40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System
Fault-generated pseudotachylytes are the product of frictional melting during high-velocity slip associated with coseismic faulting. Ar-40-Ar-39 dating of pseudotachylytes represents a powerful tool to directly determine the age of brittle faulting which is otherwise dated only indirectly. However,...
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ftunivpisairis:oai:arpi.unipi.it:11568/83839 2024-04-21T07:51:34+00:00 40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System DI VINCENZO G. ROSSETTI F. STORTI F. ROCCHI, SERGIO DI VINCENZO, G. Rocchi, Sergio Rossetti, F. Storti, F. 2004 http://hdl.handle.net/11568/83839 https://doi.org/10.1016/j.epsl.2004.04.042 eng eng info:eu-repo/semantics/altIdentifier/wos/WOS:000222961000008 volume:223 firstpage:349 lastpage:364 numberofpages:16 journal:EARTH AND PLANETARY SCIENCE LETTERS http://hdl.handle.net/11568/83839 doi:10.1016/j.epsl.2004.04.042 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-3042776524 info:eu-repo/semantics/article 2004 ftunivpisairis https://doi.org/10.1016/j.epsl.2004.04.042 2024-03-28T01:24:10Z Fault-generated pseudotachylytes are the product of frictional melting during high-velocity slip associated with coseismic faulting. Ar-40-Ar-39 dating of pseudotachylytes represents a powerful tool to directly determine the age of brittle faulting which is otherwise dated only indirectly. However, the pronounced spatial heterogeneity of most endogenically generated pseudotachylytes, due to the intimate coexistence of unmelted mineral clasts from the source rock, frictional glass and neogenic igneous minerals, often precludes a straightforward interpretation of argon data. This requires careful evaluation of the role of clasts in plaguing the age record of the pseudotachylyte matrix. This study exploits the full potential of the Ar-40-Ar-39 method, using laser step-heating and laser in situ techniques in conjunction with textural and chemical characterisation at the microscale to disentangle the complexity of the first record of pseudotachylytes generated in the right-lateral fault systems which dissect the western shoulder of the West Antarctic Rift System. Pseudotachylytes occur as fault and injection veins. They exhibit glassy matrices with a potassium feldspar-like composition, and invariably contain, at a millimeter to microscopic scale, unmelted quartz and subordinate feldspars from the source rock. Injection veins characteristically contain much fewer mineral clasts. In situ ultraviolet (UV) laser analyses indicate that quartz from the host rock and from clasts within the fault veins contains significant amounts (similar to 10-50 ppb) of parentless Ar-40, most probably hosted in microscopic to submicroscopic fluid inclusions, associated with high Cl/K ratios. Infrared laser step-heating experiments on fault vein pseudotachylyte matrices yield strongly discordant age spectra with an overall saddle shape characterised by a minimum at similar to 34 Ma, unrealistically old ages at high temperatures associated with high Cl/K ratios and total gas ages of 41.5-44.3 Ma. Petrographic data and the pronounced ... Article in Journal/Newspaper Antarc* Antarctic ARPI - Archivio della Ricerca dell'Università di Pisa Earth and Planetary Science Letters 223 3-4 349 364 |
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ARPI - Archivio della Ricerca dell'Università di Pisa |
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ftunivpisairis |
language |
English |
description |
Fault-generated pseudotachylytes are the product of frictional melting during high-velocity slip associated with coseismic faulting. Ar-40-Ar-39 dating of pseudotachylytes represents a powerful tool to directly determine the age of brittle faulting which is otherwise dated only indirectly. However, the pronounced spatial heterogeneity of most endogenically generated pseudotachylytes, due to the intimate coexistence of unmelted mineral clasts from the source rock, frictional glass and neogenic igneous minerals, often precludes a straightforward interpretation of argon data. This requires careful evaluation of the role of clasts in plaguing the age record of the pseudotachylyte matrix. This study exploits the full potential of the Ar-40-Ar-39 method, using laser step-heating and laser in situ techniques in conjunction with textural and chemical characterisation at the microscale to disentangle the complexity of the first record of pseudotachylytes generated in the right-lateral fault systems which dissect the western shoulder of the West Antarctic Rift System. Pseudotachylytes occur as fault and injection veins. They exhibit glassy matrices with a potassium feldspar-like composition, and invariably contain, at a millimeter to microscopic scale, unmelted quartz and subordinate feldspars from the source rock. Injection veins characteristically contain much fewer mineral clasts. In situ ultraviolet (UV) laser analyses indicate that quartz from the host rock and from clasts within the fault veins contains significant amounts (similar to 10-50 ppb) of parentless Ar-40, most probably hosted in microscopic to submicroscopic fluid inclusions, associated with high Cl/K ratios. Infrared laser step-heating experiments on fault vein pseudotachylyte matrices yield strongly discordant age spectra with an overall saddle shape characterised by a minimum at similar to 34 Ma, unrealistically old ages at high temperatures associated with high Cl/K ratios and total gas ages of 41.5-44.3 Ma. Petrographic data and the pronounced ... |
author2 |
DI VINCENZO, G. Rocchi, Sergio Rossetti, F. Storti, F. |
format |
Article in Journal/Newspaper |
author |
DI VINCENZO G. ROSSETTI F. STORTI F. ROCCHI, SERGIO |
spellingShingle |
DI VINCENZO G. ROSSETTI F. STORTI F. ROCCHI, SERGIO 40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
author_facet |
DI VINCENZO G. ROSSETTI F. STORTI F. ROCCHI, SERGIO |
author_sort |
DI VINCENZO G. |
title |
40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
title_short |
40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
title_full |
40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
title_fullStr |
40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
title_full_unstemmed |
40Ar-39Ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in Cenozoic fault-generated friction melts from the West Antarctic Rift System |
title_sort |
40ar-39ar dating of pseudotachylytes: the effect of clast-hosted extraneous argon in cenozoic fault-generated friction melts from the west antarctic rift system |
publishDate |
2004 |
url |
http://hdl.handle.net/11568/83839 https://doi.org/10.1016/j.epsl.2004.04.042 |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_relation |
info:eu-repo/semantics/altIdentifier/wos/WOS:000222961000008 volume:223 firstpage:349 lastpage:364 numberofpages:16 journal:EARTH AND PLANETARY SCIENCE LETTERS http://hdl.handle.net/11568/83839 doi:10.1016/j.epsl.2004.04.042 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-3042776524 |
op_doi |
https://doi.org/10.1016/j.epsl.2004.04.042 |
container_title |
Earth and Planetary Science Letters |
container_volume |
223 |
container_issue |
3-4 |
container_start_page |
349 |
op_container_end_page |
364 |
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1796934903297736704 |