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)

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 Fin
• 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.