Rutile R632 – A New Natural Reference Material for U‐Pb and Zr Determination          下载免费PDF全文

Emelie Axelsson  Jonas Pape  Jasper Berndt  Fernando Corfu  Klaus Mezger  Michael M. Raith 《Geostandards and Geoanalytical Research》2018,42(3):319-338

A new natural rutile reference material is presented, suitable for U‐Pb dating and Zr‐in‐rutile thermometry by microbeam methods. U‐Pb dating of rutile R632 using laser ablation ICP‐MS with both magnetic sector field and quadrupole instruments as well as isotope dilution‐thermal ionisation mass spectrometry yielded a concordia age of 496 ± 2 Ma. The high U content (> 300 μg g^?1) enabled measurement of high‐precision U‐Pb ages despite its young age. The sample was found to have a Zr content of 4294 ± 196 μg g^?1, which makes it an excellent complementary reference material for Zr‐in‐rutile thermometry. Individual rutile grains have homogeneous compositions of a number of other trace elements including V, Cr, Fe, Nb, Mo, Sn, Sb, Hf, Ta and W. This newly characterised material significantly expands the range of available rutile reference materials relevant for age and temperature determinations.  相似文献   

Characterization and rehabilitation of the “Porta Férrea” stone materials,University of Coimbra,Portugal     

Lídia Catarino  Francisco P. S. C. Gil  Mário Quinta-Ferreira  Fernando Marques 《Environmental Earth Sciences》2018,77(11):416

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Place and people: spatializing degrees of bonding and bridging social capital in Lisbon (Portugal)     

Acedo  Albert  Santa  Fernando  Johnson  Peter A. 《GeoJournal》2021,86(6):2905-2925

GeoJournal - Broad academic interest in measuring social relationships within an urban context has grown over recent decades. Significant research attention is focused on where social synergies...  相似文献   

Dysfunctions in common fishing regulations     

Fernando González Laxe 《Marine Policy》2010

One of the main concerns of the Common Fisheries Policy (CFP) lies in guaranteeing consistency among the different implemented actions. The main concern is establishing a relationship between the levels of compliance with the Multi-annual Guidance Programme (MAGP), the adoption of total allowable catches (TACs), and the levels of compliance with rules by producers.  相似文献   

Experiments on steady buoyancy transfer through turbulent fluid layers separated by density interfaces     

Harindra J.S. Fernando  Robert R. Long 《Dynamics of Atmospheres and Oceans》1988,12(3-4)

A laboratory experiment was performed to investigate mixing across a density interface which separates two turbulent fluid layers and coexists with a stabilizing buoyancy flux. It was found that the buoyancy flux (q₀) across the interface and through the turbulent layers (of depth D) becomes steady and constant in magnitude in the vertical direction, only when , where u is the horizontal r.m.s. velocity at the base of the mixed layers. The results suggest that mixing across the density interface is controlled by a dynamically important buoyancy gradient induced in the turbulent layers and that parameters such as the bulk Richardson number, , where Δb is the interfacial buoyancy jump, are of secondary importance. Measurements are used to infer the mixing mechanism at the interface, the mixing efficiency of stratified fluids and the entrainment law. Some geophysical applications of the results are also discussed.  相似文献   

Analysis of swarms of high-frequency seismic events at Nevado del Ruiz volcano, Colombia (January 1986–August 1987): Development of a procedure     

Fernando C. Muoz  Alvaro E. Nieto  Hansjürgen Meyer 《Journal of Volcanology and Geothermal Research》1990,41(1-4)

The determination of signal properties like frequency, amplitude, “signature” of the sequence of arrivals of P- and S-phases and the subsequent computation of hypocenter parameters, are the steps of a procedure in the analysis of swarms of high-frequency seismic events from Nevado del Ruiz volcano, which could be useful in other volcanic areas. The use of this procedure on Ruiz data led to the determination of various seismic source volumes, which together with hypocenters of non-swarmed events and the identification of geological features such as faults which cross the area, alignment of domes and volcanic edifices, and the record of low-frequency seismic events not centered in the area of the active vent, suggest the existence of a magma chamber of a rather complex geometry. This hypothesis would suggest that magma, emplaced in zones of weakness (faults) that affect the area, may act as the source of seismic activity. This demands a revision of the methodology used in the deformation measurements, and in the analysis of released energy and event occurrence too. The relations between hypocenters (sources), location and relative energy of the swarms, as well as the general volcanic activity (tremor, ash and gas emission, deformation) could turn out to be a possible means to assist in the identification of premonitory activity and thus be relevant to the process of monitoring and forecasting.  相似文献   

Simulations of strong ground motion in SW Iberia for the 1969 February 28 (M_s= 8.0) and the 1755 November 1 (M∼ 8.5) earthquakes – II. Strong ground motion simulations     

Raphaël Grandin  José Fernando Borges  Mourad Bezzeghoud  Bento Caldeira  Fernando Carrilho 《Geophysical Journal International》2007,171(2):807-822

This is the second paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to use the velocity model that was proposed and validated in the companion paper for seismic intensity modelling of the 1969 ( M _s= 8.0) and 1755 ( M = 8.5–8.7) earthquakes.
First, we propose a regression to convert simulated values of Peak Ground Velocity (PGV) into Modified Mercalli Intensity (MMI) in SW Iberia, and using this regression, we build synthetic isoseismal maps for a large ( M _s= 8.0) earthquake that occurred in 1969. Based on information on the seismic source provided by various authors, we show that the velocity model effectively reproduces macroseismic observations in the whole region. We also confirm that seismic intensity distribution is very sensitive to a small number of source parameters: rupture directivity, fault strike and fault dimensions. Then, we extrapolate the method to the case of the great ( M = 8.5–8.7) 1755 earthquake, for a series of hypotheses recently proposed by three authors about the location of the epicentral region. The model involving a subduction-related rupture in the Gulf of Cádiz results in excessive ground motion in northern Morocco, suggesting that the source of the 1755 earthquake should be located further west. A rupture along the western coast of Portugal, compatible with an activation of the passive western Iberian margin, would imply a relatively low average slip, which, alone, would could not account for the large tsunami observed in the whole northern Atlantic ocean. A seismic source located below the Gorringe Bank seems the most likely since it is more efficient in reproducing the distribution of high intensities in SW Iberia due to the 1755 earthquake.  相似文献   

The impact of hurricanes on sedimenting particulate matter in the semi-arid Bahía de La Paz,Gulf of California     

Norman Silverberg  Evgueni Shumilin  Fernando Aguirre-Bahena  Ana Patricia Rodríguez-Castañeda  Dmitry Sapozhnikov 《Continental Shelf Research》2007

From 2002 through 2004, time-series sediment trap samples were collected from a depth of 410 m in Cuenca Alfonso, Bahía de La Paz, on the SW coast of the Gulf of California. The instrument recorded the impact of the local passage of hurricanes “Ignacio” (24–26 August) and “Marty” (21–23 September) in 2003. These two events accounted for 82% of the total rainfall measured in 2003, equivalent to the annual average precipitation in years without hurricanes. Mean total mass fluxes (TMFs) of 2.88 and 3.58 g m⁻² d⁻¹ were measured during the week of each hurricane as well as the following week. This may have been enough to produce a lamina in the underlying sediment with characteristics peculiar to such events. The terrigenous component was particularly abundant, with notably higher concentrations of Fe, Sc, Co and Cs and REEs. In contrast, TMFs throughout 2002–2004 (excluding the hurricane periods) averaged only 0.73 g m⁻² d⁻¹ and had a larger marine biogenic component. The extraordinary elemental fluxes during the 29 days of hurricane-influenced sedimentation represented a great proportion of the totals over an entire “normal” year: Co (67.8%) >Sc (62.6) >Fe (59.6) >Cs (53.4)>Lu (51.5)>La (51.3)>Yb (51.0)>Ce (49.5) >Tb (48.4) >Sm (44.7)>Cr (36.5) >Ca (31.0)>Eu (25.4%). The terrigenous fraction was calculated using (a) TMF minus the sum of CaCO₃, biogenic silica and organic matter and (b) the ratio of Sc in the trap samples to the average in the Earth's crust. The latter was consistently smaller, but the two methods offered similar results following hurricanes (78% vs. 63%, respectively). For normal sedimentation, however, the difference method yielded values twice as large as the Sc method (58% vs. 30%) This suggests that the mineralogy of the terrigenous fraction may also vary, with unsorted dessert soil being carried to sea by the powerful flash floods associated with hurricanes. Eolian supply of particles, particularly Sc-free quartz grains, possibly from beyond the limited fluvial drainage basin, apparently dominates normal sedimentation.  相似文献   

Multiple sources for ore-forming fluids in the Neves Corvo VHMS Deposit of the Iberian Pyrite Belt (Portugal): strontium, neodymium and lead isotope evidence   总被引：1，自引：0，他引：1  

Jorge M. Relvas  Colombo C. Tassinari  José Munhá  Fernando J. Barriga 《Mineralium Deposita》2001,36(5):416-427

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Distribuzione geografica dell'attivita' magnetica terrestre     

Mario Bossolasco  Fernando Dalmasso 《Pure and Applied Geophysics》1939,1(1):3-20

Riassunto Richiamate le caratteristiche secondo cui le perturbazioni regolari ed irregolari del campo terrestre concorrono a definire l'attività geomagnetica, se ne analizza la distribuzione geografica mediante le grandezze:HR _H ,ZR _Z , e (10^–4.²). Di queste sono illustrati e discussi gli andamenti in funzione della latitudine geomagnetica, dedotti dai valori medi calcolati per quasi tutte le stazioni funzionanti durante l'Anno Polare 1932–33 ed il triennio successivo 1933–36. Si rileva particolarmente il massimo assoluto di attività della zone anulare delle aurore, e quello relativo delle regioni equatoriali. Segue un'indagine, a carattere piuttosto indicativo, sulla ripartizione geografica del grado di variazione dell'attività nel tempo, introducendo a tale scopo opportuni indici ed esponendone il comportamento. Conclude la Nota un cenno sugli andamenti stagionali dell'attività e della variabilità geomagnetica.  相似文献