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

Palaeomagnetic data are presented from Mid-Silurian (Homerian, Upper Wenlock, similar to 425 Ma) sediments from the Dingle Peninsula, SW Ireland, which forms part of the northern margin of the Palaeozoic microcontinent of Avalonia. Three remanence components were recognized. After removal of a low-temperature component ('L'), oriented parallel to the present Earth field at the sampling area, two higher-stability components were isolated: an intermediate-unblocking-temperature component ('I') with mean in situ D = 196.9 degrees, I = 11.0 degrees, alpha 95 = 10.8, with a corresponding palaeopole at 330.0 degrees E, 30.6 degrees S (dp = 5.6, dm = 11.0), and a high-unblocking-temperature component ('H') with mean tilt-corrected D = 218.6 degrees, I = 22.1 degrees, alpha 95 = 7.9, with a corresponding palaeopole at 309.5 degrees E, 18.3 degrees S (dp = 4.4, dm = 8.4). A primary (Wenlock) age is indicated for 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 and Laurentia was essentially closed, within the limits of palaeomagnetic resolution, by the Wenlock. There is still, however, a discrepancy between the declinations recorded by similar-aged sequences to the north and south of the Iapetus Suture. These point to either an approximately 30 degrees clockwise rotation of the entire Avalonian microcontinent relative to Laurentia during closure, or local vertical axis rotations of the sampling sites in southern Britain.