The timescale of solid-state deformation in the Northern Adamello igneous intrusive suite
Publisher DOI
Abstract
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.
Date Issued
2022
Publication Type
Article
Subject(s)
Subjects
40Ar/39Argeochronology
•
pseudotachylytes
•
mylonites
•
cataclasites solid-state deformation
•
Adamello
Language(s)
en
Author(s)
Mittempergher, S. | |
Zanchetta, S. | |
Caldiroli, F. | |
Zanchi, A. | |
Bistacchi, A. | |
Hanchar, J. M. |
Additional Credits
Journal
Journal of the Geological Society
Publisher
Geological Society of London
ISSN
0016-7649
Access(Rights)
Unknown