Evidence from Mössbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage     

C.A. Boulter  D.M. McConchie  E.M. Clarke 《地学学报》1989,1(4):365-369

Arenites in the low-grade metasedimentary rocks of the Stirling-Barren Group, Western Australia, contain discrete spaced cleavages. These in part are pure white mica, but up to 30% of the cleavage zones consists of fine-grained quartz resulting from crystal plastic deformation. A modified Gresens analysis shows that the cleavage domains formed by a 50% volume loss associated primarily with SiO₂ and MgO concentration decreases of 58% and 37%, respectively, and a 12% decrease in Fe₂O₃. Mössbauer spectroscopy shows that the Fe²⁺: Fe³⁺ ratio from lithon to cleavage changed from 50:SO to 15:85. This substantial difference cannot be accounted for by loss of iron. The data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated. In this example advectic processes appear to be important in low-grade regional metamorphism.  相似文献   

The P-SV inverse problem for a layered elastic medium: what data are required?     

Timothy J. Clarke 《Geophysical Journal International》1984,79(2):565-572

  相似文献   

In-situ U–Pb geochronology and Hf isotope analyses of the Rayner Complex,east Antarctica     

J.?A.?HalpinEmail author  C.?L.?Gerakiteys  G.?L.?Clarke  E.?A.?Belousova  W.?L.?Griffin 《Contributions to Mineralogy and Petrology》2005,148(6):689-706

In-situ zircon U–Pb and Hf isotopic analysis via laser ablation microprobe-inductively coupled plasma mass spectrometer (LAM-ICPMS) of samples from Kemp and MacRobertson Lands, east Antarctica suggests that the Kemp Land terrane evolved separately from the rest of the Rayner Complex prior to the ca. 940 Ma Rayner Structural Episode. Several Archaean metamorphic events in rocks from western Kemp Land can be correlated with events previously reported for the adjacent Napier Complex. Recently reported ca. 1,600 Ma isotopic disturbance in rocks from the Oygarden Group may be correlated with a charnockitic intrusion in the Stillwell Hills before ca. 1,550 Ma. Despite being separated by some 200 km, T^Hf_DM ages indicate felsic orthogneiss from Rippon Point, the Oygarden Group, Havstein Island and the Stillwell Hills share a ca. 3,660–3,560 Ma source that is indistinguishable from that previously reported for parts of the Napier Complex. More recent additions to this crust include Proterozoic charnockite in the Stillwell Hills and the vicinity of Mawson Station. These plutons have distinct ¹⁷⁶Hf/¹⁷⁷Hf ratios and formed via the melting of crust generated at ca. 2,150–2,550 Ma and ca. 1,790–1,870 Ma respectively.  相似文献   

An analysis of v sin (i) correlations in early-type binaries     

K. S. Howe  C. J. Clarke 《Monthly notices of the Royal Astronomical Society》2009,392(1):448-454

We use information on the   v sin ( i )  values of early-type binaries in order to search for correlations which may constrain the relative orientation of the stellar spin axes in binary systems. We find correlations in the case of close binaries which suggest that tidal synchronization is effective for binaries whose separation exceeds the stellar radius by more than an order of magnitude, in line with the theoretical predictions of Goldreich & Nicholson and the previous observational analysis of Giuricin et al. In the case of wide binaries, the   v sin ( i )  values are not well correlated, which requires that the magnitude of the spin speeds is not tightly correlated. Under this assumption, we then find that the data provide no significant constraints on the degree of alignment of spin axes. The data are therefore compatible with scenarios (such as disc fragmentation or capture) which differ widely in the expected degree of spin alignment.  相似文献   

Stuart H. Perry's contributions to meteorite collection and research, 1927–1957     

H. Plotkin  R. S. Clarke Jr. 《Meteoritics & planetary science》2009,44(8):1161-1177

Abstract— Stuart H. Perry (1874–1957), an influential Michigan newspaper editor and publisher and a vice president of the Associated Press, developed a passionate interest in collecting and studying meteorites in the 1920s and 1930s. Firmly believing that meteorites belong in great museums where they can be properly investigated, he generously donated his meteorites to various museums after he finished his own study of them. He had a sincere interest in the National Collection of Meteorites, and donated 192 specimens–‐mostly irons–‐to the U.S. National Museum; these constituted some of the most important meteorites in its collection, and moved iron meteorites to center stage, a position still occupied. By applying current metallographic methods to the study of iron meteorites, Perry directed scientists to a powerful new research tool, which led to major advances in our understanding of meteoritic irons and helped give rise to a new field within planetary sciences. His groundbreaking monograph The metallography of meteoric iron served as a standard reference collection of metallographic photomicrographs of iron meteorites for more than 30 years. It remained an insightful and useful work on the structure of meteoritic iron until improved binary and ternary phase diagrams in the Fe‐Ni(‐P) system allowed a more detailed treatment of the formation of iron meteorites. Perry received many honors for his work, and held office in the Meteoritical Society, serving as a councilor from 1941–1950, and as a vice president from 1950–1957.  相似文献   

Breadth and depth in research on health disparities: commentary on the work of Nancy Krieger   总被引：1，自引：1，他引：0  

Ellen K. Cromley 《GeoJournal》2009,74(2):115-121

Geocoding and spatial analysis of data describing populations and health events are important methods in health social science now carried out using GIS technology. This commentary considers Nancy Krieger’s work on health disparities in light of the various ways individuals and organizations use geocoded population and health data: analyzing spatial patterns of health and disease including health disparities, aggregating data spatially, assessing health status of individuals based on characteristics of aggregates, modeling neighborhood contextual factors affecting health, designing observation and intervention studies, and delivering health interventions and services. The extent to which her work addresses each of these purposes is considered. The strengths and limitations of the research including choice of spatial analytic units and techniques as reported in the published work are discussed. Krieger’s work, with her colleagues, has used standard methods of spatial analysis to raise the profile of GIS and spatial analysis in the public health community.  相似文献   

Reflections on the history of research on large wood in rivers     

Frederick J. Swanson  Stanley V. Gregory  Andres Iroumé  Virginia Ruiz-Villanueva  Ellen Wohl 《地球表面变化过程与地形》2021,46(1):55-66

Dynamics and functions of large wood have become integral considerations in the science and management of river systems. Study of large wood in rivers took place as monitoring of fish response to wooden structures placed in rivers in the central United States in the early 20th century, but did not begin in earnest until the 1970s. Research has increased in intensity and thematic scope ever since. A wide range of factors has prompted these research efforts, including basic understanding of stream systems, protection and restoration of aquatic ecosystems, and environmental hazards in mountain environments. Research and management have adopted perspectives from ecology, geomorphology, and engineering, using observational, experimental, and modelling approaches. Important advances have been made where practical information needs converge with institutional and science leadership capacities to undertake multi-pronged research programmes. Case studies include ecosystem research to inform regulations for forest management; storage and transport of large wood as a component in global carbon dynamics; and the role of wood transport in environmental hazards in mountain regions, including areas affected by severe landscape disturbances, such as volcanic eruptions. As the field of research has advanced, influences of large wood on river structures and processes have been merged with understanding of streamflow and sediment regimes, so river form and function are now viewed as involving the tripartite system of water, sediment, and wood. A growing community of researchers and river managers is extending understanding of large wood in rivers to climatic, forest, landform, and social contexts not previously investigated. © 2020 John Wiley & Sons, Ltd.  相似文献   

Multi-wavelength observations of Asteroid 2100 Ra-Shalom     

Michael K. Shepard  Beth Ellen Clark  Lance A.M. Benner  Jon D. Giorgini  Kandy Jarvis  Lucy F. Lim  James Bell  Andrew Rivkin  Daniel Scheeres 《Icarus》2008,193(1):20-38

We observed near-Earth asteroid (NEA) 2100 Ra-Shalom over a six-year period, obtaining rotationally resolved spectra in the visible, near-infrared, thermal-infrared, and radar wavelengths. We find that Ra-Shalom has an effective diameter of Deff=2.3±0.2 km, rotation period P=19.793±0.001 h, visual albedo pv=0.13±0.03, radar albedo , and polarization ratio μc=0.25±0.04. We used our radar observations to generate a three-dimensional shape model which shows several structural features of interest. Based on our thermal observations, Ra-Shalom has a high thermal inertia of ∼10³ J m⁻² s^−0.5 K⁻¹, consistent with a coarse or rocky surface and the inferences of others [Harris, A.W., Davies, J.K., Green, S.F., 1998. Icarus 135, 441-450; Delbo, M., Harris, A.W., Binzel, R.P., Pravec, P., Davies, J.K., 2003. Icarus 166, 116-130]. Our spectral data indicate that Ra-Shalom is a K-class asteroid and we find excellent agreement between our spectra and laboratory spectra of the CV3 meteorite Grosnaja. Our spectra show rotation-dependent variations consistent with global variations in grain size. Our radar observations show rotation-dependent variations in radar albedo consistent with global variations in the thickness of a relatively thin regolith.  相似文献   

Eccentricity growth of planetesimals in a self-gravitating protoplanetary disc     

M. Britsch  C. J. Clarke †  G. Lodato 《Monthly notices of the Royal Astronomical Society》2008,385(2):1067-1075

We investigate the orbital evolution of planetesimals in a self-gravitating circumstellar disc in the size regime (∼1–5000 km) where the planetesimals behave approximately as test particles in the disc's non-axisymmetric potential. We find that the particles respond to the stochastic, regenerative spiral features in the disc by executing large random excursions (up to a factor of 2 in radius in ∼1000 yr), although typical random orbital velocities are of the order of one tenth of the Keplerian speed. The limited time frame and small number of planetesimals modelled do not permit us to discern any net direction of planetesimal migration. Our main conclusion is that the high eccentricities (∼0.1) induced by interaction with spiral features in the disc is likely to be highly unfavourable to the collisional growth of planetesimals in this size range while the disc is in the self-gravitating regime. Thus if , as recently argued by Rice et al., the production of planetesimals gets under way when the disc is in the self-gravitating regime (either at smaller planetesimal size scales, where gas drag is important, or via gravitational fragmentation of the solid component), the planetesimals thus produced would not be able to grow collisionally until the disc ceases to be self-gravitating. It is unclear, however, given the large amplitude excursions undergone by planetesimals in the self-gravitating disc, whether they would be retained in the disc throughout this period, or whether they would instead be lost to the central star.  相似文献   

Clitellate worms (Annelida) in lateglacial and Holocene sedimentary DNA records from the Polar Urals and northern Norway     

Youri Lammers  Charlotte L. Clarke  Christer Ersus  Antony G. Brown  Mary E. Edwards  Ludovic Gielly  Haflidi Haflidason  Jan Mangerud  Emilia Rota  John Inge Svendsen  Inger Greve Alsos 《Boreas: An International Journal of Quaternary Research》2019,48(2):317-329

While there are extensive macro‐ and microfossil records of a range of plants and animals from the Quaternary, earthworms and their close relatives amongst annelids are not preserved as fossils and therefore the knowledge of their past distributions is limited. This lack of fossils means that clitellate worms (Annelida) are currently underused in palaeoecological research, even though they can provide valuable information about terrestrial and aquatic environmental conditions. Their DNA might be preserved in sediments, which offers an alternative method for detection. Here we analyse lacustrine sediments from lakes in the Polar Urals, Arctic Russia, covering the period 24 000–1300 cal. a BP, and NE Norway, covering 10 700–3300 cal. a BP, using a universal mammal 16S rDNA marker. While mammals were recorded using the marker (reindeer was detected twice in the Polar Urals core at 23 000 and 14 000 cal. a BP, and four times in the Norwegian core at 11 000 cal. a BP and between 3600–3300 cal. a BP), worm extracellular DNA ‘bycatch’ was rather high. In this paper we present the first reported worm detection from ancient DNA. Our results demonstrate that both aquatic and terrestrial clitellates can be identified in late‐Quaternary lacustrine sediments, and the ecological information retrievable from this group warrants further research with a more targeted approach.  相似文献