Specifying the transformations within and between geographic data models     

MARK GAHEGAN 《Transactions in GIS》1996,1(2):137-152

Geographic information is acquired according to several different underlying models of geographic space. Any meaning inherent within a dataset is intrinsically connected to the model by which it was captured. A design is presented for an integrated geographic information system offering a number of distinct views onto geographic space, of varying degrees of abstraction, to support the needs of an expanded user base. An architecture for such a system is developed by an extension of the traditional three layer architecture used in database design. The movement of data from one level of abstraction to another is formalized by a series of dataset and model transformations operating between four different geographic data models. From this formalism, a functional taxonomy of GIS operations is developed.  相似文献   

One-dimensional models of groundwater flow, sediment thermal history and petroleum generation within continental rift basins   总被引：1，自引：0，他引：1  

MARK Person  DENAH Toupin†  PETER Eadington‡ 《Basin Research》1995,7(1):81-96

We investigate the effects of convective heat transfer on the thermal history of sediments and petroleum formation within continental rift basins using one-dimensional mathematical modelling. The transport equations used in this study to describe vertical groundwater flow and conductive/convective heat transfer are solved by the finite element method. Sediment thermal history is quantitatively represented using first-order rate kinetic expressions for kerogen degradation and an empirical fanning Arrhenius model for apatite fission track annealing. Petroleum generation is also represented in the model by a suite of first-order rate kinetic expressions. The analysis provides insights into how pore fluid circulation patterns are preserved in the rock record as anomalies in palaeogeothermometric data within continental rifts. Parameters varied in the numerical experiments include the ratio of conductive to convective heat transfer (thermal Peclet number; Pe) and the composition of the disseminated organic matter in the sediment (type II and III kerogen). Quantitative results indicate that vertical groundwater flow rates on the order of a mm/yr cause a change in computed vitrinite reflectance of the rocks and a shift in the depth to oil generation by as much as 3000 m. Differences in thermal gradients between recharge and discharge areas (Pe= 0.6) also change the width of the zone of oil generation by a factor of two. Even more dramatic, however, are the large changes in predicted apatite fission track length distributions and model ages between recharge and discharge areas. For example, a sediment package buried to a depth of 2400 m over 200 Myr within the groundwater recharge column had a fission track length distribution with a computed mean and standard deviation of 12.83 μm and 0.77 μm, respectively. The fission track model age for this sediment package was 209 Ma. The same sediment package in the discharge area has a distribution with a mean track length of 5.68 μm, a standard deviation of 3.37 μm, and a fission track model age of 2.6 Ma. Transient groundwater flow simulations, in which fluid circulation ceases after a period of time within the rift basin, are also presented to illustrate how disturbances in palaeogeothermometric parameters are preserved on geological time-scales. Vitrinite reflectance profiles require about 10 Myr to return to conductive conditions within groundwater recharge areas while the convective disturbances are preserved indefinitely along the discharge column, as long as further subsidence does not occur. Ancient groundwater flow systems are preserved as anomalies in computed apatite fission track model ages and distributions much longer after groundwater flow stops, relative to organic-based geothermometers. Significant differences exist in model ages between recharge (145 Ma) and discharge (90 Ma) areas 200 Myr after flow has ceased. However, calculated fission track histogram distributions are virtually identical in recharge and discharge areas after about 50 Myr. Our study suggests that ancient groundwater flow systems can be detected by comparing thermochronometric data between suspected recharge and discharge areas within continental rifts. Vitrinite reflectance profiles, observed offsets in the depth to the onset of petroleum generation, and apatite fission track annealing studies are all well suited for detecting groundwater flow systems which have been relatively long lived (10⁷ years). Apatite fission track age data are probably best suited for identifying ancient groundwater flow systems within rifts long (>200 Myr) after flow ceases.  相似文献   

Dissolution Rates of Upper Mantle Minerals in an Alkali Basalt Melt at High Pressure: An Experimental Study and Implications for Ultramafic Xenolith Survival   总被引：7，自引：0，他引：7  

BREARLEY  MARK; SCARFE  CHRISTOPHER M. 《Journal of Petrology》1986,27(5):1157-1182

The dissolution rates of the major upper mantle minerals olivine,orthopyroxene, clinopyroxene, spinel, and garnet have been determinedin an alkali basalt melt at superliquidus temperatures and 5,12, and 30 kb. At low pressure where olivine is the liquidusphase of the basalt, olivine has a slower dissolution rate thanclinopyroxene; however, at higher pressure where clinopyroxeneis the liquidus phase, clinopyroxene has a slower dissolutionrate than olivine. The relative rates of dissolution of olivineand clinopyroxene at each pressure are, therefore, governedby their relative stabilities in the melt and hence by the structureof the melt. As the degree of superheating above the liquidusincreases at each pressure, the dissolution rates of olivineand clinopyroxene converge, suggesting that the melt undergoestemperature-induced structural changes. Orthopyroxene has a dissolution rate similar to olivine at highpressure and similar to clinopyroxene at low pressure. Spinelhas the slowest dissolution rate at each pressure. Garnet dissolvesvery rapidly at 12 kb and at a comparable rate of olivine at30 kb. The dissolution rates determined in the experiments varyfrom 9.21 ? 10^–9cm s^–1 for spinel at 5 kbar and1250?C to 3.83 ? 10^–5cm s^–1 for garnet at 30 kband 1500?C. Textures produced during the dissolution experiments are relatedto mineral stability in the melt at each pressure and are independentof the degree of superheating. The mineral phases that are stableon or near the liquidus exhibit no reaction; whereas complexreaction textures and crystallization characterize dissolutionof minerals that are relatively unstable in the melt. Concentration profiles in the melt adjacent to the same crystalfor different experimental durations are identical, indicatingthat dissolution is time-independent and a steady-state process.However, cation diffusion coefficients calculated for single-componentoxides in the melt reveal that dissolution may not be completelycontrolled by diffusion of cations away from the crystal/meltinterface. The apparent diffusivities positively correlate withthe dissolution rate, which suggests that the stability of themineral is an important factor to consider when deriving diffusioncoefficients from these experiments. Other factors that maybe involved are multi-component effects and the nature of thediffusing species in the melt. A simple model has been constructed that predicts the survivalof ultramafic xenoliths in alkali basalt magmas as a functionof xenolith radius, magma ascent time and superheating. Theresults of the model suggest that the relative proportions ofperidotite and pyroxenite xenoliths brought to the surface inalkali basalts are generally representative of their proportionsas constituents of the upper mantle. Further experiments usingdifferent melt compositions are required to extend the model.  相似文献   

Long-Term Evolution of Fluid-Rock Interactions in Magmatic Arcs: Evidence from the Ritter Range Pendant, Sierra Nevada, California, and Numerical Modeling     

HANSON  R. BROOKS; SORENSEN  SORENA S.; BARTON  MARK D.; FISKE  RICHARD S. 《Journal of Petrology》1993,34(1):23-62

A record of > 100 million years of fluid flow, alteration,and metamorphism in the evolving Sierra Nevada magmatic areis preserved in metavolcanic rocks of the Ritter Range pendantand surrounding granitoids. The metavolcanic rocks consist of:(1) a lower section of mostly marine volcaniclastic rocks, lavas,and intercalated carbonate rocks that is Triassic to Jurassicin age, and (2) an upper section comprising a subaerial caldera-fillcomplex of mid-Cretaceous age. Late Cretaceous high-temperaturecontact metamorphism (2 kbar, >450–500C) occurredafter renewed normal faulting along the caldera-bounding faultsystem juxtaposed the two sections. The style and degree of alteration and ¹⁸O values differ amongthe rocks of the upper and lower sections and the granitoids.Rocks of the lower section show pervasive lithologically controlledalkali alteration, local Mn and Mg enrichment, and oxidation.Some ash flow tuffs now contain up to 10% K²O by weight. Therocks of the upper section show lesser extents of alkali alteration.Granitoids that cut both sections are generally unaltered. Mostmetavolcanic rocks of the lower section have high ¹⁸O values(+ 11 to + 16%; whole rock and quartz phenocrysts); however,lower-section rocks within the caldera-bounding fault systemhave low ¹⁸O values of + 4 to +7. The metavolcanic rocks ofthe upper section also have low ¹⁸O values of + 2 to + 7. Granitoidshave ¹⁸O values of + 7 to + 10, typical of unaltered Sierrangranitoids. The lower section contains discontinuous veins ofhigh-temperature (450–500C) calc-silicate minerals. Theseveins are typically <5 m long, do not cross intrusive contacts,and postdate the pervasive alkali alteration. Late veins aretypically > 10 m long, formed at temperatures of less than450–500C, and cross intrusive contacts. Veins have similar¹⁸O values to those of the local host rocks. The nature of the alteration and the high oxygen isotopic valuesof the rocks of the lower section indicate that these rocksinteracted extensively with seawater at temperatures <300C,probably in superposed marine hydrothermal systems associatedwith coeval volcanic centers. Metavolcanic rocks of the uppersection evidently interacted with meteorie waters, probablyin a hydrothermal system associated with the Cretaceous caldera;rocks of the lower section that were adjacent to the calderawere also affected by this alteration. The preservation of thesignatures of these earlier events, the nature of the earlyveins, and results from numerical models of hydrothermal flowthat include fluid production indicate that during progradecontact metamorphism, the rocks of the pendant primarily interactedwith locally derived fluids. Fluid flow was predominantly upwardand away from intrusive contacts and down-temperature. Permeabilitiesare estimated to have been between 0•1 and 1µD, whichis that necessary for maintenance of lithostatic fluid pressures.In hydrothermal models with such permeabilities, large-scalecirculation of meteoric fluids develops after prograde metamorphismceases. The nature of the late veins in the Ritter Range pendantsuggests that such a flow pattern evolved only after the pendantand granitoids had cooled below 450–500C. The long-termhistory of alteration documented in the Ritter Range pendantis probably typical of wall rocks in most batholiths *Present address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721  相似文献   

Rheological Properties of Partially Molten Lherzolite   总被引：2，自引：1，他引：2  

ZIMMERMAN  MARK E.; KOHLSTEDT  DAVID L. 《Journal of Petrology》2004,45(2):275-298

Lherzolite samples synthesized from fine-grained powders preparedfrom a natural xenolith were deformed at P = 300 MPa and 1373  相似文献   

ALPINE AREAS IN THE COLORADO FRONT RANGE AS MONITORS OF CLIMATE CHANGE AND ECOSYSTEM RESPONSE*     

MARK W. WILLIAMS  MARK V. LOSLEBEN  HILLARY B. HAMANN 《Geographical review》2002,92(2):180-191

ABSTRACT. The presence of a seasonal snowpack in alpine environments can amplify climate signals. A conceptual model is developed for the response of alpine ecosystems in temperate, midlatitude areas to changes in energy, chemicals, and water, based on a case study from Green Lakes Valley–Niwot Ridge, a headwater catchment in the Colorado Front Range. A linear regression shows the increase in annual precipitation of about 300 millimeters from 1951 to 1996 to be significant. Most of the precipitation increase has occurred since 1967. The annual deposition of inorganic nitrogen in wetfall at the Niwot Ridge National Atmospheric Deposition Program site roughly doubled between 1985–1988 and 1989–1992. Storage and release of strong acid anions, such as those from the seasonal snowpack in an ionic pulse, have resulted in episodic acidification of surface waters. These biochemical changes alter the quantity and quality of organic matter in high‐elevation catchments of the Rocky Mountains. Affecting the bottom of the food chain, the increase in nitrogen deposition may be partly responsible for the current decline of bighorn sheep in the Rocky Mountains.  相似文献   

A preliminary history of Holocene colluvial (debris-flow) activity,Leirdalen, Jotunheimen,Norway     

JOHN A. MATTHEWS  SVEIN-OLAF DAHL  MARK S. BERRISFORD  ATLE NESJE  P. QUENTIN DRESSER  LISA DUMAYNE-PEATY 《第四纪科学杂志》1997,12(2):117-129

A stratigraphic succession of alternating peat and minerogenic sediments at the foot of a steep mountain slope provides the basis for the reconstruction of a preliminary colluvial history from the alpine zone of Jotunheimen, southern Norway. Layers of silty sand and sandy silt, typically 5–10 cm thick and interpreted as distal debris-flow facies, are separated by layers of peat that have been radiocarbon dated. Deposition from at least 7500 to about 3800 ¹⁴C yr BP of predominantly minerogenic material suggests relatively infrequent but large-magnitude debris-flow events in an environment warmer and/or drier than today. Particularly low colluvial activity between about 6500 and 3900 ¹⁴C yr BP was terminated by a succession of major debris-flow events between about 3800 and 3400 ¹⁴C yr BP. Unhumified peats indicative of higher water tables, separate six debris-flows that occurred between about 3300 and 2300 ¹⁴C yr BP and signify a continuing high frequency of colluvial activity. Uninterrupted peat accumulation between about 2400 and 1600 ¹⁴C yr BP indicates reduced debris-flow activity; subsequent renewed activity appears to have culuminated in the ‘Little Ice Age’ after about 600 ¹⁴C yr BP. This pattern of colluvial deposition demonstrates a long history of natural Holocene low-alpine landscape instability, suggests an increase first in the magnitude and then in the frequency of debris-flow activity coincident with late Holocene climatic deterioration, and points to the potential of debris-flow records as a unique source of palaeoclimatic information related to extreme rainfall events. © 1997 John Wiley & Sons, Ltd.  相似文献   

The China Clipper — fast advective transport of radon-rich air from the Asian boundary layer to the upper troposphere near California     

MARK A. KRITZ  JEAN-CLAUDE LE ROULLEY  EDWIN F. DANIELSEN 《Tellus. Series B, Chemical and physical meteorology》1990,42(1):46-61

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CITY OF VOLCANOES. A GEOLOGY OF AUCKLAND by Professor Searle and R. D. Mayhill.     

MARK MABIN 《New Zealand geographer》1983,39(2):98-98

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A comparative analysis of some two-dimensional orderings     

DAVID J. ABEL  DAVID M. MARK 《International journal of geographical information science》2013,27(1):21-31

Abstract

Many spatial analysis algorithms for cellular representations and data structures are based on an ordering of cells or objects to transform a two-dimensional problem to a one-dimensional one. Several orderings are available and their differing properties influence the performance of the data structures and algorithms. The relative merits of five orderings (row, row prime, Hilbert, Morton and Gray code) are assessed empirically for four paradigmatic geographical data-processing tasks in spatial analysis and data management. It is concluded that the Hilbert ordering deserves further investigation.  相似文献