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

Maino, M., Casini, L., Ceriani, A., Decarlis, A., Di Giulio, A., Seno, S., Setti, M. and Stuart, F. M. (2015) Dating shallow thrusts with zircon (U-Th)/He thermochronometry: the shear heating connection. Geology, 43(6), pp. 495-498. (doi:10.1130/G36492.1)

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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 ± 15 to 312.3 ± 37 Ma) while ages from the fault core are reset (28.8 ± 3.4 to 33.8 ± 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 °C during faulting, and confirms the illite crystallinity and fluid inclusion constraints, which indicate temperatures of 220–300 °C in the fault zone, while in those the wall rocks were <180–200 °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 °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.

Item Type:Articles (Other)
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Stuart, Professor Finlay
Authors: Maino, M., Casini, L., Ceriani, A., Decarlis, A., Di Giulio, A., Seno, S., Setti, M., and Stuart, F. M.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Geology
Publisher:Geological Society of America
ISSN:0091-7613
ISSN (Online):1943-2682
Copyright Holders:Copyright © 2015 Geological Society of America
First Published:First published in Geology 43(6):495-498
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher.

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