High resolution LA-ICP-MS mapping of U and Th isotopes in an early Pleistocene equid tooth from Fuente Nueva-3 (Orce, Andalusia, Spain)     

Mathieu Duval  Maxime Aubert  John Hellstrom  Rainer Grün 《Quaternary Geochronology》2011,6(5):458-467

We have produced detailed maps of U and Th isotopes for three cross-sections of an Early Pleistocene equid tooth from the archaeological site of Fuente Nueva-3 (Orce, Andalusia, Spain). This permits us to visualise, for the first time, U migration processes in 3 dimensions. The tooth shows a concentration gradient from the top to the base, indicating the U profile had not equilibrated after >1 Ma. The spatial pattern of ²³⁰Th/²³⁴U and ²³⁴U/²³⁸U indicates complex U-mobilisation processes over the last 100 ka, dominated by small-scale redistribution of U. Leaching from the tooth through the pulp cavity started at least 93 ka ago with several later phases in various domains of the dentine and cement. This leaching event could have been triggered by changes in the local hydrological regime associated with periods of increased erosion in the Guadix-Baza basin. The results illustrate the difficulty of dating faunal material from Early Pleistocene sites. They also demonstrate that dental tissues can neither be considered as homogeneous media for U-diffusion, nor behave as closed systems for U-series isotopes because diagenetic alterations seem to trigger U-migration. The results do not support the notion that U-uptake into dental tissues is necessarily of short duration. Nevertheless, rapid laser ablation scanning can be used to identify suitable samples for dating as well as domains within the teeth that may have preserved original isotopic signatures, i.e. domains that have not been affected by recent U-mobilisation process.  相似文献   

Field evidence for flank instability,basal spreading and volcano-tectonic interactions at Mt Cameroon,West Africa     

Lucie Mathieu  Matthieu Kervyn  Gerald G. J. Ernst 《Bulletin of Volcanology》2011,73(7):851-867

The Mt Cameroon volcano is the highest and most active volcano of the Cameroon Volcanic Line. Little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics. After reviewing the tectonic evolution of the region, the analysis of a Digital Elevation Model and results from a field campaign dedicated to mapping geological structures in the summit area and at the SE base of Mt Cameroon are presented. Mt Cameroon is a lava-dominated volcano with long steep (over 30°) flanks. It is elongate parallel to its well defined rift zone. The summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults. Geological profiles were measured along rivers cutting through a topographic step at the SE base of Mt Cameroon. This step is associated with deformed Miocene sediments from the Douala basin that are overlain by volcanic products. Weak sediments of this area are deformed by 050°–060° and 020°–030° trending asymmetrical folds verging toward the SE, and thrusts faults related to the spreading of the volcano over its mechanically weak substratum. Combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding. Both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice, repeated dyke intrusions, the weak sedimentary substratum and tectonic structures.  相似文献   

Mesozoic to Cenozoic tectono‐metamorphic history of the South Pamir–Hindu Kush (Chitral,NW Pakistan): Insights from phase equilibria modelling,and garnet–monazite petrochronology     

Mathieu Soret  Kyle P. Larson  John M. Cottle  Matthijs Smit  Alex Johnson  Sudip Shrestha  Asghar Ali  Shah Faisal 《Journal of Metamorphic Geology》2019,37(5):633-666

The Karakoram–Hindu Kush–Pamir and adjacent Tibetan plateau belt comprise a series of Gondwana‐derived crustal fragments that successively accreted to the Eurasian margin in the Mesozoic as the result of the progressive Tethys ocean closure. These domains provide unique insights into the thermal and structural history of the Mesozoic to Cenozoic Eurasian plate margin, which are critical to inform the initial boundary conditions (e.g. crustal thickness, structure and thermo‐mechanical properties) for the subsequent development of the large and hot Tibetan–Himalaya orogen, and the associated crustal deformation processes. Using a combination of microstructural analyses, thermobarometry modelling and U–Th–Pb monazite and Lu–Hf garnet geochronology, the study reappraises the metamorphic history of exposed mid‐crustal metapelites in the Chitral region of the South Pamir–Hindu Kush (NW Pakistan). This study also demonstrates that trace elements in monazite (especially Y and Dy), combined with thermodynamical modelling and Lu–Hf garnet dating, provides a powerful integrated toolbox for constraining long‐lived and polyphased tectono‐metamorphic histories in all their spatial and temporal complexity. Rocks from the Chitral region were progressively deformed and metamorphosed at sub‐ and supra‐solidus conditions through at least four distinct episodes from the Mesozoic to the Cenozoic. Rocks were first metamorphosed at ~400–500°C and ~0.3 GPa in the Late Triassic–Early Jurassic (210–185 Ma), likely in response to the accretion of the Karakoram during the Cimmerian orogeny. Pressure and temperature subsequently increased by ~0.3 GPa and 100°C in the Early‐ to Mid Cretaceous (140–80 Ma), coinciding with the intrusion of calcalkaline granitic plutons across the Karakoram and Pamir regions. This event is interpreted as the record of crustal thickening and the development of a proto‐plateau within the Eurasian margin due to a long‐lived episode of slab flattening in an Andean‐type margin. Peak metamorphism was reached in the Late Eocene–Early Oligocene (40–30 Ma) at conditions of 580–600°C and ~0.6 GPa and 700–750°C and 0.7–0.8 GPa for the investigated staurolite schists and sillimanite migmatites respectively. This crustal heating up to moderate anatexis likely resulted in the underthrusting of the Indian plate after a NeoTethyan slab‐break off or to the Tethyan Himalaya–Lhasa microcontinent collision and subsequent oceanic slab flattening. Near‐isothermal decompression/exhumation followed in the Late Oligocene (28–23 Ma) as marked by a pressure decrease in excess of ~0.1 GPa. This event was coeval with the intrusion of the 24 Ma Garam Chasma leucogranite. This rapid exhumation is interpreted to be related to the reactivation of the South Pamir–Karakoram suture zone during the ongoing collision with India. The findings of this study confirm that significant crustal shortening and thickening of the south Eurasian margin occurred during the Mesozoic in an accretionary‐type tectonic setting through successive episodes of terrane accretions and probably slab flattening, transiently increasing the coupling at the plate interface. Moreover, they indicate that the south Eurasian margin was already hot and thickened prior to Cenozoic collision with India, which has important implications for orogen‐scale strain‐accommodation mechanisms.  相似文献   

Lava discharge during Etna's January 2011 fire fountain tracked using MSG-SEVIRI     

Mathieu Gouhier  Andrew Harris  Sonia Calvari  Philippe Labazuy  Yannick Guéhenneux  Franck Donnadieu  Sébastien Valade 《Bulletin of Volcanology》2012,74(4):787-793

Etna's January 2011 eruption provided an excellent opportunity to test the ability of Meteosat Second Generation satellite's Spinning Enhanced Visible and InfraRed Imager (SEVIRI) sensor to track a short-lived effusive event. The presence of lava fountaining, the rapid expansion of lava flows, and the complexity of the resulting flow field make such events difficult to track from the ground. During the Etna's January 2011 eruption, we were able to use thermal data collected by SEVIRI every 15 min to generate a time series of the syn-eruptive heat flux. Lava discharge waxed over a ~1-h period to reach a peak that was first masked from the satellite view by a cold tephra plume and then was of sufficient intensity to saturate the 3.9-μm channel. Both problems made it impossible to estimate time-averaged lava discharge rates using the syn-eruptive heat flux curve. Therefore, through integration of data obtained by ground-based Doppler radar and thermal cameras, as well as ancillary satellite data (from Moderate Resolution Imaging Spectrometer and Advanced Very High Resolution Radiometer), we developed a method that allowed us to identify the point at which effusion stagnated, to allow definition of a lava cooling curve. This allowed retrieval of a lava volume of ~1.2 × 10⁶ m³, which, if emitted for 5 h, was erupted at a mean output rate of ~70 m³ s⁻¹. The lava volume estimated using the cooling curve method is found to be similar to the values inferred from field measurements.  相似文献   

Ground motion prediction in Beirut: a multi-step procedure coupling empirical Green’s functions,ground motion prediction equations and instrumental transfer functions     

Marleine Brax  Mathieu Causse  Pierre-Yves Bard 《Bulletin of Earthquake Engineering》2016,14(12):3317-3341

The strike slip Yammouneh fault is the longest fault in Lebanon, crossing the territory from South to North. It was responsible for major historical earthquakes like the 1202 A.D. earthquake, estimated to M_s7.6. This paper presents a site-specific estimation of the ground motion caused by a potential M_w7.5 earthquake on the Yammouneh fault, similar to the 1202 event, for various sites within the Beirut area. The empirical Green’s function technique EGF is used to estimate the median and the standard deviations of the seismic ground motion at the reference station BHL, taking into account epistemic and aleatory uncertainties related to source parameters. These uncertainties were quantified through a sensitivity analysis of the position of the rupture nucleation X_nuc, the slip roughness parameter K, the corner frequency f_c and the magnitude M_c of the EGF. The rock ground motion is then transferred to various other sites within the Beirut area, using instrumental Fourier transfer functions. Site amplification factors are next deduced by computing the ratio between response spectra at sediment sites and at a reference rock station. Considering the limits of the EGF method in the near field of extended sources, the EGF approach is considered only up to a magnitude M_w of 6.5. Selected Ground Motion Predictive Equations are then used to simulate a M_w7.5 event at a reference station. By applying the amplification factors, the response spectra at the different sites of Beirut are also calculated and compared with the actual response spectra used in the Lebanese regulations.  相似文献   

Tungsten isotopes in ferroan anorthosites: Implications for the age of the Moon and lifetime of its magma ocean   总被引：1，自引：0，他引：1  

Mathieu Touboul  Thorsten Kleine  Herbert Palme 《Icarus》2009,199(2):245-316

New W isotope data for ferroan anorthosites 60025 and 62255 and low-Ti mare basalt 15555 show that these samples, contrary to previous reports [Lee, D.C., et al., 1997. Science 278, 1098-1103; Lee, D.C., et al., 2002. Earth Planet. Sci. Lett. 198, 267-274], have a W isotope composition that is indistinguishable from KREEP and other mare basalts. This requires crust extraction on the Moon later than ∼60 Myr after CAI formation, consistent with ¹⁴⁷Sm-¹⁴³Nd ages for ferroan anorthosites. The absence of ¹⁸²Hf-induced ¹⁸²W variations in the Moon is consistent with formation of the Moon at after CAI formation that has been inferred based on the indistinguishable ¹⁸²W/¹⁸⁴W ratios of the bulk Moon and the bulk silicate Earth. The uncertainties on the age of the Moon and the age of the oldest lunar samples currently hamper a precise determination of the duration of magma ocean solidification and are consistent with both an almost immediate crystallization and a more protracted timescale of ∼100 Myr.  相似文献   

Cassini-Huygens results on Titan's surface     

Athena Coustenis  Mathieu Hirtzig 《中国天文和天体物理学报》2009,9(3)

Our understanding of Titan, Saturn's largest satellite, has recently been consid-erably enhanced, thanks to the Cassini-Huygens mission. Since the Saturn Orbit Injection in July 2004, the probe has been harvesting new insights of the Kronian system. In par-ticular, this mission orchestrated a climax on January 14, 2005 with the descent of the Huygens probe into Titan's thick atmosphere. The orbiter and the lander have provided us with picturesque views of extraterrestrial landscapes, new in composition but reassuringly Earth-like in shape. Thus, Saturn's largest satellite displays chains of mountains, fields of dark and damp dunes, lakes and possibly geologic activity. As on Earth, landscapes on Titan are eroded and modeled by some alien hydrology: dendritic systems, hydrocarbon lakes, and methane clouds imply periods of heavy rainfalls, even though rain was never observed directly. Titan's surface also proved to be geologically active - today or in the recent past - given the small number of impact craters listed to date, as well as a few possible cryovolcanic features. We attempt hereafter a synthesis of the most significant results of the Cassini-Huygens endeavor, with emphasis on the surface.  相似文献   

Oxidation state of iron and extensive redistribution of sulfur in thermally modified Stardust particles     

Hugues Leroux  Mathieu Roskosz  Damien Jacob 《Geochimica et cosmochimica acta》2009,73(3):767-3513

Two representative thermally modified Stardust samples were investigated by analytical transmission electron microscopy in order to decipher their iron oxidation state after the strong thermal episode due to the capture in aerogel. Their dominant microstructure consists of evenly distributed rounded Fe-Ni-S nano-droplets within a silica-rich glassy matrix. The mineralogy and associated redox state of iron is assessed using a Fe-Mg-S ternary diagram on which ferromagnesian silicates, sulfides and metal can be represented and potentially compared with any other extraterrestrial material. In this diagram, all the data (bulk and local analysis of silicates, sulfide + metal) scatter along a mixing line between the Mg corner and the average composition of the iron-sulfide. There is an obvious genetic relationship between the different phases observed in such samples, further supported by the very low concentration of iron in the glassy matrix. Silicate glasses contain a significant concentration of dissolved sulfur probably present as MgS complexes. This chemical signature is typical of highly reduced environments. These secondary microstructures were established during the high temperature stage of the capture. A significant part of the Fe-droplets formed in situ by reduction at high temperature of ferromagnesian silicates (olivine and pyroxenes) during the impact. At this stage, the indigenous sulfides destabilized and sulfur readily volatilized as S₂, diffused into molten materials and condensed later onto the Fe-precipitates that formed in the silicate melt. This scenario is supported by the structure of Fe-Ni-S beads with a metal core and a sulfide rim. It will be difficult to derive reliable information on the redox state of 81P/Wild 2 particles based on bulk analyses of whole tracks because particles found along the walls of tracks suffered strong reduction reactions, contrary to terminal particles that may have preserved their pristine redox state. The capture effect must be taken into account for comparison of Wild 2 particles with other chondritic material.  相似文献   

Chad Basin: Paleoenvironments of the Sahara since the Late Miocene     

Mathieu Schuster  Philippe Duringer  Jean-François Ghienne  Claude Roquin  Pierre Sepulchre  Abderamane Moussa  Anne-Elisabeth Lebatard  Hassan Taisso Mackaye  Andossa Likius  Patrick Vignaud  Michel Brunet 《Comptes Rendus Geoscience》2009,341(8-9):603-611

Since the mid 1990s, the Mission paléoanthropologique francotchadienne (MPFT) conducts yearly paleontological field investigations of the Miocene-Pliocene of the Chad Basin. This article synthesizes some of the results of the MPFT, with focus on the Chad Basin development during the Neogene. We propose an overview of the depositional paleoenvironments of this part of Africa at different scales of time and space, based on a multidisciplinary approach (sedimentary geology, geomorphology, geophysic, numerical simulations and geochronology). The Miocene-Pliocene paleoenvironments are examined through the sedimentary archives of the early hominids levels and the Holocene Lake Mega-Chad episode illustrates the last major paleoenvironmental change in this area. The sedimentary record of the Chad Basin since the Late Miocene can be schematized as the result of recurrent interactions from lake to desert environments.  相似文献   

Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data     

Amaelle Landais  Mathieu Casado  Frédéric Prié  Olivier Magand  Laurent Arnaud  Alexey Ekaykin  Jean-Robert Petit  Ghislain Picard  Michel Fily  Bénédicte Minster  Alexandra Touzeau  Sentia Goursaud  Valérie Masson-Delmotte  Jean Jouzel  Anaïs Orsi 《Comptes Rendus Geoscience》2017,349(4):139-150

Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ¹⁸O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ¹⁸O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (～ 0.7–0.8‰·°C^?1 for δ¹⁸O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C^?1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ¹⁸O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ¹⁸O of snow and surface temperature, but is associated with a much slower δ¹⁸O-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m^?2.yr^?1 may record a seasonal cycle at shallow depths.  相似文献