Late Cenozoic lithosphere dynamics in Svalbard: Interplay of glaciation, seafloor spreading and mantle convection

摘要

In the last 10 Ma, the northwest Barents Sea passive margin and Svalbard archipelago experienced tectonic reactivation including regional uplift, volcanism and fault movements. Previous studies have variously attributed this reactivation to the establishment of continuous seafloor spreading between the North Atlantic and Arctic oceans within the Fram Strait, mantle convection, or a lithospheric response to climate-driven processes such as fluvial and glacial erosion in a late Pliocene-Pleistocene time (similar to 1.3 Ma). The relative magnitudes, and the physical relationship between surface processes, plate boundaries and mantle flow, has remained unclear. In this work, I jointy interpret seismological models of the upper mantle, gravity anomalies, rates of glacial isostatic adjustment (GIA) and the spatiotemporal characteristics of earthquakes with the aim to i) constrain the thermal state and rheological structure of the upper mantle beneath Svalbard, ii) infer the magnitude of vertical motion in the late Cenozoic time related to various processes, iii) better understand the likely causes of the tectonic and volcanic activity.Most part of the northwest Barents Sea passive margin including Svalbard is underlain by a thin continental lithosphere (similar to 50-80 km) and a normal thickness of crust (30-35 km). The geophysical data indicate an average excess mantle temperature of similar to 40-100 degrees C beneath western Svalbard compared to the central Barents Sea. The peak of the mantle temperature anomaly coincides with the location of Quaternary basalt eruptions. The predicted long-wavelength ( 420 km) non-isostatic uplift of similar to 600-800 m correlates with the distribution of pre glacial uplift previously inferred from geological data in the northwest Barents Sea. The gravity anomalies within an intermediate range of wavelengths (30-420 km) allows me to estimate topography changes due to erosion by ice streams to be similar to 200-500 m. I conclude that a transient temperature anomaly in the asthenosphere northeast of Jan Mayen, combined with the northwest absolute plate motion of Eurasia, is the likely primary cause of the late Cenozoic tectonic reactivation in Svalbard.