Alpine-type Ultramafic Rocks as Evidence for Ensimatic or Ensialic Environments

Chidester and Cady suggested 1 that Alpine-type ultramafic rocks can be separated into two groups which they consider to be genetically similar but environmentally distinct: (1) plutons intruded into eugeosynclinal metasediments and generated at or near a mantle rift beneath a continental (sialic) crust; and (2) sheet-like masses associated within allochthonous ophiolite complexes, generated at a spreading plate margin beneath ocean (simatic) crust. They pointed out that the ensialic plutons of type (1) are found throughout the Lower Palaeozoic Appalachians northwards towards Newfoundland, whereas the ensimatic type (2) plutons are only found in Newfoundland.