METAMORPHIC STRATIGRAPHY OF FOOTWALL ROCKS IN THE NORTHERN SNAKE RANGE METAMORPHIC CORE COMPLEX, NEVADA

The Southern Snake Range, Northern Snake Range (NSR), and the Deep Creek Range in eastern Nevada and Western Utah constitute on of the longest extensional axes within the Basin and Range province. This series of mountain ranges is comprised of a group of north-south trending metamorphic core complexes displaying up to 300% extension. In the NSR, metamorphic rocks exposed in a 1000 m thick section of footwall consist of quartzite, quartzite mylonites, and pelitic schists. All of these rocks display the effects of intense dextral, down to the east shearing. These rocks are thought to have Precambrian sedimentary protoliths, but record Cenozoic and Mesozoic metamorphism. The latest period of deformation and metamorphism was associated with Tertiary extension and core complex development. In the interior of the core complex, these rock are well stratified and nearly horizontal. Detailed measured sections resulted in a composite stratigraphic column that documents lithologic and metamorphic variations at a finer scale than previously reported. Quartzite and schists are interlayered at variable scales. At the base of the section, the schists contain a primary amphibolite facies mineral assemblage consisting of Grt+St+Bt+Ms+Pl+Qtz, or Grt+Bt+Ms+Bt+Pl+Qtz. With decreasing depth, staurolite disappears from all units, followed by the disappearance of garnet. Near the top of the section, pelitic units display a primary greenschist facies assemblage. In the lower half of the section, the primary amphibolite facies assemblage is overprinted by a greenschist facies (Ms+Chl) assemblage. This overprint is not evenly distributed. Within a single pelitic unit, the greenschist facies overprint becomes more intense towards the top of the unit, and is most intense near the contact with an overlying quartzite unit. This distribution suggests fluid channelization during uplift of the footwall.