Fault textures in volcanic debris-avalanche deposits and transformations into lahars: The Pichu Pichu thrust lobes in south Peru compared to worldwide avalanche deposits

Autor: Jean-Claude Thouret, Karine Bernard, Benjamin van Wyk de Vries
Přispěvatelé: Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), CCSD, Accord Elsevier, Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement et la société-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)
Jazyk: angličtina
Rok vydání: 2019
Předmět:
Zdroj: Journal of Volcanology and Geothermal Research
Journal of Volcanology and Geothermal Research, 2019, 371, pp.116-136
Journal of Volcanology and Geothermal Research, Elsevier, 2019, 371, pp.116-136
Journal of Volcanology and Geothermal Research, 2019, 371, pp.116-136. ⟨10.1016/j.jvolgeores.2019.01.008⟩
ISSN: 0377-0273
DOI: 10.1016/j.jvolgeores.2019.01.008⟩
Popis: International audience; Structures, lithofacies and semi-quantitative sedimentological analysis of volcanic debris-avalanche deposits are essential to constrain syn-emplacement processes along avalanche fault zones in the setting of mass-flow runout distances. At a distance of 28 km from the extinct Pichu Pichu compound volcano, we show how internal structures of thrust lobes, faulted as to form horst- and graben-like structures, have recorded the brecciation with granular segregations. Cataclastic gradients have been recognized in more than eleven breccia structures with statistical grain-size parameters, among them fractal D-values between 1.96 and 2.53 related to an extensional fracturing in DADs with fractal D-values between 2 and 2.5 leading to granular disaggregation with fractal D-values between 2.13 and 2.22. Primary fractures related to transport processes and the secondary cataclasis produced during emplacement are quantified as having 50% matrix. The hybrid lithofacies in graben-like structures may be the precursory stages of the matrix transformation into lahar deposits. Volcanic debris-avalanche structures of eleven worldwide volcanoes that belong to the Central Andes and the Cascades volcanic arc have been compared using sedimentary and statistical methods (156 sieved samples and Shape Preferred Orientation measured on 30,342 clasts). Median diameter, sorting index, skewness and kurtosis values help differentiate four deposits and processes: (1) the proximal gravitational collapse deposits; (2) the avalanche thrust lobes, located in inverted extensional fault zones, and (3) the hybrid and mixed deposits with polymodal distributions; and (4) the bimodal, transformed matrix with clast sorting. The fractal D-values of avalanche matrix range between 2.3 and 2.7, suggesting that extensional fractures have led to granular disaggregation. From the available statistical dataset, a few equations have been developed that help pointing to a syn-emplacement cataclastic gradient along avalanche fault zone. Three textural classes of avalanche fault zones have been identified based on the ellipse/a/b values of 2.14 for the planar collapse in fault zone, 1.75 to 2 for the crushing of volcanic avalanche breccias, and
Databáze: OpenAIRE
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