Field trip - South Brittany

The blue schiste of the Groix Island, South brittany (Day 2).

From the building to the collapse of the Variscan belt

Rocks of drastically constrated geological record are exposed along the coast of South Brittany. Fresh eclogitic blueschists are particularly well preserved on the Groix Island few kilometers apart high-grade rocks in the field of partial melting. It appears therefore possible to study both subduction related processes in the early stages of the Variscan belt building but also processes related to late orogenic processes including partial melting, melt segregation, development of Metamorphic Core Complexes, strain localization and exhuming structures.

This field trip will cover a wide range of South Brittany classical outcrops including the World famous Groix Island high-pressure rock occurence. Back to the mainland, the foccus of the trip will switch to late-orogenic features spectacularly exposed in the Golfe du Morbihan area. Selected outcrops will provide a clear view of the polyphased deformation recorded in mylonite shear zones that separating hangwall units preserving the subduction/collision history or the partailly molten footwall unit. They will also provide the opportinuity to study migmatites and their relationships with melt accummulation at different scales. The last stop will allow examining mylonites of the South Armorican Shear Zone where C/S structures where defined 45 years ago.

Schedule: Thursday 12^th June to Sunday 15^th June 2024

• Day 1 Thursday 12^th June – From Paris at ca. 14:00 to Lorient. Brief presentation of the geological setting. Diner and night at Lorient.
• Day 2 Friday 13^th June – Day spent studying the structural and metamophic record of the high pressure rocks spectacularly exposed on the Groix Island. Boat at ca. 8:00 ; return at ca. 18:00. Diner and night at Lorient.
• Day 3 Saturday 14^th June – Migmatites and partial melting in the core of the Golfe du Morbihan Core Complex at the tip of the Rhuys Peninsula. Study of opposing-sense of shear in mylonites exhuming the Golfe du Morbihan MCC at the SW end of the Quiberon Peninsula. Diner and night at Auray.
• Day 4 Sunday 15^th June – Zooming in the Sarzeau shear zone, a segment of a regional-scale décollement zone. Mylonites of the South Armorican Shear Zone. Return to Orléans after lunch. Arrival expected at ca. 20:00. Brief regional integration.

Organisers:

• Romain Augier: Institut des Sciences de la Terre (ISTO), Université d’Orléans, France, romain.augier@univ-orleans.fr
• Laurent Jolivet: Institut des Sciences de la Terre (ISTeP), Université de Paris-Sorbonnes, France

Interested? Send us a message asap here  empg2025-fieldtrip@sciencesconf.org

Transportation:

• ca. 30-seater people « tourist » bus from Paris and return to Orléans.
• Point of departure: Paris downtown location to determine (likely a main train station or airport)
• Point of Return: Orléans downtown

Participant fees:

• Cost: 1,000-1,300 euros depending of the number of participants
  
• Inluded: Transport from Paris back to Orléans for the entire trip, three nights hotel accommodation, breakfast, lunch and dinner (dinner will alow discover local culinary specialities), field guides.
• Not included: Drinks. Any rail or airfares to and from the collection and drop off-point of the field trip.
• Number of participants: Min/Max: 15 / 25

Weather/Requirements: Weather is usually good in Brttany in June with temperatures around 18-25^oC. Rain is possible and a raincoat may be necessary. Warmer clothes may also be necassary at some exposed sites to the wind (most outcrops). Walking shoes essential.

All sites are easily accessible along well-made gravel paths. Day 2 is fully dedicated to the study of a succesion of outcrops on the Groix Island. Outcrops are located at ca. 3km walk (45 min) from the port following secondary roads.

Accommodation: Hotel accommodation in Lorient and Auray, in single bedded room.

Field guide: A detailed field guide will be provided for each participant to the trip.