Tectonics of the Laptev Sea and Moma rift systems, northeastern USSR

Abstract

Examination of the topography, seismicity, focal mechanisms, and structure of the extension of the Arctic mid-ocean ridge into the Laptev Sea suggests that the present-day features of the upper crust are consistent with an asymmetric, simple shear, extensional system. On a large scale, the topographically high, upper plate side alternates from Severnaya Zemlya and Taimyr Peninsula, across the rift zone to the New Siberian Islands, and then back across to the Kharaulakh Range and the Omoloi River basin. The activity of this system is indicated by moderate-size normal-faulting earthquakes and the extensive development of extensional structural features. A weakly developed axial graben, with a few teleseismic earthquakes, is developed in the eastern Laptev Sea. Further south, a NW-striking Pliocene rift system, commonly known as the Moma rift, extends through the northern Cherskii Range. Although there is a broad zone of elevated heat flow and isolated volcanoes, this system is transpressional at the present time. The zone of major seismicity passes south of the rift system near the Indigirka River and indicates that the rift is not acting as the plate boundary. The Moma rift is also asymmetric, but with the lower plate (southwest) side being topographically higher. The Moma system is inactive along most of its length and only reached an early stage of development before activity ceased.