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Erratum to 'Structural and temporal evolution of a reactivated brittle-ductile fault - Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite' [Earth Planet. Sci. Lett. 407 (2014) 221-233]
No full textPresent-day exposures of ancient faults represent only the end result of the faults’ often protracted and heterogeneous histories. Here we apply K–Ar dating of synkinematic illite/muscovite to constrain the timing of the complete temporal evolution of a complex, multiply-reactivated brittle–ductile fault, the Kvenklubben Fault in northern Norway. All obtained ages vary as a function of grain size. Geologically significant events are identified principally on the basis of detailed structural analysis presented in a companion paper (Torgersen and Viola, 2014). Faulting initiated at 531 ±11 Ma, but most strain was accommodated during Caledonian compression at 445 ±9 Ma. The fault was reactivated extensionally at 121 ±5 Ma. C and O isotopic composition of carbonates and silicates in the fault rocks demonstrates that mineral authigenesis was linked to wall–rock disintegration through dolomite decarbonation and metabasalt carbonation. We suggest that the commonly observed case of age decreasing with grain size in K–Ar and 40Ar/39Ar dating of brittle fault rocks can be interpreted as a consequence of mixing between two end-member illite/muscovite generations: an authigenic and a protolithic, in which the finest authigenic grains constrain the timing of the last faulting increment. Integrating detailed structural analysis with age dating is the key towards a better understanding of fault architecture development and the temporal evolution of strain localization and deformation mechanisms
Structural and temporal evolution of a reactivated brittle-ductile fault - Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite
No full textPresent-day exposures of ancient faults represent only the end result of the faults' often protracted and heterogeneous histories. Here we apply K–Ar dating of synkinematic illite/muscovite to constrain the timing of the complete temporal evolution of a complex, multiply-reactivated brittle–ductile fault, the Kvenklubben Fault in northern Norway. All obtained ages vary as a function of grain size. Geologically significant events are identified principally on the basis of detailed structural analysis presented in a companion paper (Torgersen and Viola, 2014). Faulting initiated at View the MathML source531±11Ma, but most strain was accommodated during Caledonian compression at View the MathML source445±9Ma. The fault was reactivated extensionally at View the MathML source121±5Ma. C and O isotopic composition of carbonates and silicates in the fault rocks demonstrates that mineral authigenesis was linked to wall–rock disintegration through dolomite decarbonation and metabasalt carbonation. We suggest that the commonly observed case of age decreasing with grain size in K–Ar and 40Ar/39Ar dating of brittle fault rocks can be interpreted as a consequence of mixing between two end-member illite/muscovite generations: an authigenic and a protolithic, in which the finest authigenic grains constrain the timing of the last faulting increment. Integrating detailed structural analysis with age dating is the key towards a better understanding of fault architecture development and the temporal evolution of strain localization and deformation mechanisms
Effects of frictional-viscous oscillations and fluid flow events on the structural evolution and Re-Os pyrite-chalcopyrite systematics of Cu-rich carbonate veins in northern Norway
No full textMesothermal chalcopyrite+pyrite+magnetite-bearing calcite-dominated vein deposits in the Repparfjord Tectonic Window, northern Norway, have been studied to constrain the mechanics of their emplacement and the timing of initial vein formation and reactivation. The veins cut across Paleoproterozoic tholeiitic metabasalts and present textural contrast between their hydrofractured, coarse-grained margins, and the fine-grained mylonitic cores. They formed under overall viscous conditions, although cyclically increased fluid pressures caused transient embrittlement. As mineral precipitation sealed the fractures, deformation was accommodated again viscously leading to mylonitization of the vein's core. Local brecciation of the calc-mylonite demonstrates the cyclicity of this process. Re-Os chalcopyrite-pyrite and K-Ar fault gouge dates define an almost continuous age range from ~2540Ma to ~460Ma. Regression of three Re-Os analyses yields a 2069±14Ma age (187Os/188Os=0.18±0.04), interpreted as the age of vein emplacement, sulfide precipitation, and initial frictional-viscous deformation. K-Ar ages are mixed ages that constrain a maximum age of faulting in association with the veins at approximately 460Ma, hence indicating structural reactivation connected with Silurian Caledonian orogenic compression. The spread in Re-Os model ages reflects this reactivation, wherein renewed strain accommodation and circulating oxidizing fluids caused fracturing, dynamic recrystallization, and isotopic disturbance of the sulfides. The study provides evidence for fluid flow during viscous deformation and demonstrates that strain, and flow of oxidizing fluids, can have a significant yet localized control on the integrity of the Re-Os systematic in pyrite and chalcopyrite
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
Initiation and development of the Pennine Basal Thrust (Swiss Alps): a structural and geochronological study of an exhumed megathrust
No full textThe Pennine Basal Thrust (PBT) is an exhumed megathrust developed during continental collision from late Eocene to Miocene. To trace its evolution, five samples, with indications for up to three microstructurally diachronous white-mica generations, were investigated by laser in-situ and step-heating Ar-40-Ar-39 dating. Three deformation-related crystallization ages can be distinguished: (1) D-1, characterized in the PBT hanging wall by an S-1 foliation defined by white mica + chloritoid, began at or before similar to 38.0 Ma; (2) D-2 formed a pervasive S-2 cleavage and synchronous white-mica rich veins dated at similar to 27 Ma; (3) D(3)produced an S-3 crenulation cleavage and chlorite + white-mica veins dated at similar to 23 Ma. Older ages of similar to 96 Ma (footwall) and similar to 115 Ma (hanging wall) are interpreted as minimum ages for the detrital component. Finally, discrete faulting produced fault gouge, with an illite K-Ar age of similar to 19 Ma. A simplified back-restored reconstruction provides a tectonic context for the dated structures. In this framework, D-1 occurred during middle to late Eocene tectonic accretion. After late Eocene initiation of continental collision, D-2 reflects Oligocene top-to-NW shearing, with both in- and out-of-sequence thrusting. D-3 then developed from 23 to 19 Ma during the progressive deactivation of the PBT
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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