Abstract
Abstract Isostasy is a well understood concept, yet rarely applied to its full capacity in regional interpretations of crustal structures. In this study, we utilize a recent density model for the entire NE Atlantic, based on refraction seismic data and gravity inversion, to calculate isostatically balanced bathymetry along the mid-Norwegian margin. Since gravity and isostatically balanced elevation are independent observables but both depend on the underlying density model, consistencies and discrepancies point towards model deficits, erroneously interpreted or poorly understood areas. Four areas of large isostatic residuals are identified. Along the outer Vøring Margin, a mass deficit points to more extensive high-density bodies or a shallower Moho than currently mapped. Farther seaward, along the Vøring Marginal High, a mass excess indicates inaccurate mapping of the continent–ocean boundary and surrounding structures. A number of eclogitic bodies along the proximal mid-Norwegian margin have been described in recent publications and their presence is now also confirmed by isostatic calculations. Major elevation and gravity residuals along the transition between the Vøring and Møre margins signify that the structure of this region is poorly understood and modifications to the mapped continent–ocean transition may be required.
Highlights
The concept of isostasy has been applied to several regional studies worldwide, helping to estimate lithospheric strength and explain the shape and origin of topography (e.g. Watts 2001; Kaban et al 2003)
A number of eclogitic bodies along the proximal mid-Norwegian margin have been described in recent publications and their presence is confirmed by isostatic calculations
Local studies which investigate the crustal structure in more detail by employing refraction and deep reflection seismic data as well as gravity modelling, often ignore the additional insight that could be gained from isostatic considerations
Summary
We use the density model exactly as it has been presented by Haase et al (2016). Because the density model was developed to match the regional gravity data of the entire NE Atlantic, but our study covers the smaller area of the mid-Norwegian margin, certain limitations and oversimplifications are expected and have to be kept in mind for the interpretation of the results. The resulting deflection di represents the difference between the isostatically compensated bathymetry of the model and the true bathymetry, referred to as elevation residual. We use the average pressure at compensation depth across the study area as the reference pressure This reference pressure is representative for large parts of the oceanic domains and the resulting elevation adjustment will here be zero. This approach leads to fairly distributed positive and negative elevation adjustments along the margin and is well suited to investigate the local density structures in the study area. A different reference pressure would lead to an overall shift in the calculated bathymetry and in the residuals
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