Crustal Petrology and Origin of the Loppa High, SW Barents Sea, from Integrated Geophysical Interpretation

Christine Fichler

The Loppa High is a major basement high located immediately north of the Norwegian mainland. Its steep western slope has come into focus due to major hydrocarbon discoveries during the last three years. Recently acquired magnetic data improve the possibility to further unravel the crustal petrology of this high. The inherited structure of the high may provide valuable hints improving the understanding of the later rift development. The plate tectonic history indicates this area to be located in the junction between collisional regimes of alternating strike directions: Sveco-Karelian (NNW-SSE), Trans-Scandinavian Igneous Belt (N-S), Timanian (WNW-ESE), Caledonian (N-S). The younger history as recorded by sediments includes rifting as well as thermal events; both may have generated magmatic intrusions. The crust is therefore expected to reflect the tectonic events and as such, it is no surprise that the geophysical expression definitely is complex. The top basement as interpreted from seismic and gravity data differs appreciably from the top of the magnetic crustal layer. This is a direct indication for inhomogeneous basement petrology. Furthermore, the dominant magnetic NNW-SSE trend is cross-cut by the main gravity trend of NE-SW direction. Earlier work focused on the post-Caledonian development of this area, as recorded by the sedimentary pile. This work aims on a more detailed internal crustal model of the Loppa High from gravity, magnetic, seismic and well data. The interpretation workflow includes: (1) adjusting the gravity data for sedimentary effects, (2) compiling Moho depths from seismic data and flexural isostasy, (3) inversion of gravity and magnetic data for internal crustal structure, (4) 2D modeling of gravity and magnetic data, (5) developing petrology models. Finally, the petrology models are evaluated with respect to tectonic origin and age. By comparison with onshore and offshore analogs – we argue that the petrology and structure of the Loppa High may be consistent with earlier subduction. Arguments include the distribution of geophysical parameters, geometry as well as internal seismic reflectivity. Possible origins are discussed, some of which are Ordovicean island arc - magmatism and Andean type – magmatism related to the Transcandinavian Igneous Belt.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013