A new Silurian palaeolatitude for eastern Avalonia and evidence for crustal rotations in the Avalonian margin of southwestern Ireland

Abstract

SUMMARY Palaeomagnetic data are presented from Mid-Silurian (Homerian, Upper Wenlock,~425 Ma) sediments from the Dingle Peninsula, SW Ireland, which forms part of thenorthern margin of the Palaeozoic microcontinent of Avalonia. Three remanencecomponents were recognized. After removal of a low-temperature component (‘L’),oriented parallel to the present Earth field at the sampling area, two higher-stabilitycomponents were isolated: an intermediate-unblocking-temperature component (‘I’)with mean in situ D=196.9°, I=11.0°, a95=10.8, with a corresponding palaeopole at330.0°E, 30.6°S(dp=5.6, dm=11.0), and a high-unblocking-temperature component(‘H’) with mean tilt-corrected D=218.6°, I=22.1°, a95=7.9, with a correspondingpalaeopole at 309.5°E, 18.3°S(dp=4.4, dm=8.4). A primary (Wenlock) age is indicatedfor the ‘H’-component by a positive intraformational conglomerate test, whereas the‘I’-component is thought to be a secondary mid-Carboniferous partial remagnetization.These data confirm that the sector of the Iapetus Ocean between Avalonia andLaurentia was essentially closed, within the limits of palaeomagnetic resolution, by theWenlock. There is still, however, a discrepancy between the declinations recorded bysimilar-aged sequences to the north and south of the Iapetus Suture. These point toeither an approximately 30° clockwise rotation of the entire Avalonian microcontinentrelative to Laurentia during closure, or local vertical axis rotations of the samplingsites in southern Britain.