A 3RD VOLCANIC CHAIN IN KAMCHATKA - THERMAL ANOMALY AT TRANSFORM CONVERGENCE PLATE BOUNDARY

The Kamchatka volcanic arc, which is located at the northern edge of t he Kurile arc, consists of three volcanic chains, all parallel to the trench axis. In contrast, most subduction zones have only two subparal lel volcanic chains. The third chain in Kamchatka, which is farthest f rom the trench, is characterized by the occurrence of voluminous plate au lavas; volcanoes in the two chains closer to the trench are stratov olcanoes typical in arc magmatism. The third chain magmatism is also u nusual in that lavas show concentrations of incompatible elements inte rmediate between those in the two trenchward chains. Both the unusual occurrence of the third volcanic chain and the unusual lava chemistry could be caused by partial melting of K-amphibole bearing periodotites in the downdragged hydrous layer at the base of the mantle wedge unde r anomalously high-temperature conditions associated with the characte ristic tectonic setting of transform/convergence transition in the reg ion.