UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

Peritectic melting of mica in fault-related pseudotachylite melts and potassium mass balance as an indicator of fluid-absent source conditions

Dobson, D; Montheil, L; Paine, J; Thomson, A; (2021) Peritectic melting of mica in fault-related pseudotachylite melts and potassium mass balance as an indicator of fluid-absent source conditions. Geochemistry, Geophysics, Geosystems 10.1029/2020GC009217. (In press).

[img] Text
PST Mass balance main text r2a.pdf - Accepted version
Access restricted to UCL open access staff until 12 August 2021.

Download (657kB)

Abstract

Pseudotachylites are generally considered to be produced by flash melting of the most fusible minerals, with compositions often dominated by biotite mica. We present phase fraction calculations for 237 pseudotachylite analyses from 28 localities spanning a range of host rock compositions from granites to peridotites. Pseudotachylite matrix compositions cannot be reproduced by a simple linear mixture of the minerals in their host rocks and commonly show a potassium deficit in pseudotachylites which contain significant contributions from biotite or muscovite. This is strongly indicative of peritectic melting of mica under fluid‐absent conditions. Occasionally, a negative contribution from an aluminosilicate phase is required but with a positive contribution from potassium feldspar. This is most consistent with peritectic melting of micas under fluid present conditions. The present data therefore suggest that, while fluid absent flash melting might be the most common mode of formation of pseudotachylite, in some instances pseudotachylites can be produced in the presence of a free fluid. Potassium mass balance of pseudotachylites might therefore be a diagnostic indicator of fluid‐absent conditions in their source regions during seismogenic rupture. We give some examples of observational evidence of peritectic liquidus phases in pseudotachylites and suggest that the significance of these phases might have been overlooked in previous studies.

Type: Article
Title: Peritectic melting of mica in fault-related pseudotachylite melts and potassium mass balance as an indicator of fluid-absent source conditions
DOI: 10.1029/2020GC009217
Publisher version: https://doi.org/10.1029/2020GC009217
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher's terms and conditions.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10109972
Downloads since deposit
1Download
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item