Petrology of the Early Paleoproterozoic Burakovsky complex,southern Karelia

The Early Paleoproterozoic Burakovsky complex contains Europe’s largest layered mafic-ultramafic pluton and giant Avdeevo gabbronorite dike. The pluton consists of two independent bodies of different age (the Aganozero and Shalozero-Burakovsky bodies), each having its own internal structure and contacting each other in their apical parts. Both bodies have a similar rock sequence including five differentiated zones (from bottom upward, based on the predominant cumulus assemblages): ultrabasic, pyroxenite, gabbronorite, pigeonite gabbronorite, and magnetite gabbronorite-diorite. Being generally similar to each other owing to a common differentiation trend of similar melts, these bodies differ notably in the character of their cumulus stratigraphy and, to a lesser extent, in mineral and geochemical composition. The pluton is distinguished by the presence of marker horizons—singular interlayers of high-temperature mafic cumulates emplaced in the sequence of lower-temperature gabbroid. Their origin is believed to have been associated with the influxes of fresh magma portions into the crystallizing magma chambers. Based on petrological, geochemical, and mineralogical data, the Aganozero and Shalozero-Burakovsky bodies, as well as additional intrusive phases, were derived from the compositionally similar but not identical melts of siliceous high-Mg (boninite like) series. The Avdeevo dike (2436 ± 46 Ma at ?_Nd(T) = ?1.5) extends along the southeastern contact of the Shalozero-Burakovsky body and was formed almost simultaneously with it. The dike is made up of pigeonite gabbronorites, which are almost identical to the rocks of the Pigeonite gabbronorite zone of the Burakovsky pluton in geochemistry and mineral composition. It was concluded that the Burakovsky Complex was a long-lived igneous center, whose origin was related to the activity of an Early Paleoproterozoic mantle superplume.