Forest-Landscape Structure along an Urban-To-Rural Gradient*     

Kimberly E. Medley  Mark J. McDonnell  Steward T. A. Pickett 《The Professional geographer》1995,47(2):159-168

Human activities and forest-landscape structure are examined along a belt transect that extends 140 km from New York City to northwestern Connecticut. The study quantifies urban structures (population density, land use. transportation) and processes (population growth, urban land development) in the transect, and tests for relationships with the distribution, sizes, and shapes of forests. Our results identify distinct characteristics of urban and suburban environments based on the landscape structure of native forest vegetation. These findings are applicable to the management of natural areas along a gradient of urbanization.  相似文献   

Discussion of "A Comparison of Ground Water Monitoring Data from CERCLA and RCRA Sites," by Russell H. Plumb, Ground Water Monitoring Review, pg. 94, Fall 1987.     

Jerry R. Garman  Vernon B. Myers  chief  Thomas Freund  chemist 《Ground Water Monitoring & Remediation》1988,8(3):166-167

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Microstructural evidence of orders of crystallization in granitoid rocks   总被引：2，自引：0，他引：2  

R. H. Flood  R. H. Vernon 《Lithos》1988,21(4):237-245

Experimental melting studies of granitoid rocks have documented variations in the order of crystallization of minerals, depending on the melt composition, total pressure, and the activity of water and other volatiles in the melt. Microstructural criteria for independent determination of the order of crystallization are needed to permit application of the experimental data to the evaluation of the conditions of crystallization. Unfortunately, few criteria can be reliably applied to infer either the order of initial crystallization on the order in which minerals cease to crystallize in granitoid rocks. Most microstructures of granitoid rocks record simultaneous rather than sequential crystallization of minerals.

Grain-size criteria (e.g., phenocrysts vs. groundmass) can be used to infer a partial order of crystallization in many volcanic rocks, but the presence of extremely large phenocrysts of K-feldspar (that from experimental data must be the last mineral to crystallize) highlights the dangers inherent in the use of grain-size criteria.

Providing it can be determined that included minerals did not form subsequently along cracks or from entrapped melt inclusions, those inclusions that are demonstrably and consistently only near the centre of large grains must have ceased to crystallize before the host mineral. Where the host mineral occurs only as rims on the early formed mineral, it is possible to infer both the order of cessation and initiation of crystallization. Common examples are provided by the rimming produced by a discontinuous reaction relationship. Most other examples of inclusion relationships could result from simultaneous crystallization.

Microstructures involving moulding and impingement relationships are unreliable, as the microstructure is produced only after the minerals have begun to crystallize in the melt or on the melt-solid interface. As most minerals continue to crystallize right to the solidus, they cease to crystallize simultaneously.

New criteria, perhaps involving detailed chemical zoning patterns, need to be developed before the orders of crystallization can be reliably determined for granitoid rocks.  相似文献   

Correlation of the lower devonian rocks of australasia     

D. L. Strusz with contribution by M. R. Banks  G. Bischoff  B. J. Cooper  R. A. Cooper  P. G. Flood  E. D. Gill  J. S. Jell  J. W. Pickett  N. M. Savage  D. L. Sherwin  J. A. Talent  B. D. Webby & A. J. Wright 《Australian Journal of Earth Sciences》2013,60(4):427-455

Alkali basaltic rocks from the Southern Highlands, N.S.W., contain oxide phases of both high and low pressure origin. The two phases are readily distinguished using chemical and textural criteria.

Chemical data for low‐pressure Fe‐Ti oxides indicate that oxygen fugacities of the host lavas range from 10‐^12.8 to 10‐⁸ atm at 950° to 1110°C. In most cases, the oxygen fugacities of the individual lava flows appear to be principally a function of temperature and intrinsic chemical equilibria existing at the time of formation of the basaltic liquid. However, some relatively differentiated flows shows a high degree of oxidation due to volatile enrichment with fractionation. Rare glassy flows show dendritic crystallization of Fe‐Ti oxides. Most flows in which abundant olivine was the first phase to be precipitated also contain Cr‐rich spinels associated, and apparently coeval, with the earliest‐crystallizing olivine.  相似文献   

Polar observations of plasma waves in and near the dayside magnetopause/magnetosheath     

J.D. Menietti  J.S. Pickett  G.B. Hospodarsky  J.D. Scudder  D.A. Gurnett 《Planetary and Space Science》2004,52(14):1321-1337

The plasma wave instrument (PWI) on board the Polar spacecraft made numerous passages of the dayside magnetopause and several probable encounters with the magnetosheath during the years 1996 and 1997. During periods of relatively high density, the PWI antenna-receiver system is coupled to the plasma and oscillates. The oscillations have been shown (cf. Radio Sci. 36 (2001) 203) to be indicative of periods of higher plasma density and plasma flows, possibly associated with magnetic reconnection. We have studied the plasma waves observed on three distinct magnetopause passes distinguished by the presence of these oscillations of the PWI receivers, and we report on the data obtained near, but not during, the times of the oscillations and the possible role of these waves in magnetic reconnection. Sweep-frequency receiver and high-resolution waveform data for some of these times are presented. The plasma wave measurements on each of the passes are characterized by turbulence. The most stable waves are whistler mode emissions typically of several hundred hertz that are seen intermittently in these regions. The data indicate the presence of impulsive solitary-like wave structures with strong electric fields both parallel and perpendicular to the magnetic field near, but not always within, suspected reconnection sites. The solitary waves show the highest occurrence when observed with electrostatic electron cyclotron waves. These latter waves have been observed in the past in the cusp, polar magnetosphere, and auroral regions and therefore may represent excursions into the cusp, but also indicate the presence of low-energy electron beams. Turbulence near the lower hybrid frequency, low-frequency EM waves, and impulsive monopolar electrostatic pulses are seen throughout the magnetopause and particularly near regions of large decrease in the local magnetic field and enhanced field-aligned flows, the suspected reconnection sites. The absence of significant solitary wave signatures within suspected reconnection sites may require modifications to some reconnection models.  相似文献   

Productivity and Resilience: Long-Term Trends and Storm-Driven Fluctuations in the Plant Community of the Accreting Wax Lake Delta     

Melissa?Vernon?CarleEmail author  Charles?E.?Sasser 《Estuaries and Coasts》2016,39(2):406-422

River deltas are dynamic geologic features where the plant community engages in critical feedbacks with geomorphology, and plant community development is impacted by both riverine and coastal drivers. A vegetation index (NDVI) calculated from a time series of 54 peak growing season Landsat-5 TM and Landsat-7 ETM+ images was used to assess the long-term trends and storm event-driven changes in the vegetation community associated with the Wax Lake Delta, an actively accreting subdelta of the Mississippi River. Multiple regression models were developed to explain variation in the vegetated area of the delta and mean delta NDVI from 1984 to 2011 as a function of date, hydrology, and seasonality. The models indicate that both vegetated area and mean NDVI increased over time from 1984 to 2011. Productivity measures following Hurricanes Lili (2002), Rita (2005), and Ike (2008) represented statistical outliers; significant decreases in NDVI following these storms suggest that hurricanes passing directly over or to the west of the delta result in short-term disturbance to the plant community, most likely related to saltwater intrusion associated with storm surge. However, in each case, both vegetated area and mean NDVI recovered to the long-term trend by the following growing season. These results demonstrate that the freshwater marshes within this mineral-rich, accreting delta are increasing in productivity as the delta matures and are extremely resilient to coastal storm disturbance.  相似文献   

Rapakivi granite problems: plagioclase mantles and ovoid megacrysts     

R. H. Vernon 《Australian Journal of Earth Sciences》2016,63(6):675-700

Mantling of alkali feldspar megacrysts by oligoclase (‘rapakivi texture’) generally can be interpreted as the result of magma mixing, although decompression is a viable interpretation, especially for high-level intrusions. Coexistence of mantled and unmantled crystals can be explained by transfer of mantled crystals (‘antecrysts’) from a mixed (hybrid) rock to a host granitoid devoid of mantled crystals, for example, by disintegration of microgranitoid enclaves. Processes capable of explaining multiple oligoclase shells include repeated increase and release of volatiles, and repeated replenishment by more mafic magma. The shells could be formed by transfer of megacrysts into and out of a magma-mixing zone during flow in dyke-like conduits or in the fronts of mafic flows moving across cumulate layers in plutons. Ovoid megacrysts, which occur especially in Proterozoic rapakivi granitoids, are difficult to interpret but are better explained by growth processes than by magmatic corrosion. The common presence of simple twinning, partial crystal faces, euhedral plagioclase inclusions and granophyre-like intergrowths with quartz favours normal magmatic growth. The common ovoid shapes with local facets could reflect incomplete development of crystal faces, owing to relatively rapid growth. Granophyre-like intergrowths in the ovoids, local granophyre occurring as megacryst rims and in the groundmass, and the common presence of miaroles suggest growth of the ovoids at relatively shallow depth, at conditions of delayed nucleation and consequent undercooling, resulting from accumulation and retention of fluid. Development of the ovoids is independent of plagioclase mantling.  相似文献   

Origin of megacrystic felsic gneisses at Broken Hill     

J. J. Vassallo  R. H. Vernon 《Australian Journal of Earth Sciences》2013,60(4):733-748

Three sheet‐like bodies of felsic gneiss containing abundant K‐feldspar megacrysts (megacrystic felsic gneiss, augen gneiss or granite gneiss) surrounding the Broken Hill Line of Lode in western New South Wales, Australia, are inferred to be pre‐ to syn‐D₁ granitoids. We interpret the Feral gneiss to be a pre‐ to early syn‐D₁ intrusion, as it contains S₁ as its earliest foliation. However, it has no magmatic flow foliation. The Alma Gneiss, and the megacrystic portions of the Rasp Ridge Gneiss, northwest of the Line of Lode, both contain S₁ parallel to a magmatic flow foliation, and are interpreted as having been magmatic during D₁. Therefore, the Alma and Rasp Ridge Gneisses may have been intruded during D₁, probably just after the Feral gneiss, as the Alma Gneiss intrudes the Feral gneiss. S₁ in the augen gneisses and the wall rocks is defined by biotite, sillimanite, garnet and ribbon quartz, and indicates that high‐grade metamorphic conditions accompanied D₁. Evidence suggesting that these rocks were originally granitoids includes: (i) the Alma Gneiss transecting and intricately intruding the Feral gneiss, the contacts being transected by S₁; (ii) euhedral to subhedral K‐feldspar porphyroclasts (former phenocrysts), especially those with concentrically arranged inclusions; (iii) microgranitoid enclaves, particularly where megacrystic and relatively large; (iv) aplite dykes (most common in plutonic rocks and therefore reliable indicators); (v) metasedimentary xenoliths; (vi) magmatic flow foliations overprinted by parallel tectonic foliations; and (vii) chemical affinities with undoubted Australian Proterozoic granitoids. Therefore, felsic gneisses at Broken Hill should not be used for stratigraphic correlation, unless they can be definitely determined to be of volcanic flow or tuffaceous origin. The inferred intrusion of granitoids early in the tectonic history of the Broken Hill Block suggests that they may have contributed to the metamorphic and/or hydrothermal heat, and may have helped concentrate metals to form orebodies.  相似文献   

Reactions involving hydration of cordierite and hypersthene     

R. H. Vernon 《Contributions to Mineralogy and Petrology》1972,35(2):125-137

Petrographic evidence for the hydration reactions: cordierite + water = gedrite + kyanite + quartz, and aluminous hypersthene + water = aluminous anthophyllite, is shown by some granulite facies rocks in the Arunta Complex, near Alice Springs, central Australia. Electron microprobe analyses enable the reactions to be written in some detail. Preliminary thermodynamic and experimental information suggests that the reactions took place at relatively high confining pressures. The reactions may have proceeded more in response to addition of water to the system, rather than a major change in P-T conditions.  相似文献   

Delineation of Ground-Water Flow Systems in the Southern Great Basin Using Aqueous Rare Earth Element Distributions     

Kevin H. Johannesson  Klaus J. Stetzenbach  Vernon F. Hodge  David K. Kreamer  Xiaoping Zhou 《Ground water》1997,35(5):807-819

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