Abstract
Summary A palaeomagnetic study of mid-Silurian (Wenlock) sediments of the Salrock Formation in NW Galway yields a reliable Silurian palaeomagnetic pole position for W. Ireland at latitude 1.6°S, longitude 287.7°E (dp = 2.5°, dm = 4.6°, N= 27 sites). A further 12 sampling sites were located in Silurian redbeds on Clare Island, S. Mayo where a palaeomagnetic remanence of Silurian age was also identified. Both remanences pre-date local late-Caledonian folding. However the Clare Island result has an anomalous azimuth when compared with the Salrock result and with published Silurian results for Britain. the two Irish results can be reconciled by anticlockwise block rotation of the Clare Island region through 40°-50°. the rotation brings both palaeomagnetic and structural trends within the two sampling regions into alignment. Strike-slip displacement across the Clew Bay fault zone, producing a sinistral shear couple, might have enabled such a rotation. the timing and geographic extent of the proposed block rotation is as yet poorly defined. However a younger age limit for rotation is provided by a late Devonian or Carboniferous partial magnetic overprint observed throughout both study areas, and from geological evidence it seems likely that rotation is confined to the Clew Bay fault zone. The Dalradian rocks of the Connemara Massif, located to the south of the Salrock district, have an E-W structural grain. Some workers have proposed clockwise rotation of the Connemara Massif of ca. 30° at between 500 and 390 Ma which would bring the structural trends in W. Ireland into parallelism with Caledonian trends in Scotland. Because the Silurian Salrock succession (which rests unconformably on the Dalradian basement of Connemara) shows no such anomaly, it provides a younger age limit for the possible rotation of Connemara.
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call