Geochemistry of late cretaceous-paleogene potassic rocks of the early evolutionary stage in the Kamchatka island arc

The first data are reported on the isotopic and trace-element composition o f potassic igneous rocks from central Kamchatka. The composition of mineral s and distribution of incompatible elements in volcanic (shoshonitic and po tassic alkaline series) and intrusive (including differentiated gabbro-syen ite and trachyba-salt-latite pairs) rocks testify to the comagmatic charact er of members of the volcano-plutonic associations and the derivation of th eir parental melts from a single primary magma source. The low HFSE concent rations of the rocks, as compared with those of MORE, and their low Sr and high Nd isotopic ratios suggest that the mantle source was similar to MORE. The high LILE concentrations of the rocks point to the involvement of a fl uid component, which was introduced into the melts during their primary mag ma evolution.