Geology

Chernorud

Position: Chernorud is located at the southwestern end of the Maloe More.

[view at Chernorud and the camp in the Buguldeyka - Chernorud - Graben]

The landscape around the village has a highland character with mountains of 1600 m altitude. The camp is in a distance of 2 km north from Chernorud, to the northwest it is divided by the Primorskij fault from the Primorskij Range.

[Primorskij fault north of the camp]

The Primorskij fault was created in the Precambrian with the separation of the Siberian Craton from the supercontinent Rhodinia. In the Oligocene, with the beginning of the Baikal rifting, the Primorskij fault was reactivated. The Maloe More is the submerged region of the Olkhon region and is bordered in the north by the Primorskij fault and in the south by the Morskij fault.

Outcrop 1:

[view on the metamorphic sequence near the camp]

The footwall was created by the metamorphosed basic rocks of the early Proterozoic. Those rocks are fine grained granulites with microfolds, whose protolith was a calcium rich tholeitic basalt.

[microfolds in the granulite]

These tholeitic basalts of the granulite facies were related to an ophiolite complex, especially the rare earth elements signature in the granulites were interpreted as a part of an island arc.
To the southeast follows a carbonate sequence and they consists of coarse grained marbles with a calcite origin. Besides the calcite the carbonates contain dolomite and disseminated graphite. In the carbonate sequence lays a quartzite horizon. On the immediate contact they are mylonitinised and skarns occur.
Between the marbles and the amphibolite facies, there is a 2 m wide interlayer. It consists of very fine, strongly cleavaged quartzite called kataklastite. In the hanging wall the amphobilit facies follows with coarse grained, strongly cleaveged amphibolite – biotite gneisses. This gneiss-sequence is folded in the range of some meters. Palaeozoic granitic pegmatite-dykes strike through this sequence. The dykes are younger than the last stage of amphibolite facies metamorphism.
A sequence of migmatites is situated between the amphibolite facies with the gneisses and the south-eastward following granite-gneiss-domes. The migmatites were created under moderate pressure (10 to 12 km depth) by partial melting of the gneisses.

Outcrop 2:

The top is formed by marbles from the carbonate sequence, which was described in the first outcrop. These have a contact to the southeast with an intrusion and they become coarser grained at the contact. Protolith of this intrusion was a gabbro which was converted by metamorphism into a garnet - pyroxenite. The included garnets are pyropes, which were formed in a depth of 40 km, under a pressure of 15 kbar and a temperature of 800°C. The pyroxenes are diopsides.

[outcrop of the pyroxenite with red pyrops]

Pegmatite veins described above in the amphibolite facies can also be found in the Pyroxenite.

[granitic pegmatite-dyke striking through the pyroxenite]

Outcrop Sarma Gate:

[the Sarma Gate at the southern part of the Maloe More]

The Sarma River crosses the Primorskij fault approximately 10 km north of Chernorud. It has created a ca. 200 m wide and 100 m high breakthrough, the Sarma Gate.

[tectonical cross-section of the Primorskij fault near the Sarma Gates from Mats et al. (1999)]

In this valley the WNW-striking Sarma fault traverses the Primorskij fault, which strikes NE/SW and dips under an angle of 60 to 65° to the southeast. The Sarma fault strikes further to the ESE through the Maloe More and forms the Strait of Olkhon Gates between the Olkhon Island and the mainland. In the northern part of the outcrop areas exposed to various degrees of stress are well visible.

[crosscut trough the Primorskij fault with the areas exposed to various degrees of stress of the fault]

The strongly fractioned middle part with a width of ca. 15 m is surrounded by the lower stressed flanks. Research studies on this sinistral strike slip movement show a displacement of 2 km in horizontal and 6 km in vertical direction.

Smelting pits east of Chernoroud camp

During a practical training in 1999, a group of geophysics students discovered magnetic anomalies about 500 m east of Chernoroud base camp. The reason for these anomalies turned out to be an ancient iron smelting facility, probably used by the Kurikan tribe that lived in the area at that time. By Radiocarbon dating on coal found at the bottom of the pits the age of this iron smelters was determined to be 2200 to 2500 years.

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