Evolution of the Laptev Continental Rifts as Revealed by 2d Gravity Modelling, Plate Reconstructions and Palaeogeographic Mapping

Stansilaw Mazur, Simon Campbell, Rkia Bouatmani, Dorothea Eue, Joanne Whittaker, and Paul Markwick
GETECH, Leeds, United Kingdom.

The Laptev Sea continental rift system is located at the propagating end of an active oceanic spreading axis, the Gakkel Ridge. From the latest Cretaceous to the Pliocene, extension across the Laptev Shelf created a series of deep rifts and high-standing basement blocks. We have used 2D gravity models, plate reconstructions and palaeogeographic mapping to understand the syn-rift geometries of these basins and their influence on sediment supply across the Laptev Shelf.

To restore the stretched continental crust to its original width, we used a 2D gravity forward profile model oriented perpendicular to the long axis of the Laptev shelf rift system. Our 2D model makes use of GETECH’s global gravity databases, which comprise the highest available resolution satellite gravity data for marine areas, and data for the continents. The 2D gravity model, supported by published seismic data, constrains the present day crustal thickness and the limit of crustal thinning, and therefore results in estimates of E-W oriented stretching along the modelled section of 450-500 km.

This calculated continental extension across the Laptev Shelf has been incorporated into our plate model for the Arctic in order to more accurately unravel relative plate motions between North America and Eurasia, from the latest Cretaceous to Cenozoic. Our revised plate model shows the relationship between extension of the Laptev Shelf and anticlockwise rotation of Eurasia relative to North America. This is consistent with the position of the Euler pole for this rotation for much of the Cenozoic, which was situated c. 1500 km south of its present position near the Lena delta, such that the vast majority of Eastern Siberia was under extension. The Euler pole moved to its present position during the Pliocene resulting in a decrease in rifting in the Laptev Shelf. The calculated amount and timing of extension allow modelling of successive pulses of subsidence within the Laptev rifts, which are recorded by thick sedimentary successions.

The palaeogeographic mapping shows that during the incipient phase of rifting in the Laptev Shelf, tectonic subsidence was associated with widespread thermal uplift of rift shoulders. Therefore, the subsequent widening of depocentres must have been caused not only by final stretching but also by the transition from active rifting to thermal sagging. This would be anticipated to have resulted in a change of sediment supply across the shelf.

AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia