Aldan Shield

Aldan Shield

 

a projection of the Precambrian foundation in the southeastern part of the Siberian Platform, primarily coinciding with the present-day Aldan Plateau.

The most ancient portion of the Aldan Shield is composed of thick (15–20 km) series of crystalline Archean shales more than 2.5 billion years old, breached by granite intrusions and containing bands of ferruginous quartzites and carbonate rocks. The strata are either warped into folds with northwest strike or else form dome-shaped structures with granite-gneiss cores. The northern and eastern portions of the Aldan Shield slope gently under a cover of transgressive sedimentary rocks of the Late Precambrian and the Cambrian; on the west (the Udokanskii and Kodar ranges) the shield is covered by a thick (more than 10 km) series of the Lower Proterozoic, which forms the most ancient platform mantle in Siberia (more than 2.0–2.2 billion years old). The southern rim of the shield rises high along a system of fractures formed at the end of the Mesozoic-Cenozoic, thus forming the Stanovoi Range; within the boundaries of the range are abundant granitoids of the Early Proterozoic (1.6–2.0 billion years old), the Paleozoic, and the Mesozoic.

Precambrian strata of the Aldan Shield contain deposits of iron, copper, and mica (phlogopite). Deposits of gold and piezoquartz are associated with the younger formations. Along the northern boundary of the Stanovoi Range are depressions filled with continental Jurassic deposits, which became sources of coal.