The oldest rocks in Arizona are schists and gneiss that are believed to represent meta-volcanics (metamorphosed volcanic rock) and meta-sediments (metamorphosed sedimentary rock) that accumulated in an ancient ocean basin. Granites and granodiorites dating to around 1700 Ma cut these metamorphic rocks and the entire sequence is capped by an erosional unconformity. Collectively, this period of metamorphism, felsic magmatism, and erosion is called the Yavapai/Ivanpah Orogeny .
The Yavapai/Ivanpah unconformity is overlain by conglomeratic sandstones and shales which were subsequently metamorphosed in southeastern Arizona. These meta-sediments are intruded by 1500 to 1600 Ma granodiorite. This succession is again capped by an unconformity. Together, the intrusions, meta-sediments and the unconformity define the Mazatzal Orogeny.
Following the Mazatzal Orogeny, deposition of a series of sedimentary rocks occurred which are preserved in the Grand Canyon area, Tonto Basin, and Salt River area, as well as in some parts of southeastern Arizona. The sediments that accumulated in the Grand Canyon area are referred to as the Grand Canyon Supergroup and include a period of mafic lava flows and sills dated at 1100 Ma. The supergroup is cut by normal faults and was tilted slightly to the northeast during an extensional tectonic event that is called the "Grand Canyon Disturbance". The supergroup is capped by an erosional unconformity, called the "Great Unconformity", that has been recognized state-wide and represents 500 Ma of missing Earth history.
Paleogeography
courtesy of Ron Blakey
Paleogeographic reconstruction of the southwestern United States. Note the position of Arizona in relation to various Proterozoic tectonic terranes. This reconstructions depicts sequential terrane accretion from the southeast to the North American craton. An alternative hypothesis suggests terrane assembly of the Mojave, Yavapai and Mazatzal Provinces and then later addition to North America.
courtesy of Ron Blakey
The Colorado River as it carves through
the lower Granite Gorge in the Grand Canyon. The dark rock is the
Vishnu Schist with lighter bands of Zoraster Granite (left foreground).
Both rocks are U-Pb dated around 1.710 to 1.720 Ga and are considered contemporaneous
with the Yavapai/Ivanpah Orogeny. The Vishnu Schist represents metamorphosed
sea floor sediments that may date back to 2.0 GA and contains meta-volcanics
and meta-sediments such as fine marble which appear to display algal matting.