Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia

Hughes, Richard; Cooper, Anthony H.; Stone, P.

doi:10.1017/s0016756800020926

Cited by 33 publications

(24 citation statements)

References 33 publications

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“…In summary then, it is most likely that both the D 1 and D2 phases on the Isle of Man occurred in latest Silurian or early Devonian time, between c. 420 and 400 Ma. This is essentially the same age as that deduced for the main deformation in the Lake District (Soper et al 1987;Hughes et al 1993) and slightly younger than the southernmost deformation in the Southern Uplands (Barnes et al 1989). The deformation in the Isle of Man is presumed to be driven by the culminating collision of Avalonia with Laurentia (Fig.…”

Section: Morris Et Al Favour Correlation Of the Dalby Groupsupporting

confidence: 68%

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In sight of the suture: the early Palaeozoic geological history of the Isle of Man

Woodcock

Quirk

Fitches³

et al. 1999

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Abstract:The pre-and syn-Caledonian rocks of the Isle of Man are now known to comprise three distinct units: the early Ordovician Manx Group, the mid-Silurian Dalby Group and the ?late Silurian-early Devonian Peel Sandstones.The Manx Group is dominated by Arenig deep-marine turbidites and debrites deposited in oxygenated basins on the northwest-facing margin of Avalonia. Its organization into a sand-rich lower part and a mud-rich upper part invites comparison with the Skiddaw Group (Lake District) and Ribband Group (Leinster) and points to control by margin-wide events, in part eustatic sealevel changes. Episodes of mass-wasting and Fe-Mn fluid exhalation also correlate along the margin. A mid-late Ordovician volcanic arc is missing above the Manx Group, although parts of its intrusive substructure may be preserved.The Dalby Group comprises northwest-derived turbidites, sedimented into an anoxic basin during Wenlock (mid-Silurian) time. These turbidites were deposited in a successor basin above the Iapetus suture zone. The Dalby Group sits with a tectonic contact on the Manx Group.No evidence has been found of a pre-Silurian cleavage. The main Caledonian D1 and D2 shortening phases are post-Wenlock, comparable in age with those further along the margin in the Lake District and Leinster. The Peel Sandstones preserve a Lower 'Old Red Sandstone' sequence, mostly removed by post-Caledonian erosion elsewhere along this outboard part of the Avalonian margin. The unit does not host a definite Caledonian cleavage, and it must have been deposited late in the deformation history. The granitic intrusions into the Manx Group range from early in D 1 to late in D2. The intrusions generate only local aureoles, and the high metamorphic grade in parts of the Manx Group may be enhanced by favourable protolith compositions.

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Section: Morris Et Al Favour Correlation Of the Dalby Groupsupporting

confidence: 68%

“…It is now important to add to the kinematic knowledge of these zones for comparison with analogous settings bordering the suture zone in the Lake District (Hughes et aL 1993;Stone et al), eastern Ireland (Vaughan & Johnston 1992;McConnell et al) and southern Scotland (Barnes & Stone).…”

Section: Late Caledonian Orogenic Eventsmentioning

confidence: 99%

In sight of the suture: the early Palaeozoic geological history of the Isle of Man

Woodcock

Quirk

Fitches³

et al. 1999

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“…A regional unconformity overlies the Skiddaw Group and records substantial uplift and erosion, possibly related to thermal expansion and hydration associated with subduction prior to BVG and Eycott Volcanic Group arc volcanism (Branney & Soper, 1988;Millward & Molyneux, 1992). Tectonic folds and cleavage are not demonstrably cut by this unconformity and deformation may have all been soft sediment in character (Hughes, Cooper & Stone, 1993). The overlying BVG is mostly a subaerial succession of volcanic and volcaniclastic rocks ~8 km thick.…”

Section: Geological Outlinementioning

confidence: 98%

“…1). This structure is assigned to the F2 generation (Roberts, 1971); F1 is now regarded as a soft-sediment deformation (Hughes, Cooper & Stone, 1993).…”

Section: E the Eycott Volcanic Group Northern Lake Districtmentioning

confidence: 99%

“…Since the Binsey outcrop on the northern limb is juxtaposed against the Skiddaw outcrop to the south by a major fault inclined to the north (Eastwood et al 1968), it is difficult to judge the validity of applying the same plunge correction to the whole structure. The Binsey outcrop is part of a southerly directed thrust slice (Hughes, Cooper & Stone, 1993) whilst the Eycott outcrop is in faulted contact with much younger Skiddaw Group rocks (Millward & Molyneux, 1992); since both the Eycott Volcanic Group and Skiddaw Group appear to have been translated by thrusting from the northwest in this region (Hughes, Cooper & Stone, 1993), the treatment of the Binsey and Eycott outcrops as part of a single fold limb is certainly an oversimplification. Nevertheless, the significant uncertainty in the direction of the overall remanence direction from the EVG is only 10°in the declination (D/I = 15/-44°fully adjusted, and D/I = 5/-43°partially adjusted; see Table 3).…”

Section: E the Eycott Volcanic Group Northern Lake Districtmentioning

confidence: 99%

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

1997

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Late Ordovician volcanic rocks of the English Lake District typically have a magnetic remanence dominated by a single characteristic component. Previous investigations have interpreted this remanence as both of primary (pre-folding) and secondary origin. Palaeomagnetic field tests have been conducted on (a) andesite blocks from an autobrecciated lava top, (b) andesite blocks in mass-flow breccias, and (c) fault-blocks tilted during Ordovician caldera collapse to establish the time of remanence acquisition. All three tests show that the lavas retain a magnetization acquired during initial cooling: magnetizations of the breccias are coherent within clasts and random between clasts, whilst magnetizations of the tilted fault blocks converge with better that 95 % confidence when corrected for the effects of caldera collapse. In contrast, the volcaniclastic sedimentary and pyroclastic rocks possess an Ordovician secondary remanence acquired after strata had been tilted by volcano-tectonic subsidence. A distributed sample of 65 andesite and basalt sheets through the Borrowdale Volcanic Group has a mean remanence direction D/I = 341.9/-48.9°( α 95 = 4.0°) yielding a positive fold test and a palaeomagnetic pole at 12.7°E, 4.3°S (dp/dm = 3.5/5.3°). A progressive steepening of the palaeofield direction is recorded during emplacement of the Borrowdale Volcanic Group (~I = -39°to I = -51°) which continued into the interval of volcanotectonic overprinting (I = -62°); the equivalent motion of Eastern Avalonia is ~20°into higher southerly latitudes.Both the Eycott and Borrowdale volcanic groups exhibit uniform normal polarity throughout. Correlation with the geomagnetic time scale for the Ordovician restores the broad correlation between the two groups by constraining their emplacement and partial overprinting to a single long normal polarity chron occupying the Nemagraptus gracilis and earlier part of the Diplograptus multidens biozones (late Llandeilo and early Caradoc). All the volcanism, therefore, occurred within a period of no more than ~5 Ma. The palaeomagnetic evidence confirms that the Borrowdale Volcanic Group was affected by both syn-volcanic deformation (caldera collapse) and regional compressive deformation prior to deposition of the (late Ordovician-Silurian) Windermere Supergroup. The succession of primary and secondary Ordovician palaeomagnetic poles from the Lake District inlier defines an anticlockwise apparent polar wander (APW) loop with the apex correlating with 'soft' closure of the Iapetus Ocean and late Ordovician deformation. The APW paths from Avalonia and Baltica converge at this point as subduction ceased and the arc subsided beneath the sea after mid-Caradoc times.

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A new record ofColpocoryphe (Trilobita) from the Skiddaw Group of the Cross Fell inlier, northern England

Romano

Webb²

2000

Geol. J.

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Structural evolution of the Skiddaw Group (English Lake District) on the northern margin of eastern Avalonia

Cited by 33 publications

References 33 publications

In sight of the suture: the early Palaeozoic geological history of the Isle of Man

In sight of the suture: the early Palaeozoic geological history of the Isle of Man

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

A new record ofColpocoryphe (Trilobita) from the Skiddaw Group of the Cross Fell inlier, northern England

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