The Geodynamic Conditions for the Generation of Adakites and Nb Rich Basalts (NEAB) in Kamchatka

Abstract

An association of adakites and rocks with intraplate geochemical parameters (NEAB) is encountered in Kamchatka, even though the Pacific plate that is plunging under Kamchatka is an old (older than 93Ma) and cold plate. Inspection and comparative analysis of NEAB–adakite associations in Kamchatka and elsewhere at Pacific subduction zones revealed the geodynamic settings that favor heating of oceanic crust until the crust is melted and adakites are generated. Two geodynamic settings are favorable for the process: (1) an initial period of subduction with the tip of the slab melted and (2) generation of subduction windows. Both of these settings have existed in Kamchatka for a short period of time. In eastern Kamchatka, melting affected the tip of the slab in a new subduction zone that was formed during the late Miocene, as the subduction zone was blocked beneath the Sredinnyi Range as this zone jumped into its present location. The NEAB–adakite association in the northern part of the Sredinnyi Range was also formed in the tip of the slab that was part of the near Commander Islands plate. Geological sections were modeled to study conditions for the generation of NEAB–adakite associations in Kamchatka on the background of the ongoing geodynamic evolution.