Description:

Unconformably overlying the Paleoproterozoic rocks within the Grand Canyon is a relatively undeformed sedimentary rock package known as the Grand Canyon Super Group. This is one of the few Precambrian sedimentary units in the southwestern US and is key to many investigations concerning the 1.4 to 0.6 Ga geological evolution. We have been dating the mafic sills and flows as well as determining single crystal muscovite ages from the sands within the Supergroup deposits. Interestingly, many of the micas are yielding ca. 1.1 Ga ages which are interpreted to record a major alteration event at this time. These data indicate that the Dox Formation, which is part of the Unkar Group of the Supergroup, is at least 1.1 billion years old. Additionally, K-feldspars from the basement metamorphic rocks constrain the Unkar to be younger than 1.2 Ga, thereby bracketing the depositional age of this unit. Studies continue to understand argon systematics of micas in sandstones and to constrain the age of the Chuar Group and the Sixty Mile Formation.