Integration of geology with geophysics : Case studies from Svalbard

Sammanfattning: This is a study where new and old geophysical data together with information found in literature has been integrated to get a better understanding of the geological evolution of Svalbard. The purpose of the study is to acquire and integrate different geophysical data over the Central Spitsbergen Basin (CSB) and across the Billefjorden Fault Zone (BFZ). The integrated data has then been interpreted to identify locations of basins and structural heights. The main goals with this project have been to plan and conduct a field study to acquire magnetic- and gravity data over the study area to constrain basins and major fault zones. Furthermore, the goal was to integrate gravity- and magnetic data together with seismic interpretations and well data, discussing implications of geophysical data and lastly to add new data to the geodata platform Svalbox.  During 10 field days 7 gravity profiles were measured over the CSB and over parts of the BFZ, magnetic data was also collected along most of the profiles. Among these 7 profiles two key profiles were analysed more in detail. Further on Ground Penetrating Radar (GPR) data was collected over a glacier to obtain the glacier thickness. The report also includes a small case study analysing the Botneheia Dolerite dyke by measuring the magnetic susceptibility across the dyke. The borehole data was mostly used for the seismic interpretations, since they only penetrate about 2000 m, they do not provide any information about the deeper subsurface. The seismic interpretations varied some depending on who interpreted it so to make an even more qualified analyse, the gravity and magnetic data are suitable complements.  The gravity anomalies proceeded in this report vary in a similar way in comparison to older gravity data provided in the same area. Both Billefjorden Fault Zone (BFZ) and Lomfjorden Fault zone (LFZ) can be identified in the gravity data acquired from the field study. After integrating seismic interpretations and gravity data, the depth from the surface to the basement in CSB is assumed to decrease in a west-east direction. In this report the basement is defined as pre-Devonian rocks. In the eastern part of profile 5, east of Reindalspasset the gravity anomalies are steadily increasing while a seismic interpretation shows a dip of the basement, which could indicate the existence of another layer on top of the basement with a high density. To sum up, integration of several geophysical methods is a good method to identify fault zones and depth to the basement. It is important to interpret all data individually and combined to be able to identify what is causing the anomalies.  Suggestions for further studies is forward modelling and to correct the ortho height measured by the DGPS on top of the glacier of profile 3 by using the collected GPR data. The geophysical data provided in this report can be used for further investigation about CO2 sequestration and geothermal energy.