Aldan Shield

ALDAN SHIELD (RU: Алданский щит) is the protrusion of the Precambrian basement at the south-east of the Siberian platform, which is basically coinciding with the modern Aldan plateau and the Stanovoy ridge (of the height of more than 2,400 metres). The shield is covered by the cover of the Upper Proterozoic and Cambrian sediments at the north and east, and is bordered by the deep faults from the Baikal and Paleozoic foldings at the south and west.

The Precambrian formations of the basement form several structural levels, which are reflecting the earliest stages of the evolution of the Earth crust. The most ancient level (more than 3.5 billion years) is represented by the gneisses, schists, marbles and quartzites of the granulite facies of the regional metamorphism. During the formation of the middle structural level (3.5-2.7 billion years), there have formed the sutural downfolds, which are formed by the zonally metamorphosed sedimentary-volcanogenic depositions. There have widely manifested themselves the processes of the granitization, of the regressive metamorphism and magmatism, with which, in particular, there is associated the introduction of the large intrusions of the anorthosites. The upper structural level (2.7-1.5 billion years) is represented by the thick complexes of the clastic or volcanogenic formations, and by the large intrusions of the basic rocks and various granitoids (including the rapakivi granites). There are confined to the Precambrian of the Aldan Shield the deposits of the ores of the iron, copper, micas, apatite, and rare metals. There formed itself at the platform stage of the development the cover of the marine carbonatic sediments, and there introduced themselves the few intrusions of the dolerites, ijolites, carbonatites, kimberlites.

The specific peculiarity of the Aldan Shield is the multiple manifestation of the processes of the activation (Late Paleozoic, Middle Mesozoic, and Cenozoic), with which there are associated the formation of the depressions, and the formation of the various arched blocky structures. The small intrusions of the moderately acidic and alkaline compositions are manifested everywhere. There are associated with the processes of activation the deposits of coal, fluorite, semi-precious (ornamental) stones and gold.