Monzonitoid association of the Kavalerovo ore district (Primorye): geochronology and some genetic problems

This paper is dedicated to the isotope-geochronological study of the rocks that compose two large intrusions and a separate group of minor intrusions in the western part of the Kavalerovo ore district. In most publications, these rocks are considered as monzonitic or trachyandesite-monzonitic association. On the basis of the amphibole and biotite K-Ar ages and the Rb-Sr whole-rock and mineral datings, the studied association was formed within the interval of 113–98 Ma. A wider interval of 115–95 Ma was obtained with allowance for other isotope data, including those on the rocks of the volcanic facies. This is consistent with the concepts that the studied association belongs to a single magmatic complex. No significant and systematic age differences have been established between the compositionally similar rocks from the different massifs. In compliance with the scheme of the geodynamic evolution of the region, the chambers of latitic melts of the volcanic and most intrusive rocks of the complex were formed prior to the initiation of the Sikhote-Alin subduction volcanic belt. The initial stage of the formation of the latter is presumably constrained by the data on the biotite from the quartz diorites from the Uglovaya VTS (90 Ma), which is located in the central part of the region, and on the late amphibole from the monzonitoids of its western part (91–92 Ma). The geochemical differences between rocks from the different intrusive bodies could be caused by the specifics of the melt evolution in the intermediate or crystallization chambers.