Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone

Spiess, R., Langone, A., Caggianelli, A., Stuart, F. M. , Zucchi, M., Bianco, C., Brogi, A. and Liotta, D. (2021) Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone. Journal of Structural Geology, 147, 104326. (doi: 10.1016/j.jsg.2021.104326)

Abstract

Exhumation and cooling of upper crustal plutons is generally assumed to develop in the brittle domain, thus determining an abrupt passage from crystallization to faulting. To challenge this general statement, we applied an integrated approach involving meso- and micro-structural studies, thermochronology, geochronology and rheological modelingto the Miocene syn-tectonic Porto Azzurro pluton on Elba (Tuscan archipelago – Italy). This pluton is emplaced in an extensional setting, and we have realized that its fast exhumation is accompanied by localized ductile shear zones, developing along dykes and veins, later affected by brittle deformation. This is unequivocally highlighted by field studies and EBSD-aided microstructural analysis. To constrain the emplacement and exhumation rate of the Porto Azzurro pluton we performed U-Pb zircon dating and (U+Th)/He apatite thermochronology, which resulted in a magma emplacement age of 6.4 ± 0.4 Ma and an exhumation rate of 3.4 to 3.9 mm/yr. Thermo-rheological modeling established that localized ductile deformation occurred at two different time steps: within felsic dykes when the pluton first entered into the brittle field at 380 kyr, and along quartz-rich hydrothermal veins at c. 550 kyr after pluton emplacement. Hence, the major conclusion of our data is that ductile deformation can affect a granitic intrusion even when it is entered into the brittle domain in a fast exhuming extensional regime.

• Item Type: Articles
• Additional Information: A.B, A.C., C.B., D.L., M.Z. received funding from the European Community’s Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE). R.S thanks the grants DOR1827303 of the University of Padova and of Italian PRIN 20178LPCP.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Stuart, Professor Fin
• Authors: Spiess, R., Langone, A., Caggianelli, A., Stuart, F. M., Zucchi, M., Bianco, C., Brogi, A., and Liotta, D.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Journal of Structural Geology
• Publisher: Elsevier
• ISSN: 0191-8141
• ISSN (Online): 1873-1201
• Published Online: 23 March 2021
• Copyright Holders: Copyright © 2021 Elsevier
• First Published: First published in Journal of Structural Geology 147: 104326
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher