Print this pageApplication of Plate Reconstructions and 2-D Gravity Modelling to Quantification of Continental Stretching - A Laptev Shelf Case Study
The Laptev Sea continental shelf is located at the propagating end of an active oceanic spreading axis, the Gakkel Ridge. Consequently, since the latest Cretaceous to Pliocene, a continental rift system developed in that area comprising several deep subsided rifts and high-standing basement blocks. To understand syn-rift basin geometries and sediment supply relationships across the Laptev shelf, accurate plate reconstructions are vital. However, the location of the Eurasia/North America plate boundary as it passes from the Gakkel Ridge into the continental Laptev shelf becomes diffuse and poorly constrained. Although the position of Eurasia relative to North America is constrained by sea-floor magnetic anomalies in the North Atlantic and Eurasia Basin, even tiny imprecisions in the magnetic data can result in significant misfit throughout northeast Asia, as exemplified by a number of previous plate models. In order to accurately unravel relative plate motions between North America and Eurasia, the amount of continental extension across the Laptev shelf was calculated and incorporated into a plate model.
To restore the stretched continental crust to its original width, we used a 2D gravity forward profile model oriented perpendicular to the Laptev shelf rift system. The 2D gravity model, supported by published seismic data, constrains the present-day crustal thickness, limits of the zone of crustal thinning and provides estimates of stretching along the modelled section.
The quantity of finite crustal stretching derived from the 2D gravity profile crossing the Laptev shelf amounts to 450-500 km. The minimum value of 450 km was implemented in the plate model as a constraint for continental extension between North America and Eurasia. The resultant tectonic model attributes extension of the Laptev shelf, in accordance with marine magnetic data, to anticlockwise rotation of Eurasia relative to North America. For most of the Cenozoic the Euler pole for this rotation was situated c. 1500 km south of its present position near the Lena delta. Therefore, the vast majority of Eastern Siberia was under extension during the Cenozoic. The Euler pole moved to the present position since 5 Ma resulting in a deceleration of rifting in the Laptev shelf. The calculated amount and timing of extension match well with predictions derived from the tectonic model of Gaina, Roes and Mueller (2002) and allow modelling of successive pulses of subsidence within the Laptev rifts.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009