Exploring the Ar isotope record of an early Miocene pseudotachylyte in an early Oligocene intrusion (Rieserferner pluton, eastern Alps)

Di Vincenzo G, Pennacchioni G, Bestmann M (2019)

Publication Type: Journal article

Publication year: 2019

Journal

Lithos Elsevier

Book Volume: 338-339

Pages Range: 1-17

DOI: 10.1016/j.lithos.2019.04.009

Abstract

We investigate the influence of unmelted clasts on the 40 Ar[sbnd] 39 Ar age record of a Miocene pseudotachylyte within the early Oligocene Riesenferner pluton (eastern Alps). This case study is ideal to investigate the effect of inherited Ar retained in survivor clasts because, although seismic faulting was only slightly younger (<20 Ma) than the igneous source rock, the pseudotachylyte includes layers with significant variations in K content, of either dominant plagioclase and biotite microlites or dominant submicrometric muscovite matrix. Numerical modeling, assuming pure diffusive loss and a short-lived thermal pulse due to frictional heating, indicates that unmelted plagioclase clasts represent the most critical issue in interpreting Ar data. Plagioclase clasts of only a few to tens micrometers in size are expected to retain most of radiogenic Ar accumulated before coseismic faulting. A comparable behavior is only predicted for much larger (ten to fifty times larger) K-feldspar clasts. In-situ 40 Ar[sbnd] 39 Ar laser analyses of low-K microlitic domains, free of discernable clasts, yield slightly, but significantly, older ages than those from the high-K matrix. Results suggest that older ages (up to ~4% on average) from low-K domains are due to contamination by plagioclase clasts and suggest an age of 17.12 ± 0.22 Ma for coseismic slip. This age dates the last stage of activity of the Giudicarie Fault during tectonic indentation of the Dolomites block of the southern Alps against the nappe stack of the eastern Alps.

Authors with CRIS profile

Michael Bestmann Professur für Tektonik

Involved external institutions

University of Padua / Universita degli Studi di Padova IT Italy (IT) Istituto di Geoscienze e Georisorse (IGG-CNR) IT Italy (IT)

How to cite

APA:

Di Vincenzo, G., Pennacchioni, G., & Bestmann, M. (2019). Exploring the Ar isotope record of an early Miocene pseudotachylyte in an early Oligocene intrusion (Rieserferner pluton, eastern Alps). Lithos, 338-339, 1-17. https://dx.doi.org/10.1016/j.lithos.2019.04.009

MLA:

Di Vincenzo, Gianfranco, Giorgio Pennacchioni, and Michel Bestmann. "Exploring the Ar isotope record of an early Miocene pseudotachylyte in an early Oligocene intrusion (Rieserferner pluton, eastern Alps)." Lithos 338-339 (2019): 1-17.

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