1,720,984 research outputs found
Structural and temporal evolution of a reactivated brittle-ductile fault - Part I: Fault architecture, strain localization mechanisms and deformation history
No full textFaults are by nature dynamic, as their architecture and composition evolve progressively in space and through time steered by the interplay between strain weakening and hardening mechanisms. This study combines structural analysis, geochemistry and chlorite geothermometry to investigate deformation and strain localization mechanisms of the Kvenklubben fault, a Paleozoic brittle-ductile thrust in northern Norway, with the goal to constrain their temporal variations and the consequences thereof on fault architecture development and rheological behavior. The fault evolved from an initially discrete brittle feature slipping mainly by seismogenic ruptures to a wide brittle-ductile phyllonite deforming by aseismic creep. The formation of mechanically weak phyllosilicates by decarbonation of footwall dolostones and carbonation of hanging wall metabasalts was the main weakening mechanism, whereas partitioning of fluid flow and fracture sealing following transient high pore pressure-driven embrittlement caused episodic and localized strain hardening. The interplay between strain weakening and hardening mechanisms caused the fault core to widen. We suggest that the ability for carbonate-hosted faults to slip by seismogenic rupture is also a function of the faults' structural-evolutionary stage, and that it decreases progressively with fault maturity. This study demonstrates the importance of calibrating the present-day fault anatomy against the dynamic character of faults, which evolve geometrically, compositionally and mechanically in space and through time
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 constraints on the formation of Cu-rich mesothermal vein deposits in the Repparfjord Tectonic Window, northern Norway
No full textThe Paleoproterozoic metasupracrustal sequence of the Repparfjord Tectonic Window (RTW) within the Caledonian Nappe System in northern Norway hosts several Cu-bearing mesothermal carbonate-quartz veins.
Structural analysis shows that the emplacement of the veins is geometrically and kinematically compatible with a phase of NW-SE shortening. Northwest- and southeast-dipping veins are related to brittle-ductile thrust faults, whereas sub-vertical E-W to NE-SW striking veins show a strong component of dextral strike-slip ductile shearing. It is proposed that the veins were emplaced under brittle-ductile conditions in a dextral transpressional shear corridor. Fluid overpressuring possibly led to fracturing of the host greenstones. The subsequent pressure drop led to metal precipitation. The newly-formed veins, which remained weaker than the surrounding metabasalts, localized subsequent fluid circulation and ductile strain increments.
Coaxial NW-SE compression is reported for both the Paleoproterozoic Svecofennian and the Silurian Caledonian orogenies. Re-Os analysis on sulfides is in progress and will provide constraints on the age of both vein formation and associated tectonic stress regime
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
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
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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