Abstract

The Laptev Shelf in the East Siberian Arctic represents a rare tectonic setting where an active oceanic spreading centre, the Gakkel Ridge, intersects a continental margin. The North America–Eurasia plate boundary follows the Gakkel Ridge and passes into a continental shelf; this has resulted in the development of a wide rift system that has been active since the Late Cretaceous. The new long-offset seismic profiles provide a reliable basis for deciphering the structural characteristics of this rift system. We use two new seismic profiles, along with one acquired in the 1990s, to examine the crustal architecture of the rift system. Our approach combines seismic interpretation, time to depth conversion of seismic profiles and 2D gravity forward modelling. The obtained results indicate the presence of hyperextended continental crust beneath the Ust' Lena Rift Basin and exhumed continental mantle at the base of the syn-rift succession along the rift axis. The upper crust was removed by brittle stretching, while the lower crust experienced extreme ductile thinning. Our results show that continental crust can be eliminated in the course of rifting without a considerable heat input from asthenospheric mantle.

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