The magma produced in the oceanic ridge, while cooling slowly, crystallizes in magmatic rocks.
The challenge for the petrologists on board the JR consists to discover the history of the oceanic crust genesis by the study of minerals in the magmatic rocks.
To resolve the enigma, it is necessary to recall the stages of the minerals crystallization.
For that, we can look at the laws which govern the cooling of the magma and the crystallization of minerals, but the observation of rocks can help too !
Enigma solution and more in attached document : see below