Charity M. Phillips and Dr. Ron A. Harris, Geology and Dr. Steve Nelson, Geology

The Precambrian rocks on Dry Mountain have been previously mapped by Davis (1983) and Witkind (1985) as Farmington Canyon Complex, found in the Wasatch Mountains near Farmington, Utah. Bryant in 1986 said that these rocks were “probably Farmington Canyon Complex” (FCC). This study was conducted to either prove or disprove a correlation between these rocks and the FCC. To do this, the complex itself had to be described by completing a deformation, pressure, temperature and time (D-P-T-t) study on its rocks. It may then be compared to other Precambrian rocks in Utah and Arizona.

The basic map units of the metamorphic complex, here after named the Santaquin Metamorphic Complex, are (1)amphibolite, (2)microcline-quartz pegmatite, (3)syenite, (4) garnet-bi schist, (5) biotite schist, (6) granite, (7) gneiss. These units are similar to the units reported by Bryant 1986. (Table 1) shows the preliminary percentages of each mineral in each rock type. The error bars are currently + 1%, but will decrease as point counts are completed. These data in conjunction with the whole rock geochemistry will help determine the protoliths of each rock type in the complex. It will also help us to understand the nature and extent of metamorphism and the nature of the proposed Proterozoic margin of North America.

These map units define the rock types found in the SC, however, their cross cutting relationships are difficult to understand because of the heavy ground cover and poor preservation of the complex. This made it difficult to collect structural data in the map area. In general, the minerals in the rock types are flattened and show non-rotational strain (Table 1). This is typical also of the rocks in the FCC and Little Willow Complex.

Perhaps the most exciting discovery to date is the gross similarities in mineralogy to and structure (inasmuch as can be discerned) to the Little Willow Complex (Neff, 1962). This lends credence to the idea that the Santaquin complex is linked in time and space to the other metamorphic complexes that are the Archean/Proterozoic margins of North America.

The results of the 40Ar/39Ar dating have not returned yet, but will be available next month. These data may be able to tie the Santaquin Complex to the Farmington Canyon and Little Willow Complexes.

These data taken together will help geologists to reassess the crustal margin of North America and may help to bring to pass greater understanding of the composition and structure of the Wasatch Mountains, Utah.

References

• Neff, Thomas Rodney, 1962, Petrology and Structure of the Little Willow Series, Wasatch Mountains, Utah. Masters, University of Utah.