Pk. Skuf'In et al., Lamprophyres in the Early Proterozoic volcanic complex of the Pechenga structure, Kola peninsula, PETROLOGY, 7(3), 1999, pp. 289-303
The upper portion of the Early Proterozoic sequence of the Pechenga structu
re was detected to contain a series of subvolcanic lamprophyre bodies. Thes
e are sills of meso- and melanocratic holocrystalline massive biotite (kers
antite) and amphibole (odinite) rocks and explosion breccias of camptonitic
composition. The U-Pb isotopic age of the micaceous lamprophyres (kersanti
tes) is 1711 +/- 12 Ma and corresponds to the Rb-Sr age of lamproites from
the Por' ya Bay area(1710 +/- 10 Ma). The lamprophyres affiliate with the s
ubvolcanic rock association of the final evolutionary stages of the Pecheng
a structure. This association also includes trachydacite, Na-trachydacite,
high-Ti Na-trachyte, and ultrasilicic ferrorhyolite. An analogous triple ro
ck assemblage (lamprophyre-trachyte-ultrasilicic ferrorhyolite) is also typ
ical of Early Proterozoic structures in eastern Finland, a fact that led us
to suggest that rock associations of this type are specific of the orogeni
c and postorogenic stages in the evolution of Early Proterozoic foldbelts i
n the Baltic Shield.