YAKUTIAN KIMBERLITE PROVINCE: POSITION IN THE STRUCTURE OF THE SIBERIAN CRATON AND COMPOSITION OF THE UPPER AND LOWER CRUST

Abstract

The Siberian craton has been tectonically regionalized. Comparison of isotopic ages shows that this craton formed in the late Paleoproterozoic (2.0-1.8 Ga) after Archean microcontinents had collided and amalgamated. The microcontinents formed 3.5, 3.1, and 2.5 Ga at the cost of the sialic matter released from the mantle. On collision they coincided along the sutures and transformed into tectonic blocks (granite-gneiss and granite-greenstone terranes). High-temperature metamorphism of terranes and granite formation in zones of collision proceeded simultaneously, which is a necessary consequence of thermal relaxation in the thickened crust of the collision prism. The first-rank structures are superterranes: Tunguska, Aldan, Stanovoy, Anabar, and Olenek tectonic provinces. The Yakutian kimberlite province lies within the Anabar and Olenek superterranes. The core of the wells drilled on the closed area of the Yakutian kimberlite province contains granulite complexes of the Magan and Daldyn terranes and granite-greenstone complexes of the Markha terrane (A nabar superterrane). Also, it demonstrates the Kotuikan zone of collision and accompanying zones of faults made up of granitoids in association with blastomylonites and cataclasites of amphibolite facies. The crust of the Yakutian province formed as part of the crust of the Siberian craton 1.8 Ga, when a collision orogen appeared. Later it had been eroded, and a peneplain formed, upon which Early Riphean clastics began to accumulate (1.65 Ga). Crustal inclusions in kimberlites characterize a drastic lateral inhomogeneity of the lower crustal horizons. Their composition in the Daldyn and Magan granulite-gneiss terranes (Muna and Mirny kimberlite fields, respectively) corresponds to the metabasite-plagiogneiss formation of the Anabar Shield, with inclusions captured at a depth of 10-20 km. In the Markha granite-greenstone terrane, the inclusions in the Nakyn kimberlites characterize the upper-crust granite-gneiss complex of amphibolite facies (0-10 km). The lower-crust granulite complexes of this terrane have no analogs on the day surface: the Daldyn field - 50% metabasites dredged from 20-30 km and the Alakit field - more than 80% metaterrigenous and metacarbonate rocks coming from 10-30 km. In the pipes of the Birekta granite-greenstone terrane (Obnazhennaya and Slyudyanka pipes), metabasites make up more than 60% of crustal xenoliths, and the basement of such terranes is supposedly enriched in basites. Spatial distribution of kimberlites reveals no direct relationship with the upper- and lower-crust complexes, but it can be inferred indirectly, from relationships between structures of the crust and lithospheric mantle. This, in turn, will advance the frontiers of the diamondiferous area in the Yakutian kimberlite province.