Characterization of mesostasis regions in lunar basalts: Understanding late‐stage melt evolution and its influence on apatite formation          下载免费PDF全文

Nicola J. Potts  Romain Tartèse  Mahesh Anand  Wim van Westrenen  Alexandra A. Griffiths  Thomas J. Barrett  Ian A. Franchi 《Meteoritics & planetary science》2016,51(9):1555-1575

Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile‐bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk‐rock basaltic composition and that of bulk‐mesostasis regions, indicating that bulk‐rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late‐stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO₂ abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite‐melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.  相似文献   

Mapping deer habitat suitability using remote sensing and geographic information systems     

Russell G. Congalton  Janine M. Stenback  Reginald H. Barrett 《国际地球制图》2013,28(3):23-33

This paper describes an effort to map the habitat for the Eastern Tehama Deer Herd located in Northern California. The range of this herd encompasses almost 600,000 hectares (1.5 million acres). Knowledge of the spatial distribution of suitable habitat is prerequisite to managing the deer herd. Remote sensing and GIS are appropriate tools for such an assessment. Remotely sensed data were used to map vegetation/land cover. These data along with elevation, aspect, slope, juxtaposition, and various buffer zones were input into a GIS and a model was used to produce a map of habitat suitability. The accuracy of the vegetation/land cover map was assessed and methods for validating the habitat suitability map are presented.  相似文献   

SOIL DEVELOPMENT AND SPATIAL VARIABILITY ON GEOMORPHIC SURFACES OF DIFFERENT AGE     

Linda R. Barrett  Randall J. Schaetzl 《自然地理学》2013,34(1):39-55

Twenty-four soil pedons on each of four sandy lake terraces in northwestern lower Michigan that ranged in age from 3000 to 11,000 years BP were studied to assess trends in soil morphological variability with time. After verifying the general uniformity of parent materials within and between the four surfaces, we examined temporal trends in the spatial variability of soil color, cementation, horizon thickness and development. E horizons attained high color values (lightness) by 3000 years and changed little after that time, whereas B horizons continued to get darker with time. Cementation within B horizons increased in strength and amount with time, as did B horizon thickness. Soils ≥4000 years old had deeper eluvial zones but much greater variabilities in the thickness of that zone than did younger soils. Soil development increased with time, but spatial variability in degree of development also increased with time. These patterns are best explained by invoking spatially random soil mixing upon a surface that is otherwise undergoing podzolization. [Key words: podzolization, chronofunction, Michigan, soil variability, soil genesis.]  相似文献   

Comment on “Estimating the distribution of snow water equivalent using remotely sensed snow cover data and a spatially distributed snowmelt model: A multi-resolution, multi-sensor comparison” by Noah P. Molotch and Steven A. Margulis [Adv. Water Resour. 31 (2008) 1503–1514]     

A.G. Slater  M.P. Clark  A.P. Barrett 《Advances in water resources》2009,32(11):1680-1684

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The Arctic’s rapidly shrinking sea ice cover: a research synthesis   总被引：21，自引：1，他引：20  

Julienne C. Stroeve  Mark C. Serreze  Marika M. Holland  Jennifer E. Kay  James Malanik  Andrew P. Barrett 《Climatic change》2012,110(3-4):1005-1027

The sequence of extreme September sea ice extent minima over the past decade suggests acceleration in the response of the Arctic sea ice cover to external forcing, hastening the ongoing transition towards a seasonally open Arctic Ocean. This reflects several mutually supporting processes. Because of the extensive open water in recent Septembers, ice cover in the following spring is increasingly dominated by thin, first-year ice (ice formed during the previous autumn and winter) that is vulnerable to melting out in summer. Thinner ice in spring in turn fosters a stronger summer ice-albedo feedback through earlier formation of open water areas. A thin ice cover is also more vulnerable to strong summer retreat under anomalous atmospheric forcing. Finally, general warming of the Arctic has reduced the likelihood of cold years that could bring about temporary recovery of the ice cover. Events leading to the September ice extent minima of recent years exemplify these processes.  相似文献   

Plesiosaur remains from the Jurassic-Cretaceous Purbeck Limestone Group of southern England     

Benjamin P. Kear  Andrew R. Milner  Paul M. Barrett 《Proceedings of the Geologists' Association. Geologists' Association》2009,120(2-3):121-125

Plesiosaur fossils from the uppermost Tithonian (Upper Jurassic) to lower Valanginian (Lower Cretaceous) Purbeck Limestone Group of Dorset, England are important because they constitute a rare record from around the Jurassic-Cretaceous boundary. Where diagnostic, the remains are referred to indeterminate plesiosauroids (Cryptocleidoidea) and represent relatively small animals including a previously undescribed juvenile individual. This observation accords with the lagoonal-lacustrine (with periodic marine influx) depositional setting of the Purbeck Limestone Group strata, a palaeoenvironment that is often associated with juvenile plesiosaur occurrences.  相似文献   

Retrospective application of boundary constraints in automated contouring by digital spatial filtering     

A. N. Barrett  D. W. Rhind 《Mathematical Geology》1974,6(1):83-89

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An assessment of the Vine Pull scheme: a case study of the southern vales of south Australia     

Steven Barrett 《The Australian geographer》1989,20(2):185-190

In 1986 the Commonwealth government implemented a Vine Pull Scheme to restore stability to Australian viticulture. This paper draws on interviews conducted with about half of the growers involved in the scheme in the Southern Vales region of South Australia and is an attempt to evaluate the implementation of the scheme in a small viticultural district. In general, this scheme has been unsuccessful because it was not effectively means tested. This enabled many growers who already had the financial resources to restructure their farms to take advantage of the scheme. In addition, the administration of the scheme did not focus on the particular grape varieties that needed to be removed. This study demonstrates that what is required is a long term commitment to restructuring all facets of the industry on a regional basis.  相似文献   

Ordnance Survey Review     

M. M. Barrett 《The Photogrammetric Record》1979,9(53):724-725

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Studies of a contaminated brackish marsh in the Hackensack Meadowlands of northeastern New Jersey: an assessment of natural recovery     

Weis P  Barrett KR  Proctor T  Bopp RF 《Marine pollution bulletin》2005,50(11):1405-1415

Eight-Day Swamp is known to be contaminated with heavy metals, especially mercury. Sediment cores were collected to approximately 32 cm at 17 sites on four transects and analyzed at 1 or 2 cm intervals for seven metals and organic matter. Very high metal levels were found throughout the site. Long and Morgan's "effects range-median" (ER-M) was exceeded in more than 50% of slices for all elements except As. Hg had the highest concentration relative to ER-M; median Hg concentration was 72 times its ER-M. On the marsh plain, all metals showed enrichment at 14-20 cm depth of 10-40X over surficial sediments. 137Cs analysis showed sedimentation rates ranging from 0.33 to 0.50 cm yr(-1) over the last approximately 40 yr. These rates indicate that metal contamination peaks occurred in sediments deposited in the early 1960s. Thus, newer, less contaminated sediments are burying older, more contaminated layers and peak levels of contaminants are becoming less available to benthos.  相似文献