HR: 10:20h
AN: V42B-01 INVITED    [Abstracts]
TI: Melt Flux Around Iceland: The Kolbeinsey Ridge Seismic Experiment.
AU: * Brandsdóttir, B
EM: bryndis@raunvis.hi.is
AF: Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, Reykjavik, IS101, Iceland
AU: Hooft, E E
EM: emilie@uoregon.edu
AF: Department of Geological Sciences, 1272 University of Oregon, Eugene, OR97403, United States
AB: Seafloor spreading within the Iceland region has been complex since the opening of the North Atlantic in late Paleocene-early Eocene. Whereas symmetric magnetic anomalies can be traced parallel to the Reykjanes Ridge and Mohns Ridge back to chrons 23-24, anomalies within the Iceland Plateau and Aegir Ridge in the Norwegian Sea, as well as along the Greenland-Iceland-Faeroe Ridge reflect plate-boundary irregularities associated with multiple-branched crustal accretion zones, rift jumps and plate boundary segmentation (volcanic systems). We observe large variations in crustal structure along two refraction/reflection/gravity profiles, a 700 km EW-profile straddling 66.5°N between the Aegir and Kolbeinsey Ridges and a 225 km NS-profile along the southern Kolbeinsey Ridge. These profiles enable us to quantify how melt flux at the N-Atlantic spreading center has been influenced by the Iceland hotspot from the initiation of spreading to present time. The westernmost 300 km of the EW profile lies across the Iceland shelf, considered to have formed by rifting at the Kolbeinsey Ridge whereas the easternmost 400 km lie across the Iceland Plateau and Norway Basin, a region formed by rifting at the Aegir Ridge and possibly containing slivers of older crust rifted off the east Greenland margin along with the Jan Mayen Ridge. Crustal thickness varies from 4-5 km across the Aegir Ridge, 12 km just east of the Iceland shelf, and 24-28 km beneath the outer shelf, to 12-13 km near the southern tip of the Kolbeinsey Ridge and 9-10 km further north along the ridge axis. Pronounced undulations in lower crustal structure across the Iceland Plateau are most likely associated with extinct spreading centers indicating that branched crustal accretion zones existed west of the Aegir Ridge prior to the westward ridge jump forming the KR at 26 Ma. Crustal thickness at the Kolbeinsey and Reykjanes Ridges support the asymmetry in plume-ridge interaction north and south of Iceland that has been inferred from differences in axial depth (400-750 m) and geochemistry between these two ridges. Gravity inversions indicate a sub-crustal residual gravity anomaly that decreases by about 20 mGal toward Iceland which implies a density reduction of about 10 kg/m³ in the upper 100 km of the mantle along the Kolbeinsey Ridge profile. If solely due to thermal expansion this suggests a temperature increase of about 100°C toward Iceland.
DE: 7220 Oceanic crust
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 9335 Europe
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting