Rifting and Volcanism in the Laptev Sea Rift System

Dieter Franke

The Laptev Sea rift system is a modern example for initial continental breakup. It occupies the North-Eastern Siberian shelf region, where the active mid-oceanic spreading ridge meets the slope of a continental margin at high angle. The tectonic and structural evolution of the Laptev Sea Rift System is likely related to opening of the Eurasia Basin and the evolution of the Gakkel spreading ridge. Since no deep wells have been drilled so far on the shelves surrounding the New Siberian Islands, the precise age and nature of the seismic horizons which have been defined remain uncertain. Here we present correlation from the geology of the New Siberian Islands to offshore based on multichannel reflection seismic data acquired by BGR in the 1990th and a joint VSEGEI/BGR expedition to the New Siberian Islands in 2011. Key marker horizons in the offshore data will be linked to major hiatuses in the onshore region to better constrain the timing of rifting. Onshore the breakup unconformity, related to the earliest opening of the Eurasia Basin is likely amalgamated with the rift-onset unconformity, indicating a major erosional phase. Offshore, the breakup unconformity seals the wedge-shaped rift deposits in the half-grabens and represents merely a depositional hiatus. Well information is available close by the Lena delta in the form of sketched stratigraphy ranging from Proterozoic to Cretaceous. Both information can be reconciled on a cross section despite a gap of approximately 25 km, providing a tentative age for a regional unconformity sitting on top of an acoustic basement. We classify both the Laptev Sea Rift and the continental margin as magma-poor. A line across the eastern Laptev Sea slope is interpreted as imaging rotated fault blocks, bounded by deep reaching listric faults; structures which are typical for magma-poor margins. There are no indications for SDRs. The major parts of the New Siberian Islands, except the De Long Islands, are reported to be lacking extrusive magmatism. The De Long volcanic province is outstanding in the magnetic field data resulting from widespread basalts. Early Cretaceous extrusives make up a 350-m succession on Bennett Island. The basalts show an intraplate geochemical signature and, together with the East Spitsbergen and Franz Josef Land basalts were interpreted as part of the Early Cretaceous Arctic large igneous province. There are in addition Paleozoic and Neogene-Quaternary basalts reported from the De Long volcanic province that may be considered as surface expression of a potentially long-lived hot-spot. Surprisingly the rifting process in the Laptev Sea did not integrate the hot-spot and developed as magma-poor rift and continental margin.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013