The Petrology of Plutonic Blocks and Inclusions from the Lesser Antilles Island Arc   总被引：20，自引：12，他引：20  

ARCULUS  RICHARD J.; WILLS  KEVIN J. A. 《Journal of Petrology》1980,21(4):743-799

Three main groups of plutonic nodules are present in the LesserAntilles arc and are interpreted as (a) phenocryst clusters,(b) metamorphosed wallrock xenoliths and (c) cumulate texturedxenoliths. Large cumulate blocks display felsic-mafic layering,slump structures and auto-intrusive features. The majority ofspecimens are ad- and heteradcumulates with fewer ortho- andcrescumulates. Interstitial scoria and glass are present ina variety of samples. Plagioclase, amphibole, cino- and orthopyroxene,olivine, magnetite, biotite, ilmenite, quartz and apatite arepresent in various proportions in individual blocks. Plagioclaseand amphibole are modally predominant. Significant variationalong the arc is displayed in the rarity of orthopyroxene andabundance of amphibole in the southern islands compared withthe common presence of two pyroxenes in the northern islands. Plagioclase varies from An_100–36 with very low orthoclasecomponent, and usually precedes amphibole in a given crystallizationsequence. Only on Grenada are plagioclase-free blocks present.Olivine is restricted to assemblages where coexisting plagioclaseis more calcic than An₈₉ and its composition range is Fo_90–59.Clinopyroxene is predominantly calcic augite and cinopyroxene,olivine and plagioclase all coexist stably with amphibole. Ageneral trend of decreasing Ca content in clinopyroxene fromsouth to north in the arc is present. Orthopyroxene ranges from En_73–49 and is most common inassemblages where the coexisting plagioclase is more sodic thanAn₈₃ Coexisting pyroxenes define temperatures in the range 800–1050?C. Amphibole compositions include pargasite, magnesiohastingsite,magnesio-hornblende and tschermakitic hornblende. The K contentof the amphiboles increases from north to south in the samesense as the general tholeiitic-calcalkalic-alkalic variationof parental magmas. Magnetite is the dominant spinel phase but ferrian chromiteand chromian magnetite are present in some Grenada cumulatesand pleonaste is found in rare St. Kitts samples. Ilmenite ispresent in blocks from several islands; coexisting Fe-Ti oxidesdefine a temperature range of 710?-950 ?C at of 15.5 to 10.0 bars. Biotite, quartz and apatiteare restricted to evolve cumulate types. Some modification of interstitial scoria/glass compositionsfrom equilibrium melts has occurred in the majority of samples,but general similarity with erupted lava types is importantevidence for the cognate relationship of the cumulate assemblages.The role of H₂O is crucial in determining the calcic natureof island arc plutonic plagioclase when compared with relativelydry, layered tholeiitic plutons. Some modal and chemical featuresof cumulate-lava comparisons suggest plagioclase flotation maybe significant. A variety of thermodynamic calculations indicate temperaturesand pressures of crystallization in the range 850–1050?C, 4–10 kb. No evidence exists for systematic along-arcvariations in these parameters. Standard amphibole crystallinesolution models give unsatisfactory results for calculations. Some distinctive contrasts between cumulate and phenocryst modesare present. The abundance of amphibole in equilibrium withbasaltic melts in the plutonic situation compared with its rarityin lavas is striking. Plagioclase coexisting with a given meltis more anorthitic in the plutonic than the phenocryst mode. Least squares fractionation tests demonstrate the possibilityof relating basalt-andesite-dacite suites by fractional crystallizationof the cumulus phases. Trace element systematics of cumulate-lavasuites for individual islands also generally support this hypothesis.The suggestion of sole amphibole fractionation for the generationof andesite from basalt is discarded. ^* Present address: CRAE, Box 39598, Darwin, N.T. 5798, Australia.  相似文献   

Relationships between sand input from rivers and the composition of sands from the beaches of Southern California*     

ROBERT M. RICE  DONN S. GORSLINE  ROBERT H. OSBORNE 《Sedimentology》1976,23(5):689-703

During the period from 1967 through 1972, a sampling programme was completed to determine the economic potential of heavy metals in the beach and river sands of the southern California coastal zone. These samples were employed to test the hypothesis that sand composition in a given beach cell is dominantly controlled by the provenance draining into that cell and is not strongly influenced by longshore leakage from upcurrent cells. Sample sets obtained before and after the exceptional flood of 1969 made it possible to compare the sediment supplied by normal river flow with that supplied by a major flood. Multivariate statistical analysis of the heavy mineral distribution of southern California beaches and rivers indicate that the sand composition of the two northern cells is controlled by the dominantly sedimentary Transverse Range provenance, whereas the composition of the three southern cells is controlled by the dioritic Peninsular Ranges. Some leakage occurs between the two northern cells around the Point Dume-Hueneme-Mugu Canyon Zone, whereas no important southward mixing occurs between cells around the Palos Verdes-Redondo Canyon Zone. Even though the Santa Clara River flows mostly through sedimentary terrains, samples from this river strongly reflect the granodioritic source present in its headlands. Although the basic sand composition within each cell persists during major flooding, leakage between cells may increase following flooding and the compositional packages present may show evidence of greater mixing.  相似文献   

Anomalous luminescence of subglacial sediment at Haut Glacier d'Arolla,Switzerland – a consequence of resetting at the glacier bed?     

DARREL A. SWIFT  DAVID C. W. SANDERSON  PETER W. NIENOW  ROBERT G. BINGHAM  IAN C. COCHRANE 《Boreas: An International Journal of Quaternary Research》2011,40(3):446-458

Swift, D. A., Sanderson, D. C. W., Nienow, P. W., Bingham, R. G. & Cochrane, I. C. 2010: Anomalous luminescence of subglacial sediment at Haut Glacier d'Arolla, Switzerland – a consequence of resetting at the glacier bed? Boreas, Vol. 40, pp. 446–458. 10.1111/j.1502‐3885.2010.00196.x. ISSN 0300‐9483. Luminescence has the potential to elucidate glacial geomorphic processes because primary glacial sediment sources and transport pathways are associated with contrasting degrees of exposure to light. Most notably, sediment entrained from extraglacial sources should be at least partially reset, whereas sediment produced by glacial erosion of subglacial bedrock should retain substantial luminescence commensurate with a geological irradiation history. We set out to test the validity of this assumption at Haut Glacier d'Arolla, Switzerland using sediment sampled extraglacially and from the glacier bed. Contrary to our expectations, the subglacial samples exhibited natural signals that were substantially lower than those of other sample groups, and further (albeit limited) analyses have indicated no obvious differences in sample‐group luminescence characteristics or behaviour that could account for this observation. For glaciological reasons, we can eliminate the possibilities that the subglacial sediment has been extraglacially reset or exposed in situ to heat or light. We therefore advocate investigation of possible resetting processes related to subglacial crushing and grinding, and speculate that such processes, if more generally present, may enable the dating of subglacially deposited tills using luminescence‐based techniques.  相似文献   

The ice-dammed lakes of Ossian Sarsfjellet (Svalbard): their geomorphology and significance     

MATTHEW R. BENNETT  MICHAEL J. HAMBREY  DAVID HUDDART  NEIL F. GLASSER  KEVIN CRAWFORD 《Boreas: An International Journal of Quaternary Research》1998,27(1):25-43

The tidewater glacier complex of Kongsvegen/Kronebreen, at the head of Kongsfjorden in north-west Spitsbergen, has advanced rapidly several times since its Neoglacial maximum. Two such advances, 1869 and 1948, are well constrained in time and space and are widely interpreted as glacier surges. During the 1869 advance an ice-dammed lake formed on the western side of Ossian Sarsfjellet. This ice-dammed lake is associated with a thrust moraine complex. Four lake levels are identified, two of which are associated with rock-cut shorelines implying a degree of lake stability. The history of this lake, the nature of the ice dam and its relationship to the thrust moraine complex are discussed. The lake history spanning 28 to 35 years is used to assess the ice-marginal dynamics of the Kongsvegen/Kronebreen glacier. It is concluded that, contrary to previous suggestions, the rapid advance of this tidewater glacier may simply be an example of a non-climatic ice-marginal fluctuation, of the type common to tidewater glacier, as opposed to a glacier surge. A second ice-dammed lake, to the east of Ossian Sarsfjellet, formed sometime after 1869 as the ice retreated, and still exists today. This largely supraglacial lake is associated with a very different geomorphological assemblage, which has a poor long-term preservation potential. The geomorphological characteristics of the two lakes on Ossian Sarsfjellet are compared and used to discuss the problems associated with the recognition of ice-dammed lakes within the Pleistocene record. On the basis of the evidence presented here, ice-dammed lakes may be more common during deglaciation than currently suggested.  相似文献   

Mystery pictures decoded     

KEVIN PRIVETT 《Geology Today》1998,14(4):140-140

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Quaternary records of the dire wolf, Canis dirus, in North and South America     

ROBERT G. DUNDAS 《Boreas: An International Journal of Quaternary Research》1999,28(3):375-385

The dire wolf was an important large, late Pleistocene predator in North and South America, well adapted to preying on megaherbivores. Geographically widespread, Canis dirus is reported from 136 localities in North America from Alberta, Canada, southward and from three localities in South America (Muaco, Venezuela; Talara, Peru; and Tarija, Bolivia). The species lived in a variety of environments, from forested mountains to open grasslands and plains ranging in elevation from sea level to 2255 m (7400 feet). Canis dirus is assigned to the Rancholabrean land mammal age of North America and the Lujanian land mammal age of South America and was among the many large carnivores and megaherbivores that became extinct in North and South America near the end of the Pleistocene Epoch.  相似文献   

Circulation regime fluctuations and their effect on intraseasonal variability in the ECHAM climate model     

MICHAEL PONATER  WINFRIED KÖNIG  ROBERT SAUSEN  FRANK SIELMANN 《地球，A辑:动力气象学与海洋学》1994,46(3):265-285

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The Jura glaciers: palaeogeography in the Würmian circum-Alpine zone     

MICHEL CAMPY  ROBERT ARN 《Boreas: An International Journal of Quaternary Research》1991,20(1):17-27

Since the first studies on the glacial formations of the Jura mountains there have been two concepts concerning type of glaciation and ice origin during the Würmian glaciation. Some authors believed that the Jura was totally inundated by ice of Alpine origin, while others believed that the Jura had its own glaciers, originating from a single ice-cap. Several recent studies on both the NW and SE slopes of the range define the problem more accurately. This paper presents a synthesis of the new results from mapping the moraine systems and studying the stratigraphic relationships between Alpine and Jura tills. It is concluded that even the highest level of Alpine glaciers could not lead to a penetration of the Jura. A reconstruction of the extension of the Jura glaciers and their relationship with the Alpine glaciers is given, and we conclude that at the Würmian maximum a local ice-cap was present.  相似文献   

A magma ocean on Vesta: Core formation and petrogenesis of eucrites and diogenites     

KEVIN RIGHTER  MICHAEL J. DRAKE 《Meteoritics & planetary science》1997,32(6):929-944

Abstract— Available evidence strongly suggests that the HED (howardite, eucrite, diogenite) meteorites are samples of asteroid 4 Vesta. Abundances of the moderately siderophile elements (Ni, Co, Mo, W and P) in the HED mantle indicate that the parent body may have been completely molten during its early history. During cooling of a chondritic composition magma ocean, equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0.80, when the convective system freezes and melts segregate from crystals by gravitational forces. The extruded liquids are similar in composition to Main Group and Stannern trend eucrites, and the last pyroxenes to precipitate out of this ocean (before convective lockup) span the compositional range of the diogenites. Subsequent fractional crystallization of a Main Group eucrite liquid, which has been isolated as a body of magma, produces the Nuevo Laredo trend and the cumulate eucrites. The predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites. Thus, eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with Vesta.  相似文献   

Sustainable development policies and measures: institutional issues and electrical efficiency in South Africa     

HARALD WINKLER  MARK HOWELLS  KEVIN BAUMERT 《Climate Policy》2013,13(3):212-229

An innovative approach is introduced for helping developing countries to make their development more sustainable, and also to reduce greenhouse gas (GHG) emissions as a co-benefit. Such an approach is proposed as part of the multilateral framework on climate change. The concept of sustainable development policies and measures (SD-PAMs) is outlined, making clear that it is distinct from many other approaches in starting from development rather than explicit climate targets. The potential of SD-PAMs is illustrated with a case-study of energy efficiency in South Africa, drawing on energy modelling for the use of electricity in industry. The results show multiple benefits both for local sustainable development and for mitigating global climate change. The benefits of industrial energy efficiency in South Africa include significant reductions in local air pollutants; improved environmental health; creation of additional jobs; reduced electricity demand; and delays in new investments in electricity generation. The co-benefit of reducing GHG emissions could result in a reduction of as much as 5% of SA's total projected energy CO₂ emissions by 2020. Institutional support and policy guidance is needed at both the international and national level to realize the potential of SD-PAMs. This analysis demonstrates that if countries begin to act early to move towards greater sustainability, they will also start to bend the curve of their emissions path.  相似文献