CU ISOTOPE COMPOSITIONS OF OLIVINE FROM MANTLE XENOLITHS IN SAN CARLOS, ARIZONA

Sitting atop the Peridot Mesa, the Tertiary/Quaternary aged basaltic flow of San Carlos is known for its abundance of peridot. The basalt erupted from the cinder cone in the southernmost corner of the mesa and spread out almost two miles to the north and east. The local Native Americans of San Carlos collect and sell much of the gem-quality peridot to buyers in Globe, Arizona. The mine remains open today. The San Carlos peridot mine is well studied because it is an ideal location for the study of mantle geochemistry. For this study, six basalt samples from the mine were collected. Using the ISOPROBE multicollector ICP-MS at the University of Arizona, this study analyzed Cu isotope compositions of San Carlos olivine. The range of δ⁶⁵Cu (per mil) of the samples was found to be -0.21 to 0.81. Studying the Cu isotope composition of igneous rocks offers insight into the isotopic composition of the mantle itself. Previous studies have found that minerals in magmatic environments have a δ⁶⁵Cu range of -1.5 to 2.5. However, the ranges of the isotope values often exhibit a wide variation. Based on other studies, the findings of this analysis are well within the expected range of isotopic values.