturbances have the potential to affect conifer germination and establishment. Furthermore, this research initiates the dialogue for future research on the distinct morphological and behavioral influences of different fossorial mammals as zoogeomorphic agents and ecosystem engineers. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Multivariate grid-free geostatistical simulation with point or block scale secondary data   总被引：1，自引：1，他引：0  

Yevgeniy Zagayevskiy  Clayton V. Deutsch 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(6):1613-1633

A novel grid-free geostatistical simulation method (GFS) allows representing coregionalized variables as an analytical function of the coordinates of the simulation locations. Simulation on unstructured grids, regridding and refinement of available realizations of natural phenomena including, but not limited to, environmental systems are possible with GFS in a consistent manner. The unconditional realizations are generated by utilizing the linear model of coregionalization and Fourier series-based decomposition of the covariance function. The conditioning to data is performed by kriging. The data can be measured at scattered point-scale locations or sampled at a block scale. Secondary data are usually used in conjunction with primary data for the improved modeling. Satellite imaging is an example of exhaustively sampled secondary data. Improvements and recommendations are made to the implementation of GFS to properly assimilate secondary exhaustive data sets in a grid-free manner. Intrinsic cokriging (ICK) is utilized to reduce computational time and preserve the overall quality of the simulation. To further reduce the computational cost of ICK, a block matrix inversion is implemented in the calculation of the kriging weights. A projection approach to ICK is proposed to avoid artifacts in the realizations around the edges of the exhaustive data region when the data do not cover the entire modeling domain. The point-scale block value representation of the block-scale data is developed as an alternative to block cokriging to integrate block-scale data into realizations within the GFS framework. Several case studies support the proposed enhancements.  相似文献   

Persistence of the surface texture of a gravel‐bed river during a large flood     

Jordan A. Clayton  John Pitlick 《地球表面变化过程与地形》2008,33(5):661-673

We present herein clear field evidence for the persistence of a coarse surface layer in a gravel‐bed river during flows capable of transporting all grain sizes present on the channel bed. Detailed field measurements of channel topography and bed surface grain size were made in a gravel‐bed reach of the Colorado River prior to a flood in 2003. Runoff produced during the 2003 snowmelt was far above average, resulting in a sustained period of high flow with a peak discharge of 27 m³/s (170% of normal peak flow); all available grain sizes within the study reach were mobilized in this period of time. During the 2003 peak flow, the river avulsed immediately upstream of the study reach, thereby abandoning approximately one half kilometer of the former channel. The abandonment was rapid (probably within a few hours), leaving the bed texture essentially frozen in place at the peak of the flood. All locations sampled prior to the flood were resampled following the stream abandonment. In response to the high flow, the surface median grain size (D_50s) coarsened slightly in the outer part of the bend while remaining nearly constant along the inner part of the bend, resulting in an overall increase from 18 to 21 mm for the study reach. Thus, the coarse bed surface texture persisted despite shear stresses throughout the bend that were well above the critical entrainment value. This may be explained because the response of the bed texture to increases in flow strength depends primarily upon the continued availability of the various grain size percentiles in the supply, which in this case was essentially unlimited for all sizes present in the channel. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

A physical–chemical model for the static water retention characteristic of unsaturated porous media     

Y. Wang  S.M. Grove  M.G. Anderson 《Advances in water resources》2008

Water retention characteristic or water retention curve (WRC) is an important constitutive feature of porous media, and also meanwhile is an indispensable requirement in hydraulic transport modelling. Previous experiments have indicated that the specific surface area of porous media has effects on the WRC. It has also been observed that a linear relationship generally exists between the air–water interface area and the water saturation within unsaturated porous media. However it seems that no detailed study on their internal linkage with the WRC has been reported yet. This paper, at first gives a review of the development of WRC modelling, then it tries to explain the water retention characteristic according to the physical and chemical behaviours of the phases involved in unsaturated porous media. Using the traditional capillary theory, the volume averaging theorem and the advances in physical chemistry of interfacial surfaces, this paper then derives out a formula which represents the water retention characteristic of porous media. This formula demonstrates the internal linkage of the WRC to the specific surface area of porosities. It also shows agreements with the experimental observations mathematically. Based on this formula, a fitting model is proposed for the static WRC of porous media. Finally, this model is tested to fit the WRC measurements of a wide range of porous materials. Comparison with other main models is presented.  相似文献   

Accounting for Parameter Uncertainty in Reservoir Uncertainty Assessment: The Conditional Finite-Domain Approach     

Olena Babak  Clayton V. Deutsch 《Natural Resources Research》2009,18(1):7-17

An important aim of modern geostatistical modeling is to quantify uncertainty in geological systems. Geostatistical modeling requires many input parameters. The input univariate distribution or histogram is perhaps the most important. A new method for assessing uncertainty in the histogram, particularly uncertainty in the mean, is presented. This method, referred to as the conditional finite-domain (CFD) approach, accounts for the size of the domain and the local conditioning data. It is a stochastic approach based on a multivariate Gaussian distribution. The CFD approach is shown to be convergent, design independent, and parameterization invariant. The performance of the CFD approach is illustrated in a case study focusing on the impact of the number of data and the range of correlation on the limiting uncertainty in the parameters. The spatial bootstrap method and CFD approach are compared. As the number of data increases, uncertainty in the sample mean decreases in both the spatial bootstrap and the CFD. Contrary to spatial bootstrap, uncertainty in the sample mean in the CFD approach decreases as the range of correlation increases. This is a direct result of the conditioning data being more correlated to unsampled locations in the finite domain. The sensitivity of the limiting uncertainty relative to the variogram and the variable limits are also discussed.  相似文献   

A two-stage fluid history for the Orocopia Schist and associated rocks related to flat subduction and exhumation,southeastern California     

Gregory J. Holk  Marty Grove  Carl E. Jacobson  Gordon B. Haxel 《International Geology Review》2017,59(5-6):639-663

ABSTRACT

Stable isotopes combined with pre-existing ⁴⁰Ar/³⁹Ar thermochronology at the Gavilan Hills and Orocopia Mountains in southeastern California record two stages of fluid–rock interaction: (1) Stage 1 is related to prograde metamorphism as Orocopia Schist was accreted to the base of the crust during late Cretaceous–early Cenozoic Laramide flat subduction. (2) Stage 2 affected the Orocopia Schist and is related to middle Cenozoic exhumation along detachment faults. There is no local evidence that schist-derived fluids infiltrated structurally overlying continental rocks. Mineral δ¹⁸O values from Orocopia Schist in the lower plate of the Chocolate Mountains fault and Gatuna normal fault in the Gavilan Hills are in equilibrium at 490–580°C with metamorphic water (δ¹⁸O = 7–11‰). Phengite and biotite δD values from the Orocopia Schist and upper plate suggest metamorphic fluids (δD ~ –40‰). In contrast, final exhumation of the schist along the Orocopia Mountains detachment fault (OMDF) in the Orocopia Mountains was associated with alteration of prograde biotite and amphibole to chlorite (T ~ 350–400°C) and the influx of meteoric-hydrothermal fluids at 24–20 Ma. Phengites from a thin mylonite zone at the top of the Orocopia Schist and alteration chlorites have the lowest fluid δD values, suggesting that these faults were an enhanced zone of meteoric fluid (δD < –70‰) circulation. Variable δD values in Orocopia Schist from structurally lower chlorite and biotite zones indicate a lesser degree of interaction with meteoric-hydrothermal fluids. High fluid δ¹⁸O values (6–12‰) indicate low water–rock ratios for the OMDF. A steep thermal gradient developed across the OMDF at the onset of middle Cenozoic slip likely drove a more vigorous hydrothermal system within the Orocopia Mountains relative to the equivalent age Gatuna fault in the Gavilan Hills.  相似文献