Isotope Composition of Strontium and Origin of Volcanic Rocks of the Raton-Clayton District, Northeastern New Mexico
The isotope composition of strontium was determined for a series of young volcanic rocks from the Raton-Clayton region, northeastern New Mexico. Olivine basalt was the most common rock type, but samples ranged from hauyne-olivine nephelinite to tridymite-bearing hornblende dacite. The 87 Sr/ 86 Sr ratios ranged from 0.7028 to 0.7040, with the exception of three visibly contaminated samples. These low ratios indicate a direct link with an upper-mantle source. The concentrations of SiO 2 , K, Rb, and Sr are reported. The 87 Sr/ 86 Sr ratio does not vary systematically with the concentrations of SiO 2 , Rb, and Sr, and Rb/Sr and K/Rb ratios, further indicating no appreciable crustal contamination, even though the magma had to traverse a considerable thickness of sialic material.