A model for the evolution of the Grampian tract in the early Caledonides and Appalachians

Abstract

Analogy with models developed for Newfoundland suggests that the ophiolites of the Grampian tract were emplaced as hot, young oceanic crust. The conversion of a mid-ocean ridge-fracture zone system into a subduction zone resulted in the northward emplacement of a giant ophiolite nappe onto the continental margin in the early Ordovician. This obduction occurred long before the collision between the Laurentian and Baltic Shields. The general features of this model may be characteristic of orogens resulting from oceanic closure.