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1992年07月02日Ching-shen Su信
No full text[[abstract]]1992年07月02日Ching-shen Su致函日本，懇請日方關照赴日求診的孫觀漢.原件原與1988、1989、1991年孫觀漢腿部X光片一批(台大、長庚、榮總)置於一處
Chemical heterogeneity of the Archaean mantle, composition of the earth and mantle evolution
No full textNew rare earth element (REE) data for Archaean basalts and spinifex-textured peridotites (STP) show a range of La/Sm ratios (chondrite-normalized) from 0.36 to 3.5, with the bulk of the data in the range 0.7–1.3. This supports the hypothesis, based on Sr isotope initial ratios, that the Archaean mantle was chemically heterogeneous. We suggest that the bulk mantle source for Archaean basaltic magmas was close to an undepleted earth material. An average chemical composition of the Archaean mantle is estimated using chemical regularities observed in Archaean STP and high-magnesian basalts. TiO2 and MgO data show an inverse correlation which intersects the MgO axis at about 50% MgO (Fo92). TiO2 abundance in the mantle source is measured on this plot by assigning anMgO= 38% for the mantle. Concentrations of other elements are also estimated and these data are then used to obtain a composition for the bulk earth. We suggest an earth model with about 1.35 times ordinary chondrite abundances of refractory lithophile elements and about 0.2 times carbonaceous type 1 chondrite abundances of moderately volatile elements (such as Na, Rb, K, Mn). P shows severe depletion in the model earth relative to carbonaceous chondrites, a feature either due to volatilization or core formation (preferred). Our data support the hypothesis of Ringwood that the source material for the earth is a carbonaceous chondrite-like material.The generation of mid-ocean ridge basalts (MORB) is examined in the light of the model earth composition and Al2O3/TiO2, CaO/TiO2 ratios. It is suggested that for primitive basalts, these values can be used to predict the residual phases in their source. Comparison of chemical characteristics of inferred sources for 2.7-b.y. Archaean basalts and modern “normal” MORB indicates that the MORB source is severely depleted in highly incompatible elements such as Cs, Ba, Rb, U, Th, K, La and Nb, but has comparable abundances of less incompatible elements such as Ti, Zr, Y, Yb. The cause of the depletion in the MORB source is examined in terms of crust formation and extraction of silica-undersaturated melts. The latter seems to be a more likely explanation, since the degree of enrichment of highly incompatible elements in the crust only accounts for up to 40% of their abundances in the bulk earth and cannot match the depletion pattern in normal MORB. A large volume of material, less depleted than the source for normal MORB must therefore exist in the mantle and can serve as the source for the ocean island basalts and “normal” MORB.Three different mantle evolution models are examined and each suggests that the mantle is stratified with respect to abundances of incompatible trace elements. We suggest that no satisfactory model is available to fully explain the spectrum of geochemical and geophysical data. In particular the Pb and Sr isotope data on oceanic basalts, the depletion patterns of MORB and the balance between lithophile abundances in the crust and mantle, are important geochemical constraints to mantle models. Further modelling of the mantle evolution will be dependent on firmer information on the role of subduction, mantle convection pattern, and basalt production through geologic time together with a better understanding of the nature of Archaean crustal genesis
Geochemical regularities and genetic significance of ophiolitic basalts
No full textAl2O3/TiO2 and CaO/TiO2 ratios of primitive mid-ocean ridge basalts increase along with degree of partial melting (TiO2 content decreases) until ratios seen in chondrites (about 20 and 17, respectively) are reached at ?0.8% TiO2. Low-Ti (<0.6%) basalts from ophiolitic complexes (for example, Troodos and Betts Cove), island arcs, and interarc basins are characterized by much higher Al2O3/TiO2 and CaO/TiO2 ratios (up to 60). Such low-Ti ophiolitic basalts could be formed by remelting of a severely depleted source that had experienced a previous episode of magma extraction of the type in mid-ocean ridges. We suggest that these low-Ti basalts are not formed at mid-ocean ridges but are products of a spreading center close to a subduction zone, for example, in an interarc basin or incipient island-arc site. In this model, remelting of the refractory source is induced by the introduction of water from subducted oceanic crust. Geochemical data on high-Mg volcanic rocks from Papua and the Mariana Trench are presented, and an analogy with low-Ti ophiolitic basalts is suggested. “Basaltic komatiites” from ophiolitic complexes are discussed, and it is suggested that there are critical geochemical differences between these and Archean komatiites
Geochemistry of Archaean spinifex-textured peridotites and magnesian and low-magnesian tholeiites
No full textMajor and trace element (Rb, Sr, Ba, Zr, Y, Nb, Ni, Co, V, Cr) data are presented for 11 spinifex-textured peridotites (STP) and a number of high-magnesian and low-magnesian tholeiitic basalts. The STP, representing high-magnesian liquids, come from the Yilgarn Block of Western Australia, Munro Township in the Abitibi Belt of Canada and one sample from the Barberton area of South Africa. All of the basaltic samples come from the Yilgarn Block.The STP and high-magnesian rocks are considered to belong to the komatiite suite (1 and 2) despite their low CaO/Al2O3 ratios. It is argued that the high values (about 1.5) reported for this ratio from the Barberton area can be explained by a combination of factors, viz. garnet separation, Al loss or Ca addition during metamorphism. The processes can be evaluated using CaO/TiO2, Al2O3/TiO2 ratios, the REE group and trace elements (e.g. Y, Sc). It would appear that most STP from other Archaean belts do not have abnormal CaO/Al2O3 ratios.The STP display close to chondritic ratios for Ti/Zr, Zr/Nb, Zr/Y, and TiO2/Al2O3 and are considered to represent liquids produced by large amounts of partial melting of the Archaean mantle. The data suggest that virtually all phases other than olivine were removed by melting during the production of STP liquids. In the STP, Ti/V, Ti/P ratios are non-chondritic, suggesting original depletion and/or incorporation into the core.For lower levels of partial melting, including mid-ocean ridge basalts (MORB) non-chondritic ratios are exhibited by Zr/Y, TiO2/Al2O3, TiO2/CaO, suggesting controlling phases in the residue for Y, Ca, Al. It is apparent that for STP, Cr is not being controlled, indicating the absence of chromite in the residual. However, at about 15% MgO the data suggest that chromite becomes a residual phase.The transition metals, with the exception of Mn, have higher abundances in Archaean basaltic rocks than in MORB. This is interpreted as being mainly due to more extensive partial melting of the mantle in the Archaean, as a result of higher temperatures.It is suggested that the generation of STP liquids with about 32% MgO is due to upwelling mantle diapirs which probably originated at depths greater than 400 km and at temperatures in excess of 1900°C.Modern equivalents to Archaean greenstone sequences are lacking. The closest tectonic analogue would be the development of oceanic crust within a rifted continental block
Petrogenesis of Archaean ultrabasic and basic volcanics: Evidence from rare earth elements
No full textRare earth element (REE) and major element data are presented on 44 Archaean samples which include spinifex textured ultramagnesian lavas (STPK) spinifex textured basalts (STB) and low MgO tholeiites. The samples come from the Yilgarn and Pilbara Blocks (W. Australia), Barberton (South Africa), Belingwe and Que Que (Rhodesia), Abitibi (Canada) and the 3.7 b.y. Isua Belt of Western Greenland. In addition REE data are given on three near primitive mid-ocean ridge basalts (MORB) and a glassy MORB-type basalt from Taiwan. We suggest that REE patterns, particularly the light REE and Eu, can be affected by metamorphism, but argue that the consistency of pattern from samples both within and between areas enables recognition of primary patterns. La/Sm ratios of 2.7 b.y. STPK are characterised by being lower than those of associated basalts. The 3.5 b.y. STPK Barberton material does not show this feature but instead displays significant heavy REE depletion. The separation of garnet from these liquids is suggested as a possible mechanism for the high CaO/Al2O3 ratios, (Al loss) and the heavy REE and Sc depletion. The REE data on Barberton material is equivocal on the derivation of the so-called basaltic komatiites from the peridotitic komatiites. However, REE analyses on STPK and high magnesian lavas from elsewhere suggests that crystal fractionation is not a viable mechanism to produce one from the other. We suggest instead, that varying amounts of partial melting of different sources is responsible for the spectrum of compositions. The STB appear to be an easily recognised rock type within the Archaean. They are characterised by quench (clinopyroxene) textures and a light REE enriched pattern. It is suggested that these are near primary melts and that their REE patterns mirror their mantle source. We propose a two stage model for the 2.7 b.y. mafic complexes, in which, prior to the generation of ultrabasic magmas, the source underwent a small amount of partial melting which resulted in the removal of a melt enriched in incompatible elements. The depletion process could be achieved either during mantle diapirism or by upward migration of interstitial melts into an Archaean low velocity zone. The spread of La/Sm ratios in STPK and STB is used as an argument that the Archaean mantle was chemically heterogeneous and that the degree of heterogeneity was similar to that observed in modern ocean volcanics. As a result, partial melting of the mantle under different P-T conditions produced a spectrum of magma types. The information presently available on Archaean mafic and silicic magmatism and the incompleteness of geochemical data on present day tectonic environments are two major obstacles in formulating Archaean tectonic models. In addition a comparison of present day and Archaean ultramafic and silicic rocks suggests that plate tectonic models as presently understood may not be suitable analogues for all Archaean tectonic environments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A New Genetic Model for the East Taiwan Ophiolite and Its Implications for Dupal Domains in the Northern Hemisphere
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