Structural control on bulk melt properties: Single and double quantum Si NMR spectroscopy on alkali-silicate glasses     

Wim J. Malfait  Werner E. Halter  Beat H. Meier 《Geochimica et cosmochimica acta》2007,71(24):6002-6018

The structure of 21 binary potassium, rubidium and cesium silicate glasses (in the range 15-50 mol% alkali oxide) was analyzed by ²⁹Si single quantum and double quantum MAS NMR spectroscopy. Their glass transition temperatures (T_g) were measured by calorimetry. The chemical shifts and the relative abundance of Qⁿ species correlate with the cationic field strength (Z/r) of the network modifier. A correlation is observed between T_g and the inverse of the entropy of mixing of the different Qⁿ species, which is explained in the framework of the Adam-Gibbs relaxation theory. At high alkali content, up to 44% of the SiO₄ tetrahedra are part of three-membered rings. At a given alkali content, the abundance of these rings increases with increasing cation size. The abundance of three-membered rings in K-silicate melts correlates with a temperature and a non-linear composition dependence of the heat capacity. It is also a possible cause for the anomalous volumetric behavior of potassium silicate glasses.  相似文献   

Utilisation of terrestrial carbon by osmotrophic algae     

Jörg Tittel  Ines Wiehle  Nicola Wannicke  Heike Kampe  Juergen Poerschmann  Jutta Meier  Norbert Kamjunke 《Aquatic Sciences - Research Across Boundaries》2009,71(1):46-54

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Monitoring the freely dissolved concentrations of polycyclic aromatic hydrocarbons (PAH) and alkylphenols (AP) around a Norwegian oil platform by holistic passive sampling     

Christopher Harman  Kevin V. Thomas  Knut Erik Tollefsen  Sonnich Meier  Olav Byum  Merete Grung 《Marine pollution bulletin》2009,58(11):1671-1679

In order to assess the environmental impact of aquatic discharges from the offshore oil industry, polar organic chemical integrative samplers (POCIS) and semipermeable membrane devices (SPMDs) were deployed around an oil platform and at reference locations in the North Sea. Exposure to polycyclic aromatic hydrocarbons (PAH) and alkylated phenols (AP) was determined from passive sampler accumulations using an empirical uptake model, the dissipation of performance reference compounds and adjusted laboratory derived sampling rates. Exposure was relatively similar within 1–2 km of the discharge point, with levels dominated by short chained C1–C3 AP isomers (19–51 ng L⁻¹) and alkylated naphthalenes, phenanthrenes and dibenzothiophenes (NPD, 29–45 ng L⁻¹). Exposure stations showed significant differences to reference sites for NPD, but not always for more hydrophobic PAH. These concentrations are several orders of magnitude lower than those reported to give both acute and sub-lethal effects, although their long term consequences are unknown.  相似文献   

Rb–Sr microchrons of synkinematic mica in mylonites: an example from the DAV fault of the Eastern Alps     

Wolfgang Müller  Neil S Mancktelow  Martin Meier 《Earth and Planetary Science Letters》2000,180(3-4):385-397

A technique for texturally controlled microsampling from rock thick sections and subsequent Rb–Sr dating of μg-sized samples has been developed. It allows direct dating of minerals unequivocally related to deformation. The technique has been applied to strictly synkinematically grown white mica prepared from mylonites related to the Defereggen–Antholz–Vals (DAV) fault south of the Tauern window (Eastern Alps). Control of deformation ages is provided by field relationships with independently dated plutons and dykes dated here by single mineral Rb–Sr. The field observations and isotopic ages are fully consistent and demonstrate that this is a reliable method for sub-mm-scale geochronology. The ages obtained establish that sinistral strike slip shearing associated with the DAV fault lasted from at least 33 Ma to 30 Ma, followed by an abrupt change to dextral transpression related to the adjacent Periadriatic fault.  相似文献   

Detection of nitrogen sulfide in Comet Hale-Bopp.     

W M Irvine  M Senay  A J Lovell  H E Matthews  D McGonagle  R Meier 《Icarus》2000,143(2):412-414

We report the first detection of the nitrogen sulfide (NS) radical in a comet. The abundance relative to water is at least a few hundredths of a percent for Comet Hale-Bopp.  相似文献   

Park Forest (L5) and the asteroidal source of shocked L chondrites          下载免费PDF全文

Matthias M. M. Meier  Kees C. Welten  My E. I. Riebe  Marc W. Caffee  Maria Gritsevich  Colin Maden  Henner Busemann 《Meteoritics & planetary science》2017,52(8):1561-1576

The Park Forest (L5) meteorite fell in a suburb of Chicago, Illinois (USA) on March 26, 2003. It is one of the currently 25 meteorites for which photographic documentation of the fireball enabled the reconstruction of the meteoroid orbit. The combination of orbits with pre‐atmospheric sizes, cosmic‐ray exposure (CRE), and radiogenic gas retention ages (“cosmic histories”) is significant because they can be used to constrain the meteoroid's “birth region,” and test models of meteoroid delivery. Using He, Ne, Ar, ¹⁰Be, and ²⁶Al, as well as a dynamical model, we show that the Park Forest meteoroid had a pre‐atmospheric size close to 180 g cm^?2, 0–40% porosity, and a pre‐atmospheric mass range of ~2–6 tons. It has a CRE age of 14 ± 2 Ma, and (U, Th)‐He and K‐Ar ages of 430 ± 90 and 490 ± 70 Ma, respectively. Of the meteorites with photographic orbits, Park Forest is the second (after Novato) that was shocked during the L chondrite parent body (LCPB) break‐up event approximately 470 Ma ago. The suggested association of this event with the formation of the Gefion family of asteroids has recently been challenged and we suggest the Ino family as a potential alternative source for the shocked L chondrites. The location of the LCPB break‐up event close to the 5:2 resonance also allows us to put some constraints on the possible orbital migration paths of the Park Forest meteoroid.  相似文献   

Young asteroid mixing revealed in ordinary chondrites: The case of NWA 5764, a polymict LL breccia with L clasts          下载免费PDF全文

Jérome Gattacceca  Agata M. Krzesińska  Yves Marrocchi  Matthias M. M. Meier  Michèle Bourot‐Denise  Rob Lenssen 《Meteoritics & planetary science》2017,52(11):2289-2304

Polymict chondritic breccias—rocks composed of fragments originating from different chondritic parent bodies—are of particular interest because they give insights into the mixing of asteroids in the main asteroid belt (occurrence, encounter velocity, transfer time). We describe Northwest Africa (NWA) 5764, a brecciated LL6 chondrite that contains a >16 cm³ L4 clast. The L clast was incorporated in the breccia through a nondestructive, low‐velocity impact. Identical cosmic‐ray exposure ages of the L clast and the LL host (36.6 ± 5.8 Myr), suggest a short transfer time of the L meteoroid to the LL parent body of 0.1 ± 8.1 Myr, if that meteoroid was no larger than a few meters. NWA 5764 (together with St. Mesmin, Dimmitt, and Glanerbrug) shows that effective mixing is possible between ordinary chondrite parent bodies. In NWA 5764 this mixing occurred after the peak of thermal metamorphism on the LL parent body, i.e., at least several tens of Myr after the formation of the solar system. The U,Th‐He ages of the L clast and LL host, identical at about 2.9 Ga, might date the final assembly of the breccia, indicating relatively young mixing in the main asteroid belt as previously evidenced in St. Mesmin.  相似文献   

Caleta el Cobre 022 Martian meteorite: Increasing nakhlite diversity     

L. Krmer Ruggiu  J. Gattacceca  B. Devouard  A. Udry  V. Debaille  P. Rochette  J.‐P. Lorand  L. Bonal  P. Beck  V. Sautter  H. Busemann  M. M. M. Meier  C. Maden  G. Hublet  R. Martinez 《Meteoritics & planetary science》2020,55(7):1539-1563

Caleta el Cobre (CeC) 022 is a Martian meteorite of the nakhlite group, showing an unbrecciated cumulate texture, composed mainly of clinopyroxene and olivine. Augite shows irregular core zoning, euhedral rims, and thin overgrowths enriched in Fe relative to the core. Low‐Ca pyroxene is found adjacent to olivine. Phenocrysts of Fe‐Ti oxides are titanomagnetite with exsolutions of ilmenite/ulvöspinel. Intercumulus material consists of both coarse plagioclase and fine‐grained mesostasis, comprising K‐feldspars, pyroxene, apatite, ilmenite, Fe‐Ti oxides, and silica. CeC 022 shows a high proportion of Martian aqueous alteration products (iddingsite) in olivine (45.1 vol% of olivine) and mesostasis. This meteorite is the youngest nakhlite with a distinct Sm/Nd crystallization age of 1.215 ± 0.067 Ga. Its ejection age of 11.8 ± 1.8 Ma is similar to other nakhlites. CeC 022 reveals contrasted cooling rates with similarities with faster cooled nakhlites, such as Northwest Africa (NWA) 817, NWA 5790, or Miller Range 03346 nakhlites: augite irregular cores, Fe‐rich overgrowths, fine‐grained K‐feldspars, quenched oxides, and high rare earth element content. CeC 022 also shares similarities with slower cooled nakhlites, including Nakhla and NWA 10153: pyroxene modal abundance, pyroxenes crystal size distribution, average pyroxene size, phenocryst mineral compositions, unzoned olivine, and abundant coarse plagioclase. Moreover, CeC 022 is the most magnetic nakhlite and represents an analog source lithology for the strong magnetization of the Martian crust. With its particular features, CeC 022 must originate from a previously unsampled sill or flow in the same volcanic system as the other nakhlites, increasing Martian sample diversity and our knowledge of nakhlites.  相似文献   

The Creston,California, meteorite fall and the origin of L chondrites     

Peter Jenniskens  Jason Utas  Qing‐Zhu Yin  Robert D. Matson  Marc Fries  J. Andreas Howell  Dwayne Free  Jim Albers  Hadrien Devillepoix  Phil Bland  Aaron Miller  Robert Verish  Laurence A. J. Garvie  Michael E. Zolensky  Karen Ziegler  Matthew E. Sanborn  Kenneth L. Verosub  Douglas J. Rowland  Daniel R. Ostrowski  Kathryn Bryson  Matthias Laubenstein  Qin Zhou  Qiu‐Li Li  Xian‐Hua Li  Yu Liu  Guo‐Qiang Tang  Kees Welten  Marc W. Caffee  Matthias M. M. Meier  Amy A. Plant  Colin Maden  Henner Busemann  Mikael Granvik   《Meteoritics & planetary science》2019,54(4):699-720

It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν₆ resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.  相似文献   

A stabilized extended finite element framework for hydraulic fracturing simulations          下载免费PDF全文

Fushen Liu  Peter Gordon  Holger Meier  Dakshina Valiveti 《国际地质力学数值与分析法杂志》2017,41(5):654-681

We present a stabilized extended finite element formulation to simulate the hydraulic fracturing process in an elasto‐plastic medium. The fracture propagation process is governed by a cohesive fracture model, where a trilinear traction‐separation law is used to describe normal contact, cohesion and strength softening on the fracture face. Fluid flow inside the fracture channel is governed by the lubrication equation, and the flow rate is related to the fluid pressure gradient by the ‘cubic’ law. Fluid leak off happens only in the normal direction and is assumed to be governed by the Carter's leak‐off model. We propose a ‘local’ U‐P (displacement‐pressure) formulation to discretize the fluid‐solid coupled system, where volume shape functions are used to interpolate the fluid pressure field on the fracture face. The ‘local’ U‐P approach is compatible with the extended finite element framework, and a separate mesh is not required to describe the fluid flow. The coupled system of equations is solved iteratively by the standard Newton‐Raphson method. We identify instability issues associated with the fluid flow inside the fracture channel, and use the polynomial pressure projection method to reduce the pressure oscillations resulting from the instability. Numerical examples demonstrate that the proposed framework is effective in modeling 3D hydraulic fracture propagation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献