COMPARISON OF PERIDOTITE NODULES FROM LANZAROTE, CANARY ISLANDS, AND THE SAN CARLOS INDIAN RESERVATION, ARIZONA

Olivine bearing peridotite nodules from Lanzarote, Canary Islands, and the San Carlos Indian Reservation, Arizona, were examined using EDS (error 0.1%). Both peridotite nodules were derived from lower crustal/upper mantle sources; important correlations and differences were noted in olivine chemistry between the two locations. The magnesium number of olivine examined from Lanzarote was 91, San Carlos olivine yielded a mean magnesium number of 90. The range in magnesium numbers from Lanzarote olivine was Mg# 84-95, San Carlos magnesium numbers clustered between Mg#86-92. The array of magnesium numbers for Lanzarote and San Carlos exhibited a statistically significant difference at the 10% significance level; the difference may be due to the nodules having experienced differing degrees of fractionation due to melting. Trace concentrations of titanium and chromium were detected in both the San Carlos and Lanzarote nodules. Zinc and cobalt also appeared in trace concentrations, within Lanzarote nodules. Nickel was detected in nodules from Lanzarote and San Carlos, but was present in higher concentrations within the San Carlos nodules. Chromium rich mineral phases (magnesian ferro chromites; spinel group) were identified in the mantle xenoliths from Lanzarote. Based on the relative proportions of olivine, orthopyroxene, and clinopyroxene, within the peridotite nodules, both the Lanzarote and San Carlos xenoliths can be classified as harzburgite. The chemical differences between the peridotite nodules from Lanzarote and the San Carlos Indian Reservation could be attributed to differences in melt evolution, magmatic emplacement history, and tectonic setting.