This contact is characterized by a high-grade orthoamphibole-bearing gneiss. This gneiss is interpreted to be a highly metamorphosed and sheared paleosol and associated regolith that originally consisted of several meters of weathered rock debris eroded from older plutonic rocks. On the basis of rock type, type of intrusion, chemistry, and age of rocks, two main groups of younger Early Paleoproterozoic igneous intrusive (plutonic) rocks have been distinguished within the Vishnu Basement Rocks. One group, which dates between 1.74 and 1.71 billion years ago, consists of large plutons such as the Zoroaster pluton, the Ruby pluton, and the Diamond Creek pluton. There is no noticeable baking and metamorphism of the country rock adjacent to them. Because of this, they were likely shallowly emplaced beneath the volcanic arc in which the metavolcanics and metasediments of the Granite Gorge Metamorphic Suite accumulated. In addition, these intrusive rocks have undergone all the deformation that has also affected their adjacent country rock. This further indicates that they are just slightly younger than the metavolcanic and metasedimentary rocks they intrude. This and their calc-alkaline granitic composition, which is similar to plutons forming in modern 'subduction zone related' volcanic arcs, indicates that they are remnants of early volcanic arc systems associated with Early Paleoproterozoic subduction zones. Comparable volcanic arc systems, which are associated with subduction zones, are active today in the Aleutian Islands and Indonesia (e.g., Sumatra and Java). The second group of younger Early Paleoproterozoic igneous intrusive rocks is quite different in style, age, and significance. These igneous intrusive rocks consist of granitic and pegmatitic dike swarms, i.e. the Cottonwood, Cremation, Sapphire, and Garnet pegmatite complexes, that cut the Granite Gorge Metamorphic Suite from east to west. They formed as granite magma, and related pegmatite fluids, filled crack-systems as magma migrated through the crust. The chemical composition of the granite and pegmatite comprising these dike swarms is indicative of the partial melting of the metasedimetary and metavolcanic rocks of the Granite Gorge Metamorphic Suite both in-place and at greater depth, in the crust. These dikes exhibit a wide variability in the degree that they have been deformed from straight and nearly undeformed – to varying degrees of folding, stretching, and shearing.