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 <img src="latex006.gif" alt="pm"> 22 Ma ( <font face="Symbol">e Nd=-3.22<img src="latex006.gif" alt="pm">0.13 ), and the latter, 2433 <img src="latex006.gif" alt="pm"> 28 Ma ( <font face="Symbol">e Nd=-3.14<img src="latex006.gif" alt="pm">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. 28 Ma ( <font face="Symbol">e Nd=-3.14<img src="/get_item_image.asp?id=21531042&img=latex006.gif" align=absmiddle border=0>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.