STRATIGRAPHY AND VOLCANISM IN THE EARLY PROTEROZOIC PECHENGA STRUCTURE (KOLA-PENINSULA)

The Pechenga structure comprising sequences, which serve as the refere nce for the northeastern Baltic Shield, includes the northern and sout hern structural zones. Both zones are composed of sedimentary-volcanog enic rocks of the Karelian Complex (the Lower Karelian Eratem) metamor phozed under conditions of prehnite to pumpellyite facies. Based on pu blished and new original data, the following formations are proposed t o be defined in the northern zone (from the base upward): the Televi, Majarvi, Kuvernerinjoki, Pirttijarvi, Orshoaijvi, Luchlompolo, Zapolya rnyi, Zhdanov, Lammas, Matert, and Suppvaara formations correlative to the Sariolian, Jatulian, and Ludicovian (Ludian) of Karelia. In the s outhern zone, the Karelian complex is divided into the Kallojaur, Brag ino, and Mennel' formations and Kaplya and Kasesjoki rock associations , which are referred to the Kalevian. The paleovolcanologic, formation al, and geochemical analyses enabled the recognition of the basaltic a ndesite, trachybasalt, tholeiite, ferropicrite, picrite-basalt-andesit e, and andesite-dacite-rhyolite volcanogenic formations, all formed du ring six megacycles of magmatism in the interval of 2350-1850 Ma. Meta morphism culminated at 1750-1700 Ma. The structural patterns of the se quences and geochemical and isotopic data agree with the model of intr acontinental riftogenesis in the Pechenga-Varzuga belt, which experien ced a complete cycle of development during the Early Proterozoic.