The succession and structure of the Borrowdale volcanic rocks Northwest of Ullswater

Abstract

The succession consists of Skiddaw Slates followed by Borrowdale Volcanic rocks (Ordovician) and is very similar to that previously described southeast of Ullswater (Moseley 1960). The Ullswater Group, more than 4OOO ft thick forms the lowest part of the volcanic succession and consists of tuffs, basalts, basic andesites, and andesites. Above this about 1OOO ft of the rocks of the Birk Fell Group, which are dominantly felsitic, are exposed.Important structural elements are the Ullswater Anticline, the Ullswater Thrust and the high angle faults. The anticlinal axis follows Ullswater as far as Glencoynedale and can be demonstrated only in the Borrowdale Volcanic rocks. The anticline does not appear to continue downwards into the Skiddaw Slates which are not only of different tectonic facies to the volcanics, but are separated from them by the southeasterly dipping Ullswater Thrust. This thrust was induced by the disharmony between the competent volcanics and the incompetent Skiddaw Slates, and is thought to be an imbricate thrust complex rather than a single dislocation.The high angle faults, the third important structural element, have northwest, northerly and westerly trends. It is probable that the northwesterly faults, at least, are wrench faults, although a strike slip component can be demonstrated in one instance only. The nature of the movement of the northerly and westerly faults cannot be ascertained.

Palaeomagnetism of the Borrowdale and Eycott volcanic groups, English Lake District: primary and secondary magnetization during a single late Ordovician polarity chron

“…The Ullswater Anticline has an overall lowangle plunge to the northeast (~25/56°E). It is not evident that a simple plunge correction is applicable to all sites, because the fold is a complex structure cut by several thrusts and high-angle faults, and includes fault-bound blocks that are tilted in different directions (Moseley, 1960(Moseley, , 1964. The net effect of adjusting for this plunge and then for the residual dip is to reduce marginally (but not significantly) the quality of grouping and to rotate the mean remanence directions by ~17°E clockwise (Table 3).…”

“…Examples of orthogonal projections are shown in Figures 10-12. The Lower Ullswater Formation (Moseley, 1964) is exposed on the northern side of Ullswater (sites 1-7, Fig. 2).…”

“…However, although there may be errors in the detailed correlation of individual units, the collective sample is thought to be a representation of the BVG succession. Units sampled include andesite and basalt sheets of the 'Ullswater Formation', the 'Place Fell Formation', the 'Airy's Bridge Formation', andesite sheets of the 'Wren Gill Formation' and, in Kentmere, the 'Garbourn Formation', as defined by Moseley (1960Moseley ( , 1964 and Soper & Numan (1974).…”

Palaeomagnetism and chronology of Caledonian igneous episodes in the Cross Fell Inlier and northern Lake District

“…The research of recent years has, however, shown that these igneous episodes occurred at several different periods between and after Caledonian tectonic events. For example, eruption of the Eycott Group of the north Lake District comprising basalts and basaltic andesites (Eastwood et al 1965) commenced during the Didymograptus bifidus time zone of the Llanvirn (Downie and Soper 1972), and was tilted prior to eruption of the Borrowdale Volcanic Group (palaeomagnetic sites 1 to 4 of this study), comprising predominantly andesites and rhyolites (Firman 1957;Mitchell 1956;Moseley 1960Moseley , 1964. This latter group lies unconformably on Llanvirnian slates east of Keswick but may be essentially conformable in the southwest of the Lake District outcrop; it was in turn folded and partly eroded prior to deposition of the (Caradocian) Coniston Limestone Group including minor volcanic components (Eastwood 1953 for palaeomagnetic study.…”

The Caledonian history of the north-eastern Irish Sea region and its relation to surrounding areas

“…In the south-west and east of the Lake District the previously deformed Skiddaw infrastructure reappears in like fashion within the cores of the subordinate end-Silurian anticlines (Fig. 5) at Black Combe (Simpson, Helm and Roberts 1963) and Ullswater (Moseley 1964).…”