Towards the definition of AMS facies in the deposits of pyroclastic density currents

Abstract Anisotropy of magnetic susceptibility (AMS) provides a statistically robust technique to characterize the fabrics of deposits of pyroclastic density currents (PDCs). AMS fabrics in two types of pyroclastic deposits (small-volume phreatomagmatic currents in the Hopi Buttes volcanic field, Ar...

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Autores principales: Ort, M.H., Newkirk, T.T., Vilas, J.F., Vazquez, J.A.
Formato: SER
Materias:
density current
facies analysis
ignimbrite
magnetic anisotropy
magnetic fabric
pyroclastic deposit
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_03058719_v396_n_p205_Ort
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling todo:paper_03058719_v396_n_p205_Ort2023-10-03T15:22:03Z Towards the definition of AMS facies in the deposits of pyroclastic density currents Ort, M.H. Newkirk, T.T. Vilas, J.F. Vazquez, J.A. density current facies analysis ignimbrite magnetic anisotropy magnetic fabric pyroclastic deposit Abstract Anisotropy of magnetic susceptibility (AMS) provides a statistically robust technique to characterize the fabrics of deposits of pyroclastic density currents (PDCs). AMS fabrics in two types of pyroclastic deposits (small-volume phreatomagmatic currents in the Hopi Buttes volcanic field, Arizona, USA, and large-volume caldera-forming currents, Caviahue Caldera, Neuquén, Argentina) show similar patterns. Near the vent and in areas of high topographical roughness, AMS depositional fabrics are poorly grouped, with weak lineations and foliations. In a densely welded proximal ignimbrite, this fabric is overprinted by a foliation formed as the rock compacted and deformed. Medial deposits have moderate-strong AMS lineations and foliations. The most distal deposits have strong foliations but weak lineations. Based on these facies and existing models for pyroclastic density currents, deposition in the medial areas occurs from the strongly sheared, high-particle-concentration base of a density-stratified current. In proximal areas and where topography mixes this denser base upwards into the current, deposition occurs rapidly from a current with little uniformity to the shear, in which particles fall and collide in a chaotic fashion. Distal deposits are emplaced by a slowing or stalled current so that the dominant particle motion is vertical, leading to weak lineation and strong foliation. © 2015 The Geological Society of London. SER info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_03058719_v396_n_p205_Ort
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic density current
facies analysis
ignimbrite
magnetic anisotropy
magnetic fabric
pyroclastic deposit
spellingShingle density current
facies analysis
ignimbrite
magnetic anisotropy
magnetic fabric
pyroclastic deposit
Ort, M.H.
Newkirk, T.T.
Vilas, J.F.
Vazquez, J.A.
Towards the definition of AMS facies in the deposits of pyroclastic density currents
topic_facet density current
facies analysis
ignimbrite
magnetic anisotropy
magnetic fabric
pyroclastic deposit
description Abstract Anisotropy of magnetic susceptibility (AMS) provides a statistically robust technique to characterize the fabrics of deposits of pyroclastic density currents (PDCs). AMS fabrics in two types of pyroclastic deposits (small-volume phreatomagmatic currents in the Hopi Buttes volcanic field, Arizona, USA, and large-volume caldera-forming currents, Caviahue Caldera, Neuquén, Argentina) show similar patterns. Near the vent and in areas of high topographical roughness, AMS depositional fabrics are poorly grouped, with weak lineations and foliations. In a densely welded proximal ignimbrite, this fabric is overprinted by a foliation formed as the rock compacted and deformed. Medial deposits have moderate-strong AMS lineations and foliations. The most distal deposits have strong foliations but weak lineations. Based on these facies and existing models for pyroclastic density currents, deposition in the medial areas occurs from the strongly sheared, high-particle-concentration base of a density-stratified current. In proximal areas and where topography mixes this denser base upwards into the current, deposition occurs rapidly from a current with little uniformity to the shear, in which particles fall and collide in a chaotic fashion. Distal deposits are emplaced by a slowing or stalled current so that the dominant particle motion is vertical, leading to weak lineation and strong foliation. © 2015 The Geological Society of London.
format SER
author Ort, M.H.
Newkirk, T.T.
Vilas, J.F.
Vazquez, J.A.
author_facet Ort, M.H.
Newkirk, T.T.
Vilas, J.F.
Vazquez, J.A.
author_sort Ort, M.H.
title Towards the definition of AMS facies in the deposits of pyroclastic density currents
title_short Towards the definition of AMS facies in the deposits of pyroclastic density currents
title_full Towards the definition of AMS facies in the deposits of pyroclastic density currents
title_fullStr Towards the definition of AMS facies in the deposits of pyroclastic density currents
title_full_unstemmed Towards the definition of AMS facies in the deposits of pyroclastic density currents
title_sort towards the definition of ams facies in the deposits of pyroclastic density currents
url http://hdl.handle.net/20.500.12110/paper_03058719_v396_n_p205_Ort
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AT newkirktt towardsthedefinitionofamsfaciesinthedepositsofpyroclasticdensitycurrents
AT vilasjf towardsthedefinitionofamsfaciesinthedepositsofpyroclasticdensitycurrents
AT vazquezja towardsthedefinitionofamsfaciesinthedepositsofpyroclasticdensitycurrents
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