Petrology and Geochemistry of Volcan Cerro Azul: Petrologic Diversity among the Western Galapagos Volcanoes   总被引：1，自引：0，他引：1  

NAUMANN  TERRY; GEIST  DENNIS; KURZ  MARK 《Journal of Petrology》2002,43(5):859-883

Cerro Azul, one of the large shield volcanoes in the westernGalápagos archipelago, has erupted a wide range of tholeiiticto alkalic basalts. These diverse compositions include someof the most primitive yet reported from the western archipelagoand are unlike those of the other, well-studied, neighboringvolcanoes of Sierra Negra and Alcedo, which have erupted basaltof fairly uniform composition. Major- and trace-element modelingshows that Cerro Azul, Alcedo and Sierra Negra share a similardepth of melting and source composition. Modeling also revealsthat there are small, systematic differences in the extent ofpartial melting between the volcanoes that can be related totheir distance from the proposed plume center below the westernmostisland of Fernandina. However, even though melts segregatingfrom the plume in the western Galápagos reflect a narrowrange of temperatures and source compositions, there are widevariations in the enrichments of major and trace elements betweenCerro Azul, Alcedo and Sierra Negra that cannot be attributedto mantle processes. We believe the observed intershield geochemicaldifferences result from magma supply and cooling rates thatare unique to each volcano, and reflect the variations in lithospherictransport and storage processes across the western archipelago. KEY WORDS: basalt; Galápagos; magma supply; mantle plume; ocean island  相似文献   

Small-scale surface wind prediction using dynamic adaptation     

MARK &#;AGAR  JO&#;E RAKOVEC 《地球，A辑:动力气象学与海洋学》1999,51(4):489-504

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The impact of cloud particle gravitational settling on soluble trace gas distributions     

MARK G. LAWRENCE  PAUL J. CRUTZEN 《Tellus. Series B, Chemical and physical meteorology》1998,50(3):263-289

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Mid-Jurassic through mid-Cretaceous extension in the Central Graben of the North Sea - part 2: estimates from faulting observed on a seismic reflection line     

JOHN G. Sclater  MARK D. Shorey 《Basin Research》1988,1(4):201-215

Abstract We present an interpretation of the structure and faulting of an industry multichannel line across the Central North Sea Graben. We observe substantial faulting between the mid-Jurassic and mid-Cretaceous and on the base Zechstein (salt) reflector. To estimate the extension from these faults we consider movement along both planar and curved faults. We demonstrate that summing the heave (the horizontal displacement) overestimates the time measure of elongation for planar, ‘domino-type’, faulting. However, for high-angle normal faults and up to 70% extension (β= 1.7) the heave only overestimates the extension by 13%. In the absence of other information, summing the heave provides a useful estimate of extension in the case of domino-type faulting. For curved ‘listric’ faults the heave is only a true measure of the elongation if the antithetic faulting which removes the voids is vertical. Antithetic movement along inclined shear planes implies significantly more extension. We used the two models; of faulting to introduce progressively greater amounts of internal deformation in the crustal rocks and sediments to attempt to reconcile the estimate of extension necessary to give the observed subsidence and that given by analysing the faults visible on the seismic line. Estimates of extension obtained by allowing antithetic faulting along inclined shear planes are consistent with the range of estimates necessary to account for the post-mid-Jurassic subsidence. The estimates for the prior mid-Jurassic faulting are still substantially less than those necessary to explain the subsidence. However, this is not of major concern as there are many reasons as to why analysis of the faulting should underestimate the pre mid-Jurassic extension. Our interpretation of the seismic line implies curved faults bottoming in the lithologically weak Zechstein salt. These faults are decoupled from the region below and, hence, do not reflect the geometry of the faulting in the basement.  相似文献   

'Science', representation and resistance: the Bt cotton debate in Andhra Pradesh, India     

MARK PEARSON 《The Geographical journal》2006,172(4):306-317

Transgenic cotton is promoted in India on the basis that it will improve rural livelihoods, but such claims are contested on the basis that they are 'unscientific'. In this study, discourse analysis is utilized to deconstruct the environmental and scientific narratives employed by two key actors (Monsanto-Mahyco and the Deccan Development Society) in the debate in India. Whilst strong differences in the ideology of the two actors are found to account for their approaches to managing the environment, significant similarities in their approach to science and their recourse to Foucauldian governmentality are also evident. The conclusion considers how the use of discourse analysis could empower the rural poor to take part in the debate in India.  相似文献   

Late Quaternary palaeoenvironment of northern Guatemala: evidence from deep drill cores and seismic stratigraphy of Lake Petén Itzá     

ANDREAS D. MUELLER  FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI  MARK BRENNER  DAVID A. HODELL  JASON H. CURTIS  JAIME ESCOBAR  ADRIAN GILLI  DUSTIN A. GRZESIK  THOMAS P. GUILDERSON  STEFFEN KUTTEROLF  MICHAEL PLÖTZE 《Sedimentology》2010,57(5):1220-1245

Long sediment cores were collected in spring 2006 from Lake Petén Itzá, northern Guatemala, in water depths ranging from 30 to 150 m, as part of an International Continental Scientific Drilling Program project. The sediment records from deep water consist mainly of alternating clay, gypsum and carbonate units and, in at least two drill sites, extend back >200 kyr. Most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes. A revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin. From ca 200 to ca 85 ka, sediments are dominated by carbonate‐clay silt, often interbedded with sandy turbidites, indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate. At ca 85 ka, an exposure horizon consisting of gravels, coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation, indicating dry climate conditions. From ca 85 to ca 48 ka, transgressive carbonate‐clay sediments, overlain by deep‐water clays, suggest a lake level rise and subsequent stabilization at high stage. From ca 48 ka to present, the lithology is characterized by alternating clay and gypsum units. Gypsum deposition correlates with Heinrich Events (i.e. dry climate), whereas clay units coincide with more humid interstadials.  相似文献