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Continent-ocean-transition across a trans-tensional margin segment: off Bear Island, Barents Sea
(2011)
P>A 410 km long Ocean Bottom Seismometer profile spanning from the Bear Island, Barents Sea to oceanic crust formed along the Mohns Ridge has been modelled by use of ray-tracing with regard to observed P-waves. The northeastern part of the model represents typical continental crust, thinned from ca. 30 km thickness beneath the Bear Island to ca. 13 km within the Continent-Ocean-Transition. Between the Hornsund FZ and the Kn circle divide legga Fault, a 3-4 km thick sedimentary basin, dominantly of Permian/Carboniferous age, is modelled beneath the ca. 1.5 km thick layer of volcanics (Vestbakken Volcanic Province). The P-wave velocity in the 3-4 km thick lowermost continental crust is significantly higher than normal (ca. 7.5 km s-1). We interpret this layer as a mixture of mafic intrusions and continental crystalline blocks, dominantly related to the Paleocene-Early Eocene rifting event. The crystalline portion of the crust within the south-western part of the COT consists of a ca. 30 km wide and ca. 6 km thick high-velocity (7.3 km s-1) body. We interpret the body as a ridge of serpentinized peridotites. The magmatic portion of the ocean crust accreted along the Knipovich Ridge from continental break-up at ca. 35 Ma until ca. 20 Ma is 3-5 km thicker than normal. We interpret the increased magmatism as a passive response to the bending of this southernmost part of the Knipovich Ridge. The thickness of the magmatic portion of the crust formed along the Mohns Ridge at ca. 20 Ma decreases to ca. 3 km, which is normal for ultra slow spreading ridges.
As a part of the DEad Sea Integrated REsearch (DESIRE) project a near-vertical incidence reflection (NVR) experiment with a profile length of 122 km was completed in spring 2006. The profile crossed the southern Dead Sea basin (DSB), a pull-apart basin due to the strike-slip motion along the Dead Sea Transform (DST). The DST with a total displacement of 107 km since about 18 Ma is part of a left-lateral fault system which connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a distance of about 1100 km. The seismic experiment comprises 972 source locations and 1045 receiver locations. Each source was recorded by similar to 180 active receivers and a field data set with 175 000 traces was created. From this data set, 124 444 P-wave first-break traveltimes have been picked. With these traveltimes a tomographic inversion was carried out, resulting in a 2-D P-wave velocity model with a rms error of 20.9 ms. This model is dominated by a low-velocity region associated with the DSB. Within the DSB, the model shows clearly the position of the Lisan salt diapir, identified by a high-velocity zone. A further feature is an unexpected laterally low-velocity zone with P-velocities of 3 km s1 embedded in regions with 4 km s1 in the shallow part on the west side of the DSB. Another observation is an anticlinal structure west of the DSB interpretated to the related Syrian arc fold belt.