Th-Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland

Bergemann, Christian; Gnos, Edwin; Berger, Alfons; Whitehouse, Martin; Wehrens, Philip Chaim; Pettke, Thomas; Janots, Emilie (2017). Th-Pb ion probe dating of zoned hydrothermal monazite and its implications for repeated shear zone activity: An example from the Central Alps, Switzerland. Tectonics, 36(4), pp. 671-689. American Geophysical Union, European Geophysical Society 10.1002/2016TC004407

Preview

Text Bergemann_et_al-2017-Tectonics.pdf - Published Version Available under License Publisher holds Copyright. Download (5MB) | Preview

Th-Pb age dating of zoned hydrothermal monazite from alpine-type fissures/clefts is a powerful tool for constraining polyphase deformation at temperatures below 350°C and presents an alternative to K/Ar and 40Ar/39Ar dating techniques for dating brittle tectonics. This study considers the relationship between cleft orientations in ductile shear zones and cleft mineral crystallization during subsequent brittle overprinting. In the Grimsel area, located in the Aar Massif of the Central Alps, horizontal clefts formed during a primary thrust dominated deformation, while younger and vertically oriented clefts developed during secondary strike-slip movements. The change is due to a switch in orientation between the principal stress axes σ2 and σ3. The transition is associated with monazite crystallization and chloritization of biotite at around 11.5 Ma. Quartz fluid inclusion data allow a link between deformation stages and temperatures to be established and indicate that primary monazite crystallization occurred in both cleft systems at 300–350°C. While cleft monazite crystallization ceases at ~11 Ma in inactive shear zones, monazite growth, and/or dissolution-reprecipitation continues under brittle deformation conditions in vertical clefts during later deformation until ~7 Ma. This younger shear zone activity occurs in association with dextral strike-slip movement of the Rhone-Simplon fault system. With the exception of varying Th/U values correlated with the degree of oxidation, there is only limited compositional variation in the studied cleft monazites.

Interest & Impact

Downloads

0 since deposited on 03 Aug 2017
52 in the past 12 months

Citations

5 Citations in Web of Science ®
6 Citations in Scopus

Search

in Google Scholar™

Services

Actions (login required)

Edit item

Actions (login required)

Edit item