Northern Snake Range metamorphic core complex

The rest of the pre-Cenozoic sequence, from the uppermost Lower Cambrian to the Permo-Triassic, consists mainly of limestones and dolomites with subsidiary amounts of interbedded shale, siltstone and sandstone.

[4] The overall geometry of the Northern Snake range metamorphic core complex is a gentle dome, elongated south to north.

In the west the strain approximates to pure shear (combined vertical thinning and horizontal extension) with units retatining about 40% of their original thickness.

[6] Other estimates come from the amount of ductile strain measured within the rocks of the lower plate, particularly the observed thinning of the Prospect Mountain Quartzite.

In contrast, given the total known stratigraphic thickness, such a degree of burial would require the presence of major thrust sheets repeating this stratigraphy that have since been eroded, for which there is currently no evidence, either from the northern Snake Range itself or from adjacent parts of eastern Nevada.

The first swarm was emplaced before or possibly during ductile extension and samples from three dikes give an age in the range 37.5–37.8 Ma (million years ago).

Samples from a single dyke that was intruded after ductile strain and shows no signs of subsequent deformation give an age of 22.49 Ma.

Combined with observed field relationships and cooling histories for the lower plate, this suggest that extension started in the late Eocene, continuing into the middle Miocene.