Sr and Nd isotope composition of the metamorphic,sedimentary and ultramafic xenoliths of Lanzarote (Canary Islands): Implications for magma sources     

Alfredo Aparicio  Colombo C.G. Tassinari  Roberto García  Vicente Araña 《Journal of Volcanology and Geothermal Research》2010,189(1-2):143-150

The lavas produced by the Timanfaya eruption of 1730–1736 (Lanzarote, Canary Islands) contain a great many sedimentary and metamorphic (metasedimentary), and mafic and ultramafic plutonic xenoliths. Among the metamorphosed carbonate rocks (calc-silicate rocks [CSRs]) are monomineral rocks with forsterite or wollastonite, as well as rocks containing olivine ± orthopyroxene ± clinopyroxene ± plagioclase; their mineralogical compositions are identical to those of the mafic (gabbros) and ultramafic (dunite, wherlite and lherzolite) xenoliths. The ⁸⁷Sr/⁸⁶Sr (around 0.703) and ¹⁴³Nd/¹⁴⁴Nd (around 0.512) isotope ratios of the ultramafic and metasedimentary xenoliths are similar, while the ¹⁴⁷Sm/¹⁴⁴Nd ratios show crustal values (0.13–0.16) in the ultramafic xenoliths and mantle values (0.18–0.25) in some CSRs. The apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source (basaltic intrusion) inducing strong isotopic exchange (⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd) between metasedimentary and basaltic rocks. Petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths.  相似文献   

OSL dating of the Middle Palaeolithic Hotel California site,Sierra de Atapuerca,north‐central Spain     

Lee J. Arnold  Martina Demuro  Marta Navazo  Alfonso Benito‐Calvo  Alfredo Pérez‐González 《Boreas: An International Journal of Quaternary Research》2013,42(2):285-305

In this study we present optically stimulated luminescence (OSL) dating results obtained at one of the most important open‐air Middle Palaeolithic sites in the Sierra de Atapuerca foothills – Hotel California. We also assess the possibility of obtaining extended‐range OSL chronologies for a nearby Middle Pleistocene fluvial deposit using several novel methods, namely OSL dating of individual quartz ‘supergrains’, multi‐grain aliquot thermally transferred OSL (TT‐OSL) dating and the first application of a single‐grain TT‐OSL dating procedure. Four single‐grain OSL ages constrain the Middle Palaeolithic occupation of Hotel California to between 71±6 and 48±3 ka. The Hotel California single‐grain equivalent dose (D_e) distributions are highly overdispersed and contain several dose populations, which are probably attributable to post‐depositional sediment mixing, partial bleaching and intrinsic scatter. The reliability of multi‐grain aliquot OSL dating is compromised by the complex underlying D_e dispersion affecting these samples, as well as by biasing multi‐grain averaging effects. Extended‐range OSL and TT‐OSL chronologies for the nearby Pico River terrace are consistent with each other and with broad independent age control. These experimental approaches yield a weighted average age of 348±16 ka for terrace T_A9 of the Arlanzón River sequence. Our results highlight the benefits of comparing ages obtained using several OSL methodologies to improve the robustness of luminescence chronologies. They also demonstrate the potential that single‐grain OSL techniques offer for establishing improved age constraints on the many other Middle Palaeolithic sites found at Atapuerca and elsewhere across north‐central Spain.  相似文献   

Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California     

Thierry Calmus  Carlos Pallares  Ren�� C. Maury  Alfredo Aguill��n-Robles  Herv�� Bellon  Mathieu Benoit  Fran?ois Michaud 《Pure and Applied Geophysics》2011,168(8-9):1303-1330

The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: ??regular?? calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific-Farallon plate formed the Comondú and central coast of the Sonora volcanic arc. In the extensional domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the Basin and Range province. The end of the Farallon subduction was marked by the emplacement of much more complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline activity became sporadic and was replaced by unusual post-subduction magma types including adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The spatial and temporal distribution of these lavas is consistent with the development of a slab tear, evolving into a 200-km-wide slab window sub-parallel to the trench, and extending from the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts of subslab origin ascended through this window, and adakites derived from the partial melting of its upper lip, relatively close to the trench. Calc-alkaline lavas, magnesian andesites and niobium-enriched basalts formed from hydrous melting of the supraslab mantle triggered by the uprise of hot Pacific asthenosphere through the window. During the Plio-Quaternary, the ??no-slab?? regime following the sinking of the old part of the Farallon plate within the deep mantle allowed the emplacement of alkali and tholeiitic/transitional basalts of deep asthenospheric origin in Baja California and Sonora. The lithospheric rupture connected with the opening of the Gulf of California generated a high thermal regime associated to asthenospheric uprise and emplaced Quaternary depleted MORB-type tholeiites. This thermal regime also induced partial melting of the thinned lithospheric mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle.  相似文献   

The Høvsøre Tall Wind-Profile Experiment: A Description of Wind Profile Observations in the Atmospheric Boundary Layer     

Alfredo Peña  Rogier Floors  Sven-Erik Gryning 《Boundary-Layer Meteorology》2014,150(1):69-89

We present an analysis of data from a nearly 1-year measurement campaign performed at Høvsøre, Denmark, a coastal farmland area where the terrain is flat. Within the easterly sector upstream of the site, the terrain is nearly homogenous. This topography and conditions provide a good basis for the analysis of vertical wind-speed profiles under a wide range of atmospheric stability, turbulence, and forcing conditions. One of the objectives of the campaign was to serve as a benchmark for flow over flat terrain models. The observations consist of combined wind lidar and sonic anemometer measurements at a meteorological mast. The sonic measurements cover the first 100 m and the wind lidar measures above 100 m every 50 m in the vertical. Results of the analysis of observations of the horizontal wind-speed components in the range 10–1200 m and surface turbulence fluxes are illustrated in detail, combined with forcing conditions derived from mesoscale model simulations. Ten different cases are presented. The observed wind profiles approach well the simulated gradient and geostrophic winds close to the simulated boundary-layer height during both barotropic and baroclinic conditions, respectively, except for a low-level jet case, as expected. The simulated winds are also presented for completeness and show good agreement with the measurements, generally underpredicting the turning of the wind in both barotropic and baroclinic cases.  相似文献   

Out‐of‐plane behaviour of a full scale stone masonry façade. Part 2: shaking table tests     

Alexandre A. Costa  António Arêde  Alfredo Campos Costa  Andrea Penna  Aníbal Costa 《地震工程与结构动力学》2013,42(14):2097-2111

  相似文献   

Slow cooling versus episodic fluid injections: Deciphering the Caledonian orogeny in Vestvågøy,Lofoten islands,Norway     

Herbert W. Fournier  James K. W. Lee  Alfredo Camacho 《Journal of Metamorphic Geology》2019,37(6):769-793

The determination of the thermal (temperature–time) histories of high‐P metamorphic terranes has been commonly based on the concepts of slow cooling and closure temperatures. In this paper, we find that this approach cannot reconcile a geochronological data set obtained from the amphibolite‐facies allochthonous Leknes Group of the Lofoten islands, Norway, which reveals an extremely complex thermal history. Using detailed results from several different geochronometers such as ⁴⁰Ar/³⁹Ar, Rb–Sr and U–Pb, we show that a model invoking multiple, short‐lived thermal pulses related to hot‐fluid infiltration channelized by shear zones can reconcile this complicated data set. This model suggests that hot fluids infiltrated throughout basement shear zones and affected the overlying cold allochthon, partially resetting U/Pb rutile and titanite ages, crystallizing new zircon and produced identical ⁴⁰Ar/³⁹Ar and Rb/Sr ages in muscovite, biotite and amphibole in various rocks throughout the region. This paper shows the enormous potential of coupling laser Ar‐spot data with thermal modelling to identify and constrain the duration of short‐lived events. An optimal P–T–t history has been derived by modelling the age data from a previously dated large muscovite crystal (Hames & Andresen, 1996, Geology, 24 :1005) and using Zr‐in‐rutile thermometry which is consistent with all geochronological data and geological constraints from the basement zones and allochthon cover. This tectonothermal model history suggests that there have been three episodic hot‐fluid and ⁴⁰Ar‐free infiltration events, resulting in the total resetting of Ar ages during the Scandian (425 Ma) for 1 Ma at 650°C and two reheating events at 415 Ma for 400 ka at 650°C and at 365 Ma for 50 ka at 600°C, which are modelled as thermal spikes above an ambient temperature of 300°C. Independent confirmation of these parameters was provided by Pb‐diffusion modelling in rutile and titanite. The model suggests that the amphibolite facies rocks of the Leknes Group probably remained cold before being exhumed for at least 60 Ma (425–365 Ma) and successfully explains the presence of different minerals that crystallized or were totally/partially reset in the allochthon and in the basement. The migration of hot fluids for short periods of times within conduits extending through the basement and allochthon rock units is likely associated with episodic seismic activity during the Caledonian orogeny.  相似文献   

Vegetation Index Methods for Estimating Evapotranspiration by Remote Sensing   总被引：2，自引：0，他引：2  

Edward P. Glenn  Pamela L. Nagler  Alfredo R. Huete 《Surveys in Geophysics》2010,31(6):531-555

Evapotranspiration (ET) is the largest term after precipitation in terrestrial water budgets. Accurate estimates of ET are needed for numerous agricultural and natural resource management tasks and to project changes in hydrological cycles due to potential climate change. We explore recent methods that combine vegetation indices (VI) from satellites with ground measurements of actual ET (ET_a) and meteorological data to project ET_a over a wide range of biome types and scales of measurement, from local to global estimates. The majority of these use time-series imagery from the Moderate Resolution Imaging Spectrometer on the Terra satellite to project ET over seasons and years. The review explores the theoretical basis for the methods, the types of ancillary data needed, and their accuracy and limitations. Coefficients of determination between modeled ET_a and measured ET_a are in the range of 0.45–0.95, and root mean square errors are in the range of 10–30% of mean ET_a values across biomes, similar to methods that use thermal infrared bands to estimate ET_a and within the range of accuracy of the ground measurements by which they are calibrated or validated. The advent of frequent-return satellites such as Terra and planed replacement platforms, and the increasing number of moisture and carbon flux tower sites over the globe, have made these methods feasible. Examples of operational algorithms for ET in agricultural and natural ecosystems are presented. The goal of the review is to enable potential end-users from different disciplines to adapt these methods to new applications that require spatially-distributed ET estimates.  相似文献   

Deconvolution of multicomponent seismic data by means of quaternions: Theory and preliminary results‡     

Giovanni M. Menanno  Alfredo Mazzotti 《Geophysical Prospecting》2012,60(2):217-238

Multicomponent seismic data are acquired by orthogonal geophones that record a vectorial wavefield. Since the single components are not independent, the processing should be performed jointly for all the components. In this contribution, we use hypercomplex numbers, specifically quaternions, to implement the Wiener deconvolution for multicomponent seismic data. This new approach directly derives from the complex Wiener filter theory, but special care must be taken in the algorithm implementation due to the peculiar properties of quaternion algebra. Synthetic and real data examples show that quaternion deconvolution, either spiking or predictive, generally performs superiorly to the standard (scalar) deconvolution because it properly takes into account the vectorial nature of the wavefields. This provides a better wavelet estimation and thus an improved deconvolution performance, especially when noise affects differently the various components.  相似文献   

Influence of substrate tectonic heritage on the evolution of composite volcanoes: Predicting sites of flank eruption, lateral collapse, and erosion     

Alessandro Tibaldi  Claudia Corazzato  Andrey Kozhurin  Alfredo F.M. Lagmay  Federico A. Pasquar  Vera V. Ponomareva  Derek Rust  Daniel Tormey  Luigina Vezzoli 《Global and Planetary Change》2008,61(3-4):151-174

This paper aims to aid understanding of the complicated interplay between construction and destruction of volcanoes, with an emphasis on the role of substrate tectonic heritage in controlling magma conduit geometry, lateral collapse, landslides, and preferential erosion pathways. The influence of basement structure on the development of six composite volcanoes located in different geodynamic/geological environments is described: Stromboli (Italy), in an island arc extensional tectonic setting, Ollagüe (Bolivia–Chile) in a cordilleran extensional setting, Kizimen (Russia) in a transtensional setting, Pinatubo (Philippines) in a transcurrent setting, Planchon (Chile) in a compressional cordilleran setting, and Mt. Etna (Italy) in a complex tectonic boundary setting. Analogue and numerical modelling results are used to enhance understanding of processes exemplified by these volcanic centres. We provide a comprehensive overview of this topic by considering a great deal of relevant, recently published studies and combine these with the presentation of new results, in order to contribute to the discussion on substrate tectonics and its control on volcano evolution. The results show that magma conduits in volcanic rift zones can be geometrically controlled by the regional tectonic stress field. Rift zones produce a lateral magma push that controls the direction of lateral collapse and can also trigger collapse. Once lateral collapse occurs, the resulting debuttressing produces a reorganization of the shallow-level magma migration pathways towards the collapse depression. Subsequent landslides and erosion tend to localize along rift zones. If a zone of weakness underlies a volcano, long-term creep can occur, deforming a large sector of the cone. This deformation can trigger landslides that propagate along the destabilized flank axis. In the absence of a rift zone, normal and transcurrent faults propagating from the substrate through the volcano can induce flank instability in directions respectively perpendicular and oblique to fault strike. This destabilization can evolve to lateral collapse with triggering mechanisms such as seismic activity or magmatic intrusion.  相似文献   

Investigating the Tsunamigenic Potential of Earthquakes from Analysis of the Informational and Multifractal Properties of Seismograms     

Luciano Telesca  Ashutosh Chamoli  Michele Lovallo  Tony Alfredo Stabile 《Pure and Applied Geophysics》2015,172(7):1933-1943

  相似文献