HR: 09:15h
AN: T11B-06    [PDF]
TI: Plume-Ridge Interaction North of Iceland: Constraints from Crustal Thickness.
AU: * Hooft, E E
EM: emilie@newberry.uoregon.edu
AF: University of Oregon, 1272 Geological Sciences, Eugene, OR 97403 United States
AU: * Hooft, E E
EM: emilie@newberry.uoregon.edu
AF: Dept. Terrestrial Magnetism,Carnegie Institution, 5241 Broad Branch Rd. N.W., Washington, DC 10015 United States
AU: Brandsd\'{o}ttir, B
EM: bryndis@raunvis.hi.is
AF: University of Iceland, Hofsvallag\"{o}tu 53, Reykjav\'{i}k, IS-107 Iceland
AU: Mjelde, R
EM: rolf@ifjf.uib.no
AF: University of Bergen, All\'{e}gt 41, Bergen, 5007 Norway
AU: Shimamura, H
EM: shima@eos.hokudai.ac.jp
AF: Hokkaido University, N-10, W-8, Sapporo, 060-0810 Japan
AB: Hotspot-ridge interactions affect the melt production at nearby mid-ocean ridges causing spatial and temporal variations in crustal thickness. We present results from a seismic refraction experiment to measure crustal thickness along and across the Kolbeinsey ridge north of Iceland. We surveyed a 230-km-long along-axis line, situated about 10 km east of the Kolbeinsey Ridge, and two cross-axis lines which are 710 and 140 km long, located 70 and 180 km north of the Icelandic coast, respectively. The ocean bottom seismometer spacing was 15 km along the ridge, 10 km across the ridge, and 30 km east of the Iceland margin. The seismic source was a 4800 cu. in. airgun array with 200 m shot spacing. For each refraction line, we invert {\it Pg} and {\it PmP} arrivals using the tomography method of {\it Korenaga et al.} ({\it JGR}, 1999). We find that crustal thickness decreases to the north along the Kolbeinsey Ridge; the crust is about 13 km (10 km) thick 200 km (400 km) from the center of the Iceland hotspot. The melt flux at the Kolbeinsey Ridge appears smaller than at similar distances along the Reykjanes Ridge south of Iceland; where crustal thickness is 16.5 km (12.5 km), at 200 km (400 km) from the hotspot center. This observation is consistent with the north-south asymmetry in geochemistry and ridge axis elevation; between 200 and 400 km from the hotspot center the axis of the Reykjanes Ridge is 500 m shallower than the axis of the Kolbeinsey Ridge. Thus the Iceland hotspot enhances melting more substantially at the Reykjanes Ridge than at the Kolbeinsey Ridge; this asymmetry has not yet been explained by geodynamic models. Quantifying crustal thickness will help determine whether the asymmetry in ridge axis depth can be explained isostatically or if dynamic support is required. Our across-axis profiles suggest undulations in crustal thickness similar to those associated with the V-shaped ridges of the Reykjanes Ridge. Thus temporal variability in the influence of the hotspot on spreading-center melt production is observed both north and south of Iceland.
DE: 7220 Oceanic crust
DE: 8100 TECTONOPHYSICS
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8180 Tomography
SC: Tectonophysics [T]
MN: 2003 Fall Meeting