Ak. Buiko et al., GEOLOGY AND ISOTOPE DATING OF THE SUMIAN-SARIOLIAN LOWER PROTEROZOIC VOLCANOPLUTONIC COMPLEX IN NORTHERN KARELIYA, THE PAANAJARVI-TSIPRINGASTRUCTURE, Stratigraphy and geological correlation, 3(4), 1995, pp. 348-361
The rocks of the Paanajarvi-Tsipringa structure, northern Kareliya, we
re studied by the U-Pb method using zircons to obtain geochronological
datings for the following: plagiomicrocline granites (2710 +/- 110 Ma
), which intrude the granite-gneisses of the Archean basement and are
covered by a pre-Sumian weathering crust; the acid metavolcanics lying
at the base of the Lower Proterozoic section (2432 +/- 22 Ma); and th
e comagmatic acid volcanics of the Nuorunen granites (2450 +/- 72 Ma).
The petrochemical characteristics of the Sumian-Sariolian basic metav
olcanics of the Paanajarvi-Tsipringa structure show an affinity with v
olcanics of continental rifts. A persistent geochemically bimodal (and
resite-basalt-dacite-rhyolite) association of volcanics can be traced,
in our opinion, at different levels in the pre-Jatulian part of the s
ection of the structure. Therefore, this association, in combination w
ith clastogenic metasedimentary and sedimentary-volcanogenic units and
tilloids, is regarded as a separate Sumian-Sariolian tectonic-facies
complex with group rank. The geological, petrochemical, and geochronol
ogical data described in the paper testify that the Sumian-Sariolian s
edimentary-volcanogenic rocks and the stratified basic and acid intrus
ives were formed in an active tectonic setting during an early stage i
n the development of a continental rife between 2.45 and 2.40 Ga as pa
rt of a single volcanoplutonic complex. The K-Ar method was used to da
te the last endogenic processes of the region as late- and post-Svecof
ennian.