Palaeomagnetic study of the Lorne Plateau Lavas, Scottish Caledonides

Abstract

The Lorne Plateau lava succession of the north-west Grampian Highlands of Scotland is an early component of post-collisional Late Silurian to Early Devonian magmatism in the Orthotectonic Caledonides emplaced in two phases between the Late Silurian (425.0±0.7 Ma U-Pb zircon) and the Siluro-Devonian boundary at ∼419 Ma. Palaeomagnetic study comprising thermal demagnetization and component analysis embracing the time frame of the preserved succession yields a coherent mean direction of magnetization from 58 sites (D/I = 43.7/-47.4°, α95 = 4.0°). A palaeomagnetic fold test is significantly positive with sills intruding unlithified sediment on the island of Kerrera confirming primary remanence. The ∼600 m thick succession has uniform normal polarity throughout permitting correlation with the beginning of a normal polarity chron extending from ∼426 to 403 Ma. The pole position at 2.7°N, 317.3°E (dp/dm = 3.8/5.8°) predicts a palaeolatitude of 26°S and corresponds precisely with remanence in contemporaneous rocks from the Midland Valley of Scotland. Regional palaeofield directions are evaluated in the context of transpressional moulding of the Acadian Orogeny on the Great Glen Fault system (∼416-380 Ma). Show more