1,721,018 research outputs found
A natural long‐term annealing experiment for the zircon fission track system in the Songpan‐Garzê flysch, China
No full textApplication of the zircon fission track (FT) method to derive reliable cooling histories requires that rocks have undergone temperatures sufficient to reach full resetting prior to cooling. Zircons commonly show significant variation in accumulated radiation damage and therefore FT annealing behaviour. Twenty‐eight samples of mainly anchizonal to lowermost greenschist facies Triassic sandstones from the Songpan‐Garzê flysch, China, were evaluated for their FT annealing status. Literature data suggest a heating period in the range of 100 myr duration. Our results define a temperature range for partial FT annealing of 270–350°C (based on illite crystallinity data), higher than the proposed range for radiation‐damaged zircons. We suggest that the long residence at high temperature has led to annealing of relevant parts of radiation damage along with FT annealing, so that even for long durations of FT annealing, full resetting requires temperatures in the range of greenschist facies conditions typical for zero‐damage zircons
Carbonate deformation through the brittle-ductile transition: The case of the SW Helvetic nappes, Switzerland
Full text linkCarbonate deformation through the brittle-ductile transition (BDT) remains incompletely documented in the field. We therefore investigate the exhumation of the SW-Helvetic nappe stack using a new multi-method approach that integrates optical observations with a revised nomenclature, thermochronology, stable isotopes, and clumped isotope thermometry, aiming to constrain the time-temperature history of BDT deformation processes in carbonates. Single grain (U-Th)/He zircon and apatite fission track ages establish new burial/exhumation trajectories from different nappes, allowing us to infer the thermal history of the Rawil Depression. This prominent doubly-plunging hinge zone between the Mont Blanc and Aar Crystalline Massifs underwent postnappe faulting, now constrained to the Tortonian-Early Pliocene, reflected in differential exhumation rates of -0.2 km/Myr between the most depressed area and its easternmost side. Calculating and modelling the rockbuffered clumped isotope temperatures (ranging from -250 degrees C to 55 degrees C), we indirectly date the BDT processes, exemplified by the Rezli Fault. On this structure, possible shear heating during mylonitisation is indirectly dated at 18-15.5 Ma. Progressive embrittlement started around 11-9 Ma at temperatures of about 150-110 degrees C. Lower clumped isotope temperatures correspond to recent brittle faulting between 9 and 5 Ma. Our results on the regional evolution can be applied to analogous seismogenic carbonate-rich crustal sections
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
Preliminary results from FT dating in the Adula nappe, Central Alps: Late tilting or not?
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