LAYERED TROCTOLITE-GABBRO-NORITE TSIPRINGA INTRUSION, NORTHERN KARELIA - GEOLOGIC STRUCTURE AND PETROLOGY

The interior structure of the layered Tsipringa intrusion, which is 31 00 m thick, was studied using geological, geophysical, petrological, a nd geochemical methods. Within the vertical section, upper and lower m arginal zones and a layered series were distinguished. Within the laye red series, the following sequence of cumulates was established (from bottom to top): olivine-plagioclase, olivine-plagioclase-augite, plagi oclase-augite-pigeonite, and plagioclase-augite-pigeonite-magnetite. P oor sulfide mineralization is associated with the latter. According to the cumulative parageneses, the layered series was divided into troct olite, olivine gabbro, gabbro-norite, and magnetite gabbro-norite zone s. On the basis of 78 bulk-rock analyses for major elements and 45 ana lyses for trace elements, the weighted average composition of the intr usion was estimated. As a result, it is suggested that the initial mag ma of the intrusion was high-alumina tholeiite. The data obtained were sufficient for computer modeling the infrusion formation using the KO MAGMAT software complex. The Nyudamolaksha massif was found to be a te ctonic block of the Tsipringa intrusion; this conclusion is important for the restoration of the sequence of geological events in the easter n part of the Panayarvinskaya structure.