761 research outputs found
Study of exhumed paleo-seismic fault as a gauge to estimate earthquake source parameters
No full textExhumed faults decorated by pseudotachylyte, solidified friction induced melt recording a seismic rupture (Sibson, 1975), might give information about the earthquake source. Two cases, representative of different seismogenic environments have been investigated: the pseudodotachylyte-mylonite association in the lower crust, in the Ivrea Zone metagabbros, and the “upper crust” pseudotachylytes in the Tertiary Adamello granitoid batholith.
In metagabbros, a cyclical and coeval production of frictional melts and high temperature localized ultramylonites, during amphibolite metamorphic conditions, has been documented.
From a selected pseudotachylyte in the Adamello batholith the earthquake energy budget has been estimated, concluding that the most energy was dissipated as frictional heat. The thermal evolution of a frictional melt was modeled, demonstrating that the pristine cataclastic structure used for the component of the surface energy estimation might locally have been preserved.Faglie esumate sigillate da pseuotachiliti, fusi di frizione solidificati che registrano una rottura sismica (Sibson, 1975), possono fornire informazioni sulla sorgente del terremoto. Sono stati studiati due casi rappresentativi di ambienti simogenetici differenti: l’associazione pseudotachiliti-miloniti nella corsta inferiore, nei metagabbri della Zona d’Ivrea e le pseudotachiliti della “crosta superiore” nel batolite granitoide terziario dell’Adamello.
Nei metagabbri è stata documentata la produzione ciclica e contemporanea di fusi di frizione e ultramiloniti localizzate di alta temperatura, entrambe prodotte in facies anfibolitica.
Studiando una pseudotachilite prescelta dal batolite dell’Adamello, si è stimato il bilancio energetico di un terremoto, concludendo che la maggior parte dell’energia si è dissipata sotto forma di calore di frizione. Infine si è modellizzata l’evoluzione termica di un fuso di frizione, dimostrando che l’originaria struttura cataclastica usata per stimare il contributo dell’energia di superficie può potenzialmente essersi localmente preservata
Amphibolite-facies pseudotachylytes in Premosello metagabbro and felsic mylonites (Ivrea Zone, Italy)
No full textPseudotachylytes (solidified friction-induced melts produced during seismic slip) that formed under high
temperature ambient conditions might retain information on earthquake mechanics beneath the brittle–
ductile (elasto-frictional/viscous-plastic) transition in the crust. Thin, sharply bounded pseudotachylytes
and ultramylonites occur together inside the granulite-facies Premosello metagabbro and inside country
felsic mylonites of the Ivrea Zone (Italian Southern Alps). Petrographic and microstructural data indicate
that the studied pseudotachylytes and ultramylonites are coeval and developed under amphibolite facies
(500–650 °C) metamorphic conditions. The occurrence of foliated pseudotachylytes and of local remnants
of cataclastic microstructures within ultramylonites suggests that pseudotachylytes might have represented
planar heterogeneities for nucleation of ultramylonites. The association of coeval pseudotachylyte and
mylonites is interpreted as caused by cyclic stages of coseismic high strain rate transients, related to downward
propagation of seismic ruptures from the upper brittle crust, followed by post-seismic stress relaxation
by ductile flow
Evolution of quartz microstructure and c-axis crystallographic preferred orientation within ductilely deformed granitoids (Arolla unit, Western Alps)
No full textWe have studied quartz microstructures and the c-axis crystallographic preferred orientations (CPOs) in four granitoid samples representative of increasing ductile shear deformation, from a weakly deformed granitoid (stage 1) to a mylonitic granitoid (stage 4). The quartz c-axis CPO measured in the mylonitic granitoid has been compared with the one observed in a fully recrystallized quartz mylonite from the same area. All the samples belong to the Austroalpine Arolla unit (Western Alps) and were deformed at greenschist facies conditions. The quartz c-axis CPO was analyzed using a U-stage and the optical orientation imaging technique. The magmatic plagioclase, forming more than 50% of the volume of the granitoid, is extensively replaced by a mica-rich aggregate even in weakly deformed samples of stage 1. These aggregates flow to form an interconnected weak matrix with increasing deformation, wrapping relatively less strained quartz grains that undergo dominantly coaxial strain. Recrystallization of quartz ranges from less than 1% in the weakly deformed granitoid to up to 85% in the mylonitic granitoid, with average grain strain of 41% and 64%, respectively. With increasing strain and recrystallization, quartz grains in the granitoids show a sequence of transient microstructures and CPOs. Crystal plastic deformation is initially accomplished by dislocation glide with limited recovery, and at 50% grain strain it results in a CPO consistent with dominantly basal 〈a〉 slip. At 60% grain strain, recrystallization is preferentially localized along shear bands, which appear to develop along former intragranular cracks, and the recrystallized grains develop a strong c-axis CPO with maxima orthogonal to the shear band boundaries and independent of the host grain orientation. Within the granitoid mylonite, at an average quartz grain strain of 64%, recrystallization is extensive and the c-axis CPO of new grains displays maxima overlapping the host c-axis orientation and, therefore, unrelated to the bulk sense of shear. The host-controlled CPO is inferred to reflect pervasive recrystallization by progressive subgrain rotation. The switch from ‘shear band-control’ to ‘host-control’ on c-axis CPO occurred between 40% and 70% of recrystallization. In the quartz mylonite, the quartz c-axis CPO develops an asymmetric single girdle consistent with the bulk sense of shear and the synkinematic greenschist facies conditions. This study indicates that the CPO evolution of quartz may significantly differ in cases of polymineralic vs. monomineralic rocks under the same deformation conditions, if quartz in the polymineralic rock behaves as a ‘strong’ phase
Lidia Shank
No full textPhotograph - Portrait of Lidia Shank, a member of the Canadian Women's Army Corps, in uniform. Athabasca, Albert
Ed and Lidia Loxam
No full textPhotograph - Ed Loxam and Lidia Loxam (nee Shank) inside a cabin, Athabasca, Albert
Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure, Brazil
No full textAbstract–Shatter cones are one of the most widely recognized pieces of evidence for
meteorite impact events on Earth, but the process responsible for their formation is still
debated. Evidence of melting on shatter cone surfaces has been rarely reported in the
literature from terrestrial impact craters but has been recently observed in impact
experiments. Although several models for shatter cones formation have been proposed, so
far, no one can explain all the observed features. Shatter cones’ from the Vista Alegre
impact structure, Brazil, formed in fine-grained basalt of the Jurassic-Cretaceous Serra
Geral Formation (Parana large igneous province). A continuous quenched melt film,
consisting of a crystalline phase, mica, and amorphous material, decorates the striated
surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine-grained
matrix, occur subparallel to the striated surface. Several techniques were applied to
characterize the crystalline phase in the melt, including Raman spectroscopy and
transmission electron microscopy. Results are not consistent with any known mineral, but
they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of
melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of
tensile fracturing at the tip of a fast propagating shock-induced rupture, which led to the
formation of shatter cones at the tail of the shock front, likely during the early stage of the
impact events
Giovanni Casertano, Tra musica e filosofia: le passioni, l’anima e il logos (a cura di Lidia Palumbo),
Get PDFAbstract Between music and philosophy: passions, soul and logos
The paper presents a comment, in a musical key, of Encomium of Elena. Gorgias famous play, produced in the fifth century BC, is about passions, soul and speeches. The author then considers the influence of this text of Gorgias on the dialogues of Plato, in relation to the great themes of soul and body, human passions, the power of words. The musical register sustains the whole paper to show how philosophy is the megiste musiké of which Socrates speaks in Phd. 61a
Non-equilibrium melting of partially differentiated asteroids: insights from partial melting experiments on L6 chondrite DAV01001
Get PDFPlanetary differentiation in small bodies is believed to be ruled by several partial end-states that were dominated by low degrees of partial melting and melt segregation, before arriving at the formation of rocky planets. Having a better understanding of non-equilibrium melting processes in undifferentiated chondritic materials is critical to characterize planetary differentiation processes and the formation of rocky planets and differentiated asteroids. In this context, partial melting experiments of natural chondrites can provide unique insights into the petrological evolution associated with early planetary differentiation of planetesimals. For this study, we performed partial melting experiments using fragments from the ordinary chondrite DAV01001. Experiments were performed in a piston-cylinder at 1 GPa pressure, at temperatures from 1100 to 1300 °C and for 24 hours run duration. Reducing conditions were imposed by the use of graphite capsules. The experimental products were analysed using electron microprobe and synchrotron radiation computed microtomography (SR-μCT)
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