Shear localization: analog modeling and anisotropy of magnetic susceptibility

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985530%3A_____%2F22%3A00602679" target="_blank" >RIV/67985530:_____/22:00602679 - isvavai.cz</a>

Výsledek na webu

<a href="https://www.socgeol.it/files/download/pubblicazioni/Abstract%20Book/Abstract_DRT_Catania%202022.pdf" target="_blank" >https://www.socgeol.it/files/download/pubblicazioni/Abstract%20Book/Abstract_DRT_Catania%202022.pdf</a>

DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

Shear localization: analog modeling and anisotropy of magnetic susceptibility

Popis výsledku v původním jazyce

The presence of large volumes of eclogite in collision and subduction zones makes their formation and deformation highly relevant for the dynamics of convergent zones. There is however no consensus on the deformation behavior of eclogite. On the one hand, mylonitic eclogite shear zones showing evidence of dominant deformation by dislocation creep have frequently been reported. On the other hand, fluid supported formation and deformation has been recently suggested as a potential mechanism in eclogite whereby the main accommodating mechanism is dissolution-precipitation creep. This raises the question of the factors controlling the deformation behavior of eclogite. In this contribution, we present microstructural, petrographical and chemical data from a series of eclogite samples derived from low Mg – high Ti gabbro collected at the eclogite type locality (Saualpe- Koralpe Complex, Eastern Alps, Austria). The rocks are characterized by a pronounced foliation defined by the shape preferred orientation of the major minerals (omphacite, amphibole, epidote and garnet). Minor euhedral quartz grains are present. Overall, grains show rather uniform extinction which is well in line with a low internal distortion detected by electron backscatter diffraction mapping. These features are interpreted as evidence of syn-tectonic diffusion dominated eclogitization. Thermodynamic forward modelling indicates that eclogitization occurred under fluid saturated conditions at around 2 GPa and 640–680°C. Locally, the eclogite fabric is crosscut by finite veins showing a similar paragenesis as the host eclogite. However, they are enriched in quartz and epidote, depleted in garnet and show overall a coarser grain size. These veins likely initiated as post-eclogitization fractures that were subsequently filled by eclogite facies minerals. Depending on their initial orientation, the veins were either reactivated as flanking structures or foliation sub-parallel shear zones. The reactivated veins are characterized by undulatory extinction, twinning and subgrain formation, all being indicative of dislocation creep. The identical paragenesis and similar mineral chemistry indicates that reactivation occurred at conditions close to those of eclogitization. The investigated samples therefore testify that eclogite can deform by different deformation mechanisms at similar conditions. Our investigations document that diffusion (and/or dissolution-precipitation) is bound to the process of eclogitization, eclogite facies vein formation is accommodated by fracturing and dissolution-precipitation whereas post-eclogitization strain localization is accommodated by dislocation creep.

Název v anglickém jazyce

Shear localization: analog modeling and anisotropy of magnetic susceptibility

Popis výsledku anglicky

The presence of large volumes of eclogite in collision and subduction zones makes their formation and deformation highly relevant for the dynamics of convergent zones. There is however no consensus on the deformation behavior of eclogite. On the one hand, mylonitic eclogite shear zones showing evidence of dominant deformation by dislocation creep have frequently been reported. On the other hand, fluid supported formation and deformation has been recently suggested as a potential mechanism in eclogite whereby the main accommodating mechanism is dissolution-precipitation creep. This raises the question of the factors controlling the deformation behavior of eclogite. In this contribution, we present microstructural, petrographical and chemical data from a series of eclogite samples derived from low Mg – high Ti gabbro collected at the eclogite type locality (Saualpe- Koralpe Complex, Eastern Alps, Austria). The rocks are characterized by a pronounced foliation defined by the shape preferred orientation of the major minerals (omphacite, amphibole, epidote and garnet). Minor euhedral quartz grains are present. Overall, grains show rather uniform extinction which is well in line with a low internal distortion detected by electron backscatter diffraction mapping. These features are interpreted as evidence of syn-tectonic diffusion dominated eclogitization. Thermodynamic forward modelling indicates that eclogitization occurred under fluid saturated conditions at around 2 GPa and 640–680°C. Locally, the eclogite fabric is crosscut by finite veins showing a similar paragenesis as the host eclogite. However, they are enriched in quartz and epidote, depleted in garnet and show overall a coarser grain size. These veins likely initiated as post-eclogitization fractures that were subsequently filled by eclogite facies minerals. Depending on their initial orientation, the veins were either reactivated as flanking structures or foliation sub-parallel shear zones. The reactivated veins are characterized by undulatory extinction, twinning and subgrain formation, all being indicative of dislocation creep. The identical paragenesis and similar mineral chemistry indicates that reactivation occurred at conditions close to those of eclogitization. The investigated samples therefore testify that eclogite can deform by different deformation mechanisms at similar conditions. Our investigations document that diffusion (and/or dissolution-precipitation) is bound to the process of eclogitization, eclogite facies vein formation is accommodated by fracturing and dissolution-precipitation whereas post-eclogitization strain localization is accommodated by dislocation creep.

Druh

O - Ostatní výsledky

CEP obor

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OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GJ16-25486Y" target="_blank" >GJ16-25486Y: Jak AMS odráží mikrostrukturu v přírodních a experimentálních střižných zónách.</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2022

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů