The early Palaeozoic evolution of northwest England

Abstract

The Lake District and smaller Craven inliers of northwest England contain a Lower Palaeozoic sequence deposited on the Gondwanan side of the Iapetus Ocean, close to the junction with the Tornquist Sea. The Tremadoc to Llanvirn Skiddaw and Ingleton groups are deep water assemblages of turbidite, olistostrome and slump deposits, formed at a continental margin. They experienced uplift and erosion as a precursor to the eruption of two largely subaerial Llandeilo-Caradoc volcanic sequences: the tholeiitic Eycott Volcanic Group in the north and the calc–alkaline Borrowdale Volcanic Group in the central Lake District. The volcanic episodes are the earliest part of a major episode of magmatism, extending through to the early Devonian and responsible for a major batholith underpinning the Lake District. Subsidence in an intra-arc rift zone preserved the subaerial volcanic sequences. A marine transgression marks the base of the Windermere Group, which comprises a mixed carbonate–clastic shelf sequence of Ashgill age, passing upwards through the Silurian into a thick, prograding foreland basin sequence of Ludlow turbidites. Deformation of the Lower Palaeozoic sequences was possibly diachronous from north to south. It is attributed to the late Caledonian (Acadian) Orogeny and resulted in folding, cleavage and thrust development. Granitic intrusions, including those at Shap, Skiddaw and beneath the hydrothermal Crummock Water Aureole, are partly syntectonic and were therefore penecontemporaneous with this deformation event. Some thrust faulting post-dates the intrusive phase. Post-deformation Devonian conglomerates are also present locally.

Trilobite faunas of the Duncannon Group: Caradoc stratigraphy, environments and palaeobiogeography of the Leinster Terrane, IReland

“…Deposition of the fossiliferous Caradoc succession in northern England, at the edge of the Anglo-Welsh sector of Avalonia, began in the Longvillian and succeeded the erosion of the early Caradoc Borrowdale Volcanic Group (Cooper et al 1993;Kneller et al 1994). Some of the Leinster faunas described here are in part slightly older than those of northern England, but perhaps more importantly, they were much more closely related both in space and time to volcanic activity.…”

Zircon ages, geochemistry, and Nd isotopic systematics of pre-Variscan orthogneisses from the Erzgebirge, Saxony (Germany), and geodynamic interpretation

“…The generation of crustally-derived magmatic rocks in a rift-related setting implies mantle-induced thermal activity. They could also indicate a change from passive to active margin setting as suggested for early Ordovician sequences of the English Lake District (Cooper et al 1993) or the Central Iberian Zone (Valverde-Vaquero and Dunning 2000). The tectonic significance of felsic orthogneisses in the Variscan belt in terms of rifting or magmatic arc development was discussed by Pin and Marini (1993), Valverde-Vaquero and Dunning (2000), Kryza and Pin (2002) and von .…”

Timing of magmatism, foreland basin development, metamorphism and inversion in the Anglo-Brabant fold belt

“…None of these boreholes reaches the base of the extrusives and estimates of the total thickness remain tentative. The thickness and the distribution of the volcanic rocks within the Upper Ordovician sedimentary sequence of the Brabant Massif is comparable in age and thickness with the youngest volcanic episode in the Lake District and the Craven Inlier (Cooper et al 1993). …”