Feedbacks of sedimentation on crustal heat flow: New insights from the V?ring Basin, Norwegian Sea

摘要

Basement heat flow is one of the key unknowns in sedimentary basin analysis. Its quantification is challenging not in the least due to the various feedback mechanisms between the basin and lithosphere processes. This study explores two main feedbacks, sediment blanketing and thinning of sediments during lithospheric stretching, in a series of synthetic models and a reconstruction case study from the Norwegian Sea. Three types of basin models are used: (1) a newly developed one-dimensional (1D) forward model, (2) a decompaction/backstripping approach and (3) the commercial basin modelling software TECMOD2D for automated forward basin reconstructions. The blanketing effect of sedimentation is reviewed and systematically studied in a suite of 1D model runs. We find that even for moderate sedimentation rates (0.5 mm year~(-1)), basement heat flow is depressed by ~25% with respect to the case without sedimentation; for high sedimentation rates (1.5 mm year~(-1)), basement heat flow is depressed by ~50%. We have further compared different methods for computing sedimentation rates from the presently observed stratigraphy. Here, we find that decompaction/backstripping-based methods may systematically underestimate sedimentation rates and total subsidence. The reason for this is that sediments are thinned during lithosphere extension in forward basin models while there are not in backstripping/decompaction approaches. The importance of sediment blanketing and differences in modelling approaches is illustrated in a reconstruction case study from the Norwegian Sea. The thermal and structural evolution of a transect across the V?ring Basin has been reconstructed using the backstripping/decompaction approach and TECMOD2D. Computed total subsidence curves differ by up to ~3 km and differences in computed basement heat flows reach up to 50%. These findings show that strong feedbacks exist between basin and lithosphere processes and that resolving them require integrated lithosphere-scale basin models.