TECTONIC AND GEOCHEMICAL EVOLUTION OF CORDILLERAN OPHIOLITES

Ophiolites show significant variations in their internal structure, geochemical fingerprints and emplacement mechanisms. These differences are controlled by (a) the proximity of their tectonic setting of magmatic construction to plumes or trenches; (b) rates, geometry and nature of spreading; (c) mantle compositions, temperatures and fertility; and, (d) the availability of fluids in these environments. The oceanic crust preserved in ophiolites may form in any tectonic setting during the Wilson cycle evolution of ocean basins from rift-drift and seafloor spreading stages to subduction initiation and terminal closure. An ophiolite is emplaced either from a down-going oceanic lithosphere via subduction-accretion or from the upper plate of a subduction zone through trench–continent collision. Subduction zone tectonics is thus the most important factor in the igneous evolution and emplacement of ophiolites into continental margins. Cordilleran ophiolites include remnants of the Paleozoic and Mesozoic oceanic lithosphere derived from both the upper and down-going plates of various subduction zone systems at different times. Therefore, their melt evolution and emplacement mechanisms were also different. In this talk, we discuss the magmatic and tectonic evolution of some key examples of the Cordilleran ophiolites within the framework of our new global ophiolite classification model and within the framework of the North American Cordilleran tectonics.