I. M. Frumkin

Geodynamic regimes in the Late Archean Aldan Shield

Abstract. Dividing the Archean complex of the Aldan Shield into structural and material complexes, and structural and formational zones, as well as matching the chemical composition of the Archean main crystalline shales to basalts led to identify the complex’s geodynamic regimes. Meanwhile, the ratio of such elements as K and Ti, K and P in metabasalts varies in different geodynamic settings. The paper considers the Timpton-Dzheltulin structural and material complex located in the eastern half of the Aldan Shield, mainly the Timpton-Uchur interstream. The Sm-Nd dating method attributed the complex to the Late Archean (2.6–2.8 bn years). There are four structural and formational zones in the complex (from east to west): Uchur, Tyrkandin, Dzheltulin, and Timpton. The geodynamic diagrams K–Ti and K–R, which locate figurative points of the metabasalts chemical analyses in each zone, demonstrate that the zones belong to different geodynamic regimes. Zones of forming Late Archean rocks in the Timpton-Dzheltulin complex establish the following regimes: the Uchur zone relates to a series of small (hundreds of km) island arcs, the Tyrkandin zone — a carbonate-volcanogenic island arc, the Dzheltulin zone — a sedimentary basin on a passive continental margin, the Timpton zone — an intracontinental sedimentary basin developed from continental rifts (aulacogens). All these geodynamic regimes are likely to demonstrate how the mechanism of lithospheric plates tectonics works during the continental crust formation already in the Archean period.

Keywords: Aldan Shield, Late Archean, metabasalts, geodynamic regimes, struc­tural and formational zones, actualism