Short Paper; Terrane rotations in the Irish Caledonides

Abstract

Palaeozoic palaeomagnetic data from Scotland and Ireland have been compared on a terrane model, and early Caledonide clockwise rotation of a terrane through 65º ± 30° (Connemara Massif) and later anticlockwise rotation of up to 50° (in the vicinity of Clew Bay) have been deduced. These are the firfirst estimates of terrane rotations in the European part of the Caledonian–Appalachian orogen. Terrane analysis of orogenic belts is currently a major field of study. To a large extent this has been stimulated by studies in the North American Cordillera where large rotations and translations have been determined palaeomagnetically (see Beck et al. 1986 and references therein). Terrane analysis may be applied to older orogenic belts such as the Caledonides, which have been particularly intensively studied. Previously published palaeomagnetic data from Connemara (Morris & Tanner 1977) and NW Galway ( Morris et al. 1973 ) had indicated local block rotations, but furnished few constraints on either their age and magnitude, or on the identities of the blocks. This paper relates the currently available palaeomagnetic dataseto a terrane model of W. Ireland (Hutton & Dewey 1986), see Fig. 1. New data. New palaeomagnetic data from the Irish Caledonides comprise the following. Connemara Gabbro ( Robertson 1988 ). The Dalradian rocks of the Connemara Massif are unique in the British Caledonides in lying to the south of a Caledonian ophiolite and also south of a thick sequence of Ordovician shales and volcanics of low metamorphic grade (in Clew Bay and the South Mayo Trough respectively). The structural