--> Abstract: Lithospheric Structures of Western Fennoscandia and their Effects on the Present-day Continental Margin, by Sofie Gradmann; #90177 (2013)

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Lithospheric Structures of Western Fennoscandia and their Effects on the Present-day Continental Margin

Sofie Gradmann

Recent studies have shown that a major change in lithosphere thickness and composition underlies southwestern Fennoscandia. This is consistent with the different tectonothermal ages of the regions and with global observations of old, thick, more depleted sub-continental lithospheric mantle (SCLM) versus younger, thinner and more fertile SCLM. Effects of this lithospheric boundary zone underneath southern NO and SE can be seen in a number of geophysical data sets such as gravity, teleseismics, geoid or topography. The edge of the thick, cratonic lithosphere is expected to continue north where it likely coincides with the edge of the Svecofennian domain and the location of the Transscandinavian Igenous Belt (TIB). In order to better constrain and characterize this lithospheric boundary zone, we perform combined geophysical-petrological forward modelling of the lithosphere and sublithospheric uppermost mantle of all of western Fennoscandia using the interactive modelling software LitMod3D. All relevant properties are functions of temperature, pressure and composition, allowing us to build self-consistent models that simultaneously fit available geophysical and petrological observables. A lateral lithosphere thickness change of several tens of kilometers from the offshore to the cratonic areas and simultaneous composition change from Palaeozoic to Proterozoic-type is consistent with the geophysical data sets. This configuration can isostatically support the existing topography and simultaneoulsy reproduce the trend of the elongated, coast-parallel gravity low. This first-order model structure is further refined in order to account for the transition to even older, and more depleted Archean SCLM in the far north. Additionally, we investigate a prominent gravity and geoid low which lies just south of the Lofoten peninsula. This is likely related to the presence of the TIB but a similar, yet larger anomaly exists on the conjugate margin in northeastern Greenland. The general correlation between crustal age and lithosphere thickness can no longer be sustained on a continental margin. In this study we investigate how deviations from this relationship affect topography, gravity, and internal stresses. In addition, pre-existing structures of the SCLM likely had an impact on the rifting history (its localization and timing), which we aim to disclose and discuss.

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