TECTONIC SETTING OF POSTOROGENIC GRANITES WITHIN SW FENNOSCANDIA BASED ON DEEP SEISMIC AND GRAVITY-DATA

Within the Sveconorwegian Province of SW Scandinavia granite intrusion s are abundant. Prominent ones are the Bohus-Iddefjord and the Fla gra nites, the so- called Bohus-Fla Granite belt. The age of these granite s, consistent at approximate to 900 Ma, coincides with the late extens ional stage of the Sveconorwegian-Grenvillian orogen. Gravity observat ions and deep seismic profiling Lines are presented that also cover th e Skagerrak Sea. The geophysical data suggest that the Bohus granite c ontinues seaward for at least 80 km and its thickness, offshore, is es timated to be 2-4 km. Where the seismic profiling Lines intersect the inferred seaward extension of the Bohus granite, a distinct reflection pattern is observed at approximate to 1.6 s. TWT. This coincides with a gravity modelled thickness of approximate to 4 km. The seismic prof iles also show a large Moho offset beneath the modelled granite. It is proposed that this offset is related to Sveconorwegian crustal undert hrusting and that the granite melt could have formed by anatexis of mi d-crustal rocks downthrusted to greater depths in the vicinity of the seismically observed Moho offset.