Tectonic pozition and metamorphism of rocks in the Chara-Tokko iron ore region

Abstract

The article provides the material on the geological structure, structures, tectonic position and metamorphism of rocks developed within the Chara-Tokko iron ore region, identified in the western part of the Aldan-Stanovoy shield. Most researchers agree that the Chara-Tokko iron ore region is confined to a trough that formed on the site of one of the long-lived deep fault zones of meridional strike. This zone received various names (Derbegelakhskaya, Charo-Imalykskaya, Tarynakhskaya, etc.). Currently, the fault zone and the trough trough are called Chara-Tokko after the name of the iron ore region. It is assumed that to the south, the iron ore deposits of the Chara group (Sulumatskoye, Nizhne-Sakukanskoye) are confined to the continuation of this trough trough. The nature and conditions of metamorphism can be judged by the mineral associations of some rocks of the sedimentary productive complex, such as metapelites or ferruginous quartzites. It is noted that metapelites, now represented by gneisses and mica schists with high-alumina minerals, are especially important for this. Based on their characteristic mineral associations, three temperature facies were identified in the Chara-Tokko iron ore region: staurolite, biotite-muscovite gneiss and orthoclase-biotite-sillimanite. The internal structure of the Chara-Tokko iron ore field were not sufficiently studied and is extremely controversial. The boundaries of metamorphic zones are mainly parallel to the general strike of the structures and only in rare cases intersect the stripes of productive sedimentary units. After the temperature maximum of progressive metamorphism and past granitization, a significant period of cooling began, which was heated and in some places impregnated with layer-by-layer injections of migmatites and bodies of granites of the Borsala sequence. Gradual cooling was accompanied by regressive metamorphism with the formation of low-temperature minerals at the expense of higher-temperature ones. It is believed that ferruginous quartzites of the western part of the Aldan-Stanovoi shield are part of sedimentary-volcanogenic rock complexes that fill suture troughs or troughs confined to long-lived deep fault zones. The processes of regressive metamorphism manifested themselves most intensively in tectonic zones. The nature of the processes depends on the composition of the host rocks. The regressive phenomena of continuous chloritization and epidotization are associated with the local movement of components, mainly calcium.