Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska)
Abstract: On Kodiak Island (Alaska), decimeter-thick black fault rocks (BFR) are at the core of 10's meters-thick foliated cataclasites. Cataclasites belong to mélanges regarded as paleo-décollement active at 12-14 km depth and 230-260oC. Each black layer is mappable for tens of meters along st...
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ftingv:oai:www.earth-prints.org:2122/5907 2023-05-15T17:04:39+02:00 Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) Meneghini, F. Di Toro, G. Rowe, D. C. Moore, C. Tsutsumi, A. Meneghini, F.; Pisa Univ. Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Rowe, D. C.; Univ. Santa Cruz, USA Moore, C.; Univ. Santa Cruz, USA Tsutsumi, A.; Kyoto Univ. Japan Pisa Univ. Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Univ. Santa Cruz, USA Kyoto Univ. Japan 2010 http://hdl.handle.net/2122/5907 en eng Geological Society of America GSA Bulletin 7-8/122 (2010) http://hdl.handle.net/2122/5907 open earthquakes fault rocks 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous article 2010 ftingv 2022-07-29T06:05:33Z Abstract: On Kodiak Island (Alaska), decimeter-thick black fault rocks (BFR) are at the core of 10's meters-thick foliated cataclasites. Cataclasites belong to mélanges regarded as paleo-décollement active at 12-14 km depth and 230-260oC. Each black layer is mappable for tens of meters along strike. The BFR feature a complex layering made at microscale by alternation of granular and crystalline microtextures, composed of micron-scale sub-rounded quartz and plagioclase in an ultrafine, phyllosilicate-rich matrix. In the crystalline microlayers, tabular zoned microlites of plagioclase make much of the matrix. No such feldspars are found in the cataclasite. We interpret crystalline microlayers as pseudotachylytes. The granular microlayers show higher grain size variability, crushed microlites and textures typical of fluidization and granular flow deformation. Crosscutting relationships between granular and crystalline microlayers include flow and intrusion structures and mutual brittle truncation. This suggests that each 10's centimeter-thick composite BFR record multiple pulses of seismic slip. In each pulse, ultracomminuted fluidized material and friction melt formed and deformed together in a ductile fashion. Brittle truncation by another pulse occurred after solidification of the friction melt and the fluidized rock. XRPD and XRF analyses show that BFR have similar mineral composition and chemical content as the cataclasites. The observed systematic chemical differences cannot be explained by bulk or preferential melting of any of the cataclasite components. The presence of an open, fluid-infiltrated system with BFR later alteration is suggested. The geochemical results indicate that these subduction-related pseudotachylytes, differ from those typically described in crystalline rocks and other tectonic settings. Published 3.1. Fisica dei terremoti JCR Journal open Article in Journal/Newspaper Kodiak Alaska Earth-Prints (Istituto Nazionale di Geofisica e Vulcanologia) |
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Open Polar |
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Earth-Prints (Istituto Nazionale di Geofisica e Vulcanologia) |
op_collection_id |
ftingv |
language |
English |
topic |
earthquakes fault rocks 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous |
spellingShingle |
earthquakes fault rocks 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous Meneghini, F. Di Toro, G. Rowe, D. C. Moore, C. Tsutsumi, A. Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
topic_facet |
earthquakes fault rocks 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous |
description |
Abstract: On Kodiak Island (Alaska), decimeter-thick black fault rocks (BFR) are at the core of 10's meters-thick foliated cataclasites. Cataclasites belong to mélanges regarded as paleo-décollement active at 12-14 km depth and 230-260oC. Each black layer is mappable for tens of meters along strike. The BFR feature a complex layering made at microscale by alternation of granular and crystalline microtextures, composed of micron-scale sub-rounded quartz and plagioclase in an ultrafine, phyllosilicate-rich matrix. In the crystalline microlayers, tabular zoned microlites of plagioclase make much of the matrix. No such feldspars are found in the cataclasite. We interpret crystalline microlayers as pseudotachylytes. The granular microlayers show higher grain size variability, crushed microlites and textures typical of fluidization and granular flow deformation. Crosscutting relationships between granular and crystalline microlayers include flow and intrusion structures and mutual brittle truncation. This suggests that each 10's centimeter-thick composite BFR record multiple pulses of seismic slip. In each pulse, ultracomminuted fluidized material and friction melt formed and deformed together in a ductile fashion. Brittle truncation by another pulse occurred after solidification of the friction melt and the fluidized rock. XRPD and XRF analyses show that BFR have similar mineral composition and chemical content as the cataclasites. The observed systematic chemical differences cannot be explained by bulk or preferential melting of any of the cataclasite components. The presence of an open, fluid-infiltrated system with BFR later alteration is suggested. The geochemical results indicate that these subduction-related pseudotachylytes, differ from those typically described in crystalline rocks and other tectonic settings. Published 3.1. Fisica dei terremoti JCR Journal open |
author2 |
Meneghini, F.; Pisa Univ. Di Toro, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Rowe, D. C.; Univ. Santa Cruz, USA Moore, C.; Univ. Santa Cruz, USA Tsutsumi, A.; Kyoto Univ. Japan Pisa Univ. Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Univ. Santa Cruz, USA Kyoto Univ. Japan |
format |
Article in Journal/Newspaper |
author |
Meneghini, F. Di Toro, G. Rowe, D. C. Moore, C. Tsutsumi, A. |
author_facet |
Meneghini, F. Di Toro, G. Rowe, D. C. Moore, C. Tsutsumi, A. |
author_sort |
Meneghini, F. |
title |
Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
title_short |
Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
title_full |
Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
title_fullStr |
Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
title_full_unstemmed |
Record of mega-earthquakes in subduction thrusts: the black fault rocks of Pasagshak Point (Kodiak Island, Alaska) |
title_sort |
record of mega-earthquakes in subduction thrusts: the black fault rocks of pasagshak point (kodiak island, alaska) |
publisher |
Geological Society of America |
publishDate |
2010 |
url |
http://hdl.handle.net/2122/5907 |
genre |
Kodiak Alaska |
genre_facet |
Kodiak Alaska |
op_relation |
GSA Bulletin 7-8/122 (2010) http://hdl.handle.net/2122/5907 |
op_rights |
open |
_version_ |
1766058968643272704 |