Migration and accumulation of ultra-depleted subduction-related melts in the Massif du Sud ophiolite (New Caledonia)   总被引：1，自引：0，他引：1  

Claudio Marchesi  Carlos J. Garrido  Marguerite Godard  France Belley  Eric Ferr 《Chemical Geology》2009,266(3-4):180-195

The Massif du Sud is a large ophiolitic complex that crops out in the southern region of New Caledonia (SW Pacific). It is dominated by harzburgite tectonite that locally shows a transitional gradation to massive dunite up section. Clinopyroxene, orthopyroxene and plagioclase progressively appear in dunite up to the transition to layered wehrlite and orthopyroxene–gabbro. The dunite–wehrlite and wehrlite–gabbro contacts are parallel and the latter defines the paleo-Moho.Highly depleted modal, mineral and bulk rock compositions indicate that harzburgites are residues after high degrees (20–30%) of partial melting mainly in the spinel-stability field. Their relative enrichment in HFSE, LREE and MREE is due to re-equilibration of melting residues with percolating melts. Dunite formed in the Moho transition zone by reaction between residual mantle harzburgite and olivine-saturated melts that led to pyroxene dissolution and olivine precipitation. Rare clinopyroxene and plagioclase crystallized in interstitial melt pores of dunite from primitive, low-TiO₂, ultra-depleted liquids with a geochemical signature transitional between those of island arc tholeiites and boninites.Ascending batches of relatively high-SiO₂, ultra-depleted melts migrated through the Moho transition zone and generated wehrlite by olivine dissolution and crystallization of clinopyroxene, orthopyroxene and plagioclase in variable amounts. These liquids were more evolved and were produced by higher degrees of melting or from a more depleted source compared with melts that locally crystallized clinopyroxene in dunite. Ultra-depleted magmas, non-cogenetic with those that formed the Moho transition zone, ascended to the lower crust and generated gabbroic cumulates with subduction-related affinity. Thus, the ultramafic and mafic rocks in the Moho transition zone and lower crust of the Massif du Sud ophiolite are not products of fractional crystallization from a single magma-type but are the result of migration and accumulation of different melts in a multi-stage evolution.The record of high partial melting in the mantle section, and migration and accumulation of ultra-depleted subduction-related melts in the Moho transition zone and lower crust support that the Massif du Sud ophiolite is a portion of forearc lithosphere generated in an extensional regime during the early phases of the subduction zone evolution. Our results show the existence of different types of ultra-depleted melt compositions arriving at the Moho transition zone and lower crust of an infant intraoceanic paleo-arc. Ultra-depleted melts may thus be a significant component of the melt budget generated in oceanic spreading forearcs prior to aggregation and mixing of a large range of melt compositions in the crust.  相似文献   

An experimental investigation of antigorite dehydration in natural silica-enriched serpentinite   总被引：1，自引：0，他引：1  

José Alberto Padrón-Navarta  Jörg Hermann  Carlos J. Garrido  Vicente López Sánchez-Vizcaíno  María Teresa Gómez-Pugnaire 《Contributions to Mineralogy and Petrology》2010,159(1):25-42

Piston cylinder experiments were performed to constrain the pressure and temperature conditions for two high-pressure antigorite dehydration reactions found in silica-enriched serpentinites from Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera, southern Spain). At 630–660°C and pressures greater than 1.6 GPa, antigorite first reacts with talc to form orthopyroxene ± chlorite + fluid. We show that orthopyroxene + antigorite is restricted to high-pressure metamorphism of silica-enriched serpentinite. This uncommon assemblage is helpful in constraining metamorphic conditions in cold subduction environments, where antigorite serpentinites have no diagnostic assemblages over a large pressure and temperature range. The second dehydration reaction leads to the breakdown of antigorite to olivine + orthopyroxene + chlorite + fluid. The maximum stability of antigorite is found at 680°C at 1.9 GPa, which also corresponds to the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene. The high aluminium (3.70 wt% Al₂O₃) and chromium contents (0.59 wt% Cr₂O₃) of antigorite in the investigated starting material is responsible for the expansion of the serpentinite stability to 60–70°C higher temperatures at 1.8 GPa than the antigorite stability calculated in the Al-free system. The antigorite from our study has the highest Al–Cr contents among all experimental studies and therefore likely constraints the maximum stability of antigorite in natural systems. Comparison of experimental results with olivine–orthopyroxene–chlorite–tremolite assemblages outcropping in Cerro del Almirez indicates that peak metamorphic conditions were 680–710°C and 1.6–1.9 GPa.  相似文献   

Grids of stellar models and frequencies with CLÉS + LOSC     

Josefina Montalbán  Andrea Miglio  Arlette Noels  Richard Scuflaire 《Astrophysics and Space Science》2008,316(1-4):179-185

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Thorough analysis of input physics in CESAM and CLÉS codes     

Josefina Montalbán  Yveline Lebreton  Andrea Miglio  Richard Scuflaire  Pierre Morel  Arlette Noels 《Astrophysics and Space Science》2008,316(1-4):219-229

This contribution is not about the quality of the agreement between stellar models computed by CESAM and CLÉS codes, but more interesting, on what ESTA-Task 1 run has taught us about these codes and about the input physics they use. We also quantify the effects of different implementations of the same physics on the seismic properties of the stellar models, that in fact is the main aim of ESTA experiments.  相似文献   

Surveying at the limits of local RTK networks: Test results from the perspective of high accuracy users     

Mª Selmira Garrido  Elena GiménezMª Clara de Lacy  Antonio J. Gil 《International Journal of Applied Earth Observation and Geoinformation》2011

Precise GNSS-based differential positioning in real time is usually known as the real-time kinematics (RTK) technique. RTK reduces the effects of orbit errors and ionospheric and tropospheric refraction by forming differences between the observables (e.g. double-differences). These effects, however, grow with increasing baseline length, although the use of corrections generated in real-time from an active GNSS network allows these distance-dependent errors to be reduced. This technology increases the reliability of the system and thereby the accuracy of real-time positioning. In this study, the test results of RTK positioning at different test points located in the border area between the Autonomous Communities of the Region of Murcia and the Community of Valencia, in SE Spain, are presented. The analysis is based on three GNSS local active networks present in this border area, namely MERISTEMUM, REGAM and ERVA networks. Test measurements with RTK rover were performed in this region in order to analyze the real-time services offered by these three networks. Moreover, precise coordinates for each test point were determined using Bernese 5.0. The results confirm that it is possible to achieve centimetre-scale accuracy with RTK positioning based on the networks studied, even in border regions.  相似文献   

On far field occurrence of seismically induced landslides   总被引：1，自引：0，他引：1  

J. Delgado  J. Garrido  C. López-Casado  S. Martino  J.A. Peláez 《Engineering Geology》2011,123(3):204

Earthquakes may induce landslides at large distances from the epicentral area. In the last two decades, there have been many studies of this phenomenon to determine the causes that contribute to the occurrence of landslides at very long distances from earthquake epicenter. In this study, which is based on previously published works, a worldwide database comprising 270 earthquakes, including 150 during the instrumental period, was compiled to analyse the features of those landslides that occur at much further distances than maximum expected distances. From the analysis of the compiled data, it was observed that susceptible slopes can be grouped into five broad geological categories: jointed rock, marly–clayey (cohesive) soils, granular alluvial and/or colluvial sediments, volcanic soils, and residual soil slopes. These categories were equally likely to be associated with far field disrupted landslides, whereas far field coherent landslides were more frequent on cohesive soil slopes. Other factors, along with slope susceptibility may also contribute to far field landslides and increase the size of the area affected. Among these factors, site effects, antecedent rain and occurrence of seismic series have been cited. The analysis of available data also showed that for events of the same magnitude, far field disrupted landslides may occur at greater distances than coherent ones. The same database has also been employed to determine, for the first time, the upper bound curves for the maximum observed epicentral distances of several types of landslides and the maximum area observed to be affected by landslides, both based on the epicentral intensity of the events.  相似文献   

Asteroseismology of the β Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification     

G. Handler  M. Jerzykiewicz  E. Rodríguez  K. Uytterhoeven  P. J. Amado  T. N. Dorokhova  N. I. Dorokhov  E. Poretti  J.-P. Sareyan  L. Parrao  D. Lorenz  D. Zsuffa  R. Drummond  J. Daszy&#;ska-Daszkiewicz  T. Verhoelst  J. De Ridder  B. Acke  P.-O. Bourge  A. I. Movchan  R. Garrido  M. Paparó  T. Sahin  V. Antoci  S. N. Udovichenko  K. Csorba  R. Crowe  B. Berkey  S. Stewart  D. Terry  D. E. Mkrtichian  C. Aerts 《Monthly notices of the Royal Astronomical Society》2006,365(1):327-338

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Photometric Studies of O-type Hot Subdwarfs     

C. Rodríguez López  A. Ulla  R. Garrido  M. Manteiga  P. Thejll 《Astrophysics and Space Science》2004,291(3-4):431-434

We present a photometric study of eight sdOs and one sdOB on which simultaneous photometry in four Strömgren filters was performed. Our study seeks to detect the possible pulsators among the candidates.  相似文献   

GHASP: A 3-D Survey of Spiral and Irregular Galaxies at Hα     

P. Amram  C. Adami  C. Balkowski  S. Blais-Ouellette  A. Boselli  J. Boulesteix  C. Carignan  V. Cayatte  L. Chemin  J.L. Gach  O. Garrido  O. Hernandez  M. Marcelin  L. Michel-Dansac  H. Plana  D. Russeil  B. Vollmer  H. Wozniak 《Astrophysics and Space Science》2002,281(1-2):393-396

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Impact of tropospheric modelling on GNSS vertical precision: an empirical analysis based on a local active network     

Mª Selmira Garrido  Mª Clara de Lacy  Ana Mª Rojas 《International Journal of Digital Earth》2018,11(9):880-896

The troposphere affects Global Navigation Satellite System (GNSS) signals due to the variability of the refractive index. Tropospheric delay is a function of the satellite elevation angle and the altitude of the GNSS receiver and depends on the atmospheric parameters. If the residual tropospheric delay is not modelled carefully a bias error will occur in the vertical component. In order to analyse the precise altimetric positioning based on a local active network, four scenarios in Southern Spain with different topographical, environmental, and meteorological conditions are presented, considering both favourable and non-favourable conditions. The use of surface meteorological observations allows us to take into account the tropospheric conditions instead of a standard atmosphere, but introduces a residual tropospheric bias which reduces the accuracy of precise GNSS positioning. Thus, with short observation times it is recommended not to estimate troposphere parameters, but to use an a priori model together with the standard atmosphere. The results confirm that it is possible to achieve centimetre-scale vertical accuracy and precision with real time kinematic positioning even with large elevation differences with respect to the nearest reference stations. These numerical results may be taken into consideration for improving the altimetric configuration of the local active network.  相似文献