THE EARLY PALEOZOIC EVOLUTION OF NORTHWEST ENGLAND

The Lake District and smaller Craven inliers of northwest England cont ain a Lower Palaeozoic sequence deposited on the Gondwanan side of the Iapetus Ocean, close to the junction with the Tornquist Sea. The Trem adoc to Llanvirn Skiddaw and Ingleton groups are deep water assemblage s of turbidite, olistostrome and slump deposits, formed at a continent al margin. They experienced uplift and erosion as a precursor to the e ruption of two largely subaerial Llandeilo-Caradoc volcanic sequences: the tholeiitic Eycott Volcanic Group in the north and the calc-alkali ne Borrowdale Volcanic Group in the central Lake District. The volcani c episodes are the earliest part of a major episode of magmatism, exte nding through to the early Devonian and responsible for a major bathol ith underpinning the Lake District. Subsidence in an intra-arc rift zo ne preserved the subaerial volcanic sequences. A marine transgression marks the base of the Windermere Group, which comprises a mixed carbon ate-clastic shelf sequence of Ashgill age, passing upwards through the Silurian into a thick, prograding foreland basin sequence of Ludlow t urbidites. Deformation of the Lower Palaeozoic sequences was possibly diachronous from north to south. It is attributed to the late Caledoni an (Acadian) Orogeny and resulted in folding, cleavage and thrust deve lopment. Granitic intrusions, including those at Shap, Skiddaw and ben eath the hydrothermal Crummock Water Aureole, are partly syntectonic a nd were therefore penecontemporaneous with this deformation event. Som e thrust faulting post-dates the intrusive phase. Post-deformation Dev onian conglomerates are also present locally.