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.

Dating shallow thrusts with zircon (U-Th)/He thermochronometry— The shear heating connection / Maino, M; Casini, Leonardo; Ceriani, A; Decarlis, A; Di Giulio, A; Seno, S; Setti, M; Stuart, Fm. - In: GEOLOGY. - ISSN 0091-7613. - 43:6(2015), pp. 495-498. [doi:10.1130/G36492.1]

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

CASINI, Leonardo;
2015

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.
Dating shallow thrusts with zircon (U-Th)/He thermochronometry— The shear heating connection / Maino, M; Casini, Leonardo; Ceriani, A; Decarlis, A; Di Giulio, A; Seno, S; Setti, M; Stuart, Fm. - In: GEOLOGY. - ISSN 0091-7613. - 43:6(2015), pp. 495-498. [doi:10.1130/G36492.1]
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11388/133782
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