10.6084/m9.figshare.3453197.v1
C. Leitner
C.
Leitner
F. Neubauer
F.
Neubauer
J. Genser
J.
Genser
S. Borojević-Šoštarić
S.
Borojević-Šoštarić
G. Rantitsch
G.
Rantitsch
<sup>40</sup>Ar/<sup>39</sup>Ar ages of crystallization and recrystallization of rock-forming polyhalite in Alpine rocksalt deposits
Geological Society of London
2016
Northern Calcareous Alps
multiphase polyhalite growth
Disturbed age spectra patterns result
Illite crystallinity points
fluid inclusions
evaporitic Haselgebirge Formation
Alpine rocksalt deposits Polyhalite rocks
deformation fabric types
Alpine test case
Ar
Geology
2016-06-21 11:12:48
Dataset
https://geolsoc.figshare.com/articles/dataset/_sup_40_sup_Ar_sup_39_sup_Ar_ages_of_crystallization_and_recrystallization_of_rock-forming_polyhalite_in_Alpine_rocksalt_deposits/3453197
<p>Polyhalite rocks of the evaporitic Haselgebirge Formation are emplaced within a rocksalt–mudrock tectonite. The rheologically
weak series served as a major detachment level during nappe stacking of the Northern Calcareous Alps (Eastern Alps). To test
the mineral polyhalite [K<sub>2</sub>Ca<sub>2</sub>Mg(SO<sub>4</sub>)<sub>4</sub>·2H<sub>2</sub>O] as a useful geochronometer for various diagenetic and deformation fabric types, <sup>40</sup>Ar/<sup>39</sup>Ar age dating was combined with microstructural analysis. Vein infills, polyhalite intergrown with anhydrite and polyhalite
within mudrock, crystallized in several stages between <em>c.</em> 235 and 210 Ma. Mylonites of fine-grained polyhalite rock indicate subsequent stages of tectonothermal overprint between
<em>c.</em> 155 and 105 Ma, which is roughly consistent with previously measured feldspar and muscovite <sup>40</sup>Ar/<sup>39</sup>Ar data from the region. Illite crystallinity points to temperatures of <em>c.</em> 200 °C. The peak temperature of overprint was at <em>c.</em> 180 °C in the Berchtesgaden mine (vitrinite reflectance, fluid inclusions) and >240 °C in the Altaussee mine (fluid inclusions).
These temperatures are below the value of 255 °C, where polyhalite starts to dehydrate. Disturbed age spectra patterns result
from multiphase polyhalite growth; however, single phases and completely recrystallized fabrics yield good results. As in
the Alpine test case, polyhalite may characteristically serve as a geochronometer for diagenetic and very-low-grade metamorphic
processes.
</p>