Skip to Main Content
Book Chapter

Cadomian and Variscan metamorphic events in the Léon domain (Armorican Massif, France): P-T data and EMP monazite dating

By
Bernhard Schulz
Bernhard Schulz
1
Institut für Mineralogie, Brennhausgasse 14, D-09596 Freiberg, Germany
Search for other works by this author on:
;
Erwin Krenn
Erwin Krenn
2
Abteilung für Mineralogie der Universität, Hellbrunner Strasse 34, A-5020 Salzburg, Austria
Search for other works by this author on:
;
Fritz Finger
Fritz Finger
2
Abteilung für Mineralogie der Universität, Hellbrunner Strasse 34, A-5020 Salzburg, Austria
Search for other works by this author on:
;
Helene Brätz
Helene Brätz
3
Institut für Mineralogie und Kristallstrukturlehre, Am Hubland, D-97074 Würzburg, Germany
Search for other works by this author on:
;
Reiner Klemd
Reiner Klemd
3
Institut für Mineralogie und Kristallstrukturlehre, Am Hubland, D-97074 Würzburg, Germany
Search for other works by this author on:
Published:
January 01, 2007

The Léon domain adjacent to the Cadomian realm in the North Armorican domain appears to be a displaced crustal block, as its metamorphism and rock types bear a resemblance to the South Armorican domain of the internal Variscan belt. The amphibolite-facies Conquet-Penze Micaschist unit overlies the high-grade Lesneven Gneiss unit in the central part of the Léon. Timing and conditions of the metamorphic evolution have been evaluated. At the base of the Lesneven Gneiss unit, a high-pressure eclogite-facies stage (700 °C at >13 kbar) was followed by a high-temperature event (800 °C at 8 kbar), which is characterized by the crystallization of garnet-cor-dierite assemblages in aluminous paragneisses. Maximal temperatures in the upper parts of the Lesneven Gneiss unit were 630 °C at 6 kbar. Zoned garnet in assemblages with staurolite recorded prograde P-T paths from 490–610 °C at 5–8 kbar in the upper and at 6–9 kbar in the lower parts of the Conquet-Penze Micaschist unit. Garnet Y, heavy rare earth elements, and Li are low in high-grade gneisses and display strong zonations in the micaschists. A younger population of monazite with a broad range of Y contents displays Th-U-Pb ages between 340 and 300 Ma. It crystallized subsequent to formation of foliations S1-S2 and Variscan peak metamorphic assemblages. In contrast, an older population of Cadomian monazite at 552–517 Ma is uniformly rich in Y, suggesting an earlier crystallization than garnet, however, at elevated temperatures. The findings do not support a South Armorican provenance of the Léon domain. The Léon units appear as part of a Cadomian crust at the northern margin of the former Armorican microplate. During a Variscan collision, this crust was strongly overprinted by underthrusting toward the southeast or east beneath the Central Armorican domain and by later uplift accompanied by Late Carboniferous dextral shear tectonics. The features are typical of the Variscan Saxo-Thuringian zone, which faced the Rheic Ocean to the north.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

The Evolution of the Rheic Ocean: From Avalonian-Cadomian Active Margin to Alleghenian-Variscan Collision

Ulf Linnemann
Ulf Linnemann
Search for other works by this author on:
;
R. Damian Nance
R. Damian Nance
Search for other works by this author on:
;
Petr Kraft
Petr Kraft
Search for other works by this author on:
;
Gernold Zulauf
Gernold Zulauf
Search for other works by this author on:
Geological Society of America
Volume
423
ISBN print:
9780813724232
Publication date:
January 01, 2007

References

Related

Citing Books via

Related Articles
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal