What is an ophiolite in geology ?
Ophiolite : definition
Ophiolites are portion of ancient ocean floors carried on the continent (we speak of obduction), thanks to collisions between continents or between a continent and an insular arc during the great movements of the tectonic plates.
We speak more of an ophiolitic complex than of an ophiolite, in order to better underline the diversity of these rocky groups made up of rocks from the oceanic crust and the upper mantle.
An ophiolitic complex is schematically made up of a stack of 4 to 5 km thick (sometimes 15 km) of rocks comprising, from bottom to top :
- foliated peridotites (harzburgites) with possible chromite clusters.
- gabbros and peridotites bedded with cumulates (dunites, lherzolites).
- a basaltic complex with at the base, dykes and sills, and at the top of pillow basalts ("pillow lavas"), poured out on the ocean floor, commonly covered with a thin layer of oceanic sediments.
We speak more of an ophiolitic complex than of an ophiolite, in order to better underline the diversity of these rocky groups made up of rocks from the oceanic crust and the upper mantle.
An ophiolitic complex is schematically made up of a stack of 4 to 5 km thick (sometimes 15 km) of rocks comprising, from bottom to top :
- foliated peridotites (harzburgites) with possible chromite clusters.
- gabbros and peridotites bedded with cumulates (dunites, lherzolites).
- a basaltic complex with at the base, dykes and sills, and at the top of pillow basalts ("pillow lavas"), poured out on the ocean floor, commonly covered with a thin layer of oceanic sediments.