Petrology of the Europe-Largest Burakovka early Paleoproterozoic layered pluton (Southern Karelia, Russia)

Abstract

The Burakovka layered pluton of basic and mafic rocks is the largest intrusive massif in the Baltic Province composed of Si-and Mg-rich boninite-like rocks. The pluton consists of two individual bodies, each having its own internal structure, and contacting each other in their apical parts, known as the Aganozero and Shalozero-Burakovka bodies. Both bodies have a similar rock sequence including five differentiated zones (upward): mafic rocks, pyroxenite, gabbro norite, pigeonite gabbro norite, and magnetite gabbro diorite (the latter found only in the Shalozero-Burakovka Body). Being generally similar to each other, these bodies differ notably in the styles of their cumulate stratigraphy and, to a lesser extent, in composition. The pluton is distinguished by the presence of markers-singular interlayers of high-temperature mafic cumulates emplaced in the sequence of lower-T formations. Their origin is believed to have been associated with the intrusion of fresh magma portions into the crystallizing magma chambers. The same mechanism is believed to have been responsible for a macrorhythmic pattern found in the southeastern portion of the Shalozero-Burakovka intrusive body. Using chemical and mineralogical data, it is shown that the bodies discussed were derived from similar high-Si and high-Mg magmas, except that the Aganozero Body was emplaced 50 million years later than the Shalozero-Burakovka intrusion: the former was dated (Sm-Nd isochron) 2372±22 Ma (ε Nd = −3.22 ± 0.13), and the latter, 2433±28 Ma (ε Nd = −3.14 ± 0.14). It is concluded that the Burakovka Pluton was a long-lived magma center which developed above a local mantle plume, the origin of which had been associated with the activity of a megaplume which had been responsible for the existence of the Baltic province throughout a period of 200 million years.

Electrical conductivity and partial melting of mafic rocks under pressure

“…It is a product of high temperature differentiation and crystallization of a magmatic pluton. This pluton was a long lived magma chamber that developed above a local mantle plume whose origin is associated with the activity of the megaplume responsible for the formation of Baltic shield province (Chistiakov et al, 2002). The age of the pluton is 2.42 to 2.44 Ga estimated from Sm-Nd and U-Pb methods (Koptev-Dvornikov et al, 2000).…”

Layered intrusions as transitional magma chambers above the local plumes of large igneous provinces: Evidence from the Early Paleoproterozoic province of a siliceous highly magnesian rock series in the Baltic Shield

“…It was believed earlier that large layered massifs had originated as a result of the one-act intrusion of huge magma volumes into the crust. However, our detailed geological, petrological, geochemical, and isotope-geochronological studies of the Burakovka and Monchegorsk layered plutons [Chistyakov et al, 2002;Sharkov et al, 2002], as well as of other layered rock complexes in the Kola and Karelia regions, revealed that all of them had been formed by the multiple replenishment of individual portions of fresh magma into the solidifying intrusive chambers. (If?).…”

“…For instance, the Burakovka Complex mentioned above consists of two intrusive bodies of different ages, Aganozero and Shalozero-Burakovka, which contact each other in their tops. The Aganozero body is approximately 50 million years younger than the Burakovka-Shalozero one, the age of the former being 2.37 Ga, and that of the latter, 2.43 Ga. Because these bodies were described in detail earlier [Chistyakov et al, 2002], their description is omitted here.…”

“…At the boundary of 2.2-2.0 Ga the first plumes of a new generation were formed . As follows from the modern views, their origin was associated with the fluid components rising from the liquid core at the base of the silicate mantle [Artyushkov, 1983;Dobretsov et al, 2001]. Thanks to its fluid content the material of these plumes was lighter than that of the previous plumes, and they were able to rise to more moderate depths.…”

Layered Intrusions of Paleoproterozoic Age in the Kola and Karelian Regions

“…The Aganozero Block was then uplifted and eroded [33,34]. According to the other hypthesis, the blocks originally formed as independent chambers with their upper portions touching each other [32,35,36]. There is no well-defined boundary between the Burakov-Shalozero and Aganozero Blocks on a map of magnetic field anomalies (Figure 4b).…”