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North East Greenland Margin, Airborne Gravity and Magnetics

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Citation:
Winter, F. (2011): North East Greenland Margin, Airborne Gravity and Magnetics , Diplom thesis, Ludwig-Maximilians-Universitaet.
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Abstract:

The North East Greenland shelf extends from 68° N to 83° N. In contrast to its counterparts offshore Norway, its structural elements and the margin evolution are still poorly understood, due to lacking geophysical data. High resolution large scale potential field data provide new constraints for small scale problems, which so far have only been interpreted along seismic surveys. Particularly, deep sounding transects across the margin north of the Jan-Mayen Fracture Zone (around 71° N) revealed vertical and lateral variations in crustal composition: A large lower crustal high velocity body was detected and interpreted as a magmatic in origin. It results from a complex history of rifting during the break-up of Greenland and Scandinavia, in a slow to ultra-slow spreading environment prior to and during late Cretaceous - early Tertiary times. While the margin offshore Scoresby Sund and Kong-Oscar-Fjord shows clear evidence for massive sub-aerial volcanism, this is not the case for the margin north of the Greenland Fracture Zone. The crustal structure of the northernmost shelf region, is poorly understood as well, due to the lack of seismic refraction data. Distinctly, the Danmarkshavn Basin shows local occurrence of salt domes. North of 78° N several seismic reflection surveys detected such features, but for an estimate on the site of the salt province the seismic network is not dense enough. To better determine the margin's crustal configuration, commercial aero-gravity data provided by TGS Nopec, Oslo, gathered in 2007/2008, is modelled in 3D offshore the Fjord Region, including information from published deep sounding data (Voss, 2007). Compared to the existing 3D gravity model for the shelf (Schmidt-Aursch and Jokat, 2005b), which gives insight into the margin's features up to 72° N, the model in this study was extended to about 77° N. Additionally, the new 3D gravity model was refined including new seismic refraction data south of 75° N (Voss and Jokat, 2007). This study confirms the assumed extent of an lower crustal high velocity body, at 72° N to 74° N, which formed during break-up in that region. Its outlines are mainly confirmed and it is supposed that it merges into continental crust beneath the coastline. Furthermore, standard methods are used for analysing gravity data in the very northern part of the North East Greenland shelf, north of 76° N. The high resolution reveals good depth estimates and yields a mean crustal thickness of about 25 km and a sediment thickness of roughly 7 km can be assumed. Additionally, structural geologic domains are classified, such as the Danmarkshavn Basin including shallow source body outlines and other prominent anomaly outlines, as well as an area in prolongation of the Greenland Fracture Zone, which is assumed to lack shallow source bodies at all. Results are discussed in conjunction with the deep seismic models. Where necessary aero-magnetic data of the same area will be used to constrain the interpretation.

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