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Dating shallow thrusts with zircon (U-Th)/He thermochronometry; the shear heating connection

Matteo Maino, Leonardo Casini, Andrea Ceriani, Alessandro Decarlis, Andrea Di Giulio, Silvio Seno, Massimo Setti and Finlay M. Stuart
Dating shallow thrusts with zircon (U-Th)/He thermochronometry; the shear heating connection
Geology (Boulder) (April 2015) 43 (6): 495-498

Abstract

New zircon (U-Th)/He (ZHe) ages from a shallow (<6-7 km) thrust fault zone and surrounding wall rocks in the Helminthoid Flysch of the Ligurian Alps were measured to test the applicability of the thermochronometer for dating brittle or brittle-ductile faults. The ages are integrated with X-ray diffraction analysis of clay minerals and fluid inclusion microthermometry on vein-filling minerals to constrain the temperature conditions of the damage zone and the wall rocks during thrusting. The wall rocks yield pre-depositional inherited ZHe ages (125.3 + or - 15 to 312.3 + or - 37 Ma) while ages from the fault core are reset (28.8 + or - 3.4 to 33.8 + or - 4.0 Ma). This is consistent with independent geological and thermochronometric evidence for early Oligocene motion of the thrust. This implies that the fault zone exceeded 200 degrees C during faulting, and confirms the illite crystallinity and fluid inclusion constraints, which indicate temperatures of 220-300 degrees C in the fault zone, while in those the wall rocks were <180-200 degrees C. Thermal modeling of the fault zone suggests that the shear heating associated with the fault motion is an efficient mechanism for generating temperature increases of 50-70 degrees C during a displacement of 10-25 km in 2-10 m.y. Our results underscore the validity of the ZHe technique for dating brittle or brittle-ductile faults characterized by relatively high strain rate.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 6
Title: Dating shallow thrusts with zircon (U-Th)/He thermochronometry; the shear heating connection
Affiliation: Universita di Pavia, Dipartimento di Scienze della Terra e dell'Ambiente, Pavia, Italy
Pages: 495-498
Published: 20150424
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Number of pages: unpaginated
References: 38
Accession Number: 2015-052307
Categories: GeochronologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. geol. sketch map
N42°02'45" - N42°02'45", E07°45'30" - E07°45'30"
Secondary Affiliation: Universita di Sassari, ITA, ItalyInstitut de Physique du Globe de Strasbourg, FRA, FranceScottish Universities Environmental Research Centre, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201524
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