A Thermodynamic Model of Chemical Remagnetization Based on the Example of the Girvas Paleovolcano in the Onega Structure of the Carelian Craton

Resumo

The Girvas paleovolcano is a structurally complex volcanic complex of Jatulian age. Apparently, it is a shield volcano, which was probably one of the feeder channels of the vast lava field of the western Onega Region within the Girvas volcanic zone. Despite the fact that the Girvas paleovolcano is only partially exposed, the flow structure is well preserved in rocks, which allows one to reconstruct the direction of the lava flow. Within the Girvas paleovolcano, a zone of post-volcanic hydrothermal alterations in volcanic rocks (mainly, tourmalization and silicification in pockets and veins, as well as subsequent epidotization, sulfidization, chloritization and albitization) is distinguished. The secondary alteration zones are confined to fault zones, while their spatial–temporal correlation is still unclear. The paleoreconstruction of the geological structure showed that there were two main stages of the development of the Girvas paleovolcano: (1) pneumatolysis due to magmatic gases released from gabbro–dolerite sills, (2) heating and circulation of exogenous waters with formation of near-ore propylites. Based on the proposed scheme, a thermodynamic model was developed.