PETROGRAPHY, MINERAL COMPOSITIONS AND GEO CHEMISTRY OF VOLCANIC-ROCKSOF KARIN RIDGE (THE NORTH PART OF LAIN CHAIN, THE PACIFIC)

Petrological data have been given on the magmatic rocks of Karin subma rine ridge. These rocks include alkaline and subalkaline basalts, hawa iites, and trachytes. Petrographic, geochemical, and mineralogical stu dy of the samples lifted from the marine bottom reveals genetic simila rity of basalts belonging to the different types which are probably un derwent the same processes of low-pressure plagioclase fractionation. Hawaiites, the representatives of a separate geochemical group, were p robably formed as a result of fractionation of basalt melt at the rela tively large depths. The association of Karin Ridge lavas corresponds to the postshield stage of hawaiian volcano type. Some differences in geochemical characteristics of the rocks may be caused by different ch emical and mineral compositions of mantle sources. Bearing this in min d, one should solve the problems of genesis of lavas from Lain Chain a nd Hawaii-Imperial Ridge with care in terms of a unique petrogenetic m odel.