Maurin's careers & pillow lavas

Or how to walk, at the top of the mountain, on the bottom of an ocean that is 160 million years old!

A link in the history of the Alps ...

The single continent, Pangea, is no more!

Strongly stretched and fractured, the torn continental crust gives way to new rocks, those of an oceanic crust. Thus open the oceans.

This opening takes place from large fractures, called mid-ocean ripples, organized in a series of sections whose “date of birth” is not the same everywhere. Thus, the Alpine Ocean (Alpine Tethys) opens around -170 million years in the Middle Jurassic, while its “big sister”, the Tethys has existed since the beginning of the Jurassic.

After opening, it is oceanic expansion. Tectonic forces continue to stretch the earth's crust, the oceans are expanding. New rocks form at the level of the wrinkles with effusions of lava.

The Alps offer some fine examples of rocks from the ancient ocean floor of the Alpine Tethys. In Haute-Ubaye, you can find Maurin's “marbles” and basalts from pillow lavas.

The rocks, from which the Maurin marbles originate, were formed and crystallized at great depths. The earth's mantle from which they originate is located from 5 km below ocean ridges and 50 km or more below continents. These rocks, peridotites, have undergone a series of transformations:

  • in the first place by deterioration due to chemical reactions in contact with sea water (serpentinization);
  • then by metamorphism, in connection with the effects of pressure and temperature, during the stages of subduction (immersion of one plate under another), chipping and collision.

These serpentinized peridotites were intensely crushed by the tectonics and lost their grainy appearance. Their color is dark green veined with white. The many crushing planes, which weaken them, are naturally polished and silky like snakeskin.

About 160 million years ago, basalts poured out from the fractures of the mid-ocean ridge. The very hot lava, immediately cooled by water from the ocean floor, formed a kind of pillows or bolsters. From their particular form comes the name of pillow lavas (pillow: pillow in English).

Initially deposited on low slopes, these basaltic lavas today form vertical walls which dominate the slopes and the torrent of the Ubaye.

Learn More….

Born a little over 160 million years ago, the Alpine Ocean (or Alpine Tethys) widened until around 90 million years ago. The relative movement of the plates was then reversed: Apulia and Eurasia came closer. Caught in a vice, the ocean floor first plunged (subduction) under the Apulian plate ;and scales of this floor, torn from the plunging plate, were carried away in the zone of confrontation of the two continents (collision). The alpine chain thus has oceanic rocks in its highest massifs.

… In connection with 22 other geosites

As the Alpine Ocean takes place and expands in southern Eurasia, the Alpes de Haute-Provence lie on the continental crust where thick black marly formations settle to the bottom of the sea. These marls are called "The Black Lands".

Above them accumulate:

  • the limestone deposits of the Upper Jurassic, illustrated by the Rocher de la Baume de Sisteron and the limestones of the Gorges du Verdon;
  •  then the limestones and marl-limestones of the lower Cretaceous which one can discover in the lake of Castillon and in the Gorges of Oppedette.

What we can decipher from the current landscape

The lava did not flow on steep slopes. Nevertheless, pillow lavas worn at altitude, then tilted, today form real vertical walls on the left bank of Chabrières, in Ubaye. Many pillow lavas can be seen all along the path and at the bottom of the torrent.

These rocks took place around 160 million years ago at the bottom of the Alpine Ocean, under more than 2500 meters of water. Today, some are visible at more than 2000 meters above sea level. They made a vertical journey of several thousand meters, as well as a horizontal journey of a few thousand kilometers by bedload.

A little anecdote?

On the surface of the lava cushions, small white circles giving the rock a pustular appearance can be observed. This evocative aspect has earned them the name variolite. Strangely, many virtues are attributed to this rock: protection against snakes, against lightning ...

Why not install them, outdoors, in the four corners of your home?