Effect of thermal contrasts on gravity modeling at passive margins: Results from the western Barents Sea

Abstract

Abstract. The western Barents Sea passive margin is a key locality to demonstrate the effect of the thermal structure of the lithosphere on forward gravity modeling. This margin developed by shear motion between the Eurasian and Greenland plates during the early Tertiary, and it is a significant border zone between young, hot oceanic lithosphere and cooler continental lithosphere. We construct two-dimensional gravity models of 125 km thick lithosphere based on expansion of mantle rocks determined from thermal modeling. The approach has a substantial impact over traditional shallow gravity models, here demonstrated on a previously published model. On the basis of a 140 mGal free-air anomaly, the old model proposes an anomalous, high-density oceanic crust emplaced in a leaky transform adjacent to the continent during early margin development. However, the lithospheric models predict a homogeneous oceanic crust, while preserving regional isostasy at base lithosphere from continent to ocean. Two further tests agree with this conclusion: A map of Bouguer corrected ERS-1 satellite data reveals no residual anomalies originating from the oceanic crust at the margin. Admittance analysis shows a strong oceanic lithosphere, and the high coherence between bathymetry and free-air gravity discounts a significant subsurface load. The high gravity anomalies at the margin are thus an edge effect, enhanced by sedimentation onto the strong oceanic lithosphere, and shaped by the effect of the lithospheric thermal field. Other results of this work include a new continent-ocean boundary map and two crustal transects across the margin.

An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

“…This is in accordance with published literature (Breivik et al 1999;Czuba et al 2011). The igneous oceanic crust is buried by a thick package of low-velocity Cenozoic sedimentary rocks (Layers 2, 3 and 4 in Fig.…”

“…More recent studies suggest that the whole province is underlain by stretched continental crust (Breivik et al 1999;Engen et al 2008). This was also the conclusion of Czuba et al (2011) who modeled a continental crust increasing in thickness from west to east in the province.…”

“…Yellow circles represent OBS positions along BIS-2008, green circle represents position of broadband OBS and purple circles represent land stations. Continent-ocean boundary (COB) from Breivik et al (1999) and magnetic anomalies (stippled orange lines) are from Engen et al (2008). Structural elements are from Ritzmann and Faleide (2007).…”

Crustal structure between the Knipovich Ridge and the Van Mijenfjorden (Svalbard)

“…Breivik et al (1998) report a similar extreme mismatch between the observed free-air anomaly and the inferred anomaly from seismic crustal models off Senja Margin and the Svalbard Platform. The mismatch along the oceanic profile section amounts up to 200 mGal with a gradual increasing deviation west of the continentocean boundary.…”

“…The mismatch along the oceanic profile section amounts up to 200 mGal with a gradual increasing deviation west of the continentocean boundary. Breivik et al (1998) simulate the complex temperature development at the margin transects to derive the thermal structure of the upper mantle to a depth of 125 km. After converting mantle temperature to density and subsequent calculation of the free-air anomaly an improved fit was achieved along the oceanic profile section.…”