The Ophiolite System of Chenaillet Mount, France
At 2,400 meters above sea level in the French Alps lies the ophiolite system of Chenaillet Mount, an exceptionally well-preserved fragment of Jurassic oceanic lithosphere from the Tethys Ocean. Dating to the Upper Jurassic (~150 Ma), it represents a classic example of a LOT (Lherzolite Ophiolite Type) sequence.
What Are Ophiolites?
Ophiolites are slices of oceanic crust and upper mantle that were emplaced onto continental margins instead of being subducted. The Chenaillet ophiolite was later uplifted during Oligo-Miocene obduction, exposing mantle and crustal rocks normally hidden beneath the seafloor.
The Chenaillet Sequence
The Ophiolite preserves a near-complete cross-section of Jurassic oceanic lithosphere:
- Serpentinite: hydrated and metasomatized upper mantle peridotite forming the basement.
- Gabbro dykes: magmatic intrusions that once fed basaltic volcanism.
- Pillow lavas: extrusive volcanic rocks erupted on the ancient seafloor.
- Radiolarites: siliceous pelagic sediments deposited in deep water.
Together, these lithologies illustrate the internal architecture of an oceanic crust–mantle system.
Geological Significance
- Age: Upper Jurassic (~150 Ma).
- Setting: Tethys Ocean mid-ocean ridge environment.
- Obduction: Oligo-Miocene, during Alpine orogenesis.
- Current elevation: 2,400 m in the Western Alps.
A Natural Laboratory
The Chenaillet ophiolite is a premier field site for structural geology and petrology, visited regularly by university classes, such as third-year Earth Science students from the University of Tours. It provides direct access to processes of mantle metasomatism, magma emplacement, and submarine volcanism—a rare opportunity to study ancient oceanic crust on land.
The Photos credit: Dimitri Le Gaffric Mfzb
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