Naslov
40Ar/39Ar ages of crystallization and recrystallization of rock-forming polyhalite in Alpine rocksalt deposits

Autori
Leitner, Christoph ; Neubauer, Franz ; Genser, Johann ; Borojević Šoštarić, Sibila ; Rantitsch, Gerd

Vrsta, podvrsta i kategorija rada
Poglavlja u knjigama, znanstveni

Knjiga
Advances in 40Ar/39Ar dating : from archaeology to planetary sciences

Urednik/ci
Jourdan, F. ; Mark, D. F. ; Verati, C.

Izdavač
The Geological Society

Grad
London : Delhi

Godina
2014

Raspon stranica
207-224

ISBN
978-1-86239-360-8

ISSN
0305-8719

Ključne riječi
Polyhalite ; argon-argon dating ; Northern Calcareous Alps (Eastern Alps) ; rock salt ; recrystallization

Sažetak
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 [K2Ca2Mg(SO4)4·2H2O] as a useful geochronometer for various diagenetic and deformation fabric types, 40Ar/39Ar age dating was combined with microstructural analysis. Vein infills, polyhalite intergrown with anhydrite and polyhalite within mudrock, crystallized in several stages between c. 235 and 210 Ma. Mylonites of fine-grained polyhalite rock indicate subsequent stages of tectonothermal overprint between c. 155 and 105 Ma, which is roughly consistent with previously measured feldspar and muscovite 40Ar/39Ar data from the region. Illite crystallinity points to temperatures of c. 200 °C. The peak temperature of overprint was at c. 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.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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