Deep crustal reflectors under Reydarfjordur, eastern Iceland: crustal accretion above the Iceland mantle plume

• Published in: Geophysical Journal International
• Main Authors: Smallwood, John R., White, Robert S., Staples, Robert K.
• Format: Text
• Language: English
• Published: Oxford University Press 1998
• Subjects: Articles; Faroe-Iceland Ridge; Iceland
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/134/1/277; https://doi.org/10.1046/j.1365-246x.1998.00593.x

Deep seismic reflection profiling on the Faroe-Iceland Ridge Experiment (FIRE) imaged a sequence of dipping events in the upper to mid-crust beneath the Tertiary lava pile in Reydarfjördur, eastern Iceland. These events dip towards the spreading centre at which the crust was formed, and continue down to ∼ 6 s two-way time, corresponding to depths down to 15–18 km. Similar crustal reflections have been observed previously within the crust in other areas of Iceland, although the reflective events located by previous surveys have not been interpreted rigorously. In this study we calculate synthetic seismograms from modelled sequences of lava flows to examine the reflective character of a lava πle. The synthesized lava pile sections are based on field measurements made in the Reydarfjördur area: the 1 km vertical exposures on the sides of the fjord are composed of lava flows within stratigraphic units which have a range of compositions, and some intercalated tuffaceous clastic horizons. We compare the synthetic seismograms with our seismic reflection data to test the interpretation that the deep dipping reflections are caused by a gently dipping sequence of subaerially erupted lavas. We conclude that the upper and mid-crustal reflections that we observe can be interpreted as lava flow sequences similar to those seen at the surface, with the main reflections resulting from packets of flows of similar thicknesses. The reflectors that we have imaged beneath Iceland are similar to those defining the seaward-dipping reflectors on the volcanic continental margins, and we therefore suggest that the seaward-dipping reflections commonly result from packets of lavas with similar distributions of thicknesses. The occurrence of lavas down to 15–18 km beneath Reydarfjördur can be explained partly by multiple episodes of accretion of the upper crust, although the volcanic processes forming the crust in Iceland generally lead to advection of extrusive material to mid-crustal levels. The production of an average extrusive layer ...