Y/Ho Ratios in the Late Cenozoic Basalts from the Eastern Tuva, Russia: An ICP‐MS Study with Enhanced Data Quality

Abstract

A set of forty seven Late Cenozoic basaltic rocks from the Eastern Tuva (southern Siberia, Russia) have been studied by ICP‐MS using In as an internal standard. Yttrium and Ho concentrations, determined along with other trace elements, varied systematically from one analytical run to another and covered the entire charge‐and‐radius‐controlled field within the range 24 < Y/Ho < 34, so obscuring any geochemical interpretation. A correction procedure was therefore developed in which the Y/Ho ratios were recalculated using concentrations of these elements determined in international and in‐house reference materials (BHVO‐1, AGV‐1, BIR‐1 and U‐94‐5). Statistical analysis of the recalculated data set revealed two groups of samples not related by their genesis but rather by their respective analytical runs. Fourteen samples originally analysed in five different runs were then re‐measured by the same instrument in peak‐hopping mode using only specific mass peaks (m/z = 89, 115 and 165). All of these samples yielded Y/Ho ratios in a narrow range between 29 and 31, thus illustrating how analytical problems in the determination of Y and Ho by routine ICP‐MS procedures can be overcome. Finally, a mean value of Y/Ho = 30.3 ± 1.1 (1s) was derived for the basaltic rocks of the Eastern Tuva. This is close to the value of 28.8 accepted for chondrites and for ocean island basalts. Despite the uniform Y/Ho ratio, the element concentrations in basaltic rocks from the Eastern Tuva show systematic enrichment in heavy rare earth elements and yttrium from the Miocene to the Quaternary.