Influence of Deformation and Fluids on Ti Exchange in Natural Quartz

Author(s)

Michel Bestmann, Giorgio Pennacchioni, Bernhard Grasemann, Benjamin Huet, Michael W.M. Jones, Cameron M. Kewish

Abstract

Using a combination of microstructural, spectroscopic, and geochemical

analyses, we investigate how subgrain rotation recrystallization and

fluid migration affect Ti concentration [Ti] in naturally deformed

quartz veins from the Prijakt Nappe (Austroalpine Unit, Eastern Alps).

These coarse-grained quartz veins, that formed at amphibolite facies

conditions, were overprinted by lower greenschist facies deformation to

different degrees. During the overprint, subgrain rotation

recrystallization was dominant during progressive deformation to

ultramylonitic stages. The initial [Ti] (3.0–4.7 ppm) and

cathodoluminescence (CL) signature of the vein crystals decrease during

deformation mainly depending on the availability of fluids across the

microstructure. The amount of strain played a subordinate role in

resetting to lower [Ti] and corresponding darker CL shades. Using a

microstructurally controlled analysis we find that the most complete

re-equilibration in recrystallized aggregates ([Ti] of 0.2–0.6 p.m.)

occurred (a) in strain shadows around quartz porphyroclasts, acting as

fluid sinks, and (b) in localized microshear zones that channelized

fluid percolation. [Ti] resetting is mainly observed along wetted high

angle boundaries (misorientation angle >10–15°), with partial [Ti]

resetting observed along dry low angle boundaries (<10–15°). This

study shows for the first time that pure subgrain rotation

recrystallization in combination with dissolution-precipitation under

retrograde condition provide microstructural domains suitable for the

application of titanium-in-quartz geothermobarometry at deformation

temperatures down to 300–350°C.

Organisation(s)

Department of Environmental Geosciences, Department of Geology

External organisation(s)

Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), University of Padova, Geologische Bundesanstalt, Queensland University of Technology, Australian Nuclear Science and Technology Organisation (ANSTO), La Trobe University

Journal

Journal of Geophysical Research: Solid Earth

Volume

126

No. of pages

26

ISSN

2169-9313

DOI

https://doi.org/10.1029/2021JB022548

Publication date

12-2021

Peer reviewed

Yes

Austrian Fields of Science 2012

105124 Tectonics

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology, Geophysics, Earth and Planetary Sciences (miscellaneous), Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/2e4768dc-39e8-4d0f-843f-db2c26130b4f