Trace element and Sr-Nd-Pb isotopic constraints on a three-component model of Kamchatka arc petrogenesis

The Kamchatka are (Russia) is located in the northwestern Pacific Ocean and is divided into three segments by major sub-latitudinal fault zones (crustal discontinuities). The southern (SS) and central (CS) segments are associated with the subduction of old Pacific lithosphere, whereas the northern, inactive segment (NS) was formed during westward subduction of young (<15 Ma) Komandorsky Basin oceanic crust. Further segmentation of the are is outlined by the development of the Central Kamchatka Depression (CKD) intra-are rift, which is oriented parallel to the are and is splitting the CS into the active Eastern Volcanic Front (EVF) and the largely inactive, rear-are Sredinny Range. The NS volcanics (15-5 Ma) include calc-alkaline lavas, shoshonites, adakites, and Nb-enriched are basalts. Isotopically all magma types share high Nd-143/Nd-144 ratios of 0.512976-0.513173 coupled with variable Sr-87/Sr-86 (0.702610-0.70356). NS lavas plot within or slightly above the Pacific MORB field on the Pb isotopic diagrams. The EVF volcanoes have more radiogenic Nd-143/Nd-144 (0.51282-0.513139) and Pb-208/Pb-204 (38.011-38.1310) than the NS lavas. CKD lavas display MORB-like Nd isotope ratios at slightly elevate. Sr-87/Sr-86 values accompanied by a slightly less radiogenic Pb composition. Kamchatka lavas are thought to be derived from a MORB-like depleted source modified by slab-derived siliceous melts (adakites) and fluids (NS), or fluids alone (CS and SS). The NS and EVF lavas may have been contaminated by small fractions of a sedimentary component that isotopically resembles North Pacific sediment. Petrogenesis in the Kamchatka are is best explained by a three-component model with depleted mantle wedge component modified by two slab components. Slab-derived hydrous melts produced incompatible element characteristics associated with northern segment lavas, while hydrous slab fluids caused melting in the depleted mantle below the southern and central segments of the Kamchatka are. Trace element characteristics of Kamchatka lavas appear to be controlled by slab fluids or melts, while radiogenic isotope ratios which are uniform throughout the are reflect depleted composition of sub-are mantle wedge. Copyright (C) 1997 Elsevier Science Ltd.