Chapter 10 Olyokma terrain

Publisher Summary The Olyokma granite–greenstone terrain is located in the west of the Aldan Shield. Its southern boundary is marked by the Stanovoy deep fault zone, which separates it from the Dzhugdzhur–Stanovoy fold belt. Its western boundary is the Baikal fold belt. The eastern contact of the Olyokma granite–greenstone terrain with the Aldan granulitegneiss terrain is a complex system of imbricate thrusts along which rocks of the Aldan megacomplex are emplaced above the Olyokma complex. As a result, the blocks and lenses of granulites belonging to the Aldan megacomplex occur in and adjacent to the collision zone within the Olyokma terrain. The Olyokma granite–greenstone terrain has three constituent structural complexes: Kurulta and Olyokma (Lower Archaean) and Olondo–Buorsalaa (Upper Archaean). Most of the terrain is occupied by granites showing a variety of ages, among which are linear belts and downwarps containing supracrustal rocks belonging to the Olondo–Buorsalaa complex and blocks of retrograde granulites of the Kurulta complex. The Olyokma complex consists mainly of granite–gneiss and biotite–plagioclase gneiss, compositionally equivalent to tonalite. It is cut by granites containing supracrustal relicts–biotite and amphibole plagioclase gneiss, amphibolite and amphiboleplagioclase schist, and rare lenses of quartz gneiss and garnet gneiss. The Olyokma complex underwent high-temperature amphibolite facies metamorphism and granitization. Two such metamorphic episodes are recorded, the second being related to the Late Archaean development of the Olyokma complex, which is the basement to the Late Archaean formations that make up the greenstone belts. This chapter presents information on ore deposits and occurrences in the Olyokma granite–greenstone terrain.