The basement complex of the Rockies is one of the oldest parts of the North American continental crust!
The basement complex is an exposure that formed in the Archean some 3.4 billion years ago. The formation is part of the Wyoming Craton that consists of igneous and sedimentary rocks that were burried deeply under the massive mountain range that is the Rockies. The deep burrial of rocks made them consists mainly of highly metamorphosed rocks like that of: mafic amphibolites, quartzilite, tonalitic gneiss, granitic gneiss, ironstone, granulites, and other quartz-rich metamorphosed rocks. It is thought that many of these rocks in the formation are supercrustal, meaning that they formed on the surface before being covered and metamorphosed deep within the crust.
The interesting part about this formation is that it is found only in a small amount of locations in the Rockies. A few of these places are the Gallatin Range, the Beartooth Range, and the Teton Range. In the places that the rocks are found, faulting or heavy erosion has generally occurred. The faulting is believed to be caused by a thick skinned orogeny called the Laramide orogeny some 75 million years ago, with a few exceptions like the Teton range.
In this website, the formations of the mountains and how the basement complex became crustal will be discussed and the rocks that are present in the layer.