Russian Journal of Earth Sciences
Vol. 6, No. 3, June 2004
Belomorian drusite (coronite) complex, Baltic Shield, Russia: An
example of dispersed intrusive magmatism in early Paleoproterozoic
mobile zones
E. V. Sharkov, I. S. Krassivskaya, and A. V. Chistyakov
Abstract
The Early Paleorpoterozic (2.46-2.36 Ga) Belomorian
drusite (coronite) complex was addressed to for the first time in
discussing the geology, petrology, and genetic conditions of
dispersed intrusive mafite-ultramafite magmatism that developed
in intercratonic mobile zones and granulite belts of Early
Precambrian age. The complex comprises numerous small rootless
synkinematic intrusions that are scattered throughout the
Belomorian Mobile Belt (BMB). The rocks of the complex are
compositionally close to the rocks of large layered intrusions in
the neighboring cratons and compose, together with them, the
Baltic Large Igneous Province (BLIP) of the silicic high-Mg
(boninite-like) series. It is demonstrated that the magma
generation regions were similar beneath the cratons and BMB, but,
in contrast to the situation at the cratons, melt portions
ascending from below the BMB could be accommodated only in small
chambers, whose position was controlled by local heterogeneities
induced by the tectonic flowage of the host rocks. Moreover, these
chambers continuously changed their position, thus precluding the
origin of large bodies and eventually giving rise to dispersed
magmatism. Upon their crystallization, the intrusions were
affected by metamorphic reworking under amphibolite-facies
conditions, so that weakly altered rocks are now preserved only in
the cores of these bodies. The rocks are characterized by the
development of drusite (coronite) textures along the grain
boundaries of primary magmatic minerals.