VARIATIONS OF COMPOSITIONS OF VOLCANIC ROCKS OF THE KURILE ISLAND ARC IN THE LIGHT OF DATA ON STRONTIUM ISOTOPES

Abstract

The authors present their analysis of new strontium-isotope data on 88 volcanic rock samples from the KIA (Kurile Island Arc) and on 10 from the Ksudach volcano, southern Kamchatka. The strontium-isotope ratios were measured on a Varian MAT-TH5 mass spectrometer to within ±0.0001. Then we corrected the measured ratios to account for stratigraphic data, using a Rb87 decay constant of 1.39·10-11 yr-1 and the Rb87/Sr86 ratio, as well as the concentrations of rubidium and strontium measured on a Philips PW-1400 X-ray spectrometer. No correlation was found between various ratios and the crustal thickness, which is the highest precisely in the northern zone of the arc where it is close to that on Kamchatka. Differences in correlation of potassium and associated large-cation elements with Sr87/Sr86 suggest a different provenance of these elements in the different volcanic rock series of the KIA.