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61.
Benjamin Kaeser Bettina Olker Angelika Kalt Rainer Altherr Thomas Pettke 《Contributions to Mineralogy and Petrology》2009,157(4):453-472
Garnet-bearing and garnet-free pyroxenite xenoliths from Quaternary basanites of Marsabit, northern Kenya, were analysed for
microstructures and mineral compositions (major and trace elements) to constrain the thermal and compositional evolution of
the lithospheric mantle in this region. Garnet-bearing rocks are amphibole-bearing websterite with ~5–10 vol% orthopyroxene.
Clinopyroxene is LREE-depleted and garnet has high HREE contents, in agreement with an origin as cumulates from basaltic mantle
melts. Primary orthopyroxene inclusions in garnet suggest that the parental melts were orthopyroxene-saturated. Rock fabrics
vary from weakly to strongly deformed. Thermobarometry indicates extensive decompression and cooling (~970–1,100°C at ~2.3–2.6 GPa
to ~700–800°C at ~0.5–1.0 GPa) during deformation, best interpreted as pyroxenite intrusion into thick Paleozoic continental
lithosphere subsequently followed by continental rifting (i.e., formation of the Mesozoic Anza Graben). During continental
rifting, garnet websterites were decompressed (garnet-to-spinel transition) and experienced the same P–T evolution as their host peridotites. Strongly deformed samples show compositional overlaps with cpx-rich, initially garnet-bearing
lherzolite, best explained by partial re-equilibration of peridotite and pyroxenite during deformation and mechanical mingling.
In contrast, garnet-free pyroxenites include undeformed, cumulate-like samples, indicating that they are younger than the
garnet websterites. Major and trace element compositions of clinopyroxene and calculated equilibrium melts suggest crystallisation
from alkaline basaltic melt similar to the host basanite, which suggests formation in the context of alkaline magmatism during
the development of the Kenya rift.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
62.
Sylvia-Monique?ThomasEmail author Monika?Koch-Müller Patrick?Reichart Dieter?Rhede Rainer?Thomas Richard?Wirth Stanislav?Matsyuk 《Physics and Chemistry of Minerals》2009,36(9):489-509
Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO2 polymorphs, and GeO2 with specific isolated OH point defects using quantitative data from independent techniques such as proton–proton scattering,
confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic
minerals using Raman spectroscopy combined with the “Comparator Technique”. In case of olivine and the SiO2 system, it turns out that the magnitude of ε for one structure is independent of the type of OH point defect and therewith
the peak position (quartz ε = 89,000 ± 15,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}), but it varies as a function of structure (coesite ε = 214,000 ± 14,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}; stishovite ε = 485,000 ± 109,000
\textl \textmol\textH2\textO-1 \textcm-2\text{l}\,\text{mol}_{{\text{H}_2}\text{O}}^{-1}\,\text{cm}^{-2}). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in
nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling
the Earth’s deep water cycle. 相似文献
63.
Rainer Kaltenbaek Gerald Hechenblaikner Nikolai Kiesel Oriol Romero-Isart Keith C. Schwab Ulrich Johann Markus Aspelmeyer 《Experimental Astronomy》2012,34(2):123-164
Quantum physics challenges our understanding of the nature of physical reality and of space-time and suggests the necessity of radical revisions of their underlying concepts. Experimental tests of quantum phenomena involving massive macroscopic objects would provide novel insights into these fundamental questions. Making use of the unique environment provided by space, MAQRO aims at investigating this largely unexplored realm of macroscopic quantum physics. MAQRO has originally been proposed as a medium-sized fundamental-science space mission for the 2010 call of Cosmic Vision. MAQRO unites two experiments: DECIDE (DECoherence In Double-Slit Experiments) and CASE (Comparative Acceleration Sensing Experiment). The main scientific objective of MAQRO, which is addressed by the experiment DECIDE, is to test the predictions of quantum theory for quantum superpositions of macroscopic objects containing more than 108 atoms. Under these conditions, deviations due to various suggested alternative models to quantum theory would become visible. These models have been suggested to harmonize the paradoxical quantum phenomena both with the classical macroscopic world and with our notion of Minkowski space-time. The second scientific objective of MAQRO, which is addressed by the experiment CASE, is to demonstrate the performance of a novel type of inertial sensor based on optically trapped microspheres. CASE is a technology demonstrator that shows how the modular design of DECIDE allows to easily incorporate it with other missions that have compatible requirements in terms of spacecraft and orbit. CASE can, at the same time, serve as a test bench for the weak equivalence principle, i.e., the universality of free fall with test-masses differing in their mass by 7 orders of magnitude. 相似文献
64.
Gated communities and enclave urbanism in China have recently drawn considerable attention of researchers and policy makers. The integration of urban space is now even on the agenda of the Chinese Central Government. This article therefore sets out to advance our understanding of how exactly urban borders function and how they change over time. This is done by applying concepts of border theory to what may be called residential borderlands. The empirical study is conducted in two such borderlands between gated communities and suburban villages in southern Guangzhou. It is based on over 70 qualitative interviews and the observation of spatial behaviour at the respective borders. Both debordering and rebordering processes are found to occur with regards to three dimensions: cross-border mobility, cross-border social connectivity and symbolic border functions. The identified dynamic processes at the neighbourhood borders are embedded in the overall urban spatial reconfiguration of Guangzhou. 相似文献
65.
66.
A new algorithm for tomographic inversion of traveltimes of reflected and refracted seismic waves is developed. The inversion gives interface configurations and velocity distributions in layers. The important features of the algorithm are: (a) the inclusion of shot time delays in the list of unknown parameters; (b) the regularization is applied in such a way that the most probable model is characterized by the similarity of neighbouring interfaces. As the problem under consideration is non-linear, several iterations are necessary in order to obtain the final model. In the case of a very inexact initial model, a 'layer-by-layer' inversion strategy is recommended as a first inversion step. The inversion program is supplied with a user interface, thanks to which one can: (a) pick interactively and identify seismic traveltimes; (b) build and edit depth/velocity models; and (c) display calculated traveltime curves and compare them with picked traveltimes as well as with the original seismic sections. The efficiency of the inversion software developed is illustrated by a numerical example and a field example in which shallow seismic data are considered. Application to wide-aperture reflection/refraction profiling (WARRP) data is also possible. 相似文献
67.
Sven O. Egenhoff Arndt Peterhänsel Thilo Bechstädt Rainer Zühlke & Jürgen Grötsch 《Sedimentology》1999,46(5):893-912
The 720-m-thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the lagoonal facies architecture of a small atoll-like carbonate platform. Facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations, which reflect a syndepositional palaeorelief. Based on tracing of lagoonal flooding surfaces, the metre-scale shallowing-upward cycles are interpreted to be of allocyclic origin. Short-term sea-level changes led to subaerial exposure of wide parts of the marginal zone, resulting in the development of a tepee belt of varying width. Occasional emergence of the entire lagoon produced lagoon-wide decimetre-thick red exposure horizons. The supratidal tepee belt in the backreef area represented the zone of maximum elevation, which circumscribed the sub- to peritidal lagoonal interior during most of the platform's development. This tepee rim, the subtidal reef and a sub- to peritidal transition zone in between stabilized the platform margin. The asymmetric width of facies belts within individual metre-scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present-day south and west. The overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit, overlain by three tepee-rich intervals, separated by tepee-poor units composed of subtidal to peritidal facies. This stacking pattern reflects two third-order sequences during the late Anisian to early middle Ladinian. 相似文献
68.
The caves near Naracoorte, South Australia, contain one of the richest and most diverse fossil faunal assemblages on the Australian continent. Three sites were selected for electron spin resonance (ESR) dating because clastic, fossiliferous sediments were sandwiched between speleothem layers. This allows independent age control by highly precise thermal ionization mass‐spectrometry (TIMS) U‐series dating. We find that all ESR results agree within the constraints given by the U‐series dates, and allow further refinement of the age of the fauna analysed, indicating that most of the fauna in the large Victoria Cave Fossil Chamber is twice as old as reported previously. Our dating results, spanning from 280 to 500 ka for the Fossil Chamber, Victoria Cave, to about 125 ka for the Grant Hall, Victoria Cave, and 170 to 280 ka for the Fossil Chamber, Cathedral Cave, indicate little change, if any, in the megafaunal assemblage from the early Middle to the early Late Pleistocene. This changed dramatically after the last interglacial, when a large proportion of the megafauna suddenly disappeared. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
69.
Geomechanics of hazardous landslides 总被引:1,自引:1,他引:0
POISEL Rainer BEDNARIK Martin HOLZER Rudolf LISCAK Pavel 《山地科学学报》2005,2(3):211-217
A catalogue of possible landslide initial failure mechanisms, taking into account the geological setting and the geometry of the slope, the joint structure, the habitus of the rock blocks, as well as the mechanical behaviour of the rocks and of the rock mass (deformation and strength parameters), is presented. Its aim is to give geologists as well as engineers the opportunity to compare phenomena in the field and phenomena belonging to particular mechanisms and to find the mechanism occurring. The presented catalogue of initial landslide mechanisms only comprises the mechanisms having a clearly defined mechanical model that can be divided into empirical relations and into mechanical models, as well as an overview of run out models, which can be divided into empirical relations and into mechanical models. 相似文献
70.