The timescale of solid-state deformation in the Northern Adamello igneous intrusive suite

Mittempergher, S.; Zanchetta, S.; Caldiroli, F.; Zanchi, A.; Bistacchi, A.; Hanchar, J. M.; Villa, Igor Maria (2022). The timescale of solid-state deformation in the Northern Adamello igneous intrusive suite. Journal of the Geological Society, 179(4), pp. 1-22. Geological Society of London 10.1144/jgs2021-101

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The Late Cenozoic Adamello batholith in the Southern Alps records solid-state deformation structures including, in order of decreasing relative age, cooling joints, mylonitic shear zones and cataclasite-pseudotachylyte faults. We constrained the age and the duration of each phase with 40Ar/ 39Ar geochronology. Host-rocks of the Avio granodiorite, sheared cooling joints, mylonites, pseudotachylytes and cataclasites were sampled and characterized through microstructural, mineralogical, µCT and EPMA analyses. The dated K-bearing phases are: (i) magmatic biotite, (ii) biotite and K-feldspar in joints and mylonites, (iii) pseudotachylytes, (iv) hydrothermal K-feldspar in cataclasites. The wall-rock biotite is 33.2 ± 0.2 Ma old, independently of grainsize, overlapping with the age of cooling joints. Bulk biotite-rich mylonites feature agesbetween 32.4 ± 0.5 and 30.8 ± 0.08 Ma. The K-feldspar cementing cataclasite is 26.4 ± 0.6 Ma old. Four pseudotachylyte matrices cluster between 29.7 ± 0.4 and 32.1 ± 1 Ma, one is 25.3 ± 0.2 Ma old. The resolvable difference in age between magmatic biotite and mylonites indicate that biotite is not a thermochronometer, as its age is mostly controlled by deformation and fluid-rock interactions. 40Ar/39Ar ages mostly confirm the relative ages determined from field relations, with mylonites active within a time window of 1.6 Ma and subsequent seismic faulting protracting for more than 6 Ma.

Item Type:	Journal Article (Original Article)
Division/Institute:	08 Faculty of Science > Institute of Geological Sciences 08 Faculty of Science > Institute of Geological Sciences > Isotope Geology
UniBE Contributor:	Villa, Igor Maria
Subjects:	500 Science > 550 Earth sciences & geology 500 Science
ISSN:	0016-7649
Publisher:	Geological Society of London
Language:	English
Submitter:	Igor Maria Villa-Toscani
Date Deposited:	13 Jan 2023 09:12
Last Modified:	13 Jan 2023 23:29
Publisher DOI:	10.1144/jgs2021-101
Uncontrolled Keywords:	40Ar/39Argeochronology, pseudotachylytes, mylonites, cataclasites solid-state deformation, Adamello
URI:	https://boris.unibe.ch/id/eprint/176706