Olivine intergranular plasticity at mantle pressures and temperatures     

Paul Raterron  Caroline Bollinger  Sébastien Merkel 《Comptes Rendus Geoscience》2019,351(2-3):80-85

The ductile behavior of olivine-rich rocks is critical to constrain thermal convection in the Earth's upper mantle. Classical olivine flow laws for dislocation or diffusion creep fail to explain the fast post-seismic surface displacements observed by GPS, which requires a much weaker lithosphere than predicted by classical laws. Here we compare the plasticity of olivine aggregates deformed experimentally at mantle pressures and temperatures to that of single crystals and demonstrate that, depending on conditions of stress and temperature, strain accommodated through grain-to-grain interactions – here called intergranular strain – can be orders of magnitude larger than intracrystalline strain, which significantly weakens olivine strength. This result, extrapolated along mantle geotherms, suggests that intergranular plasticity could be dominant in most of the upper mantle. Consequently, the strength of olivine-rich aggregates in the upper mantle may be significantly lower than predicted by flow laws based on intracrystalline plasticity models.  相似文献   

Combining ECCI and FIB milling techniques to prepare site-specific TEM samples for crystal defect analysis of deformed minerals at high pressure     

Nobuyoshi Miyajima  Tommaso Mandolini  Florian Heidelbach  Caroline Bollinger 《Comptes Rendus Geoscience》2019,351(2-3):295-301

Dislocation microstructures in experimentally deformed single-crystal pyrope-rich garnet, (Mg,Fe)₃(Al,Cr)₃Si₃O₁₂, and polycrystalline forsterite, Mg₂SiO₄, were investigated by using electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) combined with a focused ion beam (FIB)-microsampling. In the orientation-optimized ECCI method, we successfully observed individual dislocations across subgrain boundaries in a low-atomic-number mineral, pyrope-rich garnet (averaged Z-numbers, AZs ～ 10). Dislocations in a deformed forsterite (iron-free olivine) were also visible in the ECCI. In the ECCI on the single-crystal garnet, deformation bands consisting of dislocations, unusual contrasts in stripes and inhomogeneous distributions of sub-micrometer-sized pores were found. Further site-specific TEM observation on the deformation band revealed a high density of partial dislocations and stacking fault ribbons. The site-specific characterizations from ECCI to TEM, with assistance of FIB, can provide a new approach to investigate dislocation microstructures of deformed materials at high pressure and high temperature.  相似文献   

Baossi–Warack monogenetic volcanoes,Adamawa Plateau,Cameroon: petrography,mineralogy and geochemistry     

Tiabou  Anicet Feudjio  Temdjim  Robert  Wandji  Pierre  Bardintzeff  Jacques-Marie  Che  Vivian Bih  Bate Tibang  Edith Ekatah  Ngwa  Caroline Neh  Mebara  François Xavier Onana 《中国地球化学学报》2019,38(1):40-67

Acta Geochimica - Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line (CVL) are documented in this study....  相似文献   

Depth constraints on azimuthal anisotropy in the Great Basin from Rayleigh-wave phase velocity maps     

Caroline Beghein  J. Arthur Snoke  Matthew J. Fouch 《Earth and Planetary Science Letters》2010,289(3-4):467-478

We present fundamental-mode Rayleigh-wave azimuthally anisotropic phase velocity maps obtained for the Great Basin region at periods between 16 s and 102 s. These maps offer the first depth constraints on the origin of the semi-circular shear-wave splitting pattern observed in central Nevada, around a weak azimuthal anisotropy zone. A variety of explanations have been proposed to explain this signal, including an upwelling, toroidal mantle flow around a slab, lithospheric drip, and a megadetachment, but no consensus has been reached. Our phase velocity study helps constrain the three-dimensional anisotropic structure of the upper mantle in this region and contributes to a better understanding of the deformation mechanisms taking place beneath the western United States. The dispersion measurements were made using data from the USArray Transportable Array. At periods of 16 s and 18 s, which mostly sample the crust, we find a region of low anisotropy in central Nevada coinciding with locally reduced phase velocities, and surrounded by a semi-circular pattern of fast seismic directions. Away from central Nevada the fast directions are ～ N–S in the eastern Great Basin, NW–SE in the Walker Lane region, and they transition from E–W to N–S in the northwestern Great Basin. Our short-period phase velocity maps, combined with recent crustal receiver function results, are consistent with the presence of a semi-circular anisotropy signal in the lithosphere in the vicinity of a locally thick crust. At longer periods (28–102 s), which sample the uppermost mantle, isotropic phase velocities are significantly reduced across the study region, and fast directions are more uniform with an ～ E–W fast axis. The transition in phase velocities and anisotropy can be attributed to the lithosphere–asthenosphere boundary at depths of ～ 60 km. We interpret the fast seismic directions observed at longer periods in terms of present-day asthenospheric flow-driven deformation, possibly related to a combination of Juan de Fuca slab rollback and eastward-driven mantle flow from the Pacific asthenosphere. Our results also provide context to regional SKS splitting observations. We find that our short-period phase velocity anisotropy can only explain ～ 30% of the SKS splitting times, despite similar patterns in fast directions. This implies that the origin of the regional shear-wave splitting signal is complex and must also have a significant sublithospheric component.  相似文献   

Comparison of a Homemade Bacuri Shell Activated Carbon With Carbon Nanotubes for Food Dye Removal          下载免费PDF全文

Caroline Saucier  Matthew A. Adebayo  Eder C. Lima  Lizie D. T. Prola  Pascal S. Thue  Cibele S. Umpierres  Mayerly J. Puchana‐Rosero  Fernando M. Machado 《洁净——土壤、空气、水》2015,43(10):1389-1400

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A continuous plate-tectonic model using geophysical data to estimate plate-margin widths, with a seismicity-based example     

Caroline Dumoulin  David Bercovici  & Pål Wessel 《Geophysical Journal International》1998,133(2):379-389

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Organochlorine and heavy metal concentrations in blubber and liver tissue collected from Queensland (Australia) dugong (Dugong dugon)     

Haynes D  Carter S  Gaus C  Müller J  Dennison W 《Marine pollution bulletin》2005,51(1-4):361-369

Tissue samples of liver and blubber were salvaged from fifty-three dugong (Dugong dugon) carcasses stranded along the Queensland coast between 1996 and 2000. Liver tissue was analysed for a range of heavy metals and blubber samples were analysed for organochlorine compounds. Metal concentrations were similar in male and female animals and were generally highest in mature animals. Liver concentrations of arsenic, chromium, iron, lead, manganese, mercury and nickel in a number of individual animals were elevated in comparison to concentrations previously reported in Australian dugong. Dieldrin, DDT (and its breakdown products) and/or heptachlor epoxide were detected in 59% of dugong blubber samples. In general, concentrations of organochlorines were similar to those reported in dugong 20 years earlier, and were low in comparison to concentrations recorded from marine mammal tissue collected elsewhere in the world. With the exception of lead, the extent of carcass decomposition, the presence of disease or evidence of animal starvation prior to death did not significantly affect dugong tissue concentrations of metals or organochlorines. The results of the study suggest that bioaccumulation of metals and organochlorine compounds (other than dioxins) does not represent a significant risk to Great Barrier Reef dugong populations, particularly in the context of other pressures associated with coastal development and other anthropogenic activities.  相似文献   

Deep sea diapirs and bottom simulating reflector in Fairway Basin (SW Pacific)   总被引：1，自引：0，他引：1  

Auzende  Jean Marie  Van de Beuque  Sabrina  Dickens  Gerald  François  Caroline  Lavoy  Yves  Voutay  Olivier  Exon  Neville 《Marine Geophysical Researches》2000,21(6):579-587

A recent swath-bathymetry and geophysical survey of the R/V L'Atalante in the Fairway Basin between Australia and New Caledonia allowed to confirm the Cretaceous age of the creation of the basin by continental stretching. This first stage of opening of the Fairway Basin is associated with the deposition of a continuous salt/mud layer feeding today numerous diapirs, some of them piercing the 3 to 4 km thick sedimentary cover and reaching the seafloor. In close link with this salt/mud layer a Bottom Simulating Reflector indicator of gas hydrates level occupies a 70000 km² surface at about 500 to 600 m-depth beneath the sea floor. The coexistence of both BSR and diapirs suggests a thermogenic better than biogenic origin for the gas hydrates horizon.  相似文献   

Integration of High and Very High-resolution Seismic Reflection Profiles to Study Upper Quaternary Deposits of a Coastal Area in the Western Gulf of Lions, SW France     

Caroline Labaune  Michel Tesson  Bernard Gensous 《Marine Geophysical Researches》2005,26(2-4):109-122

High resolution (HR – sparker) and very high resolution (VHR – boomer) seismic reflection data acquired in shallow water environments of the Roussillon coastal area are integrated to provide an accurate image of the stratigraphic architecture of the Quaternary deposits. The complementary use of the two systems is shown to be of benefit for studies of shallow water environments. The HR sparker data improved the landward part of a general model of Quaternary stratigraphy previously established offshore. They document an incised valley complex interpreted as the record of successive late Quaternary relative sea-level cycles. The complex is capped by a polygenetic erosional surface developed during the last glacial period (>18 ky) and variably reworked by wave ravinement during the subsequent post-glacial transgression. The overlying transgressive systems tract is partly preserved and presents a varying configuration along the Roussillon coastal plain. The VHR boomer data provide information on the architecture of the uppermost deposits, both in the near-shore area and in the lagoon. These deposits overlie a maximum flooding surface at the top of the transgressive systems tract and constitute a highstand systems tract composed of two different architectural elements. In the near-shore area, a sandy coastal wedge is subdivided into a lower unit and an upper unit in equilibrium with present day dynamics. In the Salses-Leucate lagoon area, the sedimentary architecture is highly complex due to the closure of a former embayment and the formation of the present beach barrier.  相似文献   

Adaptive Management of Urban Ecosystem Restoration: Learning From Restoration Managers in Rhode Island,USA     

Kristen Hychka  Caroline Gottschalk Druschke 《社会与自然资源》2017,30(11):1358-1373

Urban aquatic restoration can be difficult to accomplish because of complications like industrial pollutants, population density, infrastructure, and expense; however, unique opportunities in urban settings, including the potential to provide benefits to many diverse people, can make urban restoration especially rewarding. The success of urban restoration projects—even those focused primarily on ecological targets—depends on community involvement and managers considering community needs. However, research on the social barriers to urban restoration and strategies managers use to overcome them is relatively rare. This work attempts to fill that gap by presenting barriers for aquatic restoration projects in urban settings and strategies to overcome them. Building from interviews with restoration managers involved in urban aquatic restoration projects in Rhode Island, we contribute through an adaptive management approach: identifying and synthesizing the lessons learned from managers’ work in urban settings. Ultimately, we suggest potential for double- and triple-loop learning by disentangling and critiquing the frames and policy/power structures that influence decision making in urban aquatic restoration.  相似文献