K Ar data for the age and evolution of Gettysburg Bank,North Atlantic Ocean |
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| Authors: | HM Prichard JG Mitchell |
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| Institution: | Department of Geology, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne England;School of Physics, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne England |
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| Abstract: | Gettysburg Bank forms the western end of the Gorringe Seamount which is situated in the North Atlantic 110 km west of the tip of the Iberian Peninsula, on the eastern end of the Azores/Gibraltar fracture zone.Gabbros dredged from the Gettysburg Bank record a complex history of events. K-Ar ages of separated mineral phases fall into three concordant groups (plus some discordant ages). The oldest ages are from three brown kaersutitic hornblendes and their mean age of135 ± 3Ma is taken to be that of their formation. Six plagioclase feldspars yielded concordant ages of105 ± 3Ma which is possibly a consequence of a thermal event occurring at that time. Ages from three deformed plagioclases are concordant with a mean of82 ± 3Ma which is believed to relate to a phase of shearing, perhaps occurring during transform motion at the plate boundary. |
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