Abstract
Coarse-grained quartz veins from the Prijakt Nappe (Austroalpine Unit,
Schober Mountains, Eastern Alps), that formed under amphibolite facies
conditions, were overprinted by lower greenschist facies deformation.
During overprinting, subgrain rotation (SGR) recrystallization was the
dominant mechanism assisting the evolution from protomylonite to
(ultra)mylonite. The initial Ti-concentration [Ti] (3.0-4.7 ppm) and
corresponding cathodoluminescence (CL) signature of the quartz vein
crystals were reset to different degrees mainly depending on the
availability of fluids and their partitioning across the microstructure.
The amount of strain played a subordinate role in resetting. In
recrystallized aggregates the most complete re-equilibration ([Ti]
of 0.2-0.6 pm) occurred in strain shadows surrounding quartz
porphyroclasts, acting as fluid sinks, and in localized shear bands that
channelized fluid percolation. We applied a correlative multi-analytical
workflow using optical and electron microscopy methods (e.g. electron
backscatter diffraction and cathodoluminescence) in combination with
secondary ion mass spectroscopy for [Ti] measurement. The most
efficient [Ti] resetting mainly occurs along wetted high angle
boundaries (misorientation angle >10-15°), and to a minor
extend (partial resetting) along dry low angle boundaries
(<10-15°). This key-study prove for the first time that pure
subgrain rotation recrystallization in combination with
dissolution-precipitation under retrograde condition is able to provide
microstructural sites to apply the TitaniQ geothermobarometer at
deformation temperatures down to 300-350 °C provided that information on
pressure and Ti-activity is available.