Degradation and Metamorphic Differentiation of the Keweenawan Tholeiitic Lavas of Northern Michigan, U.S.A.     

JOLLY  WAYNE T.; SMITH  RAYMOND E. 《Journal of Petrology》1972,13(2):273-309

The Portage Lake Lava Series of the Keweenaw Peninsula, northernMichigan, is composed of over 5000 m of tholeiitic lava flows.Chemical and petrologic study of thin undifferentiated flowsfrom this sequence shows that the bulk of the flows are olivinetholeiites; highly ironenriched tholeiites comprise up to 10per cent of the volume. In addition, a few small rhyolitic intrusives,exceedingly rich in alkalis, are exposed in the region. Duringburial the amygdular tops of each flow acted as channelwaysfor migrating fluids during a regional metamorphic event thatproduced a progressive sequence of secondary phases within theflow tops. In the upper part of the stratigraphic section, laumontite,analcime, albite, and chlorite dominate assemblages characteristicof the zeolite facies. Stratigraphically deeper. flow tops arecharacterized by metamorphic assemblages of the prehnite-pumpellyitefacies. Within the higher rank facies, rocks along fractureshave been transformed to calcium-rich monomineralic domains(metadomains) of epidote or pumpellyite. These metadomains gradeoutward through incompletely reconstituted rocks containingalbitized feldspars, and finally, in flow centers, to basaltdisplaying few signs of mineralogical readjustment. Extremechemical disparity exists within the altered flow tops, particularlywith respect to calcium and sodium content. Calculations revealthat bulk compositions of metamorphically adjusted flow topsare similar to unaltered basalts. Thus, the chemical variationdisplayed by the metamorphic rock types resulted from localizedmetamorphic differentiation. The Keweenawan sequence displays progressive dehydration fromthe top to the base of the stratigraphic section. At the topchlorite (H₂O = 12 per cent) and pumpellyite (H₂O = 6 per cent)metadomains formed by dehydration. The fact that most of theserocks were hydrated strongly suggests that fluid pressures wereless than total pressures during the metamorphic event. In rocksundergoing hydration in the uper part of the stratigraphic section,therefore, water pressures decreased away from channelways.As a result, the most hydrous rock types formed in these regions.Conversely, in rock undergoing dehydration water pressures increasedaway from channelwasys, so that the most dehydrated rocks formedin such regions. Water content of an individual rock is dependenton both position in the stratigraphic pile and position withrespect to fluid channelways.  相似文献   

Compositional Zoning in Pyroxenes from Lunar Rock 12021, Oceanus Procellarum     

BOYD  F. R.; SMITH  DOUGLAS 《Journal of Petrology》1971,12(3):439-464

Electron probe study of the pyroxene phenocrysts in rock 12021of the Apollo 12 sample reveals an extraordinary variety ofzoning phenomena. These phenocrysts have cores of relativelyhomogeneous pigeonite which are mantled by Ca-rich pyroxenes;the mantles are zoned outward from about 20 mol per cent FeSiO₃at the core-mantle boundaries to 70 mol per cent FeSiO₃ at themargins of the phenocrysts. The character of the normal zoningdiffers in each growth sector. Four different trends characterizinggrowth on (110), (100), (010), and parallel to c are described.Pronounced but erratic oscillatory effects are impressed onthe normal zoning in all sectors. Normal zoning in lunar pyroxenes is generally more extensivethan in terrestrial pyroxenes, probably because the lunar lavaswere an order of magnitude more fluid than terrestrial basalts.Turbulent flow in lunar lavas may have caused some of the oscillatoryeffects. The cyclic nature of augite and pigeonite crystallizationin these pyroxenes is probably kinetic in origin; conceivablyit could reflect the presence of an augite-pigeonite peritectic.It is likely that further knowledge of the crystal structureof pigeonite at high temperatures will be required before astructural model can be formulated that will satisfactorilyexplain the details of the sector zoning. Coarse-grained pyroxferroite and subcalcic ferroaugite havecrystallized in apparent ‘equilibrium’ in the finalstages of formation of the groundmass in rock 12021. Nevertheless,the crystallization of the pyroxferroite was probably metastablerelative to the assemblage ferroaugite+ fayalite+ tridymite.Data on the effect of Mg substitution on the stability of pyroxferroitewill be needed to establish this point. We suggest that the pigeonite cores of the phenocrysts in rock12021 crystallized under quiescent conditions, probably in amagma chamber below the lunar surface, and that the stronglyzoned augite mantles crystallized during emplacement of thelava on the surface.  相似文献   

Spatial and temporal patterns of iceberg rafting (IRD) along the East Greenland margin,ca. 68°N,over the last 14 cal.ka     

J. T. ANDREWS  L. M. SMITH  R. PRESTON  T. COOPER  A. E. JENNINGS 《第四纪科学杂志》1997,12(1):1-13

Twelve 1–2 m, 10-cm-diameter gravity cores collected in 1988 and 1991, from the continental shelf and fjords of East Greenland near Kangerlussuaq Fjord/Trough (ca. 68°N, 32°W), have distinct changes in lithofacies and in the quantity of iceberg rafted (IRD) sediments. These changes are readily observed in X-radiographs of the split cores. We quantify the IRD contribution through grain-size analyses and counting the number of clasts >2 mm from the X-radiographs. Chronological control is provided by acclerated mass spectroscopy ¹⁴C dates on foraminifera. During deglaciation, after 14 cal.ka there was one interval of IRD accumulation ca. 12–13 cal.ka, followed by a brief return to IRD conditions centred at 9 cal.ka. Thereafter, a prominent feature of most cores on the shelf is an increase in IRD accumulation that started ca. 5–6 cal.ka, and which has increased toward the present. Indicators of iceberg rafting, such as the net sand flux and numbers of clasts >2 mm ka⁻¹, follow a power law distribution when graphed against distance from the present East Greenland coast, a measure of the position of the glacier margins. The form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf. These relationships are used to estimate changes in the location of the ice margin during the late Quaternary based on a site on the East Greenland slope, Denmark Strait, and to discuss factors that can negate such a simple transfer function. © 1997 by John Wiley & Sons Ltd.  相似文献   

RECENT STUDIES IN GEOPHYSICAL HAZARDS edited by M. I. El-Sabh,T. S. Murty,S. Venkatesh,F. Siccardi and K. Andah,Kluwer Academic Publishers,Dordrecht, 1994. No. of pages: 285. ISBN 0-7923-2972-4.     

KEITH SMITH 《地球表面变化过程与地形》1996,21(10):979-979

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COPING WITH FLOODS edited by G. Rossi,N. Harmancioglu and V. Yevjevich,NATO ASI Series,Kluwer Academic Publishers,Dordrecht, 1994. No. of pages: xiii + 776. Price: £193.00. ISBN 0-7923-2706-3.     

KEITH SMITH 《地球表面变化过程与地形》1996,21(8):778-778

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The place of rural, remote and least-wealthy small islands in international water development: the nexus of geography–technology sustainability in Chuuk State, Federated States of Micronesia     

WILLIAM JAMES SMITH JR 《The Geographical journal》2008,174(3):251-268

Many least-wealthy, rural, remote and resource-poor small island communities are unlikely to benefit from high-profile global water improvement initiatives. Their small landmasses, geologic composition, geography, social and technological isolation, colonial history, and weak educational and financial resources constitute significant barriers to improving access to safe drinking water. This paper discusses the relatively unique position of such island societies in the international community, providing a case study of the Federated States of Micronesia that integrates data and information pertaining to water resources management and governance, spanning from the island village to national scale. A vision is offered regarding the interaction between small island human and biophysical water systems, manifesting ways to pursue water resource development to improve public health which are constructed to be economically, physically and culturally sustainable.  相似文献   

KBGIS-II A knowledge-based geographical information system     

TERENCE SMITH  DONNA PEUQUET  SUDHAKAR MENON  PANKAJ AGARWAL 《International journal of geographical information science》2013,27(2):149-172

Abstract

This paper describes the architecture and working of a recently implemented knowledge-based GIS (KBGIS-II) that was designed to satisfy several general criteria for GIS. The system has four major functions, query-answering, learning, editing and training. The main query finds constrained locations for spatial objects that are describable in a predicate-calculus based spatial object language. The main search procedures include a family of constraint-satisfaction procedures that use a spatial object knowledge base to search efficiently for complex spatial objects in large, multi-layered spatial data bases. These data bases are represented in quadtree form. The search strategy is designed to reduce the computational cost of search in the average case. The learning capabilities of the system include the addition of new locations of complex spatial objects to the knowledge base as queries are answered, and the ability to learn inductively definitions of new spatial objects from examples. The new definitions are added to the knowledge base by the system. The system is currently performing all its designated tasks successfully, although currently implemented on inadequate hardware.  相似文献   

Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar     

PHILIP J. ASHWORTH  GREGORY H. SAMBROOK SMITH  JAMES L. BEST  JOHN S. BRIDGE  STUART N. LANE  IAN. A. LUNT  ARNOLD J. H. REESINK  CHRISTOPHER J. SIMPSON  ROBERT E. THOMAS 《Sedimentology》2011,58(7):1860-1883

The depositional stratigraphy of within‐channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular ‘unit’ bars and complex ‘compound’ bars), as well as the infill of individual channels (herein termed ‘channel fills’). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within‐channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1·3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (< 1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground‐penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grain‐size trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object‐based models of sandy braided river alluvial architecture.  相似文献   

A Possible Influence of Tethyan Ophiolite Emplacement on North and Central Atlantic Spreading     

Alan G. SMITH 《《地质学报》英文版》2013,87(Z1):185-186

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Availability of suitable land-fast ice and predation as factors limiting ringed seal populations, Phoca hispida, in Svalbard     

THOMAS G. SMITH  CHRISTIAN LYDERSEN 《Polar research》1991,10(2):585-594

We examined the stability of fast ice areas in western and northern Spitsbergen, the area north of Nordaustlandet, the bays and sounds of Hinlopen Stretet and the large area in the northern part of Storfjorden. NOAA satellite imagery from 1974 and 1988 and NOAA (AVHRR) imagery from 1980-87 were used to determine the dates of freeze-up and break-up. The number of days of fast ice present before the nominal birth date of ringed seal pups were computed for all major bays and fjords. Ice thickness was then computed from these data. Known prime breeding habitat in Svalbard is found in areas near glacier fronts in protected fjords and bays, where densities of birth lairs are 5.46 km⁻², corresponding to a ringed seal female density of 2.6 km⁻². Most of the ringed seal breeding habitat in Svalbard, however, consists of flat fjord ice where snow accumulation is rarely deep enough to permit birth lair construction. In these areas pups are often born in the open. Based on breathing hole densities, the density of adult females in the flat ice areas in the breeding period was estimated to 0.98 km⁻². A preliminary estimate is that approximately 19,500 pups could be born annually in the fast ice of Svalbard. Annual recruitment could be quite variable given the unpredictable nature of the fast ice areas and the high predation mortality on newborn pups. Discrepancies between our calculated ringed seal production and numbers of seals required to feed the large polar bear population in the area signal cause for management concern.  相似文献