Origin of differentiated lavas at Kilauea Volcano,Hawaii: Implications from the 1955 eruption     

Ritchie A. Ho  Michael O. Garcia 《Bulletin of Volcanology》1988,50(1):35-46

Kilauea's 1955 eruption was the first major eruption (longer than 2 days) on its east rift zone in 115 years. It lasted 88 days during which 108 × 10⁶ m³ of lava was erupted along a discontinuous, 15-km-long system of fissures. A wide compositional range of lavas was erupted including the most differentiated lavas (5.0 wt% MgO) from a historic Kilauea eruption. Lavas from the first half of the eruption are strongly differentiated (5.0–5.7 wt% MgO); later lavas are weakly to moderately differentiated (6.2–6.7 wt% MgO). Previous studies using only major-element compositions invoked either crystal fractionation (Macdonald and Eaton 1964) or magma mixing (Wright and Fiske 1971) as models to explain the wide compositional variation in the lavas. To further evaluate these models detailed petrographic, mineralogical, and whole-rock, major, and trace element XRF analyses were made of the 1955 lavas. Plagioclase and clinopyroxene in the early and late lavas show no petrographic evidence for magma mixing. Olivines from both the early and late lavas show minor resorption, which is typical of tholeiitic lavas with low MgO contents. Core-to-rim microprobe analyses across olivine, augite, and plagioclase mineral grains give no evidence of disequilibrium features related to mixing. Instead, plots of An/Ab vs distance from the core (D) and %Fo vs (D)^4.5 generated essentially linear trends indicative of simple crystal fractionation. Least-squares, mass-balance calculations for major- and trace-element data using observed mineral compositions yield excellent results for crystal fractionation (sum of residuals squared <0.01 for major elements, and <5% for trace elements); magma mixing produced less satisfactory results especially for Cr. Furthermore, trace-element plots of Zr vs Sr, Cr, and A1₂O₃ generate curved trends indicative of crystal fractionation processes. There is no evidence that mixing occurred in the 1955 lavas. Instead, the data are best explained by crystal fractionation involving a reservoir that extends at least 15 km along Kilauea's east rift zone. A dike was intruded into the rift zone from the summit reservoir eight days after the eruption started. Instead of causing magma mixing, the dike probably acted as a hydraulic plunger forcing more of the stored magma to be erupted.  相似文献   

Isotopic dating of the mylonitization of the Azuaga Group in the Badajóz-Córdoba belt,SW Spain     

J. L. Garcia Casquero  H. N. A. Priem  N. A. I. M. Boelrijk  J. Chacon 《International Journal of Earth Sciences》1988,77(2):483-489

On the basis of Rb-Sr muscovite dating an age of about 355 Ma (Late Tournaisian/Early Visean) is assigned to the M₁ metamorphism and associated mylonitization of the ultramylonites of the Las Grullas Formation in the Azuaga Group, Badajóz-Córdoba belt. This age may possibly be related to the accretion process (suturing of the Ossa-Morena Zone to the Central Iberian Zone) thought to be responsible for the metamorphism and mylonitization. Muscovite from the Valencia de Las Torres Formation displays a somewhat lower Rb-Sr age of about 337 Ma. The corresponding K-Ar ages indicate that after the termination of the metamorphism it took some 20 Ma before the rocks had cooled below the closure temperature of muscovite to K-Ar. Whole-rock Rb-Sr data indicate that the Las Grullas ultramylonites were probably derived from Ordovician granitoids.

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Zusammenfassung Aufgrund von Rb-Sr-Datierungen in Muskoviten ist für die M₁Metamorphose und die damit verbundene Mylonitisierung der Ultramylonite der Las Grullas-Formation in der Azuaga-Gruppe, Badajóz-Córdoba-Gürtel, ein Alter von ca. 355 Ma (Spätes Tournais/Frühes Visé) festgestellt worden. Dieses Alter könnte mit dem Akkretionsproze\ (Sutur der Ossa-Morena-Zone zur Zentral-Iberischen-Zone) verbunden sein, der für Metamorphose und Mylonitisierung verantwortlich gemacht wird.Muskovit der Valencia de Las Torres-Formation spiegelt ein etwas geringeres Rb-Sr-Alter von ca. 337 Ma wieder. Die entsprechenden K-Ar-Alter zeigen, da\ es nach dem Ende der Metamorphose einige 20 Ma gedauert hat, bis die Gesteine unter die Schlie\ungstemperatur des Muskovits für K-Ar abgekühlt waren. Rb-Sr-Daten von Gesamtgesteinsproben zeigen, da\ die Las Grullas-Ultramylonite wahrscheinlich aus ordovizischen Granitoiden entstanden sind.

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Resumen Dataciones Rb-Sr en moscovitas de alrededor de 355 Ma (Tournaisiense tardío a Viseense) se asignan al metamorfismo M₁ y se asocian a la milonitización de ultramilonitas de la Formación Las Grullas en el Grupo de Azuaga, Eje Badajóz-Córdoba. Esta edad podría posiblemente datar el proceso de acreción (sutura de la Zona de Ossa-Morena a la Zona Centro-Ibérica) interpretado como responsable del metamorfismo y milonitización. Moscovita de la Formación Valencia de Las Torres indice una edad Rb-Sr un poco más bajo de cerca de 337 Ma. Las correspondientes edades K-Ar indican que después de la terminación del metamorfismo, se tardó cerca de 20 Ma antes que las rocas se enfriaran por debajo de la temperatura de cierre de la moscovita para K-Ar. Datos Rb-Sr de roca total indican que las ultramilonitas de Las Grullas posiblemente se deriven de granitoides ordovicicos.

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Rb/Sr m₁ Las Grullas Azuaga, Badajoz-Cordiba 355 — / /-. . Rb/Sr , Valencia de Las Torres , , 337 . , , / , , , , k/Ar . Rb/Sr , Las Grallas, , .

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Combining coastal geoscience mapping and photogrammetric surveying in maritime environments (Northwestern Iberian Peninsula): focus on methodology     

Ana Pires  Helder I. Chaminé  Francisco Piqueiro  Augusto Pérez-Alberti  Fernando Rocha 《Environmental Earth Sciences》2016,75(3):196

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Future surface temperature changes for the Iberian Peninsula according to EURO-CORDEX climate projections     

Carvalho  D.  Cardoso Pereira  S.  Rocha  A. 《Climate Dynamics》2021,56(1-2):123-138

Climate Dynamics - Future changes in the mean, maximum and minimum temperature in the Iberian Peninsula were investigated using bias-corrected EURO-CORDEX climate projections. The results show that...  相似文献   

Using a regional frequency analysis approach for calculating the Standardized Precipitation Index: an operational approach based on the two-parameter gamma distribution     

dos Santos Junior  Edimar Pereira  Xavier  Ana Carolina Freitas  Martins  Letícia Lopes  da Rocha Sobierajski  Graciela  Blain  Gabriel Constantino 《Theoretical and Applied Climatology》2022,148(3-4):1199-1216

Theoretical and Applied Climatology - The Standardized Precipitation Index (SPI) is a worldwide used probability-based drought index. Considering that the two-parameter gamma distribution (gam) is...  相似文献   

Landslide risk analysis in the area North of Lisbon (Portugal): evaluation of direct and indirect costs resulting from a motorway disruption by slope movements   总被引：1，自引：0，他引：1  

J. L. Zêzere  S. C. Oliveira  R. A. C. Garcia  E. Reis 《Landslides》2007,4(2):123-136

A risk analysis is developed for a test site located in the area north of Lisbon using a scenario of a temporary interruption of the motorway A9 due to a landslide of rotational or translational type. Landslide susceptibility is assessed at the regional scale independently for rotational and translational slides, comparing the landslide distribution with a set of assumed independent landslide predisposing factors. Susceptibility models are validated and classified through the computation of prediction rate curves based on the temporal partition of the landslide data sets. Landslide hazard maps are based on a scenario of future landslide occurrence for the next 27 years. These maps allow the definition of two critical areas on the motorway A9 with regards to landslide susceptibility. Direct costs associated with both critical spots are assessed taking into account the probable affected area of the motorway, and the reconstruction costs. Indirect costs derived from the traffic interruption are evaluated considering the alternatives paths to the motorway, and include costs resulting from: (1) additional fuel consumption; (2) decrease in tollgate income; and (3) loss of productive time. Results show that indirect costs may be 24 to 43 times higher than direct costs, assuming a temporary interruption of the motorway for 6 months.  相似文献   

Precise 40Ar/39Ar dating of volcanic tuffs within the upper Messinian sequences in the Melilla carbonate complex (NE Morocco): implications for the Messinian Salinity Crisis     

Ph. Münch  J.-J. Cornée  G. Féraud  J.-P. Saint Martin  M. Ferrandini  F. Garcia  G. Conesa  S. Roger  M. Moullade 《International Journal of Earth Sciences》2006,95(3):491-503

The Melilla carbonate complex (NE Morocco) is the only area of the Paleo-Mediterranean Sea where volcanic activity was present throughout most of the Messinian. ⁴⁰Ar/³⁹Ar dating of volcanic tuffs interbedded within the upper Messinian sedimentary deposits, known as the Terminal Carbonate Complex (TCC), yields accurate ages of paleoenvironmental and sea-level changes related to the Messinian Salinity Crisis. The new chronologic data (1) provide an average of 5.95–5.99 Ma for the base of the TCC, thus being synchronous with the onset of the Messinian Salinity Crisis, (2) demonstrate for the first time that the basal unconformity of the TCC does not represent a hiatus of long duration, (3) define a precise time line at 5.87±0.02 Ma (2σ) corresponding to sedimentary rocks exhibiting a lateral transition between continental and marine deposits typical of the TCC and (4) yield evidence that emersion of the Melilla platform during deposition of the TCC is partly related to tectono-magmatic activity. An erosional surface, capping the TCC deposits in the Melilla basin, is related to the major Messinian Mediterranean drawdown. The duration of the hiatus, associated with this surface, is estimated to be at most 450 kyr, but is probably shorter.  相似文献   

Natural iron-containing blue and colorless euclase studied by electron paramagnetic resonance     

K. J. Guedes  K. Krambrock  M. V. B. Pinheiro  L. A. D. Menezes Filho 《Physics and Chemistry of Minerals》2006,33(8-9):553-557

Natural blue and colorless rare-gem mineral specimens of euclase from Brazil are investigated by electron paramagnetic resonance (EPR). Angular dependences of Fe³⁺ EPR spectra in three mutually perpendicular crystal planes are analyzed revealing g and D tensors with significant low-symmetry effects, as for example, the high asymmetry parameter E/D = 0.28. Fourth-order degree Stevens parameters are also included in analysis. The anisotropy of both g and D tensors is consistent with Fe³⁺ substituting for Al³⁺ ions in strongly distorted AlO₅(OH) octahedra in which the oxygen distances range from 1.85 to 1.98 Å. Fe³⁺ is not responsible for the blue color because colorless and blue euclase show nearly the same Fe³⁺ concentration as measured by EPR. However, total iron content in blue sample is much higher than in the colorless one suggesting that the existing model that Fe²⁺–Fe³⁺ intervalence charge transfer transition may explain the blue color of euclase.  相似文献   

Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review     

Ioan Seghedi  Hilary Downes  Orlando Vaselli  Alexandru Szakcs  Kadosa Balogh  Zoltn Pcskay 《Tectonophysics》2004,393(1-4):43

Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with derivation from complex mantle-source regions, which included both depleted asthenosphere and metasomatized lithosphere. The mixing of DMM-HIMU-EMII mantle components within asthenosphere-derived magmas indicates variable contamination of the shallow asthenosphere and/or thermal boundary layer of the lithosphere by a HIMU-like component prior to and following the introduction of subduction components.Various mantle sources have been identified: Lower lithospheric mantle modified by several ancient asthenospheric enrichments (source A); Young asthenospheric plumes with OIB-like trace element signatures that are either isotopically enriched (source B) or variably depleted (source C); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII-EMI components and slightly influenced by Miocene subduction-related enrichment (source D); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII components and significantly influenced by Miocene subduction-related enrichment (source E). Melt generation was initiated either by: (i) finger-like young asthenospheric plumes rising to and heating up the base of the lithosphere (below the Alcapa block), or (ii) decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs (the Tisia block).  相似文献   

The big picture of field hydrology studies in Brazil     

Davi C. D. Melo  Jamil A. A. Anache  Cristiano das N. Almeida  Jaqueline V. Coutinho  Geraldo M. Ramos Filho  Lívia M. P. Rosalem 《水文科学杂志》2020,65(8):1262-1280

ABSTRACT