Geochemical Evidence for Slab Melting in the Trans-Mexican Volcanic Belt   总被引：3，自引：0，他引：3  

Gomez-Tuena  Arturo; Langmuir  Charles H.; Goldstein  Steven L.; Straub  Susanne M.; Ortega-Gutierrez  Fernando 《Journal of Petrology》2007,48(3):537-562

Geochemical studies of Plio-Quaternary volcanic rocks from theValle de Bravo–Zitácuaro volcanic field (VBZ) incentral Mexico indicate that slab melting plays a key role inthe petrogenesis of the Trans-Mexican Volcanic Belt. Rocks fromthe VBZ are typical arc-related high-Mg andesites, but two differentrock suites with distinct trace element patterns and isotopiccompositions erupted concurrently in the area, with a traceelement character that is also distinct from that of other Mexicanvolcanoes. The geochemical differences between the VBZ suitescannot be explained by simple crystal fractionation and/or crustalassimilation of a common primitive magma, but can be reconciledby the participation of different proportions of melts derivedfrom the subducted basalt and sediments interacting with themantle wedge. Sr/Y and Sr/Pb ratios of the VBZ rocks correlateinversely with Pb and Sr isotopic compositions, indicating thatthe Sr and Pb budgets are strongly controlled by melt additionsfrom the subducted slab. In contrast, an inverse correlationbetween Pb(Th)/Nd and ¹⁴³Nd/¹⁴⁴Nd ratios, which extend to lowerisotopic values than those for Pacific mid-ocean ridge basalts,indicates the participation of an enriched mantle wedge thatis similar to the source of Mexican intraplate basalts. In addition,a systematic decrease in middle and heavy rare earth concentrationsand Nb/Ta ratios with increasing SiO₂ contents in the VBZ rocksis best explained if these elements are mobilized to some extentin the subduction flux, and suggests that slab partial fusionoccurred under garnet amphibolite-facies conditions. KEY WORDS: arcs; mantle; Mexico; sediment melting; slab melting  相似文献   

Vulnerability assessment in a volcanic risk evaluation in Central Mexico through a multi-criteria-GIS approach   总被引：1，自引：1，他引：1  

José Fernando Aceves-Quesada  Jesús Díaz-Salgado  Jorge López-Blanco 《Natural Hazards》2007,40(2):339-356

The Valley of Toluca is a major industrial and agricultural area in Central Mexico, especially the City of Toluca, the capital of The State of Mexico. The Nevado de Toluca volcano is located to the southwest of The Toluca Basin. Results obtained from the vulnerability assessment phase of the study area (5,040 km² and 42 municipalities) are presented here as a part of a comprehensive volcanic risk assessment of The Toluca Basin. Information has been gathered and processed at a municipal level including thematic maps at 1:250,000 scale. A database has been built, classified and analyzed within a GIS environment; additionally, a Multi-Criteria Evaluation (MCE) approach was applied as an aid for the decision-making process. Cartographic results were five vulnerability maps: (1) Total Population, (2) Land Use/Cover, (3) Infrastructure, (4) Economic Units and (5) Total Vulnerability. Our main results suggest that the Toluca and Tianguistenco urban and industrial areas, to the north and northeast of The Valley of Toluca, are the most vulnerable areas, for their high concentration of population, infrastructure, economic activity, and exposure to volcanic events.  相似文献   

Coda Q before and after the eruptions of 13 November 1985, and 1 September 1989, at Nevado del Ruiz Volcano, Colombia     

B. John Makario Londoño  A. John Jairo Sanchez  E. Luis Eduardo Toro  Fernando Gil Cruz  Olga Patricia Bohorquez 《Bulletin of Volcanology》1998,59(8):556-561

 Coda Q^–1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September 1989) and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato 1977). Substantial changes were found before and after the eruptions. The highest value of Q^–1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value for May 1987. It seems that the changes in coda Q^–1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence was found for all periods. Also Q^–1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization is taking place in the NRV magma. The clear change of coda Q^–1 before and after the eruptions at NRV also suggests the possibility that coda Q^–1 is a premonitory tool of activity at this volcano. Received: 25 October 1996 / Accepted: 21 January 1998  相似文献   

Petrological And Geochemical Characteristics Of The Granulitic Terrain Of Brejses, Bahia, Brazil     

Johildo Salomo Figueirêdo Barbosa  Fernando Alves daSilva  Najara Santos Sapucaia  Sundaram S. Iyer 《Gondwana Research》1998,1(3-4):343-356

New petrological and geochemical characteristics of the Brejtes region, situated in the south of Bahia, Brazil are discussed. The region forms a part of the most important and extensive granulite facies terrain in Brazil of Archean/Paleoproterozoic age. Five groups of rock types all equilibrated in the granulite facies are identified in this region. They are: i) supracrustal and related rocks, ii) undifferentiated granulites, iii) hornblende bearing enderbite-charnockites, iv) hornblende free enderbite-charnockites, v) charnockites. The first group appears to be the oldest in the region as they form enclaves in the 2.9 Ga old undifferentiated granulites. The third and fourth group are enderbite-charnockites, whose protoliths constitute two series of calc-alkaline rocks, one titanium poor (hornblende free) and another titanium rich (hornblende bearing). U/Pb zircon SHRIMP dates indicate ages of formation at 2.81 Ga (hornblende free) and 2.69 Ga (hornblende bearing) for the two groups. The fifth group of rocks have charnockitic affinity and are present in the center of the Brejtes Dome. These rocks are also have calc-alkaline affinity, but show petrographic and geochemical characteristics distinct from those of other groups. Preliminary geochronological investigations by zircon Pb-Pb evaporation method yielded 2.6 Ga and 2.0 Ga for the charnockites from the inner core of the Brejtes Dome. These age data suggest that the circular structure was formed by the re-fusion of the 2.6 Ga old deep crustal material generating younger charnockites at 2.0 Ga.  相似文献   

U---Pb and Rb---Sr systematics in a polyorogenic segment of the Precambrian shield, central southern Norway     

Fernando Corfu 《Lithos》1980,13(4):305-323

U---Pb analyses of zircon, monazite and sphene as well as Rb---Sr analyses of whole rocks and minerals have been carried out in an attempt to elucidate the evolution of the Precambrian shield underlying the Caledonian Jotun-nappe in central southern Norway. The earliest event recognized in the area is a high grade metamorphism at 1518 ± 17 m.y. which followed intense magma formation, igneous activity, erosion and sedimentation over a period of maximum 300 m.y. The Sveconorwegian cycle is characterized by the intrusion of two anatectic magma generations at 1014 ± 35 m.y. and 930±10 m.y. that disturbed and partly reset the isotopic systems of the country rocks. A post-magmatic fracturing stage at 875 m.y. concludes this cycle. Rb---Sr mineral systems were not completely equilibrated in the undeformed shield during the Caledonian event in contrast to new grown minerals in strongly deformed overlying Lower Paleozoic sediments which record the main deformation at 384±18 m.y. Zircon lower intercept ages ranging between 330–370 m.y. show that lead loss of zircon in rocks subjected to low grade metamorphic conditions may be the result of such processes as annealing, alteration, dilation or a combination of them.  相似文献   

Nature and role of CO2 in some hot and cold HCO3/Na/CO2-rich Portuguese mineral waters: a review and reinterpretation     

José M. Marques  Paula M. M. Carreira  Luís Aires-Barros  Rui C. Graça 《Environmental Geology》2000,40(1-2):53-63

 At the northern part of the Portuguese mainland, the upflow zone of several hot and cold HCO₃/Na/CO₂-rich mineral waters is mainly associated with important NNE–SSW faults. Several geochemical studies have been carried out on thermal and non-thermal hydromineral manifestations that occur along or near these long tectonic alignments. The slight chemical differences that exist between these meteoric hot and cold HCO₃/Na/CO₂-rich mineral waters seem to be mainly caused by CO₂. δ¹³C_(TIDC) values observed in these groundwaters range between –6.00 and –1.00‰ versus V-PDB (V denotes Vienna, the site of the International Atomic Energy Agency; PDB originates from the CaCO₃ of the rostrum of a Cretaceous belemnite, Belemnitella americana, collected in the Peedee formation of South Carolina, USA) indicating a deep-seated (mantle) origin for most of the CO₂. Nevertheless, in the case of the heavier δ¹³C_(TIDC) values, the contribution of metamorphic CO₂ or the dissolution of carbonate rock levels at depth cannot be excluded. Concerning the hot waters, the lack of a positive ¹⁸O-shift should be attributed to water-rock interaction in a low temperature environment, rather than to the isotopic influence of CO₂ on the δ¹⁸O-value of the waters. Received: 9 August 1999 · Accepted: 8 March 2000  相似文献   

Local disappearance of bivalves in the Azores during the last glaciation     

Sérgio P. Ávila  Patrícia Madeira  C. Marques da Silva  Mário Cachão  Bernard Landau  Rui Quartau  A. M. de Frias Martins 《第四纪科学杂志》2008,23(8):777-785

The Pleistocene (Eemian) outcrops of Lagoinhas and Prainha, located at Santa Maria Island (Azores), were investigated and their fossil mollusc content reported. These studies revealed that the last glaciation affected two groups of molluscs: the ‘warm‐guest’ gastropods with West African or Caribbean affinities (e.g. Conus spp., Cantharus variegatus, Bulla amygdala, Trachypollia nodulosa) and shallow bivalve species mainly associated with sandy habitats (Ensis minor, Lucinella divaricata, and probably Laevicardium crassum). In this paper we focus on this group of bivalves, which has since locally disappeared from the Azores. We relate the local disappearance of these bivalves in the Azores with the lack of sand in the shelf. The specific characteristics of the Santa Maria shelf combined with the sea‐level drop during the Weichselian prevented deposition of the lowstand deposits and permitted erosion of the previous ones, leaving the shelf without a sediment cover. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The trade of live crustaceans in Portugal: space for technological improvements     

Barrento  Sara; Marques  Antonio; Pedro  Sonia; Vaz-Pires  Paulo; Nunes  Maria Leonor 《ICES Journal of Marine Science》2008,65(4):551-559

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Seasonality and duration in extreme value distributions of significant wave height     

Fernando J. Mndez  Melisa Menndez  Alberto Luceo  Raúl Medina  Nicholas E. Graham 《Ocean Engineering》2008,35(1):131-138

This paper presents a statistical model to characterize the long-term extreme value distribution of significant wave height, conditioning to the duration of the storm and accounting for seasonality. A time-dependent version of the peak over threshold (POT) approach is used to build the model, which is then applied to specific reanalysis time series and NOAA buoy records. The model considers the annual and semiannual cycles which are parameterized in terms of harmonic functions. The inclusion of seasonal variabilities substantially reduces the residuals of the fitted model. The information obtained in this study can be useful to design maritime works, because (a) the model improves the understanding of the variability of extreme wave climate along a year and (b) the model accounts for the duration of the storm, which is a key parameter in several formulations for rubble mound breakwater design.  相似文献   

Biochemical alterations in juvenile carp (Cyprinus carpio) exposed to zinc: glutathione reductase as a target     

Franco JL  Posser T  Mattos JJ  Sánchez-Chardi A  Trevisan R  Oliveira CS  Carvalho PS  Leal RB  Marques MR  Bainy AC  Dafre AL 《Marine environmental research》2008,66(1):88-89

The aim of this study was to investigate biochemical changes in juvenile carp (Cyprinus carpio) exposed to zinc chloride (10, 30 and 100 microM) for a period of 48 h. Zinc exposure caused a concentration-dependent reduction in glutathione reductase (GR) activity in gills, liver and brain. Gill glutathione S-transferase (GST) was reduced when animals were exposed to the highest concentration of 100 microM zinc. The phosphorylation of p38(MAPK) increased in the brain of fish exposed to zinc 100 microM, while phosphorylation of the extracellular signal-regulated protein kinase 1/2 (ERK1/2) and c-Jun N-terminal protein kinase 1/2 (JNK1/2) remained unchanged. Expression of proteins HSP60 and HSP70 were not affected by zinc exposure. Considering the significant concentration-dependent inhibition of GR in all tissues analyzed, this enzyme could be a potential biomarker of exposure to zinc, which has to be confirmed.  相似文献