View source for Timing and structural setting of Caradoc magmatism, Ordovician, Northern England

== Age and duration of the volcanism ==
[[File:P916042.jpg|thumbnail|Outline geology of the Manx Group in the central and southern parts of the Isle of Man. P916042.]]
[[File:P916043.jpg|thumbnail|Geological map showing the principal Ordovician and Devonian igneous bodies and their relationship to major structural features. BrO Broad Oak Granodiorite Pluton, Butt Buttermere Intrusion, CF Carrock Fell Centre, CW Crummock Water Granite, Dun Dunmail Intrusion, En Ennerdale Granite Pluton, Esk Eskdale Granite Pluton, Ha Haweswater Gabbro-Microdiorite Swarm, HG Haweswater intrusion, LG Loweswater Intrusion, Ryd Rydal Intrusion, Sh Shap Granite Pluton, Sk Skiddaw Granite Pluton, Th Threlkeld Microgranite Intrusion, Ulp Ulpha Intrusion, Wa Wasdale outcrop of Esk, Wear North Pennine Batholith, Wen Wensleydale Granite Pluton. P916043.]]
[[File:P916044.jpg|thumbnail|Schematic north to south cross-section through the Lake District approximately at the end of Borrowdale–Eycott volcanism. The widths of the contiguous Eycott Volcanic Group (EVG) and Borrowdale Volcanic Group (BVG) half-grabens have been obtained from the reduction of Acadian strain in the Cumberland and Westmorland monoclines. Vertical scale is approximately twice that of the horizontal. SkG = Skiddaw Group. P916044.]]
[[File:P916045.jpg|thumbnail|Map of the Borrowdale Volcanic Group showing the main depositional centres and principal faults with displacements inferred to have occurred during accumulation of the volcanic succession. P916045.]]

In the central Lake District, the age and time span of the volcanic groups are constrained biostratigraphically by the unconformities with the underlying and overlying sedimentary strata. The volcanic rocks lie within an interval of up to 15 Ma, above the lower Llanvirn, uppermost parts of the Skiddaw Group but below the Caradoc to Ashgill (Cautleyan) base of the Dent Group. At Cross Fell and in the northern Lake District, mid and late Caradoc shelly faunas have been found in the marine strata overlying the volcanic rocks whereas, in the southern Lake District, the basal beds of the Dent Group are of mid Ashgill age. No macrofossils have been found in the volcanic rocks but an acritarch assemblage, obtained from grey mudstone of the Holehouse Gill Formation in the Ulpha valley (SD 182 927), was previously thought to indicate a Caradoc age. However, the ranges of the taxa critical to this interpretation have been extended recently and it is now thought that all of the acritarchs obtained from these rocks were derived from erosion of the Skiddaw Group. The palynological assemblage from the Overwater Formation at the base of the Eycott Volcanic Group suggests a biostratigraphical age not older than Llanvirn but possibly Caradoc.

Precise U-Pb ages determined for zircons from the lower and middle parts of the Borrow-dale volcanic succession are Caradoc (451.6 ± 1.4 and 452.8 ± 0.7 Ma). Palaeomagnetic data from both the Eycott and Borrowdale Volcanic groups have been interpreted to indicate emplacement during the single period of normal magnetic polarity that lasted for about 5 Ma during Caradoc times. Thus, volcanism is now thought to have been restricted to the Caradoc.