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| Titel |
Petrology and ⁴⁰Ar/³⁹Ar-chronology of metavolcanic rocks from the Northern Phyllite Zone (Southern Hunsrück and Taunus Mountains, Germany): insights into a late Variscan ductile shear zone. |
| VerfasserIn |
Matthias Fladt, Christian Soder, Winfried Schwarz, Mario Trieloff |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151474
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| Publikation (Nr.) |
 EGU/EGU2017-16062.pdf |
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| Zusammenfassung |
| The Northern Phyllite Zone (NPZ) is a low-grade mylonitic shear zone between the high-grade rocks of the Mid-German Crystalline Zone and the very low-grade rocks of the Rhenohercynian Zone of the Variscan orogen. The NPZ comprises low-grade metasedimentary and metavolcanic rocks. Basaltic, intermediate and rhyolitic metavolcanics from the Soonwald and the Southern Taunus Mountains show the following paragenesis: actinolite + chlorite + epidote + albite + phengite + titanite + quartz ± calcite ± stilpnomelane ± pumpellyite ± aegirine-augite; blue amphibole (winchite) + chlorite + phengite + stilpnomelane + albite + titanite + quartz + magnetite ± epidote ± hematite; quartz + albite + K-feldspar + phengite + chlorite + titanite ± stilpnomelane ± ilmenite ± magnetite ± hematite. Occasionally, relict magmatic phases are present. The foliation strikes SW–NE and dips 60-70° to the NW. Stretching lineations are subhorizontal. P–T-estimations were done on the basis of equilibrium assemblage modelling yielding peak metamorphic conditions of 300–350 °C and 6–6.5 kbar. Thus, burial depths of 20–22 km and a low geothermal gradient of 15–16 °C/km are inferred.
⁴⁰Ar/³⁹Ar-dating of stepwise heated phengite separates (100–200 µm) results in plateau ages of ∼320 Ma. Two of the examined separates show argon diffusive loss ⁴⁰Ar/³⁹Ar-age spectra, which yield a period of argon loss between ~145 and 130 Ma. Diffusive argon loss is possibly related to widespread Jurassic-Cretaceous hydrothermal activity in SW Germany.
We interpret the Northern Phyllite Zone as a sinistral shear zone documenting prolonged oblique convergence following the peak of the Variscan orogeny between 340–330 Ma until ~320 Ma. |
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